797F Off-Highway Truck: Piston Pump (Steering)

Location of the steering pump (1) Fan drive pump (2) Current adjustment screw (3) Steering pump (4) Pump drive (5) Displacement solenoid (6) High pressure cutoff valve (7) Pressure and flow compensator valve(8) Minimum angle stop screw

Steering pump (3) is part of a double piston pump group. Fan drive pump (1) is the other part of the pump group. Both pumps are variable displacement piston pumps. A charging pump is located between the steering pump and the fan drive pump. The charging pump is used to keep both pumps supplied with oil. The steering pump is located at the front bottom section of pump drive (4). The pump drive is located on the right hand frame rail near the rear of the flywheel housing.

The steering pump operates only when the engine is running. The pump provides the necessary flow of oil to the steering accumulators. The Chassis ECM controls the flow of oil from the steering pump by energizing displacement solenoid (5) .

The Chassis ECM will analyze the sensor inputs for the accumulator pressure and the engine speed. The Chassis ECM will send 0 milliampere to 650 milliamperes to the solenoid. Between 0 milliampere and 100 milliamperes, the steering pump is at the maximum displacement and at the maximum flow. Between 600 milliamperes and 650 milliamperes, the steering pump is at the minimum displacement and at the minimum flow.

Displacement solenoid (5) moves a spool in pressure and flow compensator valve (7) in order to control the flow of pump output pressure to the actuator piston (minimum angle). The actuator piston (minimum angle) will move the swashplate to the position of minimum flow. Current adjustment screw (2) controls the minimum current that is required to start destroking the pump.

If the accumulator pressure sensor does not function properly, high pressure cutoff valve (6) will control the maximum pressure within the steering system. The high pressure cutoff valve controls the system pressure by controlling the flow of pump output pressure to the actuator piston (minimum angle). When the system pressure is at the maximum, high pressure cutoff valve (6) will send oil to the actuator piston (minimum angle). The actuator piston (minimum angle) will move the swashplate to the position of minimum flow.

Minimum angle stop screw (8) is located near pressure and flow compensator valve (7). The maximum angle stop screw is located on the other side of the pump.

Sectional view of the steering pump (7) Pressure and flow compensator valve (8) Minimum angle stop screw (9) Swashplate (10) Piston (11) Maximum angle actuator piston (12) Maximum angle stop screw (13) Rotary group (14) Impeller (charge pump) (15) Minimum angle actuator piston (16) Drive shaft (A) Fan drive section of the pump(B) Steering pump section

Note: The left side is the fan drive pump. The right side is the steering pump.

Oil from the hydraulic tank enters the pump in the port below impeller (14) for the charge pump. Impeller (14) is driven by drive shaft (16) which is attached to pump drive (4). The charge pump keeps the steering pump and the fan drive pump full of oil.

The large spring that is located around actuator piston (11) holds swashplate (9) at the maximum angle. Pump output pressure is always present on the left side of actuator piston (11). Pump output pressure also helps to hold swashplate (9) at the maximum angle. When swashplate (9) is at the maximum angle, the pump output is at the maximum flow. This is the position of the pump when displacement solenoid (5) receives 0 milliampere to 100 milliamperes from the Chassis ECM. When displacement solenoid (5) is receiving 100 milliamperes to 650 milliamperes from the Chassis ECM, displacement solenoid (5) will move a spool in pressure and flow compensator valve (7). The spool allows pump output pressure to flow to actuator piston (15) .

Actuator piston (15) has a larger diameter than actuator piston (11). Actuator piston (15) moves swashplate (9) toward the position of minimum flow. The swashplate angle and pump flow will modulate with the amount of current at displacement solenoid (5). When swashplate (9) is at the minimum angle, the pump output is at the minimum flow. This is the position of the pump when the displacement solenoid receives 600 milliamperes to 650 milliamperes from the Chassis ECM.

Before swashplate (9) contacts minimum angle stop screw (8), actuator piston (15) will open a small drain port to the tank. This will stop the movement of swashplate (9). Draining the oil from the actuator piston will prevent swashplate (9) from contacting minimum angle stop screw (8) repeatedly. Repeated contact between the swashplate and the stop screw can be noisy and the contact may cause damage to the pump.

(17) Case drain oil filters

Oil that leaks past the pistons into the pump housing provides lubrication for the rotating components. This oil leakage is referred to as case drain oil. Case drain oil flows through the case drain port and oil filter (17) to the hydraulic tank.

(2) Current adjustment screw (5) Displacement solenoid (6) High pressure cutoff valve (11) Maximum angle actuator piston (14) Impeller (charge pump) (15) Minimum angle actuator piston (A) Pump supply (B) To minimum angle actuator piston (C) Drain (D) Steering pump control (E) To steering solenoid and backup relief valve (F) To fan drive motor (G) From reducing valve (H) Fan drive pump control(J) Case drain

Impeller (14) for the charge pump pulls oil from the steering tank which keeps steering pump (3) and the fan drive pump full of oil. Oil flows from the steering pump to high pressure cutoff valve (6), displacement valve (5) and actuator piston (11) .

The pump output oil and the spring around actuator piston (11) holds swashplate (9) at the maximum angle. This is the position of the pump when displacement solenoid (5) receives 0 milliampere to 100 milliamperes from the Chassis ECM and the pump output pressure is low.

When displacement solenoid (5) is receiving between 100 milliamperes and 650 milliamperes from the Chassis ECM, displacement solenoid (5) will move the valve spool to the right. The spool allows pump output pressure to flow to actuator piston (15). Actuator piston (15) has a larger diameter than actuator piston (11). Actuator piston (15) moves swashplate (9) toward the position of minimum flow.

Current adjustment screw (2) controls the spring pressure in displacement valve (5). Current adjustment screw (2) changes the minimum current that is required to start destroking the pump.

High pressure cutoff valve (6) controls the maximum pressure in the steering system if the accumulator pressure sensor should not function properly. High pressure cutoff valve (6) controls the flow of pump output pressure to actuator piston (15). When system pressure is at the maximum, high pressure cutoff valve (6) sends oil to actuator piston (15). Actuator piston (15) moves swashplate (9) to the position of minimum flow.

MARYGAR

797F Off-Highway Truck: Piston Pump (Steering) 2012-12-04T17:15:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown