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| Illustration 1 | g02548396 |
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Joystick cushion-hitch control | |
The Cushion-Hitch of the Wheel Tractor-Scraper is controlled by a button on the joystick. The cushion hitch button is connected to the implement ECM by two wires and the transmission/chassis ECM by one wire. A common/ground wire J2-22 is connected to the transmission/chassis ECM and two signal wires J1-64 and J1-63 are connected to the implement ECM. The switch in the button is created in such a way that J1-64 is normally connected to ground wire J2-22 and J1-63 is normally open. When the button is pressed, the connections momentarily reverse so that J1-63 is connected to ground and J1-64 is disconnected from ground. When the button is released, the connections return to normal. Each time the button is pressed a signal is sent to the implement ECM to either energize or de-energize the cushion hitch enable solenoid. The implement ECM prevents the cushion hitch solenoid from being energized when the park brake is engaged. If the park brake switch is engaged while the cushion hitch solenoid is energized, the implement ECM will automatically de-energize the cushion hitch solenoid and lower the cushion hitch to the locked down position. This prevents the cushion hitch from lowering at a later time if the operator parks the machine with the engine running.
If the Cushion-Hitch Solenoid is energized and the keyswitch input changes from ON to OFF, the solenoid will be de-energized. By de-energizing the cushion hitch solenoid when the keyswitch input is turned OFF, the cushion hitch will disengage and lower to the locked state before the operator is outside the cab.
Cushion-Hitch Locked Down Position
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| Illustration 2 | g03646583 |
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The Cushion-Hitch Switch Is Turned Off. The Cushion-Hitch Is in the Lock Down Position. The Engine is Running. (1) Implement ECM (2) Load cylinder (3) Ride dampening valve (4) Joystick control (5) High-pressure accumulator (6) Low-pressure accumulator (7) Directional spool valve (8) Cushion-Hitch enable solenoid valve (9) Accumulator valve spool (10) Leveling spool (11) Check valve (12) Pressure compensator valve (13) Cushion-Hitch and pilot oil filter (14) Pilot pressure reducing valve (15) Cushion-Hitch leveling solenoid valve (16) Pilot control manifold (17) Cushion-Hitch pump (18) Load cylinder position sensor (19) Load cylinder head end pressure sensor (20) Cushion-Hitch ECU | |
When the engine is running, hydraulic oil from the hydraulic oil tank flows to cushion-hitch piston pump (17). Pressure compensator valve (12) regulates the output of cushion-hitch piston pump (17).
When the output pressure of cushion-hitch piston pump (17) is less than the setting of pressure compensator valve (12), the cushion-hitch piston pump (17) operates at a maximum output. When the setting of pressure compensator valve (12) is reached, pressure compensator valve (12) signals cushion-hitch piston pump (17) to move the swashplate to the minimum angle. The movement of the swashplate to the minimum angle minimizes the stroke of the pistons in cushion-hitch piston pump (17). Cushion-hitch piston pump (17) operates at a minimum displacement. Hydraulic pressure in the cushion-hitch system is at a maximum.
Refer to Testing and Adjusting, "Pump Control Valve (Cushion Hitch) - Test and Adjust" for the correct setting of the pressure compensator valve.
When the engine is first started, the cushion-hitch is in the locked down position. Leveling spool (10) is in the RAISE position. Accumulator valve spool (9) is shifted by cushion-hitch pump pressure, blocking the flow of oil from high-pressure accumulator (5) and low-pressure accumulator (6) to tank. Cushion hitch pump (17) operates at maximum displacement to send hydraulic oil around leveling spool (10) to high-pressure accumulator (5) and low-pressure accumulator (6). Hydraulic oil charges high-pressure accumulator (5) and low-pressure accumulator (6) until the pressure reaches the setting of pressure compensator valve (12). Cushion-hitch pump (17) will move to minimum displacement. Accumulator pressure passes through directional spool (7) to the rod end of load cylinder (2). The pressure in the rod end of load cylinder (2) holds the cushion-hitch in the locked down position. The head end of load cylinder (2) is open to the hydraulic oil tank because of the position of directional spool (7).
Note: When a running engine is stopped, the hydraulic pressure on accumulator valve spool (9) is relieved. The spring force on accumulator valve spool (9) pushes accumulator valve spool (9), allowing the oil in high-pressure accumulator (5) and low-pressure accumulator (6) to flow back to the hydraulic oil tank.
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| Illustration 3 | g03646588 |
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The Cushion-Hitch Switch Is Turned On. The Cushion Ride Mode is Activated. The Scraper is in the Cushion Ride Mode. The Engine Is Running. (1) Implement ECM (2) Load cylinder (3) Ride dampening valve (4) Joystick control (5) High-pressure accumulator (6) Low-pressure accumulator (7) Directional spool valve (8) Cushion-Hitch enable solenoid valve (9) Accumulator valve spool (10) Leveling spool (11) Check valve (12) Pressure compensator valve (13) Cushion-Hitch and pilot oil filter (14) Pilot pressure reducing valve (15) Cushion-Hitch leveling solenoid valve (16) Pilot control manifold (17) Cushion-Hitch pump (18) Load cylinder position sensor (19) Load cylinder head end pressure sensor (20) Cushion-Hitch ECU | |
When the cushion-hitch switch, on joystick control (4) is pressed Implement ECM (1) energizes the cushion hitch enable solenoid (8). Which directs pump pressure to the directional valve spool (7). Directional valve spool (7) shifts to connect the head end of the load cylinder (2) to high-pressure accumulator (5) and low-pressure accumulator (6). Directional valve spool (7) pressure will connect the rod end of the load cylinder (2) to the hydraulic oil tank. Oil flows from high-pressure accumulator (5) and low-pressure accumulator (6) to the head end of the load cylinder (2), raising the load cylinder (2) approximately
When the tractor is driven over rough terrain, the cushion-hitch hydraulic oil flows back and forth between head end of load cylinder (2) and the cushion-hitch accumulators (5) and (6). A cushion effect is provided by the compression and expansion of the nitrogen gas in accumulators (5) and (6). As oil flows back and forth between load cylinder (2) and cushion-hitch accumulators (5) and (6), cushion hitch ECU (20) opens and closes ride dampening valve (3) to provide the optimal damping rate to load cylinder (2) and to prevent load cylinder (2) from reaching the end range of travel. The position of ride dampening valve (3) is controlled based on measurements from load cylinder position sensor (18) and load cylinder head end pressure sensor (19).
Accumulators (5) and (6) are tied into the system in a series. Accumulator (6) is a low-pressure accumulator that is activated when the machine is empty or carrying a light load. When a heavier load is being carried, the high-pressure accumulator (5) is also activated.
Pilot pressure reducing valve (14) in pilot control manifold (16) reduces cushion hitch pump (17) discharge pressure for use in the cushion hitch leveling and implement system pilot circuits.
Note: If the engine stops or cushion hitch pump (17) pressure is lost while the cushion hitch is in ride mode, the hydraulic pressure on accumulator valve spool (9) is relieved. The spring force on accumulator valve spool (9) shifts accumulator valve spool (9), allowing the oil in high-pressure accumulator (5) and low-pressure accumulator (6) and the oil in the head end of load cylinder (2) to flow back to the hydraulic oil tank. The cushion hitch will return to the locked down position.