Normal Operation

The hydraulic function is divided into 3 operational modes, each actuated in the hydraulic unit (A7/3):

^ Normal operation,
^ ABS control operation,
^ ASR control operation.

Pressure Reservoir Charging:

All the solenoid valves (y1, y2, y3, y4 and y5) are in normal (nonenergized) position "O." The tandem master cylinder (4) is connected directly to the front brake calipers via connection V, connecting the right and left front solenoid valves (y1 and y2). The brake line from the tandem master cylinder connects to the rear wheel brake circuit at connection "H" (HZ). Switchover valve (y5) and left rear solenoid valve (y3) control the left rear brake caliper through connection (hl). Switchover valve (y5) and right rear solenoid valve (y4) control the right rear brake caliper through connection (hr).


CHARGING PRESSURE RESERVOIR
If there is no brake fluid in the pressure reservoir (13) or if the pressure is below approx. 160 bar (2320 psi), the pressure switch (s1) sends the control unit a signal to charge the pressure reservoir. The ASR charging pump (M15) activates and supplies brake fluid with an initial pressure of approx. 10 bar (145 psi) through connection BA to the ASR return/pressure pumps (m1) in the ABS/ASR hydraulic unit (A7/3). The ASR charging pump (Ml5) activates simultaneously with the ASR return/pressure pumps (m1), and together the pumps pressurize the reservoir. At a pressure of approx. 180 bar (2610 psi), the pressure switch (s1) sends the ABS/ASR control unit a signal to stop charging the pressure reservoir. It takes approx. 30 - 50 seconds to fully charge the pressure reservoir.


ABS CONTROL OPERATION
Compared to ABS without ASR, there are the following modifications:
The pistons in the tandem master cylinder drive brake fluid under pressure through switchover solenoid valve to both left and right rear solenoid valves. During ABS operation (pressure increase, pressure retention and pressure release), the solenoid valves activate simultaneously the rear wheel circuit.

ASR CONTROL OPERATION
The control operation requires a fully charged pressure reservoir. The pressure switch continuously senses pressure in the pressure reservoir.

The brake pressure for ASR operation is supplied by the pressure reservoir. If the ABS/ASR control unit recognizes that a wheel is starting to spin, it shifts switchover solenoid valve to position "2" (The switchover solenoid valve then stays in this position until the end of the control operation). Thus full reservoir pressure is applied upstream of solenoid valves. depending on which wheel spins and by how much, the solenoid valves switch between the 3 pressure phases:
pressure increase, (position 0), pressure retention, (position 1) and pressure release, (position 2).