The present invention relates to a hydraulic circuit control system for a construction machine in which an operating system of the construction machine, particularly a control lever device, comprises a joystick device of the type generating an electrical operational signal (electric signal) depending on an input amount upon shift of a control lever, and a flow control valve is controlled with the operational signal for controlling the operation of an actuator.
In recent construction machines, particularly in those machines that are employed for various kinds of works because of convenience in use as represented by hydraulic excavators, operability has become increasingly valued in making the machines adaptable for a variety of usages. Stated otherwise, taking a hydraulic excavator as an example, the machine must be able to operate a working device as intended by an operator over a wide range from work in which primary importance is put on the amount of work carried out by the machine, e.g., excavation, to work in which fine adjustment is required in operation, e.g., leveling. To that end, it has been proposed to employ a hydraulic circuit control system in which a control lever device comprises an electric joystick for generating an electrical operational signal depending on an input amount upon shift a control lever, and the operational signal is electrically processed to control a flow control valve with a processed signal. Several known examples of such a control system are as follows.
(1) Japanese Patent No. 2509311 entitled xe2x80x9cWorking Device Control Method for Construction Machinexe2x80x9d
This publication discloses a working device control method for a construction machine comprising a hydraulic control valve (operational valve), which is operated through a controller upon manipulation of an electrical lever, and a pump varying device. Modulation control is performed to absorb shocks caused upon operation of the operational valve and the pump varying device by setting a modulation pattern for rise/fall of a circuit pressure and increase/decrease of a pump delivery rate upon operation of the operational valve to restrict a maximum operating speed of the operational valve (maximum change rate of an operational signal) so that a rate of the rise/fall of the circuit pressure and increase/decrease of the pump delivery rate is gradually changed in multiple stages with a working time, and by operating the operational valve and the pump varying device so as not to move faster than the speeds set by the modulation pattern when the circuit pressure rises and falls at a constant rate with a working time. Furthermore, a cavitation is prevented from occurring upon operation of the pump varying device. This publication also discloses that a plurality of modulation patterns for the operational valve are prepared and one of the patterns is set depending on the working condition automatically or manually with selection by an operator.
(2) JP,B 7-107279 entitled xe2x80x9cWorking Device Control Method for Construction Machinexe2x80x9d
This publication discloses an improvement of the modulation control in the above-mentioned (1). At the time when an electrical lever is manipulated from a shift position on the side in one direction toward the side in an opposite direction in a continuous manner and an operational signal from the electrical lever enters the opposite direction side beyond a dead zone corresponding to a neutral position, the modulation pattern having been effective so far is released and another modulation pattern for the opposite direction side is made effective. The operation of a working device and an operating feeling in the lever-reversed operation are thereby matched with each other.
(3) JP,A 10-37247 entitled xe2x80x9cOperation Control Device and Operation Control methodxe2x80x9d
This publication discloses a hydraulic circuit controller for controlling the operation of a working device of a construction machine through a flow control valve, wherein a maximum change rate of an operational signal for the flow control valve is restrained to be not larger than a setting value, and the operation of the working device is controlled by changing the setting value depending on an input amount upon shift of a control lever.
Meanwhile, there is also known a hydraulic circuit control system in which an actuator speed is controlled by controlling a delivery rate of a hydraulic pump with an operational signal instead of controlling a flow control valve with the operational signal, and a maximum operating speed of a pump displacement varying mechanism is restrained. Several examples of such a hydraulic circuit control system are as follows.
(4) JP,B 62-13542 entitled xe2x80x9cController for Hydraulic Circuitxe2x80x9d
This publication discloses a hydraulic circuit controller for a closed circuit system wherein an actuator speed is controlled to a speed instructed by an operating device by controlling a delivery rate of a hydraulic pump (position of a pump displacement varying mechanism). When an operating speed of the pump displacement varying mechanism is restrained to be not larger a setting maximum speed, the setting maximum speed is changed depending on an input amount upon shift of a control lever, thereby controlling acceleration/deceleration of an actuator.
(5) JP,B 62-39295 entitled xe2x80x9cControl System for Hydraulic Circuit Apparatusxe2x80x9d
This publication discloses that the controller of the above-mentioned (4) is modified so as to detect a condition of the operating device (control lever) instructing the operation to be stopped or made in the reversed direction, and to set the setting maximum speed larger than that in acceleration.
The above-described prior art however has the following problems.
First problem: The setting value for restricting the maximum operating speed of the operational valve (flow control valve) (i.e., the maximum change rate of the operational signal) is not set corresponding to individual operating status, i.e., acceleration, deceleration/stop, and lever-reversed condition. Therefore, the operational valve cannot be always controlled at an optimum maximum change rate adapted for the operating status of a construction machine.
Second problem: In the lever-reversed operation, the dead zone in the vicinity of a neutral position of the flow control valve is not appropriately handled or not handled at all. When quickly reversing the control lever, therefore, the actuator undergoes a shock or stalls in the vicinity of the neutral position, causing the operator to feel a pause in the operation.
Third problem: Since the maximum change speed of the operational valve is just restrained to the fixed modulation pattern regardless of the input amount upon shift of the control lever, an appropriate acceleration/deceleration feeling corresponding to the lever shift amount cannot be provided.
More specifically, in Japanese Patent No. 2509311 and JP,B 7-107279, the modulation patterns are set for the maximum operating speed of the operational valve in acceleration and deceleration/stop, and in the lever-reversed operation, the maximum operating speed of the operational valve is restricted in accordance with the modulation pattern for deceleration/stop. However, the lever reversing is performed when it is required to quickly change the moving direction of the working device in the case of, e.g., dropping mud from a bucket, bumping a boom against a vertical surface, or avoiding a risk, and a rapid response is demanded until the working device changes the moving direction. Accordingly, restricting the maximum operating speed of the operational valve in the lever-reversed operation in accordance with the modulation pattern for deceleration/stop cannot be the as providing an optimum maximum operating speed for the lever-reversed operation, and hence cannot change the moving direction of the working device with a good response (first problem).
Also, according to JP,B 7-107279, as soon as the operational signal indicates a reversed direction, the modulation control performed so far is ceased and another modulation control adapted for the reversed direction is started for the purpose of improving response in the lever-reversed operation disclosed in Japanese Patent No. 2509311. Taking into account a delay in the operation of the actuator responsive to the operational signal, therefore, the actuator is brought into an uncontrolled state at the moment when the operating direction is changed, which leads to a possibility that a substantial shock may occur until the moving direction of the actuator is completely changed (second problem).
Further, in Japanese Patent No. 2509311 and JP,B 7-107279, because the modulation pattern is fixed and the maximum operating speed of the operational valve is always restricted to the fixed modulation pattern regardless of the input amount upon shift of the control lever, an appropriate acceleration/deceleration feeling corresponding to the lever shift amount cannot be provided (third problem). In the case of returning the control lever, for example, when the control lever is manipulated so as to operate the operational valve at a speed higher than that set by the modulation pattern, the maximum operating speed of the operational valve is determined by the fixed modulation pattern regardless of a manner in which the control lever is returned, and therefore cannot be adjusted.
In JP,A 10-37247, since the maximum operating speed of the operational valve is not set depending on the operating status of the construction machine, the operational valve cannot be controlled at an optimum maximum change rate adapted for the operating status (first problem), and an appropriate acceleration/deceleration feeling corresponding to the lever shift amount cannot be provided (third problem). Furthermore, no consideration is paid on how to handle the lever-reversed operation (second problem).
In JP,B 62-13542 and JP,B 62-39295, the position of the pump displacement varying mechanism is controlled in response to an instruction from the operating device to control the pump delivery rate, thereby controlling the actuator speed. That is to say, these are not intended to control the operation of the working device of the construction machine through the flow control valve. Also, in the system of JP,B 62-39295, a plurality of maximum change rates of the operational signal are set as a function of the operational signal. However, because a control target of the control lever is the pump displacement varying mechanism, no consideration is paid to the dead zone in the vicinity of the neutral position of the flow control valve. Accordingly, if the disclosed arrangement is applied to a hydraulic circuit control system for controlling an actuator speed through a flow control valve, the maximum change rate of an operational signal is restrained in a similar manner even when the flow control valve is within the dead zone in the vicinity of its neutral position, whereby an actuator stalls for a certain period of time, causing the operator to feel a pause in the operation (second problem).
A first object of the present invention is to provide a hydraulic circuit control system for a construction machine of the type controlling a flow control valve with an electrical operational signal to control the operation of an actuator, the control system being able to control the flow control valve at an optimum maximum change rate in any operating status of acceleration, deceleration/stop, and lever-reversed condition with resulting characteristics cited below:
(a) in acceleration/deceleration, the machine undergoes a less shock and an operator feels no delay in the operation even with the operator manipulating a control lever quickly;
(b) in moderate acceleration/deceleration, the actuator is moved as intended by the operator;
(c) in stop operation, the machine undergoes a less shock and the operator feels no delay in motion toward stop even with the operator manipulating the control lever quickly; and
(d) in quick lever reversing, the actuator can be rapidly reversed in motion.
A second object of the present invention is to provide a hydraulic circuit control system for a construction machine, which carries out, in addition to the above, proper processing for a dead zone in the vicinity of a neutral position of the flow control valve in the lever-reversed operation, whereby the machine undergoes a less shock and the operator feels neither a delay in the operation nor a pause in the operation in the vicinity of the neutral position when the control lever is quickly reversed.
A third object of the present invention is to provide a hydraulic circuit control system for a construction machine, which can give the operator an appropriate feeling in acceleration and deceleration corresponding to an input amount upon shift of the control lever.
(1) To achieve the above first object, the present invention provides a hydraulic circuit control system for a construction machine comprising a hydraulic actuator for driving a working device, a hydraulic pump driven by a prime mover and producing a pressurized hydraulic fluid, a flow control valve disposed between the hydraulic actuator and the hydraulic pump and controlling a flow rate of the hydraulic fluid, and operational signal generating means for generating an electrical operational signal to instruct a flow rate of the hydraulic fluid flowing through the flow control valve, the system computing a control signal while restraining a change rate of the operational signal to be kept not more than a preset maximum change rate, and controlling the flow control valve in accordance with the computed control signal, wherein the system comprises first determining means for determining the operating status of the construction machine based on the operational signal; and first processing means for setting therein an optimum maximum change rate of the control signal for the flow control valve beforehand for each operating status of the construction machine, determining an optimum maximum change rate adapted for the operating status of the construction machine at that time based on a determination result of the first determining means, and setting the determined optimum maximum change rate as a maximum change rate of the control signal for the flow control valve.
Thus, since the first determining means determines the operating status of the construction machine and first processing means determines an optimum maximum change rate adapted for the operating status of the construction machine at that time based on a determination result of the first determining means and then sets the determined optimum maximum change rate as a maximum change rate of the control signal for the flow control valve, the change rate of the control signal for controlling the flow rate through the flow control valve is restrained to be kept not more than the determined optimum maximum change rate. Therefore, the flow control valve can be controlled at the optimum maximum change rate in any operating status of acceleration, deceleration/stop, and lever-reversed condition with such resulting characteristics as (a) in acceleration/deceleration, the machine undergoes a less shock and an operator feels no delay in the operation even with the operator manipulating a control lever quickly; (b) in moderate acceleration/deceleration, the actuator is moved as intended by the operator; (c) in operation for stop, the machine undergoes a less shock and the operator feels no delay in the motion toward stop even with the operator manipulating the control lever quickly; and (d) in quick lever reversing, the actuator can be rapidly reversed in motion, whereby working efficiency and safety are improved.
(2) To achieve the above second object, according to the present invention, in the hydraulic circuit control system for a construction machine of the above-mentioned (1), the system further comprises second determining means for determining whether a value of the control signal for the flow control valve is within a neutral zone; and second processing means for computing the control signal in accordance with the operational signal when the value of the control signal for the flow control valve is within the neutral zone, instead of executing the processing to restrain the change rate of the control signal in accordance with the maximum change rate.
With those features, proper processing for a dead zone in the vicinity of the neutral position of the flow control valve is executed in the lever-reversed operation so that, when the control lever is quickly reversed, the machine undergoes a less shock and the operation can be performed without causing the operator to feel neither a delay in the operation nor a pause in the operation in the vicinity of the neutral position. As a result, operability in the lever-reversed operation is greatly improved.
(3) In the above-mentioned (1), preferably, the first determining means determines, based on a state of the operational signal, in which one of acceleration, deceleration/stop, and lever-reversed condition the operating status of the hydraulic excavator is, and the first processing means determines the optimum maximum change rate adapted for the operating status of the construction machine at that time based on the optimum maximum change rate of the control signal set beforehand for each operating status of acceleration, deceleration/stop, or lever-reversed condition.
With those features, as with the above-mentioned (1), the flow control valve can be controlled at the optimum maximum change rate in any operating status of acceleration, deceleration/stop, and lever-reversed condition.
(4) Also, in the above-mentioned (1) or (3), preferably, the first determining means determines the operating status of the construction machine based on the operational signal and a previously outputted control signal for the flow control valve.
With that feature, the first determining means can determine the operating status of the construction machine including acceleration, deceleration/stop, and lever-reversed condition.
(5) To achieve the above third object, according to the present invention, in any one of the above-mentioned (1), (3) and (4), the optimum maximum change rate of the control signal for the flow control valve is set beforehand as a function of the operational signal for each operating status of the construction machine, and the first processing means computes the optimum maximum change rate based on the function of the operational signal corresponding to the operating status determined by the first determining means and the operational signal at that time.
With those features, the optimum maximum change rate of the control signal is set depending the value of the operational signal, and hence an appropriate feeling in acceleration and deceleration corresponding to the input amount upon shift of the control lever can be provided.
(6) In any one of the above-mentioned (1), (3) and (4), preferably, the optimum maximum change rate of the control signal for the flow control valve is set beforehand as a function of the operational signal or a function of the previously outputted control signal for the flow control valve for each operating status of the construction machine, and the first processing means computes the optimum maximum change rate based on the function of the operational signal corresponding to the operating status determined by the first determining means or the function of the previously outputted control signal for the flow control valve and the operational signal at that time or the previously outputted control signal for the flow control valve.
With those features, the optimum maximum change rate of the control signal is set depending both the value of the operational signal and the previously outputted control signal, and hence an appropriate feeling in acceleration and deceleration corresponding to the input amount upon shift of the control lever can be provided.