Dual-clutch transmission control, basic function

Overview

This document contains information on:

 General

 Function

General

In the dual-clutch transmission, shift operation are automatically realized through a dual clutch. The clutch is controlled to match the given driver request by the dual-clutch transmission control unit or the fully integrated transmission control electrohydraulic controller unit.

Function

Dual clutch control

The dual clutch consists of two combined wet clutches. The wet clutches shift one of two respective sub-transmissions alternately. Sub-transmission 1 contains - depending on the number of gears involved - the odd gears. Sub-transmission 2 contains the even gears and the reverse gear. In drive mode, one sub-transmission gear is always engaged, while the next gear expected to be shifted to is prepared for engaging by the transmission control. The relevant clutch of the pre-engaged gear is still open and therefore torque is not transferred. In first gear, the drive torque to be transmitted is the largest compared with the remaining gears. Therefore, the clutch of the first sub-transmission is larger in size and located on the outside of the dual clutch.

 The combustion engine drives both transmission input shafts. One clutch is on the hollow drilled transmission input shaft, the other is on the transmission input shaft running in the first shaft. The next gear can always be pre-selected on the non-engaging transmission input shaft. One clutch opens at the shift point, while the other closes.

Clutch power-flow change

The power flow is changed with an overlap gearshift system operation. During overlap gearshift system operation, torque transfer is reduced through a clutch proportionate to the increase at the clutch. During torque transfer, the drive torque is also reduced, within a defined time window, by the combustion engine control unit.