Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Reexamination Certificate
1999-03-26
2001-02-06
Freay, Charles G. (Department: 3746)
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
C060S431000
Reexamination Certificate
active
06183210
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a torque control system for a hydraulic pump in hydraulic construction machines, and more particularly to a torque control system for a hydraulic pump in hydraulic construction machines such as hydraulic excavators in which a diesel engine is installed as a prime mover and hydraulic actuators are driven by a hydraulic fluid delivered from a hydraulic pump, which is rotatively driven by the engine, to carry out necessary work.
BACKGROUND ART
A hydraulic construction machine such as a hydraulic excavator, generally, includes a diesel engine as a prime mover and carries out necessary work by rotatively driving at least one variable displacement hydraulic pump by the engine and driving hydraulic actuators by a hydraulic fluid delivered from the hydraulic pump. The diesel engine is provided with input means such as an accelerator lever for instructing a target revolution speed, and an amount of injected fuel is controlled depending on the target revolution speed, whereby the revolution speed is controlled.
With respect to control of an engine and a hydraulic pump in such a hydraulic construction machine, JP, A, 62-8618, entitled “Control Method for Driving System Including Internal Combustion Engine and Hydraulic Pump”, proposes one control method. The proposed control method is an example of the so-called speed sensing control with which a difference between the target revolution speed and the actual engine revolution speed (i.e., a revolution speed deviation) is determined by a revolution speed sensor, and an input torque of the hydraulic pump is controlled using the revolution speed deviation.
The purpose of that control is to reduce the load torque (input torque) of the hydraulic pump and to prevent the engine from stalling, thereby enabling the engine output power to be effectively utilized, when the detected actual engine revolution speed is reduced relative to the target revolution speed.
DISCLOSURE OF THE INVENTION
Meanwhile, a lowering of the engine output power depends on environment around the engine. When engines are used in highland, for example, the engine output torque is reduced due to a lowering of the atmospheric pressure.
When the engine load is light, some point on a regulation curve of a fuel injection device (governor mechanism) becomes a matching point between the engine load and the output torque. Thus, regardless of a lowering of the engine output power depending on change of the environment, the engine revolution speed is given by a value which is a little higher than the target revolution speed and corresponds to some point on the regulation characteristic curve of the governor mechanism.
When the engine load increases, a matching point is established between the engine load and the output torque corresponding to the target revolution speed that is determined by an engine output torque characteristic specific to the engine. In the case of such a matching point being effective, if the engine output power lowers due to change of the environment, the above-mentioned speed sensing control is performed such that a suction torque of the hydraulic pump is reduced in accordance with a lowering of the engine revolution speed to establish a match at a point where the suction torque of the hydraulic pump and the engine output torque are equal to each other.
In the above prior art, therefore, if the engine output power lowers due to change of the environment under an increased engine load, the engine revolution speed is reduced to a large extent as the engine load changes from a light load to a high load. For example, where a hydraulic construction machine is a hydraulic excavator and excavation is to be carried out with the hydraulic excavator in high ground, the engine revolution speed is given by a value a little higher than the target revolution speed entered by an operator when a bucket is empty, but the engine revolution speed is greatly reduced when excavation of earth and sand is started.
This changes noise and vibration of a machine body attributable to the engine revolution speed, thus making the operator more fatigued.
It is an object of the present invention to provide a torque control system for a hydraulic pump in hydraulic construction machines which can suppress a reduction of the revolution speed of a prime mover at a high load even when an output power of the prime mover lowers due to change of the environment.
To achieve the above object, the constructions and associated features employed in the present invention are as follows.
(1) To achieve the above object, according to the present invention, in a torque control system for a hydraulic pump in a hydraulic construction machine comprising a prime mover, a variable displacement hydraulic pump driven by the prime mover, input means for instructing a target revolution speed of the prime mover, first detecting means for detecting an actual revolution speed of the prime mover, and speed sensing control means for calculating a deviation between the target revolution speed and the actual revolution speed and controlling a maximum suction torque of the hydraulic pump in accordance with the calculated deviation, the torque control system includes second detecting means for detecting status variables relating to the environment of the prime mover, and torque modifying means for, in accordance with values detected by the second detecting means, modifying the maximum suction torque of the hydraulic pump to be controlled by the speed sensing control means.
Here, the status variables relating to the environment of the prime mover and detected by the second detecting means may include a cooling water temperature, an intake temperature, an engine oil temperature, an exhaust temperature, an atmospheric pressure, intake pressure, exhaust pressure and so on.
By detecting the status variables relating to the environment of the prime mover by the second detecting means and modifying the maximum suction torque of the hydraulic pump in accordance with the detected values by the torque modifying means, the maximum suction torque of the hydraulic pump can be reduced beforehand in an amount by which the output power of the prime mover lowers due to change of the environment. Accordingly, even when the output power of the prime mover lowers due to change of the environment, the revolution speed of the prime mover at a maximum torque matching point is not reduced to a large extent, and satisfactory working efficiency can be ensured with a small reduction in the revolution speed of the prime mover.
(2) In the above (1), preferably, the speed sensing control means comprises means for calculating a target maximum suction torque of the hydraulic pump based on the target revolution speed and the revolution speed deviation, and means for limitingly controlling a maximum displacement of the hydraulic pump in accordance with the target maximum suction torque, and the torque modifying means modifies the target maximum suction torque in accordance with the values detected by the second detecting means.
By so modifying the target maximum suction torque, the maximum suction torque of the hydraulic pump can be modified.
(3) In the above (1), preferably, the torque modifying means comprises means for, for each of the status variables relating to the environment of the prime mover, determining an output power change of the prime mover corresponding to the detected value of the instantaneous status variable from a preset relationship between the status variable and the output power change, and means for modifying the maximum suction torque of the hydraulic pump in accordance with the output power change.
With this feature, the torque modifying means can estimate an amount by which the output power of the prime mover lowers due to change of the environment, and the maximum suction torque of the hydraulic pump can be reduced in accordance with the estimated value.
(4) In the above (3), preferably, the torque modifying means further comprises means for determining a modification value correspon
Freay Charles G.
Hitachi Construction Machinery Co. Ltd.
Mattingly, Stanger & Malur
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