Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1992-07-16
1994-07-26
Look, Edward K.
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
60452, F16D 3102
Patent
active
053318129
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a traveling speed changeover device for a hydraulic excavator and, more particularly, to a traveling speed changeover device for a hydraulic excavator capable of changing the traveling speed over three or more stages to provide an optimum traveling speed according to the condition of the work while improving the simultaneous operation characteristic during fine control of the working machine.
BACKGROUND ART
Conventionally, the traveling speed of a hydraulic excavator is controlled by supplying hydraulic pressure from a hydraulic pump 51 to left and right traveling motors motor 54a, 54b via a swivel joint 53, after controlling the hydraulic pressure by left and right travel operation valves 52a, 52b, as shown in FIG. 3. When a traveling speed changeover switch 55 is set to a first stage travelling speed, the solenoid of a control pressure changeover valve 56 is de-energized so that the control pressure changeover valve 56 is set to a position a. Therefore, pilot cylinders 59a, 59b of the traveling speed changeover valves 58a, 58b for the left and right traveling motors 54a, 54b are connected to a tank 66 via the swivel joint 53 and the control pressure changeover valve 56, so that the traveling speed changeover valves 58a, 58b also are set to their position a. Consequently, traveling motor capacity control cylinders 60a, 60b are connected to the tank 66, so that the capacities of the left and right traveling motors 54a, 54b are increased to a value corresponding to the first stage of the traveling speed.
Subsequently, a traveling operation lever (not shown) is operated to set the traveling operation valves 52a, 52b to their position a, so that the hydraulic oil discharged from the hydraulic pump 51 is supplied to the left and right traveling motors 54a, 54b through associated driving lines 61a, 61b, and is discharged from the left and right traveling motors 54a, 54b into discharge lines 62a, 62b. In this state, counterbalance valves 63a, 63b have been set to their position a by the operating hydraulic pressure existing in the driving lines 61a, 61b, so that the oil discharged to the discharge lines 62a, 62b is returned to the tank 66 via a return line (not shown, past the counterbalance valves 63a, 63b, swivel joint 53 and the running operation valves 52a, 52b. Therefore, the left and right traveling motors 54a, 54b, which have been set to first stage traveling speed, are operated at a speed corresponding to the amount of operation of the above-mentioned traveling operation lever, whereby the excavator travels forward or backward at the corresponding speed. The positions a of the travel operation valves 52a, 52b are assumed to correspond to the forward traveling of the excavator. Thus, the positions b of the same correspond to backward traveling. The operation for the backward traveling is not described because it is substantially the same as that for the forward traveling. Numeral 64 designates a load sensing valve which has a first pilot chamber 64b for receiving oil discharged from the hydraulic pump 51 and a second pilot chamber 64c for receiving the higher one of the load pressures existing in the driving lines 61a, 61b of the traveling motors 54a, 54b, via the traveling operation valves 52a, 52b and check valves 65a, 65b. The discharge pressure of the hydraulic pump 51 is so reduced as to maintain a balance of force and counter force produced by the pressures in the first and second pilot chambers 64b and 64c and the force produced by a spring 64a, thereby controlling the capacity control cylinder 51a of the hydraulic pump 51. That is, a pressure differential corresponding to the force of the spring 64a always exists across each travel operation valve 52a, 52b, so that the rate of discharge of oil from the hydraulic pump 51 is increased and decreased in accordance with the amounts of operation of the travel operation valves 52a, 52b.
For attaining the second speed stage, the traveling speed changeover switch 55 is set to the second stage traveling s
REFERENCES:
patent: 3203165 (1965-08-01), Parr
patent: 5085051 (1992-02-01), Hirata
Kabushiki Kaisha Komatsu Seisakusho
Look Edward K.
Lopez F. Daniel
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