Spring packs are used in a variety of clutched applications, although their most common use is within the clutches of automatic transmission. Clutches are engaged in order for a particular part of a machine to perform work. In the case of automatic transmissions, different clutches are engaged in order to optimize engine performance.The purpose of a spring pack is to return the piston to its “home position” during clutch disengagement. They also perform a secondary function by ensuring the piston does not apply the clutch plates through centrifugal force in rotating clutches.
Clutch plates engaged
Oil pressure is applied to the piston, which engages the clutches plates, allowing the clutch to perform its required task. As a result of the clutch plates engaging, the spring pack is fully compressed.
Clutch plates disengaged
When the clutch is ready to disengage, the oil pressure applied to the piston is reduced. The compressed spring pack can then release its stored energy and provides a return force to the piston to return it to its original starting position, and thereby disengaging the clutch plates. The spring pack also serves a secondary function in rotating clutches by providing a static load against the piston to prevent the piston from applying as a result of centrifugal forces.