Small Displacement Change Operation
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| Illustration 1 | g02176067 |
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Small displacement change operation (HIGH SPEED MODE) (1) Passage (2) Piston chamber (3) Piston (4) Passage (oil flow from the main pumps) (5) Passage (return oil) (6) Body (7) Fitting (8) Displacement change valve (9) Port (pilot system oil pressure) (10) Spool (11) Spring (12) Swashplate (13) Port (supply oil or return oil) (14) Check valve (15) Check valve (16) Port (supply oil or return oil) | |
When the travel speed control switch on the keypad is pushed and the rabbit appears on the display, the machine is in HIGH SPEED MODE. In this condition, an input signal from the travel speed control switch is sent to the machine ECM. The pressure sensor for the pump delivery also provides an input signal to the machine ECM. When the travel load is light and when the pump delivery pressure is below a certain level, the output signal from the pressure sensor for the pump delivery is below a certain level. When the pump delivery pressure is below a certain level, the machine ECM energizes the travel speed solenoid. When the travel speed solenoid is energized, pilot system oil flows into pilot port (9) of displacement change valve (8). Spool (10) shifts to the left against the force of spring (11) until the spool contacts body (6). Main pump oil flows from passage (16) of the travel motor through check valve (15). The main pump oil then flows through passages (4) and passage (1) to piston chamber (2). The oil in piston chamber (2) moves piston (3) against swashplate (12). As a result, the angle of swashplate (12) is decreased and the motor displacement is decreased. The travel speed is maximum in this condition.
Large Displacement Change Operation
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| Illustration 2 | g02176109 |
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Large displacement change operation (LOW SPEED MODE) (1) Passage (2) Piston chamber (3) Piston (4) Passage (oil flow from the main pumps) (5) Passage (return oil) (6) Body (7) Fitting (8) Displacement change valve (9) Port (pilot system oil pressure) (10) Spool (11) Spring (12) Swashplate (13) Port (supply oil or return oil) (14) Check valve (15) Check valve (16) Port (supply oil or return oil) | |
When the angle of swashplate (12) in the travel motor increases, the displacement of the travel motor increases. The angle of swashplate (12) in the travel motor will increase and the travel speed will decrease during the following two conditions.
- The angle of swashplate (12) in the travel motor will increase and the travel speed will decrease when an increase in pump pressure occurs.
When the machine is in HIGH SPEED MODE and the pump delivery pressure increases above a certain level, the machine ECM de-energizes the travel speed solenoid. When the travel speed solenoid is de-energized, pilot system oil stops flowing into pilot port (9) of displacement change valve (8). Spool (10) shifts to the right by the force of spring (11) until the spool contacts fitting (7). Main pump oil flow from passage (16), check valve (15), and passage (4) is blocked by spool (10).
The force of swashplate (12) moves piston (3) to the left. The oil in piston chamber (2) now flows through passages (1) and (5) to the hydraulic tank. Swashplate (12) rotates counterclockwise. The angle of swashplate (12) is increased by the counterclockwise rotation. The displacement of the travel motor increases and the travel speed decreases.
- The angle of swashplate (12) in the travel motor will increase and the travel speed will decrease when the travel speed control switch is pushed in order to obtain LOW SPEED MODE.
When the travel speed control switch on the keypad is pushed and the tortoise appears on the display, the machine is in LOW SPEED MODE. In this condition, an input signal from the travel speed control switch is sent to the machine ECM. The machine ECM de-energizes the travel speed solenoid. The angle of swashplate (12) increases and the displacement of the travel motor increases. The travel speed decreases.