Control of Shift Operations

During a shift operation certain elements are released while others are actuated. Ideally, this process takes place simultaneously (synchronously) to avoid jerky gear shifting.

The time for the shift operation should remain within the time limits provided.

When the shift operation is controlled conventionally, the pressure buildup and reduction at the shift elements are set and defined for ideal conditions (synchronous shifting).

As there is no way of influencing the control in the event of different levels of wear in the shift elements, when the transaxle has been used for a fairly high mileage it is possible that the pressure buildup and reduction may no longer be synchronous.

The result or premature pressure reduction at the element to be switched off is an unwanted rise in the Turbine Shaft Speed (TSS) as the element to be switched on cannot transmit the input torque.

The result of delayed pressure reduction at the element to be switched off is an unwanted decrease in the TSS as both shift elements transmit the input torque. In the process the torque is transmitted to the transaxle housing through internal locking.

In both cases, a jerk will be felt during the shift operation.

In addition, wear in the shift elements leads to a lengthening of the shift operation. Therefore, shifting takes longer when the transaxle has accumulated a higher mileage.