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| Illustration 1 | g00794071 |
Hydraulic Schematic for Travel Motor Circuit (right travel motor) (1) Rotary group. (2) Gauge port (service). (3) Swashplate control piston. (4) Gauge port (stroking pressure). (5) Line relief valves. (6) External supply port. (7) Brake valve. (8) Check and relief valves. (9) Shuttle valve. (10) Brake pilot valve. (11) Port (pump oil). (12) External port (parking brake). (13) Internal port (parking brake). (14) Port (pump oil). (15) Gauge port (service). (16) Displacement change valve. (17) Case drain port. (18) Travel motor circuit. | |
The travel motor can be divided into the following three groups:
- The rotary group
- The displacement change valve
- The motor head
Rotary Group
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| Illustration 2 | g00791390 |
Rotary Group (3) Swashplate control piston. (19) Drive shaft. (20) Bearings. (21) Housing. (22) Pin. (23) Pistons. (24) Retainer. (25) Adjustment screw (output flow). (26) Barrel. (27) Spring. (28) Swashplate. | |
The travel motors are piston type motors.
The flow of the oil from the pump depends on the direction of travel. The oil from the pump flows into the travel motor through port (11) or port (14). Pump oil is forced out of the travel motor through port (11) or port (14) .
The case drain oil returns to the hydraulic tank through a drain port on the head of the travel motor.
The oil from the lower pump flows into the right travel motor through port (11) during forward travel. The oil from port (11) flows through an internal passage in the motor head. The oil then flows through a passage in swashplate (28) into barrel (26). The oil forces pistons (23) to move to the left.
When piston (23) moves, barrel (26) rotates. Oil is discharged through a passage in swashplate (28) by pistons (23) as barrel (26) rotates. The oil flows through an internal passage in the motor head. The oil then flows through port (14).
Pistons (23) are connected to output shaft (19) by retainer (24). Output shaft (19) rotates sending power to the final drives.
Displacement Change Valve
Small Displacement Change Operation
When the travel speed control switch on the control panel is set at the HIGH SPEED position the travel speed solenoid valve that is located on the pilot manifold is de-energized. The pilot system oil flows through a port to displacement change valve (16) in the motor head.
The pilot oil forces a spool in displacement change valve (16) to shift. Oil from the pump moves swashplate control piston (3). The angle of swashplate (28) decreases. As a result, the motor displacement is decreased and travel speed is increased.
Large Displacement Change Operation
When the angle of swashplate (28) in the travel motor increases, the displacement of the travel motor increases. The angle of swashplate (28) in the travel motor will increase and the travel speed will decrease when the travel speed control switch is moved to the LOW SPEED position.
When the travel speed control switch on the control panel is moved to the LOW SPEED position, the travel speed solenoid is energized. The pilot system oil is blocked. The spool in displacement change valve (16) is shifted by the force of the spring in displacement change valve (16). Oil from the pump moves swashplate control piston (3). This increases the angle of swashplate (28). The angle of swashplate (28) increases and the displacement of the travel motor increases. The travel speed decreases.
Motor Head
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| Illustration 3 | g00792446 |
Motor Head (2) Gauge port (service) (4) Gauge port (stroking pressure) (5) Line relief valves (6) External supply port (7) Brake valve (8) Check and relief valve (9) Shuttle valve (10) Brake pilot valve (11) Port (pump oil) (14) Port (pump oil) (15) Gauge port (service) (29) Passage (30) Passage (31) Passage (32) Passage (33) Passage (34) Spring (35) Spring (36) Throttle pin (37) Poppet (38) Throttle pin (39) Piston (40) Spring (41) Spring (42) Poppet (43) Spring (44) Poppet (45) Spring (46) Passage (47) Poppet (48) Passage | |
The motor head consists of brake valve (7), crossover relief valves (5), check and relief valves (8), shuttle valve (9) and brake pilot valve (10). The motor head is bolted to the travel motor. The motor head has the following four functions.
- The motor head prevents a shock load when travel is stopped.
- The motor head prevents overspeed while the machine is travelling down a slope.
- The motor head prevents cavitation.
- The motor head routes a portion of the oil to the travel parking brake in order to release the brake.
During forward travel operation, pump oil is supplied to port (11) from the travel control valve on the main implement valve. The oil flows through an internal passage to check and relief valve (8). A portion of the oil flows to shuttle valve (9). The oil then flows to brake pilot valve (10). Brake pilot valve (10) directs oil to the parking brake. The parking brake is released before the oil from the pump reaches the travel motor.
The oil flows through a passage in poppet (47) of check and relief valve (8). The oil pressure overcomes the force of spring (41). Poppet (44) opens allowing oil to flow through passage (46). The oil flows from passage (46) to passage (32) and passage (31). The oil that flows through passage (32) is directed to rotary group (1) of the travel motor.
At the same time, oil flows to brake valve (7) from passage (46). Brake valve (7) consists of the following components: spring (34), spring (35), throttle pin (36), throttle pin (38) and piston (39) .
Oil flows through a passage in piston (39) through throttle pin (38) to the spring chamber. Oil fills the spring chamber of brake valve (7). This forces piston (39) to shift to the right. Piston (39) overcomes the force of spring (35). Passage (30) and passage (33) opens to passage (48) .
Return oil from rotary group (1) flows through passage (33) to passage (48). The oil in passage (48) overcomes the force of spring (43). Poppet (37) opens allowing return oil to flow through a passage to port (14). The return oil flows from port (14) to the travel control valve. The oil then flows to the oil cooler, and then back to the hydraulic tank.
When the machine stops, the travel control valve blocks the flow of oil to port (11). The force of spring (41) moves poppet (44). Poppet (44) closes blocking passage (46). The oil in the spring chamber of brake valve (7) flows through throttle pin (38). The oil pressure in the spring chamber gradually decreases. This allows spring (35) to shift piston (39) to the left. Passage (30) and passage (33) close. Return oil from the travel motor is blocked and the rotation of the travel motor stops. Spring (43) closes poppet (37) .
When the direction of travel is reversed, pump oil flows to port (14). The return oil flows through port (11). During reverse travel, the motor head operates in the same manner as the forward travel operation.