General System Description
The ABS/TCS/ESP systems integrate several functional units and provide the pressure volume flow required for the modulation of brake torque in response to wheel slip information supplied by the wheel speed sensors. The TCS system serves to produce a stabilizing torque at the driven wheel running with the highest slip, or to reduce slip at both driven wheels, thereby optimizing the utilization of adhesion of the other driven wheel or driven wheels. The ESP system stabilizes the vehicle in the event of a yawing motion of the vehicle which is not in correlation with the sensed steering angle. It serves to reconcile the yawing motion of the vehicle with the driver’s intentions. As input variables for ESP control, the signals of a lateral acceleration sensor, a yaw rate sensor, a steering angle sensor and a pressure sensor are required in addition to the signals provided by the wheel speed sensors available for ABS/TCS control. In addition, these systems may integrate an electronic brake force distribution (EBD) system to regulate effective brake force at the rear wheels in place of the traditional proportional valve.
The MK25E is based on a housing with solenoid valves, integrated pump and ECU. Each brake circuit incorporates pairs of valves (NO inlet valve/NC outlet valve) permitting the brake pressure to be modulated at the front wheels (individual wheel control) and at the rear wheels (select low control or stability control with ABS plus) in response to suitable electrical signals.
The TCS ICU is based on the ABS MK25E with additional components in the valve block for braking intervention during TCS operation and active yaw control. The isolation valves with integrated pressure relief valve in the TCS valve block permit braking pressure for TCS/ESP control to be built up by means of the pump, by-passing the actuation unit. The electric shuttle valves (ESV’s) change the suction connection of the pump from the low pressure accumulators to the TMC. The suction dampers optimize the suction performance of the pump, and minimizes the cut-out impact at the end of a TCS control cycle.