Antilock Brakes / Traction Control Systems: Description and Operation

PSM 8 Components







4530 Hydraulic Unit

The hydraulic unit consists of the control module, the electronic circuit breakers for the pump and the solenoid valves, proportioned (linear) solenoid valves and a pump unit. The entire valve block was optimized in the area of the port guidance, the valves and the pump so that the pre-charge pump could be omitted. These measures, in conjunction with an optimized brake master cylinder, allow for simplified intake of brake fluid, particularly in cold state. This also enables an easy and rapid pressure increase on the respective wheel.







To avoid confusing the hydraulic lines, the connections are manufactured differently with M 10 or M 12 threads and identified with letters on the connections. In order to disengage noise, the lines between the brake master cylinder and the hydraulic unit are manufactured from so-called "Steelflex" lines.

In each brake circuit there are the inlet valves (1, 2, 3, 4) and the outlet valves (5, 6, 7, 8) enabling braking pressure modulation on the front and rear wheels when activated accordingly. Within the respective brake circuit, the isolating valves (9, 10) enable pressure increase via the pump to the ABD and VDC controls. The pump's suction side is switched to the tandem brake master cylinder (expansion tank) using the electrical switch-over valves (11, 12).







Pressure Sensor

The pressure sensor for detecting the brake pressure is integrated in the valve block. With this active braking pressure sensor, the braking pressure is detected (deceleration request) and used by the PSM control module to calculate the wheel brake forces (longitudinal forces). If an automatic control (ABS, driving dynamics, electronic brake-force distribution) becomes necessary during the braking procedure, the existing wheel brake forces are taken into account for the calculation of the lateral support forces.

PSM Control Module

The PSM control module is integrated into the hydraulic unit. The incoming singals are processed inside the control module and forwarded directly to the integrated valves and to the relays.