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| Illustration 1 | g06192969 |
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View of steering pump (1) Steering pump (2) Swash plate (3) Steering solenoid (4) Pump piston | |
Steering pump (1) is driven by the pump drive that is on the right-hand frame rail near the rear of the flywheel housing. The pump drive is driven by a drive shaft. The drive shaft is connected between the pump drive and the engine. Steering pump (1) operates only when the engine is running.
The steering pump is electronically controlled by the Chassis ECM. As the pump rotates, hydraulic oil is drawn down from the steering hydraulic tank and enters through the steering pump inlet. The steering pump increases the flow of hydraulic oil. As the oil passes through the pump. oil pressure is increased as oil exits the pump outlet and goes into the steering system. The steering pump operates at maximum pressure upon startup until system demand is met. The Chassis ECM monitors the signals from the pump pressure sensor on the steering solenoid and relief valve and both accumulator pressure sensors. Once the Chassis ECM reads that both accumulators and system pressure demand have been met, a signal is sent to the steering solenoid (3) to activate.
Steering solenoid (3) responds and de-strokes the piston pump by moving the angle of swash plate (2). As the swash plate moves and decreases angle, the pump pistons (4) stroke shortens and decreases pump flow to the system until the pump is on standby.
Steering system pressure is maintained until needed by a check valve in the steering system.
When system pressure is needed, the Chassis ECM reads a drop in both accumulator and system pressure from the pressure sensors. The ECM sends a signal to the steering pump solenoid to upstroke the pump. The steering solenoid responds by shifting the angle of the steering pumps swash plate increasing the angle of attack of the pump pistons. This action increases the flow of the steering pump to fulfill the pressure demand of the system until demand is again met. The margin spool on the steering pump is adjusted all the way in to block pressure oil and to serve as only a pressure compensator to de-stroke the pump if there is a pressure spike in the steering system during operation.