Valve Block

ABS Brake Master Cylinder:

VALVE BLOCK
The valve block contains three pairs of solenoid valves, one pair for each of the front brakes and one pair for the rear brakes. Each pair contain an outlet and an inlet valve. The valves are electronically operated by signals from the ECM. During braking with ABS control, the electronic control module provides a voltage to the inlet and outlet solenoid valves, which influence the hydraulic pressure to the brakes. The control to the rear brakes is determined by the wheel which first shows a tendency to lock. The brake pressure at both rear wheels is thus determined by the wheel having the lowest friction coefficient.

This ensures that in the case of braking on a surface with low friction coefficient neither of the rear wheels will lock.

All the valves with the exemption of the main valve have a common ground point which is connected to pin 11 of the control module.

The ground connection pin 11 is known as the reference ground, via this connection the electronic control module receives test pulses for the valves.

NOTE: During normal braking the anti-lock system will not be activated. However, if the braking force applied is sufficient to overcome tire/road adhesion, the anti-lock system will automatically be activated preventing the road wheel from locking.

With no current flowing through the inlet solenoids the valves are open so that during braking the brake pressure can be applied direct to the wheel brakes.

With no current flowing through the outlet solenoids the valves are closed and disconnect the wheel brakes from the reservoir.

Valve Block:

To maintain pressure, the outlet valve (1) stays closed, and the inlet valve (2) to a 'wheel with a tendency to lock' closes, ensuring the brake pressure to that wheel cannot be increased.

To decrease pressure the inlet valve closes and the outlet valve opens. The brake pressure to the wheel is decreased.

To increase the pressure to the wheel the inlet valve opens and the outlet valve closes and the brake pressure to the wheel is again increased almost up to the locking pressure limit.

These phases are repeated up to six times a second until the tendency for the wheel to lock is eliminated.

SOLENOID VALVE OPERATION

Solenoid Valve Operation - Phase One:

Phase One

Solenoid Valve Operation - Phase Two & Three:

Phase Two