JPH06137309A - Variable capacity type hydraulic pump control device - Google Patents

Abstract

PURPOSE:To prevent the unevenness in discharge quantity of pressure oil by selectively switching a control pressure switching means and other control pressure means on high pressure side according to the kind of a switched directional control valve at the time of switching either one of plural kinds of directional control valves from neutral position in the low rotating speed are of a motor. CONSTITUTION:When either one of plural kinds of directional control valves 22A, 22B is switched from neutral position in the low rotating speed area of a motor 9, a set pressure of a pressure reducing valve 21 and a pressure higher than this can be selected as the control pressure supplied to a capacity control means 16 according to the kinds of the directional control valves 22A, 22B. When the higher pressure is selected, both the capacity variable parts 11A, 11B of hydraulic pumps 10A, 10B can be held in minimum tilting position. When both the capacity variable parts 11A, 11B are laid in the minimum tilting position, each hydraulic pump 10A, 10B has less unevenness in discharge quantity of pressure oil, compared with a position in the course of tilting, and the pressure oil of the substantially equal flow rate can be discharged from each hydraulic pump 10A, 10B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable displacement hydraulic pump control device that is preferably used for construction machines such as hydraulic excavators, and particularly to variable displacement hydraulic motors for left and right traveling hydraulic motors. The present invention relates to a variable displacement hydraulic pump control device that supplies pressure oil from a pump.

[0002]

2. Description of the Related Art FIGS. 4 to 6 show a hydraulic excavator provided with a conventional variable displacement hydraulic pump control device and its hydraulic circuit.

In the figure, 1 is a pair of left and right crawler belts 1A,
1A, an undercarriage 2 which moves forward and backward in the directions of arrows A and B, 2 indicates an upper revolving structure rotatably mounted on the lower revolving structure 1, and the upper revolving structure 2 includes a machine room 3 A driver's cab 4 located at the front of the machine room 3 and a counterweight 5 located at the rear of the machine room 3, and inside the machine room 3 is driven by a prime mover 9 and a prime mover 9 described later. The respective hydraulic pumps 10A, 10B, etc. are provided.

Reference numeral 6 denotes a working device provided in the front part of the upper swing body 2. The working device 6 includes a boom 6A and an arm 6
B, a bucket 6C, etc. are generally configured, and the boom 6A is lifted and lowered in the directions C and D indicated by the left and right boom cylinders 6D and 6D (see FIG. 5).

Reference numerals 7 and 7 are left and right traveling speed reducers (only one is shown) provided on the lower traveling body 1, and 8A and 8B are provided on the lower traveling body 1 together with the respective speed reducers 7 to provide a plurality of hydraulic pressures. The left and right traveling hydraulic motors constituting the actuator are shown. The traveling hydraulic motors 8A and 8B are supplied with pressure oil from separate hydraulic pumps 10A and 10B, respectively, as shown in FIG. Each crawler belt 1A of the lower traveling body 1 is driven via 7.

Reference numeral 9 denotes a prime mover provided in the cab 4, and 10
Reference characters A and 10B denote variable displacement hydraulic pumps that are rotationally driven by the prime mover 9, and the hydraulic pumps 10A and 10B have variable displacement units 11A and 11B, respectively, and the variable displacement units 11A and 11B are regulators 16 to be described later. The displacement, that is, the discharge amount Q of the pressure oil is variably controlled by being tilt-driven by. The hydraulic pumps 10A and 10B together with the tank 12 have a pair of main pipelines 13A, 14A, 1
It is connected to the traveling hydraulic motors 8A and 8B via 3B and 14B, and the pressure oil is individually supplied to and discharged from the traveling hydraulic motors 8A and 8B. Also, the hydraulic pump 10
A and 10B are connected to the boom cylinders 6D together with the tank 12 through main pipe lines 15A and 15B, and supply and discharge pressure oil to expand and contract the boom cylinders 6D.

Reference numerals 16 and 16 denote regulators as displacement control means for tilt-driving the variable displacement portions 11A and 11B of the hydraulic pumps 10A and 10B. Each regulator 16 is a sub-device via control pipe lines 17, 17A and 17B. The hydraulic pumps 10A, 10 are connected to the pilot pump 18 serving as a hydraulic pressure source and the tank 12 in accordance with the control pressure P from the control pipeline 17.
By tilting the capacity variable portions 11A and 11B of B, the hydraulic pump 1 is moved as shown by characteristic lines 19A and 19B in FIG.
The discharge amount Q of 0A and 10B is variably controlled based on the control pressure P.

Reference numeral 20 is a control line 17 and control lines 17A, 1
7B shows a solenoid valve as a control pressure switching means provided between the solenoid valve 20 and the solenoid valve 7B. The solenoid valve 20 is switched from a low pressure side switching position a to a high pressure side switching position b by a switching signal from a controller 40 described later. The control line 17 is connected to the control line 17A,
Switch to 17B.

Reference numeral 21 is a pilot pump 18 and a tank 12.
Shows a pressure reducing valve provided in the middle of the control line 17B between the solenoid valve 20 and the solenoid valve 20, and the pressure reducing valve 21 controls the control pressure P in the control line 17 when the solenoid valve 20 is switched to the switching position b. Is reduced to below the set pressure P1 (see FIG. 6).

22A and 22B are main pipelines 13A and 13A, respectively.
14A, 13B, 14B, etc., showing traveling control valves as left and right directional control valves provided in the middle, the traveling control valves 22A, 22B being constituted by hydraulic pilot type directional control valves, By manually operating the operating levers 24A and 24B of the pressure reducing valve type hydraulic pilot valves 23A and 23B provided in FIG. 4, the neutral position shown in FIG. 5 is switched to the left and right switching positions, and the hydraulic pumps 10A and 10B.
The flow rate and the direction of the pressure oil supplied to and discharged from the traveling hydraulic motors 8A, 8B are controlled.

Here, the hydraulic pilot valves 23A, 23B
The high pressure side is connected to the pilot pump 18 via the pipelines 25, 25A, 25B, and the low pressure side is pipelines 26A, 26B.
To the tank 12, and the output side is connected to the respective hydraulic pilot portions of the traveling control valves 22A and 22B via the pilot conduits 27A, 28A, 27B and 28B, respectively.

Reference numerals 29A and 29B denote work control valves provided in the middle of the main pipelines 15A and 15B, and the work control valves 29A and 29B are constituted by hydraulic pilot type directional control valves and are provided in the cab 4. By manually operating the operating lever 31 of the other pressure reducing valve type hydraulic pilot valve 30 provided, both the left and right switching positions are switched from the neutral position shown in FIG. 5, and the hydraulic cylinders 10A, 10B are used to move the boom cylinders 6D. Controls the flow rate and direction of pressure oil supplied to and discharged from. In this case, the hydraulic pilot valve 30 has the high pressure side on the conduit 2
Connected to the pilot pump 18 via 5, 25A,
The low-pressure side is connected to the tank 12 via the pipeline 26A, and the output side is connected to the hydraulic pilot portions of the work control valves 29A and 29B via common pilot pipelines 32A and 32A.

Reference numerals 33 and 34 branch off from the pipe line 25, and a traveling control valve 22 is provided between the pilot pump 18 and the tank 12.
A, 22B and a control pipe for working 29A, 29B show a branch pipe line connected to the branch pipe line 33, and the branch pipe line 33 is the traveling control valve 2
When both 2A and 22B are returned to the neutral position, the pilot pump 18 and the tank 12 are communicated with each other via the throttle 35, and when at least one of the traveling control valves 22A and 22B is switched from the neutral position. The communication state is cut off. The branch pipe 34 connects the pilot pump 18 and the tank 12 via the throttle 36 when the work control valves 29A and 29B are both returned to the neutral position, and the travel control valves 29A and 29B are neutralized. When the position is switched, the communication state is cut off.

Reference numeral 37 denotes a pressure switch as an operation detecting means for traveling which is provided between the traveling control valve 22A and the throttle 35 and is provided in the middle of the branch conduit 33. The pressure switch 37 is for traveling. When the control valves 22A and 22B are both returned to the neutral position, the inside of the branch pipe line 33 becomes low in pressure, so that the valve is opened and at least one of the traveling control valves 22A and 22B is switched from the neutral position. By sometimes closing, a detection signal is output to the controller 40.

A pressure switch 38 is located between the work control valve 29A and the throttle 36 and is provided in the middle of the branch conduit 34 as a work operation detecting means. The pressure switch 38 is a work switch. When the control valves 29A and 29B are returned to the neutral position, the pressure inside the branch pipe line 34 becomes low, and thus the valves are opened, and when the work control valves 29A and 29B are switched from the neutral position, the valves are closed. , And outputs a detection signal to the controller 40.

Reference numeral 39 denotes a rotation speed sensor as rotation speed detection means provided in the prime mover 9, and the rotation speed sensor 3
9 detects the actual number of revolutions of the prime mover 9 and outputs the detection signal to the controller 40. Reference numeral 40 denotes a controller composed of a microcomputer or the like, the input side of the controller 40 is connected to the pressure switches 37 and 38, the rotation speed sensor 39 and the like, and the output side is connected to the solenoid valve 20 and the like. Then, the controller 40, based on the detection signals from the pressure switches 37 and 38 and the rotation speed sensor 39, when the prime mover 9 is in a predetermined low rotation speed region, the traveling control valves 22A and 22B and the work control valve 29.
When at least one of A and 29B is switched from the neutral position, a switching signal is output to the solenoid valve 20 to switch the solenoid valve 20 from the switching position a to the switching position b.

Further, 41 is a pilot pump 18 and a pump.
Located between the link 12 and the conduit 12
A low pressure relief valve is shown, the relief valve 41 being a gear pump
The discharge pressure of the pilot pump 18 including
0 Kg / cm²Limit the pressure to about P2 (P2> P1)
By relieving the tank 12 with a pressure higher than this,
Prevents excessive pressure from acting on the pilot pump 18 etc.
Stop is doing.

In the prior art having such a configuration, the prime mover 9 rotationally drives the hydraulic pumps 10A, 10B and the pilot pump 18, and, for example, when the operation levers 24A, 24B in the operator's cab 4 are tilted, they are used for traveling. The control valves 22A, 22B are switched from the neutral position to the switching position, and the pressure oil from the hydraulic pumps 10A, 10B is supplied to the left and right traveling hydraulic motors 8A, 8B via the main pipelines 13A, 14A, 13B, 14B, respectively. Since the oil is supplied and discharged, the traveling hydraulic motors 8A and 8B are used to drive the respective speed reducers 7 to the left,
The right crawler belts 1A, 1A are driven, and the hydraulic excavator moves forward or backward in the directions of arrows A, B in FIG.

When the operation lever 31 in the operator's cab 4 is tilted to switch the work control valves 29A and 29B from the neutral position to the left and right switching positions, the hydraulic pump 10 is operated.
Since the pressure oil from A and 10B is supplied to and discharged from each boom cylinder 6D through the main conduit 15A or 15B, the boom cylinder 6D causes the boom 6A of the working device 6 to move in the directions indicated by arrows C and D in FIG. You can lie down on the bucket 6
With C, excavation work such as earth and sand can be performed.

Then, the controller 40, based on the detection signals from the pressure switches 37, 38 and the rotation speed sensor 39, when the prime mover 9 is in a predetermined low rotation speed region, the traveling control valves 22A, 22B and the work control. Valve 29A, 29
When at least one of B is switched from the neutral position, a switching signal is output to the solenoid valve 20 to switch the solenoid valve 20 from the switching position a to the switching position b. Control pressure P supplied to the regulator 16
Will rise to the set pressure P1 of the pressure reducing valve 21 as indicated by the characteristic lines 19A and 19B shown in FIG.
6 is a hydraulic pump 10A, 1 according to the control pressure P at this time.
The displacement variable units 11A and 11B of 0B are tilted so that the tilt angle is small, and the discharge amount Q of the hydraulic pumps 10A and 10B is changed.
To reduce.

In this case, for example, the driver operates the operation lever 24.
A, 24B or 31 is tilted to control the traveling control valve 2
2A, 22B or the work control valves 29A, 29B are discharged from the pilot pump 18 to the tank 12 via the pipe lines 25, 25A and the branch pipe lines 33, 34 when the stroke is made from the neutral position to the switching position. Since the pressure oil to be supplied is shut off by the traveling control valves 22A, 22B or the work control valves 29A, 29B at an intermediate position of the branch pipeline 33 or 34, the pressure in the branch pipeline 33 or 34 is increased by this. , The pressure switch 37 or 38 is closed by the pressure at this time, and the detection signal is sent to the controller 40.
Output to.

When the controller 40 reads the detection signal from the pressure switch 37 or 38 in the state where the motor 9 determines that the prime mover 9 is in the low rotation speed region based on the rotation speed detection signal from the rotation speed sensor 39, the solenoid valve 20 is read. A switching signal is output to switch the solenoid valve 20 from the switching position a to the switching position b. As a result, the control pressure P supplied from the control line 17 to each regulator 16 is the characteristic line 19 shown in FIG.
As in A and 19B, the pressure rises to the set pressure P1 of the pressure reducing valve 21,
The regulator 16 reduces the discharge amount Q of the hydraulic pumps 10A and 10B to the discharge amounts Qa and Qb illustrated in FIG. 6 based on the control pressure P at this time, that is, the set pressure P1 to load the prime mover 9. Is controlled to prevent engine stall (stalling) by overload prevention control.

[0023]

By the way, in the above-mentioned prior art, the pressure reducing valve 21 is provided in the middle of the control line 17B between the pilot pump 18, the tank 12 and the solenoid valve 20, and the solenoid valve 20 is controlled by the controller 40. Is switched from the switching position a to the switching position b, and when the overload prevention control of the prime mover 9 is performed, the control pressure P in the control line 17 is reduced to the set pressure P1 (see FIG. 6) of the pressure reducing valve 21, Each regulator 1
Since the control pressure P supplied to 6 exceeds the set pressure P1 and is controlled to rise, in the low speed region of the prime mover 9, the traveling control valves 22A and 22B and the working control valve 2 are controlled.
When at least one of 9A and 29B is switched from the neutral position, the discharge amount Q of the pressure oil discharged from the hydraulic pumps 10A and 10B is prevented from decreasing below the discharge amounts Qa and Qb shown in FIG. For example, it is possible to supply the hydraulic oil for traveling 8A, 8B or each boom cylinder 6D with the pressure oil of the discharge amounts Qa, Qb, and the operating speed of these can be significantly reduced in the low rotation speed region of the prime mover 9. I try to prevent it.

However, in the prior art, the hydraulic pump 10
When there is a slight dimensional error in the respective parts when manufacturing A and 10B, the characteristic line 19A shown in FIG. 6 is used when the displacement varying parts 11A and 11B of the hydraulic pumps 10A and 10B are tilt-driven by the respective regulators 16. , 19B, an error occurs in the discharge amount Q of the hydraulic pumps 10A, 10B. When the control pressure P from the control line 17 is reduced to the set pressure P1 by the pressure reducing valve 21, the hydraulic pump 10
Since there is a flow rate difference between the discharge amounts Qa and Qb of the pressure oil discharged from A and 10B, the travel control valves 22A and 22B are both switched from the neutral position to operate the pressure oil from the hydraulic pumps 10A and 10B. When the hydraulic motors 8A and 8B are supplied to and discharged from the hydraulic motors 8A and 8B respectively, a speed difference occurs in the rotational speeds of the traveling hydraulic motors 8A and 8B based on the flow rate difference, and the traveling hydraulic motors 8A and 8B cause left and right crawler belts 1A. , 1A may be driven at different speeds.

Therefore, in the prior art, for example, when the hydraulic excavator is advanced in the direction of arrow A in FIG. 4 to be loaded on the trailer or the like, the traveling hydraulic motors 8A, 8B are used to drive the left and right crawler belts 1A, 1A. However, there is a problem in that the hydraulic excavators meander as they are driven at different speeds, making it difficult to move the hydraulic excavator straight to a trailer or the like and load it.

The present invention has been made in view of the above-mentioned problems of the prior art. The present invention discharges pressure oil discharged from each hydraulic pump when performing overload prevention control or the like in a low speed region of a prime mover. A variable displacement hydraulic pump control device that can prevent variations in quantity and that can be easily loaded on a trailer by moving the hydraulic excavator straight when installed in a hydraulic circuit for traveling of a hydraulic excavator, etc. It is intended to be provided.

[0027]

The feature of the configuration adopted by the first invention to solve the above-mentioned problems is that the auxiliary hydraulic pressure is provided in the middle of a control line connecting each capacity control means to the auxiliary hydraulic pressure source. Another control pressure switching means connected in parallel with the control pressure switching means to the power source and switching the control pressure supplied to each of the capacity control means to a pressure higher than the set pressure of the pressure reducing valve when switched to the high pressure side. And a high pressure selecting means for selecting a high pressure side control pressure among the control pressures via the other control pressure switching means and the control pressure switching means and supplying the high pressure side control pressure to each of the displacement control valves. When any one of a plurality of types of directional control valves is switched from the neutral position in the low rotation speed region of the prime mover, the control pressure switching means and other controls are operated according to the type of the directional control valve that has been switched. A mechanism for selectively switching the pressure switching means to the high pressure side. Lies in the fact that with the.

Further, the feature of the configuration adopted by the second invention is that the controller controls the control pressure when any one of the plural kinds of directional control valves is switched from the neutral position in the low rotation speed region of the prime mover. The switching means is configured to switch to the high voltage side,
And when the control pressure switching means is switched to the high pressure side,
Control pressure selection means is provided for selectively switching the control pressure supplied to each capacity control means between the set pressure of the pressure reducing valve and a pressure higher than the set pressure in accordance with the type of the directional control valve that has been switched. It is in.

[0029]

With the above construction, when any of a plurality of types of directional control valves is switched from the neutral position in the low rotation speed region of the prime mover, the control pressure supplied to the capacity control means depends on the type of directional control valve. The set pressure of the pressure reducing valve and a pressure higher than this can be selected, and when the high pressure is selected, both the variable volume portions of the respective hydraulic pumps can be held at the minimum tilt position. Further, in each of the hydraulic pumps, when the displacement changing parts are both in the minimum tilting position, there is no more variation in the discharge amount of the pressure oil than in the position in the middle of tilting. It is possible to discharge the pressure oil at the same flow rate.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the embodiment, the same components as those of the prior art shown in FIGS. 4 to 6 described above are designated by the same reference numerals, and the description thereof will be omitted.

1 and 2 show a first embodiment of the present invention.

In the figure, 50 is a control line 5 used in this embodiment.
1 and the control lines 51A and 51B, the electromagnetic valve as another control pressure switching means is shown. The electromagnetic valve 50 is a tank 12, a pilot pump 18, and each regulator 16
Between them and are arranged in parallel with the solenoid valve 20. Then, the solenoid valve 50 is switched from the switching position a on the low pressure side to the switching position b on the high pressure side by a switching signal from a controller 54, which will be described later, and the control line 51 is switched and connected to either of the control lines 51A and 51B. To do. Here, the control line 51 is provided in parallel with the control line 17 described in the related art, the control line 51A is connected to the tank 12 together with the control line 17A, and the control line 51B is connected to the control line 1.
It is connected to the pilot pump 18 together with 7B.

Reference numeral 52 denotes a shuttle valve as a high pressure selecting means for selecting the high pressure side of the control pipes 17, 51, and 53 denotes another control pressure P on the high pressure side selected by the shuttle valve 52 to each regulator 16. A control line is shown, and the control line 5
3 is a solenoid valve 5 in response to a switching signal from the controller 54.
When 0 is switched from the switching position a to the switching position b,
By selecting the control pressure P from the control line 51 with the shuttle valve 52, the pressure higher than the set pressure P1 of the pressure reducing valve 21, that is, the pressure P2 which is the set pressure of the low pressure relief valve 41 is applied to each regulator 16 as the control pressure P. Supply as.

When the solenoid valve 20 is switched from the switching position a to the switching position b by the switching signal from the controller 54 and the electromagnetic valve 50 returns to the switching position a, the control line 53 is controlled by the shuttle valve 52. Control pressure P from line 17
Is selected, the set pressure P1 (P1 <P2) of the pressure reducing valve 21 is supplied to each regulator 16 as the control pressure P.

Further, reference numeral 54 denotes a controller composed of a microcomputer or the like, and the controller 54 has its input side connected to the pressure switches 37, 38, the rotation speed sensor 39, etc., similarly to the controller 40 described in the prior art. However, the output side of the controller 54 is connected to the solenoid valves 20, 50 and the like.
The controller 54 stores the program shown in FIG. 2 in its storage circuit and performs switching control processing of the solenoid valves 20 and 50 to execute overload prevention control of the prime mover 9. . In addition, the controller 5
The storage circuit of No. 4 stores, in its storage area (not shown), a determination value or the like for determining whether or not the rotation speed of the prime mover 9 is within a predetermined low rotation speed region.

The variable displacement hydraulic pump control device according to the present embodiment has the above-mentioned structure, and its basic operation is not significantly different from that of the prior art.

Therefore, the solenoid valve 2 by the controller 54
The switching control processing of 0 and 50 will be described with reference to FIG.

First, when the processing operation is started, in step 1, the respective detection signals are read from the traveling pressure switch 37, the working pressure switch 38, and the rotation speed sensor 39, and the routine proceeds to step 2, where the rotation speed of the prime mover 9 is read. Is within a predetermined low rotation speed region based on the rotation speed detection signal from the rotation speed sensor 39, and when the result is "NO", the rotation speed of the prime mover 9 is relatively high and an engine stall occurs. Since the possibility is very low, the process moves to step 3 and both the solenoid valves 20 and 50 are held at the switching position a, and the control pressure P supplied from the control line 53 shown in FIG. By lowering the pressure, each of the regulators 16 tilts the capacity varying portions 11A, 11B of the hydraulic pumps 10A, 10B to the maximum tilt position, and the hydraulic pumps 10A, 1B. The discharge amount of pressure oil discharged from the B set to the maximum discharge amount of about Qt shown in FIG. 6, repeat steps 1 and subsequent treatment with returns at step 4.

Next, when "YES" is determined in step 2, since the rotation speed of the prime mover 9 is within a predetermined low rotation speed range and there is a possibility of engine stalling, the process moves to step 5 and the traveling pressure switch is used. It is determined whether or not 37 is closed, and when the determination is "YES", the traveling control valve 22
Since at least one of A and 22B is switched from the neutral position and at least one of hydraulic motors 8A and 8B is rotationally driven by the pressure oil from hydraulic pumps 10A and 10B, rotation from hydraulic pumps 10A and 10B is performed. To prevent the prime mover 9 from stall due to load,
In step 6, a switching signal is output to the solenoid valve 50 to switch the solenoid valve 50 from the switching position a to the switching position b.

At this time, the low pressure relief valve 41
The pressure P2 from the pilot pump 18 set by the control line 53 is controlled via the control line 51B, the shuttle valve 52 and the like.
Since the control pressure P is introduced into each regulator 16,
The pressure P2 (P2> higher than the set pressure P1 of the pressure reducing valve 21).
P1) can be supplied as control pressure P, and each regulator 16
With the variable capacity portion 11A of the hydraulic pumps 10A and 10B,
11B can be tilted to the minimum tilt position.

As a result, the hydraulic pumps 10A, 10B
The discharge amount Q of the pressure oil discharged from the can be reduced to the minimum discharge amount Qn, and as shown in FIG.
In addition, it is possible to prevent variations between the hydraulic pumps 10A and 10B. Further, after switching the solenoid valve 50 from the switching position a to the switching position b in step 6, the process returns in step 7 and the processes from step 1 onward are repeated.

On the other hand, when it is judged "NO" in step 5, the traveling pressure switch 37 is opened, the traveling control valves 22A and 22B are both returned to the neutral position, and the traveling hydraulic motors 8A and 8B are stopped. Therefore, the routine proceeds to step 8 to judge whether or not the work pressure switch 38 is closed, and when it is judged to be "YES", the work control valves 29A and 29B are switched from the neutral position, and Since the boom cylinder 6D is operated by the pressure oil from the hydraulic pumps 10A and 10B, in order to prevent the prime mover 9 from stall due to the rotational load from the hydraulic pumps 10A and 10B, the process proceeds to step 9 and the solenoid valve 20 is operated. A switching signal is output to switch the solenoid valve 20 from the switching position a to the switching position b.

In this case, the solenoid valve 20 is switched to the switching position b, while the solenoid valve 50 is at the switching position a, so the control pressure P from the pilot pump 18 is changed.
Is reduced to a set pressure P1 by a pressure reducing valve 21, and this set pressure P1 can be supplied to each regulator 16 as a control pressure P. As a result, when the work control valves 29A and 29B are switched from the neutral position in the low rotation speed region of the prime mover 9, the discharge amount Q of the pressure oil discharged from the hydraulic pumps 10A and 10B is the discharge amount shown in FIG. The quantity Qa, Qb can be suppressed to an extent that an overload can be prevented from acting on the prime mover 9 and, at the same time, the operating speed of the prime mover 9 can be controlled by supplying the hydraulic oil of the discharge quantity Qa, Qb to each boom cylinder 6D. It is also possible to prevent a large decrease in the low rotation speed region.

When it is determined to be "NO" in step 8, the pressure switches 37 and 38 are both opened, and the traveling control valves 22A and 22B and the work control valves 29A and 29 are operated.
Since B is in the neutral position and the prime mover 9 does not stall due to the rotational load of the hydraulic pumps 10A and 10B, the routine proceeds to step 3, where both solenoid valves 20 and 50 are returned to the switching position a, and the routine returns at step 4. To do.

Thus, according to this embodiment, for example, when the hydraulic excavator is advanced in the direction of arrow A in FIG. 4 to be loaded on the trailer or the like, the left and right operation levers 24A,
When both 24B are tilted and the traveling control valves 22A and 22B are both largely switched from the neutral position, the control pressure P in the control line 53 automatically becomes the pressure P2 shown in FIG. Since the variable displacement parts 11A and 11B of the hydraulic pumps 10A and 10B can be tilt-driven to the minimum tilt position, both the discharge amount Q of the pressure oil discharged from the hydraulic pumps 10A and 10B can be reduced to the minimum discharge amount Qn. As shown in FIG. 6, it is possible to prevent variation in the discharge amount Qn between the hydraulic pumps 10A and 10B.

Therefore, in this embodiment, when the hydraulic excavator is run in the low rotation speed region of the prime mover 9, each regulator 16 causes the capacity varying portion 11 of the hydraulic pumps 10A and 10B to move.
By fixing both A and 11B to the minimum tilt position, it is possible to prevent a difference in flow rate between the hydraulic oils supplied to and discharged from the hydraulic pumps 10A and 10B to the traveling hydraulic motors 8A and 8B. , 8B, left and right tracks 1A, 1
By driving A at substantially the same speed, for example, a hydraulic excavator can be moved straight onto a trailer or the like and easily loaded.

Further, in order to stop the hydraulic excavator and operate the boom cylinders 6D with the pressure oil from the hydraulic pumps 10A and 10B, the operating lever 31 is tilted to make the work control valves 29A and 29B relatively large. When the stroke is made, the control pressure P in the control line 53 can be reduced to the set pressure P1 (see FIG. 6) of the pressure reducing valve 21 in the same manner as in the prior art,
The control pressure P supplied to each regulator 16 is the set pressure P
Since it becomes 1, the hydraulic pump 1 is operated in the low speed region of the prime mover 9.
The discharge amount Q of the pressure oil discharged from 0A, 10B becomes the discharge amounts Qa, Qb shown in FIG. 6, and it is possible to supply the pressure oil of about the discharge amount Qa, Qb toward each boom cylinder 6D, and these operating speeds are Various effects can be achieved, such as a large reduction in the low rotation speed region of the prime mover 9 can be prevented.

Next, FIG. 3 shows a second embodiment of the present invention. The feature of this embodiment is that the pressure reducing valve 21 used in the prior art is replaced in the middle of the control line 17B, and the control pressure is selected. The hydraulic pilot type switching valve 61 is provided as a means.

Here, the switching valve 61 has left and right hydraulic pilot portions connected to the pilot lines 62A and 62B,
The pilot line 62A guides the pilot pressure between the solenoid valve 20 and the switching valve 61 from the middle of the control line 17B. The pilot line 62B guides the pilot pressure from the middle of the branch line 33 between the traveling control valve 22A and the throttle 35, and at least one of the traveling control valves 22A and 22B is switched from the neutral position. At times, the switching valve 61 is held at the high pressure position c.

When the traveling control valves 22A and 22B are switched from the neutral position in the low rotation speed region of the prime mover 9, the pressure switch 37 is closed and the controller 40 causes the solenoid valve 20 to switch from the switching position a. Since the switching valve 61 is switched to the switching position b and the switching valve 61 is held at the high pressure position c, at this time, the pressure P2 from the pilot pump 18 set by the low pressure relief valve 41 is applied to each regulator 16.
Can be supplied as a control pressure P to each of the hydraulic pumps 10A and 10B by the regulators 16 and the variable capacity portions 11A and 11B of the hydraulic pumps 10A and 10B.
The hydraulic pumps 10A, 10
The discharge amount Q of the pressure oil discharged from B can be reduced to the minimum discharge amount Qn.

On the other hand, when the drive control valves 22A and 22B are both in the neutral position and the work control valves 29A and 29B are switched from the neutral position in the low speed region of the prime mover 9, the pressure switch 38 is closed. Controller 40
Causes the solenoid valve 20 to switch from the switching position a to the switching position b. However, at this time, the traveling control valve 22A and the throttle 3
The pressure in the pilot line 62B that guides the pilot pressure from the middle of the branch line 33 to 5 decreases to about the tank pressure, and the switching valve 61 becomes a pressure reducing valve and switches from the high pressure position c to the pressure reducing position d. The control pressure P in the control line 17 can be reduced to the set pressure P1 (see FIG. 6) as in the prior art, and the control pressure P supplied to each regulator 16 is restricted from rising above the set pressure P1. it can.

Thus, in this embodiment having such a structure, it is possible to obtain substantially the same operational effects as in the first embodiment, but especially in this embodiment, the pressure reducing valve 21 used in the prior art is used. The hydraulic pilot type switching valve 61 can be constructed only by substantially adding the pilot conduit 62B to
It is possible to greatly simplify the entire hydraulic circuit as compared with the above embodiment.

In the first embodiment, when it is determined in step 5 shown in FIG. 2 that the traveling pressure switch 37 is closed, the process proceeds to step 6 and a switching signal is sent to the solenoid valve 50. Although it has been described that the electromagnetic valve 50 is output and the electromagnetic valve 50 is switched from the switching position a to the switching position b, instead of this, a switching signal is output to the electromagnetic valves 20 and 50 in step 6, and the electromagnetic valves 20 and 50 are output. Both may be switched from the switching position a to the switching position b, and in this case, the same effect can be obtained. Then, in this case, the solenoid valve 50 can be operated as the control pressure selecting means which is a constituent feature of the second invention.

In each of the above embodiments, the work control valve 2 is used.
By switching the 9A and 29B from the neutral position, the boom cylinders 6D are moved to the hydraulic pumps 10A and 10B.
Although the present invention is not limited to this, the present invention is not limited to this, and in addition to the boom cylinders 6D, the arm cylinders, the bucket cylinders, the turning hydraulic motor, and the like are applied with the pressure oil from the hydraulic pumps 10A and 10B. It can also be applied to a hydraulic circuit adapted to operate.

Furthermore, in each of the above-mentioned embodiments, the hydraulic circuit of the hydraulic excavator has been described as an example, but the present invention is not limited to this, and the hydraulic pressure of a construction machine having a lower traveling body such as a hydraulic crane. Can be used in circuits.

[0056]

As described above in detail, according to the present invention, when any one of a plurality of types of directional control valves is switched from the neutral position in the low engine speed region, the directional control valve is switched. The control pressure to be supplied to the capacity control means is selectively switched between the set pressure of the pressure reducing valve and a pressure higher than the set pressure, so that the control pressure to be supplied to the capacity control means is reduced. When a pressure higher than the set pressure is selected, it becomes possible to hold both the variable displacement parts of each hydraulic pump in the minimum tilt position, and discharge the pressure oil discharged from each hydraulic pump at this minimum tilt position. The amount can be made constant, and it is possible to reliably prevent the discharge amount from varying for each hydraulic pump. Therefore, for example, when the hydraulic excavator is moved forward and loaded on a trailer or the like, it is possible to discharge the pressure oil of substantially the same flow rate from each hydraulic pump in a state where the rotation speed of the prime mover is reduced, and It has various effects such as being able to be straightly loaded onto a trailer or the like and easily loaded.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing a variable displacement hydraulic pump control device according to a first embodiment of the present invention.

FIG. 2 is a flow chart showing a switching control process of a solenoid valve.

FIG. 3 is a hydraulic circuit diagram showing a variable displacement hydraulic pump control device according to a second embodiment of the present invention.

FIG. 4 is a perspective view showing a conventional hydraulic excavator.

FIG. 5 is a hydraulic circuit diagram showing a variable displacement hydraulic pump control device according to a conventional technique.

FIG. 6 is a characteristic diagram showing a relationship between a control pressure for overload prevention control and a discharge amount of a hydraulic pump.

[Explanation of symbols]

1 Lower Traveling Body 2 Upper Revolving Body 6 Working Device 6D Boom Cylinder 8A, 8B Traveling Hydraulic Motor 9 Motors 10A, 10B Variable Capacity Hydraulic Pumps 11A, 11B Capacity Variable Section 12 Tanks 13A, 13B, 14A, 14B, 15A, 15B Main pipeline 16 Regulator (capacity control means) 17, 17A, 17B, 51, 51A, 51B, 53
Control pipe 18 Pilot pump (auxiliary hydraulic power source) 20 Electromagnetic valve (control pressure switching means) 21 Pressure reducing valve 22A, 22B Travel control valve (direction switching valve) 29A, 29B Work control valve (direction switching valve) 37, 38 Pressure switch (operation detection means) 39 Rotation speed sensor (rotation speed detection means) 40, 54 Controller 41 Low pressure relief valve 50 Electromagnetic valve (other control pressure switching means) 52 Shuttle valve (high pressure selection means) 61 Hydraulic pilot type switching valve (Control pressure selection means) 62A, 62B Pilot line

Front Page Continuation (72) Inventor Masao Takagi 650, Kazunachi-cho, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Engineering Co., Ltd.

Claims (2)

[Claims] 1. A prime mover and driven by the prime mover,
A plurality of variable displacement hydraulic pumps each having a variable displacement portion; and a plurality of displacement control means for tilt-driving the variable displacement portion of each hydraulic pump by external control pressure to control the displacement of each hydraulic pump. A control pressure switching means that is provided in the middle of a control line connecting each of the displacement control means to the auxiliary hydraulic pressure source, and that switches the control pressure supplied from the auxiliary hydraulic pressure source to each of the displacement control means between a low pressure side and a high pressure side. Provided between the control pressure switching means and the sub-hydraulic power source and provided in the middle of the control line, and when the control pressure switching means is switched to the high pressure side, the control pressure is reduced to a set pressure. A plurality of pressure reducing valves and a plurality of pressure control valves that are provided in the middle of the main pipes that connect the hydraulic pumps and the tanks to a plurality of types of hydraulic actuators and that control the flow rate and direction of the pressure oil supplied from the hydraulic pumps to the hydraulic actuators. Seed A directional control valve, a plurality of operation detecting means for detecting whether or not each directional control valve is switched from a neutral position, a rotational speed detecting means for detecting the rotational speed of the prime mover, the rotational speed detecting means, and A variable displacement hydraulic pump control device comprising a controller that outputs a switching signal to the control pressure switching means based on a detection signal from each operation detecting means, and controls switching of the control pressure switching means. Is connected in parallel to the control pressure switching means with respect to the sub-hydraulic power source in the middle of the control line connecting the sub-hydraulic power source, and the control pressure supplied to each of the capacity control means when switched to the high pressure side. Is controlled to a pressure higher than the set pressure of the pressure reducing valve, and the control pressure on the high pressure side is selected from the control pressures via the other control pressure switching means and the control pressure switching means. The above capacity system And a high pressure selecting means for supplying the valve to the controller, wherein the controller performs the switching operation when one of the directional switching valves of the plurality of types is switched from a neutral position in a low rotation speed region of the prime mover. A variable displacement hydraulic pump control device, characterized in that the control pressure switching means and other control pressure switching means are selectively switched to a high pressure side in accordance with the type of the directional control valve. 2. A prime mover, driven by the prime mover,
A plurality of variable displacement hydraulic pumps each having a variable displacement portion; and a plurality of displacement control means for tilt-driving the variable displacement portion of each hydraulic pump by external control pressure to control the displacement of each hydraulic pump. A control pressure switching means that is provided in the middle of a control line connecting each of the displacement control means to the auxiliary hydraulic pressure source, and that switches the control pressure supplied from the auxiliary hydraulic pressure source to each of the displacement control means between a low pressure side and a high pressure side. Provided between the control pressure switching means and the sub-hydraulic power source and provided in the middle of the control line, and when the control pressure switching means is switched to the high pressure side, the control pressure is reduced to a set pressure. A plurality of pressure reducing valves and a plurality of pressure control valves that are provided in the middle of the main pipes that connect the hydraulic pumps and the tanks to a plurality of types of hydraulic actuators and that control the flow rate and direction of the pressure oil supplied from the hydraulic pumps to the hydraulic actuators. Seed A directional control valve, a plurality of operation detecting means for detecting whether or not each directional control valve is switched from a neutral position, a rotational speed detecting means for detecting the rotational speed of the prime mover, the rotational speed detecting means, and A variable displacement hydraulic pump control device comprising a controller that outputs a switching signal to the control pressure switching means based on a detection signal from each of the operation detecting means, and controls switching of the control pressure switching means. The control pressure switching means is configured to switch to the high pressure side when any one of the plurality of types of directional control valves is switched from the neutral position in the low rotation speed region of the prime mover, and the control pressure switching means has a high pressure side. When the pressure is switched to the side, the control pressure supplied to each of the displacement control means is set to the set pressure of the pressure reducing valve and a pressure higher than the set pressure according to the type of the directional control valve that has been switched. Variable displacement hydraulic pump control system is characterized by providing a control pressure selection means for switching the 択的.