JP2716617B2 - Hydraulic drive for construction machinery - Google Patents

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 for a construction machine such as a hydraulic excavator, and more particularly to a construction device capable of switching a maximum drive pressure of a specific actuator to a plurality of stages by operating an overload relief valve. The present invention relates to a hydraulic drive for a machine.

[0002]

2. Description of the Related Art Conventionally, there has been provided a variable displacement hydraulic pump, discharge displacement control means for controlling the displacement of the variable displacement hydraulic pump, and at least one switching valve supplied with pressure oil from the variable displacement hydraulic pump. A hydraulic drive device for a construction machine including a switching valve group, a main relief valve for limiting a maximum discharge pressure of the hydraulic pump, and a predetermined switching valve included in the switching valve group and including an overload relief valve. By setting the relief setting pressure of the overload relief valve to a pressure lower than the relief setting pressure of the main relief valve, only the specific actuator driven and controlled by the above-described predetermined switching valve is set to the relief setting pressure of the main relief valve. Techniques for lower driving pressures are known.

[0003] A technique in which the set pressure of the main relief valve can be switched in two stages, and the drive pressure is switched in two stages according to the type of actuator, such as a traveling actuator and a front attachment actuator of a hydraulic shovel, for example. Is known.

[0004]

In the prior art for setting the relief set pressure of the overload relief valve to a pressure lower than the set pressure of the main relief valve as described above, the overload relief valve provided for the specific actuator is provided. When the capacity of the relief valve is sufficiently large, a drive pressure lower than the set pressure of the main relief valve can be obtained as expected.

[0005] However, the overload relief valve is designed to relieve a slight flow rate when an unexpected overload is applied to the actuator, thereby generating an abnormally high pressure and damaging the actuator or structural members of the construction machine. The relief valve is provided to prevent the life of the main relief valve from shortening and shortening the service life. Usually, a relief valve having a smaller capacity than the main relief valve is selected. With such a small-capacity relief valve, the relief pressure when passing a large flow rate is significantly higher than the relief set pressure, so that all of the flow rate allowed by the input torque limit of the hydraulic pump flows to the overload relief valve. In that case, the relief pressure will be much higher than the expected relief set pressure, and in some cases, only a large pressure that is not so different from the main relief valve set pressure will be obtained, and the drive pressure lower than the main relief valve set pressure will be reduced. Can not be generated, and therefore, a desired operation with a low driving pressure cannot be performed. In addition, large power loss occurs as a result of relief of a large flow rate in the overload relief valve, and there is also a problem of fuel economy.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances in the prior art, and has as its object the construction of a small-capacity overload relief valve capable of obtaining a drive pressure lower than a desired main relief set pressure. It is to provide a hydraulic drive for a machine.

[0007]

In order to achieve this object, the present invention provides a variable displacement hydraulic pump, a displacement displacement control means for controlling the displacement of the variable displacement hydraulic pump, and a variable displacement hydraulic pump. A switching valve group provided with at least one switching valve supplied with pressurized oil, a main relief valve for limiting a maximum discharge pressure of the hydraulic pump, and a predetermined valve included in the switching valve group and provided with an overload relief valve A hydraulic drive device of a construction machine having a switching valve of
An input limit for limiting a pump discharge capacity to an allowable discharge capacity determined according to a discharge pressure of the variable displacement hydraulic pump so that an input torque to the variable displacement hydraulic pump does not exceed a predetermined limit value; Means for limiting the pump discharge capacity to a discharge capacity smaller than the allowable discharge capacity limited by the input limit means when the discharge pressure of the variable displacement hydraulic pump exceeds a predetermined cut-off set pressure. And the relief set pressure of the overload relief valve is set to a pressure value lower than the relief set pressure of the main relief valve, and the value of the cutoff set pressure is set to the relief set pressure of the overload relief valve. The pressure is set to exceed.

[0008]

According to the present invention, since the overload relief valve is operated and the relief pressure becomes larger than the relief set pressure of the overload relief valve and exceeds the cutoff set pressure, the discharge is performed. The capacity limiting means provided in the capacity control means is smaller than the allowable discharge amount of the input limiting means for limiting the pump discharge capacity to an allowable discharge amount in which the input torque to the variable displacement hydraulic pump does not exceed a predetermined limit value. The pump discharge capacity is limited to the discharge amount, whereby the discharge pressure is kept low, and a drive pressure sufficiently lower than the main relief set pressure can be obtained.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a hydraulic drive device for a construction machine according to the present invention. FIG. 1 is a circuit diagram showing the configuration of a first embodiment of the present invention, and FIGS. 2 and 3 show the first embodiment shown in FIG.
FIG. 4 is a block diagram showing a configuration of a main part of a control means provided in the embodiment, and FIG. 4 is a characteristic diagram showing pressure / flow rate characteristics obtained in the first embodiment shown in FIG.

The first embodiment shown in FIG. 1 shows, for example, a drive unit of a hydraulic shovel, and includes an engine 1 and an engine speed for controlling the speed of the engine 1 near a specified target speed. Control means 2, rotation speed setting means 3 for designating a target rotation speed of engine 1, two variable displacement hydraulic pumps 4, 5 driven by engine 1, and electricity for operating the displacements of these pumps 4, 5 Pumping means having dynamic discharge capacity operation means 6, 7 and a center bypass passage.
A first switching valve group including at least one switching valve supplied with pressure oil from the pump, and a second switching valve having a center bypass passage and also including at least one switching valve supplied with pressure oil from the pump 5 Switching valve group.

The above-mentioned first switching valve group includes switching valves 8 to 11
The switching valve 8 is assigned to the traveling right, the switching valve 9 is assigned to the bucket, the switching valve 10 is assigned to the boom, and the switching valve 11 is assigned to the arm (joining) actuator.
The second switching valve group includes switching valves 12 to 16, wherein the switching valve 12 is swivel, the switching valve 13 is an arm, the switching valve 14 is a boom (merge), and the switching valve 15 is a spare for attachment. The switching valve 16 is assigned to each of the left actuators. 8a, 8b, 9a, 9
b, 10a, 10b, 12a, 12b, 13a, 13
Each of b, 15a, 15b, 16a, and 16b is an overload relief valve provided in the switching valves 8 to 16 of the corresponding reference signs except the switching valves 11 and 14. The hydraulic pilot valves 24 and 25 shown in FIG. 1 generate an operating pilot pressure for switching a specific switching valve of the first switching valve group, for example, the switching valve 8 related to the right actuator for traveling. The valves 26 and 27 generate an operating pilot pressure for switching a specific switching valve of the second switching valve group, for example, the switching valve 16 relating to the actuator on the left side of travel.

Fixed throttles 17 and 18 are provided on the center bypass passages of the first and second switching valve groups, respectively. The fixed throttles 17 and 18 are provided together with the fixed throttles 17 and 18. There are provided relief valves 19 and 20 for adjusting the generated pressure so as not to exceed a specified pressure, and pressure detecting means 22 and 23 for detecting a differential pressure generated in the fixed throttles 17 and 18 and outputting pressure signals 22i and 23i. .

A low-pressure side main relief valve 30 and a high-pressure side main relief valve 31 for setting the maximum discharge pressure of the hydraulic pumps 4 and 5 are provided in the discharge pipelines of the hydraulic pumps 4 and 5. The relief valves 30 and 31 are appropriately selected to set the maximum discharge pressure. That is, when the switching valve 36 is in the state shown in FIG. 1, the driving section of the low-pressure side main relief valve 30 is connected to the tank, so that the low-pressure side main relief valve 30 is in an operable state. Hydraulic pump 4,5
Is the pressure set by the low pressure side main relief valve 30. When the switching valve 36 is switched from the state shown in FIG. 1 to the lower position, the pilot pressure of the pilot pump is applied to the drive section of the low-pressure side main relief valve 30, whereby the low-pressure side relief valve 30 becomes inoperable. The maximum discharge pressure of the hydraulic pumps 4 and 5 at this time is the pressure set by the high-pressure side main relief valve 31. The switching valve 36 is provided with the hydraulic pumps 4, 5,
The main relief setting pressure changing means is configured to change the maximum discharge pressure of at least two steps.

In FIG. 1, reference numeral 28 denotes a hydraulic pilot valve 24,
An operation detecting unit that detects that each of the hydraulic pilot valves 25 and the hydraulic pilot valves 26 and 27 has been operated and outputs a detection signal 28i. The operation detecting means 28 includes an operation detecting means for detecting the operation of the right switching valve 8 included in the first switching valve group and the operation of the left switching valve 16 included in the second switching valve group. It also serves as second operation detecting means for detecting an operation. Also, 32, 33 are hydraulic pumps 4,
5 are respectively detected and the detection signals 32i, 33 are detected.
The electric discharge capacity detecting means 34, 35 for outputting i,
Electrical pressure detecting means for detecting the discharge pressures of the hydraulic pumps 4 and 5 and outputting detection signals 34i and 35i, that is, discharge pressure detecting means. Reference numeral 29 denotes a second target rotation speed setting unit that allows the operator to arbitrarily set and output a target rotation speed signal 29i different from the target rotation speed signal 3i of the engine 1 specified by the above-described target rotation speed setting unit 3;
Reference numeral 37 denotes a selection command unit that outputs a signal 37i for selecting high-voltage driving of a specific actuator.

Reference numeral 21 denotes a control means, which is a target rotation speed signal 3i output from the above-mentioned target rotation speed setting means 3, a second target rotation speed signal 29i output from the second target rotation speed setting means 29, and a pressure. The pressure signals 22i and 23i output from the signal detection means 22 and 23, the detection signal 28i output from the operation detection means 28, the command signal 37i output from the selection command means 37, and the output signals from the discharge capacity detection means 32 and 33. Detection signals 32i, 33i, discharge pressure detecting means 3
4 and 35, the detection signals 34i and 35i are input, and the driving signal 2
ou are supplied to the discharge capacity operation means 6 and 7 with drive signals 6 ou and 7.
ou, and outputs a drive signal 36 ou to the switching valve 36. This control means 21 has the configuration shown in FIGS.

That is, first, as shown in FIG. 2, the pressure signal 22i output from the pressure signal detecting means 22, 23
(Pn1) and 23i (Pn2) are provided with function generating means A1 and A2 for outputting discharge capacities q11 and q21, which increase as the respective values decrease, as target values. Input limiting means for limiting the pump discharge capacity to an allowable discharge capacity determined according to the discharge pressure of the pumps 4, 5 so that the input torque to the hydraulic pumps 4, 5 does not exceed a predetermined limit value; That is, the discharge pressure detecting means 34, 3
5, a detection signal 34i (value Pd1), 35i
Function generating means B1 and B2 are provided which output the discharge capacities q12 and q22 decreasing as the respective values of (value Pd2) increase as target values. Also, the hydraulic pumps 4, 5
Capacity limiting means for limiting the pump discharge capacity to a discharge capacity smaller than the allowable discharge capacity limited by the input limiting means when the discharge pressure exceeds a predetermined cutoff set pressure, that is, discharge pressure detecting means The detection signals 34i (value Pd1) and 35i (value Pd) output from
2) It decreases as each value increases, and
Function generating means C1, C2 that output positive discharge speeds qs13, qs23 that shift to a positive speed in a region where the pressure is low with respect to the discharge pressures Pd1 and Pd2, and shift to a negative speed as the pressure becomes high. Target displacement change rate qs1 output from the function generating means C1 and C2
3, and integrators D1 and D2 for integrating qs23 and outputting discharge capacities q13 and q23 as target values. Further, a minimum value selecting means E1 for selecting the minimum value among the above-mentioned discharge capacities q11, q12, q13 and outputting it as a target discharge capacity q1r, and discharge capacities q21, q22, q23.
And a minimum value selecting means E2 for selecting the minimum value among the above and outputting the selected value as the target discharge capacity q2r. Further, the target discharge amount q1 output from the minimum value selecting means E1, E2.
r, q2r and the target value deviation Δq from the values q1, q2 of the detection signals 32i, 33i of the discharge capacity detection means 32, 33.
1, and adders U1 and U2 for obtaining Δq2, and drive signals 6ou and 7ou corresponding to the target value deviations Δq1 and Δq2 obtained by the adders U1 and U2 are used to control the discharge capacity of the hydraulic pumps 4 and 5. It has amplifiers F1 and F2 that output to the capacity operation means 6 and 7. When the detection signal 28i of the operation detecting means 28 for detecting the operation of the hydraulic pilot valves 24 to 27 shown in FIG. 1 is input, the function generating means C1, C2 constituting the capacity limiting means and the integrator D
1, the operation of D2 is prevented.

Here, among the above-described overload relief valves, the relief set pressure of the overload relief valves 9a and 9b related to a specific actuator, for example, a bucket, is exemplified by a relief set pressure characteristic line O in FIG. A pressure value between two pressure values that can be changed by switching the switching valve 36, that is, a pressure lower than the relief set pressure of the high-pressure side main relief valve 31 and higher than the relief set pressure of the low-pressure side relief valve 30. 4, and the cutoff set pressure is set in advance to a pressure value exceeding the relief set pressure of the overload relief valve as shown by the cutoff set pressure characteristic line R in FIG. Therefore, the functional relationship between the function generating means C1 and C2 of the control means 21 shown in FIG.
When the pressure values Pd1 and Pd2 corresponding to the cut-off set pressures are exceeded, the discharge capacities qs13 and qs23 become smaller than the discharge capacities q12 and q22 of the function generators B1 and B2, so that these function generators B1 and B2 are used. , The function relationship between the function generating means C1 and C2 is set in advance.

The control means 21 also has a configuration shown in FIG. 3 in addition to the above-described configuration. That is, an OR circuit G for inputting the detection signal 28i of the operation detecting means 28 for detecting the operation of the hydraulic pilot valves 24 to 27 and the command signal 37i of the selection commanding means 37, and amplifying the signal output from the OR circuit G. And an amplifier H that outputs a drive signal 36 ou to the switching valve 36. A function generating means I for outputting a target value Nr1 of the rotation speed of the engine 1 which increases in accordance with an increase in a target rotation speed signal 3i (value Nr10) output from the target rotation speed 3; Detection signal 34i of discharge pressure detecting means 34, 35 for detecting discharge pressure
(Value Pd1), the maximum value selecting means J for selecting the maximum value of the values of 35i (value Pd2) and outputting the selected value as the target value Pd of the pressure, and the target value of the pressure output from the maximum value selecting means J A function generator K capable of outputting a target value Nr2 of the rotation speed of the engine 1 having a value smaller than the target value Nr1 as the Pd increases, a target value Nr1 output from the function generator I and a function A minimum value selecting means L for selecting the smaller one of the target values Nr2 output from the generating means K and outputting the selected value to the engine speed control means 2 as a target speed signal 2ou (value Nr). . The function relationship of the function generating means K is, for example, the target rotation speed signal 29i output from the second target rotation speed setting means 29.
, That is, it can be changed by an arbitrary operation of the operator.

In the first embodiment, the control means 21, the discharge capacity operation means 6, 7, the discharge capacity detection means 32, 33 and the discharge pressure detection means 34, 35 A discharge capacity control means for controlling the discharge capacity of the pumps 4 and 5 is constituted.

The operation of the first embodiment configured as described above will be described below. In the first embodiment, the switching valves 8 to 1
6, the differential pressure generated in the fixed throttles 17, 18 provided on the respective center bypass passages of the first and second switching valve groups is generated by the pressure detecting means 22, 2,
3 and performs electrical control according to well-known negative control (abbreviated as "negative control") in accordance with the pressure signals 22i and 23i output from the pressure detecting means 22 and 23. The discharge capacities of 4 and 5 are adjusted. That is, the center bypass passages of the first and second switching valve groups are gradually narrowed in accordance with an increase in the operation amount of the hydraulic pilot valves 24 to 27 or a hydraulic pilot valve (not shown), and are finally fully closed. But
At this time, since the flow rate flowing through the center bypass passage decreases, the differential pressure generated in the fixed throttles 17 and 18 decreases, and the differential pressure is detected by the pressure detecting means 22 and 23, and the pressure signal 22i (value Pn1) ), 23i (value Pn2)
Is a function generator A1 of the controller 21 as shown in FIG.
Input to A2. The function generators A1 and A2 output as the target values the discharge capacities q11 and q21 that increase as the values Pn1 and Pn2 of the pressure signals 22i and 23i decrease. Accordingly, a gradually increasing flow rate is supplied from the hydraulic pumps 4 and 5 in accordance with one of the switching operations of the switching valves 8 to 16, and the corresponding unillustrated actuator can be operated by the large flow rate.

The discharge pressure of the hydraulic oil discharged from the hydraulic pumps 4 and 5 is detected by discharge pressure detecting means 34 and 35, and detection signals 34i (value Pd1) and 35i (value Pd
2) is the function generating means B1, B of the control means 21 shown in FIG.
2 is input. As described above, the function generators B1 and B2 use the values Pd1 and Pd2 of the detection signals 34i and 35i.
Discharge capacity q12, q that decreases so that the input torque to the hydraulic pumps 4, 5 does not exceed a predetermined limit value in accordance with the increase of
22 is output as the target value. Thereby, an efficient flow rate can be supplied from the hydraulic pumps 4 and 5 within a range where engine stall does not occur.

Here, for example, in order to switch the switching valves 8 and 16 relating to the traveling right and the traveling left, the hydraulic pilot valves 24 to
When the user operates the button 27, the operation is detected by the operation detecting means 28, and a detection signal 28i is input to the control means 21. The function generating means C1, C2 and the integrators D1, D2 constituting the capacity limiting means shown in FIG.
The detection signal 28i is input to the OR circuit G shown in FIG. 3, whereby the drive signal 36ou is output from the amplifier H to the switching valve 36 shown in FIG. The switching signal 36 is switched to the lower position in FIG. 1 by the drive signal 36 ou. As a result of this switching, the low-pressure side main relief valve 30 that has been operating up to that time becomes inoperable, and the maximum discharge pressure of the hydraulic pumps 4 and 5 is changed to the set pressure of the high-pressure side main relief valve 31. Therefore, a large driving pressure can be secured during traveling.

When the selection command means 37 shown in FIG. 1 is operated, the command signal 37i is supplied to the control means 21 shown in FIG.
, The switching valve 36 is switched to the lower position of FIG. 1 in the same manner as described above, and the maximum discharge pressure of the hydraulic pumps 4 and 5 is reduced by the high-pressure side main relief valve 31. The pressure is changed to the set pressure. The set pressure at this time is the largest set pressure PM2 which is the intersection of the set pressure characteristic line M2 of the high pressure side main relief valve 31 in FIG. 4 and the pump PQ characteristic line N. When the maximum discharge pressure of the hydraulic pumps 4 and 5 before switching of the switching valve 36 is the set pressure specified by the low-pressure relief valve 30, the low-pressure main relief valve 3 in FIG.
The smallest set pressure PM1, which is the intersection of the set pressure characteristic line M1 of 0 and the pump PQ characteristic line N, is obtained.

In the state where the maximum discharge pressure of the hydraulic pumps 4 and 5 is regulated to the set pressure of the high-pressure side main relief valve 31 as described above, only the specific actuator, for example, the Is relieved by the overload relief valve,
Thus, for example, when trying to obtain a low drive pressure for fine operation, the pressure P01 which is the intersection of the set pressure characteristic line O of the overload relief valve and the hydraulic pump PQ characteristic line N in FIG. There is almost no difference from the set pressure PM2 of the main relief valve 31, so that a desired low drive pressure cannot be obtained.

On the other hand, in the first embodiment of the present invention, when the bucket cylinder is operated by the function generating means C1 and the integrator D1 shown in FIG. When the discharge pressure Pd1 increases to the cut-off set pressure by the detection signal 34i of the pressure detecting means 34 for detecting the discharge pressure of No. 4, the small discharge capacity q1r selected by the minimum value selecting means E1
(Corresponding to q13 output from the integrator D1), that is, the characteristic line R of the cutoff set pressure and the set pressure characteristic line O of the overload relief valve in FIG.
And the driving pressure sufficiently lower than the set pressure PM2 of the high-pressure side main relief valve 31 can be secured. That is, even if an overload relief valve having a relatively small capacity is provided, a drive pressure sufficiently lower than the set pressure PM2 of the high-pressure side main relief valve 31 can be secured, and an output load suitable for a specific actuator can be realized.

In the first embodiment described above, when it is necessary to ensure a predetermined minimum flow rate for the purpose of exerting a strong sense of operation or for lubricating a hydraulic pump, etc. As shown in FIG. 4, the characteristic indicated by the characteristic line S for maintaining the predetermined minimum flow rate may be set during the capacity reduction operation, and the same applies when the characteristic indicated by the characteristic line S is taken into consideration. A relatively low drive pressure, which is the intersection of the characteristic line S of FIG. 4 and the set pressure characteristic line O of the overload relief valve, can be secured.

Further, as described above, the displacement capacity of the hydraulic pumps 4 and 5 is determined by the capacity limiting means as a value (q1) determined by the function generating means B1 and B2 constituting the input limiting means.
If the value (q13, q23) is smaller than (q13, q23), the load on the engine 1 decreases, the engine speed increases, and an invalid power loss occurs. Therefore, the first embodiment of the present invention has a configuration shown in FIG. That is, the target rotation speed signal Nr1 is obtained by the function generation means I according to the signal 3i (value Nr10) output from the target rotation speed setting means 3 shown in FIG. The detection signal 34i (value Pd
1) For 35i (Pd2), the maximum value selection means J selects the larger value, that is, the larger pressure, as the discharge pressure Pd, and according to the discharge pressure Pd, the function generation means K
The target rotation speed signal Nr2 is determined by the above, and the smaller one of the target rotation speed signals Nr1 and Nr2 determined in this way is selected by the minimum value selection means L, and is set as the final target rotation speed Nr by the engine rotation speed control means. Output to 2. This allows
When the discharge capacity is reduced by the capacity limiting means as described above, the rotation speed of the engine 1 becomes low, and power loss can be suppressed. The function relation of the function generating means K is, for example, a plurality of function relations set in advance, and can be changed according to the signal 29i of the second target rotation speed setting means 29 by the operation of the operator.

FIG. 5 is a circuit diagram showing the configuration of a second embodiment of the hydraulic drive system for construction equipment according to the present invention. In the second embodiment shown in FIG. 5, the switching valve 36a provided to prevent the operation of the low-pressure side main relief valve 30 is configured to be directly operable by the command signal of the selection command means 37, Discharge capacity control means 6A and 7A for controlling the discharge capacity of the pumps 4 and 5 are hydraulically configured. In other words, each of the discharge capacity control means 6A and 7A is provided with a corresponding one of the discharge capacity operation means 6c and 7c formed of a hydraulic cylinder and the hydraulic pressure so that the input torque to the hydraulic pumps 4 and 5 does not exceed a predetermined limit value. Input limiting means 6b and 7b, which are switching valves for limiting the pump discharge capacity to an allowable discharge amount determined according to the discharge pressures of the pumps 4 and 5, and a cut-off in which the discharge pressures of the hydraulic pumps 4 and 5 are predetermined. When the pressure exceeds the set pressure, there is provided a capacity limiting means 6a, 7a comprising a servo valve for limiting the pump discharge capacity to a discharge capacity smaller than the allowable discharge capacity limited by the input restricting means 6b, 7b. The control unit 21a has a configuration of the lower part of FIG. 3, that is, a configuration including only the function generation unit I, the maximum value selection unit J, the function generation unit K, and the minimum value selection unit L. Other configurations are the same as those in the first embodiment described above.

In the second embodiment constructed as described above, the set pressure characteristic line O and the cutoff set pressure characteristic line R of the overload relief valve shown in FIG. , That is, a drive pressure sufficiently lower than the set pressure PM2 of the high-pressure side main relief valve 30 can be obtained, and the same operational effects as those of the first embodiment can be obtained.

[0030]

According to the present invention having the above-described structure, a driving pressure lower than a desired main relief set pressure can be ensured by an overload relief valve having a small capacity, which is superior to the prior art. This has the effect of providing improved workability.

In addition, the power loss generated when the overload relief valve is relieved can be reduced, which has an economic effect.

In the invention according to the twelfth to fourteenth aspects of the present invention, in addition to the above effects, when a low driving pressure is secured by the overload relief valve, the engine speed is simultaneously reduced. There is also an effect that the power loss can be further reduced by lowering the power.

[Brief description of the drawings]

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

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

FIG. 3 is a block diagram showing a configuration of a main part of a control means provided in the first embodiment shown in FIG. 1;

FIG. 4 is a characteristic diagram showing pressure-flow characteristics obtained in the first embodiment shown in FIG.

FIG. 5 is a circuit diagram showing a configuration of a hydraulic drive device for a construction machine according to a second embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 engine 2 engine speed control means 3 target speed setting means 4, 5 variable displacement hydraulic pump 6, 7 discharge capacity operation means 6A, 7A discharge capacity control means 6a, 7a input limit means 6b, 7b capacity limit means 6c, 7c Discharge capacity operating means 8 to 11 First switching valve group 8a, 8b Overload relief valve 9a, 9b Overload relief valve 10a, 10b Overload relief valve 12a, 12b Overload relief valve 13a, 13b Overload relief valve 15a, 15b Overload relief valve 16a, 16b Overload relief valve 12-16 Second switching valve group 17, 18 Fixed throttle 19, 20 Relief valve 21, 21a Control means 22, 23 Pressure detection means 24, 25 Hydraulic pilot valve 26, 27 Hydraulic pilot valve 2 Operation detection means 29 second target discharge rotational speed setting means 30 low-pressure side main relief valve 31 the high pressure side main relief valve 32, 33 capacitance sensing means 34, 35 the discharge pressure detecting means 36,36a switching valve 37 selecting command means

Claims (14)

(57) [Claims] 1. A switching valve comprising: a variable displacement hydraulic pump; a discharge displacement control means for controlling a displacement of the variable displacement hydraulic pump; and at least one switching valve supplied with pressure oil from the variable displacement hydraulic pump. A group, a main relief valve that limits the maximum discharge pressure of the hydraulic pump, and a hydraulic drive device for a construction machine including a predetermined switching valve that is included in the switching valve group and includes an overload relief valve.
An input limit for limiting a pump discharge capacity to an allowable discharge capacity determined according to a discharge pressure of the variable displacement hydraulic pump so that an input torque to the variable displacement hydraulic pump does not exceed a predetermined limit value; Means for limiting the pump discharge capacity to a discharge capacity smaller than the allowable discharge capacity limited by the input limit means when the discharge pressure of the variable displacement hydraulic pump exceeds a predetermined cut-off set pressure. And the relief set pressure of the overload relief valve is set to a pressure value lower than the relief set pressure of the main relief valve, and the value of the cutoff set pressure is set to the relief set pressure of the overload relief valve. A hydraulic drive device for construction machinery, wherein the hydraulic pressure is set to a pressure value exceeding. 2. The apparatus according to claim 1, further comprising a main relief setting pressure changing means for changing a setting pressure of the main relief valve in at least two stages, and a value of the overload relief setting pressure settable by the main relief setting pressure changing means. 2. The hydraulic drive device for a construction machine according to claim 1, wherein the pressure value is set to a value between the two levels of pressure values. 3. The hydraulic drive device for a construction machine according to claim 2, further comprising selection command means, wherein the main relief setting pressure changing means is operated in accordance with a command signal from the selection command means. 4. An operation detecting means for detecting an operation of a specific switching valve among the predetermined switching valves of the switching valve group,
4. The hydraulic drive device for a construction machine according to claim 2, wherein the operation of the capacity limiter is substantially prevented based on a detection signal from the operation detector. 5. A second pump different from said variable displacement hydraulic pump.
Variable displacement hydraulic pump, second displacement control means for controlling the displacement of the second variable displacement hydraulic pump, and at least one switching valve supplied with pressure oil from the second variable displacement hydraulic pump And a second operation detecting means for detecting an operation of a specific switching valve of the second switching valve group, wherein a detection signal from the operation detecting means or the second operation is provided. 5. The hydraulic drive device for a construction machine according to claim 4, wherein the operation of the capacity limiter is substantially prevented based on at least one of the detection signals from the detector. 6. The hydraulic pressure of a construction machine according to claim 2, wherein said discharge capacity control means includes an electric pressure detection means for detecting a discharge pressure of said variable displacement hydraulic pump. Drive. 7. The construction machine according to claim 5, wherein said second discharge capacity control means includes an electric pressure detection means for detecting a discharge pressure of said second variable displacement hydraulic pump. Hydraulic drive. 8. The hydraulic drive device for a construction machine according to claim 6, wherein said discharge capacity control means includes an electric discharge capacity operation means for controlling a discharge capacity of said variable displacement hydraulic pump. 9. The construction machine according to claim 7, wherein said second displacement control means includes an electric displacement control means for controlling a displacement of the second variable displacement hydraulic pump. Hydraulic drive. 10. The hydraulic drive system for a construction machine according to claim 6, wherein said discharge capacity control means includes an electric discharge capacity detection means for detecting a discharge capacity of said variable displacement hydraulic pump. 11. The construction according to claim 7, wherein said second discharge capacity control means includes an electric discharge capacity detection means for detecting a discharge capacity of said second variable displacement hydraulic pump. Hydraulic drive of the machine. 12. An engine for driving the variable displacement hydraulic pump, an engine speed control means for controlling the engine speed to be substantially constant regardless of load, and an engine speed control means set and operated by an operator. Target rotation speed setting means for providing a target rotation speed signal, a second target rotation speed setting means for providing a second target rotation speed signal of the engine rotation speed control means, the target rotation speed signal and the second rotation speed.
A rotation speed selection means for selecting a lower rotation speed signal among the target rotation speed signals and outputting the selected rotation speed signal to the engine rotation speed control means, wherein the second target rotation speed signal is output when the displacement control means is activated. 12. The method according to claim 1, wherein the setting means outputs a predetermined rotation number equal to or less than a maximum rotation number specified by the target rotation number setting means as the second target rotation number signal. Construction machinery hydraulic drive. 13. An engine for driving both the variable displacement hydraulic pump and the second variable displacement hydraulic pump, engine speed control means for controlling the speed of the engine to be substantially constant regardless of load, and Setting operation, a target speed setting means for providing a target speed signal of the engine speed control means; a second target speed setting means for providing a second target speed signal of the engine speed control means; A rotation speed selection unit that selects a lower rotation speed signal of the target rotation speed signal and the second target rotation speed signal and outputs the selected rotation speed signal to the engine rotation speed control unit; Then, the second target rotation speed setting means outputs a predetermined rotation speed equal to or less than the maximum rotation speed specified by the target rotation speed setting device as the second target rotation speed signal. The hydraulic drive device for a construction machine according to any one of claims 5 to 11, wherein 14. The second target rotation speed setting means according to claim 2, wherein
14. The hydraulic drive device for a construction machine according to claim 12, wherein the target rotation speed signal can be arbitrarily set by an operator.