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| Illustration 1 | g03862894 |
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Steering hydraulic system (1) Steering cylinders (2) Supplemental crossover relief valve (3) Steering valve (4) Steering neutralizer valve (5) Pilot valve (6) Hydraulic screen (7) Piston pump (8) Secondary steering pump (9) Filter (10) Oil cooler core (11) Gear pump (12) Hydraulic tank and filters | |
The steering system provides the high-pressure oil that is needed to turn the machine. The steering pumps also supply oil to the steering pilot system.
The steering system uses two variable displacement piston pumps (7). The steering pumps are load sensing pumps. The pumps are located near the top of the rear pump drive. There is a pressure and flow compensator valve attached to each steering pump. The pressure and flow compensator valves control the amount and pressure of hydraulic oil that is delivered to the steering system from the steering pumps. Pressure and flow compensator valves keep the oil pressure and flow from the steering pumps at a level that is needed in order to fulfill the requirements of the steering system.
Steering pumps (7) draw hydraulic oil from hydraulic tank (12). The case drain oil from the steering pumps flows through case drain filters. The case drain filters remove debris from the oil. The filters prevent contamination of the oil that is in the hydraulic tank. Filter bypass switch actuates when the flow of oil through the filter is restricted. Filter bypass switch is monitored by the Vital Information Management System (VIMS). Then, the case drain oil flows to the hydraulic tank for the steering and brake systems.
The pressure oil from steering pumps (7) flows through oil screen (6). The oil screens filter debris from the pressure oil. The screens prevent contamination of the oil that is in the steering system.
The pressure oil then flows from oil screen (6) to steering control valve (3). A check valve prevents pressure oil from flowing back to steering pumps (7).
The steering control valve contains the following components: the main relief valve , cylinder crossover relief valve and shuttle valve .
If an outside force tries to turn the machine, and the steering control valve spool is in the NO STEER position, an increase in hydraulic oil pressure will occur at the steering cylinders. The increase in hydraulic oil pressure will open steering crossover relief valve . The steering crossover relief valve limits the amount of hydraulic oil pressure at steering cylinders. The crossover relief valve ensures that the hydraulic oil pressure at the steering cylinders does not exceed the specifications.
The shuttle valve permits the highest system pressure to control the output of steering pumps (7). When the steering pump pressure rapidly increases, main relief valve will open. This limits the hydraulic oil pressure to the steering system. The steering system is in the NO STEER position, the signal pressure from the shuttle valve to steering pumps (7) is low. Therefore, the steering pump output is minimal.
Pilot oil from the steering pilot system moves the valve spool in steering control valve (3) to either the LEFT TURN position or the RIGHT TURN position. The valve spool directs the pressure oil to flow to steering cylinders (1). The pressure oil in the steering cylinders causes the machine to turn.
Return oil from the steering cylinders flows through the steering control valve. The pressure switch is monitored by the VIMS.
Secondary steering oil flow is not used during the normal operation of the machine. Reduced steering pressure oil acts on unloader spool in the secondary steering diverter valve. The unloader spool directs the secondary steering oil flow back to hydraulic tank (12) for the steering and brake systems. If the flow of reduced steering pressure to the unloader spool stops, the unloader spool will shift. Reduced steering pressure causes the secondary steering oil flow to be directed to the primary steering system and the steering pilot system.
Note: If the engine is stopped, steering can only be performed when the machine is moving.
Cooling Circuit for the Steering and Brake Systems
Gear pump (11) draws hydraulic oil from hydraulic tank (12).
The hydraulic oil then flows to oil cooler (9) for the steering and brake systems. The check valve for the cooler bypass allows the hydraulic oil to bypass the oil cooler. This occurs when the hydraulic oil is cold. The hydraulic oil then flows to hydraulic tank (12) for the steering and brake systems.
The oil then passes through filter (9) for the steering and brake systems. The filter removes any debris that is in the hydraulic oil. This prevents contamination of the hydraulic tank for the steering and brake systems. A bypass valve in the filter allows the hydraulic oil to bypass the oil filter. This occurs when the flow of oil through the filter is restricted and an adequate oil flow cannot be maintained. This also occurs in cold start-up conditions when the hydraulic oil is cold. The pressure switch actuates when the flow of the oil through the filter is restricted. The pressure switch is monitored by the VIMS.
The Fluid sampling valve is available for scheduled oil sampling analysis (S·O·S analysis). The fluid sampling valve is mounted to the gear pump for the cooling circuit.
Note: For additional information on the VIMS, refer to Service Manual, RENR6318, "Vital Information Management System (VIMS)".