Transmission – Function

Design and Function

Applies to: 2003–2016; AW50/51 AWD, AW55-50/51SN

Transmission, general

The basic parameters for shifting are the accelerator pedal (AP) position and the vehicle speed.

The gear shift quality is determined by the torque control by reading off speed changes of the transmission input shaft and comparing the calculated value.

This is used to calculate the pressure setting for the clutches and brakes.

Torque converter

The torque converter functions as an hydraulic automatic clutch. When the engine is idling the pump effect is too weak to drive the turbine and the vehicle will not move. As the engine speed (RPM) rises it successively starts to drive in a gradual way. At higher engine speeds (RPM) the power transfer to the turbine can be up to 95%. The torque converter functions as an hydraulic clutch.

Thanks to a third, smaller wheel, the stator wheel, the torque converter also reinforces the engine torque at low engine speeds.

The rotating impellers and the oil in the torque converter ”slip” slightly and create a slight loss of power, which increases fuel consumption slightly.

Differential

The differential distributes power equally between the drive wheels, even if they are rotating at different speeds.

When driving straight ahead, the ring wheel and differential housing rotate at the same speed as the drive shafts and the driving wheels.

When cornering, the differential gears rotate to compensate for the different speeds of the wheels. Because the small side gears are rotating on the shaft journal, the drive shafts can rotate at different speeds. Power is transferred from the differential housing to the drive shafts via the small side gears in the same way as when driving straight ahead. Both drive wheels still have the same driven power.

Cars with four wheel drive have a splined pin on the differential housing. The sleeve on the pin connects the differential housing with the bevel gear. This transfers the power to the rear wheels.

Gear selector assembly

The gear selector assembly is positioned in the center console and is mechanically connected to the transmission by a cable which affects the gear valve.

Gear selectors and cables are shaped differently depending on which car model they are installed in.

Gear selector assemblies with Geartronic, in addition to P/R/N/D modes, also have a manual (M) shifting mode. The manual gear positions can be selected at any point while driving. The engaged gear is locked until the driver selects another gear. The automatic transmission only down shifts if the vehicle slows down to very low speed.

To downshift the gear selector must be moved to minus (-). To upshift the gear selector must be moved to plus (+). At start, 3rd is the highest possible gear.

The engine can only be started in position P or N.

The different gear selector positions

Power flow

When throttling off, the output shaft's power in 5th, 4th, 3rd, 2nd or reverse gear goes directly to the input shaft without any freewheel, which provides engine braking. 1st gear does not have any engine braking since the power transmission is interrupted by freewheel F2.

Position P (parking)

Primary shaft

The input shaft rotates clockwise. All clutches and brakes are disengaged, and no power is transferred to the planetary trains.

Output (secondary) shaft

No power is transmitted to the output (secondary) shaft. Brake band B4locks the sun gear so that it cannot rotate in any direction. Shiftlock P, which is affected by the mechanical link system, is engaged with the lock wheel on the output shaft and prevents the vehicle from rolling.

Position N (neutral)

Primary shaft

The input shaft rotates clockwise. All clutches and brakes are disengaged, and no power is transferred to the planetary trains.

Output (secondary) shaft

No power is transmitted to the output (secondary) shaft. Brake band B4 locks the sun gear so that it cannot rotate in any direction. Shift-lock P is disengaged. The planetary gears can rotate freely around the sun gear and the vehicle will start to roll if it is on an incline.

The reason for the brake B4 being activated in both P as N-position is to minimize the engagement shock that otherwise is produced when several brakes and clutches are activated at the same time when the gear selector is moved to D or R-position. Since B4 is still activated in both first gear and reverse, in this way simultaneous engagements are reduced.

Position D (drive) and 1st gear

Main section

The input shaft rotates clockwise. Clutch C1 connects the input shaft to the rear ring gear, which rotates clockwise. The rear planetary gear rotates clockwise. The front large planetary gear rotates clockwise with the rear planetary gear as a unit.

The front small planetary gear rotates clockwise. The front ring gear rotates counter-clockwise. Freewheel F2 locks the front ring gear's rotation counter-clockwise.

The front and rear planetary carriers are turned clockwise because of the reactive forces from the small gear. The primary intermediate gear rotates clockwise with the front and rear planetary carriers as a unit.

U/D section

The secondary intermediate gear rotates counter-clockwise. The front ring gear rotates counter-clockwise with secondary intermediate gear as a unit.

The front planetary gear rotates clockwise. The front planetary gear rotates clockwise. The rear sun gear rotates clockwise with the front sun gear as a unit.

The rear planetary gear rotates counter-clockwise. Brake B5 locks the rear planetary carrier's rotation. The rear ring gear rotates counter-clockwise. The front planetary carrier and final drive pinion rotates counter-clockwise with the rear ring gear as a unit. The final drive rotates clockwise.

Engine brake

The primary intermediate gear and front and rear main planetary carriers rotate clockwise. The rear planetary carrier rotates clockwise. The rear planetary gear is turned counter-clockwise while it rotates counter-clockwise because of the resistance from the rear ring gear.

The front large gear wheel is turned clockwise while it rotates counter-clockwise and the small gear wheel is turned clockwise while it rotates clockwise. The front planetary carrier is turned clockwise.

The front ring gear rotates clockwise because the front small gear rotates clockwise, but drive force is reduced because freewheel F2 is disengaged. Therefore the engine brake does not operate.

Position D and 2nd gear

Main section

The input shaft rotates clockwise. Clutch C1 connects the input shaft to the rear ring gear. The rear ring gear rotates clockwise. The rear planetary gear rotates clockwise.

The front large planetary gear rotates clockwise with the rear planetary gear as a unit. Brake B2, freewheel F1 and brake B1 lock the sun gear's rotation.

The front and rear planetary carriers are turned clockwise because of the reactive forces from the front large gear. The primary intermediate gear rotates clockwise with the front and rear planetary carriers as a unit.

U/D section

The secondary intermediate gear rotates counter-clockwise. The front ring gear rotates counter-clockwise with the secondary intermediate gear as a unit. The front planetary gear rotates clockwise. The front planetary gear rotates clockwise.

The rear sun gear rotates clockwise with the front sun gear as a unit. The rear planetary gear rotates counter-clockwise. Brake B5 locks the rear planetary carrier's rotation. The rear ring gear rotates counter-clockwise.

The front planetary carrier and final drive pinion rotates clockwise with the rear ring gear as a unit. The final drive rotates clockwise.

Engine brake

Drive force is transferred directly to the input shaft without the one way clutch. Therefore the engine brake operates.

Position D and 3rd gear

Main section

The input shaft rotates clockwise. Clutch C1 connects the input shaft to the rear ring gear. The rear ring gear rotates clockwise. The rear planetary gear rotates clockwise.

The front large planetary gear rotates clockwise with the rear planetary gear as a unit. Brake B2, freewheel F1 and brake B1 lock the sun gear's rotation.

The front and rear planetary carriers are turned clockwise because of the reactive forces from the front large gear. The primary intermediate gear rotates clockwise with the front and rear planetary carriers as a unit.

U/D section

The secondary intermediate gear rotates counter-clockwise. The front ring gear rotates counter-clockwise with the secondary intermediate gear as a unit. The front planetary gear rotates clockwise. Brake B4 locks the rotation of the front and rear sun gear.

The front planetary carrier is turned clockwise because of the reactive forces from the front large planetary gear. The front planetary carrier and final drive pinion rotate clockwise with the rear ring gear as a unit. The final drive rotates clockwise.

Engine brake

Drive force is transferred directly to the input shaft without the one way clutch. Therefore the engine brake operates

Position D and 4th gear

Main section

The input shaft rotates clockwise. Clutch C1 connects the input shaft to the rear ring gear. The rear ring gear rotates clockwise. The rear planetary gear rotates clockwise.

The front large planetary gear rotates clockwise with the rear planetary gear as a unit. Brake B2, freewheel F1 and brake B1 lock the sun gear's rotation.

The front and rear planetary carriers are turned clockwise because of the reactive forces from the front large gear. The primary intermediate gear rotates clockwise with the front and rear planetary carriers as a unit.

U/D section

The secondary intermediate gear rotates clockwise. The front ring gear rotates counter-clockwise with the secondary intermediate gear as a unit. Clutch C3 connects the sun gear to the front planetary carrier.

The front planetary gear cannot rotate and the U/D unit rotates counter-clockwise as a unit. The final drive pinion rotates counter-clockwise with the U/D unit as a unit. The final drive rotates clockwise.

Engine brake

Drive force is transferred directly to the input shaft without the one way clutch. Therefore the engine brake operates.

Position D and 5th gear

Main section

The input shaft rotates clockwise. Clutch C1 connects the input shaft to the rear ring gear. Clutch C2 connects the input shaft to the sun gear.

The rear planetary gear cannot rotate and the rear planetary gear unit rotates clockwise as a unit. The front planetary gear cannot rotate with the rear planetary gear as a unit. The front planetary unit rotates clockwise as a unit. The primary intermediate gear rotates clockwise with the front planetary unit as a unit.

U/D section

The secondary intermediate gear rotates counter-clockwise. The front ring gear rotates counter-clockwise with the secondary intermediate gear as a unit. Clutch C3 connects the sun gear to the front planetary carrier.

The front planetary gear cannot rotate and the U/D unit rotates counter-clockwise as a unit. The final drive pinion rotates counter-clockwise with the U/D unit as a unit. The final drive rotates clockwise.

Engine brake

Drive force is transferred directly to the input shaft without the one way clutch. Therefore the engine brake operates.

Position R (reverse gear)

Main section

The input shaft rotates clockwise. Clutch C2 connects the input shaft to the sun gear. The sun gear rotates clockwise.

The rear planetary gear rotates counter-clockwise. The front large planetary gear rotates counter-clockwise with the rear planetary gear as a unit. The front small planetary gear rotates clockwise.

Brake B3 locks the front ring gear's rotation counter-clockwise. The front and rear planetary carriers are turned clockwise because of the reaction forces from the front small gear. The primary intermediate gear rotates counter-clockwise with the front and rear planetary carriers as a unit.

U/D section

The secondary intermediate gear rotates clockwise. The front ring gear rotates clockwise with the secondary intermediate gear as a unit. The front planetary gear rotates clockwise. The front sun gear rotates counter-clockwise.

The rear sun gear rotates counter-clockwise with the front sun gear as a unit. The rear planetary gear rotates clockwise. Brake B5 locks the rear planetary carrier's rotation. The rear ring gear rotates clockwise. The front planetary carrier and final drive pinion rotate clockwise with the rear ring gear as a unit. The final drive rotates counter-clockwise.

Engine brake

Drive force is transferred directly to the input shaft without the one way clutch. Therefore the engine brake operates.

Towing

Towing is only permitted in the vehicle's forward direction at max. 80 km/h for max. 80 km.

The gear selector shall be in position N.

Applies to: 2006–2011; M66 AWD

Shift cables

Shift cable:

• pulled when 1st, 3rd and 5th gears are selected
• pushed when 2nd, 4th and 6th gears are engaged.

Mechanical transmission cable for lateral travel:

• pulled when the gear selector lever is moved to the position between 1st and 2nd gears
• pushed when the gear selector lever is moved to the position below 5th and 6th. Gives maximum lateral movement when the lever is moved to back-up (reverse) gear.

There is a return spring on the lateral movement lever. The control unit in the transmission has a return spring.

The mechanical transmission cable for lateral travel is adjustable lengthwise. The adjuster is positioned on the mounting towards the lever on the transmission (1). The spring in the gear selector assembly pulls the mechanical cable and then the mechanical cable is locked by hand using the catch. When locking the gear selector lever and the components in the transmission must be in neutral position.

Power flow

1st gear

When 1st gear is selected, the coupling sleeve for 1st-2nd gear is moved by a gear selector fork along the synchronizing hub towards the idler wheel for 1st gear. The coupling sleeve and synchronizing hub lock the idler wheel for 1st gear at the intermediate shaft 1-2, 5-6.

Engine torque is transferred to the input shaft via the clutch. The 1st gear rack on the input shaft transfers the power to the idler wheel for 1st gear. From there power is transferred to intermediate shaft 1-2, 5-6 and to the final drive, which in turn transfers the power to the ring gear. The ring gear is connected to the drive shafts through the differential.

2nd gear

When 2nd gear is selected, the coupling sleeve for 1st-2nd gear is moved by a gear selector fork along the synchronizing hub towards the idler wheel for 2nd gear. The coupling sleeve and synchronizing hub lock the idler wheel for 2nd gear at the intermediate shaft 1-2, 5-6.

Engine torque is transferred to the input shaft via the clutch. The 2nd gear rack on the input shaft transfers the power to the idler wheel for 2nd gear. From there power is transferred to intermediate shaft 1-2, 5-6 and to the final drive, which in turn transfers the power to the ring gear. The ring gear is connected to the drive shafts through the differential.

3rd gear

When 3rd gear is selected, the coupling sleeve for 3rd-4th gear is moved by a gear selector fork along the synchronizing hub towards the idler wheel for 3rd gear. The coupling sleeve and synchronizing hub lock the idler wheel for 3rd gear at the intermediate shaft 3-4.

The torque of the engine is transferred via the clutch to the input shaft. The 3rd gear gearwheel on the input shaft transfers the power to the idler wheel for 3rd gear. From there power is transferred on to intermediate shaft 3-4 and to the final drive which in turn transfers the power to the ring gear. The ring gear is connected to the drive shafts through the differential.

4th gear

When 4th gear is selected, the coupling sleeve for 3rd-4th gear is moved by a gear selector fork along the synchronizing hub towards the idler wheel for 4th gear. The coupling sleeve and synchronizing hub lock the idler wheel for 4th gear at the intermediate shaft 3-4.

The torque of the engine is transferred via the clutch to the input shaft. The 4th gear gearwheel on the input shaft transfers the power to the idler wheel for 4th gear. From there power is transferred on to intermediate shaft 3-4 and to the final drive which in turn transfers the power to the ring gear. The ring gear is connected to the drive shafts through the differential.

5th gear

When 5th gear is selected, the coupling sleeve for 5th-6th gear is moved by a gear selector fork along the synchronizing hub towards the idler wheel for 5th gear. The coupling sleeve and synchronizing hub lock the idler wheel for 5th gear at the input shaft.

The torque of the engine is transferred via the clutch to the input shaft. The 5th-6th coupling sleeve and 5th gear idler wheel, located on the input shaft, transfer the power to the gear wheel for 5th gear. From there power is transferred on to intermediate shaft 1-2, 5-6 and to the final drive which in turn transfers the power to the ring gear. The ring gear is connected to the drive shafts through the differential.

6th gear

When 6th gear is selected, the coupling sleeve for 5th-6th gear is moved by a gear selector fork along the synchronizing hub towards the idler wheel for 6th gear. The coupling sleeve and synchronizing hub lock the idler wheel for 6th gear at the input shaft.

The torque of the engine is transferred via the clutch to the input shaft. The 5th-6th coupling sleeve and 6th gear idler wheel on the input shaft transfer the power to the gear wheel for 6th gear. From there power is transferred on to intermediate shaft 1-2, 5-6 and to the final drive which in turn transfers the power to the ring gear. The ring gear is connected to the drive shafts through the differential.

Back-up (reverse) gear

When back-up (reverse) gear is selected, the coupling sleeve for back-up (reverse) gear is moved by a gear selector fork along the synchronizing hub towards the idler wheel for back-up (reverse) gear.

The coupling sleeve and synchronizing hub lock the idler wheel for back-up (reverse) gear at the back-up (reverse) shaft.

The torque of the engine is transferred via the clutch to the input shaft. The 1st gear gearwheel on the input shaft transfers the power to the idler wheel for 1st gear. From there to the back-up (reverse) gear idler wheel and then to the coupling sleeve for back-up (reverse) gear. From there power is transferred on to intermediate shaft 1-2, 5-6 and to the final drive which in turn transfers the power to the ring gear. The ring gear is connected to the drive shafts through the differential.

Shift mechanism

The transfer from the control unit to the selector forks is divided between two locations in the transmission:

• The upper gear selector affects back-up (reverse) gear and 1st and 2nd gears
• The lower gear selector affects 3rd, 4th, 5th and 6th gears.

4 gear selector forks transfer the movement from the control to the relevant coupling sleeve.

The shift lever actuates the shift forks, which are mounted in bearings in the housing.

Two carrier plates are used to transfer the torque from the longitudinal movement lever to the axially sliding gear selectors. The carriers run in a groove in the gear selector plate.

The gear selector panel is affected by a carrier plate connected to the lateral movement lever.

The carrier plates move vertically between four possible positions. The different gears can be activated in the different positions.

• In the uppermost position the upper gear selector activates back-up (reverse) gear
• In the next highest position the lower gear selector activates 5th and 6th gears
• In the next lowest position the lower gear selector activates 3rd and 4th gears
• In the lowest position the upper gear selector activates 1st and 2nd gears.

The longitudinal movement lever acts on the shift lever so that the correct gear is engaged. The control unit also contains two springs (10 and 12) that help return the shift lever to the neutral position.

Back-up (reverse) inhibitor

The shift lever assembly houses a solenoid that serves as an electronically controlled reverse inhibitor. If vehicle speed exceeds 25 km/h (15.5 mph), the solenoid is activated and it is not possible to engage reverse gear. When speed drops below 15 km/h (9 mph), the solenoid releases and reverse gear can be engaged.

Differential

When driving straight ahead, the ring wheel and differential housing rotate at the same speed as the drive shafts and the driving wheels.

When cornering, the differential gears rotate to compensate for the different speeds of the wheels. Because the small side gears are rotating on the shaft journal, the drive shafts can rotate at different speeds. Power is transferred from the differential housing to the drive shafts via the small side gears in the same way as when driving straight ahead. Both drive wheels still have the same driven power.

Cars with four wheel drive have a splined pin on the differential housing. The sleeve on the pin connects the differential housing with the bevel gear. Torque is directed from the bevel gear to the rear wheels.

Clutch, general

The primary role of the clutch system is to disengage the transmission when shifting, transfer torque and to allow comfortable starting.

Disengagement of the clutch driven plate when shifting is a very important part of this functionality. When the driver presses the clutch pedal, the throwout bearing moves a given distance towards the diaphragm spring and disengages the clutch driven plate. The clutch is raised and held in position by the springs riveted to the pressure plate.

Complete disengagement takes place during the last quarter of clutch pedal travel.

The clutch driven plate is trapped between the flywheel and pressure plate to transfer the torque. The torque is transferred via the clutch to the input shaft.

The torque is transferred across the crankshaft via the flywheel to the clutch driven plate. Half of the torque is transferred via the clutch screw to the clutch housing through lifting springs, over to the pressure plate and to the clutch driven plate. The clutch driven plate then transfers the torque via its hub and splines to the input shaft.

During down-shifting the rotation speed of the clutch driven plate increases. It decreases during up-shifting. The engine speed (RPM) is then synchronized with the vehicle speed when the clutch is released. If there is no disengagement during shifting, there would be abnormal synchronization wear in the transmission.

Pre-tensioned lifting springs connect the clutch housing and the pressure plate.

The clutch is defined by the 3 characteristic curves:

• pressure plate pressure against the clutch driven plate
• diaphragm spring pressure against the throwout bearing
• the lift of the pressure plate.

The pressure of the pressure plate increases as the clutch driven plate wears. This increase in pressure increases the pressure at the diaphragm spring and with it pedal effort as the clutch driven plate wears. The diaphragm spring moves backwards as the clutch driven plate wears. The clutches are guaranteed to tolerate wear of 1.5 mm to the facing. This means that the clutch cover has a wear capacity of 8-9 mm to compensate for rearward movement of the throwout bearing.

Hydraulic clutch control mechanism with concentric slave cylinder (CSC)

In order to change gears, the transmission must be disengaged from the engine. This is done by the clutch pedal. When the clutch pedal is pressed, fluid is transferred from the master cylinder through a pipe to the concentric slave cylinder (CSC) in the clutch cover. This then acts on the clutch, disengaging the clutch driven plate.

Sound and vibration is also transferred from the engine. The pipe and hose are balanced so that they absorb vibration. On diesel engines, a damping unit is also used. The fluid is encapsulated between two membrane discs which are balanced to the correct rigidity.

Self-adjusting clutch (SAC)

When the facing on a clutch driven plate wears, the normal working position (travel) of the pressure plate and the disengagement position increase.

On the self-adjusting clutch an adjuster ring responds to the wear of the clutch driven plate. As wear increases, the adjustment ring moves automatically slightly at the next disengagement and adjusts the bearing position of the diaphragm spring. This means that the operating travel of the pressure plate and therefore engagement pressure remain constant.