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| Illustration 1 | g01135392 |
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Hydraulic schematic for the wheel steering system (1) Steering cylinder (2) Steering cylinder (3) Implement and steering solenoid valve (4) Steering cylinder crossover relief valve (5) Steering cylinder crossover relief valve (6) Steering control valve (7) Parking brake solenoid valve (8) Portable hydraulic pump quick connect coupler (9) Brake accumulator charging valve (10) Line to the braking system (11) Secondary steering pump (12) Spool (13) Line to the parking brakes (14) Portable hydraulic pump quick connect coupler (15) Check valve (16) Steering system pressure tap (17) Selector and pressure control valve (18) Oil cooler (19) Secondary steering diverter valve (20) Primary steering flow switch (21) Check valve (22) Steering neutralizer valve (23) Steering lockout valve (24) check valve (25) Line from the implement lift circuit (26) Check valve (27) Pilot oil filter (28) Pilot system pressure tap (29) Pilot relief valve (30) Steering neutralizer valve (31) Steering metering pump (32) Breaker relief valve (33) Hydraulic filters (34) Hydraulic tank (35) Pilot and braking pump (36) Steering pump | |
Note: Illustration 1 shows a machine with the secondary steering system. Machines without the secondary steering system will not have secondary steering pump (11), secondary steering diverter valve (19) and primary steering flow switch (20).
The primary steering system is made up of two circuits. The two circuits are the pilot circuit and the high pressure circuit.
The pilot circuit controls the movement of spool (12) in steering control valve (6).
With the engine running, oil is drawn from hydraulic tank (34) by the pilot and braking pump (35). Pilot and braking pump (35) supplies oil through check valve (15) to brake accumulator charging valve (9). Pilot oil from brake accumulator charging valve (9) flows through pilot oil filter (27) to pilot relief valve (29).
Pilot relief valve (29) maintains the pilot system at a constant pressure. Pilot relief valve (29) relieves excess pilot system pressure through a line to the hydraulic tank.
The pilot oil, flows through check valve (26) to the selector and pressure control valve (17). While pilot and braking pump (35) is supplying oil to the pilot system, selector and pressure control valve (17) will block the flow of alternate oil into the pilot system.
If pilot and braking pump (35) fails, or pilot oil is not available, then selector and pressure control valve (17) will allow alternate pilot oil to flow into the pilot system from the lift cylinders. If oil is not available from the lift cylinders, then selector and pressure control valve (17) will allow alternate pilot oil to flow into the pilot system from steering control valve (6).
Pilot oil from the pilot system flows to implement and steering solenoid valve (3). Implement and steering solenoid valve (3) prevents pilot oil from flowing to steering lockout valve (23) and steering metering pump (31) when the implement and steering solenoid valve (3) is de-energized.
When the implement and steering solenoid valve (3) is energized, pilot oil from implement and steering solenoid valve (3) flows to steering lockout valve (23) and steering metering pump (31).
Steering metering pump (31) is a small hydraulic pump that is used as a metering valve and as a directional control valve. When the operator turns the steering wheel, a spool and a sleeve rotates inside the metering pump. The oil flows to steering lockout valve (23).
Steering lockout valve (23) stops oil flow from steering metering pump (31) to steering neutralizer valve (22) and steering neutralizer valve (30) when the implement and steering solenoid valve (3) is de-energized.
When the implement and steering solenoid valve (3) is energized, steering lockout valve (23) allows the oil to flow to steering neutralizer valve (22) or steering neutralizer valve (30). The oil from steering metering pump (31) can flow to either end of spool (12) in steering control valve (6), causing spool (12) to move. When spool (12) moves, high pressure oil from steering pump (36) can flow to steering cylinders (1) and (2).
The high pressure circuit provides the high pressure oil for steering cylinders (1) and (2).
With the engine running, oil is drawn from hydraulic tank (34) by steering pump (36). Steering pump (36) supplies oil to steering control valve (6). Oil supplied to steering control valve (6) flows to spool (12).
When the oil from steering metering pump (31) moves spool (12), the pressure oil is directed to steering cylinders (1) and (2).
When a right turn is made, the pressure oil flows to the head end of steering cylinder (1) and to the rod end of steering cylinder (2). This causes the machine to turn right.
When a left turn is made, the pressure oil flows to the head end of steering cylinder (2) and to the rod end of steering cylinder (1). This causes the machine to turn left.
Oil displaced from the steering cylinders when a turn is made returns through spool (12) and steering control valve (6) to hydraulic oil cooler (18). The return oil flows through hydraulic oil cooler (18) and hydraulic filters (33) to hydraulic tank (34).
Steering cylinder crossover relief valves (4) and (5) prevent excessive pressure in steering cylinders (1) and (2). The pressure could develop if one of the tires hits an object.