Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1995-09-21
1997-05-20
Lopez, F. Daniel
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
60449, 60452, F16D 3102
Patent
active
056303173
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a controller for a hydraulic drive machine including construction machines such as hydraulic shovels, and relates in particular to a controller that makes it possible to vary an amount of change in a drive velocity of a work machine actuator per fixed amount of operation of the operation amount of a flow rate operation valve according to operating conditions of the hydraulic drive machine.
BACKGROUND ART
Conventionally, control techniques for varying a differential pressure between a load pressure of work machine actuators and a discharge pressure of a hydraulic pump according to an externally designated work mode indicating a type of work in order to obtain an operability for operation levers that corresponds to the nature of the work of a construction machine have been disclosed in, for example, Japanese Patent Application Laid-Open No. 2-76904.
With this publicly disclosed technology, it is possible, when the work mode is varied from "normal work" mode to "micro operation" mode, to perform finer work suitable for the "micro operation" mode by making the aforementioned differential pressure smaller than in the case of the "normal work," and by making the change in the drive velocity of the work machine actuators per fixed amount of operation of the operation levers smaller than in the case of the "normal work."
Japanese Patent Application Laid-Open No. 2-164941 also discloses this type of control system, and involves effecting control such that the aforementioned differential pressure is reduced in accordance with a reduction in the rotational speed of the engine, thereby increasing the so-called metering region, which decreases as the engine rotational speed decreases (or, to put it another way, decreases the dead band that increases as the rotational speed decreases), and thus improving the operability of the operation levers.
In this way, these conventional techniques are control methods that vary the differential pressure depending on the work mode or engine rotational speed, that thereby vary the relationship (hereafter referred to as the "operating characteristics") between the work machine actuator velocity and the operation amounts of the operation levers, and that consequently improve the operability of the operation levers; these conventional techniques, however, only involve a one-to-one correspondence between the change in the differential pressure and the work mode or engine rotational speed, and do not involve controlling the correlation with the actual load on the work machine actuators.
However, hydraulic shovels and the like are generally equipped with a device that effects equivalent horsepower control or the like so that the absorbing torque of a hydraulic pump is matched with the engine output torque (see FIG. 7(c)), and that controls the discharge quantity of the hydraulic pump according to the so-called PQ curve of FIG. 7(b) so that the absorbing torque value at this matching point is obtained. Such devices are well-known devices which are constructed with, for example, a TVC valve as a main component.
However, when control is effected in this way so that the torque is kept at or below a certain value, then when the hydraulic pump discharge pressure Pp, that is, the load on the work machine actuators, is high, the hydraulic pump quantity of discharge Qp is low, as shown by the P2 (>P1) of FIG. 7(b). For this reason, as shown in FIG. 7(a), compared to when the load pressure Pp is, on the contrary, low, at P1, when the load pressure Pp is high, at P2, the work machine drive velocity v is affected by the low quantity of discharge Qp, and is kept low, as shown by the break line, and the dead band increases and lever operation is greatly degraded.
With the conventional techniques, moreover, controlling the differential pressure according to the work mode does not involve effecting control according to the actual work machine drive state pertaining to the work machine. Specifically, when there are a plurality of work machines, the op
REFERENCES:
patent: 4116587 (1978-09-01), Liesener
patent: 4139987 (1979-02-01), Budzich
patent: 5077975 (1992-01-01), Kauss
patent: 5085051 (1992-02-01), Hirata
patent: 5267440 (1993-12-01), Nakamura et al.
patent: 5285642 (1994-02-01), Watanabe et al.
PCT Publication No. WO 92/06306 published Apr. 16, 1992 (Abstract).
Akushichi Shuki
Nakayama Tetsuya
Takamura Fujitoshi
Kabushiki Kaisha Komatsu Seisakusho
Lopez F. Daniel
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