離合器的壓力控制,電腦控制會盡量讓離合器有一定的打滑程度: Clutch control adaptation: Comfortable clutch operation must be maintained in all operating states and throughout the useful life of the clutch. For this purpose, the relationship between clutch valve control current and clutch torque is subject to continuous updating. This process of updating is necessary since the friction coefficients of the clutches are continuously variable. The coefficient of friction is dependent on the following continuously variable factors: – ATF (quality, ageing, wear) – Oil temperature – Clutch temperature – Clutch slip To compensate for these influences, the relationship between control current and clutch torque is determined in various driving conditions, e.g. under microslip, and stored.
Clutch cooling: To avoid overheating of the clutches, the clutches are cooled by a separate oil flow. The clutch cooling system is activated at the same time as the clutch is controlled. The near-permanent microslip ensures that the clutches are continuously cooled and lubricated. The cooling oil flow is shown overleaf on Fig. 386_021. The mechatronic control unit J743 activates N218 depending on clutch state/cooling oil demand by applying a defined electrical current, which in turn produces a proportionate control pressure. This control pressure acts upon the piston of the clutch cooling valve (CCV). Depending on the control pressure, a corresponding oil flow is branched off the system oil pressure and fed to the clutches. The maximum cooling output is approx. 20 l/min at 2.0 bar. The N218 has a falling current/pressure characteristic. This means that in case of failure of the N218, the maximum cooling oil flow is set at all times and, therefore, the maximum possible cooling output is available. Fig. 386_058 (adjacent) shows this state.