The toggle switch steering system is composed of two toggle switches, the IQAN monitoring and control system, the steering activation switch, the seat direction switch, the implement control valve, and the steering cylinders. The steering metering system is composed of the steering metering pump, the priority valve, a pressure reducing valve, and the steering cylinders.
Toggle Switch Steering System
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| Illustration 1 | g00662971 |
Diagram of the Steering System (1) Toggle switch steering (2) Terrain toggle switch steering (3) Activation switch (toggle switch steering) (4) Seat direction switch (5) Steering cylinders (6) IQAN (7) Implement control valve (A) Line to the steering metering pump (B) Line to the steering metering pump | |
The toggle switch steering system is activated by activation switch (3). When activation switch (3) is in the OFF position only the steering wheel can be used to articulate the machine.
Either of the two toggle switches can be used to control the speed of turning. As the toggle switch is moved further from the CENTER position the machine will turn faster.
As the toggle switch moves further from the CENTER position, the resistance in the circuit changes. This changes the voltage that is sent to the IQAN. At the LEFT position, the voltage is approximately 0.5 Volts. At the RIGHT position, the voltage is approximately 4.5 Volts. At the CENTER position, the voltage is approximately 2.5 Volts.
The magnitude of the voltage from the toggle switch controls the current from the IQAN to the proportional solenoids in implement control valve (7). Two solenoids in the implement control valve control the steering. One solenoid controls the oil flow for left turns. The other solenoid controls the oil flow for right turns.
The magnitude of the current to the proportional solenoids controls the amount of movement of the solenoids. The movement of the solenoids controls the flow of oil to the steering cylinders. More oil flow to the cylinders will increase the speed of steering.
When the operator rotates the seat, seat direction switch (4) is switched. The IQAN then sends current to the other proportional solenoid. This enables the operation of toggle switch (1) to function in the same manner in the forward direction or the reverse direction.
Steering Metering System
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| Illustration 2 | g00814866 |
Schematic of the Steering Metering System for the 554 Forwarder (5) Steering cylinders (7) Implement control valve (8) Steering metering pump (9) Spool (10) Check valve (11) Priority valve (12) Pressure reducing valve (C) Signal line to pump (D) Pump pressure line (E) Load sensing port | |
Note: Load sensing port (E) is not used on the 574 Forwarder.
When the engine is running, the implement pump supplies pressure oil to priority valve (11) through pressure line (D). When the steering wheel is not being turned, the valve spool in the priority valve moves to the RIGHT position.
A small amount of oil flows through the priority valve to spool (9). This ensures that the supply of oil to the metering pump is always at operating temperature.
The steering column is attached to the steering metering pump by a spline coupling. When the operator turns the steering wheel, the spline coupling turns. Spool (9) moves from the HOLD position. The oil pressure at the outlet of the priority valve decreases. The decreased oil pressure causes the valve spool to shift to the LEFT position.
With valve spool (11) in the LEFT position, an increased amount of oil flows to the steering metering pump. Pressure oil then flows through the spool to the steering cylinders.
As the operator turns the steering wheel faster, the spool moves farther from the HOLD position. The rate of oil flow to the steering cylinders increases and the speed of turning increases.
Spool (9) is a modulating spool. As spool (9) moves farther from the HOLD position, more oil flows through spool (9). The modulating spool is represented in the schematic by the adjustable orifice symbol.
When the operator turns the steering wheel, signal pressure oil flows from the steering metering pump to the priority valve and pressure reducing valve (12) .
When the steering system reaches the end of range of articulation or an external force acts on the machine, the oil pressure in the signal circuit increases. The increased pressure in the signal circuit keeps the valve spool in the priority valve shifted to the LEFT position. Pressure oil will continue to be available for flow to the steering metering pump.
The maximum pressure in the signal circuit is limited by pressure reducing valve (12). Limiting the signal pressure limits the maximum oil flow to the steering metering pump by controlling the maximum upstroke of the implement pump.
If the pressure in the steering circuit suddenly decreases during a turn, check valve (10) opens. The check valve prevents cavitation in the steering metering pump and steering cylinders. Oil from the return lines can flow into the circuit.