scania retarder 2
DESCRIPTION
Scania Retarder 2TRANSCRIPT
Scania Retarder
Function description, mechanical system and hydraulic system
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© Scania CV AB 1999, Sweden
Contents
2 © Scania CV AB 1999, Sweden 10:05-06 en
Contents
System description General............................................................ 3
New cable harness and new controlunit .................................................................. 3
Auxiliary brake system, descriptionof operation..................................................... 4
Braking effect ................................................. 7
Mechanical system General ........................................................... 9
Mechanical system, overview....................... 10
Retarder installation in vehicle .................... 11
Retarder function ...................................................................... 12
Hydraulic system General ......................................................... 14
Hydraulic system, overview of old design.................................. 15
Hydraulic system, overview of later design................................ 16
When the retarder is not braking .................. 19
When the retarder is to start braking............. 20
When the retarder is braking......................... 21
When the brake torque is to be increasedor reduced .................................................... 23
When the retarder is to stop braking............. 26
Safety system ............................................... 27
1050f16b.mkr © Scania CV AB 1999, Sweden 3
System description
GeneralThe same integrated auxiliary brake system with the Scania Retarder is used in both trucks and buses. The main difference between the truck and bus installation is how the auxiliary brake is connected to the other electrical equipment in the vehicle.
Connection to the rest of the Scania electrical system is matched to the specification of the particular vehicle. This is described in the Workshop Manual, main group 16, and is not included in this description.
The location of external components such as the oil cooler and oil accumulator varies between trucks and buses and even sometimes between engine types. This has no effect on operation. This description applies to all 4 series vehicles with Scania Retarder.
New cable harness and new control unit
A new cable harness is introduced from 9908 for trucks and from 9910 for buses. The main difference is that the proportional valve for retarder control, the solenoid valve for retarder air supply and the solenoid valve for the retarder oil accumulator are now incorporated into one unit with the part name V97. See Hydraulic system, under Overview, later design, New design of proportional valve and main group 10 Scania Retarder, Trouble shooting using fault codes, under Wiring diagrams.
From 9911, CAN communication is used between the control unit of the auxiliary brake system and the EBS control units using (applies only to trucks). For further information, see main group 10 Scania Retarder, Function description, under Interaction with other systems, Retarder CAN and information in the relevant section.
System description
4 © Scania CV AB 1999, Sweden 1050f16b.mkr
Auxiliary brake system, description of operation
The Scania integrated auxiliary brake system is additional to the vehicle's wheel brakes. The auxiliary brake is stronger than the diesel engine and this gives considerable braking capacity.
The auxiliary brake is intended for long periods of braking on downhill gradients. In this way, the wheel brakes can be reserved for short periods of braking in order to reduce speed. This means that both brake wear and the risk of fading are considerably reduced.
The auxiliary brake is available for vehicles both with and without ABS/EBS. The latter have a simplified version of the auxiliary brake, but it is basically the same system. The controls, however, differ somewhat.
The main components of the auxiliary brake system are the retarder R and the exhaust brake EB. These are both controlled by the same electronic control unit E.
The control unit uses the exhaust brake and retarder to ensure optimum interaction between their fields of operation. On the other hand, it is the responsibility of the driver to downshift and keep the engine speed up in order to achieve maximum braking effect.
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System description
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The exhaust brake EB gives the best effect at high engine speeds and in low gears.
The driver maximises the use of the exhaust brake when he downshifts in good time and allows the engine speed to rise, preferably towards (but not into) the red zone on the rev counter. He then also gains maximum benefit from the braking properties of the diesel engine.
The retarder R is an oil brake driven by the gearbox output shaft. The retarder is most effective at high speeds. The control unit gradually increases the quantity of oil and the oil pressure as the speed decreases, in this way retaining the braking capacity down to approx. 20 km/h.
The retarder provides most of the overall braking power of the system. The power may reach 400 kW (approx. 540 hp) continuously and up to 650 kW (about 880 hp) for short periods. In short, retarder braking generates a great deal of heat which must be dissipated by the vehicle's ordinary cooling system.
System description
6 © Scania CV AB 1999, Sweden 1050f16b.mkr
The engine coolant pump is most effective at high engine speed. The driver should therefore keep engine speed at minimum 1500 rpm, or higher, when using the auxiliary brake. He then gains maximum effect from both the retarder and the exhaust brake. The maximum available braking power is directly proportional to the engine speed.
The braking power of the retarder is automatically adjusted down if the cooling system cannot manage to dissipate all the heat generated.
When the coolant temperature has returned to normal level, the retarder can again be used at full power.
High engine speeds cool the retarder most effectively and allow it to be used for the maximum amount of time.
System description
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Braking effectThe braking effect obtained depends upon:
• System characteristics
• Rear axle ratio
• The driver's experience
System characteristics
If the vehicle is equipped with ABS/EBS, EDC or Opticruise, then system interaction gives special brake characteristics. With for example Opticruise and EDC, Opticruise can downshift during retarder braking.
Rear axle ratio
The rear axle ratio of the truck or bus gives different braking power, see graph. During short periods of braking, the rear axle ratio and tyre size are the determining factors. During prolonged braking, heat generation (cooling) is the determining factor.
Brake performance on downhill gradients
The effect of downhill gradients and rear axle ratio on brake performance. Higher axle ratio increases the brake performance.
1 _____ = At 60 km/h and in 9th gear
2 ------- = At 77 km/h and in 10th gear
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System description
8 © Scania CV AB 1999, Sweden 1050f16b.mkr
The driver's experience
The driver's habit of utilising the system's capacity, especially during manual gearchanges, see illustrations below. Engine braking can be used on vehicles with as well as without retarder.
Engine braking without retarder
On vehicles without retarder, engine braking occurs in low gear, at low vehicle speed and at high engine speed.
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Engine braking with retarder
On vehicles with retarder, engine braking occurs in a higher gear (engine braking and retarder braking), at a higher vehicle speed and at high engine speed.
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System description
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Mechanical system• This description covers the function of the
entire mechanical system in general, but covers the retarder in detail.
• More information regarding the mechanical design can be found in main group 10 Scania Retarder, Work description, under dismantling and assembling.
• The hydraulic functions of the mechanical components are more fully described under Hydraulic system.
General
A vehicle with this auxiliary brake system has, besides the retarder itself, several other modifications, such as to the cooling system.
High flow coolant thermostats are used. They are fitted in a separate, double thermostat housing. The same type of thermostats and housing are used on both trucks and buses, irrespective of engine type.
Note: The ordinary thermostat housings used in the equivalent vehicles without the retarder should not have any thermostats.
The above is detailed in the spare parts catalogue for each chassis type with the gearbox designation ending in R, e.g. GRS900R or GR801R.
Mechanical system
10 © Scania CV AB 1999, Sweden 1050f16b.mkr
Mechanical system, overview
The retarder has an independent oil system with an oil sump connected directly to the retarder housing. The oil sump consists of two halves; the valve housing and the oil sump cover.
A proportional valve A receives an accurately regulated drive current from the control unit. The strength of this current corresponds to the required brake torque. The proportional valve in turn applies an appropriate air pressure to a control valve in the retarder valve housing.
The control valve lets in oil between the retarder rotor and both the stators. The control valve assumes a position that achieves the correct oil pressure for the particular brake torque required.
The position of the control valve then changes as the vehicle speed decreases. The position is continuously adjusted using oil pressure from behind so that the required brake torque is actually achieved.
The required torque may of course be changed at any time by either the driver or by the integrated downhill speed control regulator in the control unit.
An oil accumulator B is used to rapidly fill the retarder when activated.
The oil is greatly heated during retarder braking and is cooled in a designated oil cooler C by the engine coolant.
The thermostats and thermostat housing are described in Mechanical system, under General.
A valve block V97 is introduced from 9908 on trucks and 9910 on buses. The valve block replaces the 3 valves:
• Proportional valve V76, A
• Air supply for solenoid valve (ON/OFF) V74, D
• Solenoid valve V75 for oil accumulator, E
Component locations, old design
The new valve block
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Mechanical system
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Retarder installation in vehicle
The retarder is fitted to the planetary gear part of the gearbox. The drive is the same on gearboxes GR801R, GR900R, GRS890R/900R and GRSH900R.
Retarder
Actual installation in the vehicle is essentially the same for trucks and buses; the locations of the oil cooler and the oil accumulator are different, but their operation is the same.
IMPORTANT! The retarder oil hoses move a great deal due to pressure pulses. The retarder loses its braking power if a hose ruptures or starts to leak.
The location of hose clips, coolant pipes and similar components varies with chassis as well as engine type. See Scania's parts information.
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Retarder installation in a truck
Retarder installation in a bus
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Mechanical system
12 © Scania CV AB 1999, Sweden 1050f16b.mkr
Retarder functionWhen the retarder is braking, oil enters between the stators 1 and the rotor 2. The flow of oil then swirls, See illustration Retarder braking. The flow of oil acts on the rotor with a damping effect that opposes its movement. In this way, the retarder shaft is braked.
The speed of the rotor is proportional to the road speed of the vehicle. The higher the speed of the rotor, the faster the flow of oil. This means that less and less oil is required to achieve a particular brake torque as the speed of the rotor increases. Conversely, this means that the quantity of oil must be increased in order to maintain the required brake torque as road speed (and thus shaft speed) decreases.
The retarder shaft 3 has a gear 4. The torque is transmitted via an intermediate gear 6 to a gear 5. The gear 5 drives the retarder shaft from the output shaft on the planetary part and also takes up the braking power from the retarder. The retarder shaft and the intermediate gear are carried on two taper roller bearings each.
Retarder function
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Retarder drive
The retarder shaft is driven by a cylindrical gear set whose ratio is 2:1. The retarder shaft thus rotates at twice the speed of the gearbox output shaft.
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Retarder braking
When the retarder is filled with oil, the shaft that drives the retarder rotor is damped. Higher oil pressure means an increase in the quantity of oil between the rotor and the stators and thus increased braking power.
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Retarder function
14 © Scania CV AB 1999, Sweden 1050f16b.mkr
Hydraulic system
General
This description begins with a general overview of the complete hydraulic system. We then show different operational conditions.
The electrical function of the hydraulic components is described in greater detail in main group 10 Scania Retarder, Function description.
The design of the hydraulic components is shown in the exploded views in main group 10 Scania Retarder, Work description, under Valve housing and retarder housing.
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Working parts of the retarder. When oil enters between the rotor and the two stator rings, a resistance is created that slows the rotor.
Hydraulic system
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Hydraulic system, overview of old design
Components in the hydraulic system
1 Stators
2 Rotor
3 Shaft
7 Oil pump
8 Sump
9 Filter
10 Control valve
11 Oil cooler
12 Chamber
13 Air ducts
14 Coolant oilway
15 Radial seals
16 Accumulator
17 Solenoid valve V75
18 Non-return restriction valve
19 Proportional valve V76
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20 Solenoid valve V74
21 Bypass valve
22 Safety valve
23 Channel
24 Spring
25 Cone
Hydraulic system
16 © Scania CV AB 1999, Sweden 1050f16b.mkr
Hydraulic system, overview of later design
Components in the hydraulic system
1 Stators
2 Rotor
3 Shaft
7 Oil pump
8 Sump
9 Filter
10 Control valve
11 Oil cooler
12 Chamber
13 Air ducts
14 Coolant oilway
15 Radial seals
16 Accumulator
17 Solenoid valve
18 Non-return restriction valve
19 Proportional valve
20 Solenoid valve
21 Bypass valve
22 Safety valve
23 Channel
24 Spring
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Hydraulic system
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New design of the proportional valve
A new valve block, V97, is introduced in production from 9908 on trucks and from 9910 on buses. The functions for the following are incorporated into the valve block:
• Proportional valve 19
• Air supply for solenoid valve (ON/OFF) 20
• Solenoid valve for oil accumulator 17
Note: The new valve block V97 requires a higher control frequency, 360 Hz. This frequency is available from control units manufactured from 9902. Otherwise, the system is not modified but works in the same way irrespective of valve design.
Retarder
There is an oil pump 7 on shaft 3 which receives oil from the sump 8, via the filter 9. From there, the oil is directed via the control valve 10, either to the rotor 2 for braking or to the oil cooler 11 for cooling in disengaged mode.
There are two annular chambers 12 between the rotor 2 and the stators 1. When these are filled with oil, the rotor and the stators force the oil to change direction repeatedly. The flow of oil thus provides resistance to the rotor and counteracts its rotation.
The oil flows extremely quickly and in a curved spiral path. Centrifugal force causes the oil in the chambers to accumulat on the periphery and attempt to escape. The oil is therefore retained in the chambers by back pressure from the outside. Higher pressure gives more oil in the chambers and higher brake torque.
The chambers are connected to the sump via air ducts 13. These are necessary to enable the quantity of oil to be adjusted quickly when the driver wants to adjust the brake torque.
The oil pump 7 rotates as soon as the vehicle is in motion. When braking, the oil is directed via the control valve to the rotor and the oil cooler. When the retarder is disengaged, most of the oil is directed via the control valve to the oil cooler and the sump. A small proportion is directed via the coolant oilway 14 for lubrication and cooling.
Safety valve 22 is fitted with an additional sealing ring from chassis number SS1251239, SN4414949, SA9043610, SBK1835768.
The retarder and gearbox oil systems are separated by two radial seals 15.
Hydraulic system
18 © Scania CV AB 1999, Sweden 1050f16b.mkr
Oil accumulator
The accumulator 16 is emptied and quickly fills the retarder when braking begins. This is activated with compressed air from a solenoid valve 17. There is a non-return restriction valve 18 in the accumulator outlet.
The left-hand position is the non-return valve position. The oil then passes both through the restriction and on the outside of the bushing. The non-return valve position is used both when emptying and refilling when the driver ceases braking.
The right-hand position is the restriction valve position. The oil then passes only through the restriction. The restriction valve position is used when refilling the accumulator during braking.
Oil cooler
The oil cooler 11 transmits the heat from the retarder oil to the engine cooling system where the heat is finally dissipated by the vehicle's ordinary radiator.
Proportional valve
The supply air solenoid valve 20 and the proportional valve 19 are both actuated by the control unit. Unreduced air pressure is fed from solenoid valve 20 to the proportional valve 19.
The control unit supplies a current, whose strength corresponds to the required brake torque, to the proportional valve. This then delivers air pressure to control valve 10 which creates the oil pressure necessary to achieve the required brake torque.
Safety system
See When the retarder is to stop braking, under Safety system
Hydraulic system
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When the retarder is not braking
Disengaged position
The supply air solenoid valve 20 and the proportional valve 19 are not activated. This means that the compressed air chambers below the control valve 10 and the safety valve 22 are vented.
The oil flow from pump 7 is therefore directed via the control valve to the oil cooler 11 and back to the retarder via the bypass valve 21 to oil sump 8.
Bypass valve 21 is intended to maintain a return pressure to the accumulator.
A certain amount of oil is also pumped through the coolant oilway 14 to the retarder chambers 12 for lubrication and cooling. This oil is drained through the upper outlet port in the control valve.
The oil accumulator's solenoid valve 17 is also unactivated. The piston in the accumulator 16 is at its starting point and the accumulator is full of oil.
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Disengaged position (retarder not braking)
Hydraulic system
20 © Scania CV AB 1999, Sweden 1050f16b.mkr
When the retarder is to start braking
Engaging position
When the retarder is engaged, the supply air solenoid valve 20 releases air to the proportional valve 19. The proportional valve in turn delivers an air pressure corresponding to the required brake torque. Control valve 10 switches over to the filling position and safety valve 22 closes.
The oil pump 7 now pumps oil into the retarder oil chamber from the inlet side. The oil accumulator 16 is activated by its solenoid valve 17 and fills the retarder oil chamber from the outlet side. In this way, quick activation of the retarder is achieved.
Oil pressure starts to build up on the top side of the control valve via channel 23, which goes through the piston. Safety valve 22 and bypass valve 21 are kept closed during the entire engaging process.
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Engaging position (retarder about to start braking)
Hydraulic system
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When the retarder is braking
Engaged position
Proportional valve 19 maintains an air pressure to control valve 10 which is proportional to the required brake torque. An oil pressure builds up above the piston via channel 23 in the control valve. This, together with spring 24, moves the piston down to equilibrium.
In this equilibrium position, the flow will go through the retarder part and the oil cooler. A certain amount of oil is used to fill the accumulator.
Oil pump 7 always supplies a little excess oil. In the equilibrium position, the control valve opens a passage via a cone 25, which directs the excess oil on through the bypass valve 21 to the sump.
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Engaged position (retarder braking)
Hydraulic system
22 © Scania CV AB 1999, Sweden 1050f16b.mkr
Change in vehicle speed
When the speed of the vehicle is changed, the speed of the rotor also changes. If the driver wishes to continue braking with the same torque, the following applies.
Note: Neither the air pressure from the proportional valve nor the oil pressure regulated by the control valve is changed.
When vehicle speed decreases, centrifugal force also decreases. For this reason, a larger quantity of oil remains in the chambers 12 and the required brake torque is maintained. The control valve 10 also changes its position in order to create a narrower passage at cone 25. This is because pump flow is dependent on vehicle road speed. The control valve is forced to set itself in this manner to maintain the equilibrium in pressure.
As speed increases, centrifugal force also increases. More oil is therefore drained from the chambers 12 and the required brake torque is maintained. The control valve 10 therefore changes its position in order to create a larger passage at cone 25.
Hydraulic system
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When the brake torque is to be increased or reduced
Increasing brake torque
Proportional valve 19 raises the air pressure to control valve 10, which once again assumes the filling position. The oil in the retarder chambers 12 is topped up so that the oil pressure increases, causing the brake force to increase.
After a moment, the control valve assumes a new equilibrium position corresponding to the higher oil pressure. During this change in pressure, the oil accumulator is not used as the system is already filled with oil.
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Increasing brake torque
Hydraulic system
24 © Scania CV AB 1999, Sweden 1050f16b.mkr
Reducing brake torque
Proportional valve 19 reduces the air pressure to control valve 10, which assumes a lower position. The seepage gap at cone 25 on the control valve increases and allows more oil to pass. The quantity of oil in the retarder chambers 12 decreases and the pressure thus also decreases.
After a moment the control valve assumes a new equilibrium position which corresponds to the lower oil pressure.
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Reducing brake torque
Hydraulic system
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Change in speed
When the speed of the vehicle is changed, the speed of the rotor also changes. If the driver wishes to continue braking with the same torque, the following applies.
Note: Neither the air pressure from the proportional valve nor the oil pressure regulated by the control valve is changed.
• When vehicle speed decreases, centrifugal force also decreases. For this reason, a larger quantity of oil remains in the chambers 12 and the required brake torque is maintained. The control valve 10 also changes its position in order to create a narrower passage at cone 25. This is because pump flow is dependent on vehicle road speed. The control valve is forced to set itself in this manner to maintain the equilibrium in pressure.
• As speed increases, centrifugal force also increases. More oil is therefore drained from the chambers 12 and the required brake torque is maintained. The control valve 10 therefore changes its position in order to create a larger passage at cone 25.
Hydraulic system
26 © Scania CV AB 1999, Sweden 1050f16b.mkr
When the retarder is to stop braking
Disengaging position
The proportional valve 19 drains all the air from the control valve 10 which moves down to its lowest position, at which point the oil flows back to the sump 8 via the bypass valve 21 and the upper outlet port. In doing this, disengaging position is resumed and retarder braking ceases. The flow of oil is now mainly directed to the cooling circuit.
The oil flow in the coolant oilway 14 is not used exclusively for cooling. A small proportion is also used to lubricate the moving parts of the retarder.
When the control valve 10 is completely open, the retarder is drained via the upper outlet port in the control valve.
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Disengaging position (retarder about to stop braking)
Hydraulic system
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Safety system
The safety system ensures that retarder braking can be interrupted on request from the ABS/EBS control units, even in case of a fault somewhere in the retarder control system.
Dual safety is provided by the system which works as follows.
• The supply air solenoid valve 20 and safety valve 22 can drain the pressure even if proportional valve 19 or control valve 10 should seize and are blocked. The solenoid valve is then drained via a check valve.
• The supply air solenoid valve 20 can have its electrical supply cut directly by the ABS/EBS system, via a relay, even if the auxiliary brake control unit is attempting to keep the solenoid valve activated.
• If a coolant hose ruptures and the oil overheats, safety valve 22 operates as a circuit breaker and drains the oil to the oil sump.
Hydraulic system