Drive Clutches
Multiplate Drive or Brake Clutch - Typical
| ITEM | DESCRIPTION |
|---|---|
| 1 | Cylinder |
| 2 | Piston |
| 3 | Disk spring |
| 4 | Metal plates |
| 5 | Friction plates |
| 6 | Baffle plate |
| 7 | Pressure equalization chamber |
| 8 | Piston chamber |
There are two multiplate drive clutches and two multiplate brakes used in the ZF 9HP48 automatic transmission. Each clutch or brake comprises a number of friction plates dependent on the output controlled. A typical clutch or brake consists of a number of steel outer plates and inner plates with friction material bonded to each face.
The drive clutches have both the friction plate and the metal plates rotating when the clutch is open. Multiplate brakes have either the friction plate or the metal plate rotating, with one fixed stationary.
| CLUTCH/BRAKE | OPERATION |
|---|---|
| Multiplate clutch 'B' | Connects the input shaft to sun gear 'S1' |
| Multiplate clutch 'E' | Connects the input shaft to planet carrier 3 and ring gear 4 |
| Multiplate brake 'C' | Locks sun gear 'S1' |
| Multiplate brake 'D' | Locks ring gear 2 |
The multiplate clutch and brake plates are held apart mechanically by a disk spring and hydraulically by ATF pressure. The ATF pressure is derived from a lubrication channel which supplies ATF to the transmission components. The ATF is passed via drillings in the input shaft into the chamber between the baffle plate and the piston. To prevent inadvertent clutch application due to pressure build up produced by centrifugal force, the fluid in the pressure equalization chamber overcomes any pressure in the piston chamber and holds the piston off the clutch plate assembly. The multiplate brakes do not require a baffle plate and pressure equalization chamber to compensate for centrifugal pressure which occurs in a rotating piston.
When clutch application is required, pressure from the ATF pump is applied to the piston chamber from the supply port. This pressure overcomes the low pressure fluid present in the pressure equalization chamber. The piston moves, against the pressure applied by the disk spring, and compresses the clutch plate assembly. When the pressure falls, the disk spring pushes the piston away from the clutch plate assembly, disengaging the clutch.