Principle of Operation
For normal brake operation, the brake booster assembly assists brake pedal pressure and the force is transmitted to the master cylinder assembly. The master cylinder assembly converts brake pedal movement to hydraulic pressure. Primary and secondary brake pipe circuits supply the hydraulic pressure via the ABS hydraulic unit to the brake calipers.
The primary circuit supplies the front right and rear left brakes while the secondary circuit supplies the front left and rear right brakes. The engine intake manifold provides the brake booster assembly with vacuum through a pipe and non-return valve.
The EHPS has two connections: a 2-pin power cable connection and a 3-pin connection which consists of terminal 15, terminal 61 (to determine if the engine is running) and the Diagnosis bus for communication with the control electronics integrated in the pump. The pump is operational only when the engine is running.
A DC motor, capable of drawing a maximum current of 120 Amperes, but running at an average 11.5 Amperes, powers the system. In standby mode with the engine running but the vehicle stationary the draw is 7.0 Amperes ±10%.
There are two modes of operation for the EHPS: no steering assistance and steering assistance.
With the engine running and no steering assistance required the pump operates at approximately 80% capacity at a speed of 3,500 rpm. Movement of the steering changes the hydraulic pressure within the circuit which in turn effects the operation of the pump, this is identified at the control electronics by the increase in current, the pump speed is increased to 4,500 rpm and now operates at full capacity.