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| Illustration 1 | g00815579 |
(1) Pilot operated hydraulic control ( hydrostatic) (2) Solenoid valve ( hydrostatic) (3) Solenoid valve ( work tool) (4) Pilot operated hydraulic control ( work tool) (5) Ball valve ( manual work tool lowering) (6) Control valve ( work tool) (7) Lift cylinders (8) Tilt cylinders (9) Auxiliary couplings (10) Accumulator (11) Solenoid valve ( parking brake) (12) Return manifold (13) Oil filter (14) Gear motor ( fan drive) (15) Speed sensing valve (16) Charge relief valve (17) Piston pump ( hydrostatic) (18) Gear pump (19) Hydraulic tank | |
The pilot hydraulic system is used to move the spools in the control valve (work tool) (6). The pilot hydraulic system is also used to control the operation of the hydrostatic system. The pilot system uses lower pressure oil to control higher pressure oil.
In order for the pilot system to function, the interlocks must be disengaged. The interlock system consists of the following components: the solenoid valve ( hydrostatic) (2), the solenoid valve ( work tool) (3) and the solenoid valve ( parking brake) (11). In order for the interlock system to be disengaged, the following conditions must be met:
- The seat must be occupied.
- The armrest must be in the DOWN position.
- The parking brake must be disengaged.
The charge relief valve (16) regulates the maximum pressure of the charge system. The charge system pressure is 3300 kPa (480 psi) at high idle.
When the interlock system is disengaged, oil flows from the hydraulic tank (19) to the front section of the gear pump (18) and then oil flows to the gear motor (fan drive) (14). After the gear motor, oil flows through the oil filter (13). Then, the oil flows to the piston pump ( hydrostatic) (17). Some of the oil will flow in order to supply the pilot operated hydraulic control ( work tool) (4) .
The rest of the oil continues to flow to the piston pump. At the piston pump, the oil is regulated by the speed sensing valve (15). The oil that flows to the pilot operated hydraulic control ( hydrostatic) (1) is regulated at a pressure of 2500 kPa (365 psi).
The rest of the oil is makeup oil for the hydrostatic system. Any leakage in the hystat system is replaced by this oil.
Pilot Operated Hydraulic Control ( Hydrostatic)
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| Illustration 2 | g00815692 |
(1) Pilot operated hydraulic control ( hydrostatic) (2) Solenoid valve ( hydrostatic) (10) Accumulator (11) Solenoid valve ( parking brake) (15) Speed sensing valve (16) Charge relief valve (17) Piston pump ( hydrostatic) (18) Gear pump (19) Hydraulic tank (20) Resolver network (21) Left piston motor ( hydrostatic) (22) Right piston motor ( hydrostatic) (23) Actuator piston (24) Actuator piston (X3) Pilot pressure ports (X4) Pilot pressure ports | |
Oil that comes from the speed sensing valve (15) flows to the pilot operated hydraulic control ( hydrostatic) (1). When the interlock system is disengaged, signal oil will not flow through the pilot operated hydraulic control until the hydraulic control is moved out of the HOLD position. The hydraulic control will return to the HOLD position when the hydraulic control is released from any of the positions. Table 1 shows the direction of machine travel when the signal ports are pressurized by the pilot operated hydraulic control ( hydrostatic).
| Ports that are Pressurized | Direction of Machine Travel |
| Port (X3) on Rotating group 1 and Port (X3) on Rotating group 2 | REVERSE |
| Port (X3) on Rotating group 1 and Port (X4) on Rotating group 2 | LEFT TURN |
| Port (X4) on Rotating group 1 and Port (X3) on Rotating group 2 | RIGHT TURN |
| Port (X4) on Rotating group 1 and Port (X4) on Rotating group 2 | FORWARD |
When the hydraulic control is moved to the FORWARD position, signal oil flows from the speed sensing valve (15) through the solenoid valve ( hydrostatic) (2). Then, the oil flows through the plunger in the hydraulic control that is for the FORWARD position. Oil then flows into the resolver network (20). When the balls in the resolver network are unseated, the resolver network routes the signal oil to the two rotating groups in the piston pump (17). In the following example, the signal oil is routed to the ports (X4) that are on the piston pump. The signal oil flows into the ports (X4) and the signal oil shifts the actuator pistons (23) and (24). This causes the swashplates to move and oil flows out of the ports (B) on the piston pump. This will propel the machine forward.
When the operator releases the hydraulic control, the hydraulic control returns to the HOLD position. This causes the flow of pilot oil to stop. The actuator pistons will return to the center position and the swashplates will move back to the minimum displacement position. No oil will flow out of the piston pump. This causes the machine to stop.
Refer to the Systems Operation, "Piston Pump (Hydrostatic)" for more information on the piston pump. Refer to the Systems Operation, "Piston Motor (Hydrostatic)" for more information on the piston motor.
Pilot Operated Hydraulic Control ( Work Tool)
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| Illustration 3 | g00884130 |
(3) Solenoid valve ( work tool) (4) Pilot operated hydraulic control ( work tool) (5) Ball valve ( manual work tool lowering) (6) Control valve ( work tool) (7) Lift cylinders (8) Tilt cylinders (9) Auxiliary couplings (10) Accumulator (11) Solenoid valve ( parking brake) (16) Charge relief valve (18) Gear pump (19) Hydraulic tank (25) Check valve | |
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| Illustration 4 | g00800728 |
(6) Control valve ( work tool) (10) Accumulator (25) Check valve | |
The oil that flows through the check valve (25) is considered to be pilot oil. The pilot oil flows through the check valve, to the control valve ( work tool) (6), and to the pilot operated hydraulic control ( work tool) (4). The pilot oil that flows to the control valve is used to activate the auxiliary circuit spool and the pilot oil is used to charge the accumulator (10). The pilot oil that flows to the pilot operated hydraulic control ( work tool) is used to activate the lift spool and the pilot oil is used to activate the tilt spool.
The interlock system must be disengaged for the pilot oil to flow. The auxiliary circuit can function with the armrest in the UP position, if the machine is equipped with an interlock override control. Refer to the Operation and Maintenance Manual, "Continuous Flow and Interlock Override Control" for more information.
When the interlock system is disengaged, pilot oil will not flow through the hydraulic control until the hydraulic control is moved out of the HOLD position. The hydraulic control will return to the HOLD position when the hydraulic control is released from any of the positions except for the FLOAT position. The FLOAT position has a detent that keeps the hydraulic control in this position until the operator moves the hydraulic control.
When the hydraulic control is moved to the TILT BACK position, pilot oil flows through the check valve (25) and through the solenoid valve (work tool) (3). Then, the pilot oil flows through the plunger in the hydraulic control that is for the TILT BACK position. Then, the pilot oil flows to the control valve in order to shift the tilt spool to the TILT BACK position. Oil then flows out of port (A) to the rod ends of the tilt cylinders (8) in order to tilt the work tool backward. When the operator releases the hydraulic control, the hydraulic control will move back to the HOLD position. This shuts off the flow of pilot oil. The tilt spool will move back to the HOLD position and the tilt cylinders will stop retracting.
Refer to the Systems Operation, "Control Valve (Work Tool)" for more information on the control valve.
Accumulator
The accumulator (10) is mounted on the control valve ( work tool). The accumulator provides a limited amount of pilot oil after the engine is shut OFF. The oil capacity of the accumulator is 0.32 L (0.34 qt). The accumulator is charged to 900 kPa (130 psi) with 30.0 cc (1.83 in3) of dry nitrogen.