city & guilds automotive glossary of terms · pdf filecity & guilds automotive...

City & Guilds Automotive Glossary

City & Guilds Automotive Glossary of Terms ABDC After Bottom Dead Centre - when the piston is at a position after

BDC.

ABS Anti-lock braking system – prevents wheels locking during braking. AC Alternating Current – an electric current that continuously changes

direction.

Air cooling A system where air is used to cool the engine.

Alternator A component, normally driven by the engine, which generates electrical current.

Anti-dive Suspension design that reduces or prevents the front of the vehicle dipping down during braking.

Antifreeze Added to a liquid cooling system to reduce the freezing temperature of the coolant.

‘A’ post The upright body member in front of the front door. Also known as the ‘A’ pillar.

API American Petroleum Institute – sets standards, etc., for the

American petroleum industry.

ATDC After Top Dead Centre – when the piston is at a position before TDC.

AWD All Wheel Drive - usually refers to four wheel drive.

Battery A component that stores electrical energy.


Baulk ring

Part of a synchromesh unit that prevents gear selection until the appropriate time.

Bendix drive

A method used to engage the starter motor pinion with the flywheel ring gear. The pinion moves along a shaft with a helical groove.

BHP

Brake Horse Power - an imperial measurement of the power developed by the engine.

Breakout box

A ‘box’ that allows connection to parts of the vehicle electrical/electronic system.

BSI

British Standards Institute – sets the standards for the United Kingdom.

BDC Bottom Dead Centre – when the piston is at the bottom of the cylinder.

BBDC Before Bottom Dead Centre – when the piston is at a position before reaching BDC.

‘B’ post The upright body member is just behind the front door. Also known as the ‘B’ pillar.


BTDC Before Top dead centre – when the piston is at a position before reaching TDC.

CAD

Computer Aided Design – software system to aid drawing and design.

CAM

Computer Aided Manufacture – a software system that allows computerised manufacture, often linked to a CAD system

Camshaft An engine component that operates the valves and some other components.

CAN

Controller Area Network – a protocol system used for transmitting data and used for multiplexing.

Carburettor A fuel system component that vaporises the fuel (petrol) and mixes it with the correct amounts of air.

Catalytic convertor

An exhaust system component used to reduce the harmful gases from the exhaust.

Cetane number

A rating used for measuring the ignition delay of diesel fuel. Although different it is the equivalent of Octane rating for petrol.

CI Engine Compression Ignition – an engine that relies on compression in the cylinders to provide sufficient heat to ignite the fuel. Also known as a diesel engine.

Clearance volume

The volume above the piston when it is at top dead centre (TDC).

Closed loop

An automatic control where feedback, usually from sensors, provides a signal to monitor and then adjust the output to suit conditions, if required.


CO

Carbon Monoxide - a toxic gas created when incomplete combustion occurs.

CO2 Carbon Dioxide – a non toxic gas formed during combustion.

Cold cranking rate

A rating for batteries – it is the current drain when the starter motor is operating, usually stated for a specific time. Also known as Cold Cranking Amps (CCA).

Combustion chamber

A part of the cylinder head where the burning of the air and fuel occurs. It also contains the spark plugs and valves, and if a diesel engine will contain the injectors.

Connecting rod

An engine component that connects the piston to the crankshaft.

COSHH Control Of Substances Hazardous to Health – regulation governing

precautions, storage, etc., of certain substances.

‘C’ post The upright body member behind the rear door. Also known as the ‘C’ pillar.

Crankshaft An engine component that converts the reciprocating (up and down) movement of the piston into a rotary motion.

Cross flow

This is where the gases flow across the cylinder head, usually achieved by having the inlet and exhaust valves on opposite sides of the combustion chamber.


CVJ Constant Velocity Joint – a universal joint which allows the input and output to rotate at the same speed under all operating conditions.

CVT Constantly or Continuously Variable Transmission – a transmission system that provides a constantly changing gear ratio to suit the conditions.

Cylinder block Is the main casting for the engine unit and contains the cylinders, water ways and other major components.

Cylinder head An engine component that is fitted to the top of the cylinder block

and contains the combustion chamber and valves.

DC Direct Current – current that flows in one direction only.

Dead axle The non driven axle.

Desmodromic valves

A system where the engine valves are opened and closed by positive action.

Detonation

A very rapid combustion rate, almost causing an explosion in the combustion chamber. Also known as ‘pinking’.

DIN rating Deutsche Industre Normen- an international (German) standard for measurement and applies to a range of specifications.


Direct injection (DI)

A system used on compression ignition engine where the fuel is injected directly into the combustion chamber.

Distributor An ignition system component driven by the engine. It is used to switch the primary ignition circuit on and off, and to distribute the spark to the spark plugs.

Dog clutch

A system which allows drive to be transmitted usually by the engagement of two sets of metal teeth.

DOHC

Double Overhead Cam Shaft – an arrangement that uses two cam shafts, usually one for each set of valves and is positioned at the top of the cylinder head.

DOT Department of Transport – a government organisation responsible for transport issues.

‘D’ post The rear most upright body member in an estate car. Also known as the ‘D’ pillar.

Driveability The operating characteristics of a vehicle and includes flexibility, smoothness, acceleration, etc.


DTC Diagnostic Trouble Code – this uses a five character alphanumeric code to indicate vehicle faults. Also see OBD and EOBD.

Double declutching

A clutch operation that is necessary to allow the gear speeds to be synchronised when changing gear when synchromesh is not fitted. A method that was essential with sliding mesh gearboxes.

Down draught carburettor

A carburettor where the flow is vertically downwards.

Dry sump

A system where the oil for the engine is stored in a separate reservoir and not the sump.

Duplex chain

A roller chain with two parallel sets of rollers, used for some cam shaft drives.

Dynamic balancing

Where components are balanced when being rotated. Especially used for balancing road wheels and engine crankshafts.

EBD or EBFD Electronic Brake Force Distribution – linked to the ABS to vary the brake force at each wheel depending on conditions.

ECM Electronic Control Module – see ECU.

ECU Electronic Control Unit - a form of computer and is used to control a number of vehicle systems.

EGR Exhaust Gas Recirculation – a system which recirculates some of the exhaust gas into the induction to reduce combustion temperature and exhaust emissions.

EMC Electromagnetic Compatibility – how the electrical system is affected by external electromagnetic fields.

End float Longitudinal movement or free play in a component.

EOBD European On Board Diagnostics – the European standard for on-board diagnostic systems. Also See DTC and OBD


EPA Environmental Protection Act – legislation to protect the environment from pollution.

EP lubricant Extreme Pressure – a special lubricant for use with some gears.

EVC Exhaust Valve Closes – the point at which the exhaust valve closes, usually ATDC.

EVO Exhaust Valve Opens – the point at which the exhaust valve opens, usually BBDC.

Expansion tank

See Header Tank.

Filter A component used to remove, or filter, dirt. The main types of filter are oil filter, fuel filter and air filter.

Fixed head An engine where the cylinder head and cylinder block as one casting.

Flammable A substance that is easily ignited. The same as inflammable.

Flinger

A disc that is used to prevent oil leakage from a shaft, also known as oil flinger, thrower and oil thrower

Forced downshift

A system of forcing an automatic gearbox to change down a gear, also known as downshift.

Fuel pump A component used to deliver the fuel from the tank through the system. They can be engine driven (mechanical) or electrical.

FWD Front Wheel Drive.


Fuse A device used in electrical circuits to prevent overloading.

Generator

A machine for producing electric current, on a vehicle this is usually the alternator. Earlier vehicle were fitted with dynamos.

Gross axle weight

The maximum specified carrying capacity for an axle.

Gross combination weight

The total weight of the vehicle with all equipment, fuel, driver, passengers, etc.

Gross power

The maximum power output of the engine with no ancillary equipment fitted.

Gross vehicle weight

The maximum legal weight that a vehicle can be operated.

Harmonic balancer

A component that rotates and is used to counter balance forces created in an engine.

Hazard A source of an accident.

HC Hydrocarbons – chemical compound of fuel.

Header tank A cooling system component used to contain coolant that has overflowed from the radiator. This coolant can then be returned to the radiator when the engine cools. Also known as an Expansion tank.

Helper spring

An additional; spring that can be fitted to the suspension to assist the main spring. Often fitted if the vehicle is used to tow a caravan or trailer.

Homofocal headlamp

A headlamp fitted with a reflector that provides different focal lengths.


Hotchkiss drive

A rear wheel drive system using a live beam axle driven by a propeller shaft.

HT

High Tension - this is a term that refers to a high voltage usually associated with the ignition system.

HT lead A cable used in the ignition system to carry the high voltage through the ignition system.

Hydrokinetic transmission

A transmission system where drive is transmitted by movement of a fluid. This action occurs in a torque converter.

Hydrometer A tool used to measure specific gravity. Its two main uses in connection with motor vehicles are for checking battery condition and antifreeze solutions.

Hydrostatic transmission

A system where drive is transmitted to each wheel through a hydraulic motor.

IC engine Internal Combustion engine.

ICE In Car Entertainment.

IFS

Independent Front Suspension – where the deflection of one front wheel is not directly transmitted to the other front wheel.


Indirect injection (IDI)

A system used on compression ignition engine where the fuel is injected into a pre-combustion and initially ignited, it then passes to the main combustion chamber.

Inert gas A gas, which under normal circumstances will not react with any other gas. Some inert gases are – argon, helium and nitrogen.

Ignition coil An ignition system component used to convert battery voltage into a higher voltage to cause a spark at the spark plug.

Injector A fuel system component that sprays fuel into the inlet manifold or combustion chamber.

Inlet Valve An engine component used to control the flow of air, or air and fuel into the combustion chamber.

Inter axle differential

A differential that is fitted between two axles on four wheel drive systems. Also known as a ‘third differential’.


Intercooler A heat exchanger that is used to cool, and so increase the volume, of air after it has passed through a turbo-charger.

IVC Inlet Valve Closes – the point at which the inlet valve closes, usually ABDC.

IVO Inlet Valve Opens – the point at which the inlet valves open, usually BTDC.

Kinetic energy This is defined as ‘the work needed to accelerate a body from rest to its current velocity’. It is the energy that an object possesses due to movement.

Knock sensor

Fitted to the engine to sense knock, caused by detonation, and so cause the ignition timing to be retarded.

Lambda sensor

Fitted in the exhaust to measure the oxygen level and so monitor the air/fuel ratio.

Laminated glass

Used for screens and consists of two layers of glass with a plastic film between the two layers.

LCD Liquid Crystal Display – an optical digital display used for some instrumentation.

Lean burn engine

An engine designed to operate on a weak air/fuel ratio.

LED

Light Emitting Diode – a semiconductor device used for digital displays, etc., they have a very low power usage and long life.


Liquid cooling A system where a liquid is used to cool the engine. This liquid is usually water but will have additives such as antifreeze added.

Loop scavenging

A method used in some two stroke engines where the incoming air/fuel mixture assists in forcing out the burned gases.

LPG

Liquefied petroleum gas – propane or butane gas which can be used in modified spark ignition engines. Also known as ‘Autogas’.

Mass damper A device which reduces or prevents vibration, often used on drive shafts.

MAF sensor

Mass Air Flow sensor – measures the amount of air passing through the induction.

MAP Manifold Absolute Pressure – the mean, or average, pressure in the inlet manifold.

Mean effective pressure

The mean, or average, pressure that acts on the piston during the power stroke.

MIG welding Metal Inert Gas – where the filler wire forms a an electric arc which is cooled and shielded by an inert gas.

MON Motor Octane Number – obtained from test specifications, similar to RON but under different test conditions.

Monobloc construction

Where the cylinder block and crankcase is formed as one unit.

MoT Ministry of Transport – a government department originally responsible for the annual vehicle tests, this is now the responsibility of VOSA.


Naturally aspirated

An engine that has air supplied to the induction at atmospheric pressure.

Nearside

The side of the vehicle nearest to the kerb. NSF – nearside front, NSR – nearside rear.

Negative toe Where the wheels toe-out when the vehicle is stationary. Net power

The power produced by an engine when fitted with all ancillary equipment.

NOx

Nitrogen Oxides – produced during combustion especially at high temperatures when Nitrogen, an inert gas, is ‘forced’ to mix with Oxygen.

OBD On Board Diagnostics – a system used to allow connection to the vehicle to read diagnostic trouble codes (DTC). Also see EOBD and DTC.

Octane number

This is a measure of the anti-knock ability of petrol. See also MON and RON.

OEM Original Equipment Manufacturer – the maker of the equipment originally fitted to a vehicle. Any replacement parts fitted must meet the same specification as OEM parts.

Offside

The side of the vehicle furthest from to the kerb. OSF – offside front, OSR – offside rear.

Open loop control

An automatic control where feedback is measured against pre-set parameters.

OHC

Overhead Camshaft – where the camshaft is fitted at the top of the cylinder head.

OHV

Overhead Valve – where the valves are fitted in the top of the combustion chamber above the piston.

Over square engine

An engine where the cylinder bore diameter is greater than the length of the stroke.


Particulates

Contents of the exhaust gas in the form of carbon usually associated with compression ignition engines.

PCD Pitch Circle Diameter – the diameter of circle formed by the holes for wheel studs.

PCV Positive Crankcase Ventilation – part of the emissions system where the crankcase gases are passed to the induction.

Pinking See detonation.

Piston A component used in the engine. It moves up and down the cylinder and is attached to the connecting rod.

Piston rings These are fitted to the piston to act as a seal to prevent the loss of gases, or to control oil flow.

Ply rating

An index used to indicate the strength of a tyre, it does not refer to the actual number of plies, it is only a comparison.


Poly V belt A drive belt with multiple ‘V’s cut length ways into the belt. Also know as a ‘serpentine’ belt.

Positive toe Where the wheels toe-in when the vehicle is stationary.

Primary couple

An out of balance force that causes the engine to pitch from side to side.

Primary Ignition Circuit

This is the low voltage circuit of the ignition system.

Proportional control

This is a closed loop system which provides proportional feedback.

PTO

Power Take Off – a device used to provide drive, usually from the gearbox, to auxiliary equipment.

Ram air induction

Where the air speed and mass is increased by inlet manifold design to provide a form of pressure charging.

Reed valve An automatic one way valve.

Regenerative braking

Where the kinetic energy from braking is stored and fed back to provide tractive effort.

Relay An electrical component used to switch electrical circuits on and off using a small current.

Risk Assessment

This is a simple but careful examination of what, in your work causes harm to people, so that you can decide whether you have taken enough precautions to prevent harm.

Rolling radius This is the radius of the tyre when it is loaded.

RON

Research Octane Number - obtained from test specifications, similar to MON but under different test conditions. This is the octane rating quoted in the UK.

SAE Society of Automotive Engineers - a European standard for measurement and applies to a range of specifications.


Sealing ring A rubber ring used to provide a seal where liquids are present.

Secondary Ignition Circuit

This is the high voltage, or high tension, circuit of the ignition system.

Schrader valve A non return valve used for tyres.

Serpentine belt

See Poly V belt.

Side camshaft

A camshaft that is fitted at the side of the cylinders, the valves are usually operated through pushrods and rockers.

Side draft carburettor

A carburettor where the flow is horizontal.

Single plan crankshaft

A crankshaft where the crankpins are in-line.

Sipe Channels in the tyre tread to reduce road noise and dissipate heat.


SMG Sequential manual gearbox – a manually operated gearbox that has a sequential (i.e. 1-2-3-4-5-6) gear shift pattern.

SOHC Single Overhead Camshaft – where one camshaft, placed at the top of the cylinder head, is used to operate both inlet and exhaust valves.

Soak time

The time it takes for all of the components of the engine to reach operating temperature.

SI Engine

Spark Ignition Engine - an engine that relies on an electrical spark to ignite the fuel. Also known as a petrol engine.

Silencer An exhaust system component through which the exhaust gases pass to reduce their noise.

Spark plug An ignition system component fitted in to the combustion chamber. When a high current flows a spark is caused at the gap which ignites the mixture.


Split crankshaft

A crankshaft that is manufactured in several parts.

Sprung mass (weight)

The mass (weight) of the parts of the vehicle that are supported by the suspension springs. Depending on the design it may also include some of the mass of the suspension and other components.

Square engine

An engine where the cylinder bore diameter is equal to the length of the stoke.

SRS Safety Restraint System – refers to systems that restrain drivers and passengers in the event of an accident. It includes air bags and seat belts.

Stoichiometric ratio

This is the mass of air and fuel at which complete combustion will occur. It is approximately 14.7:1.

Supercharge

Where the pressure of the incoming air is increased by the use of a pressure charger.

Supercharger An engine drive pressure charger.

Symmetrical beam

A light beam where each side of the beam is the same.

Synchronous motor

An alternating current motor that operates at speeds equal to, or in multiples of, the input frequency.

Tachometer

An instrument used to measure engine speed, measured in revolutions per min (revs/min)or rpms.

TDC Top Dead Centre – when the piston is at the top of the cylinder.

Thermal efficiency

This is the ratio of useful work performed by the engine compared to the total energy produced. Most engines will have a thermal efficiency of between 30 & 35%.


Thermosyphon

Where the cooling system relies on the circulation of the coolant by convection. Although this exists in most cooling systems the circulation is assisted by an impeller.

Third differential

See inter axle differential.

TIG welding Tungsten Inert Gas – a welding method using a tungsten electrode and an inert shielding gas.

Toughened glass

A screen that fractures into to small non sharp pieces.

Track The distance between the centres of the wheels on each side.

Tracking

The amount of positive (toe-in) or negative (toe-out) toe of the wheels when the vehicle is stationary.

Traction The driving force of the vehicle.

Tractive effort The measurement of ‘pull’ produced by the vehicle.

Transaxle

An assembly that consists of both the gearbox and final drive as one unit.

Transfer box

An additional gearbox that provides high & low ratio and two & four wheel drive usually for off-road use.

Turbocharger An exhaust driven pressure charger.

Turbulence

Where the gases are agitated to produce movement in order to improve mixing.

Type approval

Compliance of a vehicle with national or international regulations.

Under square engine

An engine where the cylinder bore diameter is less than the length of the stroke.


Unsprung mass (weight)

This is the mass (weight) of the vehicle that does not act through the springs. It should be kept as low as possible

Urban cycle A test procedure that simulates typical driving conditions.

UJ Universal joint – a coupling that allows angular movement.

V or Vee belt

A reinforced rubber belt with a cross section in the shape of a ‘V’. Often used to drive ancillary equipment such as the alternator.

Valve bounce

This is where the valves ‘bounce’ on their seat rather that open and close correctly. Usually occurs at high speed or if the valve springs become weak.

Vapour lock Where a fluid vaporises in the pipes or lines and flow is restricted.

VIN Vehicle Identification Number – a unique number used by manufacturers for vehicle and vehicle specification identification.

VCM

Vehicle Conditioning Monitoring – a system to monitor faults that may occur.

Viscosity A term used in reference to the ability of oil to flow. More simply it is how thick or thin the oil is.

Viscous coupling

A drive system that uses friction within a fluid to provide drive.

Volumetric efficiency

The ability of an engine to fill the engine with air and fuel at atmospheric pressure. If it, at the end of the induction stroke, was completely filled the engine would be 100% volumetric efficient.

VOSA Vehicle and Operator Services Agency – provides a range of licensing, testing and enforcement services to improve roadworthiness of vehicles. This now includes annual vehicle testing.

Weight transfer

The change in axle load as the vehicle accelerates and brakes.


Welch plug

A disc shaped plug used for closing off casting holes in a cylinder block. Also known as core plugs.

Wheel base The distance between the centres of the front and rear axles.

Yaw The movement of the vehicle about its vertical axis when moving.

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