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| Illustration 1 | g00774031 |
(1) Piston pump group (2) Pilot port (one per rotating group) (3) Maximum angle stop screw (one per rotating group) (4) Shaft (5) Pilot port (one per rotating group) (6) Cross over relief valves and makeup valves (two per rotating group) (7) Charge pressure relief valve (8) Adjustment for the pump null (one per rotating group) | |
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| Illustration 2 | g00772209 |
(4) Shaft (9) Piston (10) Control arm for the swashplate (11) Actuator (12) Slider (13) Swashplate (14) Retraction plate (15) Rotating group 1 (16) Rotating group 2 (A) Passage to port (B) Passage to port | |
The pump group consists of the following components: two rotating groups (15) and (16), two actuators (11), two swashplates (13), shaft (4), four cross over relief valves (6), charge pressure relief valve (7) and speed sensing valve.
The pilot ports (2) and (5) are used to control the angle of the swashplate (13). The angle of the swashplate and the engine rpm controls the output of the pump. The pilot ports are connected to the resolver network on the pilot valve.
The piston pump operates in a closed loop system. The standard piston pump is a variable displacement piston pump with a maximum displacement of 45 cc/rev (2.75 in3/rev). The piston pump for machines that are equipped with two speed has a maximum displacement of 38.4 ± 0.6 cc/rev (2.34 ± 0.04 cu in/rev). The pump is driven from the engine flywheel by a coupling that is splined to the pump input shaft.
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| Illustration 3 | g00774128 |
(17) Spring collar (18) Actuator piston (19) Spring collar (20) Spring | |
The shaft (4) for the rotating groups consists of two shafts that are splined together between the two rotating groups. Each swashplate within the rotating group can operate independently. Rotating group 1 (15) supplies the left hand piston motor and rotating group 2 (16) supplies the right hand piston motor. For the following example of the operation of the pump, rotating group 1 will be used. Rotating group 2 will operate in the same manner.
When the operator moves the pilot valve in order to move the machine forward, pilot oil flows out of the pilot valve and into pilot port (5). This causes the actuator piston (18) to move to the right in illustration 3. The movement of the piston to the right causes the slider (12) to move the control arm for the swashplate (10). The movement of the control arm increases the angle of the swashplate (13). Half of the pistons in the cylinder barrel pull oil into each cylinder as the pistons rotate around the swashplate. The oil enters the rotating group through port (A). The other half of the pistons push oil out of each cylinder. The oil exits the rotating group through port (B). As the angle of the swashplate increases the output of the rotating group increases.
When the operator moves the pilot valve in order to move the machine backward, pilot oil flows out of the pilot valve and into pilot port (2). This causes the actuator piston (18) to move to the left in illustration 3. The movement of the piston to the left causes the slider (12) to move the control arm for the swashplate (10). The movement of the control arm increases the angle of the swashplate (13). Half of the pistons in the cylinder barrel pull oil into each cylinder as the pistons rotate around the swashplate. The oil enters the rotating group through port (B). The other half of the pistons push oil out of each cylinder. The oil exits the rotating group through port (A). As the angle of the swashplate increases the output of the rotating group increases.
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| Illustration 4 | g00774939 |
(21) Speed sensing valve | |
The speed sensing valve (21) senses the change in the flow of oil from the gear pump as the engine speed changes. An orifice in the speed sensing valve creates a pressure differential within the valve. The valve uses the pressure differential to route more flow or less flow to the pilot valve in order to control the piston pump. An increase in the pressure differential will cause more oil to flow to the pilot valve. The pilot valve uses this oil to control the swashplates in the pump group. The pressure of the speed sensing valve to the pilot valve fluctuates from 1100 kPa (160 psi) to 2600 kPa (380 psi). The solenoid for the pilot valve must be energized in order for the pilot valve to be functional.