JP2000291074A - Hydraulic drive unit for construction machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the frequency with which each portion of hydraulic equipment included in a hydraulic circuit provided for the hydraulic drive unit is exposed to high pressure. SOLUTION: There is provided a hydraulic drive unit which comprises a variable relief valve 2 for defining discharging pressure of a main hydraulic pump 1, a solenoid valve 12 which can vary relief pressure of the variable relief valve 2, a pressure sensor 9 for detecting pilot pressure applied to a boom flow rate control valve 5, a pressure sensor 10 for detecting pilot pressure applied to an arm flow rate control valve 6, and a control device 13 which can output a control signal Y for actuating the solenoid valve 12 so as to increase the relief pressure in response to signals output from the pressure sensors 9, 10. The control device 13 includes a second signal generating block in which the relationship between a signal value of the pressure sensor 10 and a threshold value corresponding to a time limit for canceling the increase in the relief pressure is set, for outputting an off signal indicative of cancellation of the increase in the relief pressure when the signal value exceeds the threshold value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive device provided in a construction machine such as a hydraulic shovel, and more particularly to a variable relief valve for setting a relief pressure for defining a maximum discharge pressure of a main hydraulic pump. The present invention relates to a hydraulic drive device for a construction machine, comprising: a relief pressure changing unit capable of changing a relief pressure set by a variable relief valve.

[0002]

2. Description of the Related Art FIG. 8 is a hydraulic circuit diagram showing a first example of a conventional hydraulic drive device for construction equipment, and FIG. 9 is a block diagram showing a relief pressure boosting system provided in the first example shown in FIG. It is.

As shown in FIG. 8, a first example of the prior art includes a main hydraulic pump 31 and a variable relief valve 32 for setting a relief pressure for defining a maximum value of the discharge pressure of the main hydraulic pump 31. A relief pressure changing means that can change the relief pressure set by the variable relief valve 32, for example, an electromagnetic valve 41 is provided. The solenoid valve 41 is connected to the pilot hydraulic pump 40 and selectively supplies the pressure oil discharged from the pilot hydraulic pump 40 to the spring chamber of the variable relief valve 32, whereby the relief pressure of the variable relief valve 32 can be changed. It has become.

A plurality of hydraulic actuators driven by hydraulic oil discharged from the main hydraulic pump 31, such as a hydraulic cylinder 33, a hydraulic motor 34, etc., and a hydraulic pressure supplied from the main hydraulic pump 31 to each of the hydraulic actuators described above. A main control valve circuit 35 including a plurality of flow control valves for controlling the oil flow;
5, a plurality of operating means for controlling the operation of the flow control valve, for example, a hydraulic pilot valve 36, and an operating state detecting means for detecting whether these operating means are in an operating state, for example, the hydraulic pilot valve 36, etc. are operated. And a pressure switch 39 for outputting a pressure signal when it is pressed.

Further, a lever top switch 38 for outputting an on / off signal in response to a pressing operation is provided at a grip portion of the operation lever 37 of the hydraulic pilot valve 36. The signals output from the above-described pressure switch 39 and lever top switch 38 correspond to the AND circuit 43 shown in FIG.
Is input to a controller having a built-in controller, that is, the controller 42. As shown in FIG. 9, the controller 42 having the AND circuit 43 increases the relief pressure of the above-described variable relief valve 32 when signals from both the pressure switch 39 and the lever top switch 38 are input. A control signal Y for operating the electromagnetic valve 41 is output.

In the first example of the prior art, for example, when the hydraulic cylinder 33 and the like are operated by operating the hydraulic pilot valve 36 and the like to perform a desired operation,
When the lever top switch 38 is operated, as shown in FIG. 9, in a state where the signal value “1” is output from the pressure switch 39 in accordance with the operation of the hydraulic pilot valve 36 and the like, the signal value “ Since “1” is output, the control signal Y is output from the AND circuit 43 of the controller 42 to the solenoid valve 41. This allows
The solenoid valve 41 shown in FIG. 8 is switched to the upper position in FIG. 8, and the pilot pressure discharged from the hydraulic pilot pump 40 is supplied to the spring chamber of the variable relief valve 32. As a result, the variable relief valve 32 operates to increase the relief pressure. Therefore, the discharge pressure of the main hydraulic pump 31 is higher than before.

When the operation of the lever top switch 38 is released from such a state, that is, while the operation state of the hydraulic pilot valve 36 and the like is maintained, as shown in FIG. Becomes "0", so that the control signal Y is not output from the AND circuit 43. Accordingly, the solenoid valve 41 shown in FIG.
8 is switched to the lower position in FIG. 8 by the force of the spring, and the spring chamber of the variable relief valve 32 communicates with the tank via the solenoid valve 41. Thereby, the variable relief valve 32 in which the relief pressure is set high as described above operates to reduce the relief pressure. Accordingly, the discharge pressure of the main hydraulic pump 31 changes so as to be lower than in the above-described case.

A technique corresponding to the first conventional example shown in FIGS. 8 and 9 is disclosed in Japanese Patent Application Laid-Open No. Hei 8-60704.

FIG. 10 is a hydraulic circuit diagram showing a second example of a conventional hydraulic drive device for construction machinery, and FIG. 11 is a hydraulic circuit diagram of the second example shown in FIG.
FIG. 4 is a block diagram illustrating a configuration of a control device provided in the example of FIG.

The second conventional example also employs a main hydraulic pump 51
A variable relief valve 52 for setting a relief pressure that defines the maximum value of the discharge pressure of the main hydraulic pump 51; and a relief pressure changing means capable of changing the relief pressure set by the variable relief valve 52, such as an electromagnetic valve. 62.
The solenoid valve 62 is connected to the pilot hydraulic pump 61 and selectively supplies the pressure oil discharged from the pilot hydraulic pump 61 to the spring chamber of the variable relief valve 52, whereby the relief pressure of the variable relief valve 52 can be changed. It has become.

Also, a plurality of hydraulic actuators driven by hydraulic oil discharged from the main hydraulic pump 51, for example, a boom cylinder 53, an arm cylinder 54, etc., and a hydraulic pressure supplied from the main hydraulic pump 51 to each of the above-described hydraulic actuators. Boom flow control valve 5 for controlling oil flow
5. Flow control valve 56 for arm and flow control valve 5 for boom
5 is provided with a boom operating means, for example, a boom pilot valve 57, and an arm operating means for controlling the operation of the arm flow control valve 56, for example, an arm pilot valve 58. In addition, the boom pilot valve 5
7. Operation state detecting means for detecting whether the arm pilot valve 58 is in an operation state, for example, a boom pressure sensor 59 for detecting the operation amount of the boom pilot valve 57 and outputting a pressure signal Pa, and an arm pilot An arm pressure sensor 60 that detects the amount of operation of the valve 58 and outputs a pressure signal Pb.

Further, according to the pressure signal Pa output from the boom pressure sensor 59 and the pressure signal Pb output from the arm pressure sensor 60, the electromagnetic pressure is increased so as to increase the relief pressure of the variable relief valve 52 described above. A control device 63 for outputting a control signal Y for operating the valve 62 is provided. As shown in FIG. 11, the control device 63 controls the operation amount of the boom pilot valve 57, that is, the pressure sensor 59.
The relationship between the value of the pressure signal Pa output from and the threshold value PaO corresponding to the time period for executing the pressure increase of the relief pressure is set, and when the value of the pressure signal Pa exceeds the threshold value PaO, A boom signal generator 64 that outputs a pressure increase command signal, that is, an ON signal, and an operation amount of the arm pilot valve 58, that is, a pressure signal Pb that is output from the pressure sensor 60
And a threshold value PbO corresponding to a time period for executing the pressure increase of the relief pressure, and when the value of the pressure signal Pb exceeds the threshold value PbO, a pressure increase command signal, that is, an ON signal And a control for driving the above-described electromagnetic valve 62 when a pressure increase command signal is output from any of the boom signal generation unit 64 and the arm signal generation unit 65. And an OR circuit 66 for outputting a signal Y.

In this second conventional example, when only the boom pilot valve 57 is operated in order to perform a desired operation via the operation of the boom cylinder 53, for example,
The pilot pressure from the hydraulic pilot pump 51, which is output in accordance with the operation amount of the boom pilot valve 57, is given to any control unit of the boom flow control valve 55, whereby the boom flow control valve 55 is neutralized. The position is switched from the position to the operating position, and the pressure oil discharged from the main hydraulic pump 51 is supplied to the boom cylinder 53 via the boom flow control valve 55. As a result, the boom cylinder 53 operates, and a desired operation is performed.

At this time, the operation amount of the boom pilot valve 57 is detected by the boom pressure sensor 59, and the pressure signal Pa is input to the control device 63. As shown in FIG. 11, when the value of pressure signal Pa is in a range not exceeding threshold value PaO, a signal not instructing pressure increase, that is, an off signal, is output from boom signal generation section 64. Here, in this state, since the arm pilot valve 58 is not operated, the value of the pressure signal Pb output from the arm pressure sensor 60 is almost 0, and the threshold value of the arm signal generation unit 65 Does not lead to PbO and therefore
A signal that does not instruct pressure increase, that is, an off signal is also output from the arm signal generation unit 65. That is, since neither the boom signal generator 64 nor the arm signal generator 65 outputs a pressure increase command signal, the control signal Y is not output from the OR circuit 66 to the solenoid valve 62. In this case, the solenoid valve 62 is kept at the lower position in FIG. 10, and the spring chamber of the variable relief valve 52 communicates with the tank. Accordingly, the relief pressure of the variable relief valve 52 is set relatively low, the pressure discharged from the main hydraulic pump 51 becomes a relatively low pressure, and the pressurized oil of the pressure is supplied to the boom cylinder 53.

In such a state, the operation amount of the boom pilot valve 57 increases, and the boom pressure sensor 59
When the value of the pressure signal Pa output from the above exceeds the threshold value PaO of the boom signal generation unit 64 shown in FIG. 11 described above, the pressure increase command signal, that is, the ON signal is output from the boom signal generation unit 64. The OR circuit 66 outputs a control signal Y to the solenoid valve 62,
As described above, the relief pressure is increased.

A technique corresponding to the second conventional example shown in FIGS. 10 and 11 is disclosed in Japanese Patent Application Laid-Open No. Hei 9-184170.

[0017]

As an example of a construction machine to which the above-mentioned first and second examples of the prior art are applied, for example, a hydraulic shovel for carrying out a load operation, an excavation operation, and a leveling operation In consideration of this, among the work performed by this excavator, in general, the lifting work requires a particularly large power, so it is preferable to increase the pressure, and the normal excavation work for excavating earth and sand, that is, the hard ground, etc. Excavation work except heavy drilling work that requires large power to excavate
In the case of a light load leveling operation for leveling the ground, it is originally preferable not to increase the pressure. In addition, among the above-mentioned operations, the excavation operation is currently performed at a significantly higher frequency than other lifting operations or leveling operations.

For example, the first example shown in FIGS. 8 and 9 is applied to the hydraulic excavator in which the excavation work is easily performed, and the excavation work is performed by driving the hydraulic cylinder 33 and the like. In this case, when the operator operates the hydraulic pilot valve 36 or the like while pressing the lever top switch 38, the relief pressure set by the variable relief valve 32 increases as described above, and the pressure is increased. Therefore, while the excavation work is continued, the hydraulic cylinder 3
It is possible that the pressure of the pressure oil supplied to the third or the like becomes higher than necessary. In such a state, each part of the hydraulic circuit provided in the hydraulic shovel is constantly exposed to high pressure, which causes a problem that the durability of hydraulic equipment included in the hydraulic circuit is deteriorated. In this case, for example, during normal excavation work, the operator only needs to recognize that it is better not to press the lever top switch 38, but the lever top switch 38 can be easily pressed by the operator even in terms of layout. Is not a strong regulatory force. Therefore, in the first example described above,
The pressure is increased even during normal excavation work, and there is a great concern that the durability of hydraulic equipment included in the hydraulic circuit shown in FIGS.

Further, the above-described second example shown in FIGS. 10 and 11 is applied to the above-described hydraulic excavator, and the boom cylinder 5
3. When performing an excavation operation of earth and sand, that is, a normal excavation operation by performing a combined operation of the arm cylinder 54, it is common to increase the operation amounts of the boom pilot valve 57 and the arm pilot valve 58. Conceivable. However, when the operation amounts of the boom pilot valve 57 and the arm pilot valve 58 are increased, the value of the pressure signal Pa of the boom pressure sensor 59 exceeds the threshold value PaO shown in FIG. Pressure sensor 60
Of the pressure signal Pb exceeds the threshold value PbO shown in FIG. That is, the pressure increase command signal is supplied to the OR circuit 66 shown in FIG. 11, the control signal Y is supplied from the control device 63 to the electromagnetic valve 62, and the electromagnetic valve 62 is switched, and the variable relief valve 32 , The relief pressure set by the above becomes high, and the pressure increase is performed.

That is, in the second example, the pressure is constantly increased during the normal excavation work, and each part of the hydraulic circuit is continuously exposed to the high pressure. Therefore, even in the second example, there is a problem that the durability of the hydraulic equipment included in the hydraulic circuit provided in the hydraulic shovel is deteriorated from a different viewpoint from the first example described above.

The present invention has been made in view of the above-mentioned situation in the prior art, and a first object of the present invention is to provide a method of exposing each part of a hydraulic device included in a hydraulic circuit provided in the hydraulic drive device to a high pressure. It is an object of the present invention to provide a hydraulic drive device for a construction machine capable of reducing the load.

A second object of the present invention is to provide a hydraulic drive device for a construction machine capable of suppressing an increase in relief pressure during a digging operation which is frequently performed.

[0023]

In order to achieve the first object, an invention according to claim 1 of the present application is directed to a main hydraulic pump and a relief pressure for defining a maximum value of a discharge pressure of the main hydraulic pump. , A relief pressure changing means capable of changing a relief pressure set by the variable relief valve, a plurality of hydraulic actuators driven by pressure oil discharged from the main hydraulic pump, and A plurality of flow control valves for controlling the flow of pressure oil supplied from the pump to each of the hydraulic actuators; a plurality of operating means for controlling the operation of these flow control valves; and In a hydraulic drive device for a construction machine comprising a control device capable of outputting a control signal for operating the relief pressure changing means, a signal for suppressing an increase in the relief pressure, Serial are the configurations with increasing pressure suppression means capable of outputting the relief pressure change means.

According to the first aspect of the present invention, when the pressure increase suppressing means is operated in, for example, a normal excavation operation, the signal from the pressure increase suppressing means suppresses the increase in the relief pressure. Is output to the relief pressure changing means,
Thereby, the relief pressure changing means operates the variable relief valve so that the relief pressure becomes low. For this reason,
The maximum value of the discharge pressure of the main hydraulic pump is lower than that in the pressure increasing state, and the pressure oil having the reduced pressure is supplied from the main hydraulic pump to the corresponding hydraulic actuator via the corresponding flow control valve. . Since the frequency of such normal excavation work is generally high, in the invention according to claim 1, it is possible to reduce the frequency with which each part of the hydraulic equipment included in the hydraulic circuit provided in the hydraulic drive device is exposed to high pressure. .

In order to achieve the second object,
The invention according to claim 2 of the present application is characterized in that, in the invention according to claim 1, the pressure increase suppressing means outputs a signal for suppressing an increase in the relief pressure during excavation work. I have.

According to the second aspect of the present invention, since the pressure increase suppressing means operates during excavation work,
It is possible to suppress an increase in the relief pressure during the digging operation that is frequently performed.

According to a third aspect of the present invention, in accordance with the second aspect of the present invention, there is provided an operation state detecting means for detecting whether or not the operation means is in an operation state, and the control device comprises While operating the relief pressure changing means so as to increase the relief pressure in accordance with a signal output from the state detecting means, the pressure increase suppressing means is provided in the control device, and the operation state detecting means When the output signal is a signal corresponding to the excavation work, the pressure increase cancellation command means is capable of outputting a cancellation command signal for canceling the increase in the relief pressure.

According to the third aspect of the present invention, when the signal output from the operation state detecting means is a signal corresponding to the excavation work, the relief pressure canceling means of the control device transmits the relief pressure. A cancellation command signal for canceling the pressure increase state is output to the relief pressure changing means. Thereby, the relief pressure changing means operates the variable relief valve so that the relief pressure becomes low. Accordingly, the maximum value of the discharge pressure of the main hydraulic pump is lower than that in the above-described pressure increasing state, and the pressure oil having the reduced pressure is applied from the main hydraulic pump to the corresponding actuator via the corresponding flow control valve. Supplied. That is, during excavation work that is frequently performed, increase in the relief pressure can be suppressed.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the operation state detecting means includes:
The operation amount detection means for detecting the operation amount of the operation means, and the pressure increase cancellation command means of the control device cancels the operation amount detected by the operation amount detection means and the increase in the relief pressure. A relationship with a threshold value corresponding to the time limit is set, and when the manipulated variable exceeds the threshold value,
The signal generation unit outputs the cancellation command signal for canceling the increase in the relief pressure.

In the invention according to claim 4 configured as described above, the threshold value corresponding to the time period for canceling the increase in the relief pressure is set in advance in relation to the excavation work. Then, when the operation amount detected by the operation amount detection unit in accordance with the operation of the operation unit exceeds the threshold value of the signal generation unit, that is, when it is detected that the excavation operation is performed, the relief pressure is increased. Is output to the relief pressure changing means.

According to a fifth aspect of the present invention, in the fourth aspect of the invention, the plurality of hydraulic actuators include a boom cylinder and an arm cylinder, and the plurality of flow control valves are connected to the boom cylinder. A boom flow control valve for controlling the drive of the boom; and an arm flow control valve for controlling the drive of the arm cylinder, wherein the plurality of operating means control the operation of the boom flow control valve. And an operating means for an arm for controlling the operation of the flow control valve for the arm, wherein the operating state detecting means detects an operating amount of the operating means for the boom, and an operating amount detecting means for the boom; Arm operation amount detection means for detecting the operation amount of the operation means.

According to the fifth aspect of the present invention, when both the operating means for the boom and the operating means for the arm are operated during the excavation operation, the flow control valve for the boom and the flow control valve for the arm are operated. At the same time, the operation amounts of the boom operation means and the arm operation means are detected by the boom operation amount detection means and the arm operation amount detection means.
When the operation amount detected by the operation amount detection means for the boom and the operation amount detection means for the arm exceeds the threshold value of the signal generation unit, the cancellation command signal for canceling the relief pressure increase state is changed to the relief pressure change. Output to the means. Thereby, the relief pressure changing means operates the variable relief valve so that the relief pressure becomes low. Therefore, the maximum value of the discharge pressure of the main hydraulic pump is lower than in the pressure increasing state, and the pressure oil having the reduced pressure is supplied from the main hydraulic pump via the boom flow control valve and the arm flow control valve. It is supplied to the boom cylinder and the arm cylinder. Thus, the boom cylinder and the arm cylinder are driven at a relatively low pressure, and a desired excavation operation can be performed.

According to a sixth aspect of the present invention, in the invention according to the fifth aspect, the boom operation amount detecting means comprises a boom pressure sensor, and the arm operation amount detecting means comprises an arm operation amount detecting means. And a pressure sensor.

According to the sixth aspect of the present invention, the signal generator corresponds to the time period for canceling the increase in the relief pressure and the signal value of the boom pressure sensor, the signal value of the arm pressure sensor. The relationship with the threshold is set. During the excavation work, when the operating means for the boom and the operating means for the arm are operated, signals from the boom pressure sensor and the arm pressure sensor are read into the signal generation unit, and the boom pressure sensor and the arm pressure sensor are read. When the signal value exceeds the threshold value, a cancellation command signal for canceling the relief pressure increasing state as described above is output to the relief pressure changing means.

According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the pressure increasing means for outputting an instruction signal for increasing the relief pressure to the control device is provided. It is characterized by having.

In the invention according to claim 7 configured as described above, a desired pressure increase can be performed by operating the pressure increase instruction means, for example, when a situation requiring a temporary pressure increase occurs. At this time, a control signal is output from the control device to the relief pressure changing means in response to the instruction signal output from the pressure increasing instruction means, and the variable relief valve operates to increase the relief pressure. Accordingly, the discharge pressure of the main hydraulic pump becomes higher than that in a state where the pressure has not been increased, and the high-pressure oil is supplied to the corresponding actuator via the corresponding flow control valve, and the desired pressure increase is performed. The required work can be performed.

According to an eighth aspect of the present invention, in the invention according to the seventh aspect, the pressure increase instructing means comprises an on / off switch, and the instruction signal includes the on / off switch.
It is an on signal output from the off switch.

According to the sixth aspect of the present invention, when the on / off switch is operated, an ON signal is output, and a control signal is output from the control device to the relief pressure changing means in response to the ON signal. Thereby, the variable relief valve operates so as to increase the relief pressure.

According to a ninth aspect of the present invention, in the invention according to the seventh or eighth aspect, the control device includes a timer unit, and the timer unit is provided with a pressure increasing command signal corresponding to the instruction signal. And the time during which the pressure increase command signal is output is limited to a predetermined time.

According to the ninth aspect of the present invention, when the pressure increasing instruction means is operated, an instruction signal output from the pressure increasing instruction means is input to the timer section, and the pressure increasing instruction signal is transmitted from the timer section. Is output. The control device outputs a control signal to the relief pressure changing means according to the pressure increase command signal. Thereby, the variable relief valve operates so as to increase the relief pressure. When this state exceeds a predetermined time set by the timer unit, the output of the pressure increase command signal from the timer unit stops. Therefore, even if the operation of the pressure increasing instruction means is continued, the control signal from the control device is not output to the relief pressure changing means, and the variable relief valve operates so that the relief pressure becomes lower.

According to a tenth aspect of the present invention, in the invention of the seventh aspect, the pressure increase instructing means is selected according to the type of a work mode performed through the operation of the hydraulic actuator. A mode changeover switch capable of outputting the instruction signal.

In the invention according to claim 10 constructed as described above, the work mode includes, for example, an excavation work, a leveling work, a hanging load work, and the like. It is determined whether to output. For example, it is determined not to output an instruction signal to increase the relief pressure when the work mode of the smoothing work is selected by the mode change switch, and to increase the relief pressure when the work mode of the lifting work is selected. It is determined to output an instruction signal. In this case, when the mode changeover switch is operated and the leveling operation is selected, the control signal from the control device is not output to the relief pressure changing means, and the variable relief valve is
It operates so that the relief pressure becomes low.

When the mode changeover switch is operated to select the lifting operation, a control signal is output from the control device to the relief pressure changing means, whereby the variable relief valve operates to increase the relief pressure. .

Further, the invention according to claim 11 of the present application is characterized in that, in the invention according to any one of claims 1 to 10, the construction machine comprises a hydraulic shovel.

According to the eleventh aspect of the present invention, the work performed by the excavator includes a lifting work in which the pressure is preferably increased and an excavation work in which the pressure is preferably not increased. Applicable to

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic drive device for a construction machine according to the present invention will be described below with reference to the drawings. FIG. 1 is a hydraulic circuit diagram showing a first embodiment of a hydraulic drive device for a construction machine of the present invention, and FIG. 2 is a block diagram showing a configuration of a control device of the first embodiment shown in FIG. The first embodiment shown in FIG. 1 is provided, for example, in a hydraulic shovel, but has a configuration substantially the same as that shown in FIG. 8 described above except for the configuration of the control device.

That is, also in the first embodiment, the main hydraulic pump 1, the variable relief valve 2 for setting the relief pressure that defines the maximum value of the discharge pressure of the main hydraulic pump 1, and the variable relief valve 2 And a relief pressure changing means, for example, an electromagnetic valve 12, capable of changing the relief pressure to be performed.
The solenoid valve 12 is connected to the pilot hydraulic pump 11 and selectively supplies the pilot pressure discharged from the pilot hydraulic pump 11 to the spring chamber of the variable relief valve 2 so that the relief pressure of the variable relief valve 2 can be changed. It has become.

A plurality of hydraulic actuators driven by hydraulic oil discharged from the main hydraulic pump 1, for example, a boom cylinder 3, an arm cylinder 4, and a main hydraulic pump 1
Flow control valve 5 for controlling the flow of hydraulic oil supplied to each of boom cylinder 3 and arm cylinder 4 from boom, arm flow control valve 6, and boom operation for controlling the operation of boom flow control valve 5 There are provided means, for example, a boom pilot valve 7, and an arm operating means for controlling the operation of the arm flow control valve 6, for example, an arm pilot valve 8. Also, operating state detecting means for detecting whether the boom pilot valve 7 and the arm pilot valve 8 are in the operating state, for example, operating the boom flow control valve 5 so as to extend (boom up) the boom cylinder 3. The operation amount of the boom pilot valve 7 at the time is detected, and the boom pressure sensor 9 for outputting the pressure signal Pa and the arm flow control valve 6 for operating the arm cylinder 4 so as to extend the arm cylinder 4 (arm cloud). An arm pressure sensor 10 for detecting an operation amount of the arm pilot valve 8 and outputting a pressure signal Pb is provided.

Further, according to the pressure signal Pa output from the boom pressure sensor 9 and the pressure signal Pb output from the arm pressure sensor 10, the variable relief valve 2 described above is used.
And a control device 13 for outputting a control signal Y for operating the solenoid valve 12 so as to increase the relief pressure of the solenoid valve 12.

In the first embodiment, the control device 13 has the configuration shown in FIG. As shown in FIG. 2, the control device 13 corresponds to the operation amount of the boom pilot valve 7, that is, the value of the pressure signal Pa output from the pressure sensor 9 and the time period for executing the increase of the relief pressure. Threshold PA
O is set, and the value of the pressure signal Pa becomes the threshold value P
When the pressure exceeds AO, a first signal generation unit 14 that outputs a pressure increase command signal, that is, an ON signal, an operation amount of the arm pilot valve 8, that is, a value of the pressure signal Pb output from the pressure sensor 10, A relationship with a threshold value PBO corresponding to a time period for canceling the pressure increase is set, and when the value of the pressure signal Pb exceeds the threshold value PBO, a cancel command signal for canceling the pressure increase of the relief pressure, that is, OFF. A second signal generator 15 that outputs a signal.

The threshold value P of the first signal generator 14 described above
AO is set to a signal value of the pressure sensor 9 corresponding to an operation amount slightly larger than the operation amount of the boom pilot valve 7 which is empirically performed during a leveling operation, for example.
In addition, the threshold value PBO of the second signal
Is set to a signal value of the pressure sensor 10 corresponding to an operation amount slightly larger than an operation amount of the arm pilot valve 8 which is empirically performed at the time of a load operation, for example. At the time of excavation work, the operation amount of the boom pilot valve 7 and the arm pilot valve 8 increases, so that the signal value of the pressure sensor 9 corresponding to the operation amount of the boom pilot valve 7 also exceeds the threshold value PAO. Pressure sensor 1 corresponding to the amount of operation of the arm pilot valve 8.
It is empirically known that the signal value of 0 also becomes a large value exceeding the threshold value PBO. That is, the threshold value PAO of the first signal generation unit 14 and the threshold value PBO of the second signal generation unit 15 are determined by the operation performed by the operation of the boom pilot valve 7 and the arm pilot valve 8 by the excavation. It constitutes a detecting means for detecting the operation.

The above-mentioned second signal generation unit 15 is provided with a pressure increase suppression means capable of outputting a signal for suppressing the increase of the relief pressure to the solenoid valve 12, that is, the boom pressure sensor 9 and the arm pressure sensor 10 When the signal output from the operation state detecting means consisting of: is a signal corresponding to excavation work, the pressure increasing canceling instruction means capable of outputting an off signal which is a cancel instruction signal for canceling the increase in the relief pressure is constituted. ing.

The control device 13 shown in FIG. 2 includes an AND circuit 16 that outputs a drive signal when both of the first signal generator 14 and the second signal generator 15 output an ON signal.
And an output unit 17 for outputting a control signal Y for operating the electromagnetic valve 12 in accordance with the drive signal output from the AND circuit 16.

In the first embodiment configured as described above, for example, when the boom cylinder 3 and the arm cylinder 4 are contracted, the signals from the boom pressure sensor 9 and the arm pressure sensor 10 are output. not,
Therefore, an off signal is output from the first signal generation unit 14 to the AND circuit 16 shown in FIG. 2, no drive signal is output from the AND circuit 16, and no control signal Y is output from the output unit 17. In the case of the operation of extending only the arm cylinder 4, a signal is output from the pressure sensor 10 in accordance with the operation amount of the arm pilot valve 8, and the signal value is larger than the threshold value PBO of the second signal generation unit 15. When the value is small, the ON signal is output to the AND circuit 16, but the OFF signal is output to the AND circuit 16 from the first signal generator 14, so that the AND circuit 16 does not output a drive signal. Also, the control signal Y is not output from the output unit 17.

In such a case, the solenoid valve 1 shown in FIG.
2 is maintained at the lower position of FIG. 1, the spring chamber of the variable relief valve 12 communicates with the tank, and the relief pressure is maintained at a relatively low value. Therefore, the discharge pressure of the main hydraulic pump 1 becomes a relatively low pressure.

Further, for example, when carrying out the lifting work, if both the boom pilot valve 7 and the arm pilot valve 8 are operated to extend each of the boom cylinder 3 and the arm cylinder 4, the operation amount is as described above. As described above, it is empirically known that the operation amount is smaller than the operation amount in the excavation work. As a result, the value of the signal Pa output from the pressure sensor 9 exceeds the threshold value PAO of the first signal generation unit 14, and the value of the signal Pb output from the pressure sensor 10 is The threshold value PBO is maintained at a value that does not reach the threshold value PBO of 15. For this reason, the first signal generator 14,
The ON signal is output from both of the second signal generation units 15 to the AND circuit 1.
6 is output. The AND circuit 16 outputs a driving signal to the output unit 17 in response to the control signal Y.
Is output to the solenoid valve 12.

As a result, the solenoid valve 12 is switched to the upper position in FIG. 1, and the pilot pressure discharged from the pilot hydraulic pump 7 is changed via the solenoid valve 12 to the variable relief valve 2.
Of the spring chamber. As a result, the variable relief valve 2 operates to change the relief pressure to a higher value, that is, to increase the relief pressure, and accordingly, the discharge pressure of the main hydraulic pump 1 increases. The high discharge pressure hydraulic oil is supplied from the main hydraulic pump 1 to the boom cylinder 3 and the arm cylinder 4 via the boom flow control valve 5 and the arm flow control valve 6 to perform a desired lifting operation. Can be.

In the case of an operation of extending only the boom cylinder 3 (boom raising independent operation), the operation amount of the boom pilot valve 7 is large, and as a result, the pressure signal output from the pressure sensor 9 is increased. Also when the value of Pa exceeds the threshold value PAO of the first signal generation unit 14, an ON signal is output from both the first signal generation unit 14 and the second signal generation unit 15 to the AND circuit 16 as described above. Therefore, the relief pressure is increased, and the discharge pressure of the main hydraulic pump 1 is maintained at a high pressure.

Further, for example, when the boom pilot valve 7 and the arm are used when the boom is not operated, or at the most, only the fine operation is performed, and the ground is leveled mainly by operating the arm and the bucket. When both of the pilot valves 8 are operated to extend each of the boom cylinder 3 and the arm cylinder 4, the operation amount of the boom cylinder 3 is small, and therefore, the signal value detected by the pressure sensor 9 is small. At this time, the signal value does not reach the threshold value PAO of the first signal generator 14, and the first signal generator 14 outputs an off signal to the AND circuit 16. In this case, as in the case of the independent operation of the arm cylinder 4 described above, the drive signal is not output from the AND circuit 16, and the control signal Y is not output from the output unit 17 at this time as well.

Therefore, the solenoid valve 12 shown in FIG. 1 is maintained at the lower position in FIG. 1, the spring chamber of the variable relief valve 12 communicates with the tank, and the relief pressure is maintained at a relatively low value. As a result, the discharge pressure of the main hydraulic pump 1 becomes a relatively low pressure. The relatively low pressure oil is supplied from the main hydraulic pump 1 to the boom flow control valve 5 and the arm flow control valve 6.
And is supplied to the boom cylinder 3 and the arm cylinder 4 via the controller, so that a desired leveling operation can be performed.

In particular, when the boom cylinder 3 and the arm cylinder 4 are extended to perform the excavation work, if both the boom pilot valve 7 and the arm pilot valve 8 are largely operated, the large amount of operation is required. The signal values detected by the boom pressure sensor 9 and the arm pressure sensor 10 are also large. That is, the signal value output from the boom pressure sensor 9 exceeds the threshold value PAO of the first signal generation unit 14 shown in FIG. 2, and the signal value output from the arm pressure sensor 10 is
The value exceeds the threshold value PBO of the second signal generator 15 shown in FIG. For this reason, although an ON signal is output from the first signal generation unit 14, an OFF signal is output from the second signal generation unit 15 to the AND circuit 16. Therefore, the drive signal is not output from the AND circuit 16, and the control signal Y is not output from the output unit 17 also at this time.

In this case, as described above, the solenoid valve 12 shown in FIG. 1 is in the lower position, the relief pressure of the variable relief valve 12 is maintained at a relatively low value, and the discharge pressure of the main hydraulic pump 1 is relatively low. Low pressure. This relatively low pressure oil is supplied from the main hydraulic pump 1 to the boom cylinder 3 and the arm cylinder 4, so that a desired excavation operation can be performed.

In the first embodiment configured as above, the relief pressure can be increased during the lifting operation, and the lifting operation requiring large power can be performed. The relief pressure increase can be canceled during the excavation operation. This excavation operation can be performed while suppressing the target power, and the leveling operation can be performed without increasing the relief pressure during the leveling operation.

In particular, during a digging operation that is frequently performed, a desired digging operation can be performed without supplying an excessive discharge pressure from the main hydraulic pump 1 to the boom cylinder 3 and the arm cylinder 4. The frequency with which each part of the hydraulic device is exposed to high pressure can be reduced, and the durability of the hydraulic drive device can be improved.

FIG. 3 is a hydraulic circuit diagram showing a second embodiment of the present invention, FIG. 4 is a block diagram showing a configuration of a control device provided in the second embodiment shown in FIG. 3, and FIG. 5 is a control diagram shown in FIG. FIG. 4 is a diagram illustrating characteristics of a timer unit provided in the device.

In the second embodiment, as shown in FIGS. 3 and 4, pressure increasing instruction means for outputting an instruction signal for increasing the relief pressure of the variable relief valve 2 to the control device 13, for example, increasing the relief pressure. An on / off switch 18 that outputs an on signal as an instruction signal to perform the operation is provided.

Further, as shown in FIG.
A timer unit 19 is provided which outputs a pressure increase command signal corresponding to the ON signal output from the ON / OFF switch 18, for example, an ON signal, and limits the time for outputting the ON signal to a predetermined time T1 of about several seconds. ing. As shown in FIG. 5, the characteristics of the timer unit 19 are such that when the ON signal Sa is output from the ON / OFF switch 18, the output of the ON signal S2 is started, and the ON / OFF switch 18 is turned off within a predetermined time T1. When the operation is stopped, the output of the ON signal S2 is stopped at that time. That is, an off signal is output. When the operation of the on / off switch 18 is continuously performed for a predetermined time T1 or more, the output of the on signal S2 is stopped at the time when the predetermined time T1 is reached, and the off signal is output.

In the second embodiment, an OR circuit 21 is provided between the AND circuit 20 and the output unit 17.
The OR circuit 21 includes a drive signal S1 output from the AND circuit 20 and an ON signal S1 output from the timer unit 19.
When any one of the two is input, a signal S3 for instructing driving of the solenoid valve 12 is output to the output unit 17. Other configurations are the same as those of the above-described first embodiment.

In the second embodiment having the above-described structure, the same operation and effects as those of the above-described first embodiment can be obtained. In particular, only the boom cylinder 4 is operated to the contracted side, or only the arm cylinder 3 is operated. Is operated and the relief pressure is not increased, or the leveling operation is performed and the relief pressure is not increased and the ON signal S1 is not output from the AND circuit 20. In the case where the pressure is temporarily increased and the on / off switch 18 is operated, the timer unit 19 does not exceed the predetermined time T1 shown in FIG. The ON signal S2 is output to the circuit 21. As a result, the OR circuit 21 outputs the pressure increase command signal S3 to the output unit 1.
7, and the output section 17 outputs a control signal Y to the solenoid valve 12. Therefore, as described above, the solenoid valve 12 is switched to the upper position in FIG. 3, and the pilot pressure discharged from the pilot hydraulic pump 11 is supplied to the spring chamber of the variable relief valve 2 via the solenoid valve 12. As a result, the variable relief valve 2 operates to change the relief pressure to a high value, that is, to increase the pressure, and accordingly, the discharge pressure of the main hydraulic pump 1 increases. The high discharge pressure oil is supplied from the main hydraulic pump 1 through the boom flow control valve 5 and the arm flow control valve 6 to the boom cylinder 3 and the arm cylinder 4.
To perform temporary work requiring power. The time for increasing the pressure is automatically limited to a predetermined time T1 of about several seconds, so that the influence of the hydraulic circuit on the durability of the hydraulic device can be suppressed.

FIG. 6 is a hydraulic circuit diagram showing a third embodiment of the present invention, and FIG. 7 is a block diagram showing a configuration of a control device provided in the third embodiment shown in FIG.

In the third embodiment, As shown in FIGS. 6 and 7, as a pressure increasing instruction means for outputting an instruction signal for increasing the relief pressure of the variable relief valve 2, a type of a work mode performed through the operation of the boom cylinder 3 and the arm cylinder 4. , A mode changeover switch 22 capable of outputting an instruction signal for selectively increasing the relief pressure, that is, an ON signal. As shown in FIG. 7, when the mode changeover switch 22 is switched to a switching position A corresponding to a normal excavation work mode for excavating earth and sand, an ON signal Sb
1 is output and the switching position B corresponding to the break-in operation mode is output.
Is switched off, an off signal Sb2 is output, and when switched to the switching position C corresponding to the lifting operation mode, the on signal Sb2 is output.
3 is output. Furthermore, unlike the usual excavation work, the excavation work requires a particularly large power and excavates the hard ground, that is,
When switching to the switching position D corresponding to the heavy excavation work mode,
The ON signal Sb4 is output.

As shown in FIG. 7, the control device 13 closes the circuit between the AND circuit 16 and the output section 17 in accordance with the ON signals Sb1 and Sb3 output from the mode changeover switch 22, and turns off the OFF signal. A switch unit 23 that opens according to Sb2 is provided. When a drive signal is output from the AND circuit 16, the switch unit 23 outputs a signal for instructing pressure increase to the output unit 17 when the circuit is closed, and outputs the signal to the output unit 17 when the circuit is open. Output a command signal that does not increase the pressure. The ON signal Sb4 output from the mode changeover switch 22 is directly input to the output unit 17. When receiving the ON signal Sb4, the output unit 17 outputs a control signal Y for instructing pressure increase to the solenoid valve 12. Other configurations are the same as those described in the first embodiment.
This is equivalent to the embodiment. Note that the switching position B corresponding to the above-described mode changeover switch 22 in the break-in operation mode is:
Another pressure increase suppression means capable of outputting a signal for suppressing the increase in the relief pressure is provided. This mode switch 22
The device serves as both a pressure increase instructing unit for instructing an increase in the relief pressure and a pressure increase suppressing unit for suppressing the increase in the relief pressure.

In the third embodiment configured as described above, when the mode changeover switch 22 is switched to the changeover position A or C during normal excavation work or lifting work, the ON signal Sb is output from the mode changeover switch 22.
1 or Sb3 is output, whereby the switch unit 2
3 is closed. This state is equivalent to the above-described first embodiment. That is, the pressure is increased while the lifting work is performed, and when the normal operation is performed, the pressure is increased when the operation amounts of the boom pilot valve 7 and the arm pilot valve 8 are small. Pressure sensor 1
When the value of the signal Pb output from 0 exceeds the threshold value PBO of the second signal generator 15, the pressure increase is canceled.

When the mode changeover switch 22 is switched to the changeover position B during the leveling operation, an off signal Sb2 is output from the mode changeover switch 22.
The switch unit 23 is opened. Therefore, in this case, the relief pressure is not increased during the leveling operation regardless of the operation amounts of the boom pilot valve 7 and the arm pilot valve 8. Further, when the mode changeover switch 22 is switched to the changeover position D during heavy excavation work, an ON signal Sb4 is output from the mode changeover switch 22, and the electromagnetic valve 12 is output from the output unit 17 in response to the ON signal Sb4. A control signal Y for switching to the upper position in FIG. 6 is output.

The third embodiment configured as described above has substantially the same operation and effect as the above-described first embodiment. In particular, in the case of work such as leveling work that does not require pressure increase at all, On the other hand, the discharge pressure of the main hydraulic pump 1 is lowered in a state where the pressure is not forcibly increased, and conversely, in the case of heavy excavation work requiring a large power different from the normal excavation work, the pressure is forcibly increased. As a state, the discharge pressure of the main hydraulic pump 1 can be increased.

During normal excavation work for excavating earth and sand, since the switch section 23 is closed as described above, the operation of the boom pilot valve 7 and the arm pilot valve 8 causes Until the value of the pressure signal Pb discharged from the pressure sensor 10 exceeds the threshold value PBO set by the second signal generation unit 15, a drive signal is output from the AND circuit 16 and the output unit 17 outputs the solenoid valve 12 Is output to increase the relief pressure. When the value of the pressure signal Pb exceeds the threshold value PBO, the control signal Y is output along with the OFF signal output from the second signal generation unit 15. , The driving signal is no longer output from the AND circuit 16,
As a result, the control signal Y is not output from the output unit 17. Therefore, the relief pressure of the variable relief valve 2 is kept at a relatively low pressure.

The same as the timer unit 19 provided in the second embodiment is replaced with the control unit 13 of the third embodiment.
Of the mode changeover switch 22 and the output unit 17 may be provided.

[0078]

According to the invention of each claim of the present invention,
The pressure increase of the relief pressure can be appropriately suppressed, whereby the frequency of each part of the hydraulic equipment included in the hydraulic circuit provided in the construction machine is exposed to high pressure can be reduced. Durability can be improved.

In particular, according to the second to fifth aspects of the present invention, it is possible to suppress an increase in the relief pressure during a normal digging operation with a high frequency of operation, which is included in a hydraulic circuit provided in the construction machine. The frequency with which each part of the hydraulic device is exposed to high pressure can be reduced more reliably, and the durability of the hydraulic drive device can be significantly improved as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing a first embodiment of a hydraulic drive device for a construction machine according to the present invention.

FIG. 2 is a block diagram showing a configuration of a control device provided in the first embodiment shown in FIG.

FIG. 3 is a hydraulic circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a control device provided in the second embodiment shown in FIG.

FIG. 5 is a diagram showing characteristics of a timer unit provided in the control device shown in FIG. 4;

FIG. 6 is a hydraulic circuit diagram showing a third embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a control device provided in the third embodiment shown in FIG.

FIG. 8 is a hydraulic circuit diagram showing a first example of a conventional hydraulic drive device for a construction machine.

9 is a block diagram showing a relief pressure boosting system provided in the first example shown in FIG. 8;

FIG. 10 is a hydraulic circuit diagram showing a second conventional example.

FIG. 11 is a block diagram showing a configuration of a control device provided in the second example shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Main hydraulic pump 2 Variable relief valve 3 Boom cylinder (hydraulic actuator) 4 Arm cylinder (hydraulic actuator) 5 Flow control valve for boom 6 Flow control valve for arm 7 Pilot valve for boom (operating means for boom) 8 Pilot valve for arm (Arm operation means) 9 Boom pressure sensor (Boom operation amount detection means)
[Operation state detecting means] 10 Pressure sensor for arm (operation amount detecting means for arm)
[Operation state detecting means] 11 Pilot hydraulic pump 12 Solenoid valve (Relief pressure changing means) 13 Control device 14 First signal generation unit 15 Second signal generation unit (Pressure increase cancellation command means) [Pressure increase suppression means] 16 AND circuit 17 output section 18 ON / OFF switch (pressure increase instruction means) 19 timer section 20 AND circuit 21 OR circuit 22 mode changeover switch (pressure increase instruction means) [pressure increase suppression means] 23 switch section PAO threshold value PBO threshold value

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Koji Ishikawa 650 Kandamachi, Tsuchiura-shi, Ibaraki F-term in the Tsuchiura Plant of Hitachi Construction Machinery Co., Ltd. (Reference) 2D003 AA01 AB03 AB05 BB03 CA02 DA03 DA04 DB02

Claims (11)

[Claims] 1. A main hydraulic pump, a variable relief valve for setting a relief pressure that defines a maximum value of a discharge pressure of the main hydraulic pump, and a relief pressure changer capable of changing a relief pressure set by the variable relief valve. Means, a plurality of hydraulic actuators driven by pressure oil discharged from the main hydraulic pump, and a plurality of flow control valves for controlling the flow of pressure oil supplied to each of the hydraulic actuators from the main hydraulic pump, Hydraulic drive of a construction machine comprising a plurality of operation means for controlling the operation of these flow control valves, and a control device capable of outputting a control signal for operating the relief pressure changing means so as to increase the relief pressure. The apparatus according to claim 1, further comprising: a pressure increase suppression unit that can output a signal for suppressing the increase in the relief pressure to the relief pressure change unit. Hydraulic drive system 械. 2. The hydraulic drive device for a construction machine according to claim 1, wherein the pressure increase suppression means outputs a signal for suppressing the increase in the relief pressure during excavation work. 3. An operating state detecting means for detecting whether the operating means is in an operating state, and the control device increases the relief pressure in accordance with a signal output from the operating state detecting means. Operating the relief pressure changing means, the pressure increase suppressing means is provided in the control device, and when the signal output from the operation state detecting means is a signal corresponding to excavation work, the relief pressure changing means 3. The hydraulic drive device for a construction machine according to claim 2, wherein the hydraulic drive device is a pressure increase cancellation command unit capable of outputting a cancellation command signal for canceling the pressure increase. 4. The operation state detection means is an operation amount detection means for detecting an operation amount of the operation means, and the pressure increase cancellation command means of the control device is detected by the operation amount detection means. A relationship between an operation amount and a threshold value corresponding to a time period for canceling the relief pressure increase is set, and the cancellation for canceling the relief pressure increase when the operation amount exceeds the threshold value is set. The hydraulic drive device for a construction machine according to claim 3, wherein the signal drive unit is a signal generation unit that outputs a command signal. 5. The boom cylinder and the arm cylinder, wherein the plurality of hydraulic actuators include a boom cylinder and an arm cylinder, and the plurality of flow control valves control the boom flow control valve for controlling the drive of the boom cylinder and the drive of the arm cylinder. An arm flow control valve, wherein the plurality of operation means comprises: a boom operation means for controlling operation of the boom flow control valve; and an arm operation means for controlling operation of the arm flow control valve. The operation state detection means includes a boom operation amount detection means for detecting an operation amount of the boom operation means, and an arm operation amount detection means for detecting an operation amount of the arm operation means. The hydraulic drive device for a construction machine according to claim 4, wherein: 6. The hydraulic pressure of a construction machine according to claim 5, wherein said operation amount detecting means for a boom comprises a pressure sensor for a boom, and said operation amount detecting means for an arm comprises a pressure sensor for an arm. Drive. 7. The hydraulic drive of a construction machine according to claim 1, further comprising a pressure increasing instruction means capable of outputting an instruction signal for increasing the relief pressure to the control device. apparatus. 8. The construction machine according to claim 7, wherein said pressure increasing means comprises an on / off switch, and said instruction signal is an on signal output from said on / off switch. Hydraulic drive. 9. The control device includes a timer unit, which outputs a pressure increase command signal corresponding to the instruction signal, and limits a time for outputting the pressure increase command signal to a predetermined time. 8. The method according to claim 7, wherein
Or a hydraulic drive for a construction machine according to item 8. 10. The pressure increasing means comprises a mode changeover switch capable of selectively outputting the instruction signal in accordance with the type of work mode performed through the operation of the hydraulic actuator. The hydraulic drive device for a construction machine according to claim 7. 11. The hydraulic drive device for a construction machine according to claim 1, wherein the construction machine comprises a hydraulic shovel.