Steering Control System
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| Illustration 1 | g00739128 |
(1) Front steering cylinder (2) Load sensing line (3) Selector valve for the steering mode (4) Bank valve (5) Rear steering position sensor (if equipped) (6) Rear steering cylinder (7) Hydraulic tank (8) Load sensing line for the steering (9) Steering metering pump (10) Hydraulic pump | |
The hydraulic pump (10) is a variable displacement axial piston type. The pump output is matched to system requirements by a load sensing system in bank valve (4). The pump supplies oil to the steering section of the bank valve. When the steering system is not in operation, a small amount of oil from the steering section of the bank valve is metered to metering pump (9). The rest of the oil from the pump is directed to the implement control valves. The metering pump is connected to the load sensing system by line (8) .
When the steering system is not in operation, a small amount of supply oil flows through a dynamic signal orifice in the steering section of the bank valve. The orifice allows a constant flow of hydraulic oil to flow through the signal line to the metering pump and to the tank when the steering wheel is stationary. This improves steering response time in cold weather.
Steering mode selector valve (3) is a three-position solenoid operated valve which controls the rear axle steering cylinder.
Self-Aligning Rear Steering (If Equipped)
Rear steering position sensor (5) consists of a proximity switch that is mounted on the right side of the rear axle, and a target which is mounted on the right side steering yoke. The position sensor is de-energized when the upper half of the master steering select switch is depressed for operation in crab steer mode or circle steer mode.
Right Turn in Two-Wheel Steer Mode
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| Illustration 2 | g00739134 |
(1) Front steering cylinder (2) Load sensing line (3) Selector valve for the steering mode (4) Bank valve (5) Rear steering position sensor (if equipped) (6) Rear steering cylinder (7) Hydraulic tank (8) Load sensing line for the steering (9) Steering metering pump (10) Hydraulic pump (R) Return oil (P) Pump oil (B) Blocked oil | |
When the top of the master steering select switch is depressed, the solenoids on mode selector valve (3) and position sensor (5) are de-energized. The valve spool is then centered by spring force, and the ports that connect rear steering cylinder (6) are blocked. Oil that is locked into the cylinder by the valve spool holds the rear wheels in the straight ahead position and the rear axle operates as a rigid axle.
When a right turn is made in two-wheel steer mode, oil flows through metering pump (9), through mode selector valve (3), and to the right side of front steering cylinder (1). Oil that enters the cylinder causes the tie rods to move to the left. This causes the wheels to move to the right. Oil in the left side of the steering cylinder flows to tank (7) through the metering pump.
Note: The wheels will turn faster when the steering wheel is turned faster.
If the steering cylinder reaches the end of the stroke and the operator continues to turn the steering wheel, pressure in the steering system will increase. The increase in pressure causes the signal relief valve in the end section of bank valve (4) to open and excess signal oil is directed to the tank in order to relieve the pressure.
When the steering wheel is turned to the left the flow of oil is reversed. Oil flows directly to the left side of the steering cylinder and return oil is routed through the mode selector valve and back to the tank.
Note: If the engine stops and the machine is in motion, the machine can still be steered. When the steering wheel is turned in this situation, the metering section of metering pump (9) acts as a pump.
Right Turn in Circle Steer Mode
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| Illustration 3 | g00739138 |
(1) Front steering cylinder (2) Load sensing line (3) Selector valve for the steering mode (4) Bank valve (5) Rear steering position sensor (if equipped) (6) Rear steering cylinder (7) Hydraulic tank (8) Load sensing line for the steering (9) Steering metering pump (10) Hydraulic pump (R) Return oil (P) Pump oil (D) Displaced oil | |
Note: In circle steer, the front wheels and the rear wheels turn in opposite directions. Circle steer allows the machine to make sharper turns.
When the bottom half of the master steering select switch is depressed, and the circle steer mode is selected, solenoid (A) on mode selector valve (3) is energized. The selector valve spool is offset to the circle steer position.
When a right turn is made in circle steer mode, oil flows through mode selector valve (3) to the right side of rear steering cylinder (6). Oil that is displaced from the left side of the rear steering cylinder flows through the mode selector valve to the right side of the front cylinder (1) .
Return oil from the left side of the front cylinder flows to tank (7) through metering pump (9). The front cylinder rods move to the left. This causes the front wheels to pivot to the right. The rear cylinder rods move to the left. This causes the rear wheels to pivot to the left.
Left Turn in Circle Steer Mode
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| Illustration 4 | g00739141 |
(1) Front steering cylinder (2) Load sensing line (3) Selector valve for the steering mode (4) Bank valve (5) Rear steering position sensor (if equipped) (6) Rear steering cylinder (7) Hydraulic tank (8) Load sensing line for the steering (9) Steering metering pump (10) Hydraulic pump (R) Return oil (P) Pump oil (D) Displaced oil | |
When a left turn is made in circle steer mode, oil flows directly from metering pump (9) to the left side of front steering cylinder (1). Oil that is displaced from the right side of the front steering cylinder flows through mode selector valve (3) to the left side of rear steering cylinder (6) .
Oil that is displaced from the right side of the rear steering cylinder flows through mode selector valve (3), and metering pump (9) to tank (7). The front cylinder rods move to the right. This causes the front wheels to pivot to the left. The rear cylinder rods move to the right. This causes the rear wheels to pivot to the right.
Right Turn in Crab Steer Mode
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| Illustration 5 | g00739142 |
(1) Front steering cylinder (2) Load sensing line (3) Selector valve for the steering mode (4) Bank valve (5) Rear steering position sensor (if equipped) (6) Rear steering cylinder (7) Hydraulic tank (8) Load sensing line for the steering (9) Steering metering pump (10) Hydraulic pump (R) Return oil (P) Pump oil (D) Displaced oil | |
Note: In crab steer, the front wheels and the rear wheels turn in the same direction. Crab steer allows the machine to move in a sideways manner for maneuverability in confined areas.
When the top half of the master steering select switch is depressed, and the crab steer mode is selected, solenoid (B) on mode selector valve (3) is energized. The selector valve spool is offset to the crab steer position.
When the steering wheel is turned clockwise in crab steer mode, oil flows through mode selector valve (3) to the left side of rear steering cylinder (6). Oil that is displaced from the right side of the rear steering cylinder flows through the mode selector valve to the right side of the front cylinder (1) .
Return oil from the left side of the front cylinder flows to tank (7) through metering pump (9). The front steer cylinder rods move to the left, and the rear cylinder rods move to the right. This causes the front wheels and the rear wheels to pivot to the right. All the wheels are now turned in the same direction and all wheels are steered.
Left Turn in Crab Steer Mode
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| Illustration 6 | g00739143 |
(1) Front steering cylinder (2) Load sensing line (3) Selector valve for the steering mode (4) Bank valve (5) Rear steering position sensor (if equipped) (6) Rear steering cylinder (7) Hydraulic tank (8) Load sensing line for the steering (9) Steering metering pump (10) Hydraulic pump (R) Return oil (P) Pump oil (D) Displaced oil | |
When the steering wheel is turned counterclockwise in crab steer mode, oil flows directly from metering pump (9) to the left side of front steering cylinder (1). Oil that is displaced from the right side of the front steering cylinder flows through the mode selector valve to the right side of rear cylinder (6) .
Return oil from the left side of the rear cylinder flows to tank (7) through mode selector valve (3) and metering pump (9). The front steer cylinder rods move to the right, and the rear cylinder rods move to the left. This causes the front wheels and the rear wheels to pivot to the left. All the wheels are now turned in the same direction and all wheels are steered.