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12.1.1 Functions of systems

For this purpose, the system must …● … store fuel in the fuel tank.● … deliver bubble-free fuel.● … filter fuel.● … generate fuel pressure and keep it constant.● … return excess fuel.● … prevent fuel vapours from escaping.

12.1.2 Design of systems (Fig. 1)

The fuel is stored in the fuel tank. From there it issupplied under pressure by a fuel pump to the fuelinjectors. A fuel filter is connected downstream ofthe fuel pump to retain any contaminants. The fuelpressure is kept constant or adapted to the intake-manifold pressure by a pressure regulator. In orderto be able to provide sufficient fuel in all operatingstates, the system always supplies more fuel thanis actually required at any time. The excess fuel re-turns from the pressure regulator to the fuel tank.An expensive ventilation system is required in viewof the fact that neither fuel nor fuel vapours are per-mitted to escape into the environment and thatpressure compensation must be created in thetank. The fuel vapours are temporarily stored in thecarbon canister of the regenerating (purge) system

and specifically directed via the regenerating(purge) valve for combustion. The fuel tank must bemonitored for leaks when On-Board Diagnosis II(OBD II) comes into force.

12.1.3 Components of systems

Fuel tankSheet-steel fuel tanks, on account of their simplestructural shape and associated problem-free man-ufacture, are usually used in commercial vehicles.They are coated on both the inside and the outsidewith anticorrosion linings. In the case of large andpartially filled fuel tanks, sudden, severe weighttransfers may occur when the vehicle is cornering.This is prevented by the use of perforated partitionswhich divide the tank into several small compart-ments. Steel fuel tanks are increasingly being manufac-tured for use in passenger cars as well. To obtain acategorisation as a low-emission vehicle (LEV) inthe USA, it is necessary to limit greatly the emissionof hydrocarbons, which also include vaporised fu-els. (According to OBD II the evaporative losses inthe fuel system must not exceed 2 g per day).Theserestrictive figures can be achieved more easily byusing steel tanks rather than plastic tanks.

For complicated fuel-tank shapes, as are common-ly found in passenger cars, the tanks are manufac-tured predominantly from plastic, e.g. PE (polyeth-ylene). These provide a high level of safety againstbursting. (The tanks must be able to withstand acrash at 80 km/h.) However, there is the risk of plas-tic deformation at high fuel temperatures (morethan 120 °C in diesel-injection systems) as well asthe problem of heavy diffusion of the fuel vapours.

1122 MMiixxttuurree ffoorrmmaattiioonn

12.1 Fuel-supply systems in spark-ignition engines

The fuel-supply system (Fig. 1) is intended tosupply the engine's mixture-formation systemwith sufficient fuel in all operating states.

Service expansion tank

Fuelpump

Fuel-pressureregulator

Distributorrail

Fuel injector

Solenoid valvefor carbon-canister system

Carboncanister

Gravityvalve

Catch tank withelectric fuelpump

Fuelfilter

M

Fig. 1: Design of a fuel-supply system

Vent valve

Fuellingexpansion tank

Serviceexpansion tank

Fuel-supplysensor

Gravity valve

Filler neck

Fuel-supply pump

Fig. 2: PE fuel tank for a passenger car

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In extreme cornering situations or driving on steepterrain and with only a small amount of fuel left inthe tank, the fuel is displaced to one side. Catchtanks (Fig. 1, Page 247) are used to ensure a suffi-cient supply of fuel to the fuel-supply pump and tobe able to empty all the branched tank compart-ments. There are tanks inside the fuel tank whichare filled by suction-jet pumps. The fuel-supplypumps are also located in the catch tanks (see alsoFuel-delivery modules).

Fuel-supply pumpsModern fuel-injection systems exclusively use elec-tric fuel pumps for fuel supply and delivery. The de-livery quantities of such pumps at nominal voltagerange between 60 l/h and 200 l/h. In the process apressure of 3 bar … 7 bar (as a presupply pump indirect-injection systems) must be achieved at50 % … 60 % of the nominal battery voltage. Be-cause this delivery at nominal voltage results in amultiple of the required fuel quantity being deliv-ered at idle and part load, the electric fuel pumps goover to being activated by the ECU with pulse-width-modulated signals. In this way, the deliveryquantity can be adapted to the operating condi-tions, which can save drive power, stop the fuelfrom being unnecessarily heated and extend theservice life of the pumps.

A pump of this type consists of the

● fitting cover with electrical connections, non-re-turn valve and pump outlet

● electric motor with armature and permanentmagnet

● pump section

Two different types are used, depending on their in-stallation locations: inline pumps and in-tankpumps.

Inline pumps. These can be installed at any point inthe fuel line. They are therefore easier to replacewhen faulty than in-tank pumps. However, they andin particular their electrical connections are ex-posed to increased corrosion when installed underthe vehicle floor.

In-tank pumps. These usually form part of fuel-de-livery modules which are installed in the fuel tanks.In-tank pumps are provided with extensive corro-sion protection in the fuel tank. The noises generat-ed by the pump in the tank are also damped.

The pumps are divided into positive-displacementand flow-type pumps, depending on the way inwhich they operate.

Positive-displacement pumps (Fig. 2). These aredesigned as either roller-cell pumps or internal-gear pumps. The fuel is drawn into the pump anddelivered in a sealed chamber which decreases insize to the high-pressure side. Positive-displace-ment pumps facilitate system pressures of morethan 4 bar and also have high delivery rates at lowvoltages. However, they do cause relatively strongpulsation noises. They are also subject to a markeddrop in power if vapour bubbles are formed in thehot petrol. For this reason, these pumps usuallyhave a flow-type pump as a preliminary stage fordegassing.

Flow-type pumps (Fig. 3). These are designed asperipheral or side-channel pumps. In flow-typepumps the fuel is accelerated by numerous vanesand pressure is built up by a constant exchange ofpulses. Flow-type pumps operate with little noisebecause the pressure build-up is virtually pulsa-tion-free and continuous. They are also insensitiveto vapour-bubble formation as fuel in the vapourstate can be separated via a degassing bore. How-ever, these pumps only achieve system pressuresof max. 4 bar.

Pump section Armature Fittingcover

Non-returnvalve

Pumpoutlet

Electrical connection

Fig. 1: Design of an electric fuel pump

A

B

A

B

Chamber enlargement and reduction

a) b)

Fig. 2: Roller-cell pump (a) and internal-gear pump (b)

A

B

B

A

a) b)

Fig. 3: Peripheral pump (a) and side-channel pump (b)

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Two-stage electric fuel pumps (Fig. 1). Two-stageelectric fuel pumps are used if high system pres-sures are required. A peripheral pump is connectedupstream in order to prevent vapour bubbles fromforming in the pump. It assumes the fuel presupplyrole and separates vapour bubbles. The down-stream positive-displacement pump serves to buildup the system pressure.

Suction-jet pumps (Fig. 2)These are hydraulically driven pumps which serveto pump fuel inside the fuel tank. Thanks to the fuelflow of an electric fuel pump, fuel is drawn at thenozzle opening of a suction-jet pump for exampleout of the side chamber of a fuel tank. This fuel isthen delivered to the catch tank.

Fuel linesSteel pipes or hoses made from flame-retardant,fuel-resistant rubber or plastic are used as fuellines. Because rubber and plastic hoses changechemically (age) when used for long periods, theybecome hard and porous. This may result in leaks.

It is important when laying fuel lines to ensurethat …

● … they are able to withstand the torsion of thevehicle and the movements of the engine.

● … they are protected against mechanical dam-age.

● … the lines are not routed past hot parts - inorder to avoid vapour-bubble formation.

● … they are where possible laid in a steadilyrising direction so that vapour bubbles can bequickly removed from the system.

● … no fuel vapours can collect in the vehicle inthe event of leaks.

Fuel filters

Fuel-pressure regulator (two-line system)

The diaphragm-controlled fuel-pressure regulator(Fig. 3) with intake-manifold connection is locatedin two-line systems on the fuel rail. It consists oftwo chambers which are separated by a diaphragm:a spring chamber for housing the spring which actson the diaphragm and a chamber for the fuel. Whenthe preset fuel-system pressure is exceeded, avalve actuated by the diaphragm opens the open-ing for the return line, through which the excess fu-el can flow back to the fuel tank.

Because the spring chamber is connected via a lineto the intake manifold shortly after the throttlevalve, the diaphragm is deformed by not only the

Degassingconnection

Inlet fitting

Preliminary stage,flow-type pump

Main stage, positive-displacement pump

Outlet

Pressure-limiting valve

Connecting cable

Pressure-holding valve

DC motor

Fig. 1:Two-stage inline fuel pump

Electricfuel pump

Catch tank

Suction-jet pump

Fuel tank

Feed Return

Fig. 2: Suction-jet pumps

These are intended to protect the fuel systemagainst contaminants because, for example, thefuel injectors of a petrol injection system can bedestroyed even by tiny dirt particles.

The fuel-pressure regulator must keep the fueldifferential pressure in the two-line system con-stant under all conditions.

Fuel return lineto fuel tank

Fuelchamber

Valve plate

Valveholder

Springchamber

Connection tointake manifold

Fuel feed fromfuel pump

Fuel rail Systempressure

Diaphragm

Control spring

Fuel injector

Intake-manifoldpressure

Fig. 3: Fuel-pressure regulator

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fuel pressure but also by the vacuum pressure act-ing in the intake manifold. Thus the fuel-pressureregulator alters the system pressure in the fuel railor at the fuel injectors in such a way that the differ-ential pressure between the intake manifold andthe fuel system remains constant.

If, for example, there is a vacuum pressure of – 0.6 bar in the intake manifold, the valve di-aphragm is opened by fuel and intake-manifoldpressure against spring force to such an extent thatthe system pressure drops for instance to 3.4 bar.The differential pressure Δp is therefore 3.4 bar – (– 0.6) bar = 4.0 bar.

In Return-Less Fuel Systems (RLFS) the almostidentically designed pressure regulator is located inthe fuel tank (Fig. 1). The fuel-system pressure iskept constant by the spring and the diaphragm.There is no intake-manifold connection. The excessfuel returns directly to the fuel tank, which is whythere is no return line from the intake manifold.

Because the injected fuel quantities change as theintake-manifold pressures change, the ECU mustadapt the injection time as a function of the intake-manifold pressure. It receives information on theintake-manifold pressure from an intake-manifoldpressure sensor.

Fuel-delivery modules (Fig. 1)The fuel-delivery components are combined infuel-delivery modules, which are installed in thefuel tank.

Fuel gauge. Lever sensors or submerged-tube sen-sors are normally used to indicate the fuel level.These sensors pick off the conductor tracks of apotentiometer via a linkage. The voltage drop at theresistor is the measure of the amount of fuel in thefuel tank.

Fuel-consumption measurement. The fuel con-sumption is calculated by multiplying the valve-opening time by a valve constant. This specifieshow much fuel flows out of the nozzle at a fixeddifferential pressure per unit of time.

12.1.4 Fuel-tank ventilation

It is necessary to ventilate the fuel tank to be able tocreate pressure compensation in the tank and to en-able the vehicle to be refuelled without complica-tions. Thus, it is essential under the influence ofheat to ensure that expanding fuel and the in-creased gas pressure caused by this can be takenup in expansion tanks. On the other hand, the fueltank must be ventilated when fuel is consumed dur-ing vehicle operation. Under no circumstances mayfuel vapours be allowed to escape into the environ-ment. The ventilation system comprises the follow-ing components (Fig. 2):

Service expansion tank. This takes up the fuel thatexpands as a result of heat. The volume, dependingon the size of the fuel tank is 2 l … 5 l. The expansiontank is connected via a vent line to the carbon can-ister.

Differential pressure = system pressure – intake-manifold pressure

Differential System Intake-pressure pressure manifold

pressure

Idle 4.0 bar 3.4 bar – 0.6 bar

Part load 4.0 bar 3.7 bar – 0.3 bar

Full load 4.0 bar 3.9 bar – 0.1 bar

Table 1: Examples of fuel pressures

Fuelprefilter

Suction-jetpump

Tankfill-levelsensor

Pressureregulator

Fuel-supplypump

Catch tank

Fuel finefilter

Fig. 1: Fuel-delivery module

Non-returnvalve

Regenerating(purge) valve

Intake manifold

Fuel tank

Ventline

Ventvalve

Gravity floatvalve

Throttlevalve

Enginecontrol unit

Serviceexpansiontank

Refuellingpipe

Carboncanister

Shutoff valve

Pressuresensor withpump

Fuellingexpansion tank

Fig. 2:Ventilation system

Carbon canister. This filter stores gaseous hydro-carbons by adsorption on the activated carbon un-til they are drawn in by the vacuum pressure pre-vailing in the intake manifold when the regenerat-ing valve is open and supplied for combustion inthe cylinder.

Shutoff valve (from OBD II). When the engine isstopped, the line supplying incoming air to the car-bon canister must be closed to prevent fuelvapours from escaping to the atmosphere. Whenthe activated carbon is regenerated and the storedfuel vapours forwarded for combustion, the sole-noid valve is clocked and opened by the engineECU parallel to the regenerating valve.

Regenerating (purge) valve. This solenoid valve isclocked by the engine ECU depending on the oper-ating status. When it opens, the fuel particles storedin the carbon canister are purged while the shutoffvalve is also open by fresh air and drawn in by theintake-manifold vacuum pressure.

Diagnosis pump for fuel system, pressure sensor.The fuel system must be checked for leaks in ac-cordance with OBD II. For this purpose, the fuel tankcan be subjected to a pressure generated by a di-agnosis pump. A pressure sensor transmits thepressure characteristic to the engine ECU. The ECUdecides whether the system satisfies the require-ments with regard to leaks.

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Fuelling expansion tank. The function of this tank isto take up briefly gases in the fuel tank which aredisplaced when the vehicle is being refuelled and todirect these gases via a vent line to the refuellingpipe. There these vapours are drawn off by the suc-tion device of the fuel-pump nozzle.

Vent valve. This prevents fuel vapours from escap-ing from the service expansion tank into the envi-ronment or being drawn off. The valve is closedduring refuelling.

Gravity float valve (Fig. 1) (rollover valve, safetyvalve). When the tank is absolutely full and the ve-hicle is in an inclined position or if the vehicle rollsover, fuel could escape to atmosphere via the car-bon canister. To prevent this from happening, theline to the carbon canister is closed by the valve insuch a situation.

Gravity valve

To carboncanister

Vent valve

To tank compensatingvolume Refuelling pipe

Fig. 1: Gravity and vent valve

WORKSHOP NOTES

Notes on servicing/maintenance:● Regularly change the fuel filters (follow manu-

facturer's instructions).● Visually inspect the system for leaks.● Visually inspect the electrical connection

(for corrosion, damage).

Faults and possible causes:● Engine fails to fire:

– No fuel in the tank– Pump not running

● Insufficient engine power:– Delivery rate too low– Delivery pressure too low due to

kinked or crushed fuel line,lack of pump power supply,clogged filters,faulty pump (wear),vapour-bubble formation

Diagnostic options:● Checking the delivery rate: measurement at

the pressure regulator (in the return line).● Checking the delivery pressure: measurement

at the fuel rail (in the feed line).

● Pump power supply: faults in the electrical sys-tem are generally detected by self-diagnosis.Therefore the fault memory must be read outor an actuator diagnosis carried out. The posi-tive and negative supply can be checked with amultimeter.

Fault causes: (Fig. 1, Page 252)

– Faulty fuse in the fuel-supply pump (checkcontinuity)

– Faulty fuel-pump relay (to check, jumperterm. 30 – term. 87)

– Damaged leads and corroded contacts (mea-sure voltage drop)

In addition to a faulty power supply, a fuel-supplypump which is not working may be caused byamong others the following:

● Fuel-supply pump is faulty.● Engine ECU receives no engine-speed signal

after the ignition is switched on.● Engine ECU receives no enable from the im-

mobiliser.● Engine ECU receives a crash-situation signal

from a built-in crash-detection system (airbag).

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12.2 Mixture formation in spark-ignition engines

12.2.1 Basic principles

Function of mixture-formation systems

Complete combustion of a fuel-air mixtureThis is understood to mean that all the carbonatoms and all the hydrogen atoms of the fuel areoxidised by the oxygen in the air into carbon diox-ide (CO2) or water (H2O) under heat dissipation. Because fuels, depending on the structure and sizeof their molecules, have differing amounts of car-bon and hydrogen atoms, a quite specific air massis needed for complete combustion of the fuel.Combustion deteriorates as the amount of defi-cient or excess air increases. The fuel will onlycombust incompletely. Combustion will not takeplace at all if specific limit values for the mixtureratio (ignition limits) are undershot or exceeded.

Mixture ratio

Theoretical mixture ratio (stoichiometric ratio =theoretical air requirement). This specifies howmany kg of air are required for the complete com-bustion of 1 kg of fuel. To burn 1 kg of petrol, thisfigure is roughly 14.8 kg or 10,300 l of air.

Practical mixture ratio.This deviates from the theo-retical mixture ratio, depending on the engineoperating state. A mixture with a larger proportionof fuel, e.g. 1 : 13, is known as a "rich" mixture (airdeficiency). A mixture with a smaller proportion offuel, e.g. 1 : 16, is known as a "lean" mixture (excessair).

Fuse

ECU

Fuel-pumprelay

Electricfuel pump

30

30 85

87 86

31

M

15

AirbagRotationalspeed

Fig. 1: Circuit diagram of fuel-supply pump

Safety instructions

Petrol has a flash point of< 21 °C and therefore comes un-der danger class AI in accor-dance with the Directive onCombustible Liquids.

It is highly inflammable. It is therefore absolute-ly essential to follow the relevant safety precau-tions when welding, soldering or grinding.

Fuel vapours are heavier than air. They cantherefore form hazardous mixtures in pits ordrainage shafts.

Fuels contain benzene, methanol, toluene andxylene. These substances are toxic and mustnot be inhaled. Contact with the skin and mu-cous membranes must be avoided. Petrolshould therefore never be used for cleaningpurposes.

REVIEW QUESTIONS

1 Which components make up the fuel-supplysystem?

2 Which types of fuel pump are used in a motorvehicle? In what way do they differ?

3 What is the function of the fuel-pressure regula-tor in a 2-line system?

4 Why do 1-line systems require an intake-mani-fold pressure sensor?

3 What are the functions of the intake-manifoldpressure sensor?

6 What do you understand by a fuel-deliverymodule?

7 What important factors must be borne in mindwhen laying fuel lines?

8 Which components make up the ventilationsystem of a fuel-supply system?

9 What is the function of the service expansiontank?

10 For what purpose is a gravity float valve needed?

11 Why must fuels not be used for cleaning pur-poses?

Spark-ignition engines can be run on petrol,methanol or liquefied petroleum gas. The com-pressed fuel-air mixture is ignited at the end ofthe compression stroke by a spark-ignitionsystem.

They should for each engine operating stateform a fuel-air mixture which is sufficient inquantity and is combusted in the engine as fullyas possible.

The mixture ratio describes the composition ofthe fuel-air mixture. There are two differenttypes of mixture ratio: the theoretical and thepractical.

Air ratio (λ = lambda)The air ratio λ is the ratio of the actual air mass sup-plied for combustion to the air mass theoreticallyrequired for complete combustion.

With a theoretical mixture ratio of 1 : 14.8 the air ra-tio λ = 1 for petrol. Here the engine receives pre-cisely the right amount of air that is needed forcomplete combustion of the fuel. If, on the otherhand, 16 kg of air are supplied in the combustion of1 kg of fuel, the air ratio is

λ = �1

1

6

4

.

.

0

8

k

k

g

g

L

L

u

u

f

ft

t� = 1.08

i.e. a lean fuel-air mixture is formed containingmore air than is needed for complete combustion.The excess air here is 8 %.

The basic relationship between air ratio, torque andspecific fuel consumption is shown in Fig. 2.

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253

If engines with manifold injection are to be operat-ed with an exhaust-gas catalyst, an air ratio of λ = 1must be adhered to as closely as possible in orderto obtain favourable exhaust-gas values.

Mixture compositionHomogeneous mixture. The mixture compositionis the same in the entire combustion chamber. In or-der to achieve a homogeneous mixture composi-tion, sufficient time must be made available for auniform and thorough mixing of the fuel-air mix-ture. This is achieved by an advanced injectionpoint during induction or by injection of fuel intothe intake manifold.Heterogeneous mixture. The combustion chamberhas areas of differing mixture composition (strati-fied charge). A retarded injection of fuel into thecylinder during the compression stroke and pre-cisely matched air turbulence facilitate a nonuni-form mixture composition. There must be an air ra-tio of λ approximately equal to 1 to ensure safe ig-nition of the mixture in the spark-plug area inspark-ignition engines. The mixture is lean in themarginal areas of the combustion chamber.

Mixture formation

Air ratio λ =

Engine speed rpm

Mix

ture

ra

tio

Ric

h

L

ea

n

Air

de

fici

en

cy

Ex

cess

air

Air

ra

tio

(e

xce

ss-a

ir f

act

or)

l

0.2

1.6

1.5

1.4

1.3

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

1:3

1:23.7

1:22.2

1:20.7

1:19.2

1:17.8

1:16.3

1:14.8

1:13.3

1:11.5

1:10.4

1: 8.9

1: 7.4

0Idle Maximum speed

kg of fuel

kg of air

kg supplied air quantity

kg theor. air requirement

Mixture too rich

Ignition limit rich

Idle range

Maximum power

Theor. correct mixture

Lean mixturePart-load range

Ignition limit lean

Ignition limit forlean-burn engines

Fig. 1: Mixture ratios, air ratios for petrol

Consumption, power and exhaust-emissionbehaviour are dependent on the air ratio in therespective operating state of the spark-ignitionengine.

Nmg/kWh

beff

M

(Ignition point 30° before TDC)

Rich Lean

340

660

580

500

420

50

110

100

90

80

70

60

0.8 1.0 1.2 1.4Air ratio l

Sp

ec.

fu

el

con

sum

pti

on

be

ff

Torq

ue

M

Fig. 2: Influence of air ratio

Fig. 3: Exterior mixture formation

Supplied air mass in kg

Theoretical air requirement in kg

12 Mixture formation

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254

Exterior mixture formation (Fig. 3, Page 253). Herethe fuel is injected into the intake manifold shortlybefore the engine inlet valve, which is still closed atthe start of injection. As a result of the admissionprocess during the induction stroke and the subse-quent compression of the fuel-air mixture, there re-mains sufficient time to create a homogeneousmixture in the combustion chamber.

Interior mixture formation (Fig. 1). In engines withinterior mixture formation the fuel is injected di-rectly into the combustion chamber. If this takesplace shortly before the fuel-air mixture ignites, fu-el and air cannot mix uniformly.The mixture is het-erogeneous.

Power regulationQuantity regulation. In engines with exterior mix-ture formation and a homogeneous mixture powerregulation takes the form of the throttle valve beingopened more or less depending on the load state.In this way, the amount of air inducted (quantity) isaltered. The composition of the mixture must re-main virtually the same here (λ = 1).

Quality regulation. In engines with interior mixtureformation and a heterogeneous mixture power reg-ulation takes the form of differing amounts of fuelbeing injected while the throttle valve is open. Theamount of air inducted remains virtually the samehere. In this way, the composition (quality) of themixture in the combustion chamber changes de-pending on the load state.

12.2.2 Adaptation of mixture tooperating states

Depending on the operating state, engines requirequite specific mixture amounts (quantity) and mix-ture compositions (quality).

Cold start: In a cold engine only the low-boiling fu-el constituents evaporate. The majority of the fuel

condenses on the cold intake-manifold and cylin-der walls. Thus these proportions of the fuel cannotbe combusted or are only incompletely combusted.In order nonetheless to create an ignitable mixturein the combustion chamber, it is necessary to injecta very large amount of fuel (up to λ = 0.3). Theamount of fuel injected is dependent here on theengine temperature.

More power must be generated in view of the factthat the frictional-resistance values are very highwhen the engine is cold, for instance due to the en-gine oil being cold. This is achieved by a greateramount of mixture.

Warming-up. This refers to the period from whenthe engine is started up to the point when normaloperating temperature is reached. The fuel quantityis reduced as a function of temperature during thewarming-up period. Enrichment of the mixture isreduced in stages as the condensation losses in theintake manifold and on the cylinder walls decreas-es as the engine warms up.

Transition, acceleration. The mixture is brieflyleaned when the throttle valve is opened. More fu-el must be injected briefly in order to prevent a mo-mentary dip in power.

Full load. The operating condition in which thethrottle valve is fully open is known as full load. Inorder to achieve maximum engine power in this op-erating state, the mixture is normally enriched toλ = 0.85 … 0.95 (Fig. 2, Page 253).

Overrun fuel cut-off. Here the throttle valve isclosed and the engine runs with increased revs.This occurs, for example, in downhill-driving situa-tions or when the driver takes his/her foot off theaccelerator pedal at high speed (overrun). In orderto save fuel, no petrol is injected until the enginespeed drops below a preprogrammed level or thethrottle valve is reopened.

Fig. 1: Interior mixture formation

REVIEW QUESTIONS

1 What do you understand by the theoreticalmixture ratio?

2 Explain the air ratio λ.

3 What are the consequences in each case of alean, a rich and a stoichiometric mixture?

4 Up to what mixture ratio or air ratio is a petrol-airmixture ignitable?

5 What characterises an interior mixture formation?

6 What do you understand by a homogeneous/heterogeneous mixture?

7 What characterises an exterior mixture forma-tion?

8 Why must the mixture be greatly enriched duringcold-starting?

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12.3 Carburettor

12.3.1 Basic operating principle

The air flow is drawn into the carburettor by the en-gine piston during the induction stroke. The veloci-ty of the air flow is increased by narrowing thecross-section of the streamlined choke tube (ven-turi tube, Fig. 1). The highest flow velocity and thegreatest vacuum (suction) occurs at the narrowestpoint, which is why the fuel outlet tube is located atthis point. The fuel is carried by the air flow, atom-ised and mixed with the air flow in the mixing-chamber area. Fine atomisation is achieved byfoaming the fuel with a supply of air through the airjet below the fuel level into a fuel-air mixture (pre-liminary mixture). The throttle valve serves to con-trol the fuel-air mixture quantity (quantity control)and with it the engine power and speed.

12.3.2 Carburettor types

The following different types may be used, de-pending on the layout of the intake manifold on theengine and the direction of the suction flow in thecarburettor itself: down draught, side draught andsemi-down draught carburettors.

Down draught carburettors are normally used be-cause here the fuel-air mixture descends into thecylinder in the direction of gravitational force. Theyare installed above the cylinder head.

Side draught and semi-down draught carburettorshave very short intake paths. They are also used

where low installation heights are required and areinstalled below the cylinder head.

The following different types may be used based onthe number and function of mixing-chamber bores:

● Single-barrel carburettors (Fig. 2) and two-stagecarburettors (Fig. 3) (staged carburettors withstages opening in succession) for one intakemanifold

● Staged dual-barrel carburettors (Fig. 4)

● Dual-barrel carburettors (Fig. 5)

● Multiple carburettors are used for separate in-take manifolds

● Constant-vacuum carburettors (Fig. 6) operatewith a variable choke-tube cross-section and vir-tually constant vacuum

● Constant-vacuum slide carburettors (Fig. 7) areused in motorcycles

Choke tube(venturi tube)

Throttle valveMixing chamber

Air flow

Vacuum

Foamed fuelAir inlet

Airjet

Atmosphericpressure

Plastic jet

Fuel

Fig. 1: Carburettor operating principle

The carburettor is intended to atomise the fueland mix it with air in the correct proportion. Itmust adapt the required amount of mixture tothe respective engine operating state.

Main-airinflow

Main-mixtureoutlet

Choketube

Throttlevalve

Fig. 2: Single-barrelcarburettor

Stage 1

Stage 2

Mix

ing

cha

mb

er

Fig. 3: Two-stagecarburettor

Fig. 4: Staged dual-barrelcarburettor

Fig. 5: Dual-barrelcarburettor

Pistondiaphragm

Plunger

Needlejet

Nozzleneedle

Fig. 6: Constant-vacuumcarburettor

Throttle slide

Needle jet

Nozzleneedle

Main jet

Fig. 7: Constant-vacuumslide carburettor

12.3.3 Design of a single-barrel carburettor

Carburettors usually consist of three main components: throttle-valve assembly, carburettor housing andcarburettor cover.The following devices are housed in the main carburettor components (Fig. 1):

Float deviceThe float device consists of the float housing, floatand float needle valve. It is intended to regulate thefuel supply to the float chamber and keep the fuellevel in the carburettor constant in all operatingstates.

Starting deviceThis is intended to induce a very rich fuel-air mix-ture of up to λ ≈ 0.2 to be formed in the carburettorduring cold-starting. This ensures that an ignitablemixture of approx. λ = 0.9 is available in the com-bustion chamber.

Idle deviceThis is intended to deliver the correct idle fuel-airmixture, ensure the correct idle speed and safe-guard the transition from the idle system to themain-jet system.

Transition deviceThe idle mixture is briefly leaned when the throttlevalve is opened. Additional fuel is therefore addedto the air. This is intended to ensure a sound tran-

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Pump seal

Mixing-tube channel

Main jet

Additional-mixtureadjustment screw

Idle-mixtureadjustmentscrew

Sealing plug(pressed in)

Mixing tube

Float

Carburettor housing

Carburettor-covergasket

Idle cut-offvalve (supple-mentarydevice) Outlet channel, idle mixture Bypass bores Throttle valve

Pumpspring

Strainer

Pump suction valve

Pump pressure valve

Mixing chamber

Choketube

Pumppiston

Acceleratorpump

Pump push rod

Injection tube

Boost venturi

Main-mixtureoutlet

Mixing tube foradditionalmixture

Choke valveEnrichment tube

Additional-fuel air jet

Air correction jet

Idle-fuel air jet

Float needle valve

Fuel-supplyconnection

Carburettorcover

Fig. 1: Solex down draught carburettor 1B3, schematic section

sition from the idle system to the main-injector sys-tem and good running performance in the lowerpart-load range.

Main-jet systemThis consists of the main jet, air correction jet andmixing tube. It is intended to draw in and atomisefuel, mix it with air and supply the correct mixtureratio in the entire part-load range.

Supplementary devicesSupplementary devices can be used in mixturepreparation in order to have a beneficial effect ondrive comfort and fuel consumption.

Acceleration deviceWhen the throttle valve is opened suddenly, lean-ing of the mixture must be prevented and addition-al fuel must be made available.

Enrichment deviceThis is intended to bring about the enrichment of thelean part-load mixture at full load and/or part load inorder to obtain the greatest possible engine power.

12.4 Petrol injection

12.4.1 Basic principles of petrol injection

Functions of petrol-injection systems

In fuel-injection systems the fuel is sprayed into theair in finely atomised state with the aid of nozzlesand the pressure built up by the fuel pump. This in-creases the surface area of the injected fuel. Thiscauses the fuel to carburate more quickly, which inturn leads to improved mixing with air, more com-plete combustion and better exhaust-gas values.

In the case of indirect injection (exterior mixtureformation), the fuel injectors are arranged in such away as to inject into the intake manifold or into thethrottle-valve housing. In the case of direct injection(interior mixture formation), the fuel injectors arearranged in such a way as to inject into the com-bustion chamber.

Electronic control of the systems is intended opti-mally to adapt the fuel-air ratio (quality) and theamount of the mixture created (quantity) to the re-spective engine operating state.

The following objectives should be achieved:

● High engine torque

● High engine power

● Favourable engine performance curves

● Low fuel consumption

● Favourable exhaust-gas values

Types of injectionIndirect injectionWith this type of injection, fuel and air already startto be mixed outside the combustion chamber. Auniformly distributed, homogeneous fuel-air mix-ture should be created in the whole combustionchamber during the induction and compressionstrokes.

The following different types of injection are used:

● Single-point injection(SPI) and

● Multipoint injection(MPI)

Single-point injection (Fig. 1). Here the fuel is in-jected centrally into the throttle-valve housing be-fore the throttle valve. Atomisation in the throttle-valve gap and evaporation on hot intake-manifoldwalls or additional heater elements improve the

preparation of the fuel-air mixture. Routes andmanifolds of different lengths cause the fuel not tobe distributed uniformly to all the cylinders. Pe-ripheral turbulence and wall-applied film moisten-ing especially in cold engines result in unequal mix-ture compositions. The have a negative effect onmixture formation. Single-point injection systemsare much simpler in design than their multipointcounterparts.

Multipoint injection (Fig. 2). Each cylinder is as-signed a fuel injector. These injectors are situated inthe intake manifold usually directly before the inletvalves. The mixture is therefore subject to intakepaths of equal length and uniform distribution. Anarrangement close to the inlet valves reduces theformation of wall-applied film when the engine iscold and reduces the build-up of noxious exhaustgases.

Direct injection (Fig. 1, Page 258)Systems with direct injection are always multipointsystems. The fuel is sprayed by the electrically ac-tuated nozzles under high pressure (up to 120 bar)directly into the combustion chamber (interior mix-ture formation). There, depending on the enginelayout and on the operating state, a homogeneousor heterogeneous mixture is formed with the in-ducted air.

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Fuel

Throttlevalve

Air

Fuel-airmixture

Fuel injector

Intakemani-fold

Fuel

Air

Fuel-airmixture

Air cleaner

Fuel rail

Fig. 2: Multipoint injection

The function of petrol-injection systems is tospray fuel in finely atomised state into the in-ducted air. The required mixture quantity in eachcase and the mixture ratio must be adapted tothe respective operating state in the process.

Air cleaner

Fuel

Throttle valve

Air

Fuel-airmixture

Fuel injector

Intakemanifold

Fuel

Air

Fuel-airmixture

Fig. 1: Single-point injection

Group injection (Fig. 3)The fuel injectors of cylinder 1 and cylinder 3, andof cylinder 2 and cylinder 4, are opened once perpower cycle. In each case the entire fuel quantity isinjected before the closed inlet valves. The times forvaporising the fuel vary in length.

Sequential injection (Fig. 4)The fuel injectors inject into the intake manifold thesame entire fuel quantity in succession in firing se-quence directly before the start of the inductionstroke. This encourages optimal fuel-air mixtureformation and improves internal cooling.

Cylinder-specific injection (Fig. 5)This type of injection is a sequential-injectionarrangement. Thanks to improved sensor technolo-gy and increased control sophistication, the ECU isable to apportion a specific fuel quantity to each in-dividual cylinder.

Direct injection eliminates disruptive influencessuch as the formation of wall-applied film or un-equal fuel distribution. This process, however,places very high demands on the electronic controlof fuel-injection systems.

Opening of fuel injectorsThe fuel injectors are hydraulically opened by thefuel pressure or electromagnetically opened.

Continuous injection (see KE-Jetronic). The injec-tors are forced open by the fuel pressure and re-main open for the entire time that the engine is inoperation. They inject fuel continuously. The fuel isapportioned by a variable system pressure.

Intermittent injection. The injectors are electro-magnetically opened for a brief period only and,once the calculated injection quantity has been in-jected, closed again. They are therefore only inter-mittently opened. The fuel is apportioned by a vari-able opening time of the fuel injectors.

Depending on how the fuel injectors are actuatedby the ECU, there are four different types of inter-mittent injection:

● Simultaneous injection

● Group injection

● Sequential injection

● Cylinder-specific injection

Simultaneous injection (Fig. 2)All the engine fuel injectors are actuated simulta-neously. The time available for vaporising the fuelvaries greatly for the individual cylinders. In ordernonetheless to achieve as uniform a mixture com-position as possible and good combustion, half ofthe fuel quantity required for combustion is inject-ed in each case per crankshaft revolution.

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Throttle valve

Fuel injector

Intakemanifold

Air cleaner

Fuel rail

Intakepipe

FuelAir Mixture

Fig. 1: Direct injection

– 360° 0° 360° 720° 1,080° CA

Inlet valve open

Cyl. 1

Cyl. 3Cyl. 4Cyl. 2

TDC Cyl. 1

Injection Ignition

Fig. 2: Simultaneous injection

Cyl. 1

Cyl. 3

Cyl. 4

Cyl. 2

TDC Cyl. 1

– 360° 0° 360° 720° 1,080° CA

Fig. 3: Group injection

Cyl. 1

Cyl. 3

Cyl. 4

Cyl. 2

TDC Cyl. 1

– 360° 0° 360° 720° 1,080° CA

Fig. 4: Sequential injection

Cyl. 1

Cyl. 3

Cyl. 4

Cyl. 2

TDC Cyl. 1

– 360° 0° 360° 720° 1,080° CA

Fig. 5: Cylinder-specific injection

Table 1 shows the classification of electronic fuel-injection systems with intermittent injection

12.4.2 Design and function of electronic petrol injection

Electronic petrol-injection systems (Fig. 1, Page 260)consist of at least three subsystems:

● Air-intake systemAir cleaner, intake manifold, throttle valve, indi-vidual intake pipes

● Fuel systemFuel tank, fuel pump, fuel filter, pressure regula-tor, fuel injector

● Open- and closed-loop control system– Sensors, e.g. temperature sensor– ECU and– Actuators, e.g. fuel-pump relay

The open- and closed-loop control system operatesaccording to the IPO concept. This means:

Input: Sensors record and transmit information inthe form of electrical voltage signals to the ECU.

Processing: The ECU processes the informationcontained in the voltage signals and compares thedetermined actual values with setpoint values usu-ally stored in program maps. It calculates the actu-ation of the corresponding actuators.

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CentralIntake-manifold

Systeminjection

L-Jetronic LH-Jetronic pressure-controlled Direct injectioninjection

External Central

Fuel rail with electrically actuated fuel injectors and High-pressure fuelfeatures

injection unitAir-flow Air-mass Intake-manifold pump, pressuresensor meter pressure sensor sensor and actuator

Injection type Indirect injectionDirect

injection

Injection location Beforethrottle valve

Before inlet valve Cylinder

Number of One fuel injectorfuel injectors single-point

According to number of cylinders, multipoint

IntermittentSimultaneous or Sequential orinjection Clockedgroup injection cylinder-specific

Sequential Cylinder-specific

Main controlled ● Throttle- ● Intake-manifold Requested variables valve angle

● Air flow ● Air masspressure torque (air mass,

● Speed● Speed ● Speed

● Speed speed)

Table 1: Distinguishing features of electronic fuel-injection systems

Output: The relevant actuators, e.g. the fuel injec-tors, are supplied with power by the ECU. The de-sired system operating state is established.

Electronic petrol injection follows the sequence(function) below:

In the case of systems with homogeneous mixtureformation, the engine draws in a quantity of air fil-tered in the air cleaner and regulated by the throt-tle valve. This air quantity is electronically recordedby a sensor.

The ECU uses stored program maps to calculate thebasic injection quantity from the engine speed andthe air quantity (main controlled variables).

If mixture adaptation to special operating states,e.g. cold-starting, is required, the conditions (cor-rection quantities) must be recorded by additionalsensors and transmitted to the ECU again in theform of electrical signals. The ECU adapts the open-ing time of the fuel injectors to the changed oper-ating conditions and supplies the injectors withpower for the calculated time period.

The electromagnetic fuel injectors open and thefuel is injected at the pressure set by the pressureregulator. When the ECU terminates the supply ofpower, the injectors are closed by the closingspring. The injection process is completed.

12.4.3 Operating-data acquisition

The ECU requires information from various sen-sors in order to correctly actuate the actuators con-tained in the fuel-injection system.

Load and engine speed are used to form the basicinjection quantity. These quantities are known asmain controlled variables. The signals from furthersensors are required for the purpose of adaptingthe mixture to the respective operating states.These are known as correction quantities.

Main controlled variablesLoad sensing. This can be performed by varioussensors:

● Airflow sensor

● Hot-wire air-mass meter

● Hot-film air-mass meter

● Hot-film air-mass meter with return-flow detec-tion

● Intake-manifold pressure sensor

● Throttle-valve potentiometer

Airflow sensor (Fig. 2). This incorporates the sensorflap, which is under coil-spring tension. The sensorflap is deflected against spring force by the air flow

during induction and moved into a specific angularposition. This position is transmitted to a poten-tiometer. The ECU detects the sensor-flap positionfrom the voltage drop at the resistor and calculatesthe inducted air quantity or flow with the aid ofstored characteristic values. The compensationflap, which is permanently joined to the sensor flap,compensates mechanical vibrations acting fromthe outside in combination with the air cushion ofthe damping chamber.

Hot-wire air-mass meter (Fig. 1, Page 261). A hotwire tensioned in the air duct acts as the sensor.This wire is kept by electric current at a constanttemperature of 100 °C above the intake-air temper-

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+

Exhaust-gas recirculation valve

Air-temperaturesensor

Idle-speedactuator

Tankventvalve

Throttle-valvepotentiometer

Air-mass sensor

Air cleaner

ECU

Carbon canisterFuel filter

Fuel tank

Engine-speedsensor

Engine-temperature sensor

Lambdaoxygen sensor

Reference-mark sensor

Electric fuel pump

Fuelinjector

Fuel railPressureregulator

Fig. 1: Design of an electronic petrol-injection system

REVIEW QUESTIONS

1 What is the function of petrol injection?

2 What are the characteristic features of indirectinjection and direct injection respectively?

3 Describe intermittent and continuous injection.

4 How does simultaneous injection differ fromsequential injection?

5 A petrol-injection system consists of whichsubsystems? Name the main components.

6 What do you understand by the main controlledvariables for electronic petrol injection?

7 What do you understand by the correction quanti-ties of electronic petrol injection?

8 How can the ECU alter the injected fuel quantityfor intermittent injection?

Compensationflap

Sensor flap

Potentiometer

Intake-airtemperaturesensor

Fig. 2: Airflow sensor

ature. More or less air mass is inducted in differentdriving states. This air mass cools the hot wire. Theheat dissipated to the air must be compensated bythe heating current. The magnitude of the requiredheating current is regulated by the correspondingvoltage. Thus the heating current or the voltage re-quired for the heating current is the measure of theair mass. The air mass is measured approximately1,000 times per second. If the hot wire breaks, theECU switches to emergency operation. The vehiclecan continue to be driven under restricted condi-tions.

Because the hot wire is situated in the intake pas-sage, deposits may form which can distort themeasurement result. Every time the engine isswitched off, therefore, the ECU sends a signal toheat the hot wire briefly to approx. 1,000 °C andthereby burn off any deposits.

Hot-film air-mass meter (Fig. 2). A hot-film sensoris installed in the measurement channel situated inthe intake passage.

This sensor is made up of three electrical resistors(NTC) (Fig. 3).● Heating resistor RH (platinum-film resistor)

● Sensor resistor RS

● Temperature resistor RL (intake air)

The resistors, which are combined to form an elec-trical bridge circuit, are each attached as a thin filmto a ceramic layer.

The electronics in the hot-film air-mass meter reg-ulates the temperature of the heating resistor RH

via a variable voltage in such a way that it is 160 °Cabove the intake air. The intake-air temperature isrecorded by the temperature resistor RL for this pur-pose. The temperature of the heating resistor RH isdetermined by the sensor resistor RS. The heatingresistor is cooled to a greater or lesser extent in theevent of an increased or reduced air-mass flow. Theelectronics regulates the voltage at the heating re-sistor by comparing the sensor resistor RS andtemperature resistor RL in order to obtain the tem-perature difference of 160 °C again. From this con-trol voltage the electronics generates a signal forthe inducted air mass (air throughput).

Because this sensor is largely insensitive to conta-minants, it is not necessary to burn off deposits asis the case with the hot-wire air-mass meter.

Hot-film air-mass meter with return-flow detection(Fig. 1, Page 262). Hot-film air-mass meters with re-turn-flow detection are installed in order to min-imise errors caused by the pulsating air column inthe intake manifold. These sensors prevent themeasurement result from being distorted by returnflow. This enables the fuel to be apportioned moreprecisely (error max. +/– 0.5 %).

The sensors each contain a heating zone, whichheats the inducted air flowing past. Thus, a highertemperature is measured at measuring cell M2 thanat measuring cell M1. When air flows back from theengine side, measuring cell M2 is cooled and mea-suring cell M1 is heated. Both flows, suction flow

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PCB

Hybridcircuit

Inner pipe(measurementchannel)

Protective grille

Intake passage Protective grille Retaining ring

Temperaturecompensationresistor

Precision resistor

Hot-wire element

Hot wire

Fig. 1: Hot-wire air-mass meter

Electricalconnection

Housing

Inner pipe

Intake air

Protective grille

Measurementchannel

Hot-filmsensor

Electronics housing

Fig. 2: Hot-film air-mass meter

RLRH RS

Intake air

Housing

Electronics

Electricalconnection

Measurement channel

Fig. 3: Bridge circuit of hot-film sensor

and return flow, thus have an effect on the measur-ing-cell temperatures. The temperature differenceΔT is converted in the evaluating circuit into a volt-age, from which the ECU determines the inductedair mass.

The diagram (Fig. 2) shows that the signal voltagevaries as a function of load between approx. 1 V(idle) and 5 V (full load).

Intake-manifold pressure sensor (Fig. 3). The func-tion of this sensor is to record the pressure in theintake manifold. It can be mounted directly on theintake manifold or housed in the ECU. In the lattercase, it is connected to the intake manifold by wayof a hose. The sensor contains an evaluating circuitand a pressure cell with two sensor elements.

Each sensor element consists of a diaphragm whichcontains a reference-pressure chamber with a spe-cific internal pressure. On the diaphragm are resis-tors the conductivity of which varies as a functionof pressure when they are exposed to mechanicalstresses as the result of deformation of the di-aphragm.

The functions of the evaluating circuit are to:

● Amplify the voltage change generated by the re-sistance change

● Compensate temperature influences

● Generate as linear a curve as possible

The inducted air flow is determined from the volt-age change (Fig. 5) by way of the intake-manifoldpressure.

Throttle-valve potentiometer (Fig. 1, Page 263). Thefunction of this sensor is to record the position ofthe throttle valve. When the throttle valve isopened, the throttle-valve shaft moves the wiper

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Intake air

Measurement pipewith air-mass meter

Heatingzone

Meas- uringcell 1

Meas- uringcell 2

Intakeair

Fig. 1: Signal generation, hot-film air-mass meter

0

Air-mass flow

200 400 600 kg/h0

1

2

3

4

5

V

Sig

nal

vo

ltag

e

Return flow

Forward flow

Fig. 2: Curve, hot-film air-mass meter with return-flowdetection

Pressure cell Evaluating circuit

Fig. 3: Intake-manifold pressure sensor

Intake-manifoldpressure pPiezoelectric

resistors

Diaphragm

Reference-pressurechamber

Ceramic layer (ceramic substrate)

Fig. 4: Sensor cell of intake-manifold pressure sensor

250

4.65

V

1.87

100 kPa

Ou

tpu

t vo

ltag

e

Compression

Fig. 5: Curve of intake-manifold pressure sensor

arms, which sweep the resistor paths. Due to thechange in the voltage drop at the resistor paths, theECU is able to determine the position of the throt-tle valve. Together with the speed and the intake-airtemperature, the inducted air flow can be deter-mined from the throttle-valve position.

If the throttle-valve signal is to be used as the mainload signal, potentiometers with twin resistor pathsand two wiper arms are used. This increases the ac-curacy and reliability of the system. The voltagesfalling at the two potentiometers are then usuallyopposing (Fig. 2).

If the load is determined by sensors other than thethrottle-valve potentiometer, it serves as the sensorfor the dynamic function (opening speed of thethrottle valve), for range detection (idle, part load,full load) and as a limp-home signal if the main loadsensor fails.

The sensor housing frequently features an addi-tional switch for detecting the idle position.

Speed recording: This can be performed by varioussensors:

● Inductive speed sensor on the crankshaft● Hall-effect sensor in the distributor (with dia-

phragm rotor)● Hall-effect sensor on the camshaft (with magnet)● Hall-effect sensor on the crankshaft (with pulse-

generator wheel)

Inductive speed sensor (Fig. 3). A ferromagneticpulse-generator wheel is mounted on the crank-shaft. An inductive speed sensor, which consists ofa soft-iron core with copper winding (sensor coil)and a permanent magnet, scans the tooth se-quence. As the crankshaft rotates, the teeth of thepulse-generator wheel generate magnetic fluxchanges in the sensor coil, which induces an alter-nating voltage (Fig. 4). The ECU can determine theengine speed from the frequency of the induced al-ternating voltage.

If the crankshaft position is to be recorded by thissensor at the same time, a larger gap is incorporat-ed on the pulse-generator wheel to act as a refer-ence mark (Fig. 5).

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Resistor pathThrottle-valve shaft Wiper arm

Fig. 1:Throttle-valve potentiometer

Potentiometer 1

Potentiometer 2

5

4

3

2

1

0

Vo

ltag

e U

V

a

0° 20° 40° 60° 80° 90°30° 50° 70°10°

Fig. 2: Signal voltages with twin potentiometers

Permanentmagnet

Soft-iron coreSensor winding

Pulse-generator wheel(incremental wheel)

Fig. 3: Inductive speed sensor with pulse-generatorwheel

Vo

ltag

e U

Time t

Fig. 4: Speed signal

Pulse-generator wheel(incremental wheel)

Referencemark

Fig. 5: Speed and reference-mark sensor

As the gap on the induction-type pulse generatorrotates past, a higher voltage is induced on accountof the greater magnetic flux change (Fig. 1). More-over, this voltage pulse has a lower frequency thanthe pulses generated for speed recording. It is theinformation for a specific crankshaft position. Thereference mark indicates that the piston of cylinderno. 1 is, for example, at 108° CA before TDC.

The advantage of Hall-effect sensors over inductivespeed sensors is that the level of their signal volt-age is dependent on the speed. In this way, very lowspeeds can also be recorded.

The main component of such a sensor is the Hallgenerator (Fig. 2), which consists of a semiconduc-tor layer through which supply current IV is passed.

If there is a magnetic field (B) at right angles to thesemiconductor layer, the free electrons in the semi-conductor are displaced by the magnetic field toone side; the Hall voltage UH is created. The level ofthe Hall voltage created is dependent on thestrength of the magnetic field.

The Hall principle is applied in different ways.

Hall-effect sensor in the distributor with diaphragmrotor (Fig. 3)This consists of the Hall generator, the permanentmagnet and the integrated circuit, which amplifiesand converts the Hall voltage into a square-wavesignal (sensor voltage UG). The distributor rotor isdesigned as a diaphragm rotor which moves in theair gap between the Hall IC and the magnetic barri-er. If a diaphragm slides between the Hall IC and thepermanent magnet, the magnetic field is shieldedand the Hall voltage UH is zero (Fig. 4).

As the diaphragm rotor continues to rotate, themagnetic field can penetrate the Hall IC and the Hallvoltage is created. Because the number of di-aphragms is stored in the ECU, the ECU can calcu-late the speed from the number of voltage changes.

Hall-effect sensor on the camshaft (Fig. 5).The sen-sor consists of the Hall generator and the integrat-ed circuit for signal conditioning. The magnetic fieldfor creating the Hall voltage UH is generated by amagnetic plate mounted on the camshaft. When themagnetic plate moves past the sensor as thecamshaft rotates, the Hall voltage UH is created.

The signal (Fig. 1, Page 265) of this sensor is onlyused to calculate speed in emergency operation ifthe engine-speed sensor malfunctions. However,when single-spark ignition coils are used or in thecase of selective petrol injection, the engine ECU

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Vo

lta

ge

U

Time t

Reference mark

Fig. 1: Speed signal with reference mark

Permanent magnet

Hall generator

Diaphragm rotor

Diaphragm

Hall generator

Connecting cable

Fig. 3: Hall-effect sensor with diaphragm rotor

NS

Semiconductor layer

Free electrons

Hall voltage UH

Supplycurrent IV

Magnetic field BUH

IV

NS

Fig. 2: Hall generator

Diaphragm

In gap

Flu

xd

en

sity

BS

en

sor

vo

lta

ge

UG

Ha

llvo

lta

ge

UH

In gap In gap In gap

0

0

0

Fig. 4: Pulse shape of Hall-effect sensor with diaphragmrotor

60°

Fig. 5: Hall-effect sensor on the camshaft

requires the firing TDC of cylinder no. 1 to be clear-ly determined in order to actuate the correct igni-tion coil or the correct fuel injector. For this pur-pose, the signals of the engine-speed sensor on thecrankshaft and the signal of the camshaft sensorare combined (Fig. 2). If the reference marks of theTDC sensor and the speed sensor line up, the fol-lowing TDC of cylinder no. 1 is the firing TDC. If on-ly the reference mark of the speed sensor appears,the following TDC lies between the exhaust and in-duction strokes.

Hall-effect sensor on the crankshaft with pulse-generator wheelThis sensor consists of two Hall generators, a per-manent magnet and the evaluation electronics,which evaluates the Hall voltages of the two Hallgenerators and amplifies these voltages for thesensor voltage. Like the inductive engine-speedsensor, it is mounted on the crankshaft and scans apulse-generator wheel which is designed as anapertured diaphragm. When a diaphragm rotatespast the sensor, the magnetic field is amplified dif-ferently, depending on the position of the di-aphragm. In this way, the magnetic fields which acton the Hall generators vary in strength at times,which causes different Hall voltages (Fig. 3). Theevaluating circuit generates from the Hall voltagesUH created in each case the sensor voltage UG

(Fig. 4). As with the inductive engine-speed sensor,a reference-mark signal can also be generated hereincreasing the opening in the apertured diaphragm.

The signal of the Hall-effect sensor on the crank-shaft can, like the signal of an inductive engine-speed sensor, be combined with the Hall-effect sen-sor on the camshaft to determine the firing TDC.

Correction quantitiesThe following are used to record the required cor-rection quantities:

● Temperature sensors (NTC) for e.g. engine tem-perature, intake-air temperature

● Pressure sensors (piezo sensors) for e.g. ambi-ent pressure, intake-manifold pressure

● Lambda sensors (see Page 316)

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Vo

lta

ge

U

Time t

Hall-voltage shape

Fig. 1: Hall voltage by sensor on CA

Vo

ltag

e U

Reference-mark signal

Time t

Fig. 4: Sensor voltage UG

Strongmag-neticfield

Weakmagneticfield

Sensorvoltage

Diaphragm DiaphragmWindow

Ha

ll v

olt

ag

e U

H

UH1

UH2

N

S

Fig. 3: Magnetic-field change by apertured diaphragms

Reference markspeedsensor

Signalspeedsensor

Exhaust TDC

U =10 V/div; T=1 ms

Reference markTDC sensor

SignalTDC sensor Firing TDC

Fig. 2: Determining firing TDC

REVIEW QUESTIONS

1 Which sensors are used to determine the load?

2 Which signals are generated by the respectivesensors?

3 Which sensors for recording speed are used?

4 Which signals are generated by the respectivesensors?

5 How in the case of selective injection does theECU identify which fuel injector is to be actuat-ed?

6 Which sensors are chiefly used to record the cor-rection quantities?

7 Why are Hall-effect sensors increasingly beingused instead of inductive sensors?

Pressure line

Fuel screen

Fuel filter

Lambda oxygensensor

Catalyst

Engine-temperaturesensor

Speedsensor

Intakemanifold

Throttle-valveactuator

Centralinjectionunit

Throttle-valve actuator

Regenerating(purge) valve

Aircleaner

Pressureregulator

Fuel injector

Air-temperature sensor

Carboncanister

Fresh air ECU

Diagnosisconnection

Relay

Ignition/starter switchBattery

Intake-manifold heating

– +

Fueltank

Throttle valve

12.4.4 Single-point injection

Single-point injection systems are electronicallycontrolled petrol-injection systems with a singleelectromagnetically actuated fuel injector (SPI =Single-Point Injection). The injector is opened bythe ECU for each power cycle in line with the num-ber of cylinders in the engine. (See also Indirect in-jection, Single-point injection). The fuel is injectedbefore the throttle valve.

12.4.4.1 Single-point injectionsubsystems

Air-intake system. The air inducted and filtered inthe air cleaner flows through the central injectionunit. There, the temperature of the air is recorded bythe intake-air sensor, which transmits it in the formof an electrical voltage to the ECU. The throttle-valve actuator, also located in the central injectionunit, regulates the required air flow rate at idle insuch a way that a stored setpoint idle speed can bemaintained. Fuel is injected before the throttlevalve into the inducted air (exterior mixture forma-tion). The mixture regulated in terms of quantity bythe throttle valve flows through the intake manifoldon account of the vacuum pressure acting in the

cylinders. The intake-manifold walls or the inductedmixture are heated in order to counteract excessivecondensate formation on the intake-manifold wallsin cold engines. Finally, it passes through theopened inlet valves into the cylinder.

Fuel system. An electric fuel pump delivers the fu-el from the fuel tank via a fuel filter to the central in-jection unit. The pressure regulator installed therein the return keeps the fuel pressure constant at ap-proximately 1 bar (low-pressure system). When theelectromagnetic fuel injector is supplied with pow-er, fuel is injected before the throttle valve into theinducted air.

Regenerating system.The hydrocarbons temporar-ily stored in the carbon canister must be suppliedfor combustion in an appropriate operating state,e.g. part load. For this purpose, the regeneratingvalve is clocked by the engine ECU so that air andhydrocarbons can be drawn in by the vacuum pres-sure acting in the intake manifold.

Operating-data acquisition. The main informationon the engine operating state is provided by throt-tle-valve angle α and engine speed n (main con-trolled variables, α - n - system). From them the ba-sic injection quantity (quantity) and thus the basicinjection time can be calculated in the ECU. In orderto determine the precise fuel quantity (quality), theECU must receive further information, e.g. air tem-perature, engine temperature and mixture compo-sition, from the lambda sensor.

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In the case of single-point injection all the cylin-ders of an engine are supplied with fuel by acentrally situated fuel injector.

Fig. 1: Single-point injection

12.4.4.2 Single-point injection components

Central injection unit (Fig. 1).This comprises:

● Hydraulic section with fuel supply, return, fuel in-jector, pressure regulator, air-temperature sensor

● Throttle-valve section with throttle valve, throt-tle-valve potentiometer, throttle-valve actuator

Fuel-pressure regulator (Fig. 1).This keeps the sys-tem pressure in the return constant at 1 bar. The in-jected fuel quantity is therefore dependent on thefuel-injector opening time. If the fuel-pump pres-sure exceeds the system pressure, the spring-loaded poppet valve opens and releases the fuel re-turn. The fuel flowing to the pressure regulatorflows through and around the fuel injector before-hand for cooling. This ensures a good hot-start re-sponse.

Throttle-valve actuator (Fig. 2).This is used for idle-speed control to a low speed level and stabilises theidle speed, for example, even when the air-condi-tioning system is switched on. The ECU suppliesthe actuating signal for positioning the throttlevalve to the DC motor as a function of engine speedand engine temperature. The actuating push rod,which acts on the throttle valve, is extended and re-tracted by way of a screw thread.

Central fuel injector (Fig. 3). This consists of thevalve housing and the valve group. The valve hous-ing accommodates the field winding with the elec-trical connection. The valve group consists of thevalve body and the valve needle with solenoid ar-mature guided in the body.The helical spring press-es the valve needle into its seal seat with the assis-tance of the system pressure. When the field wind-ing is excited, the pintle valve lifts off its seal seatby roughly 0.06 mm so that fuel can emerge fromthe annular orifice. The shape of the pintle nozzleprovides for good atomisation together with a ta-pered injection jet. The fuel injector is triggered intime with the ignition pulses.

12.4.4.3 Electronic control of single-point injection

The single-point injection system is electronicallycontrolled in accordance with the IPO concept, i.e.the different operating states are recorded by sen-sors and transmitted to the ECU in the form of elec-trical signals. The ECU calculates the required start-ing values with the aid of various stored programmaps and actuates the corresponding actuators bymeans of electrical signals (see block diagram, Fig. 1,Page 268 and circuit diagram, Fig. 1, Page 269).

The single-point injection ECU thus demonstratesthe following functions: starting, warm-up, accel-eration and full-load enrichment, overrun fuel cut-off, lambda closed-loop control, hot-starting con-trol, engine-speed limitation, adaptive idle-speedcontrol, fuel-pump-relay activation, regenerating-valve activation, limp-home-mode function, self-diagnosis.

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Fuel supply

Fuel return

Throttlevalve

Fuel-pressure regulator

Fuel injector

Air-temperaturesensor

Hydraulicsection(upper part)

Heat-insulatingintermediateplate

Throttle-valvehousing(lower part)

Poppetvalve

Fig. 1: Central injection unit

Actuating push rodDampingspring

DC motor

Worm gear

Screwthread

Worm

Actuator shaft Housing

Fig. 2:Throttle-valve actuator

Electricalconnection

Return topressureregulator

Intake-airtemperaturesensor

Solenoid coil

Valve spring

Solenoidarmature

Valve housing

Pintle valve

Strainer

Pintle nozzle

Supply

Fig. 3: Central fuel injector

Engine speed. This is transmitted to the ECU by aHall-effect sensor located in the distributor. TheECU uses the engine speed together with the throt-tle-valve position to calculate the length of timeduring which the fuel injector is supplied with pow-er and thus the basic fuel quantity to be injected. Ifsensor B5 fails, engine operation is no longer pos-sible because the ECU is unable to calculate eitherthe required injected fuel quantity or the number ofinjection operations. B5 can be checked at pin 26(terminal 7), pin 27 (terminal 8h) of the ECU and ter-minal 31 (terminal 31d).

Throttle-valve position. This is recorded by thethrottle-valve potentiometer located in the centralinjection unit and transmitted to the ECU in theform of electrical voltages. From the level of thesevoltages the ECU is able to calculate with the aid ofstored program maps the opening angle and to-gether with the speed the inducted air quantity. Ifthe voltages assume extreme values, the ECU de-tects full load from these values. In this case, lamb-da closed-loop control is shut down and the mix-ture to be formed is enriched. From the voltagechange per unit of time the ECU is able to detect thedriver's acceleration command. If a stored value isexceeded, it cuts out lambda closed-loop controland enriches the mixture. If sensor B3 fails, limp-home operation can be maintained by the lambdasensor under certain circumstances. B3 is checkedat pin 7, pin 8, pin 18 of the ECU and terminal 31.

Idle position. The ECU receives this informationfrom idle switch Y2, which is attached to the throt-tle-valve actuator. When the throttle valve is in theidle position, idle-speed control or overrun fuel cut-off is activated. If the signal fails, no idle-speed con-

trol or overrun fuel cut-off is possible because theidle position is no longer being detected. Compo-nent check Y2: pin 3, terminal 31M.

Intake-air temperature.This is recorded by an NTCresistor B1 located in the central injection unit. Thevoltage drop at the resistor gets smaller as temper-ature increases. The signal is required so that morefuel (up to 20 %) can be injected at low tempera-tures. Increased contact resistances at e.g. corrod-ed plug connections may result in an incorrect mix-ture formation. If the signal fails completely on ac-count of an open circuit or a short circuit, the ECUcan switch to a stored default value. The signal fromB1 can be checked at pin 14 and terminal 31.

Engine temperature. The signal from the engine-temperature sensor (NTC) is required so that the fu-el quantity can be adapted as a function of the en-gine temperature when the engine is cold (correc-tion quantity). Extending the injection time by up to70 % prevents the mixture from leaning heavily asa result of condensation losses in the intake mani-fold and cylinder. As with the air-temperature sen-sor, an increased contact resistance at a plug con-nection can also result in an incorrect mixture for-mation here. The ECU can switch to a stored defaultvalue in the event of an open circuit or a short cir-cuit. Component check B2: pin 2, terminal 31M.

Fuel-pump relay.The function of this relay is to sup-ply the electric fuel pump with power. The relaycontrol current flows if the ECU connects pin 17 toearth/ground. In this way, the operating current forthe fuel-supply pump can flow from terminal 30 tothe pump. If the ECU receives no signal from the

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Diagnosis

Idle

(idle switch)

Residual oxygen

(lambda sensor)

Engine temperature

(NTC-engine)

Air temperature

(NTC-air)

Throttle-valve pos.

(potentiometer)

Engine speed

(Hall generator)

Fuel-pumprelay/fuel pump

Relay forintake-manifoldpreheating

ECU

Tank vent valve

Throttle-valveactuator

Fuel injector

Fig. 1: Block diagram of single-point injection system

engine-speed sensor for a period of three seconds,it interrupts the relay control current and the pumpis deactivated. This feature is intended to preventfuel from getting into the engine or escaping intothe environment when the engine is stopped andthe fuel injector is open (safety cut-out).

Fuel injector. The fuel injector sprays the fuel infinely atomised state before the throttle valve. Thefuel is injected in each case on two crankshaft rev-olutions in accordance with the number of cylin-ders in the engine. The valve opens when …

● … fuel-pump relay K1 is closed and current flowsfrom terminal 30 via the relay and the series resis-tor to the valve.

● … the ECU connects pin 13 to earth/ground.

The length of time during which power is supplieddetermines the injected fuel quantity.

Throttle-valve actuator.The ECU uses this actuatorto control the idle speed in such a way that a set-point value dependent on the engine temperatureis maintained. When the ECU detects the idle posi-tion, it activates the throttle-valve actuator via pin23 and pin 24 so that the throttle valve, dependingon the actual value, is opened or closed further. Forcorrect idle-speed control the ECU requires the sig-nals from Hall-effect sensor B5, from engine-tem-perature sensor B2 and from idle contact switch inthrottle-valve actuator Y2.

Intake-manifold heating. This has the function ofheating the intake-manifold walls when the engine

is cold. In this way, condensation of the fuel on thecold intake-manifold walls should be reduced orprevented. The intake-manifold heating relay clos-es if the ECU connects pin 29 to earth/ground. Thuscurrent can flow from terminal 30 via relay K3 to theintake-manifold heating (positive supply). The heat-ing receives earth/ground from terminal 31.

12.4.4.4 Diagnosis

Whereas in older systems the stored faults wereread out in the form of flashing codes, in newer sys-tems stored faults can be read out by way of faultreadout devices (engine testers). Actuator diagno-sis is also possible for the throttle-valve actuator,for the intake-manifold preheating relay and for theregenerating valve.

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B1 Air-temperature sensor

B2 Engine-temperature sensor

B3 Throttle-valvepotentiometer

B4 Heated lamdba sensor

F2

30

15

Special functions

15 16 6 10 11 22

3015

X1 TD

113 14 2 3 2423 25 8 7 18 5 20 12 17 4 9

31M31

31M31

F1

K1 K2

Y1 B1 B2 Y2 B3 B4 Y3 R1 Y4

t0t0

M

LL t0t0

lM

8 A 8 A

87 30

85 86

87 30

85 86

2826 27

L29

K3

B5

15

O

P

Q

Y5

4

30 85

8687

1

K4

A

AB

B

B5 Hall generator

F1 Fuse 8A

F2 Fuse 8A

K1 Fuel-pump relay

K2 Main relay

K3 Relay for intake-manifoldpreheating

K4 ECU

R1 Series resistor

Y1 Fuel injector

Y2 Throttle-valve actuatorwith idle contact switch

Y3 Regenerating (purge) valve

Y4 Fuel pump

Y5 Intake-manifold heating

31d

7 8h

Fig. 1: Circuit diagram of single-point injection system

REVIEW QUESTIONS

1 List the essential features of a single-point injec-tion system.

2 Describe the fuel system of the single-point injec-tion system.

3 From which subassemblies is the central injec-tion unit made up? Explain their functions andeffects.

4 Which sensors are required by the single-point in-jection system? Which variables/quantities dothey record?

5 Which actuators are activated by the ECU?

6 Explain the function of the throttle-valve actuator.

12.4.5 LH-Motronic

LH-Motronic is a further developed variant of L-Jetronic. The electromagnetic fuel injectors are se-quentially actuated by the ECU. The fuel is injectedinto the intake manifold shortly before the engineinlet valves, which are still closed at the start of in-jection. Engine speed and inducted air mass areused as the main controlled variables (m/n-sys-tem). The latter is determined by a hot-wire or hot-film air-mass meter, which is also the external fea-ture of LH-Motronic.

12.4.5.1 LH-Jetronic subsystems (Fig. 1)

Air-intake system.The air filtered by the air cleanerand inducted by the engine flows into the intakemanifold. There the air mass is recorded by the air-mass meter and transmitted to the ECU in the formof a voltage signal. An NTC resistor, which can alsobe integrated in the air-mass meter, is used as theair-temperature sensor. The voltage drop at thethermistor is the measure of the intake-air temper-ature.

Fuel system. Two-line systems are usually used inLH-Jetronic. An electric fuel pump, which is locatedeither in the fuel tank (in-tank pump) or on the ve-hicle underbody (inline pump), delivers the fuel

from the fuel tank via a fuel filter to the fuel rail. Allthe fuel injectors are supplied with fuel from thefuel rail. At the end of the fuel rail is a pressure reg-ulator, which keeps the differential pressure con-stant at approx. 3.5 bar. The excess fuel returnsfrom the pressure regulator to the fuel tank.

Regenerating system.The hydrocarbons temporar-ily stored in the carbon canister must be suppliedfor combustion in an appropriate operating state,e.g. part load. For this purpose, the regeneratingvalve (tank vent valve) is clocked by the engine ECUso that air and hydrocarbons can be drawn in by thevacuum pressure acting in the intake manifold.

Exhaust-gas recirculation. An exhaust-gas recircu-lation system can be used to improve the exhaust-gas values.

Idle-speed control

The internal-resistance levels of the engine whenthe engine is cold are greater than when it is hot onaccount of the viscous engine oil and increased fric-tion. In order to overcome this resistance and facil-itate stable idle speeds, the engine must generatemore power. This is achieved by an increasedamount of mixture. Furthermore, idle-speed fluctu-ations must be compensated by a loaded vehicleelectrical system or by a cut-in A/C compressor.

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The LH-Motronic injection system is an elec-tronically controlled fuel-injection system withmultipoint injection, in which the air mass isused as one of the main controlled variables.

ECU

+

Exhaust-gas recirculation valve

Air-tempera-turesensor

Idle-speedactuator

Tankventvalve

Throttle-valvepotentio-meter

Air-massmeter

Air cleaner

Carboncanister

Fuel filter

Fuel tank

Engine-speedsensor Engine-

temperature sensor

Lambda oxygensensor

Reference-marksensor

Electricfuelpump

Fuelinjector

Fuel railPressureregulator

Fig. 1: LH-Jetronic

Its function is to keep the engine speed constantwith the throttle valve closed at a setpoint valuedependent on the engine temperature.

The ECU requires the signals from the followingsensors for idle-speed control:

● Engine-speed sensor (actual speed)

● Engine-temperature sensor (determination ofthe setpoint speed)

One of the following actuators is used for speedcontrol.

Idle-speed actuator (Fig. 1). This permits additionalair depending on the requirement to flow in a by-pass around the closed throttle valve. For this pur-pose, it is actuated by the ECU by means of pulse-width-modulated signals, a process which opensthe air duct to a lesser or greater extent.

Throttle-valve actuator (Fig. 2). This subassemblyconsists of an electric motor, a gearing and thethrottle valve. At idle the electric motor is actuatedby the engine ECU in such a way that it opens orcloses the throttle valve depending on the actualspeed so that a prespecified setpoint speed is main-tained.

Overrun fuel cut-off

When the engine is running with increased revsand with the throttle valve closed (overrunning, e.g.in downhill-driving situations), overrun fuel cut-offprevents fuel from being injected. Fuel injection re-sumes when the throttle valve opens or when theengine speed drops below a stored threshold, e.g.1,200 rpm.

The ECU requires the following information foroverrun fuel cut-off:

● Throttle-valve position from the throttle-valveswitch or throttle-valve potentiometer

● Engine speed from the engine-speed sensor

Acceleration, full-load enrichment

Engines with three-way catalysts are operated asfar as possible in the λ = 1 range on account of ex-haust-gas regulations. To be able to output the max-imum engine power, the inducted mixture is en-riched, depending on the engine, to lambda 0.85 to0.95. Lambda closed-loop control must be cut outfor this purpose. Enrichment begins when the throt-tle-valve potentiometer signals full load to the ECUor the voltage change per unit of time at the poten-tiometer exceeds a specific stored value. Extreme-ly powerful engines do not necessarily require full-load enrichment.

Altitude adaptationThere is no need for special altitude adaptation innon-supercharged engines because the air-massmeter takes into account a reduced air density, forinstance at greater altitudes.

Engine-speed limitation

Engine-speed limitation is activated when the ECUreceives from the engine-speed sensor a signalfrom which it detects that the stored maximumspeed has been reached. The moment of ignition ismoved in the retard direction to limit the power andwith it the maximum speed and also the top road-speed. Fuel injection is cut out in exceptional casesonly.

LH-Jetronic as MotronicAll LH-Jetronic systems (fuel-injection systems) areessentially designed as Motronic systems, i.e. bothmixture formation and ignition of the fuel-air mix-ture is controlled by a common engine ECU. Here,depending on the manufacturer's requirementsand year of manufacture, different ignition systemscan be combined with LH-Jetronic. By usingMotronic systems, it is possible to reduce designcomplexity, increase operational reliability and im-prove the efficiency of the systems.

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Airoutlet

Airinlet

Adjustable stopDiaphragm

Rotary slide

Air duct

Fig. 1: Idle-speed actuator (rotary actuator)

Gearing

Servo-motor

Fig. 2:Throttle-valve actuator

No fuel is injected when overrun fuel cut-off isactive.

The mixture is enriched in order to facilitatemaximum engine power output.

The function of this facility is to prevent the en-gine from overrevving.

12.4.5.2 LH-Motronic fuel injectors

Function. When the valve field winding is suppliedwith power by the ECU, a magnetic field is gener-ated in it which attracts the solenoid armature. Thisraises the nozzle needle off its seat and fuel is in-jected. The needle stroke, depending on the valvedesign, is 0.05 mm…0.1 mm. When the ECU stopssupplying power as a function of the operatingstate (after 1.5 ms…18 ms), the magnetic field col-lapses and the closing spring forces the nozzle nee-dle into its seat. Fuel injection is terminated. Themass of the injected fuel is dependent on …

● … the valve opening time.

● … the injected fuel quantity per unit of time(valve constant).

● … the fuel density.

● … the fuel pressure.

Powering of valves.The fuel injectors are switchedto negative by the ECU. In this way, the ECU can beprotected against being destroyed by the short-cir-cuit current in the event of a short circuit toearth/ground. The positive supply is provided via arelay switched by the ECU from terminal 15. Thevalve opening time can be determined by display-

ing the injection operation on an oscilloscope(Fig. 2). The voltage peak during the closing opera-tion is created by the switch-off induction of thefield winding.

Types. With LH-Motronic different fuel injectors areused for engines with two- or multiple-valve tech-nology. They differ in the shape of the fuel jet orspray and in the angle at which the fuel is injectedby the nozzle (Fig. 3).

Air-shrouded fuel injectors are used for finer atom-isation of the fuel and for better mixing with air(Fig. 4). For this purpose, air is diverted before thethrottle valve and routed via a line into the injector.In the narrow injector air gap the air is greatly ac-celerated by the pressure differential acting in theintake manifold at part load. The air emerging athigh speed is mixed with the injected fuel and thisprocess finely atomises the fuel.

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With LH-Jetronic each cylinder is assigned anelectromagnetically actuated fuel injector(Fig. 1) which injects fuel sequentially into the in-take manifold.

Solenoidarmature

Fieldwinding

Valve body

Nozzle needle

Electricalconnection

FilterClosing spring

Fig. 1: Fuel injector

30

15

31Valve opens Valve closesECU

Relay

F

IV

0V

10 V/DIV 2.5 ms/DIV

Fig. 2: Powering of fuel injector

Ring-gapmetering

Jet shapes

Dual-streaminjector

a) b)

Fig. 3: Fuel injectors for two-valve technology (a) andmultiple-valve technology (b)

Air Fuel

Fuel-airmixture

Fig. 4: Air-shrouded fuel injectors

When the fuel injectors are supplied with fuel fromthe fuel rail, this fuel is fed from the top (top-feed).The top end of the injector, sealed by an O-ring, isintegrated in the fuel rail while the bottom end, al-so sealed by an O-ring, is integrated in the intakemanifold. In the interests of saving space, the fuelinjectors are often integrated in fuel-rail modules.In this case, so-called bottom-feed fuel injectors areused).The fuel is supplied from the side with theseinjectors. These injectors have good fuel-coolingproperties and thus exhibit a good hot-start re-sponse.

12.3.5.3 Electronic control of LH-Jetronic

The block diagram on Page 274 and the circuit dia-gram on Page 275 show in simplified form the de-sign of electronic control of LH-Motronic. The fol-lowing sensors and actuators are used here.

Hot-film air-mass meter B3.This determines the in-ducted air mass and transmits it in the form of avoltage signal to the ECU, which calculates the ba-sic injection quantity (quantity) from it togetherwith the engine speed. If the sensor fails, the sys-tem can generate a substitute signal from the throt-tle-valve position. The vehicle can continue to bedriven under restricted conditions (limp-home op-eration). The air-mass meter is supplied with pow-er from pin 10 and receives earth/ground from ter-minal 31. The voltage signal transmitted to the ECUcan be picked off at pins 10 and 12.

Engine-speed sensor B1. The signal from this sen-sor serves first and foremost, together with the sig-nal from the air-mass meter, to calculate the basicinjection quantity. The system uses inductivespeed sensors which are accommodated in thearea of the crankshaft and scan a specific pulse-generator wheel. These sensors more often thannot also supply the reference mark which is need-ed to determine the exact TDC of cylinder no. 1. Theengine cannot be operated should this sensor fail.The signal is also needed for idle-speed control,overrun fuel cut-off and engine-speed limitation.Oscilloscope readings can also be taken at pin 6and pin 7.

Throttle-valve potentiometer B4. This is located onthe throttle valve and serves to record both the throt-tle-valve position and the opening speed. The inte-grated idle switch signals to the ECU when the throt-tle valve is closed. If the sensor fails, a default valuestored in the ECU is taken as the basis for the mini-mum speed. This is usually expressed in an in-creased idle speed. Idle-speed control, overrun fuelcut-off and full-load and acceleration enrichment areno longer possible. The potentiometer signal can bepicked off at pins 13 and 14 or pin 12. The throttle-valve switch is checked at pin 15 to terminal 31.

Some systems, especially when a throttle-valve ac-tuator is utilised, use a double potentiometer forsafety and accuracy reasons.

Intake-air temperature sensor B7.This is an NTC re-sistor, the function of which is to record the tem-perature of the intake air. It is located in the intakemanifold. The ECU needs this signal to adapt thefuel quantity. The injection time can be extended byup to 20% when the air is very cold. If the signalfails, it is possible to switch to a stored default val-ue. The resistance of the sensor can be checked atpin 18 and pin 19.

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Fuelsupply

Fuel injector

Pressureregulator

Electrical connection

Contact rails Fuel return

Fig. 1: Fuel-rail module with bottom-feed injectors

Filter strainer

Filter strainer

Electricalconnection

Fieldwinding

Armature

Valve body

Valve needle

Top-feed Bottom-feed

Fig. 2:Top-feed and bottom-feed fuel injectors

Engine-temperature sensor B5. This NTC resistorrecords the engine temperature. Depending on thevoltage drop at the resistor, the engine ECU adaptsthe injected fuel quantity to the operating state as afunction of temperature. Thus the injection time isextended by up to 70% when the engine is cold. Inaddition, the moment of ignition, idle speed, ex-haust-gas recirculation and knock control are mod-ified when the engine is cold. The ECU can switch toa stored default value in the event of a signal inter-ruption or a short circuit. An increased resistance,for example at a plug connection, is not detectedhowever. This fault results in an enrichment of themixture and thus among other things in increasedCO emission. The resistance of the NTC resistor canbe checked at the ECU plug at pin 12 and pin 16.

Reference-mark sensor B2. The signal from the in-ductive reference-mark sensor on the crankshaftand the signal from the Hall-effect sensor mountedon the camshaft are needed for the purpose ofclearly identifying firing TDC. From both signals to-gether with the engine speed the ECU calculatesthe correct moment for injection into the respectivecylinder and the corresponding ignition angle. Os-

cilloscope readings of the sensor signal can be tak-en at pin 8 and pin 5. Terminals on the sensor: 7 (1)= signal positive; 31d (31d) = earth/ground supply.Power is supplied via pin 9 = terminal 8h (2).

Lambda sensor (voltage-jump sensor) B6. Thisregisters the residual oxygen in the exhaust gasand, by means of feedback in the form of a voltagesignal to the ECU, enables the injected fuel quan-tity to be regulated to λ = 1. Because the sensor isonly operated at approx. 250 °C to 300 °C, it is elec-trically heated in order to achieve the quickest pos-sible response. If the sensor fails, λ regulation isno longer possible. The failure is detected by theECU. The mixture-formation system then operatesas an open-loop control system. Oscilloscopereadings of the sensor signal can be taken at pin17 and terminal 31. The sensor heater receives pos-itive from terminal 87 of K2 and negative from ter-minal 31.

Main relay K1.When the ignition is switched on, themain relay receives positive to terminal 85 from ter-minal 15 and negative to terminal 86 from ECU

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Engine speed

Induction-typepulse generator

Firing TDC offirst cylinder

Hall generator

Air mass

Air-mass meter

Throttle-valveposition

Throttle-valvepotentiometer

Engine temperature

NTC-engine

Residual oxygen

Lambda oxygensensor

Air temperature

NTC-air

InputSensors Processing Output Actuators

Diagnosis

Basic adjustment viaprogram map

Starting control

Post-start/full-load/acceleration enrichment

Overrun fuel cut-off

Engine-speed limitation

Lambda closed-loopcontrol

Idle-speed control

Tank-ventilation system

Exhaust-gas recirculation

Main relay

Fuel-pumprelay/fuel pump

Fuel injectors

Idle-speedactuator

Tank ventvalve

Exhaust-gasrecirculationvalve

Lambda-sensorheater

ECU

Fig. 1: Block diagram of LH-Jetronic sensors and actuators

REVIEW QUESTIONS

1 From which signals is the basic injection quantitycalculated in LH-Motronic?

2 Which subsystems are featured in LH-Motronic?

3 Describe the various idle-speed control possibili-ties.

4 Which sensors does the ECU require for overrunfuel cut-off?

5 Explain the term "Motronic“.

6 In terms of which features do LH-Jetronic fuelinjectors differ?

7 What advantage do air-shrouded fuel injectorsoffer over conventional injectors?

8 Which sensors does LH-Motronic require and forwhat purpose are their signals used?

9 Which actuators are activated by LH-Motronic?

10 How is the fuel-pump relay actuated?

11 Explain the term "pulse-width-modulated signal".

pin 3. In this way, the relay operating circuit closesand the ECU is supplied with power to pin 4. Like-wise, solenoid valves Y1 to Y7 and the control circuitare supplied with power by K2 to terminal 85.

Fuel-pump relay K2.This relay closes when main re-lay K1 terminal 85 is supplied with positive and ECUterminal 86 is supplied with earth/ground. In orderto establish the earth/ground connection, pin 30must be connected to earth/ground. The operatingcircuit supplies fuel pump M and the lambda-sen-sor heater with power. The power supply is inter-rupted if the speed signal from the engine-speedsensor fails.

Fuel injectors Y1 to Y4. Like fuel-pump relay K2,these receive power from main relay K1. If the fuelinjectors are top open, the ECU must connect ineach case pins 26, 27, 28, 29 to earth/ground.

Idle-speed actuator Y5. The ECU uses this actuatorto regulate the idle speed as a function of engine

temperature. It is supplied with positive by K1 ter-minal 87. To facilitate stepless opening and closingof the bypass cross-section, the actuator is clockedby the ECU by means of pulse-width-modulatedsignals with negative.

Tank vent valve Y6. This solenoid valve opens andcloses the connecting line between the intake man-ifold and the carbon canister. It is opened by pulse-width-modulated signals, during which the positivesupply is provided by terminal 87 K1 and the nega-tive supply by the ECU via pin 24. The valve remainsclosed if the signal fails.

Exhaust-gas recirculation valve Y7. This solenoidvalve for exhaust-gas recirculation opens andcloses the connecting line between the exhaustmanifold and the intake manifold. It is opened bya pulse-width-modulated signal, during which itreceives positive from terminal 87 K1 and negativefrom ECU pin 23. The valve closes if the signalfails.

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30

87 Y6Y5Y4Y3Y2

30

15

31

31

15

30

V

K1

K2 M

CS

1 2

CA

3 1 2 TM

O2

B1 B2 B4 B5 B6

K2/87

1 2 3 4 5 6 7 8 9 10 11 12 1315

16

ECU

HeaterLambdasensor

Y1

H

3231 30 29 28 27 26 25 24 23

86

85

87

85

86

30

XD

17 1814

B7

20

19

22 21

Y7

B3

TA

3334

K1 Main relayV Incorrect-polarity protection

diodeK2 Fuel-pump relayM Fuel pumpB1 Speed and reference-mark

sensorB2 Camshaft sensorB3 Air-mass meterB4 Throttle-valve potentiometerB5 Engine-temperature sensorB6 Heated lambda sensorB7 Air-temperature sensorH Telltale lamp/fault lampY1...Y4 Fuel injectorsY5 Idle-speed actuatorY6 Tank vent valveY7 Exhaust-gas recirculation valveXD Diagnosis connection

SensorsActuators

Fig. 1: LH-Jetronic circuit diagram

12.4.6 ME-Motronic

In previous systems the driver opened and closedthe throttle valve by operating the accelerator ped-al. The inducted air mass and the fuel quantity in-jected accordingly determined together with theengine speed (main controlled variables) thetorque requested by the driver. Additional torquerequests, e.g. by the A/C compressor, occurred asdisturbance values and had to be corrected by thesystem, e.g. by idle-speed control. Because oftorque management, the accelerator-pedal posi-tion is now no longer the sole deciding factor forthe torque to be generated. All the systems andcomponents which influence the drive torque, e.g.automatic gearbox, A/C compressor, catalystheaters, TCS/ASR, ESP, are used to calculate theengine torque to be generated. Motronic gener-ates a substitute value, on which the requirementsof the individual systems have an influence withdifferent priorities. When, for instance, the A/Ccompressor is switched on, the drive torque is re-duced. In order to avoid this, the ECU receives asignal before the A/C compressor is cut in. Thiscauses the torque to be generated to be modified

by the required amount by means of opening ofthe throttle valve, increased fuel injection and inother cases also a modified ignition angle. To fa-cilitate this, it is necessary to isolate the throttle-valve position from the accelerator-pedal position.This is achieved by using an ETC (electronic throt-tle control) function. This also means that the ac-celerator-pedal position is from now on only to beviewed as a driver command, e.g. in the case of aTCS intervention.

12.4.6.1 ME-Motronic subsystems

Air-intake system. A significant, visible differencefrom LH-Jetronic is the introduction of the so-calledETC function. For this purpose, the driver com-mand is recorded via an accelerator-pedal module.This is performed for safety reasons by two redun-dant potentiometers or Hall-effect sensors whichare integrated in the module. The position and therate of motion of the accelerator pedal are trans-mitted by the generated voltage signals to the en-gine ECU. The ECU uses stored program maps tocalculate a necessary and useful torque and movesthe throttle valve to a corresponding position bymeans of a servo-motor. This position is monitoredby two potentiometers. Thus there is no longer anymechanical connection at all between the accelera-tor pedal and the throttle valve (drive by wire). Inthe event of faults within the system caused by un-clear sensor signals, the throttle valve is moved in-to a limp-home position.

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ME-Motronic (Fig. 1) is a further development ofLH-Motronic. A significant innovation is the re-placement of mixture-formation control by so-called torque management. This has made itnecessary to use electronic throttle control (ETCfunction). EOBD has also been integrated in thesystem.

Electricfuelpump

Lambdaoxygensensor

Lambdaoxygensensor

Secondary-air valve

Secondary-air pump

Reference-mark sensor,camshaft

Ignition coil

Fuelinjector

Intake-manifoldpressure sensor

Carboncanister

Shutoff valve

Air-mass sensor

Knocksensor

Fuelfilter

Ex-haust-gas re-circulation valve

Diagnosis lamp

Diagnosisinterface

Differential-pressure sensor

Throttle-valvepotentiometer

Air-temp.sensor

ECUSpeedsensor

Accelerator-pedal module

Tankventvalve

Pressure actuator

Temperaturesensor

Fig. 1: ME-Motronic

Fuel system.The fuel supply is increasingly sup-plied by one-line systems and delivery modulesintegrated in the tank. When one-line systems (Re-turnless Fuel Systems) are used, the fuel supplypressure is usually kept constant at 3 bar in rela-tion to the ambient pressure. As the intake-mani-fold pressure varies, so the differential pressure atthe fuel injector changes, which results in differ-ent injected fuel quantities. This fault is correctedby a compensation function. For this purpose, theintake-manifold pressure is recorded by an in-take-manifold pressure sensor and the injectiontime is extended or shortened by the ECU accord-ingly.

Pollutant-reducing systemsThe increasingly stringent environmental-protec-tion legislation passed over the years calls for pol-lutant-reducing subsystems to be elaborated andimproved.

Mixture-formation system. More precise recordingof the inducted air mass by hot-film air-mass me-ters with return-flow detection enable the engine tobe operated in a narrower lambda window.

The recording of the lambda value by broadbandlambda sensors enables the lambda value to beregulated more precisely than was previously pos-sible with voltage-jump sensors.

The use of rapid-starting pulse-generator wheelson the camshaft enables the firing-TDC position tobe detected earlier and therefore the engine to bestarted more quickly.

Tank-ventilation system.The fuel-supply system isoutwardly sealed airtight. The carbon canister canbe ventilated by a shutoff valve, which is connectedin parallel to the regenerating valve.

Exhaust-gas recirculation. Cooling the exhaust gas-es recirculated in the combustion chamber im-proves NOx reduction. An exhaust-gas recirculationcooler is installed for this purpose.

Secondary-air system. This consists of the sec-ondary-air pump and valve. The system is used inthe cold-starting phase to reduce CO and HC. It al-so heats up the catalyst very quickly to operatingtemperature (catalyst heating).

Introduction of OBD. Monitoring of all componentswhich may cause changes in the exhaust-gas be-haviour if they malfunction or are damaged mustbe guaranteed. Faults that have occurred must bestored and displayed.

12.4.6.2 Electronic control of ME-Motronic

In addition to the sensors and actuators used in LH-Motronic, the following components are used (seeblock diagram on Page 278 and circuit diagram onPage 279).

Intake-manifold pressure sensor B9. The signalfrom this sensor is needed to record the intake-manifold pressure and to compensate the differentdifferential pressure at the fuel injector by adaptingthe injection time. This signal is also used to calcu-late the purging flow of the carbon canister. If theair-mass meter fails, an approximately precise sub-stitute signal for the inducted air mass can be gen-erated via the intake-manifold pressure sensor. Thesensor is connected via pins 49, 50 and 53(earth/ground) to the ECU.

Differential-pressure sensor B10. Self-diagnosis isused to check the fuel tank for leaks by monitoringits internal pressure. The sensor is connected viapins 51, 52 and 53 (earth/ground) to the ECU.

Lambda sensor II B11. The post-catalyst sensorserves to monitor the catalyst function. It is alsoused to adapt the pre-catalyst sensor. If the sensorfails, the fault is detected and stored by OBD. Con-tinued lambda closed-loop control by lambda sen-sor I is possible, however the catalyst function is nolonger monitored. Oscilloscope readings of thesensor signal can be taken at pin 10 and pin 11. Thesensor is heated via pin 9 (earth/ground) and K1(positive).

Sensor for accelerator-pedal position B12. In thecase of electronic throttle control, the driver com-mand is determined from the position and rate ofmotion of the accelerator pedal. The necessary sig-nal for the ECU is generated by two redundant po-tentiometers in the accelerator-pedal module. Po-tentiometer 1 is connected via pins 37, 38 and 39and potentiometer 2 via pins 40, 41 and 42 to theECU.

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Sensors Actuators

CAN

Moni-toring

module

μC

M

Fig. 1: ETC system

Sensor for throttle-valve position B4. The throttle-valve position must be recorded exactly by theECU for the setpoint/actual-value comparison. Aswith the sensor for the accelerator-pedal position,two redundant potentiometers are also used herefor safety and accuracy reasons. If the plausibilitycheck of the four potentiometers by the ETC moni-toring system reveals a deviation from the setpointstatus, the system initially falls back on substitutesignals. In emergency situations, e.g. two poten-tiometers on the throttle valve deliver different sig-nals, the throttle valve is closed to such an extentas to permit only a low engine speed. The sensorscan be checked at pins 31, 32, 33 (potentiometer 1)and at pins 31, 33, 34 (potentiometer 2) of the ECUplug.

ETC servo-motor B4.The throttle-valve servo-motoris actuated by the ECU via pin 35 and pin 36. The rel-evant throttle-valve position is calculated as a result

of the ECU determining the setpoint torque. Thiscan be generated by a specific charge, for which inturn a quite specific throttle-valve position is nec-essary. If the motor fails, the throttle valve is movedinto a limp-home position which only permits a lowengine speed.

Secondary-air pump M1. This pumps fresh airshortly after the engine exhaust valve into the ex-haust manifold as a function of the engine temper-ature under restricted time conditions. It is suppliedwith power via relay K3, where the positive supplyis provided by K1 and the negative supply via ter-minal 31. The function of the pump is monitored byself-diagnosis.

Secondary-air valve Y9.This valve protects the sec-ondary-air pump and prevents hot exhaust gasesfrom flowing into the pump when the pump isstopped. It is opened by positive from K1 and neg-ative from ECU pin 19.

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Engine speedInduction-typepulse generatorFiring TDC offirst cylinder

Hall generator

Air mass

Air-mass meter

Throttle-valvepositionThrottle-valvepotentiometer

Engine temperature

NTC-engine

Residual oxygenbefore cat.

Lambda sensor I

Air temperature

NTC-air

InputSensors Processing Output Actuators

Diagnosis

CAN bus

Main relay

Fuel-pumprelay/fuel pump

Fuel injectors

Tank ventvalve

Exhaust-gasrecirculation valve

Heater, lambdasensor IIIntake-manifold

pressure

Pressure sensor

Differential pressure

Pressure sensor

Residual oxygenafter cat.Lambda sensor II

Accelerator-pedal positionAccelerator-pedalpotentiometer

ETC servo-motor

Shutoff valve

Heater, lambdasensor II

Secondary-airvalve

Secondary-airpump

Basic adjustment viaprogram map

Starting control

Post-start/full-load/acceleration enrichment

Overrun fuel cut-off

Engine-speed limitation

Lambda closed-loopcontrol

Idle-speed control

Tank-ventilation system

Exhaust-gas recirculation

Torque management

ETC function

Cruise control

Load-change control

Secondary-air injection

EOBD II

CAN-bus system

ECU

Fig. 1: ME-Motronic block diagram

Shutoff valve Y8. The function of this valve is toshut off the air supply to the carbon canister whenregeneration is deactivated. The shutoff valve isopened by positive from K1 and negative from ECUpin 18 parallel with the tank vent valve.

Connection of Motronic ECU with anothersystem by CAN busAll the data which are needed for a precise mixtureformation in every operating state and in every op-erating situation must be made available to the en-gine ECU. For this purpose, all the ECUs which caninfluence the vehicle drive are interconnected bymeans of a high-speed bus system (CAN bus).

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279

30

15

31

+

–

31

l l c M

K1

M

+–+ c

1 2 3 4

CA

N B

US

H

CA

N B

US

L

QP

PU

PU

K2

F1 F2 F3 F4

Y1 Y2 Y3 Y4 B6 B11 Y6 B3 B7Y7 Y8 Y9 K3 M1

F5

S1

F6F7 F8

K4

S3

S2

M2B4 B12 B2 B1 B8 B9 B10

B5

T1 T2

1 2 3 4 5 6 7 8 9 1110 12 1315

14 16 17 18 19 20 21 2223

2425

26 27 28 29 30

3132

3334

35 3637

3839

4041

42 43 44 45 46 47 48 49 50 51 5253

54 55 5657

58 6059

61 6263 6465

66

M

Key to circuit diagram

B1 Crankshaft speed sensor

B2 Camshaft TDC sensor

B3 Air-mass meter

B4 Sensor for throttle-valve po-sition with ETC servo-motor

B5 Engine-temperature sensor

B6 Heated lambda sensor I

B7 Intake-air temperature sensor

B8 Knock sensor

B9 Intake-manifold pressuresensor

* Cruise-control system

B10 Differential-pressure sensor

B11 Heated lambda sensor II

B12 Sensor for accelerator-pedalposition

F1…F8 Fuses

K1 Fuel-pump relay

A ME-Motronic ECU

K3 Relay, secondary-air pump

K4 Relay, output stage, ignition system

M1 Secondary-air pump

M2 Electric fuel pump

S1 Switch for CC*

S2 Clutch-pedal switch

S3 Brake-pedal switch for CC*

T1,T2 Twin-spark ignition coils

Y1…Y4 Fuel injectors

Y6 Regenerating valve

Y7 Exhaust-gas recirculationvalve

Y8 Shutoff valve

Y9 Secondary-air valve

1…4 Inputs and outputs of othersystems

REVIEW QUESTIONS

1 Which sensors and actuators are used in ME-Motronic?

2 At which pin can sensors B4, B9, B10, B11 andB12 be checked?

3 Describe the design and operating principle of anETC system.

4 Which systems and measures for protecting theenvironment are used in ME-Motronic?

5 At which pin can actuators M1, Y9 and M2 bechecked?

6 Which ignition system is used in the systemshown in the system diagram?

7 What happens when K1 closes?

Fig. 1: ME-Motronic circuit diagram