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Control valve

Control valve



1. Servo pressure from the power steering pump

2. Return to the power steering fluid reservoir

3. To the servo cylinder on right turn

4. To the servo cylinder on left turn


The housing surrounding the control valve is a part of the steering gear housing. It has four connections for the flow of hydraulic fluid: Servo pressure from the power steering pump (1), return to the power steering fluid reservoir (2), to the servo cylinder on right turn, alternatively from the servo cylinder on left turn (3) and to the servo cylinder on left turn, alternatively from the servo cylinder on right turn (4).

During a left turn, hydraulic fluid is pressed to the left side of the servo cylinder via the control valve connection (4). At the same time, the right side of the servo cylinder is drained via the control valve connection (3). Hydraulic fluid passes through the valve to the return line (2) and then back to the power steering fluid reservoir. During a right turn, the procedure is the opposite.

When the steering wheel is turned, the movement is transferred via the torsion bar to the pinion. Since the torsion bar twists slightly, there will be a difference between the degree of rotation of the intermediate shaft and the pinion. As a result, the fluid can no longer flow through the control valve and directly back to the power steering fluid reservoir. Instead, passages in the control valve are opened for delivery to and return from the servo cylinder.

As long as the torsion bar is twisted, hydraulic fluid will act on the rack so that the servo affect is retained. The difference between the steering wheel movement and the resulting reaction of the steering decreases when the servo cylinder acts on the rack. When this difference ceases, the passages that lead the hydraulic fluid through the valve and directly back to the power steering fluid reservoir are once again opened.

A certain amount of hydraulic fluid passes through the valve constantly, except when full lock is applied. This is necessary so that the control valve in the power steering pump will operate and the circulation helps to cool the hydraulic fluid.