sets of planetary gears. A compound planetary gearset is used to provide more forward gear ratios than a simple planetary gearset.

CLUTCHES AND BANDS

Automatic transmission clutches and bands are friction devices that drive or lock planetary gearsets members. They are used to cause the gearset to transfer power.

Multiple-Disc Clutch

The multiple-disc clutch is used to transmit torque by locking elements of the planetary gearsets to rotating members within the transmission. In some cases, the multiple-disc clutch is also used to lock a planetary gearset element to the transmission case so it can act as a reactionary member. The multiple-disc clutch is made up of the following components (fig. 4-31).

DISCS AND PLATES. - The active components of the multiple-disc clutch are the discs and the plates. The discs are made of steel and are faced with a friction material. They have teeth cut into their inner circumference to key them positively to the clutch hub. The plates are made of steel with no lining. They have teeth cut into their outer circumference to key them positively with the inside of a clutch drum or to the inside of the transmission case. By alternately stacking the discs and plates, they are locked together or released by simply squeezing them.

CLUTCH DRUM AND HUB. - The clutch drum holds the stack of discs and plates and is attached to the planetary gearset element that is being driven. The clutch hub attaches to the driving member and fits inside the clutch discs and plates.

Figure 4-31. - Multiple-disc clutch.