Module 2- Apply and Hold Devices (Page 4 of 6)
Automatic transmission clutch packs perform similar functions to brake bands. There are several differences. One of the most important differences is:
- Unlike a brake band which can only hold a component stationary, a clutch pack can connect two devices together as well as hold a component stationary.
Construction of Transmission Clutch Packs
A clutch pack consists of many fibre discs with friction material on both sides and splines on the inside. These are called "frictions." The inside splines of a "friction" splines onto a transmission component. See diagram below.
Between each "friction" is a thin steel plate with external splines called "steels." The "steels" have no friction material on either side. They have external splines. These splines may either spline onto the transmission case or another transmission component. Pictured below is a set of steels. Notice the external splines.
Pictured below is the matching set of frictions. Notice the friction material on both sides and the internal splines.
These clutch packs are typically located in a clutch housing or drum assembly. See diagrams below.
The valve body directs fluid pressure to apply the clutch pack piston at the appropriate time. Pressurized fluid pushes the piston forward. The piston overcomes spring pressure and applies the clutch pack.
When the fluid pressure is exhausted, the clutch release / return springs (see diagram below) pushes the piston back. See diagram below. The clutch pack is unapplied. When the clutch is unapplied, the frictions spins independently from the steels.
In the diagram below, the clutch piston is applied by fluid pressure. The valve body - the brains - decides when to apply the clutch pack. When the clutch piston applies, the clutch piston overcomes the force of the clutch release spring. The frictions are squeezed together with the steels.
The component that is splined onto the frictions is now connected / attatched to the component that is splined onto the steels. Thus, these two components, whatever they may be, are locked together.
Module 2 (Page 4 of 6)