Multidisk Clutch, Component Description - GF28.50-P-1100AVJ
Model 253 with transmission 725.096
Sectional view of multi-disk clutch with actuator
Location
The multi-disk clutch (5) is located in the middle in the transmission housing in the multi-disk clutch cage.
Task
The multi-disk clutch (5) connects the front axle transmission output with the rear axle output shaft. It thereby enables variable torque distribution between the front and rear axle and is used as a load change damper.
Function
Multi-disk clutch function
In non-actuated condition the multi-disk clutch (5) is opened, the piston return springs (12) reset the clutch piston (10) so that the coupling is always open in the design position. No torque is transferred from the inner plates (5a) with the friction lining (5b) onto the outer plates (5c). The power flow to the drive gear on the front axle transmission output (1) is disconnected when the multi-disk clutch (5) is not actuated. The output torque of the transmission is transferred 100 % to the rear-axle output shaft (6) and thereby to the rear wheels.
If the all-wheel drive control unit (N45) actuates the all-wheel drive actuator (N45/1), the ramp disk with sector gear (7) is rotated against the ring (9) attached to the housing through the worm gear (14). The ball ramps (8a) convert the rotation of the worm into an axial clutch motion, whereupon the clutch is then operated. The multi-disk clutch (5) frictional connection is then made. With an operated (closed) multi-disk clutch (5) the torque is transferred from the inner plates (5a) using the friction lining (5b) to the outer plates (5c). The outer plates (5c) are frictionally connected to the multi-disk clutch cage (13). The multi-disk clutch cage (13) transfers the torque to the frictionally connected drive gear on the front axle transmission output (1). Consequently, the output torque coming from the automatic transmission is distributed, depending on the driving situation, from 0 % to 50 % to the drive gear on the front axle transmission output (1) and the other part to the rear-axle output shaft (6). This then results in a variable torque distribution.
Variable torque distribution
The multi-disk clutch (5) on a left-hand drive vehicle transfer a maximum of 1150 Nm and on a right-hand drive vehicle a maximum of 850 Nm torque to the front axle. The difference is down to the parameter control in the all-wheel drive control unit (N45). This variable torque distribution principle improves the traction and driving stability of the vehicle on low friction surfaces in particular (e.g. snow-covered and icy roads).
Load jerk damping
The pre-compressed multi-disk clutch (5) acts as a load change damper. It reduces the shock during the load change (change from traction mode to deceleration mode or from deceleration mode to traction mode). During a load change, the complete changeover play of the drive train is run through first. The driver notices this as a load change shock. Because the changeover play is greatly increased by the additional drivetrain to the front axle on all-wheel drive, the load change shock is particularly pronounced here.
Immobilization of both drive trains leads to the changeover play of the drive trains being run through at the same time. The load change behavior of 4MATIC vehicles can therefore be reduced to the level of a rear-wheel driven vehicle.
Changeover play
The changeover play is the sum of the play between all gears and other positive-locking connections in the drivetrain during throttle change.