JPH09177138A - Hydraulic circuit of hydraulic shovel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to hold oil pressure necessary for up-motion of a boom when horizontal levelling work is executed with simultaneous operation of both arm and boom and, at the same time, to prevent a motor from lowering its motion efficiency. SOLUTION: Based on discharge pressure Pp of a first hydraulic pump 15 detected by a discharge pressure sensor 34, a controller 33 outputs a branch flow control signal having value obtained by performing an operation based on a transformation function prescribing relation between the discharge pressure Pp of the first hydraulic pump 15 read out from a storage section and target opening area ST of an auxiliary selector valve 23 and a plurality of transformation functions into a proportional electromagnetic valve 32. The opening area SS of the auxiliary selector valve 23 is controlled by pilot oil flowing out from the proportional electromagnetic valve 32, and when the discharge pressure Pp is in excess of lower limited discharge pressure P0 , branch flow of driving pressure oil flowing out to oil suppy side of a combined flow selector valve 17 passing through an alternative bypass oil passage is increased with the transformation function.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a hydraulic circuit of a hydraulic excavator having a plurality of hydraulic sources and an actuator drive system circuit composed of a tandem circuit.

[0002]

2. Description of the Related Art Water averaging work is one of the standard works of a hydraulic excavator which is a typical construction machine. This water leveling work involves extending the arm to almost the maximum reaching position, then pulling the arm while slightly lifting the boom, pulling the bucket tip or bottom along the horizontal plane and leveling the ground horizontally. To tell. As the arm is pulled toward you, the boom's rising speed is reduced, and the arc trajectory caused by the arm's pulling motion is corrected to a horizontal trajectory. When the arm reaches the bottom dead center, the boom's rising speed is reduced to 0. To In order to perform the water averaging work by such simultaneous operation of the arm and the boom quickly and efficiently, the hydraulic circuit of the actuator drive system including the boom switching valve and the arm switching valve has a plurality of hydraulic sources. Often composed of tandem circuits.

As an example of such a prior art, an actual fair 7-
There is a device described in Japanese Patent No. 30776. In order to mitigate the driver's uncomfortable feeling in water leveling work, this device supplies the oil for the merging switching valve to the tandem-connected arm cylinder from the oil path for the boom switching valve connected on the upstream side. An auxiliary switching valve is placed between the bypass bypass oil passages that reach the road, and this auxiliary switching valve is linked with the switching operation of the boom switching valve to operate in the order of closing, opening, and closing as the spool moves. As a result, the combined flow rate of pressure oil to the arm cylinder is compensated for, and the operational discomfort caused by closing the outlet to the central bypass oil passage at the early switching operation of the boom switching valve is alleviated. It is a thing.

[0004]

As described above, the above-mentioned prior art is intended to reduce the operator's uncomfortable feeling in water averaging work by changing the boom switching valve from the boom switching valve. The sudden decrease in the flow rate of pressure oil flowing out to the side of the central bypass oil passage is compensated to some extent by the switching operation of the auxiliary switching valve through the bypass oil passage. If the load on the arm is light, there may occur a problem that sufficient drive pressure cannot be obtained for performing the boom raising operation. Therefore, the opening amount of the auxiliary switching valve when the arm lever is operated is made too large. I can't. Therefore, it is not sufficient to supply a large amount of pressure oil required for the arm cylinder during water averaging work, and the discharge oil supplied to the supply oil passage on the upstream side of the boom switching valve is not shown in the drawing. Since the oil is discharged to the oil tank through the valve, there is a problem that the operation efficiency of the prime mover is poor. The present invention has been made to solve the above problems in the prior art, and when performing water leveling work by simultaneous operation of the arm and the boom, it is possible to maintain the hydraulic pressure necessary for the raising operation of the boom and the prime mover. It is an object of the present invention to provide a hydraulic circuit for a hydraulic excavator that does not reduce the operating efficiency of the hydraulic excavator.

[0005]

In order to solve the above problems, the present invention provides a bypass bypass oil passage for bypass connection between the oil supply side of a boom switching valve and the oil supply side of a merging switching valve. By providing an auxiliary switching valve and controlling the flow rate of the auxiliary switching valve according to the discharge pressure of the first oil supply source, it is possible to suppress wasteful energy loss of the discharge oil of the first oil supply source. Preferably, the relationship between the discharge pressure sensor that detects the discharge pressure of the first oil supply source and the branch flow rate of the drive pressure oil that passes through the auxiliary switching valve corresponding to the discharge pressure of the first oil supply source is defined. First detected by the discharge pressure sensor based on the conversion function
The control means for determining the branch flow rate corresponding to the discharge pressure of the oil supply source and controlling the opening area of the auxiliary switching valve in accordance with the branch flow rate.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention comprises at least two oil supply sources, one of which has a boom switching valve and a merging switching valve for joining to an arm cylinder in tandem from the upstream side in this order. Hydraulic pressure that is connected so that pressure oil flowing out from the arm switching valve and pressure oil flowing out from the merging switching valve or pressure oil blocked from flowing out by the merging switching valve merges and flows into the arm cylinder. It is applied to a hydraulic excavator equipped with a circuit and realizes water pressure averaging to efficiently distribute pressure oil while maintaining the drive oil pressure necessary for raising the boom, while eliminating energy loss, that is, waste. It is a measure to prevent waste of fuel. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0007]

1 is a hydraulic circuit diagram according to a first embodiment of the present invention. In the figure, 11 is an arm, 12 is an arm cylinder, 13 is a boom, 14 is a boom cylinder,
Reference numeral 15 is a first hydraulic pump, 16 is a boom switching valve to which the discharge oil of the first hydraulic pump 15 is supplied, 17 is a merging switching valve tandem-connected to the boom switching valve 16, and 18 is a second
A hydraulic pump, 19 is an arm switching valve to which the discharge oil of the second hydraulic pump 18 is supplied, 20 is a bucket, 21 is a boom switching pilot valve for switching the boom switching valve 16, and 22 is an arm switching valve. An arm switching pilot valve for switching 19 and 23 is the first hydraulic pump 1
The discharge oil of No. 5 is an auxiliary switching valve that is provided in the middle of the pipeline that is bypassed to the merging switching valve 17 side to prevent outflow of the passing pressure oil or control the flow rate, 31 is a pilot hydraulic pump, and 32 is an auxiliary switching valve. A proportional solenoid valve for controlling the flow rate of the pilot oil guided to the pilot chamber of 23 in proportion to the branch flow rate control signal, and 33 for joining the discharge oil of the first hydraulic pump 15 based on the discharge pressure of the first hydraulic pump 15. Switching valve 17
A controller that outputs a branch flow rate control signal that defines the branch flow rate to the side to the proportional solenoid valve 32, and 34 is a discharge pressure sensor that detects the discharge pressure of the first hydraulic pump 15.

FIG. 2 is an opening characteristic diagram of the opening area S _S of the auxiliary switching valve 23 with respect to the pilot pressure P _e from the proportional solenoid valve 32. As shown in the figure, the opening area S _S of the auxiliary switching valve 23 increases linearly through a predetermined dead zone as the pilot pressure P _e from the proportional solenoid valve 32 increases until it reaches the maximum opening area. It has an opening characteristic. FIG. 3 is a block diagram showing the internal configuration of the controller. In the figure, 25 is an input unit for receiving various signals such as a discharge pressure signal from the discharge pressure sensor 34, and 26 is, for example, the input unit 2
A computing unit that computes the above-mentioned branch flow rate control signal based on the function of the discharge pressure signal input to 5 and the characteristic curve stored in the storage unit described later, and 27 is the discharge pressure P _P of the first hydraulic pump 15 and the auxiliary. A storage unit that stores in advance a conversion function of a characteristic curve that defines the relationship with the target opening area S _T of the switching valve 23 and a plurality of conversion functions, and 28 is an output unit that outputs the branch flow rate control signal calculated by the calculation unit 26. is there.

FIG. 4 is a characteristic curve of a conversion function that defines the relationship between the discharge pressure P _P of the first hydraulic pump 15 read from the storage unit 27 and the target opening area S _T of the auxiliary switching valve 23, and a plurality of conversion functions. 6A is a graph showing characteristic curves of a plurality of conversion functions in the process of calculating the branch flow rate control signal according to the above, in which (a) is the discharge pressure P _P of the first hydraulic pump 15 and the target opening area S _T of the auxiliary switching valve 23. characteristic curve defining the relationship between, (b) the characteristic curve representing the relationship between the target opening area S _T with the target pilot pressure P _e from the proportional solenoid valve 32,
(C) shows a characteristic curve representing the relationship between the target pilot pressure P _e and the current value I _C of the branch flow rate control signal.

The operation of this embodiment will be described with reference to FIGS. The present invention was made by paying attention to the water averaging work of the hydraulic excavator. Since the characteristic operation is performed in the work, here, the water averaging work in which the arm 11 and the boom 13 are simultaneously operated is performed. The operation will be described. First, the arithmetic processing of the controller 33 will be described.
First, from the storage unit 27, the discharge pressure P _P of the first hydraulic pump 15 and the target opening area S of the auxiliary switching valve 23 shown in FIG.
Read the conversion function of the characteristic curve that defines the relationship with _T.
The conversion function of this characteristic curve is determined based on the operating characteristics of the hydraulic excavator and the like, and is stored in the storage unit 27 in advance. As shown in the figure, in this embodiment, the target opening area S _T
Is ₀ until the discharge pressure P _P of the first hydraulic pump 15 reaches the lower limit discharge pressure P 0, that is, the auxiliary switching valve 23 is closed,
When the discharge pressure P _P exceeds the lower limit discharge pressure P ₀ , the target opening area S _T is gradually increased to the maximum opening area S _M.

The calculation unit 26 calculates the conversion function between the discharge pressure P _P and the target opening area S _T as the discharge pressure P _P and the proportional solenoid valve 3.
Using the conversion function between the target pilot pressure P _e from 2, into a transformation function between a target opening area S _T and the pilot pressure P _e (FIG. 4 (b)), further, the target opening area S
_It is converted into a conversion function (FIG. 4 (c)) between the pilot pressure P _e giving _T and the current value I _C of the branch flow rate control signal. Using the three kinds of conversion functions thus obtained, the input unit 25
A branch flow rate control signal having a current value I _C is calculated from the discharge pressure P _P signal input to the output signal and output from the output unit 28 to the proportional solenoid valve 32.

As described above, in the water averaging work, the arm cylinder 12 and the boom cylinder 14 are contracted so that the bucket 20 reaches the maximum reaching position, and then the arm cylinder 12 is extended to move the arm 11 to the driver seat side. The boom cylinder 14 and the boom 1
3 is started at a middle level, and thereafter, it is executed by an operation of lifting while gradually decelerating. This operation will be described with reference to FIG. 1. At the start of the water averaging operation, the boom switching pilot valve 21 is operated with a medium operation amount and the arm switching pilot valve 22 is operated with a maximum operation amount at the same time. By such a lever operation of the driver, the pilot oil flowing out from the boom switching pilot valve 21 and the arm switching pilot valve 22 is supplied to the right pilot chamber of the boom switching valve 16 and the merging switching valve 17 and the arm switching valve 19, respectively. It flows into the left pilot chamber and switches the boom switching valve 16, the merging switching valve 17, and the arm switching valve 19 to the right switching position and the left switching position, respectively. This allows
Since the supply of pressure oil to the central bypass oil passage of the boom switching valve 16 is throttled, the discharge oil of the first hydraulic pump 15 passes through the boom switching valve 16 to the bottom side of the boom cylinder 14 and the second hydraulic pump 18 The discharge oil of is the switching valve 19 for the arm.
And flows into the bottom side of the arm cylinder 12.

At this time, since the spool opening of the boom switching valve 16 is considerably open, the oil discharged from the first hydraulic pump 15 flows into the boom cylinder 14 with almost no throttling resistance by the boom switching valve 16. Therefore, since the discharge pressure P _P of the first hydraulic pump 15 has not reached the lower limit discharge pressure P ₀ , the target opening area S _T = 0, the target pilot pressure P _e of the proportional solenoid valve 32 is the initial discharge pressure P _e0 , and the branch The current value I _C of the flow rate control signal becomes the initial value I _C0 , the auxiliary switching valve 23 is closed, and the discharge oil of the first hydraulic pump 15 passes through the bypass bypass oil passage to the oil supply side of the merging switching valve 17. Does not flow. After that, the boom switching pilot valve 21 is returned to reduce the rising speed of the boom 13. As a result, the spool position of the boom switching valve 16 is slightly returned to the right side, and the spool opening is gradually narrowed.

At this time, since the spool opening of the boom switching valve 16 to the central bypass oil passage is still closed,
Since the discharge oil of the first hydraulic pump 15 cannot flow out to the actuator through the boom switching valve 16 at a sufficient flow rate, the first hydraulic pump 1 detected by the discharge pressure sensor 34.
The discharge pressure P _{P of} 5 gradually increases, and eventually the lower limit discharge pressure P ₀
Beyond. Therefore, the target opening area S _T > 0, the target pilot pressure P _e > P _{e0 of} the proportional solenoid valve 32, the current value I _C > I _{C0 of} the branch flow rate control signal, and the auxiliary switching valve 23 is gradually opened and the first hydraulic pressure is increased. A part of the oil discharged from the pump 15 flows out to the oil supply side of the merging switching valve 17 through the bypass oil passage. When the discharge pressure P _P of the first hydraulic pump 15 rises as the boom switching pilot valve 21 is returned, the target opening area S _T , the target pilot pressure P _e of the proportional solenoid valve 32, and the branch flow rate control signal. The first hydraulic pump 1 whose current value I _C increases and flows out to the oil supply side of the merging switching valve 17 through the auxiliary switching valve 23 and the bypass bypass oil passage.
5 increases the flow rate of the discharge oil, and works to suppress the rise of the discharge pressure P _P of the first hydraulic pump 15.

Therefore, the discharge pressure P _P of the first hydraulic pump 15
Rises and the first hydraulic pump 1 passes through a pressure relief valve (not shown).
It is possible to prevent the discharged oil of No. 5 from being unnecessarily released and discharged to the oil tank. Eventually, when the bucket 20 is pulled back to a distance approximately halfway the maximum reaching position, the boom switching pilot valve 21 is returned to the neutral position, and the flow rate of the pilot oil supplied to the right pilot chamber of the boom switching valve 16 is increased. Since it becomes 0, the spool position of the boom switching valve 16 returns to the neutral position. At this time, the switching valve 16 for the boom has already been
Since the spool opening to the central bypass oil passage is greatly opened, the discharge oil of the first hydraulic pump 15 flows out to the oil supply side of the merging switching valve 17 through the central bypass oil passage of the boom switching valve 16. A large amount of pressure oil is supplied to the oil supply side of the merging switching valve 17 together with the pressure oil merging to the oil supply side of the merging switching valve 17 through the bypass bypass oil passage. The discharge pressure P _{P of} 15 decreases.

Then, when the bucket 20 passes a distance approximately halfway of the maximum reaching position, the boom switching pilot valve 2
1 is operated to lower the boom 13, the spool opening of the boom switching valve 16 to the central bypass oil passage is closed, and the spool position is switched to the left switching position with the throttling. As a result, the discharge pressure P _P of the first hydraulic pump 15 rises, so the controller 33 outputs to the proportional solenoid valve 32 a branch flow rate control signal having a current value I _C commensurate with the discharge pressure P _P , and the auxiliary switching valve 23. The opening area S _S is opened so as to correspond to the discharge pressure P _P.
In this way, the retracting operation of the arm 11 and the lowering operation of the boom 13 are performed until the bucket 20 reaches the maximum approach position.

As described above, in this embodiment, when the water leveling operation is performed, when the boom switching lever is operated in the vicinity of the neutral position, the spool opening of the boom switching valve 16 to the central bypass oil passage is closed. When the spool position is switched to the left or right switching position with the throttle in the opened state, the accumulated oil of the discharge oil of the first hydraulic pump 15 is adjusted to the discharge pressure P _P of the first hydraulic pump 15 by the auxiliary switching valve 23. Since it is opened so as to have a large opening area, it merges with the oil supply side of the merging switching valve 17 via the bypass bypass oil passage, so that it can be effectively utilized for the retracting operation of the arm 11. It is possible to prevent wasteful discharge of discharged oil from the hydraulic pump 15 to the oil tank. In addition, the first hydraulic pump 15
So that the opening area S _S commensurate with the discharge pressure P _P of the first hydraulic pump 15 based on the relationship between the target opening area S _T of the discharge pressure P _P and the auxiliary switching valve 23 to the function of the regulatory characteristic curve Since the opening / closing control of the auxiliary switching valve 23 is performed, the flow rate of the discharge oil of the first hydraulic pump 15 to be merged with the oil supply side of the merging switching valve 17 via the bypass bypass oil passage is set to a value according to a desired characteristic. You can

FIG. 5 is a hydraulic circuit diagram according to the second embodiment of the present invention. In the figure, 17a is an arm merging switching valve, and 24 is a high-pressure selection valve. The parts which are the same as or considered to be the same as those in the first embodiment are designated by the same reference numerals, and the duplicated description thereof will be omitted. . The same applies to the following description. In this embodiment, the merging switching valve 17 in the first embodiment is replaced by the arm merging switching valve 17a, and the pilot chamber thereof is selected by the high-pressure selection valve 24 and is switched from one switching valve of the arm switching pilot valve 22. The outflowing pilot oil flows in, and the discharged oil of the first hydraulic pump 15 outflowing from the auxiliary switching valve 23 further flows into the oil supply side of the arm merging switching valve 17a via the bypass bypass oil passage. At the same time, it also flows into the oil supply side of the arm switching valve 19.

Therefore, when the arm switching pilot valve 22 is in the neutral position, the oil supply side of the arm merging switching valve 17a is connected to the oil tank, and when the arm switching pilot valve 22 is operated in either direction. To be closed. When the water leveling operation is performed, the boom switching pilot valve 21 and the arm switching pilot valve 22 are simultaneously operated, so the arm merging switching valve 17a is closed and the pressure oil flowing out from the auxiliary switching valve 23 is transferred to the arm. It flows only into the oil supply side of the operation switching valve 19 and joins with the oil discharged from the second hydraulic pump 18. In the operation of the present embodiment configured as described above, the flow path of the pressure oil flowing out from the auxiliary switching valve 23 in the water averaging work is different, but in the end, it joins the pressure oil flowing into the arm cylinder 12 and is therefore the first. It is basically the same as that of the embodiment.

FIG. 6 is a hydraulic circuit diagram according to the third embodiment of the present invention. In the figure, reference numeral 35 is a mode changeover switch. This embodiment is different from that of the first embodiment in that the other end of the mode changeover switch 35, one end of which is connected to the ground potential, is connected to the controller 33. The conversion function of the characteristic curve that defines the relationship of the target opening area S _T of the auxiliary switching valve 23 with respect to the discharge pressure P _P of the first hydraulic pump 15 is changed.

FIG. 7 is a graph showing characteristic curves of two modes 1 and 2 selected by switching the mode selector switch 35. The graph of mode 1 is the same as that of the first embodiment, and the graph of mode 2 has the same shape as the characteristic curve of mode 1, but the lower limit discharge pressure is mode 1.
It is slightly major lower discharge pressure P ₀₂ than the lower discharge pressure P ₀₁ in.

In this way, by switching between the two modes, the two modes are switched according to the weight of the bucket 20, and when the heavy bucket 20 is mounted, the mode 2 can be selected to select the boom 13. It is possible to secure a sufficient drive pressure for the boom cylinder 14 required during the raising operation. In this embodiment, the first hydraulic pump 1
Although the mode for changing the characteristic of the target opening area S _T of the auxiliary switching valve 23 with respect to the discharge pressure P _{P of} 5 can be selected in two stages, of course, it may be switched in multiple stages and the characteristic curve is arbitrary. Can be made up of curves.

Further, in the above embodiment, the target opening area S _T of the auxiliary switching valve 23 is proportional to the controller 33 based on the discharge pressure signal from the discharge pressure sensor 34 which detects the discharge pressure P _P of the first hydraulic pump 15. A branch flow control signal is output to the solenoid valve 32 to open the opening area S _S of the auxiliary switching valve 23 so that the opening area corresponds to the discharge pressure P _P. Alternatively, the controller 33 may directly switch the auxiliary switching valve 23, or a characteristic curve defining the relationship between the discharge pressure P _P of the first hydraulic pump 15 and the target opening area S _T of the auxiliary switching valve 23. Is approximated by a straight line, the first hydraulic pump 1
The discharge pressure P _{P of} 5 may be directly guided to the pilot chamber of the auxiliary switching valve 23.

[0024]

As described above, according to the first aspect of the invention, the discharge of the first oil supply source is controlled by controlling the flow rate of the auxiliary switching valve according to the discharge pressure of the first oil supply source. Since the wasteful energy loss of oil is suppressed, the hydraulic pressure required for raising the boom can be maintained and the decrease in operating efficiency of the prime mover can be suppressed when performing water leveling work by simultaneous operation of the arm and boom. be able to. According to the second aspect of the invention, the first oil supply is based on the conversion function that defines the relationship of the branch flow rate of the driving pressure oil that passes through the auxiliary switching valve corresponding to the discharge pressure of the first oil supply source. Since a branch flow rate corresponding to the discharge pressure of the first oil supply source detected by the discharge pressure sensor for detecting the discharge pressure of the oil source is obtained, and the control means for controlling the opening area of the auxiliary switching valve according to the branch flow rate is provided, The branch flow rate of the oil discharged from the first oil supply source can be set to a value according to desired characteristics. According to the third aspect of the invention, the conversion function that defines the relationship of the branch flow rate of the driving pressure oil that passes through the auxiliary switching valve corresponding to the discharge pressure of the first oil supply source is changed by switching the mode switching switch. Therefore, by selecting a desired conversion function, the branch flow rate corresponding to the discharge pressure of the first oil supply source can be appropriately adjusted. For example, the branch flow rate is required according to the weight of the boom during the raising operation. The drive pressure of the boom cylinder can be secured.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram according to a first embodiment of the present invention.

FIG. 2 is an opening characteristic diagram of the opening area of the auxiliary switching valve with respect to the pilot pressure from the proportional solenoid valve.

FIG. 3 is a block diagram showing an internal configuration of a controller.

FIG. 4 is a graph showing a characteristic curve of a conversion function that defines the relationship between the discharge pressure of the first hydraulic pump and the target opening area of the auxiliary switching valve, and a characteristic curve of a plurality of conversion functions in the process of calculating the branch flow rate control signal.

FIG. 5 is a hydraulic circuit diagram according to a second embodiment of the present invention.

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

FIG. 7 is a graph showing a characteristic curve of a mode selected by switching the mode selector switch.

[Explanation of symbols]

 11 Arms 12 Arm Cylinders 13 Booms 14 Boom Cylinders 15 1st Hydraulic Pump 16 Boom Switching Valves 17 Merging Switching Valves 17a Arms Merging Switching Valves 18 2nd Hydraulic Pumps 19 Arm Switching Valves 20 Buckets 21 Boom Switching Pilot Valves 22 Arms Changeover pilot valve 23 Auxiliary changeover valve 24 High pressure selection valve 31 Pilot hydraulic pump 32 Proportional solenoid valve 33 Controller 34 Discharge pressure sensor 35 Mode changeover switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichi Furuwato 650 Jinrachi-cho, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. Tsuchiura factory (72) Inventor, Shigehiro Yoshinaga, 650 Jinrachicho, Tsuchiura City, Ibaraki Prefecture Hitachi Construction Machinery Co., Ltd.

Claims (3)

[Claims] 1. An oil supply source of a plurality of drive pressure oils, and a first oil supply source of one of the oil supply sources are connected in tandem from upstream to downstream, and the drive pressure oils to the boom cylinder are connected. Connected to a boom switching valve for switching the direction and flow rate, a merging switching valve for merging driving pressure oil to the arm cylinder, and another one second oil supply source of the oil supply source, In a hydraulic circuit of a hydraulic excavator equipped with an arm switching valve for switching the direction and flow rate of driving pressure oil to the arm cylinder, an oil supply side of the boom switching valve and an oil supply side of the merging switching valve. By providing an auxiliary switching valve in a bypass bypass oil passage that makes a detour connection between the two, and controlling the flow rate of the auxiliary switching valve according to the discharge pressure of the first oil supply source, Suppresses wasteful energy loss of discharged oil The hydraulic circuit of a hydraulic excavator characterized by 2. A relationship between a discharge pressure sensor that detects the discharge pressure of the first oil supply source and a branch flow rate of the driving pressure oil that passes through an auxiliary switching valve corresponding to the discharge pressure of the first oil supply source. Control means for determining the branch flow rate corresponding to the discharge pressure of the first oil supply source detected by the discharge pressure sensor on the basis of a conversion function that defines, and controlling the opening area of the auxiliary switching valve in accordance with the branch flow rate. It has the following.
Hydraulic circuit of the described excavator. 3. A conversion which has a mode changeover switch, and defines the relationship of the branch flow rate of the driving pressure oil passing through the auxiliary changeover valve corresponding to the discharge pressure of the first oil supply source by switching the mode changeover switch. The hydraulic circuit of the hydraulic excavator according to claim 2, wherein the function is changed.