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| Illustration 1 | g00459311 |
Steering Control Valve | |
The steering control valve is located between the operator's cab and the engine. The steering control valve is also located on the left side of the machine.
NEUTRAL Position
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| Illustration 2 | g00309983 |
Schematic of the Steering Control Valve NEUTRAL Position (1) Steering control valve. (2) Directional spool. (3) Pilot load check valve for left turns. (4) Port for the steering cylinders during left turns. (5) Crossover relief valve for the steering cylinders. (6) Port for the steering cylinders during right turns. (7) Pilot load check valve for right turns. (8) Makeup check valve. (9) Makeup check valve. (10) Drain port for the metering pump. (11) Hydraulic oil tank port. (12) Backup relief valve for the steering system. (13) Inlet from the steering pump. (14) Damping orifice for the spool. (15) Selector spool. (16) Pilot port for left turns. (17) Pilot port for right turns. (18) Damping orifice for the spool. (19) Steering metering pump supply port. (20) Flow control orifice. | |
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| Illustration 3 | g00464024 |
Steering Control Valve (3) Pilot load check valve for left turns (4) Port for the steering cylinders during left turns (5) Crossover relief valve for the steering cylinders (6) Port for the steering cylinders during right turns (7) Pilot load check valve for right turns (9) Makeup check valve (10) Drain port for the metering pump (11) Hydraulic oil tank port (12) Backup relief valve for the steering system (13) Inlet from the steering pump (14) Damping orifice for the spool (15) Selector spool (16) Pilot port for left turns (17) Pilot port for right turns (18) Damping orifice for the spool (19) Steering metering pump supply port (20) Flow control orifice | |
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| Illustration 4 | g00464023 |
Steering Control Valve View C-C NEUTRAL Position (2) Directional spool (3) Pilot load check valve for left turns (4) Port for the steering cylinders during left turns (5) Crossover relief valve for the steering cylinders (6) Port for the steering cylinders during right turns (7) Pilot load check valve for right turns (14) Damping orifice for the spool (15) Selector spool (16) Pilot port for left turns (17) Pilot port for right turns (18) Damping orifice for the spool (21) Drain passage to the hydraulic oil tank (22) Passage for the inlet from the steering pump (23) Drain passage for the metering pump (24) Spring (25) Retainer (26) Passage to the steering cylinder for right turns (27) Passage to the steering cylinder for left turns | |
With the engine in operation, oil is drawn from the hydraulic oil tank to the steering pump. The 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 a secondary steering valve. If your machine includes the secondary steering attachment, the pressure oil from the steering pump flows to the secondary steering valve before the oil flows to 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 (13) .
From inlet (13), the pressure oil flows through flow control orifice (20). Flow control orifice (20) reduces the amount of oil flow that is directed to the metering pump. The pressure oil also flows to steering backup relief valve (12) and directional spool (2) .
Because the steering wheel is stationary, there is no flow of steering pilot oil from the metering pump. However, a small quantity of oil flows to the hydraulic oil tank through orifices that are located in the steering metering pump.
Any pilot oil that had been acting on an end of selector spool (15) 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 (2) is kept in the center of the steering control valve by spring (24). This causes directional spool (2) to block the flow of pressure oil from the steering pump. Because no pressure oil is allowed to flow through passages (27) or (26), the steering cylinders do not actuate.
Similarly, if the steering neutralizer valve for a left turn or the steering neutralizer valve for a right turn is actuated, the flow of steering pilot oil to either end of selector spool (15) stops.
Pump standby pressure is sensed by steering backup relief valve (12). Pump standby pressure is connected to the steering metering pump through flow control orifice (20) .
If the operator does not turn the steering wheel, the position of the steering cylinders will not change. This is because of oil that is blocked in passages (26) and (27) .
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.
A hydraulic oil line connects between the metering pump and the steering pump. The hydraulic oil line allows signal pressure oil to flow to the pressure and 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 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 (26) or (27). Crossover relief valve (5) senses oil pressure in passages (26) and (27) .
If the pressure exceeds the setting of crossover relief valve for the steering cylinders (5), the crossover relief valve opens. This causes the oil to flow to the passage with the lower pressure.
Makeup check valves (8) and (9) connect with passages (26) and (27). Makeup check valves (8) and (9) allow oil to be drawn through hydraulic oil tank port (11). This prevents voiding in the steering cylinder that causes crossover relief valve (5) to open. Makeup check valves (8) and (9) are normally seated by spring force.
RIGHT TURN Position
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| Illustration 5 | g00326805 |
Schematic of the Steering Control Valve RIGHT TURN Position (1) Steering control valve. (2) Directional spool. (3) Pilot load check valve for left turns. (4) Port for the steering cylinders during left turns. (5) Crossover relief valve for the steering cylinders. (6) Port for the steering cylinders during right turns. (7) Pilot load check valve for right turns. (8) Makeup check valve. (9) Makeup check valve. (10) Drain port for the metering pump. (11) Hydraulic oil tank port. (12) Backup relief valve for the steering system. (13) Inlet from the steering pump. (14) Damping orifice for the spool. (15) Selector spool. (16) Pilot port for left turns. (17) Pilot port for right turns. (18) Damping orifice for the spool. (19) Steering metering pump supply port. (20) Flow control orifice. | |
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| Illustration 6 | g00464022 |
Steering Control Valve View C-C RIGHT TURN Position (2) Directional spool (4) Port for the steering cylinders during left turns (5) Crossover relief valve for the steering cylinders (6) Port for the steering cylinders during right turns (7) Pilot load check valve for right turns (14) Damping orifice for the spool (15) Selector spool (16) Pilot port for left turns (17) Pilot port for right turns (18) Damping orifice for the spool (21) Cavity (22) Passage to the hydraulic oil tank (23) Passage for the inlet from the steering pump (24) Drain passage for the metering pump (25) Metering orifices (26) Chamber (27) Spring (28) Retainer (29) Passage to the steering cylinder for right turns (30) Passage to the steering cylinder for left turns | |
When you turn the steering wheel clockwise in order to make a right turn, pilot oil flows from the steering metering pump. The pilot oil then flows through the port for right turns (17) .
The pilot oil then flows through an orifice. This causes selector spool (15) to move left. As selector spool (15) moves left, the oil is allowed to flow through a passage. The oil then fills cavity (21) .
The oil pressure in cavity (21) causes directional spool (2) to move left. This causes spring (27) to compress. The movement of directional spool (2) causes metering orifices (25) to open into a passage. Load check valve (7) is located inside the passage. This causes pilot oil pressure to unseat load check valve (7). Pilot load check valve (7) is for right turns.
Oil that is displaced from chamber (26) by the movement of directional spool (2) flows back to the hydraulic oil tank.
As directional spool (2) moves left, pressure oil from the steering pump flows through inlet (13). The oil then fills the passage to the steering cylinder for right turns (29) .
The pressure oil then flows out of the port for steering cylinder for right turns (6). The pressure oil then flows to the rod end of the steering cylinder on the right side of the machine. The pressure oil also flows to the head end of the steering cylinder on the left side of the machine.
At the same time, return oil from the rod end of the steering cylinder on the left side of the machine flows through port (4). Return oil from the head end of the steering cylinder on the right side of the machine flows through port (4). This causes the machine to articulate to the right.
The oil then flows into the passage to the steering cylinder for left turns (30). From passage (30), the oil flows through a passage to port (11). Port (11) connects to the hydraulic oil tank.
Steering metering pump port (19) is connected to the control section of the steering pump. The control section consists of a pressure and flow compensator valve. The pressure and flow compensator valve regulates the output of the steering pump.
The movement of directional spool (2) and the turning speed of the machine depend on two factors. The turning speed of the steering wheel is the first factor. The speed of the engine is the second factor.
Flow control orifice (20) regulates the oil supply to the steering metering pump. Flow control orifice (20) therefore regulates the maximum turning speed of the steering wheel.
As the maximum speed is reached, pilot oil pressure between the steering metering pump and directional spool (2) decreases. The pump output decreases slightly as the signal pressure of the sensing line decreases. This causes greater effort to turn the steering wheel. This results in slower rotation of the steering wheel.
When the operator stops turning the steering wheel, the pilot oil flow to the steering control valve is cut off. The flow of oil stops because the spool in the steering metering pump is spring centered. Also, if the steering neutralizer valve for a left turn or the steering neutralizer valve for a right turn is actuated, the flow of steering pilot oil to either end of selector spool (15) stops.
Steering cylinder pressure closes pilot load check valve (7). This causes spring (27) to move directional spool (2) to the NEUTRAL position. Pilot oil in cavity (21) is displaced through metering orifices (25) .
When a wheel hits 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 (29) or (30). Oil pressure in passages (29) and (30) is sensed by crossover relief valve (5) .
If the pressure exceeds the setting of crossover relief valve (5) for the steering cylinders, the crossover relief valve opens. This causes the oil to flow to the passage with the lower pressure.
Makeup check valves (8) and (9) connect with passages (29) and (30). Makeup check valves (8) and (9) allow oil to be drawn from the hydraulic oil tank. This prevents voiding in the steering cylinder which causes crossover relief valve (5) to open. Makeup check valves (8) and (9) are normally seated by spring force.
LEFT TURN Position
When the machine is turned to the left, the steering control valve operates in a similar manner.
For a left turn, pilot oil enters pilot port (16). Pressure oil from pump inlet port (13) flows through passage (23). The oil then flows past directional spool (2). From directional spool (2), the oil flows out of steering cylinder port (4) .
The pressure oil then flows to the rod end of the steering cylinder on the left side of the machine. The oil also flows to the head end of the steering cylinder on the right side of the machine.
At the same time, the return oil flows from the head end of the steering cylinder on the left side of the machine. The oil also flows from the rod end of the steering cylinder on the right side of the machine. This causes the machine to articulate to the left.
Crossover Relief Valve for the Steering Cylinders
Note: In the following illustration, the operator's cab is removed for clarity.
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| Illustration 7 | g00459320 |
Crossover Relief Valve for the Steering Cylinders | |
The crossover relief valve for the steering cylinders is located on the back left side of the steering control valve as you face the back left side of the machine.
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| Illustration 8 | g00313326 |
Schematic for the Steering Control Valve Crossover Relief Valve for the Steering Cylinders | |
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| Illustration 9 | g00279630 |
Crossover Relief Valve for the Steering Cylinders (1) Screw. (2) Jam nut. (3) Spring. (4) Spring chamber. (5) Sleeve. (6) Holes. (7) Valve face. (8) Passage. (9) Poppet for the relief valve. (10) Drain hole. (11) Face of sleeve. (12) Passage. (13) Valve face. (14) Valve seat. | |
The crossover relief valve for the steering cylinders relieves shock loading in the steering system. The crossover relief valve operates when the steering system is in neutral or when the steering system is articulating the machine.
Steering cylinder pressure is sensed in passages (8) and (12) of the steering control valve. Steering cylinder pressure is also sensed on valve faces (7) and (13) .
When the steering cylinders are moved by external steering forces, the pressure in passages (8) and (12) can increase suddenly.
A pressure increase in passage (8) acts on valve face (7). If the pressure is greater than the valve setting, poppet (9) moves left. This causes spring (3) to compress. The pressure is relieved to passage (12) through holes (6) .
If the pressure in passage (12) is greater than the pressure setting of the crossover relief valve, the pressure acts on valve face (13). The pressure also acts on the face of sleeve (11) .
Sleeve (5) and poppet (9) move to the left against spring (3). The pressure in passage (12) is relieved to passage (8) through holes (6) .
Spring chamber (4) is connected to the hydraulic oil tank through drain hole (10) .
The pressure setting of the crossover relief valve for the steering cylinders is adjustable.
Reference: For additional information on the adjustment procedure for the crossover relief valve, refer to the Service Manual module for Testing And Adjusting, RENR2109, "966G Wheel Loader and 972G Wheel Loader Steering System", " Relief Valve (Steering Cylinder Crossover) - Test and Adjust".
Backup Relief Valve for the Steering System
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| Illustration 10 | g00459321 |
Backup Relief Valve for the Steering System | |
The backup relief valve for the steering system is located on the right side of the steering control valve.
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| Illustration 11 | g00313329 |
Schematic for the Steering Control Valve Backup Relief Valve for the Steering System | |
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| Illustration 12 | g00279628 |
Backup Relief Valve for the Steering System (1) Screw. (2) Jam nut. (3) Spring chamber. (4) Spring. (5) Outlet hole to the hydraulic oil tank. (6) Outlet hole. (7) Inlet hole from the steering pump. (8) Valve seat. (9) Poppet for the relief valve. (10) Drain hole. (11) Drain hole. (12) Annular face. | |
Pressure may suddenly increase due to steering resistance. The load control of the steering pump may not regulate the pump output at a fast enough rate. If this occurs, the backup relief valve for the steering system connects the inlet passage of the steering control valve to the hydraulic oil tank.
Spring (4) holds steering relief valve poppet (9) against valve seat (8) .
Steering pump pressure is sensed in the backup relief valve through holes (7). This pressure acts on annular face (12) .
If the pressure that is acting on annular face (12) exceeds the pressure setting on the backup relief valve, poppet (9) moves to the left against spring (4) .
Pressure is then relieved to the hydraulic oil tank through outlet holes (5) and (6) .
Drain holes (10) and (11) connect spring chamber (3) to the hydraulic oil tank.
The pressure setting of the backup relief valve for the steering system is adjustable.
Reference: For additional information on the adjustment procedure for the backup relief valve, refer to the Service Manual module for Testing And Adjusting, RENR2109, "966G Wheel Loader and 972G Wheel Loader Steering System", "Relief Valve (Pump Backup) - Test and Adjust".