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This text from my SAAB 9000 Service Manual 6: Front assembly and steering.
Steering, Low Engine Speed
The pressure raised by the pump (shaded portion in the illustration) is reduced slightly by the restriction in the pump outlet. The reduced
pressure is also communicated to the spring loaded side of the control valve, giving rise to a slight pressure difference between the two
sides of the valve. Owing to the low speed of the pump, the hydraulic pressure is insufficient to overcome the force of the spring and
actuate the valve.
Steering, High Engine Speed (Pump In Flow Regulation Position)
With increased engine speed the flow of hydraulic fluid increases to the pump. The flow velocity also increases because of the restriction
in the pump outlet. This causes a drop in pressure in the connecting passage and as a result the pressure on the spring loaded side of the
control valve will be lower than that acting on the outlet side of the valve. The valve, therefore, overcomes the force of the spring,
opening a port to the suction side of the pump and allowing internal recirculation of the fluid. A constant flow out of the pump is
achieved, independent of pump/engine speed.
Wheel Turned To Full Lock
In this case the pump speed is often low. When the wheel is turned against the end stop the control valve of the steering gear is closed.
The flow from the pump is therefore zero.
The resulting high pressure is guided via a connecting pipe to the spring side of the control valve. The pressure opens the overflow valve
and allows the fluid to flow to the intake side of the pump. The pressure difference at the control valve forces this to move against the
spring and therefore opens a passage for the recirculation of the whole pump flow. The discharged maximum pressure is maintained as long as the steering gear is closed.
The control valve functions to control pressure and flow as required by the steering. One side of the control valve is in direct communication with the delivery pressure (4) from the pump. The pump outlet (5) incorporates a diameter of restriction from which a connecting passage (1) leads to the other side of the valve, that is fitted with a spring (2). In the inactive position, the valve is pressed against the outlet side. A relief valve is incorporated into the control valve (3), that is effected, at high pressure, by the hydraulic pressure on the spring loaded side of the control valve. For the valve to operate, a certain amount of fluid must circulate continuously through the valve, although not when the steering is at full lock. The pump delivers a maximum pressure of approximately. 95 bars and a maximum flow of approximately. 7.5 liters per minute
Anyway, I'd like to calculate the power usage but unfortunately I do not have the detailed specs of the pump.
posted by 62.195.11...
, Sat, 18 Apr 2009 14:07:53
, Sat, 18 Apr 2009 08:20:03
, Mon, 20 Apr 2009 20:08:15, Wed, 22 Apr 2009 14:03:48
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