Power plants – Pressure fluid source and motor – Condition responsive control of or by input to input pump...
Patent
1988-05-31
1990-07-24
Look, Edward K.
Power plants
Pressure fluid source and motor
Condition responsive control of or by input to input pump...
60433, 60434, 91461, F16D 3102
Patent
active
049427377
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a drive control system for hydraulic construction machines such, as for example, a hydraulic excavator, a wheel loader and the like and, more particularly, to a drive control system for a hydraulic construction machine, which comprises a prime mover and a hydraulic pump driven thereby.
BACKGROUND ART
In general, a conventional drive control system for a hydraulic construction machine comprises a prime mover, a hydraulic pump driven by the prime over, a hydraulic actuator driven by discharge hydraulic fluid from the hydraulic pump, rotational speed setting means including a fuel lever for setting rotational speed of the prime mover, and an operating lever for controlling operation of the hydraulic actuator. Connected between the hydraulic pump and the hydraulic actuator is a control valve for controlling flow rate and direction of the discharge hydraulic fluid from the hydraulic pump. Operation of the operating lever controls the position of the control valve to control operation of the hydraulic actuator.
In the above conventional system, rotational speed of the prime mover or an engine is set by displacement of the fuel lever, to vary a horsepower characteristic of the engine in accordance with the set rotational speed. The maximum horsepower of the engine is determined on the basis of the horsepower characteristic. Specific fuel consumption (g/PS.h) of the engine is determined depending upon the set rotational speed and the magnitude of an operational load at that time. If, for example, the rotational speed is set to the maximum value, the specific fuel consumption is brought to the best value, at the heavy load operation in the vicinity of the maximum horsepower of the horsepower characteristic obtained by the set rotational speed. On the other hand, at the light load operation which requires only horsepower lower than the maximum horsepower, the engine rotational speed increases to a value higher than the rotational speed at the maximum horsepower of the horsepower characteristic, so that the specific fuel consumption is deteriorated. In general, at the actual operation of the hydraulic excavator, for example, the proportion of the operation which is carried out under the load excellent in the specific fuel consumption is extremely low. For example, in one operational cycle including excavating, boom raising-swing, dumping and boom lowering swing which are repeated in the mentioned order, the operations necessitating the above-mentioned maximum horsepower are only the relief excavating during the operation and the operation at acceleration at the initial stage of the swing during the operation Thus, it is not preferable from the energy-saving point of view to set the rotational speed to the maximum value.
In the drive control system of the kind referred to above, Japanese Patent Application Laid-Open No. 52-53189 has proposed an arrangement in which not only is the rotational speed of the engine set by the fuel lever, but also the engine rotational speed is interlocked with the operating lever for controlling operation of the hydraulic actuator in such a manner that when the operating lever is operated, the engine rotational speed is set also by displacement of the operating lever, to vary the horsepower characteristic, thereby controlling the maximum horsepower. With this arrangement, when displacement of the operating lever is small, the engine rotational speed is set to a low value to give the maximum horsepower required for the light load operation, while as the displacement increases, the engine rotational speed is set to a high value to raise also the maximum horsepower of the engine so as to give the maximum horsepower required for the heavy load operation. Thus, the operation is carried out always in a region excellent in the specific fuel consumption, thereby preventing deterioration of the specific fuel consumption. Further, in a similar drive control system, Japanese Patent Application Laid-Open No. 58-204940 has proposed an arrangement in
REFERENCES:
patent: 3943715 (1976-03-01), Miyao et al.
patent: 4102132 (1978-07-01), Palmer
patent: 4124095 (1978-11-01), Ezure
patent: 4373850 (1983-02-01), Durham
patent: 4400939 (1983-08-01), Moranduzzo et al.
patent: 4738104 (1988-04-01), Hahmann et al.
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
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