Hydraulic Schematic
 | |
| Illustration 1 | g03010342 |
(1) Steering cylinders (2) Steering check and relief valve (3) Secondary relief valve for the secondary steering (4) Primary relief valve for the primary steering (5) Primary relief valve for the secondary steering (6) Check valve (7) Steering pump pressure switch (8) Pressure reduction valve (9) Shuttle Valve (10) Load sensing valve (11) Secondary steering section (12) Parking brake release section (13) Electric drive pump for the secondary steering and brake release (14) Breaker relief valve (15) Steering system filter (16) Steering hydraulic tank (17) Steering pump case drain filter (18) Steering piston pump (19) Pressure and flow compensator valve (20) Steering metering pump (21) Steering disable valve (22) Check valve | |
Location of Components
 | |
| Illustration 2 | g01251851 |
Top view of the steering oil lines (1) Steering cylinders (15) Steering system filter (16) Steering hydraulic tank (17) Steering pump case drain filter (18) Steering piston pump (19) Pressure and flow compensator valve (20) Steering metering pump | |
 | |
| Illustration 3 | g01251858 |
Side view of the steering oil lines (14) Breaker relief valve (15) Steering system filter (16) Steering hydraulic tank (18) Steering piston pump (20) Steering metering pump | |
 | |
| Illustration 4 | g01260994 |
(14) Breaker relief valve (15) Steering system filter (16) Steering hydraulic tank (17) Steering pump case drain filter | |
 | |
| Illustration 5 | g01251625 |
(18) Steering piston pump (19) Pressure and flow compensator valve | |
Primary Steering System Operation
The steering system is hydraulic. There is no mechanical connection between the steering wheel and steering cylinders (1) that move the front wheels. The steering system is a closed center system. The steering system is independent of all other hydraulic systems. Oil for the steering system is stored in steering hydraulic tank (16) .
Steering piston pump (18) is a pressure compensated piston type pump. The steering piston pump is mounted on the back side of the engine. The steering piston pump (18) is driven by the pump drive. Steering piston pump (18) operates only when the engine is running. The output of the steering piston pump is controlled by pressure and flow compensator valve (19) . Metering pump (20) receives signal oil from the pressure and flow compensator valve. The signal oil flows through shuttle valve (9) and to the steering metering pump. The signal oil determines the pressure and the flow of the steering piston pump. The pressure and flow compensator valve is fastened to the steering piston pump. The flow compensator valve in the pressure and flow compensator valve causes the steering piston pump to change from low pressure standby to full flow. The high-pressure cutoff valve limits the maximum steering pressure.
Internal leakage from steering piston pump (18) is returned to steering hydraulic tank (16) through steering pump case drain filter (17) . Return oil from the steering system flows through steering oil filter (15) . The steering oil filter is bolted to the steering hydraulic tank. Normally, oil flows through steering oil filter (15) and clean oil is returned to steering hydraulic tank (16) .
If the filter element for steering oil filter (15) becomes full of debris, the restriction to flow causes a pressure increase. The bypass valve for steering oil filter (15) will open when the pressure increases above the setting of the bypass valve. When the bypass valve opens, oil is allowed to bypass the filter. The oil goes directly to steering hydraulic tank (16) . When the oil bypasses the filter element, debris in the oil will cause damage to other system components. Proper maintenance must be used to ensure that the filter element does not stop the flow of clean oil to the hydraulic system.
Steering hydraulic tank (16) supplies oil to steering piston pump (18) . The steering piston pump (18) pumps oil to steering check and relief valve (2) . Primary steering relief valve (4) is mounted in steering check and relief valve (2) . Primary steering relief valve (4) prevent the oil pressure from being too high. Primary steering relief valve (4) protects the primary steering system if the high-pressure cutoff valve in pressure and flow compensator valve (19) fails to limit the maximum pressure of the system. The steering check valve (6) prevents oil from flowing back to steering piston pump (18) if the engine stops.
From steering check and relief valve (2) , the pressure oil flows to the steering metering pump (20) . When the steering wheel is turned, steering metering pump (20) sends a fixed amount of oil to steering cylinders (1) . The speed of the turn is determined by the rate of the steering wheel rotation. The steering linkage is designed in order to use the head end of each cylinder as a mechanical stop.
Two steering cylinder check and relief valves are located inside steering metering pump (20) . Steering cylinder check and relief valves prevent damage from high-pressure oil in the cylinder circuit. This occurs when the steering wheel is stationary and an outside force on a front wheel suddenly moves a cylinder rod into a cylinder or out of a cylinder. When the front wheels strike a large object, pressure oil from a steering cylinder will open one of the steering cylinder check and relief valves . This will allow oil flow to the low-pressure side of steering cylinders (1) .
Pressure reducing valve (8) protects the steering pump pressure switch (7) from high-pressure oil. High-pressure oil will damage the switch. Pressure reducing valve (8) modulates the flow of oil when the pressure of the steering system is above the pressure setting of the pressure reducing valve. Steering pump pressure switch (7) now senses the pressure setting of pressure reducing valve (8) . The pressure reducing valve shifts when the steering system pressure drops below the setting of the pressure reducing valve. The steering pump pressure switch (7) now senses the steering system pressure. Steering pump pressure switch (7) monitors the output of the steering piston pump.
Secondary Steering System Operation
 | |
| Illustration 6 | g01267633 |
(2) Steering check and relief valve (3) Secondary relief valve (4) Primary relief valve | |
 | |
| Illustration 7 | g01251867 |
(22) Steering lockout switch (23) Advisor monitor display (24) Secondary brake lever (25) Secondary steering and parking brake release switch | |
 | |
| Illustration 8 | g01251626 |
(7) Steering pump pressure switch (13) Electric drive pump for the secondary steering and brake release | |
Steering hydraulic tank (16) also supplies oil to electric drive pump (13) for the secondary steering and the brake release. Electric drive pump (13) for the secondary steering and the brake release is located on the front crossmember. The electric drive pump for the secondary steering and the brake release provides oil in order to steer the front wheels if the normal flow is lost from the primary steering system or if the engine stops.
Electric drive pump (13) for the secondary steering and the brake release operates according to the position of brake release and secondary steering switch (25) that is located in the cab. During normal machine operation, brake release and secondary steering switch (25) is placed in the AUTO position. The electric drive pump for the secondary steering and the brake release will only operate when additional pressure oil is needed in the steering system.
When the engine is started, the Power Train Electronic Control Module (Power Train ECM) activates a relay that is located behind the cab. The relay behind the cab activates a larger relay that is located on the inside of the left frame rail next to the engine. Then, the larger relay activates electric drive pump (13) for the secondary steering and the brake release. The electric drive pump for the secondary steering and the brake release will operate for three seconds. Secondary steering indicator light will turn on when the pump is operating.
Brake release and secondary steering switch (25) is moved to the MANUAL position only when the machine is towed. This switch sends a signal to the Power Train ECM. The Power Train ECM then activates electric drive pump (13) for the secondary steering and the brake release and the secondary steering indicator.
The monitoring system is designed in order to alert the operator of an immediate problem or impending problem in the steering system or other machine system.
If the steering system pressure decreases to the deactuation pressure of the pressure switch, steering pump pressure switch (7) will send an electrical signal to the Power Train ECM . Advisor monitor display (23) for the secondary steering will flash when the steering pressure is low. Secondary steering indicator will turn ON when the pump is operating. The secondary steering indicator light will turn ON when the pump is operating. The Power Train ECM will then activate electric drive pump (13) for the secondary steering and the brake release.
Load sensing signal pressure oil will flow through load sensing valve (10) and shuttle valve (9) to the steering metering pump. The load sensing signal pressure moves the spool of the load sensing valve. The load sensing valve controls the flow of oil from the electric drive pump for the secondary steering and the brake release to steering check and relief valve (2) .
Secondary steering backup relief valve (3) is located in steering check and relief valve (2) . Secondary steering backup relief valve (3) prevents too high of pressure oil from flowing to steering metering pump (20) . Secondary steering relief valve (3) receives oil from the electric drive pump for the secondary steering and the brake release. If the pressure oil opens secondary steering check valve (3) , the oil flows to the tank. If the oil pressure is below the setting for secondary steering relief valve (3) , the oil flows through check valve (22) in Illustration 1 to steering metering pump (20) . Check valve (6) in Illustration 1 prevents the oil from flowing backward through steering check and relief valve (2) . The operation of the secondary steering system and the primary system is identical after the pressure oil flows past primary steering check valve (6) .
The main relief valve (5) for the secondary steering is located in the load sensing valve (10) behind a plug for electric drive pump (13) for the secondary steering and the brake release. The main relief valve for the secondary steering controls the maximum pressure of the secondary steering system.