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| Illustration 1 | g03718271 |
| (1) Location of steering control valve | |
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| Illustration 2 | g03718003 |
The steering control valve is mounted to the transmission transfer gears near the articulation hitch.
For more information on the steering control, refer to System Operations, "Steering Control (Control System)".
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| Illustration 3 | g03718007 |
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Steering Control Valve (2) Pilot port for left turns (3) Selector spool (4) Damping orifice for the spool (5) Damping orifice for the spool (6) Pilot port for right turns (7) Back up relief valve for the steering system (8) Drain port for the metering pump (9) Crossover relief valve for the steering cylinders (10) Pilot load check valve for left turns (11) Port for the steering cylinder for left turns (12) Inlet from the steering pump (13) Hydraulic oil tank port (14) Port for the steering cylinder for right turns (15) Pilot load check valve for right turns (16) Pilot orifice (17) Makeup check valve (18) Hand metering unit supply port | |
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| Illustration 4 | g03718008 |
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Steering Control Valve View C-C NEUTRAL Position (2) Pilot port for left turns (3) Selector spool (4) Damping orifice for the spool (5) Damping orifice for the spool (6) Pilot port for right turns (9) Crossover relief valve for the steering cylinders (10) Pilot load check valve for left turns (11) Port for the steering cylinder for left turns (14) Port for the steering cylinder for right turns (15) Pilot load check valve for right turns (19) Passage to the steering cylinder for left turns (20) Passage to the steering cylinder for right turns (21) Retainer (22) Spring (23) Directional spool (24) Drain passage for the metering unit (25) Passage for the inlet from the steering pump (26) Drain passage to the hydraulic oil tank | |
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| Illustration 5 | g03718009 |
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Schematic of the Steering Control Valve NEUTRAL Position (1) Steering control valve (2) Pilot port for left turns (3) Selector spool (4) Damping orifice for the spool (5) Damping orifice for the spool (6) Pilot port for right turns (7) Back up relief valve for the steering system (9) Crossover relief valve for the steering cylinders (10) Pilot load check valve for left turns (11) Port for the steering cylinder for left turns (12) Inlet from the steering pump (13) Hydraulic oil tank port (14) Port for the steering cylinder for right turns (15) Pilot load check valve for right turns (16) Pilot orifice (17) Makeup check valve (18) Hand metering unit supply port (23) Directional spool (28) Makeup check valve (29) Drain port for the metering unit | |
With the engine in operation, oil is drawn from the hydraulic oil tank to the steering pump. The high-pressure oil then flows to steering control valve (1).
Note: Machines that are equipped with the secondary steering attachment have several additional components. The components include the secondary steering pump and electric motor, and a secondary steering valve. If the machine includes secondary steering attachment, the pressure oil from the steering pump flows to the secondary steering valve before the steering control valve.
When the steering wheel is stationary, the steering control valve is in the NEUTRAL position. The pressure oil from the steering pump enters steering control valve (1) through inlet (12).
From the inlet, the pressure flows to back up relief valve (7) and to directional spool (23). High-pressure oil flows through pilot orifice (16) to create pilot oil pressure which exits the steering valve at port (18). The pilot oil is sent to the hand metering unit.
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| Illustration 6 | g03718010 |
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(A) Pilot oil from steering control valve
(B) Signal pressure to the steering pump (C) To steering control valve via the neutralizer valves (27) Hand metering unit | |
Because the steering wheel is stationary, there is no flow of steering pilot oil through the metering unit. However, oil flows through orifices and provides a signal circuit for the steering pump and the rest of the oil is returned to the hydraulic oil tank.
Signal pressure oil is connected to the flow compensator valve that is attached to the steering pump. If the pressure of the signal oil is low, the steering pump will destroke. If the pressure of the signal oil is high, the steering pump will upstroke.
When the steering wheel is held stationary, there is no demand for pressure oil. The low signal pressure causes the steering pump to destroke. A small amount of oil flow will still compensate for system leakage.
Any pilot oil that had been acting on an end of selector spool (3) is forced across an orifice. The oil then flows back to the hydraulic oil tank.
Because there is no flow of pilot oil, directional spool (23) is kept in the center of the steering control valve by spring (22). This process causes the directional spool to block the flow of pressure oil from the steering pump. Because no pressure oil is allowed to flow through passages (19) or (20), the steering cylinders do not actuate. If the operator does not turn the steering wheel, the position of the steering cylinders will not change.
If the left or right steering neutralizer valve is actuated, the flow of steering pilot oil to either end of selector spool (3) stops.
When the wheels contact a stationary object, the steering cylinders may experience a sudden shock load. Any pressure that is generated in the steering cylinders from the shock load is sensed in passages (19) or (20). Crossover relief valve (9) senses oil pressure in both steering cylinder passages.
If the pressure exceeds the setting of crossover relief valve for the steering cylinders (9), the crossover relief valve opens. This process causes the oil to flow to the passage with the lower pressure.
Makeup check valves (17) and (28) connect with passages (19) and (20). The makeup check valves allow oil to be drawn through hydraulic oil tank port (13) to prevent voiding in the steering cylinders when crossover relief valve (9) opens. Makeup check valves (17) and (28) are normally seated by spring force.
Electrohydraulic Steering Valve
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| Illustration 7 | g03718378 |
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(1) Primary steering pilot supply solenoid
(2) Primary steering solenoids (3) Redundant steering solenoids (4) Steering work port relief and make-up valves (5) Pump back-up relief valve (6) Spool position sensor | |
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| Illustration 8 | g03718382 |
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(4) Steering workport relief and make-up valves
(5) Pump back-up relief valve (6) Spool position sensor (7) Passages to steering cylinder ports (8) Pilot chamber "A" (9) Passage for the inlet from the steering pump (10) Directional spool (11) Backpressure valve (12) Drain passage to the hydraulic oil tank (13) Pilot chamber "B" | |
When the key start switch is moved to the ON position, the Implement ECM, will detect the system voltage at the key ON input. The ECM will energize the Primary Steering Pilot Supply ON/OFF solenoid (1). This solenoid is located on the Steering Control Valve. When the engine is started and solenoid is energized, pilot hydraulic oil is supplied to left and right steer solenoid valves on the control valve. The ECM will continue to energize the solenoid until the key start switched is turned OFF. The ECM will also continue to energize the solenoid until the secondary steer system is activated and primary steering valves are deactivated.
Oil is drawn from the hydraulic oil tank by the steering pump. The steering pump provides flow to the steering control valve through the inlet passage (9). This flow is controlled by the pressure and flow compensator valve attached to the steering pump. Pump supply oil is also sent to the fan brake valve for implement and steering redundant pilot pressure. This oil provides a secondary source of pilot oil in the event of fan brake pump failure.
The primary steering solenoids (2) regulate the pilot oil sent through pilot chambers "A" (8) and "B" (13) to the directional control spool (10). Pilot oil sent to the steering valve is regulated by the amount of current sent to the primary steering solenoids (2) from the implement ECM. The directional control spool (10) directs supply oil to the steering cylinders. The implement ECM receives input from the spool position sensor (6) of the steering valve to indicate the position of the steering valve spool. The implement ECM will monitor the position of the steering cylinders as well as the directional spool position sensor (6). The implement ECM will decrease the current to the primary steering solenoids as the steering cylinders approach the desired position.
When pilot oil shifts the directional spool (10), high-pressure oil is directed to the steering cylinders through passages to the steering cylinder ports (7). When turning right, oil flows to the rod end of the right steering cylinder and to the head end of the left steering cylinder. This action causes the machine to turn right. When turning left, the oil flows to the rod end of the left steering cylinder and to the head end of the right steering cylinder. This action causes the machine to turn left. Steering workport relief and make-up valves (4) prevent excessive pressure spikes and voiding in the steering cylinders.
The steering control valve contains a pump back-up relief valve (5) and a back pressure valve (11). The pump back-up relief valve (5) limits the maximum pressure in the steering control valve. The pump back-up relief valve limits this pressure in case the pressure cutoff spool in the pump controller would fail. The back pressure valve (11) restricts the return oil flow to the hydraulic tank through passage (12). Back pressure valve (11) maintains enough pressurized oil in an internal passage to prevent cylinder voiding when articulating the machine on a slope.
The steering work port relief valves (4) protect the steering cylinders from sudden pressure spikes. Steering work port relief valves (4) will dump oil in the drain passage when pressure raises above the relief setting. The make-up valve that is part of the work port relief valve eliminates cylinder voiding.
The redundant solenoid valves (3) provide a backup to the primary steering solenoid valves. The redundant solenoid valves are identical to the primary steering solenoid valves (2).
Note: The redundant solenoid valves are a backup for the primary steering solenoid valves. When the redundant solenoid valves are activated, a problem has been detected in the primary steering system. The redundant solenoid valves should only be used to move the machine to a safe location for machine shutdown. The problem in the primary steering system must be repaired. Do not use the redundant solenoid valves for normal machine operation. For more information refer to System Operations, "Secondary Steering System".