Prelude L4-2056cc DOHC (1990)
Power Steering Pump Speed Sensor: Description and Operation
Speed Sensor
The speed sensor is a trochoid-rotor, hydraulic pump combined with a relief valve and a one-way valve. It is driven by the speedometer gear shaft
which in turn is driven by a helical gear on the differential.
It turns only when the car is moving, controlling the cut-off valve by regulating fluid pressure in the control unit according to the speed of the car.
With the engine running in a parked car, fluid flow through the sensor rotors is blocked because the rotors are not turning.
As the car is driven away, the rotors start turning and pump fluid back to the reservoir, reducing pressure at the cut-off valve. The cut-off valve begins
cycling, staying open for longer and longer intervals as the car accelerates and the sensor reduces the pressure further. This allows pressure in the
reaction chambers to rise, restricting control valve movement more and more, and gradually reducing the assist as speed increases.
One-way Valve (In Speed Sensor)