M56

Function

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 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.
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.
Complete disengagement takes place during the last quarter of clutch pedal travel.
During downshifting the rotation speed of the clutch driven plate increases. It decreases during upshifting. 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:
1. pressure plate pressure against the clutch driven plate
2. diaphragm spring pressure against the throwout bearing
3. 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.
An auxiliary spring at the pedal reduces the effort required for disengagement. When the pedal is released, the auxiliary spring is trying to extend, pressing the pedal upwards. As the pedal is pressed and there is little resistance from the clutch, the spring is compressed until the clutch reaches the biting point. The spring then expands as it turns upwards so that it presses down the pedal, minimizing the pedal effort required.
The clutch pedal does not need to be lubricated. All connections in the pedal system are low friction.

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.

Shock load limiter




In vehicles which have high torque engines the return time for the clutch may be too short. This means that the torque peak is so high that the drive train could be damaged.
On those occasions where the torque peak is too high, the hydraulic flow is choked by a shock load limiter in the engagement direction between the concentric slave cylinder (CSC) and master cylinder.

Power flow
The torque of the engine is transferred from the clutch to the input shaft and then onwards via different gear sets and driving final drives, depending on the gear selected, to the final drive/differential, drive shafts and out to the front wheels.

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 lower output (secondary) shaft.
The engine torque is transferred from the clutch to the input shaft to the gear and idler wheel for 1st gear, through the lower output (secondary) shaft and on to the final drive gear and out to the final drive.

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 lower output (secondary) shaft.
The engine torque is transferred from the clutch to the input shaft to the gear and idler wheel for 2nd gear, through the lower output (secondary) shaft and on to the final drive gear and out to the final drive.

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 primary shaft.
The engine torque is transferred from the clutch to the input shaft, to the idler wheel for 3rd gear. It is then transferred to the gear for 3rd gear on the lower output (secondary) shaft, and on to the final drive gear and out to the final drive.

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 primary shaft.
The engine torque is transferred from the clutch to the input shaft, to the idler wheel for 4th gear. It is then transferred to the gear for 4th gear on the lower output (secondary) shaft, and on to the final drive gear and out to the final drive.

5th gear









When 5th gear is selected, the coupling sleeve for 5th/back-up (reverse) 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 upper output (secondary) shaft.
The engine torque is transferred from the clutch to the input shaft, to the gear on the primary shaft for the idler wheel for 5th gear on the upper output (secondary) shaft, and on to the final drive gear and out to the final drive.

Back-up (reverse) gear









When back-up (reverse) gear is selected, the coupling sleeve for 5th/back-up (reverse) gear is moved by a gear selector fork along the synchronizing hub towards the idler wheel for back-up (reverse). The coupling sleeve and synchronizing hub then lock the idler wheel for back-up (reverse) at the upper output (secondary) shaft.
The engine torque is transferred from the clutch to the input shaft, to the gear on the primary shaft for the idler wheel for 1st gear (which also acts as intermediate gear for back-up (reverse) gear) on the lower output (secondary) shaft. It is then transferred to the idler wheel for back-up (reverse) gear on the upper output (secondary) shaft, and on to the final drive gear and out to the final drive.
Because the idler wheel for 1st gear is used as the intermediate gear for back-up (reverse) gear, there is no separate shaft for back-up (reverse) gear.

Shift mechanism




1. gear selector fork
2. gear selector
3. -
4. flange
5. lever
6. link arm
7. mechanical cable for lateral movement
8. mechanical cable for longitudinal movement
9. gear selector lever
10. lever for lateral movement
11. input gear selector rod
12. twist piece
13. ball limiter
14. lever for longitudinal movement
15. selector pin
16. spring-loaded back-up (reverse) inhibitor.
The lever for lateral movement is secured to the outside of the input gear selector rod, on which the gear selector and gearshift gate are positioned. The selector pin, which is on the shaft/gear in the transmission housing. It engages and disengages the gears. The shaft/gear and lever are connected to the gear selector lever by mechanical cables.
When the gear selector lever is moved to the side, the outer lever on the gear selector assembly converts this movement to a pulling-sliding movement in the mechanical cable. If the gear selector lever is moved longitudinally however, the second cable is affected directly by the gear selector lever.
The lever for lateral movement acts on the input gear selector rod. At the other end of the gear selector rod there is a spring-loaded neutral return gate. The neutral return gate attempts to engage the neutral position between gears 3rd and 4th gears (when no gear is engaged).
The lever for longitudinal movement is secured to a shaft which is connected to the selector pin. The selector pin acts on the gear selector. The gear selector acts on the flanges and gear selector forks for each gear. These in turn act on the coupling sleeves for the various idler wheels.
When the gear selector lever is moved to the side, the neutral return gate will turn the gear selector to the correct position. When the gear selector lever is moved longitudinally, the gear selector bevel arm and selector pin will act on the gear selector so that the selector fork moves.

Example
When the gear selector lever is moved forwards towards 1st gear, this creates a dragging force in the mechanical cable which turns the lever for longitudinal movement. The gear selector bevel arm will then act on the selector pin and therefore the gear selector so that the lever for 1st and 2nd gear moves in the same direction. The jointed lever then moves the gear selector fork in the opposition direction and engages the synchronizing sleeve with the idler wheel for 1st gear.
When other gears are engaged, this works in a similar way. The gearshift gate then turns the gear selector to the correct position. The gear selector then directly (5th/back-up (reverse) gear) or via another component (other gears) moves the relevant gear selector fork sideways.

Back-up (reverse) inhibitor
There is a spring-loaded back-up (reverse) inhibitor connected to the plate for the gearshift gate which prevents the gear selector lever from moving to back-up (reverse) gear from 5th gear.
The gear selector lever must be moved to neutral before back-up (reverse) gear can be selected. Only then can the gear selector be moved sideways towards back-up (reverse) gear. No separate back-up (reverse) inhibitor is required in the gear selector assembly with this arrangement.

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.