6.1 6 DRIVE TRAIN 1DRIVE TRAIN 6.1Tasks and main assemblies x Drive train with planetary drive axle 1 2 3 4 5 6 6 LEGEND 1 Engine 2 Clutch 3 Standard gearbox 4 Propshafts 5 Middle drive 6 Planetary drive gear BASIC PRINCIPLES Drive train main assemblies The drive train has the task of providing the necessary pulling and pushing forces for the movement of a vehicle in accor- dance with the effective road resistance. It can be divided into main assemblies (➜ Fig.). As it is a very complex component, the engine is described in detail in this ma- nual in chapter 5. In order to ensure the drive of the com- mercial vehicle from a standstill through the desired partial speeds all the way to the maximum speed, the drive train must perform the following functions: Driveaway Conversion (adaptation) of torque and engine speed Balancing different engine speeds of inner and outer wheel on cornering Operation forwards and backwards Operation of the engine in the opti- mised range for consumption and exhaust gas of the characteristic map (➜ page 5.70). Drive for secondary consumers FUNCTION Driveaway element In most cases, the driveaway element is a clutch. It temporarily interrupts the con- nection between the engine and gearbox, bringing the vehicle to a standstill with a gear engaged and initiating the driveaway. On driveaway, the clutch "slips", bridging the rotational speed difference between the engine and gearbox (➜ page 6.14). Standard gearbox In the standard gearbox with front-moun- ted or rear-mounted group, engine torque and engine speed are converted accor- ding to the currently required tractive force. Here, the power output, i.e. the pro- duct of the torque and engine speed, should remain as constant as possible. The standard gearbox is controlled via ac- tuators and shifting elements operated di- rectly or electropneumatically by the driver (➜ page 6.22). Propshafts So-called propshafts are required to transfer the engine output from the gear- box to the transfer cases and/or final drives (depending on the number of driven axles). These have shifting section too- thing in order to be able to balance out the vertical movement of the axles (length compensation). With longer wheelbases, rubber-cushio- ned intermediate propshaft bearings are used. Middle drive The middle drive, also called the final dri- ve, consists of the axle drive with the axle- drive ratio and the differential gear. The axle drive (➜ page 6.32) transforms the rotational movement of the drive shaft into a rotational movement of the axle shafts of the wheels. The gear ratio in the axle drive serves to reduce the rotational speed and increase the torque of the drive shaft. The differential gear enables balancing of the rotational speed difference between the wheels of an axle on cornering (➜ page 6.33). Planetary drive gear In the case of planetary drive axles, the torque and rotational speed of the axle shafts are transferred to the drive wheels and reinforced or reduced there in a pla- netary gear set, as the case may be (➜ page 6.26).
Drive train main assembliesThe drive train has the task of providing the necessary pulling and pushing forces for the movement of a vehicle in accor-dance with the effective road resistance. It can be divided into main assemblies (➜ Fig.). As it is a very complex component, the engine is described in detail in this ma-nual in chapter 5.
In order to ensure the drive of the com-mercial vehicle from a standstill through the desired partial speeds all the way to the maximum speed, the drive train must perform the following functions:
Driveaway
Conversion (adaptation) of torque and engine speed
Balancing different engine speeds of inner and outer wheel on cornering
Operation forwards and backwards
Operation of the engine in the opti-mised range for consumption and exhaust gas of the characteristic map (➜ page 5.70).
Drive for secondary consumers
FUNCTION
Driveaway elementIn most cases, the driveaway element is a clutch. It temporarily interrupts the con-nection between the engine and gearbox, bringing the vehicle to a standstill with a gear engaged and initiating the driveaway. On driveaway, the clutch "slips", bridging the rotational speed difference between the engine and gearbox (➜ page 6.14).
Standard gearboxIn the standard gearbox with front-moun-ted or rear-mounted group, engine torque and engine speed are converted accor-ding to the currently required tractive force. Here, the power output, i.e. the pro-duct of the torque and engine speed, should remain as constant as possible. The standard gearbox is controlled via ac-tuators and shifting elements operated di-rectly or electropneumatically by the driver (➜ page 6.22).
PropshaftsSo-called propshafts are required to transfer the engine output from the gear-box to the transfer cases and/or final drives (depending on the number of driven axles). These have shifting section too-thing in order to be able to balance out the vertical movement of the axles (length compensation).
With longer wheelbases, rubber-cushio-ned intermediate propshaft bearings are used.
Middle driveThe middle drive, also called the final dri-ve, consists of the axle drive with the axle-drive ratio and the differential gear.
The axle drive (➜ page 6.32) transforms the rotational movement of the drive shaft into a rotational movement of the axle shafts of the wheels. The gear ratio in the axle drive serves to reduce the rotational speed and increase the torque of the drive shaft.
The differential gear enables balancing of the rotational speed difference between the wheels of an axle on cornering (➜ page 6.33).
Planetary drive gearIn the case of planetary drive axles, the torque and rotational speed of the axle shafts are transferred to the drive wheels and reinforced or reduced there in a pla-netary gear set, as the case may be (➜ page 6.26).
6.2
6
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Speed and axle-drive ratio
01020304050607080
100110120130
90
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 G
v max [km/h]
a b
LEGENDColumns:a Planetary drive axle AP 1352
with gear ratio 3.63b Hypoid axle HY 1350
with gear ratio 3.36Formula symbols:G Gear stepvmax Maximum speed
BASIC PRINCIPLES
Drive train operating principleThe manual gearbox and final drive have the main task of transferring the right amount of engine torque and rotational speed to the wheels depending on the dri-ving situation.
The crankshaft of a commercial vehicle engine (➜ page 5.14) rotates many times faster than the wheels during driving. The same rotational speed of the crankshaft and wheels would result in very high speeds depending on the tyres and po-wer output. As the engine speed cannot be reduced (this is only to provide ade-quate power output from the engine), va-rious gear ratios have to be engaged in the standard gearbox. This enables the ef-fective torque and tractive force to be ad-apted to the specific driving needs.
Depending on the area of application of a commercial vehicle, various axle-drive ra-tios are also fitted. They determine the maximum speed and tractive force. The tractive force is a measure of the climbing capacity of a commercial vehicle.
FUNCTION
Tractive forceThe torque of the engine is gradually con-verted by the standard gearbox. For each engaged gear, certain torque characteris-tics with the corresponding rotational speeds are provided.
The torque is boosted once again in the fi-nal drive. Diving the effective torque at the wheels by the radius of the wheels results in the tractive force effective at the wheels.
If the tractive force characteristics for the individual gear steps are applied over the speed in a diagram and the points of the maximum power output are connected, the result is the torque or tractive force hy-perbola (➜ Fig. page 6.3). This is also re-ferred to as a tractive force chart or driving chart. It shows the tractive force characte-ristics depending on the speed of the ve-hicle.
Axle-drive ratioThe axle-drive ratio in the final drive influ-ences the final speed and climbing capa-city of the vehicle.
EXAMPLE
The 4x2 vehicle TGA 18.480 with the D2876LF12 engine with 480 hp and the ZF 16 S 221 OD Comfort Shift gearbox can be equipped with eight different drive axles for the different areas of application (required climbing capacity as well as achievable speeds in each gear).
The configuration to a theoretical maxi-mum speed of more than 120 km/h is ne-cessary so that the engine can be opera-ted in the economical speed range at the speed of 85 to 90 km/h that is usual in traffic.
Two characteristic axles for a driveaway climbing capability of 18 % (skid limit) with 40 t total weight serve as an example:
The HY 1350 hypoid axle with i = 3.36 is a typical axle for long-distance transport. It enables a theoretical maximum speed of up to 130.6 km/h (➜ Fig.).
The AP 1352 planetary drive axle with i = 3.63 is used above all in construction site vehicles. The theoretically achievable maximum speed is 120.9 km/h (➜ Fig.).
6.3
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EXAMPLE
Formula symbols:α Climbing capabilityG Gear stepR Slip limit (18 %)Columns:a Axle-drive ratio 3.7b Axle-drive ratio 3.4c Theoretical values
Note:This diagram serves only as an example for visualisation, i.e. the values do not represent a current vehicle.
Climbing capacity and axle-drive ratio
Formula symbols:FZ Tractive forceM Torquev Speedα Climbing capability at maximum
torquesNote:This diagram serves only as an example for visualisation, i.e. the values do not represent a current vehicle.
Curves:a Torque characteristics in the indi-
vidual gearsb Tractive force hyperbola
Tractive force hyperbola
α
[%]
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 G
R
0
10
20
30
40
50
b
c
a
0 120110100908070605040302010
20
40
60
80
100
120
140
FZ [kN]
v [km/h]
FZ
41,7%
33.9%
27.6%
22.7%
19%
15.7%
12.5%
10.3%
7.9%6.5%
5.3%4.3%
3.5% 2.8% 2.0% 1.5%0.0%
M
M α
a
b
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Heavy construction site vehicle with four axles
BASIC PRINCIPLES
Drive conceptDepending on the arrangement of the en-gine and drive axles, fundamental distinc-tions are made between the following dri-ve concepts:
Rear-wheel drive (standard drive)
Front-wheel drive (usually passenger cars)
Multiple-axle drive
All-wheel drive
As four or more axles are used on com-mercial vehicles as opposed to passenger cars, there are a large number of drive concepts. These are described by the wheel formulas (➜ page 2.2).
Depending on the drive concept, a num-ber of axles are configured as drive and/or steer axles (➜ page 3.3).
Almost all modern commercial vehicles are conceived as cab-over-engine vehic-les (➜ page 2.1). Underfloor vehicles are no longer built. Rear engines are used ex-clusively in buses (➜ page 15.14).
Alternative drive systems such as the na-tural gas engine, hydrogen engine, fuel cell and hybrid drive system (diesel-elec-tric) are described in the chapter entitled "Buses". These have been developed above all for buses in public short-dis-tance passenger transport.
FUNCTION
Two-axle commercial vehiclesThe standard versions of two-axle com-mercial vehicles have a driven rear axle. These are suitable mainly for road use.
For construction site deployment, two-axle vehicles are equipped with an additi-onal driven front axle.
High driveaway torques and climbing ca-pacity are required and can be achieved using all-wheel drive.
Three-axle commercial vehiclesCommercial vehicles with rear-axle drive and a leading or trailing axle (➜ page 3.6) are used in freight road transport.
Commercial vehicles with two driven rear axles or with all-wheel drive, i.e. three dri-ven axles, are suitable for construction site deployment. The latter are regarded as classical off-road and construction site commercial vehicles.
Four-axle commercial vehiclesFour-axle commercial vehicles are often used above all in the area of construction sites with two driven rear axles and two steered front axles, and with high permit-ted total weights (➜ Fig.).
The four-axle vehicle with all-wheel drive is used for heavy-duty construction site de-ployment when a high level of off-road mobility is required.
With more than four axles, special drive concepts are applied, usually with special steering systems. These are used in spe-cial vehicles.
6.5
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Force transmission by means of a friction clutch
1 2 3
LEGEND1 Engine2 Clutch3 Gearbox
BASIC PRINCIPLES
Clutch designsIn motor vehicle engineering, the clutch is generally defined as a disengageable con-nection between the engine and drive ele-ment. It serves as the driveaway element in the drive train.
A fundamental distinction is made bet-ween two clutch designs:
Adherent clutch
Positive-engaged clutch
Adherent clutches use the friction to transfer the torque. They are thus also re-ferred to as friction clutches.
Positive-engaged clutches use the shapes of two clutch elements that fit into one another to transfer the torque.
Only adherent clutches are used for the force transmission to drive vehicles.
FUNCTION
Friction clutchThe clutch in a commercial vehicles must perform the following main tasks:
Speed balancing between drive and output
Transferring the engine torque
Separating the power flow between the engine and multi-ratio gearbox
Enabling soft and jolt-free driveaway
Damping torsional vibrations
Protection against component over-load
In conjunction with a standard gearbox, dry single-disc clutches are normally used.
Due to the high engine torques (at MAN up to 2500 Nm), heavy commercial vehic-les require dry double-disc clutches. Compared to single-disc clutches, they can transfer greater torque.
EXAMPLE
All of the clutches used in MAN commer-cial vehicles have asbestos-free linings and are configured for a clutch service life of more than 600,000 km.
The large friction surfaces mean that de-spite low operating forces and small ope-rating paths adequately high torques can be transferred.
6.6
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Clutch disengagement force
150
175
200
0 21 3 4 5 6
225
F [N]
s [mm]
a
b
LEGENDCurves:a Coil-spring clutchb Diaphragm-spring clutchFormula symbols:F Disengagement forces Path of the clutch operator
BASIC PRINCIPLES
Standard clutch for commercial ve-hiclesThe most important components of a clutch are (➜ Fig. page 6.7):
Flywheel
Clutch or driving plate
Pressure plate
Release lever
Clutch operator
Torsional absorber
The pressure plate is pressed against the driving plate by 6 to 36 coil springs or a di-aphragm spring.
Diaphragm springs (disc springs) are more compact than coil springs. They re-quire less disengagement force (➜ Fig.) and are also insensitive to high rotational speeds.
Diaphragm-spring clutches are the stan-dard clutches used nowadays in commer-cial vehicles and passenger cars.
FUNCTION
Engaged stateOn both designs, the spring force applies a normal force in the pressure plate and this presses the friction linings of the clutch or driving plate against the flywheel. With the clutch closed, the engine torque is transferred without slip to the multi-ratio gearbox by the clutch disc, which is mounted on the gearbox input shaft in such a way that it cannot turn.
Disengaged stateThe release lever presses against the dia-phragm-spring reeds and relieves the pressure plate to the extent that the clutch disc runs freely between the flywheel and pressure plate. In this state, a shift in the gearbox (gear change) is possible without difficulty.
On MAN commercial vehicles of the Evo-lution series, L2000 model, the clutch operator presses against the diaphragm-spring reeds; on the heavy M2000 models as well as the TGA model series, it pulls the diaphragm springs and thus releases the clutch disc.
The total of the distances between the clutch lining surfaces and the flywheel sur-face and the pressure plate surface is re-ferred to as the air gap. The total air gap should be 0.6 to 1.0 mm.
Clutch discEvery combustion engine creates torsio-nal vibrations that spread through the clutch into the gearbox. This leads to ratt-ling noises and increased wear.
To prevent these effects or reduce them significantly, clutch discs are equipped with torsional absorbers. Torsional absor-bers consist of tangentially arranged coil springs and axially loaded friction rings.
In order to achieve soft engagement and prevent harsh driveaway, virtually all clutch discs nowadays are also equipped with lining springs. These axial springs between the clutch linings lead to even force transmission and minimise wear.
MAN clutches have pre-absorbers that si-gnificantly reduce idling rattle in particular.
Hydrodynamics in the torque converter on driveaway
3
1
2
LEGEND1 Pump gear2 Stator3 Turbine
BASIC PRINCIPLES
Hydrodynamic force transmissionOn the hydrodynamic clutch, the torque is transferred by means of the hydrodyna-mic forces of a fluid. A hydrodynamic clutch cannot change the initiated torque; it can only transfer it (output and input torque always remain the same).
The hydrodynamic converter can vary the output moment in relation to the torsion or work as a pure hydrodynamic clutch wit-hout torque conversion.
Hydrodynamic clutches and converters in commercial vehicles bridge the rotational speed difference between the engine and drive train. They are thus very good as dri-veaway elements. However, to shift gears, the hydrodynamic clutch must have a downstream friction clutch with downstream standard gearbox or auto-matic gearbox (➜ page 6.28).
FUNCTION
Hydrodynamic clutchThe hydrodynamic clutch consists of a housing, a pump gear (primary gear) and a turbine (secondary gear). The vanes of the pump gear are firmly attached to the housing. The fluid used for force transmis-sion is hydraulic fluid (➜ page 17.9).
The pump gear is connected to the crankshaft. The turbine is seated on the gearbox input shaft in such a way that it cannot turn. When the pump gear turns, the hydraulic fluid in the chambers of the pump gear is pressed outwards by the centrifugal force and from there into the turbine chambers. The turbine also starts to turn. It conveys kinetic energy to the downstream gearbox.
On account of the force transmission using fluid, the hydrodynamic clutch ab-sorbs vibrations and is non-wearing.
Hydrodynamic torque converterIn contrast to the hydrodynamic clutch, a housing, pump gear and turbine and an additional guidance system (deflection or reaction gear) is used on the hydrodyna-mic torque converter. Converters used in commercial vehicles are usually built ac-cording to the so-called "Trilok" design. With this design, the guidance system is located between the turbine and pump gear and is equipped with a one-way overrun. The stator deflects the flow of flu-
id from the turbine back to the pump gear. This deflection increases the torque.
Depending on the layout of the converter, the stator achieves 1.9 to 2.5 times the torque increase on driveaway (➜ Fig.).
With increasing equalisation of the turbine speed to the pump speed, the rotational speed difference between the pump gear and turbine falls. With the same rotational speed, fluid flows onto the guide vanes of the stator from the rear. The stator also turns; torque conversion is no longer pos-sible.
Converter lockup clutchOnce the highest rotational speed match has been reached, a converter lockup clutch connects the turbine with the pump gear by means of frictional engagement. This prevents the slip caused by the fluid on force transmission, which is normally so unfavourable for the efficiency.
The converter lockup clutch is usually ac-tivated automatically.
6.9
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FUNCTION
Converter lockup clutch opened Converter lockup clutch closed
1 Flow of force (from engine to gearbox)2 Drive3 Turbine4 Stator5 Pump gear6 Overrun7 Output8 Converter lockup clutch
Force characteristics in the hydrodynamic converter with lockup clutch
2 3 4 5 6 7 81
6.10
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Dog clutch in a differential lock
4
1
2
3
LEGEND1 Clutch dogs2 Gearshift sleeve of the differential
lock (can be shifted on the axle shaft toothing)
3 Pneumatic gearshift element4 Control fork
BASIC PRINCIPLES
Special forms of clutchThe wide range of tasks to be performed by clutches leads to special forms of dis-engageable connections in the drive train that are exactly geared to the tasks.
Positive-engaged clutch
Dog clutch
Adherent clutches
Multi-disc clutch
Centrifugal clutch
Dual clutch
Torque converter with lockup clutch
FUNCTION
Dog clutchA dog clutch is a positive-engaged clutch that is used on commercial vehicles for manual shifting of longitudinal and trans-verse differential locks as well as for enga-geable all-wheel drive (➜ Fig.).
A dog clutch can only be shifted when the vehicle is at a standstill.
Multi-disc clutchMulti-disc clutches have a number of discs. Depending on the area of applicati-on, the discs run in an oil bath or dry. Mul-ti-disc clutches require less space, as the large number of friction pairings means that they can transfer relatively high tor-ques despite their small dimensions. When engaged, intermediate discs loca-ted between the discs are connected ad-herently by spring force.
Multi-disc clutches are used most fre-quently for motorcycles, automatic gear-boxes and automatic differential locks (➜ page 6.34).
Centrifugal clutchA centrifugal clutch consists of a clutch drum connected to the gearbox and the engine. Articulated clutch elements are pressed against the clutch drum, by an in-creasing centrifugal force, as the engine speed rises, thus enabling the transfer of the engine torque.
Dual clutchIn the dual clutch, two clutches are grou-ped into one unit. One clutch serves to transfer the engine torque to the multi-ra-tio gearbox; the second clutch transfers the engine torque, for example, to a po-wer take-off (➜ page 6.29).
6.11
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Converter shift clutch (WSK 440)
1 3 4
6 7 8
Power flow schema in the WSK 440
1
A4
5
7
8
1
B3
7
8
1
C
2 5
76
8
LEGENDA Driveaway or manoeuvering in the
converter rangeB Driving with closed converter lockup
clutchC Overrun operation (braking with
engine via overrun one-way clutch and with retarder)
Converter shift clutch WSKThe converter shift clutch WSK is a sys-tem combination especially developed for heavy-duty operation consisting of a hy-draulic torque converter and a dry clutch.
Essentially, a converter shift clutch con-sists of the following components (➜ Fig.):
Hydrodynamic torque converter with overrun
Lockup clutch (bridges the converter at high engine speed)
Overrun one-way clutch (bridges the converter in the overrun condition)
Retarder (optional boosting of the bra-king torque in the overrun condition)
Shift clutch
To shift the gears, the shift clutch inter-rupts the power flow. After the gear step has been engaged, the torque converter ensures a smooth build-up of the torque transfer.
On driveaway, the shift clutch opens while the first gear is being engaged. On closing the clutch, there is no need to press the accelerator, as the converter only trans-fers very low torque on idling. Only when the shift clutch has closed is the engine speed increased by pressing the accele-rator. In this phase, the converter ensures a peak in the output torque up to 2.5 ti-mes the input torque.
If the drive and output speeds approach one another up to a certain speed gap, the lockup clutch bridges the converter and thus achieves a rigid drive-through.
The overrun one-way clutch bridges the converter in the overrun condition, which means that the engine braking torque can be exploited. As an option, the converter shift clutch is given a retarder to boost the braking torque in the overrun condition (➜ Fig.).
The converter shift clutch permits jolt-free driveaway and manoeuvering with cen-timetre precision, even under difficult cir-cumstances. The driveaway and shifting operations are virtually wear-free, even with high road-train weights, as the shift clutch (dry clutch) can close without fric-tional slip. The converter completely assu-mes the necessary conversion of the torque.
EXAMPLE
MAN TipMatic gearshift system with WSKAn innovation is the use of the converter shift clutch on the MAN TipMatic gearshift system (➜ page 6.24). A converter shift clutch (instead of the electropneumatically operated, mechanical clutch) in combina-tion with an automatic standard gearbox enables easy driveaway operations. This includes automatic gearshifts; the clutch pedal can be eliminated.
The MAN TipMatic gearshift system with the converter shift clutch WSK 440 has been specially developed by MAN for transporting heavy loads. It was fitted for the first time on the four-axle heavy-duty semitrailer tractors of the Trucknology Ge-neration (TGA). Here, the converter shift clutch means that the huge torque of the V10 engine can be used for driveaway and manoeuvering virtually without clutch wear. From a technical point of view, this powerful drive train permits total road-train weights of up to 250 t.
Clutch control via pedalTwo types of clutch control are distingu-ished:
Mechanical clutch control
Hydraulic clutch control
The cable pull versions of mechanical clutch control is used nowadays almost exclusively on passenger cars.
Hydraulic clutch control is self-adjusting and is standard equipment for commer-cial vehicles and upper class passenger cars on account of the high effective forces .
On commercial vehicles with high power output, clutches with strong diaphragm springs are necessary to ensure adherent connection in all situations. To reduce the operating forces, clutch boosters (servo clutches) are used.
FUNCTION
Hydraulic clutch controlWhen the clutch pedal is operated, the piston movement builds up pressure in the master cylinder; this is routed through the hydraulic line to the slave cylinder, where it is converted back into a longitu-dinal movement. The master and slave cy-linders are connected to one another via pipe and hose lines (➜ Fig.).
The enhancement of hydraulic clutch con-trol has led to the clutch operator with in-tegrated slave cylinder. Here, the clutch operator and slave cylinder form a unit that encloses the gearbox input shaft, whereby a release fork is not required.
For operation of the diaphragm-spring clutch, a distinction is made between clut-ches that are operated by "pulling" or "pushing" (➜ page 6.6).
Due to the more favourable lever relation-ships, the efficiency is better with a pulled clutch. The clutches used in heavy com-mercial vehicles have pulled clutch cont-rol.
The routing of hydraulic lines can be pro-tected in the vehicle and they permit long transfer paths without difficulty, e.g. on buses with rear engines.
Clutch boosterThe clutch booster is a hydraulic slave cy-linder combined with a compressed air
cylinder. The pedal forces are reduced to one fifth.
The clutch booster provides relief for the driver on conventional clutches, as lower pedal forces and paths are required. If the compressed air fails, the clutch remains operable but with greater pedal forces.
Electropneumatic clutch controlThe use of compressed air cylinders for clutch boosting or clutch control forms the technical basis for electronic clutch cont-rol on commercial vehicles. Depending on the gearbox version, MAN offers the follo-wing systems for electropneumatic clutch control:
MAN ComfortShift with button on the gearshift lever (alternative to clutch pedal)
MAN TipMatic fully automatic (without clutch pedal)
The electronic lining wear monitor with au-tomatic clutch readjustment is of decisive significance for exact functioning of the electropneumatic clutch control. A travel sensor monitors the disengagement travel of the clutch and transfers the measured value via the vehicle management compu-ter to the central on-board computer, which then determines the wear. If the li-ning thickness reaches 10 % of its original value, a warning is displayed in the driver display.
FUNCTION
MAN ComfortShiftOn the MAN ComfortShift gearshift sys-tem with ZF-Ecosplit gearbox (➜ page 6.23), there is an optional button on the gearshift lever for clutch control in addition to the conventional hydraulic actuation with compressed-air support controlled via the clutch pedal.
When the button is pressed, the vehicle management computer synchronises the engine and gearbox rotational speeds on shifting gear steps. Only then is the clutch closed. The driving pedal can remain in an unchanged position during this operation.
MAN TipMaticOn the MAN TipMatic gearshift system with automatic ZF gearbox (➜ page 6.24), all of the clutching operations required for shifting gears are automated. The electro-pneumatically operated clutch – the clutch pedal is eliminated – completely frees the driver of clutch control.
The MAN TipMatic control unit processes all the influencing variables and transfers the corresponding signals to the shift mo-dule and to various solenoid valves for pneumatic clutch control.
The travel sensor integrated in the clutch actuator monitors the disengagement tra-vel. The lining wear is re-established for each clutch engagement operation. The
actuation travel is redefined accordingly for the clutching operation.
Electronic clutch protectionFrequent excessive engine speeds lead to wear on clutches of up to 95 % on drivea-way and manoeuvering. On gearshifts, however, the clutch is subjected to less stress. The electronic clutch protection on MAN commercial vehicles reduces the li-ning wear and increases the clutch service life by means of the following functions:
Limitation of the driveaway engine speed to 1400 rpm with the clutch protection function of MAN ComfortS-hift
Lower clutch wear by means of engine management and optimised clutch control via vehicle management computer on MAN ComfortShift
Comfortable driveaway by means of sensitive clutch control and the high-est economy on MAN TipMatic by means of computerised influence on various variables on the clutching operation
Forced closure of the clutch if there is danger of overheating (MAN TipMatic)
6.14
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Types of gearbox
1
2 3
LEGEND1 Spur gears2 Bevel gears3 Worm gears
BASIC PRINCIPLES
Types of gearboxA gearbox serves to transfer, route, distri-bute and convert torques and rotational speeds. A gearbox can thus also be refer-red to as a torque or rotational speed con-verter. The relationship between the input and output rotational speed is referred to as the gear ratio or reduction ratio (➜ page 1.11).
A gearbox on which a number of gear ra-tios can be engaged and disengaged is referred to as a multi-ratio gearbox (➜ page 6.15). These are usually gear-driven. This applies both to automatic and manu-al gearboxes.
The a wide variety of requirements in ve-hicle construction for gearboxes has led to the development of a large number of variants.
The force transmission on gearbox in gear-driven and chain-driven gearboxes is positive-engaged; in belt-wrap gearboxes it is adherent. Belt-wrap gearboxes are used as continuously variable gearboxes on vehicles with low power output.
FUNCTION
Spur gearsSpur gears are used above all in standard gearboxes. The torque transfer is via spur gears. The axles of driven and driving wheels are parallel (➜ Fig.).
Bevel gearsBevel gears are used as axle drives (➜ page 6.32). Besides the gear ratio, they also enable deflection of the transferred torque by 90°. The axles of the gear wheels are arranged crosswise (intersec-ting ➜ Fig.).
Worm gearsWorm gears are used as axle drives in special vehicles, but also e.g. for the drives of windscreen wipers or as steering gears. With worm gears, the axles are also arranged crosswise (➜ Fig.).
Planetary gear setPlanetary gear sets (➜ page 6.26) are used on planetary drive axles, range-shift gearboxes, as rear-mounted groups and in automatic gearboxes.
Chain drivesChain drives are used above all as the pri-mary drive system on motorcycles.
Belt-wrap gearboxesBelt-wrap (or chain-wrap) gearboxes are intended for use as continuously variable gearboxes and they only differ with regard to the structure and material of the belt.
Either rubber belts reinforced with Kevlar or link chains are used.
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5.2.
1Des
igns
x
Gear steps on the three-speed sliding-gear countershaft gearbox
1z1
z1
z3
z2
z1
z2
z8
z7
zR
z1
z2
z3
z4
z5
z6
2 3
A B
C D
LEGENDA 1st gearB 2nd gearC 3rd gearD Reverse gear1 Sliding gears with control forks2 Main shaft3 Countershaft
BASIC PRINCIPLES
Multi-ratio gearboxA multi-ratio gearbox enables the setting of a number of different gear ratios and thus the torque and rotational speed con-version:
Converting and transferring the engine torque to provide the required tractive force
Stepping up the engine speed to achieve different speeds
Interrupting the power flow when the vehicle is stationary
Reversing the direction of rotation for reversing
To shift gears, the two connecting gear-box elements (gear wheels) must be brought to the same rotational speed. This operation is referred to as synchroni-sation (➜ page 6.18).
Designs of multi-ratio gearboxesThe following designs of multi-ratio gear-boxes are distinguished:
Sliding-gear countershaft gearbox
Shift dog gearbox
Gearshift-sleeve or gearshift sleeve synchromesh gearbox (coaxial and deaxial ➜ page 6.16),
Front-mounted and rear-mounted range-change gearbox (➜ page 6.20).
Shift dog gearboxes are used above all in motorcycles.
Gearshift sleeve synchromesh gearboxes are the gearboxes currently used in pas-senger cars and commercial vehicles.
In commercial vehicles, they are frequent-ly used with front-mounted groups (➜ page 6.20) as range-change gearboxes.
Nowadays, sliding-gear countershaft ge-arboxes are no longer used in motor ve-hicles. However, the simple structure clearly illustrates the power flow as well as the general function of multi-ratio gearbox and will be used as an example here.
FUNCTION
Sliding-gear countershaft gearboxSliding-gear countershaft gearboxes have a main shaft and a countershaft. The sli-ding gears are seated on the main shaft. They can be shifted with the help of gear-shift rods and control forks. Depending on the engagement, different rotational speeds and moments affect the output shaft (➜ Fig.):
1st gear: the gearwheel pair z1.2 and z5.6 boosts the input torque and redu-ces the input rotational speed.
2nd gear: the gearwheel pairs z1.2 and z3,. also boost the torque and reduce the rotational speed.
3rd gear: gear wheel z3 shifts like a sleeve over the smaller interlacing on gear wheel z1. In this way, the left-hand and right-hand section of the main shaft are adherently connected. There is no torque and rotational speed conversion (direct gear).
Reverse gear: gearwheel pair z1.2 engages. The reverse gear wheel zR reverses the direction of rotation once again between the gear wheels z7 and z8. The torque is boosted, the rotatio-nal speed is reduced.
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Coaxial synchronised gearshift sleeve gearbox made by EATON
1
3
2
LEGEND1 Drive shaft (front section of main
shaft)2 Output shaft (rear section of the
main shaft)3 Countershaft
FUNCTION
Gearshift sleeve gearboxGearshift sleeve gearboxes are equipped with a main shaft, a countershaft, a re-verse shaft with reverse gear wheel and a gearwheel pair per driving position.
All gearwheel pairs of the forward gears are continuously engaged. The gear wheels of the main shaft rotate freely. The gear wheels of the countershaft are firmly attached to it (➜ Fig. page 6.17).
The gearshift sleeves are mounted in key-ways on the main shaft and can be shifted axially on the shaft. Shifting the gearshift sleeves attaches the corresponding gear to the main shaft in such a way that it can-not turn; the desired gear ratio is created.
Distinctions are made between:
Coaxial gearboxes
Deaxial gearboxes
Coaxial gearboxIn coaxial gearboxes, the torque is trans-ferred via two externally toothed spur gear pairs on two parallel shafts (except for the direct gear). The drive and output shafts are aligned.
Deaxial gearboxIn deaxial gearboxes, the torsion is routed via an externally toothed gearwheel pair for each driving position from the drive shaft to a parallel output shaft. The drive and output shafts are not aligned.
EXAMPLE
Toothing of multi-ratio gearboxesDepending on the type, different toothings are used. In the case of unsynchronised multi-ratio gearboxes, e.g. the EATON-Fuller gearbox, straight-toothed spur ge-ars are normally used, which means that no axial forces take effect in the gearbox.
The disadvantage of straight-toothed (spur-cut) gearboxes, however, is the high level of noise development, which is clear-ly noticeable when driving fast in reverse with modern synchromesh gearboxes (the reverse gear is usually straight-toothed).
For this reason, helical-toothed gearwheel pairs are normally used on modern syn-chronised gearboxes. The engagement length of the teeth is greater. A number of teeth are always engaged. With the same width, helical-toothed gear wheels can thus transfer higher torques compared to straight-toothed gear wheels.
6.17
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FUNCTION
1 Drive shaft (from engine via clutch)= main shaft (split into item 1 and 6)
2 Countershaft3 Roller bearings between drive and output shaft4 Sliding sleeve on synchroniser body5 Gearshift rail with control forks
6 Output shaft (to axle or transfer case)= Main shaft (split into item 1 and 6)
7 Straight-toothed spur gears(first gear and reverse gear)
8 Helical-toothed spur gears
Coaxial synchronised gearshift sleeve gearbox made by ZF
Gearbox with synchromesh mecha-nismIn order to be able to shift gear on an un-synchronised gearshift sleeve gearbox, the gearshift sleeve and gear must rotate at the same speed (only then is it possible for the toothing of the corresponding spur gears to engage). Without a synchromesh mechanism, this is only possible with "double-clutching" for upward shifts and "double-declutching" for downward shifts.
In synchronised gearboxes, the gearshift sleeve and gear are synchronised by fric-tion. They enable:
Fast, silent and low-wear shifts in dri-ving position
Balancing of the speed difference bet-ween gearshift sleeve and gear
Locking of the gearshift sleeve in the event of unmatched rotational speeds
However, synchromesh mechanisms will disappear in future to an increasing ex-tent, above all for cost reasons, and will be replaced by more intelligent control sys-tems and better engine management (au-tomated standard gearbox ➜ page 6.24).
FUNCTION
Synchromesh mechanismAll one-sided synchromesh mechanisms are based on the same principle of friction. They only differ with regards to the form and actuation of the locking element. Alongside the common systems for com-mercial vehicles made by ZF and EATON, systems such as "Borg-Warner" and "Porsche" are used above all in passenger cars.
Locking synchronisation system "ZF"Also on the synchronised gearbox, the gear wheels of the countershaft and main shaft are continuously engaged. The ge-arshift sleeve is fixed in the circumferential direction and connected longitudinally with the main shaft in such a way that it can be shifted. This means it always has the same rotational speed as the main shaft (➜ Fig. page 6.17).
Each gearshift sleeve is fitted with a syn-chroniser ring (➜ Fig., item 2). The gear wheels (items 4+8) have a conical friction surface.
For each gearshift operation, the corres-ponding sliding sleeve must be prevented from engaging in the toothing of the clutch body until the existing rotational speed dif-ference has been balanced out.
On the ZF-BK synchromesh mechanism, an axial movement of the sliding sleeve (item 3) presses the pressure pin (item 7)
against the toothed synchroniser ring (item 2). This presses it against the friction cone of the clutch body (item 1).
The friction and the existing rotational speed difference mean that the synchro-niser ring runs a rotational movement that is limited by the synchroniser body (item 6). The result of this is that the helical tooth end face of the synchroniser ring press against the sliding sleeve.
Only when the conical friction faces have set up the synchronisation does the per-sistent pressure of the sliding sleeve lead to the synchroniser ring being turned back. This releases the lock and the slee-ve can be inserted in the toothing of the clutch body.
6.19
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FUNCTION
Neutral position(legend ➜ page 6.18)
Synchronising
Shifting gears
Sequence of synchronisation
1 2 3
1 2 3
48 567
6.20
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Double-H gearshift
2 4 6 8R
1 3 5 7
1 3 5 7
2 4 6 8R
N N
II
I
A
B
Single-H gearshift
B
A
1 3
5 7
2 4
6 8
R
1
5
3
5
1
7
2 4
8
6 8
4
R
N
–
–II
IR+
C
LEGENDA Gearshift lever for main gearbox
4-speed + reverse gearB Slide switch for front-mounted
group (splitter unit)Step I (slow) or II (fast)
C Rocker switch for rear-mounted group(range shift)
N Neutral position (switchover point for rear-mounted group)
BASIC PRINCIPLES
Range-change gearboxIn order to enable economical driving, the number of gears of a multi-ratio gearbox is to be configured in such a way that the tractive force characteristics of the indivi-dual gears approach the tractive force hy-perbola (➜ page 6.3) with the smallest gaps possible. To achieve this, the num-ber of gears must be chosen as necessary according to the engine characteristics.
There are two possibilities to increase the number of gears on multi-ratio gearboxes:
For each additional gear, another gearwheel pair is fitted
The multi-ratio gearbox is combined with a front-mounted and/or rear-mounted group
The combination of multi-ratio gearbox and a front-mounted and/or rear-moun-ted group is referred to as a range-change gearbox. In a range-change gearbox, the number of gears are multiplied without the number of gearwheel pairs and shifting elements in the main gearbox having to be changed.
FUNCTION
Front-mounted groupIn order to achieve a finer stepping of ge-ars, a gearwheel pair is mounted in upstream of the multi-ratio gearbox; this is referred to as a front-mounted group.
If the front-mounted group is not operated on changing gear, the jump in steps cor-responds to the gear steps in the main ge-arbox. A full step is shifted in each case. If the front-mounted group is engaged first, the jump in steps of the main gearbox is reduced and the output shaft rotates fas-ter in the same gear. This measure halves the jump in rotational speed. For this re-ason, the front-mounted group is also called a "splitter unit". The slide switch (➜ Fig., item B) can be used to choose bet-ween the slow (I) and fast splitter unit (II).
The number of driving positions is thus doubled with the step-up range unchan-ged. If a front-mounted group is combi-ned with a 4-speed multi-ratio gearbox, 8 driving positions (1 to 4, slow and fast) re-sult.
Rear-mounted groupA rear-mounted group is also referred to as a "range shift". It usually consists of two spur gear pairs as a unit or a planetary gear set (➜ page 6.26). As in the case of the front-mounted group, the range shift also enables two additional gear ratio steps and doubles the number of gears. The gear in the range shift is changed by
lightly tapping a hand against the gearshift lever (double-H gearshift) or by means of a rocker switch (➜ item C). The range shift is then pneumatically activated.
After shifting through the first eight gears (a slow and fast splitter unit for each gear of the main gearbox), switching to the ran-ge shift means another eight gears can be used. A range-change gearbox with a 4-speed multi-ratio gearbox, a front-moun-ted and a rear-mounted group thus has 16 gear steps (➜ Fig. page 6.21).
DD or OD gearboxThe gearbox power dissipation (➜ page 1.12) is at its lowest in the direct gear (wi-thout stepping down or up). In the so-called DD gearbox, the last gear is confi-gured directly (Direct Drive). This is an ad-vantage for long-distance vehicles, for ex-ample, as they frequently drive on motor-ways in the fastest gear. In the OD gearbox on the other hand, the last gear has a step-up to overdrive (OD) and the second-last gear is direct. This is an ad-vantage e.g. for construction site vehicles, which as a rule are unable to drive in the fastest gear.
6.21
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FUNCTION
Gearbox:ZF 16 S 222 EcosplitA Main gearbox
4-speed (3 gearwheel pair and direct drive-through) and reverse gear
B Front-mounted group(splitter unit)Step I: slowStep II: fast
C Rear-mounted group(range shift)(planetary gear set on/off)
Components ➜ page 6.17
Power flow example:3rd gear, slow
1st gear, slow
1st gear, fast
2nd gear, slow
2nd gear, fast
3rd gear, slow
3rd gear, fast
4th gear, slow
4th gear, fast
5th gear, slow
5th gear, fast
6th gear, slow
6th gear, fast
7th gear, slow
7th gear, fast
8th gear, slow
8th gear, fast
Reverse gear, slow
Reverse gear, fast
Power flow in the 16-speed range-change gearbox (DD gearbox)
A BB A C
1 I
1 II
2 I
2 II
3 I
3 II
4 I
4 II
5 I
5 II
6 I
6 II
7 I
7 II
8 I
8 II
R I
R II
6.22
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ServoShift
1
32
LEGEND1 Hydraulic slave cylinder for shift gut-
ter2 Hydraulic slave cylinder for gear
position3 Pneumatic cylinder, gearshift power
support ServoShift
BASIC PRINCIPLES
Gearshift mechanismAfter the introduction of power steering and power clutch, the gearshift mecha-nism is regarded as the vehicle-driver in-terface with the greatest physical load. Purely mechanical shifting of non-syn-chronised gearboxes is no longer state-of-the-art with regard to today's require-ments in the areas of ergonomics, safety and economy.
Nowadays, in order to make the gearshift operation as fast and for the driver as comfortable as possible, pneumatic, hy-draulic and electrical components or combinations are used.
Current solutions are electropneumatic or hydrostatic gearshift mechanisms and even electronically controlled automated standard gearboxes (➜ page 6.24).
Above all due to the high costs, so-called converter powershift gearboxes (auto-matic gearboxes ➜ page 6.28), where ge-arshifts are completely eliminated, play a subordinate role in the field of commercial vehicles with exception of buses, munici-pal vehicles and in the area heavy-load transport.
FUNCTION
Pneumatic gearshift power supportGears on multi-ratio gearboxes are shifted using the gearshift lever; this is connected to the gearbox by a mechanical transmis-sion unit. In the gearbox, the correspon-ding gearshift sleeve is moved via gear-shift rods and control forks.
In the case of range-change gearboxes (➜ page 6.20), the front-mounted and rear-mounted group are usually controlled pneumatically.
In the case of the ZF Ecosplit gearbox (➜ Fig.), a switching valve is controlled by the turning shaft of the four-speed section; it only releases the compressed air to a dual-action shift cylinder in the neutral po-sition (➜ page 6.23).
The integrated, front-mounted splitter unit is also operated pneumatically by means of a pilot valve fitted on the gearshift lever. The pilot valve is used to preselect each splitter unit I or II (➜ Fig. page 6.20) via a relay valve.
The clutch pedal is fitted with a release valve. The release valve only releases the compressed air to the shift cylinder when the clutch has completely disengaged; the splitter unit is switched over according to the preselection.
EPS gearshiftEPS stands for electropneumatic stan-dard gearbox. On this gearbox control de-
veloped by Mercedes-Benz, there is no mechanical connection between the gear-shift lever and the gearshift rods in the ge-arbox.
The gearshift lever is mounted on a pulse-generator device that sends pulses to the electronics. Following a switch pulse, compressed air controlled by solenoid valves flows into the corresponding gear or group cylinder. The pistons move out and in turn move the gearshift rods with the corresponding control forks. The cor-responding gears are shifted in the same way as on a conventional gearbox.
6.23
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Pneumatic gearshift power support 'ServoShift'
3
12
5
7
4
9
10
8
6
MAN ComfortShift
3
1
2
LEGEND1 Rocker switch for shifting the group
(rear-mounted group)2 Sliding switch for shifting the split
ter6 Gearshift rod7 Control fork8 Hydraulic slave cylinder for gear
position9 Pneumatic cylinder of gearshift
power support ServoShift10 Gearshift lever, turning-shaft shifting
FUNCTION
Hydrostatic gearshift mechanismThe hydrostatic gearshift mechanism (HGS) MAN ServoShift is offered for all manual gearboxes of the Trucknology Ge-neration. In the case of MAN ServoShift, force transmission from the gearshift lever to the gearbox is via hydraulic lines with a heated master cylinder at the gearshift le-ver and slave cylinder at the gearbox. The gearshift linkage is eliminated (➜ Fig.).
This hydrostatic gearshift mechanism is additionally combined with pneumatic ge-arshift power support. The pneumatic ge-arshift power support ServoShift consists of a mechanical-pneumatic and dual-ac-tion compressed air cylinder. This is series standard equipment for all mechanical ge-arboxes.
The hydrostatic gearshift mechanism MAN ServoShift means an increase in comfort for the driver, as impacts and vib-rations are no longer transferred from the drive train to the gearshift lever. There is also lower noise development in the dri-ver's cab.
EXAMPLE
Gearshift mechanism with single-HThe hydrostatic gearshift mechanism MAN ServoShift also simplifies the gear-shift operation. The 16 gears are shifted by means of a splitter unit and a range shift with only two shift gutters (single-H gearshift pattern). The shifting travels of the large and small range shift are overlaid (➜ Fig. page 6.20).
Shifting from 4th gear to 1st gear within a group is prevented by a gutter lock. Fur-thermore, the vehicle management com-puter prevents incorrect gearshifts to the wrong range shift.
MAN ComfortShiftWith the MAN ComfortShift gearshift sys-tem, switching operations can be run wit-hout using the clutch pedal and without changing the driving pedal position. Both the split operations and gear changes can be run in this way.
Activated by a button on the left-hand side of the gearshift knob, the driving clutch is operated electropneumatically during the gearshift operation (➜ Fig.). The button must remain pressed during the gearshift operation with ComfortShift.
The engine speed is automatically adap-ted via the vehicle management compu-ter. The driving pedal can remain in an un-changed position during this operation. The vehicle is prevented from "jumping"
by the vehicle management computer ali-gning the speed and rotational speed.
In conjunction with MAN ComfortShift, HGS provides a completely new gearshift experience with comfort similar to that in a passenger car .
6.24
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Automated standard gearbox ZF AS-Tronic
1
3 2
LEGEND1 Gearshift module2 Base gearbox3 Electropneumatic clutch actuator
BASIC PRINCIPLES
Automated standard gearboxModern gearshift systems, e.g. MAN Tip-Matic, enable gear changes with one touch of the steering-column switch wit-hout the driver operating the clutch or ta-king his or her foot from the accelerator. On request, they are even fully automatic. MAN TipMatic works with an automated standard gearbox on which all of the ope-rations required for shifting gears are au-tomated.
In conjunction with engine control EDC and the MAN BrakeMatic for brake cont-rol, the MAN TipMatic gearshift system is integrated via the CAN bus in the MAN Tronic. According to the wish of the driver (accelerator or brake pedal), the vehicle management computer (FFR) combines with the central on-board computer (ZBR) to provide the control units involved with the corresponding target values and handles all the required control functions (➜ page 11.8).
Other automated gearshift systems that work in a similar manner are e.g. Telligent EAS (Mercedes), Opticruise (Scania), Ge-artronic (Volvo), EuroTronic (Iveco) or the Opti-Driver system from Renault.
FUNCTION
MAN TipMatic gearshift systemThe MAN TipMatic gearshift system com-bines an electropneumatic manually or automatically engaging and disengaging gearbox with an automated mechanical clutch. The electropneumatic clutch cont-rol (without clutch pedal) fully relieves the driver of the task of clutch control.
The automated standard gearbox used (ZF AS-Tronic ➜ Fig.) has 12 or 16 gears and is used without a synchromesh me-chanism in the four-speed section; the splitter unit and range shift are synchro-nised. Despite the automated switching operations, both manual and automatic gear selection is possible depending on what the driver wants.
With manual operation, the driver selects the gear step using a steering-column switch. The driveaway situation is prese-lected using a rotary switch in the centre console beside the driver's seat.
In the automatic mode, the driver only operates the accelerator or brake pedal. Selection and execution of the shifting operations are handled by the MAN Tip-Matic system quickly and smoothly.
Rotary switchOn the MAN TipMatic, the driver uses the rotary switch to select the gear step be-fore moving off depending on the load (➜ Fig. page 6.25, items D1 ... D5).
In the manoeuvering positions DM and RM, upward gearshifts are prevented. The FFR also only provides reduced torque and thus prevents the vehicle from "jum-ping".
Steering-column switchIn manual operation, the gear step is se-lected using the steering-column switch. After every operation, the steering-column switch moves back on a spring to its initial position. A button can be used to switch between manual and automatic operati-on.
Displays in the driver displayDuring manual operation, the engaged gear is displayed. Arrows in front of the display pointing upwards and behind the display pointing downwards show the possibilities for upward and downward gearshifts. During automatic operation, the message "AUTO" and the engaged gear are displayed.
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EXAMPLE
Function schema ZF 12 AS-Tronic 2601Components:A 3-speed main gearbox
(2 gears via gearwheel pairs as well as 1 gear as direct drive) and reverse gear (R)
B Front-mounted group (splitter unit)Step I: slowStep II: fast
C Rear-mounted group (range shift)Planetary gear set on/off
Power flow:K1 Power output split via front-mounted group (Step
I or II) on both countershafts (in the direct gear, drive-through without power output split)
K2 Return of the power output split in the 3-speed section to the main shaft in the corresponding gear
K3 Output via the rear-mounted group (planetary gear set on) in the lower driving positions 1–6 and R (gears 1–3 and reverse gear each via slow and fast splitter unit)
K4 Output directly to propshaft (planetary gear set off) in the upper driving positions 7–12 (gears 1–3 each via slow and fast splitter unit)
Rotary switch in the centre consoleDM Manoeuvering forwards in slowlyD1 Driving forwards with driveaway gear 1D3 Driving forwards with driveaway gear 3D5 Driving forwards with driveaway gear 5N Neutral (gearbox in neutral position, driving
switch without function)R ReversingRM Manoeuvering backwards
Steering-column switch+ Shifting up one step
(lever upwards towards driver)++ Shifting up several steps
(multiple touch)– Shifting down one step
(lever downwards way from driver)– – Shifting down several steps
(multiple touch)
MAN TipMatic gearshift system
A
K1 K2 K3
K4
B
C
III
22 1
1 RR
3
3
+++
_ __
6.26
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Single planetary gear set
1
2
3
4
a
6
11
10
b
7
8
9
5
LEGENDa Driveb Output1 Planetary gears2 Planet carrier3 Drive shaft for planet carrier4 Drive shaft for sun gear5 Sun gear6 Drive shaft for internal gear7 Internal gear carrier8 Internal gear9 Brake shoes10 Output shaft for internal gear11 Output shaft for planet carrier
BASIC PRINCIPLES
Planetary gear setPlanetary gearboxes consist of interme-shed gear wheels. The individual gear wheels or gear wheel groups each have a shaft.
A single planetary gear set consists of:
Sun gear with carrier and shaft
Internal gear with carrier and shaft
Planet gears with carrier and shaft
Normally, three planet gears mounted on a planet carrier are used. They revolve around the centrally mounted sun gear; an internally toothed internal gear revolves around the planet gears. The shafts for the planet carrier and for the internal gear are hollow shafts (➜ Fig.).
Planetary gearboxes are used in the follo-wing areas:
in automatic gearboxes (➜ page 6.28),
as rear-mounted groups on range-change gearboxes (➜ page 6.20),
in transfer cases (➜ page 6.35),
in planetary drive axles (➜ page 3.4).
FUNCTION
Gear wheels of the planetary gearboxAll gear wheels are continuously engaged; the sun gear, internal gear and planet car-rier can be driven or also fixed. They can be used either as drive or output.
The various gear ratios can be created by fixing and/or connecting or separating the sun gear, internal gear or planet carrier. They are connected or separated by mul-ti-disc clutches or gearshift sleeves and fixed by brake couplings or brake bands.
With the internal gear fixed, sun gear dri-ven and output on the planet carrier, there is a step down towards slow. This corres-ponds to the 1st gear of a three-speed gearbox (➜ Fig. page 6.27). In the case of a planetary gear set used as a rear-moun-ted group (➜ page 6.20), this position is referred to as the 'slow group'.
With the sun gear fixed, the internal gear driven and output at the planet carrier, there is a smaller step down towards slow (2nd gear).
A blocked planetary gear set results in the direct gear ratio of 1:1. All three compon-ents rotate in the same direction with the same rotational speed (3rd gear). This gear shift on a rear-mounted group corre-sponds to the 'fast group'.
With a fixed planet carrier and driving sun gear, the internal gear rotates in the oppo-
site direction to that of the sun gear (re-verse gear).
Single planetary gear sets are adequate for use in rear-mounted groups of range-change gearboxes or in axle drives. For use in automatic gearboxes, a number of planetary gear sets are placed in succes-sion or two planetary gear sets are cou-pled with shared components. A distinc-tion is made between two designs:
Ravigneaux gearboxWith this design, two single planetary gear sets are coupled to a shared internal gear. Three to five short and three to five long planet gears connect the two sun gears. The output is via the internal gear or the planet carrier.
Simpson gearboxThe Simpson gearbox consists of two sin-gle planetary gear sets that have a shared sun gear. The output is via one of the two internal gears.
6.27
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FUNCTION
1st gear:internal gear fixed, sun gear driven,
output on planet carrier
2nd gear:sun gear fixed, internal gear driven,
output on planet carrier
3rd gear:sun gear, internal gear and planet carrier blocked:
direct gear
Reverse gear:planet carrier fixed, sun gear driven,
output at internal gear with reverse direction
a Outputb Drivec Internal rotational movement
2 Planet gear carrier5 Sun gear8 Internal gear
Gear ratios with single planetary gear set
c c
b ba
a
5
82
c
ca
a
b
b
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Automatic gearbox
3
4
2
1
5
LEGEND1 Converter lockup clutch2 Torque converter3 Multi-disc clutch or brakes4 Planet gear sets5 Electrohydraulic control unit
BASIC PRINCIPLES
Automatic gearboxAutomatic gearboxes enable automatic changes of gears without intervention on the part of the driver. The clutch is elimina-ted; all driving operations, including dri-veaway and manoeuvering, are auto-matic. However, a selector lever or push-buttons can be used to preset certain gearshift programs or step-up ranges. Another possibility to influence gear chan-ges is the "kickdown". Pressing the dri-ving pedal as far as it will go leads to the earliest possible downward shift to the next-lowest gear.
Due to the torque converter, the efficiency of automatic gearboxes is poorer than that of manual gearboxes. Electronic con-trol of automatic gearboxes, however, en-ables operation of the engine in ranges that favour the fuel consumption level. This compensates for the poorer efficien-cy.
With the exception of buses and munici-pal vehicles, automatic gearboxes play a subordinate role in the area of commercial vehicles. The reason for this is the higher costs compared to those for manual gear-boxes.
FUNCTION
Components of automatic gearboxesThe connection between the drive shaft and the actual gearbox is by means of a hydrodynamic torque converter, usually constructed according to the "Trilok" prin-ciple. This increases the engine torque and also ensures a soft, smooth drivea-way. At higher rotational speeds, the con-verter is bridged to avoid slip inherent in the design principle (converter lockup clutch ➜ page 6.8).
Upstream of the converter is a planetary gearbox with a number of planetary gear sets (➜ page 6.26). The number of sets results from the number of gear steps. The planetary gear sets convert the torque and rotational speed and reverse the direction of rotation for reverse gear.
The gears are shifted without tractive po-wer interruption. Multi-disc clutches shift the planetary gear sets and connect the individual gears or gear carriers of the pla-netary gear sets, thus creating the diffe-rent gear ratios. Multi-disc brakes provide the corresponding blocking of the plane-tary gear sets.
Control of automatic gearboxesControl is either purely hydraulic or elec-trohydraulic. It has the task of effecting the automatic upshift and downshift of the in-dividual gears at the right time. Control takes place depending on the following factors:
Selector lever position
Driving speed
Engine load
With the purely hydraulic control system, an oil pump generates a working pressu-re. The selector lever (setting by the driver) and a hydraulic shifting block activate and engage the drive clutches depending on requirements.
In the case of an electrohydraulic control system, activation of the drive clutch is hy-draulic; the electronics distribute the pres-sures and thus the gear selection.
6.29
6
DR
IVE
TR
AIN
6.5.
5Pow
er ta
ke-o
ffs
x
Mounting options for power take-offs (example ZF)
2
1
(NMV 130 E)
(ZF 16 S 109)
LEGEND1 Engine-dependent power take-off2 Clutch-dependent power take-offs
BASIC PRINCIPLES
Power take-offsPower take-offs are used to drive feed pumps, cranes, cement mixer pumps and other power units.
Distinctions are made between:
Engine-dependent power take-offs
Clutch-dependent power take-offs
Depending on the intended use, they are connected to the engine, in the propshaft train or the transfer case (➜ page 6.35).
The operation of modern power take-offs is often possible with the vehicle either stationary or moving. Above all cement mixers require the power take-off also while the vehicle is being driven.
Clutch-dependent power take-offs are the classical power take-offs for external po-wer units. Various connection options are integrated in each gearbox by the large gearbox manufacturers such as ZF and EATON.
FUNCTION
Engine-dependent power take-offsEngine-dependent power take-offs are mounted in front of the standard gearbox and clutch and are usually connected di-rectly to the camshaft of the engine. They are integrated in the clutch bell and always run at engine speed. Force transmission is independent of the driving clutch.
The engine-dependent NMV 130 E (➜ Fig.) is can also be engaged while the ve-hicle is being driven or under load by means of a built-in hydraulic multi-disc clutch. It is used where extremely high po-wer output is required:
Cement pumps
Transport cement mixers
High pressure cleansing and vacuum trucks
Drill carriers
Airfield fire engines
Truck-mounted cranes
Clutch-dependent power take-offsClutch-dependent power take-offs are normally flanged onto the output end of the gearbox and driven by the coun-tershaft of the gearbox (➜ page 6.17). The connection is by means of a dog sleeve.
When the engine is running and the clutch engaged, the countershaft turns the gear-box. Operating the clutch interrupts the connection between the engine and gear-
box; the power take-off can be engaged. The PTO must be engaged and disen-gaged when the vehicle is stationary.
Depending on the area of application, more or less powerful power take-offs are used. Depending on the type, they are suitable for short-term or continuous use:
PropshaftsTo transfer the power output from the ge-arbox to the transfer case and/or final dri-ve (depending on the number of driven ax-les), shafts with universal joints (cardan joints) are required, so-called propshafts. At MAN, these are connected by cross-toothed mounting flanges (➜ Fig.).
A fundamental distinction is made in the arrangement of propshafts: the Z arrange-ment and W arrangement. The Z arrange-ment or Z inflection is regarded as the usual application on commercial vehicles. It is also used in MAN commercial vehic-les.
On account of the vertical movement of the axles, the propshafts must be fitted with a length compensation (shifting sec-tion toothing).
With wider wheelbases, MAN uses propshaft intermediate bearings muffled with rubber. These are very quiet, run smoothly and require little maintenance.
FUNCTION
Gimbal errorInflected propshafts with only one univer-sal joint are unable to transfer even rotati-onal movements. The circular rotation of the drive shaft only leads to sinusoidal ro-tation of the driven shaft. This also redu-ces the angular velocity of the driven shaft when the joint forks of the drive shaft are horizontal (flattened range of the ellipse path of the driven shaft). This effect is all the stronger the greater the angle of in-flection α of the propshaft. This is also re-ferred to as "gimbal error".
These synchronisation fluctuations can be balanced out by fitting a second universal joint. All the propshafts in the drive trains of commercial vehicles must therefore be fitted with at least two universal joints.
Angle of inflectionThe angle of inflection α refers to the angle by which the universal joint of a propshaft is set.
It must not be too large, as otherwise uni-form force transmission is no longer pos-sible, resulting in excessive loads on the joints and thus heavier wear. The angle of inflection is normally approximately α = 8°. However, angles of up to 35° are also technically possible.
Z arrangementFor complete synchronisation of the drive and output shafts connected by the
propshaft, the joint forks of shared shaft must lie on one level. The amount of the two angles of inflection must also be the same size (➜ Fig. page 6.31).
W arrangementAlso in the case of the W arrangement, the universal joint forks must lie on one level and the angles of inflection must be the same size to balance out the gimbal error (➜ Fig. page 6.31). With the W arrange-ment, only the drive or output shaft can be arranged horizontally.
The W arrangement is not usual on com-mercial vehicles. It is only used for acces-sories of the superstructure.
6.31
6
DR
IVE
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x
FUNCTION
Z arrangement
W arrangement
α Angle of inflection
Propshafts
α1 α1 = α2
α2
α1 = α2
α1
α2
6.32
6
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IVE
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6.7D
riven
axl
es6.
7.1F
inal
driv
e
6.7.
1.1A
xle
driv
e x
Axle drive
B
A2
1
2
1
LEGENDA Drive without axle offsetB Hypoid drive (with axle offset)1 Ring gear2 Bevel gear
BASIC PRINCIPLES
Axle driveThe final drive, also referred to as the middle drive, transfers the rotational mo-vement of the propshaft to the drive shafts of the wheels. The middle drive includes the axle drive with the axle-drive ratio and the differential gear (differential ➜ page 6.33).
The axle drive has the following tasks:
Torque transfer and increase (ade-quate for every driving state)
Stepping down the rotational speed of the drive propshaft to slow
Deflection of the power flow, normally by 90° (when the engine is fitted towards the vehicle longitudinal axis)
In order to be able to perform these tasks, axle drives are built as bevel gears or worm gears (➜ page 6.14). In commercial vehicle construction, bevel gear axle drive are normally used.
FUNCTION
Bevel gear axle driveA simple bevel gear axle drive consists of a drive bevel gear (drive pinion) and a ring gear.
The drive bevel gear is mounted on the drive axle, which is connected to the propshaft by means of a universal joint. It drives the ring gear and thus the axle. De-pending on the arrangement, a distinction is made between:
Hypoid drive (axle of drive and ring gear are offset),
Drive without axle offset.
Toothing of hypoid drivesThe toothing of hypoid drives is usually spiral toothing. In commercial vehicles, the following advantages mean that main-ly hypoid drives are used:
The axle offset enables use of larger drive bevel gears with correspondingly larger and stronger teeth; the service life of the axle increases.
A greater number of teeth is engaged; in conjunction with the spiral toothing, this means greater running smooth-ness.
With the same gear ratio, the ring gear can be made smaller. The hypoid drive is smaller.
Normally, a single gear ratio is sufficient for the axle drive (➜ page 6.2). It results
from the ratio of number of teeth on the drive bevel gear and ring gear.
6.33
6
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IVE
TR
AIN
6.7.
1.2D
iffer
entia
l gea
r
x
Axle drive with differential gear (differen-tial)
457
42 5 631a
b
b
c
c
dd
Speed balancing in the final drive on cornering
LEGENDa Drive (propshaft)b Gear ratio (force transmission)c Rotational speed difference com-
Differential gearOn cornering, the wheel nearest to the curve and the wheel furthest from the cur-ve cover different distances (➜ page 3.23). The outer wheel must cover a grea-ter distance than the inner wheel. This means it has to roll at higher speed; its ro-tational speed is greater than that of the inner wheel.
Depending on the speed of a vehicles, the corner radius, the condition of the road surface and the weather conditions, diffe-rent rotational speeds can occur on the wheels of one axle.
In order to balance out these rotational speed differences, a differential gear (dif-ferential) must distribute the revolutions from the ring gear of the axle drive to the axle shafts of the wheels.
A general distinction is made between be-vel gear and spur gear differential gears. Bevel gear differential gears are normally used in commercial vehicles.
FUNCTION
Basic function of the differentialThe differential gear consists of the diffe-rential housing and four differential bevel gears as well as two drive bevel gears (ax-le drive bevel gears).
The ring gear that is firmly attached to the differential housing is driven by the cardan shaft via the drive bevel gear.
The four differential bevel gears in the hou-sing engage in the two drive bevel gears on the axle shafts (which is why they are also called axle drive bevel gears).
Driving straight aheadWhen driven straight ahead, both axle dri-ve bevel gears rotate at the same speed; the differential bevel gears do not turn, rather they revolve with the ring gear. They equally distribute the propelling force to the axle drive bevel gears.
CorneringOn cornering, the outer axle shaft rotates more quickly than the inner shaft. The dif-ferential bevel gears enable the different speeds of the two axle drive bevel gears. The differential bevel gears rotate around their axes and thus balance out the rotati-onal speed difference between the axle drive bevel gears.
Differential of planetary drive axlesIn contrast to hypoid axles, where the po-wer flow and torque is only stepped up and distributed in the middle drive (➜
page 3.4), planetary drive axles each have a planetary gear set on the wheel hubs (➜ Fig. page 3.5). The two sets of planetary gears assume most of the torque conver-sion and gear stepping. This is why the torque transfer in the middle drive is not very great. It is significantly smaller than the middle drive of a hypoid axle.
The smaller differential means that plane-tary drive axles have greater ground clea-rance. This is why they are often used for construction site vehicles. The additional planetary gear set on the wheel hubs means they are recommended for the transport of heavy loads.
Inter-axle differentialAn inter-axle differential is included as a differential gear in a drive-through axle (➜ page 3.4). In principle, it works in the same way as the differential in the axle dri-ve to balance different wheel speeds. Ho-wever, the inter-axle differential is arran-ged in the drive-through axle, balancing the speed between the 1st and 2nd axles of the tandem-axle assembly.
6.34
6
DR
IVE
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AIN
6.7.
1.3D
iffer
entia
l loc
k
x
Final drive of a hypoid axle with differential lock
8
1
2
6
6 3
7 5 49
LEGEND1 Differential lock (dog clutch)2 Gearshift sleeve of the differential
lock (can be shifted on the axle shaft toothing)
3 Axle shaft toothing4 Pneumatic gearshift element5 Control fork of the differential lock6 Axle drive bevel gears7 Differential bevel gears8 Differential housing with ring gear9 Drive bevel gear
BASIC PRINCIPLES
Differential lockWith different traction of the two drive wheels (one-sided smooth road surface, mud, sand, gravel) or with an extreme in-clination of the vehicle, the following effect can occur:
One of the driven wheels spins due to the lack of propulsion power transfer; the other remains at a standstill due to the function of the differential (differential ge-ar). The vehicle cannot be moved.
A differential lock uses a mechanical or electropneumatic dog clutch to reconnect the axle shafts separated in the differential via housing and ring gear. Different rotati-onal speeds of the two drive wheels are then no longer possible.
Also in drive-through axles, which have an inter-axle differential for speed balancing between the 1st and 2nd axle of the tan-dem-axle assembly, there is usually an engageable differential lock. The inter-axle differential lock is engaged when all the wheels on one of the two driven axles spin.
FUNCTION
Engaging and disengaging differenti-al lockThe engaging and disengaging differential lock connects an axle shaft with the diffe-rential housing and ring gear. This means the differential bevel gears can no longer roll on the axle drive bevel gears. This cre-ates a rigid connection of the two axle shafts in the differential housing. The speed balancing is then locked.
Due to the high propelling force that fully affects the differential on driveaway, the differential may only be locked in the situ-ations described and at lower speed (ma-ximum of 15 to 20 km/h).
Automatic differential lockAutomatic differential locks feed more torque to the wheel with the better road grip, as determined per wheel sensors, even at higher speeds.
EXAMPLE
In commercial vehicles, engaging and dis-engaging differential locks are preferred. Automatic differential locks with multi-disc clutches (➜ page 6.10) are used above all in racing cars and high-quality passenger cars.
Engaging and disengaging differential locks may only be switched on when the vehicle is stationary or at low speed.
6.35
6
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IVE
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AIN
6.7.
2All-
whe
el d
rive
6.7.
2.1T
rans
fer
case
x
Transfer case (schema)
a
bc
1
3
2
MAN transfer case
1
23
a
c
LEGENDa Power flow from gearboxb Power flow to rear axlec Power flow to front axle1 Gearshift sleeve2 Gear ratio steps3 Shift cylinder for engaging the front
axle via dog clutch (all-wheel drive)
BASIC PRINCIPLES
Transfer caseCommercial vehicles that are deployed under difficult conditions (construction si-te, off-road, winter) usually have a number of driven axles. If all axles of a vehicle are driven, this is referred to as all-wheel drive.
In order to implement all-wheel drive, torque distribution is necessary. As a rule, a transfer case is used for this purpose on commercial vehicles.
The transfer case is connected to the mul-ti-ratio gearbox by means of a propshaft or is directly flanged on. The transfer case has one flange to secure a propshaft to the drive of the front axle and one flange to secure a propshaft to the drive of the rear axle (➜ Fig.).
With a two-stage transfer case, the step-up range of the drive train can also be ex-panded.
FUNCTION
Engageable front axleNo differential gear is required on transfer cases with engageable front axles. The driving torque is transferred in equal parts to the front and rear axles. The difference in travel when the vehicle is being driven is not balanced out. For this reason, all-wheel drive may only be switched on if there is poor traction, so as not to subject the components of the drive train to unne-cessary loads and to keep the tyre wear as low as possible.
Permanent all-wheel driveWhen the vehicle is being driven, there are differences in the travel between the drive axles. In order to balance out the resulting rotational speed difference, vehicles with permanent all-wheel drive must be equip-ped with a differential gear in the transfer case.
In addition, using a planetary gear set as a differential gear can adapt the torque dis-tribution to the axle loads. This is done by changing the sun gear and internal gear diameters. The front axle, for example, can be supplied with 30 % of the torque and the rear axle, due to the greater axle load, with 70 % of the torque. To halve the torque, a bevel gear differential (➜ page 6.33) is used.
In order to be able to transfer the maxi-mum engine torque even with poor trac-tion, the differential gear in the transfer
case is also equipped with a lock. In the case of manual locks, a dog clutch (➜ page 6.10) is normally used.
Drive-through axleIn the case of the all-wheel drive concept with more than two driven axles (e.g. 6x6), so-called drive-through axles are used. There is an output at the rear end, where a propshaft to the drive of the second axle is flanged on (➜ Fig. page 6.36).
On the drive-through axle, torque and ro-tational speed are picked up via a spur gear ratio (➜ page 3.4). The drive-through also contains an inter-axle differential for speed balancing between the 1st and 2nd axles of the tandem-axle assembly, which as a rule is equipped with an engaging and disengaging differential lock (inter-axle differential lock).
6.36
6
DR
IVE
TR
AIN
6.7.
2.2D
rive
conc
epts
x
FUNCTION
4x2 hydrostatic driveThe hydrostatic drive is an engageable all-wheel drive technique for vehicles with oc-casional off-road operation. On a conven-tional all-wheel drive (➜ Fig. 4x4 and 6x6), the transfer elements of the front axle dri-ve are always moved. On commercial ve-hicles with hydrostatic drive, only the rear wheels are driven conventionally when the vehicle is driven on roads.
In driving situations that require all-wheel drive, the hydrostatic drive can be enga-ged at any time. If the hydrostatic drive is engaged, a hydraulic pump (➜ Fig., item 2) supplies the hydrostatic wheel motors (4) directly with pressure up to 420 bar. The front wheels are then driven up to a speed of 30 km/h.
The use of hydrostatic wheel motors elimi-nates the transfer case that is typical of all-wheel drive. The advantages are:
More favourable fuel consumption
Weight advantage of around 400 kg
No raising of the driver's cab and frame is required (the visual appea-rance of the road vehicle is retained)
4x4 all-wheel driveWith conventional all-wheel drive, the ge-arbox is connected to the transfer case (➜ Fig., item 5) via a propshaft (1), to which propshafts are flanged onto the drives of the front and rear axles. Depending on the version of the transfer case, the drive of the front axle is engageable or permanent (➜ page 6.35).
6x6 all-wheel driveThe 6x6 all-wheel drive is based on the 4x4 drive concept. However, the 1st rear axle is designed as a drive-through axle, which has an inter-axle differential for speed balancing between the 1st and 2nd axle of the tandem-axle assembly (as a rule with engageable differential lock). The drive-through to the 2nd rear axle is via a propshaft.
LEGEND1 Propshaft2 Hydraulic pump3 High-pressure line4 Hydrostatic wheel motors5 Transfer case
EXAMPLE
Hydrostatic drive and conventional all-wheel drive
