Solenoid valves

Solenoid valves

1.

Piston

2.	Return spring

3.	Control module

4.	Pressure accumulator

5.	Return pump

Normal position (pressure build-up)

The solenoid valve is without current. The piston (1) is pressed down to the normal position by the return spring (2). The brake fluid can now flow freely from the master cylinder to the wheel cylinder.

This position is the normal position for ordinary braking with no ABS activation and the pressure build-up position when the ABS is activated.

During ABS activation the control module can operate the ABS at up to 10 activation cycles per second.

1.

Piston

2.	Return spring

3.	Control module

4.	Pressure accumulator

5.	Return pump

Holding pressure

The solenoid valve has received about half current strength from the ABS control module. The piston has assumed the holding pressure position by rising slightly and so closing the passage from the master cylinder to the wheel cylinder.

This is one of the three positions (normal, pressure holding and pressure relieved) used by the control module (3) during ABS activation.

1.

Piston

2.	Return spring

3.	Control module

4.	Pressure accumulator

5.	Return pump

Pressure relieved

The solenoid valve receives full current strength from the control module. The piston in the valve has risen to the pressure relieved position, thus opening the passage from the wheel cylinder to the pressure accumulator (8) which can promptly receive the pressure from the wheel cylinder. The control module (3) applies current to the return pump (5) and the pressure can be pumped back to the master cylinder.