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| Illustration 1 | g03716679 |
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View of the cushion hitch pump and the pump control valve | |
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| Illustration 2 | g03716736 |
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Piston Pump (Cushion-Hitch) (1) Spring for swashplate (2) Control piston (3) Pistons (Nine) (4) Swashplate (5) Barrel (6) Outlet opening to the cushion-hitch hydraulic system (7) Pump drive shaft (8) Pump control valve (cushion-hitch) (9) Inlet opening from the hydraulic tank | |
The cushion-hitch pump is an axial piston type pump which is mounted to the steering pump on the front of the transfer case at the rear of the tractor.
The cushion-hitch pump has nine pistons (3). When pump drive shaft (7) turns, barrel (5), the retraction plate, and the slippers turn. The piston ends connect to the slippers. Swashplate (4) does not turn. There is a bearing journal on each side of the swashplate. The two bearing journals are inside bearings which allow movement of the swashplate. Oil flow through the passages in the pistons lubricates the internal components of the pump.
When swashplate (4) is at the maximum angle and pump drive shaft (7) is turning, pistons (4) are moved in and out of barrel (5). As the pistons move out of the barrel, the pistons create a vacuum at inlet opening from the hydraulic tank (9). The hydraulic tank pressure is maintained at a sufficient level to not allow cavitation as the oil is drawn into the pump. The oil passes through the inlet opening and into the piston bore in the barrel. As the barrel continues to turn, the pistons are pushed into the barrel as the slippers rotate up the angle of swashplate (4). The pistons push the oil from the piston bore through pump the outlet opening to the cushion-hitch system.
When the engine is operating, the pump will produce flow and pressure in order to satisfy the following conditions:
- The demand of the cushion-hitch system
- The demand for the pilot pressure for the leveling valve
- The pressure setting of the pressure compensator
- The internal lubrication of the pump components
- The demand of the pilot pressure for the implement system
- The demand of the push-pull hydraulic system
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| Illustration 3 | g03723123 |
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Pump Control Valve (Cushion-Hitch) (9) ( 10) Pressure compensator spool (11) Passage from the outlet opening of the piston pump (cushion-hitch) (12) Passage to the control piston of the piston pump (cushion-hitch) (13) Drain passage (14) Springs (15) Setscrew | |
The pump control valve is set to function only as a pressure compensator. Setscrew (15) is set so that the flow compensator does not function.
The pressure compensator regulates the output flow of the cushion-hitch piston pump. The output of the pump is controlled by the angle of the swashplate.
When the engine is operating and the oil pressure in the cushion-hitch hydraulic system is less than the pressure setting of the pressure compensator, the oil from the outlet opening of the piston pump flows through passage from the outlet opening of the piston pump (cushion-hitch) (11). The oil is stopped by pressure compensator spool (10) and opposing force from springs (14). There is no flow to the control piston in the piston pump and the swashplate is at the maximum angle. When the system pressure setting has been obtained, full pump output is no longer needed. Full pump output continues, until the oil in the passage from the outlet opening of the piston pump (cushion-hitch) (11) overcomes the opposing force of springs (14).
The oil in passage from the outlet opening of the piston pump (cushion-hitch) (11) moves pressure compensator spool (10) to the right. The oil in the inlet passage now flows through the passage to the control piston of the piston pump (cushion-hitch) (12). The flow of oil from passage to the control piston of the piston pump (cushion-hitch) (12) moves the control piston. The control piston moves the swashplate toward the minimum angle. The pump output is decreased.
The stroke of pistons in the piston pump is shortened since the slippers follow the reduced swashplate angle. The shortened stroke of the pistons will continue to provide enough flow in order to maintain the system pressure setting. The shortened stroke of the pistons will also provide internal lubrication to the pump components.
When the pressure of the oil in the cushion-hitch hydraulic system decreases, there is a decrease in the pressure of the oil in passage from the outlet opening of the piston pump (cushion-hitch) (11). Springs (14) move pressure compensator spool (10) to the left. The oil flow to the control piston in passage to the control piston of the piston pump (cushion-hitch) (12) decreases. The spring in the piston moves the swashplate toward the maximum angle. This movement toward the maximum angle causes the pump output to increase.