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| Illustration 1 | g06111140 |
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(1) Steering pump
(2) Hydraulic tank (3) STIC steering pilot valve (4) Steering Neutralizers (5) Quad check valve (6) Steering Valve (7) Steering cylinders | |
Steering System Operation - No Turn
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| Illustration 2 | g06265711 |
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Steering hydraulic system - no turn (1) Steering pump (2) Tank (3) STIC Steering Pilot Valve (4) Neutralizer Valve (5) Quad Check Valve (7) Steering Cylinder (8) Pressure Compensator Valve (9) Pilot Pressure (from brake charge) (10) Shuttle Valve (11) Cross-Over Relief Valve (12) Directional Spool (13) Back-Up Relief Valve (14) Pressure Reducing Valve | |
Tank (2) supplies oil to steering pump (1) which is a variable displacement, piston-type pump. Steering pump (1) provides oil flow to the steering control valve and the steering cylinders to turn the machine.
Pilot oil (9) from the brake combination valve flows through shuttle valve (10) to the STIC steering pilot valve (3). When the STIC lever is moved left or right, the respective valve spool moves in the pilot control valve. The pilot oil flows past the pilot control valve spools through neutralizer valves (4) and quad check valve (5) to the steering control valve.
The neutralizer valves block pilot oil flow to the steering control valve when the machine makes a maximum turn (either left or right).
Quad check valve (5) dampens the movement of steering control valve directional spool (12) by restricting the pilot oil returning from the steering control valve directional spool to the pilot control valves (located inside the STIC steering pilot valve). This action is completed by restricting the pilot oil returning from the steering control valve directional spool to the pilot control valves (located inside the STIC steering pilot valve)
The steering control valve directional spool directs steering pump oil flow to the steering cylinders (7) and sends signal oil through the shuttle valve (10) to the pump control valve on the steering pump.
Back-up relief valve (13) serves as a back-up to the pump high-pressure cutoff spool and limits the maximum steering system pressure. Crossover relief valve (11) limits oil pressure in the steering cylinders due to an external force on the machine. The pressure reducing valve decreases the steering system pressure to less than pilot pressure. Oil from pressure reducing valve (14) is used as pilot oil if there is a loss of pilot oil pressure from the brake combination valve.
When the engine is running and the steering system is in the "NO TURN" position, pilot pump oil is blocked at the STIC pilot control valve. Oil from the main steering pump flows to the steering control valve. The control valve spool blocks oil flow to the steering cylinders and no signal pressure is generated.
With no signal pressure, the pump is in "LOW PRESSURE STANDBY" as previously described. The pump produces enough flow to compensate for system leakage. The pump also provides sufficient pressure to provide for immediate response when the steering control valve is moved.
Steering System Operation - Left Turn
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| Illustration 3 | g06265714 |
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Steering hydraulic system - no turn (1) Steering pump (2) Tank (3) STIC Steering Pilot Valve (4) Neutralizer Valve (5) Quad Check Valve (7) Steering Cylinder (8) Pressure Compensator Valve (9) Pilot Pressure (from brake charge) (10) Shuttle Valve (11) Cross-Over Relief Valve (12) Directional Spool (13) Back-Up Relief Valve (14) Pressure Reducing Valve | |
Steering pump (1) supplies oil to the steering control valve. STIC pilot valve (3) is moved for a "LEFT TURN". Pilot oil passes through left neutralizer valve (4) and the quad check valve (5) to shift the directional spool (12). When the spool shifts, oil is directed to steering cylinders (7) to make a "LEFT TURN" and to shuttle valve (10) to send signal oil to the pump.
Steering System Operation - Right Turn
When the operator moves the STIC lever to the right, pilot oil flows through the pilot control valve inside STIC steering pilot valve (3) and right neutralizer valve (5) to steering control valve directional spool (12). Pilot oil pressure moves the steering control valve directional spool. The steering control valve directional spool directs oil from the steering pump (1) to the steering cylinders (7). Oil flows to the rod end of the right steering cylinder and to the head end of the left steering cylinder. The machine articulates to the"RIGHT".
As, pressure increases in the steering cylinders oil will pass through the shuttle valve (10) to become signal oil for the steering pump control valve. This increase in signal pressure causes the pump to upstroke, which increases pump oil flow as previously described.