Method for Identification of the Kiss Point as well as Takeoff Point of a Hydraulically Actuated Friction Clutch

For control of most automatic transmissions with wet clutches (e.g. dual clutch transmission), it is important to know the kiss point with high accuracy. The kiss point describes the value of the control variable for which the friction clutch begins to transmit torque. Another significant value during the filling process of a wet clutch is the takeoff point. This is the hydraulic pressure which causes the clutch piston to begin to move. This paper presents an innovative approach that enables the joint determination of the kiss point as well as the takeoff point in only one identification procedure. In contrast to existing methods, this method is able to identify both points without the necessity for undesired auxiliary system excitation. Therefore it is possible to reduce wear on system components such as synchronization rings.

The method presented in this paper analyzes the measured filling pressure characteristic over time as the system response to a defined excitation. The innovation of this method consists of dividing this pressure characteristic into three phases, where the separation is motivated by physical considerations. Each of these phases is approximated by appropriate linear and nonlinear functions. With the help of offline methods for system identification, the parameters of the approximation function are adjusted to reach the optimal approximation of the pressure characteristic. The takeoff point and the kiss point are distinct points between the approximating functions of the neighboring phases of the filling pressure characteristic. These points can be analytically determined for all phases of the characteristic. The choice of a suitable identification method has to take into account the electronic control units used for transmission control in modern vehicles and the capabilities they have. These methods are designed to work with noisy signals and allow for the accurate determination of the system parameters.