Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1989-11-13
1992-01-28
Look, Edward K.
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
60452, 91517, 91531, 91444, 91448, 13759614, F16D 3102
Patent
active
050834304
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic driving circuit for a hydraulic machine equipped with a plurality of hydraulic actuators, such as a hydraulic excavator, a hydraulic crane or the like and, more particularly, to a hydraulic driving apparatus for controlling flow rate of hydraulic fluid supplied to a plurality of hydraulic actuators respectively by pressure-compensated flow control valves, while controlling discharge rate of a hydraulic pump in such a manner that discharge pressure of the hydraulic pump is raised more than the maximum load pressure of the hydraulic actuators by a predetermined value.
BACKGROUND ART
In recent years, in a hydraulic driving apparatus for a hydraulic machine equipped with a plurality of hydraulic actuators, such as a hydraulic excavator, a hydraulic crane or the like, a variable displacement type hydraulic pump has included a load-sensing control as disclosed in DE-A1-3422165 (corres. to JP-A-60-11706). The load sensing control controls the discharge rate of the hydraulic pump in such a manner that discharge pressure of the hydraulic pump is raised more than maximum load pressure of the plurality of hydraulic actuators by a predetermined value. In this case, pressure compensating valves are arranged respectively in meter-in circuits for the hydraulic actuators, and the flow rate of hydraulic fluid supplied to the hydraulic actuators is controlled by flow control valves equipped respectively with the pressure compensating valves. By doing so, the discharge rate of the hydraulic pump increases and decreases depending upon the requisite flow rates for the hydraulic actuators, so that economical running is made possible. In addition, by the pressure compensating valves, in sole operation, precise flow control is made possible without being influenced by load pressure of the operated actuator, while, in combined operation, smooth combined operation is made possible without being influenced by the mutual load pressures, in spite of the fact that the hydraulic actuators are connected in parallel relation to each other.
In this hydraulic driving apparatus, there is the following problem peculiar to the load sensing control.
The discharge rate of the hydraulic pump is determined by the displacement volume or, in the case of a swash plate type, by the product of an amount of inclination and rotational speed of the swash plate such that the discharge rate increases in proportion to an increase in the amount of the inclination. In this amount of inclination of the swash plate, there is a maximum amount of inclination as a limit value which is determined from the constructional point of view. The discharge rate of the hydraulic pump is maximized at the maximum amount of inclination. Further, driving of the hydraulic pump is effected by a prime mover. When input torque to the hydraulic pump exceeds output torque from the prime mover, rotational speed of the prime mover starts to decrease and, in the worst case, the prime mover reaches stall. In order to avoid this, input-torque limiting control is carried out in which a maximum value of the amount of inclination of the swash plate is so limited that the input torque to the hydraulic pump does not exceed the output torque from the prime mover, to control the discharge rate.
As described above, there is the maximum-limit discharge flow rate in the hydraulic pump. Accordingly, at the combined operation of the plurality of hydraulic actuators, when the sum of the requisite flow rates for the plurality of hydraulic actuators commanded by their respective operating levers is brought to a value higher than the maximum-limit discharge flow rate of the hydraulic pump, it is made impossible to increase the discharge rate of the hydraulic pump to the requisite flow rate by the load sensing control, so that an insufficient state of the discharge rate with respect to the requisite flow rate occurs. In the present specification, the hydraulic pump is thus said to be saturated when the hydraulic pump is saturated in this mann
REFERENCES:
patent: 4020867 (1977-05-01), Sumiyoshi
patent: 4129987 (1978-12-01), Blume
patent: 4425759 (1984-01-01), Krusche
patent: 4535809 (1985-08-01), Andersson
patent: 4617854 (1986-10-01), Kropp
patent: 4662601 (1987-05-01), Andersson
patent: 4769991 (1988-09-01), Johnson
patent: 4884402 (1989-12-01), Strenzke et al.
patent: 4938022 (1990-07-01), Hirata et al.
patent: 4945723 (1990-08-01), Izumi et al.
patent: 4967557 (1990-11-01), Izumi et al.
Hirata Toichi
Nozawa Yusaku
Sugiyama Genroku
Tanaka Hideaki
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Mattingly Todd
LandOfFree
Hydraulic driving apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydraulic driving apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydraulic driving apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1853407