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| Illustration 1 | g03718387 |
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Typical view of steering system (1) Steering wheel (2) Hydraulic tank (3) Right steering cylinder (4) Left steering cylinder (5) Steering pump (6) Secondary steering pump (7) Steering control valve (8) Hand metering unit (HMU) | |
The primary steering system is made up of two basic circuits. The two basic circuits are the pilot circuit and the high-pressure circuit. When a machine is equipped with the secondary steering attachment, the steering system includes one additional circuit.
Hand metering unit (HMU) (8) is attached to the bottom of the steering column, and located under the floor of the cab.
Steering control valve (7) is located on the left-hand frame rail of the tractor. Hydraulic oil tank (2) is located on the right side of the machine.
Steering pump (6) is mounted to the front of the transfer gear case on the rear of the tractor. A pressure and flow compensator valve is attached to steering pump (6).
The pilot circuit consists of the following components. hand metering unit (HMU) (8), steering pump (6) and hydraulic tank (2).
The pilot system controls the movement of the selector spool and the directional spool in steering control valve (6).
Steering pump (6) draws oil from hydraulic oil tank (2). Pressure oil from steering pump (6) flows to steering control valve (7). The oil then flows through the flow control orifice. The flow control orifice reduces the amount of oil flow to hand metering unit (HMU) (8).
Hand metering unit (HMU) (8) is a small hydraulic pump that is used as a metering valve and as a directional control valve. When the operator turns steering wheel (1), a spool and a sleeve rotate inside the metering pump.
The high-pressure circuit consists of the following components. Steering control valve (6), crossover relief valve for the steering cylinders, left steering cylinder (4), right steering cylinder (3), steering pump (6), backup relief valve and hydraulic tank (2).
The high-pressure circuit provides the high-pressure oil for the steering cylinders. Oil is drawn from hydraulic tank (2) by steering pump (6). Steering pump (6) is a variable piston pump. A pressure and flow compensator valve is attached to steering pump (6). The pressure and flow compensator valve helps control the output of the pump.
A backup relief valve in steering control valve (5) prevents excessive pressure in the high-pressure circuit if there is a malfunction with the pressure and flow compensator valve.
When the pilot oil moves the directional spool, the pressure oil is directed to the steering cylinders. When a right turn is made, the pressure oil flows to the head end of right steering cylinder (3). The pressure oil also flows to the rod end of left steering cylinder (4). This causes the machine to turn right. When a left turn is made, the pressure oil flows to the head end of left steering cylinder (4). The high-pressure oil also flows to the rod end of right steering cylinder (3). This causes the machine to turn left.
The crossover relief valve prevents excessive pressure spikes in the steering cylinders. The pressure spikes could develop if one of the front tires hits an object.
The secondary steering system is powered by a ground driven gear pump. The gear pump is turned by the ring gear of the differential when the wheels are turning. In the event of a drop in oil pressure in the steering system, the gear pump will supply oil to a diverter valve that will allow oil pressure to flow to the steering system.
The amount of oil from secondary steering pump is relative to the RPM of the wheels. When the RPM of the wheels decreases, the output of oil from secondary steering pump decreases. This causes the steering cylinders to move slowly. If the speed of the wheels decrease, the machine turns slowly.
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| Illustration 2 | g03717641 |
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(1) Steering control valve
(2) Selector spool (3) Directional spool (4) Crossover relief valve (5) Left steering cylinder (6) Right steering cylinder (7) Backup relief valve (8) Hand metering unit (HMU) (9) Secondary steering pump (10) Unloading valve (11) Pressure sensor (12) Steering pump | |