KR20000052452A - The hydraulic circuit for construction machine - Google Patents

Abstract

PURPOSE: A hydraulic circuit of a construction equipment is provided to obtain sufficient binding force for a burden and to improve performance by inhibiting reduction of speed for binding the burden. CONSTITUTION: In binding a burden, a binding mode switch(23) is turned on and a boom lever(21) is lifted at the same time. A controller(26) inputs the lift signal of a lift sensor(22) and a binding mode signal of the switch(23). The controller(26) excites first and second electronic change valves(24,25) if an actuator such as a bucket lever is in a neutral range. Thereby, a pilot pressure unit(14d) of a relief valve(14) is connected to a control pump(5) through a b position of the first electronic change valve(24) to boost the set pressure of the relief valve(14) up to a high pressure. In addition, a pilot pressure unit(8a) of the cutoff valve(8) is communicated to the control pump(5) through a b position of the second change valve(25) to stop operating the cutoff valve(8).

Description

Hydraulic circuit of construction machinery {THE HYDRAULIC CIRCUIT FOR CONSTRUCTION MACHINE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit of a construction machine, and more particularly, in the hydraulic circuit of a construction machine having a cut-off function, a force and a speed of a work machine in the case of hanging a load, raising a tree stump or raising a seat. At the same time, the invention relates to a hydraulic circuit of a construction machine which releases the cutoff function when needed and at the same time improves the ability to suspend the maximum discharge pressure of the hydraulic circuit.

Background Art Conventionally, a hydraulic excavator sometimes carries out a load-bearing operation by raising and lowering a boom. The first prior art of the hydraulic circuit of the construction machine shown in FIG. 7 will be described.

The discharge line 1a of the variable displacement pump 1 is connected to the boom cylinder 3 via the boom direction switching valve 2, and the discharge line 1a of the variable displacement pump 1 has the highest discharge pressure ( The relief valve 4 for setting the set pressure P1 is connected. The discharge oil of the control pump 5 is set to a constant pressure by the fixed relief valve 6, and the capacity control means of the variable displacement pump 1 from the cutoff valve 8 via the torque variable control valve 7 ( 9) is connected. The torque variable control valve 7 inputs the pump discharge pressure P of the variable displacement pump 1, and discharges the discharge oil of the control pump 5 set to a constant pressure to the pump of the variable displacement pump 1. It outputs by controlling with the control pressure which makes constant the torque K2 which the capacity | capacitance (V) (cc / rev) shows by P * V. That is, it becomes orthogonal hyperbola as shown by torque K2 in FIG. The cutoff valve 8 inputs the control pressure output from the torque variable control valve 7 so that the pump discharge pressure P of the variable displacement pump 1 is near the set pressure P1 of the relief valve 4. (I.e., Pa), as shown by the curve C in FIG. 8, the pump capacity V of the variable displacement pump 1 is gradually reduced to the set pressure P1 of the relief valve 4 to minimize the pump. The control pressure set to the capacitor V1 is output. The capacity control means 9 inputs a control pressure output from the cutoff valve 8 to control the pump capacity V of the variable displacement pump 1 as indicated by K2 and C in FIG. 8. It consists of a control valve and a capacity control cylinder (both not shown).

The operation of the first prior art will be described with reference to Figs.

The pump capacity V of the variable displacement pump 1 is K2 in FIG. 8 in accordance with the pump discharge pressure P of the variable displacement pump 1 determined by the load pressure acting on the boom cylinder 3. And a torque curve represented by C. In addition, although the pump capacity | capacitance (V) was taken in the horizontal axis in FIG. 8, when the pump discharge amount Q (m <^3> / min) is taken, the torque curve shown by K2 and C will become a horsepower curve. Therefore, the loss torque K1 at which the variable displacement pump 1 reliefs at point A at the cutoff (i.e., P1V1) is the loss torque at which the variable displacement pump 1 reliefs at point B at the time of cutoff release. It decreases compared with (K2) (that is, P1 and V2). Therefore, the loss horsepower which the variable displacement pump 1 reliefs at the point A decreases compared with the loss horsepower which the variable displacement pump 1 reliefs at the point B, and can save energy.

A second prior art (for example, described in Japanese Patent Laid-Open No. 6-72437) shown in FIG. 9 will be described. In addition, in the parenthesis after each component, the component of this invention is shown, and after describing the component of this invention, the same code | symbol is attached | subjected to the component same as a 1st prior art, and the description is abbreviate | omitted. do.

In the working machine hydraulic circuit of the hydraulic excavator, the return passage 10 passing through each of the directional valves is connected to the tank 12 via the throttle 11. The discharge oil of the hydraulic pump (control pump) 5 set to a constant pressure is connected to the pilot pressure receiving portion 14b of the variable relief valve (relief valve) 14 via the solenoid valve 13, and also to the shuttle valve. It is connected to the capacity control means 16 of the variable displacement hydraulic pump (variable displacement pump) 1 from one side of the fifteenth side. The other side of the shuttle valve 15 is connected to the upstream side of the throttle 11 established in the return flow path 10. The solenoid valve 13 is excited by pressing the switch 19 provided at the front end of the operating lever 18 to switch to the b position, and the control pump 5 is connected to one of the pilot hydraulic pressure section 14b and the shuttle valve 15. It is connected to the side, and when it releases the hand which pushed the switch 19, it is switched to the a position, and one side of the pilot water pressure part 14b and the shuttle valve 15 is connected to the tank 12. As shown in FIG. The relief valve 14 is set to the normal set pressure P1 when the pilot pressure is not supplied to the pilot hydraulic pressure section 14b, and to the high set pressure P2 higher than the normal set pressure P1 when the pilot pressure is supplied. Is switched.

The operation of the second prior art will be described. In the case of performing a normal excavation work by a hydraulic excavator, since the switch 19 is not pressed, the solenoid valve 13 is elementary and becomes a position. Therefore, since one side of the pilot hydraulic pressure section 14b and the shuttle valve 15 is drained, the relief valve 14 is normally set to a pressure P1, and the pressure oil of the return flow path 10 upstream of the throttle 11 is increased. It acts on the capacity control means 16 from the other side of the shuttle valve 15. As a result, when none of the directional valves, such as the boom directional valve 2, is operated, the flow rate of the return flow passage 10 increases, so that the pump capacity V of the variable displacement pump 1 is minimized. When any one of the direction switching valves, such as the direction switching valve 2, is operated, the flow volume will be lost in the return flow path 10, and the pump capacity V of the variable displacement pump 1 will be controlled to the maximum.

Subsequently, in the case of using the hydraulic excavator as a crane for loading work, when the switch 19 of the operation lever 18 is pressed, the solenoid valve 13 is excited to be in the b position. Therefore, the pilot oil from the control pump 5 flows to the pilot hydraulic pressure section 14b, and as shown in FIG. 10, the pressure is raised to the high set pressure P2 of the relief valve 14, so the hanging force is increased. In addition, since the control pressure of the control pump 5 acts on the capacity control means 16 from one side of the shuttle valve 15, as shown in FIG. 10, the variable displacement pump 1 has a pump capacity ( V) This small capacity V3 is set.

However, each of the above prior arts has the following problems.

(I) According to the first prior art, the pump discharge pressure P rises when the load is put, and the load is put around the point A in FIG. 7. For this reason, the working speed is reduced due to the reduction of the pump capacity (V), and the working efficiency is lowered. In addition, the pump discharge pressure P is set to P1 by the relief valve 4, and since the ability to suspend more than this cannot be obtained, the ability to suspend hanging is insufficient, and sufficient load cannot be suspended.

(II) According to the second prior art, if a user inadvertently presses the switch 19 or touches a part of the body during the excavation operation by lowering the boom during normal excavation, the relief valve 14 ) Increases the digging force by increasing the pressure up to the high set pressure (P2), and the variable displacement pump (1) is reduced to a small capacity (V3) to obtain a sufficient working speed. Thus, the operability of the operator is lowered. In addition, the hydraulic pressure of the lowering side of the boom also requires the same pressure resistance as that of the raising side, resulting in high cost.

(III) When performing the normal excavation work in the second prior art, if the directional directional valve 2 is not operated, as shown in FIG. 10, the pump capacity V of the variable displacement pump 1 is minimal. The capacity Vmin is set, and the pump capacity V of the variable displacement pump 1 becomes the maximum capacity Vmax when the directional directional valve 2 is operated. In addition, when the switch 19 is pressed during the hanging operation, the pump capacity V of the variable displacement pump 1 is not only switched from the minimum capacity Vmin or the maximum capacity Vmax to the small capacity V3, but also the relief. The valve rapidly changes in pressure from the set pressure P1 to the high set pressure P2. As described above, since the pump capacity V and the set pressure of the relief valve of the variable displacement pump 1 change abruptly, the impact of each hydraulic device and, moreover, the construction machine as a whole increases, resulting in deterioration of the durability of the device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. The present invention provides a hydraulic circuit of a construction machine, in which a sufficient hanging capacity is obtained at the time of putting a load, while at the same time suppressing a decrease in the speed of putting a load. The purpose.

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

FIG. 2 is a detailed view of the cutoff valve shown in FIG. 1. FIG.

3 is a detailed view of the Q part of FIG. 2.

4 is a pump discharge pressure-pump capacity curve diagram of the hydraulic circuit diagram shown in FIG. 1.

FIG. 5 is a diagram showing a change in oil pressure at the time of switching between the normal set pressure and the elevated high set pressure.

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

7 is a hydraulic circuit diagram of the first prior art.

FIG. 8 is a pump discharge pressure-pump capacity curve diagram of the hydraulic circuit diagram shown in FIG. 7.

9 is a hydraulic circuit diagram of a second prior art.

FIG. 10 is a pump discharge pressure-pump capacity curve diagram of the hydraulic circuit diagram shown in FIG. 9.

Explanation of symbols on the main parts of the drawings

1: Variable displacement pump 1a: Discharge line

2: Direction change valve for boom 3: Boom cylinder

5: control pump 6: fixed relief valve

7: Torque variable control valve 8: Cutoff valve

8a: pilot hydraulic unit 9: capacity control means

14: relief valve 14a: pressure setting spring

14b: Pilot hydraulic pressure section 14A: Normally set pressure relief valve

14B: High setting pressure relief valve 21: Boom lever

22: lift detection sensor 23: falcon mode switch

24, 24A: first electronic switching valve 25: second electronic switching valve

26: controller 27: other operation sensor

28: First Throttle 29: Second Throttle

30: control power

In order to achieve the above object, the hydraulic circuit of the construction machine according to the first invention connects a variable displacement pump to an actuator driving a corresponding work machine through a plurality of directional valves, and discharges the variable displacement pump. Connect the relief valve which sets the maximum discharge pressure to the pipeline, and when the discharge pressure of the variable displacement pump approaches the relief pressure of the relief valve, the discharge volume of the variable displacement pump is gradually reduced to minimize the variable displacement type through the cutoff valve. In the hydraulic circuit of a construction machine that cuts off the capacity of a pump, a hawk-like mode switch for setting a work mode to hawk-like mode, a lift-up sensor for detecting that a predetermined actuator has been loaded, and a relief valve Relief valve control means that can freely set the set pressure to the normal set pressure and the high set pressure higher than the normal set pressure Cut-off valve control means for freely switching the cut-off valve to cut-off operation and cut-off operation release, and relief valve control when a lift-off detection signal is input from the lift-up detection sensor while inputting a pull-off mode signal from the pull-up mode switch. And a controller for outputting a command to the means to boost the set pressure of the relief valve and outputting the command to the cutoff valve control means to release the cutoff function of the cutoff valve.

According to the first aspect of the invention, the controller inputs a lift detection signal from a lift detection sensor and at the same time inputs a lift signal to the relief valve switch, outputs a command to the relief valve control means to boost the set pressure of the relief valve. At the same time, a command is output to the cutoff valve control means to release the cutoff function of the cutoff valve. Therefore, the ability to suspend the set pressure of the relief valve by the increased pressure increases, and at the same time, the cutoff function is released to increase the working speed by the increase in the pump capacity of the variable displacement pump. In addition, when the operation of raising and lowering the predetermined actuator alone (for example, raising the boom of the hydraulic excavator) is automatically raised and the cutoff function is released, there is no need to operate the switch every time the operator increases the hanging ability. Therefore, it is possible to improve the work efficiency and operability of a work that requires the power and speed of the work machine at the same time, for example, to carry a load, to raise a tree stump, or to raise a stone.

The hydraulic circuit of the construction machine according to the second invention includes, in the first invention, an other operation sensor for detecting that an actuator other than the predetermined actuator has been operated, and the controller inputs a detection signal from the other operation sensor. And when the command is output to the relief valve control means to return the high set pressure of the relief valve boosted to the normal setting pressure, the command is output to the cutoff valve control means to restore the cutoff function of the cutoff valve. .

According to the second aspect of the present invention, when the controller inputs an operation signal from another operation sensor of an actuator other than a predetermined actuator, the controller outputs a command to the relief valve control means to return the set pressure of the relief valve that has been boosted to its normal state. At the same time as the set pressure, a command is output to the cutoff valve control means to restore the cutoff function of the cutoff valve. Therefore, since the relief valve is normally set at the time of a complex operation such as during normal excavation, the pressure is not applied to other actuators more than necessary, so that problems such as oil leakage are prevented and durability is improved. In addition, when the cutoff function is restored and the discharge oil of the variable displacement pump is released, the pump capacity is reduced and driving horsepower is reduced, thereby reducing energy consumption such as fuel consumption of the engine.

The hydraulic circuit of the construction machine according to the third invention is the first buffer means for reducing the rate of change with respect to the time of the set pressure by the relief valve in the first invention or the second invention, the cutoff function and the cutoff function of the cutoff valve. And a second buffer means for reducing the rate of change over time of the control pressure for switching to release.

According to the third aspect of the present invention, the control rate at which the rate of change when the set pressure of the relief valve is switched to the normal set pressure or the elevated high set pressure is reduced by the first buffer means, and the control is switched to the cutoff function and the cutoff function release of the cutoff valve. The rate of change over time of the pressure is reduced by the second buffer means. Therefore, the impact at the time of the pressure change in the hydraulic circuit is reduced, so that the impact on each hydraulic machine, and moreover, the construction machine as a whole, is alleviated and the durability of the device is improved.

Embodiment of the invention

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described based on FIGS. In addition, the same code | symbol is attached | subjected to the component same as the prior art shown in FIGS. 7-10, and the description is abbreviate | omitted.

First, the structure of 1st Embodiment is demonstrated with FIG. 1 and FIG.

The relief valve 14 which can freely set the maximum discharge pressure in multiple stages is connected to the discharge line 1a of the variable displacement pump 1. This relief valve 14 has a pilot hydraulic pressure part 14b which increases the setting load of the pressure setting spring 14a. The lift detection sensor 22 and the bucket cylinder (an example of other actuators) that detect that the boom cylinder 3 (an example of a predetermined actuator) is operated toward the lift side by detecting the lift operation of the boom lever 21 are operated. The other operation sensor 27 which detects the old one by the detection of the operation of the bucket lever, and the like mode mode switch 23 which sets the operation mode to the like mode are provided. When the controller 26 inputs the raising detection signal of the raising detection sensor 22 and the likening mode signal of the falconing mode switch 23 and inputs the detection signal of the rudder operation sensor 27, the first electronic switching is performed. The valve 24 (an example of the relief valve control means) and the second electromagnetic switching valve 25 (an example of the cutoff valve control means) are excited.

The first electromagnetic switching valve 24 controls the a position at which the pilot pressure receiving portion 14b of the relief valve 14 is connected to the tank 12 when the element is closed, and the pilot pressure receiving portion 14b when the excitation is controlled by the control pump 5. It switches to the b position connected to (control pressure source). The second electromagnetic switching valve 25 controls the a position at which the pilot hydraulic pressure section 8a of the cutoff valve 8 is connected to the tank 12 when the element is closed, and the pilot hydraulic pressure section 8a when the excitation is controlled by the control pump 5. Is switched to the b position connected to. In addition, the controller 26 inputs the detection signal of the bucket cylinder operated from the rudder operation sensor 27 when the detection signal of the lift detection sensor 22 and the resemblance mode signal of the resemblance mode switch 23 are input. The first electronic switching valve 24 and the second electronic switching valve 25 and the first electronic switching valve 24 and the second electronic switching valve 25 when the detection signal is operated. I'm having a woman again. A first throttle 28 (an example of the first shock absorbing means) is provided in the pipeline connecting the pilot pressure receiving portion 14b and the first electromagnetic switching valve 24, and the pilot pressure receiving portion 8a and the second electromagnetic switching valve are provided. A second throttle 29 (an example of the second shock absorbing means) is established in the pipeline connecting the 25. And 30 is a control power supply.

The structure of the cutoff valve shown in FIG. 2 and FIG. 3 is demonstrated.

The cutoff valve 8 inputs the output pressure Pt of the torque variable control valve 7 and controls the output pressure Pc of the cutoff valve 8 to control the capacity control means of the variable displacement pump 1 ( 9) It has a function to output to.

The spool 8s is fitted in the spool hole 41 formed in the cutoff valve main body 40 (indicated by diagonal lines) of the spool 8 so as to be able to slide freely. At one end of the spool hole 41, a first piston hole 42 communicating with the spool hole 41 is formed, and a second piston hole 44 is formed at the outside thereof. Moreover, between the 1st piston hole 42 and the 2nd piston hole 44, the 1st pressure chamber 43 which the pump discharge pressure P of the variable displacement pump 1 shown in FIG. 1 acts is formed. The second pressure chamber 45 on which the output pressure Pc of the cutoff valve 8 acts is formed outside the second piston hole 44. A first piston 8b whose one end is in contact with one end of the spool 8s is inserted into the first piston hole 42 so as to be able to slide freely, and one end is inserted into the second piston hole 44 by the first piston 8b. The second piston 8c, which abuts with the other end of the c), is fitted to be able to slide freely.

At the other end of the spool hole 41, a spring chamber 46 communicating with the spool hole 41 is formed, and at the outer side, a pilot hydraulic pressure section 8a is formed via the third piston hole 47. do. In the spring chamber 46, a spring 8d, one end of which contacts the other end of the spool 8s, and a spring sheet 8g, which the other end of the spring 8d abuts, are provided, and the spring sheet 8g is a spring 8d. Is normally brought into contact with the end face 48 on the other end side of the spring chamber 46. The 3rd piston 8h is fitted in the 3rd piston hole 47 so that it can slide freely, and the one end of the 3rd piston 8h is in contact with the spring seat 8g. The discharge oil is supplied to the pilot pressure receiving section 8a from the control pump 5 shown in FIG. 1 through the second electromagnetic switching valve 25, and the pilot pressure of the pilot pressure receiving section 8a is provided at the other end of the third piston 8h. This works.

The Q part detail of FIG. 2 is shown in FIG. As shown in the figure, a throttle body 8t is formed in the spool 8s, and one side of the throttle body 8t and the spool hole 41 vary the output oil chamber b of the cutoff valve 8 and the torque. A first throttle portion 8e is formed between the input oil chamber a in communication with the control valve 7, and the other side of the throttle body 8t and the spool hole 41 have a cutoff valve 8. The 2nd throttle part 8f which interposes between the output oil chamber b of this and the drain chamber c which communicates with the tank 12 is formed.

The operation of the cutoff valve will be described based on FIG. 4 with reference to FIGS. 2 and 3.

When the second electromagnetic switching valve 25 is demagnetized and the control pressure of the control pump 5 is not acting on the pilot hydraulic pressure section 8a, the load increases and the pump discharge pressure P of the variable displacement pump 1 is increased. ) Becomes a predetermined pressure Pa near the normal set pressure P1 of the relief valve 14 shown in FIG. 4 (set by the spring 8d), the first acting on one end side of the spool 8s. The sum of the force of the piston 8b and the second piston 8c depresses the spring force of the spring 8d, so that the spool 8s starts to move in the direction of the arrow in FIG. Therefore, since the opening of the first throttle portion 8e is reduced and the opening of the second throttle portion 8f is enlarged, the output pressure Pc of the cutoff valve 8 of the output oil chamber b gradually decreases. . Since the capacity control means 9 is a positive control mechanism in which the pump capacity V decreases when the control pressure decreases and the pump capacity V increases when the control pressure rises, the output pressure of the cutoff valve 8 With the gradual decrease of Pc), the pump capacity V is also gradually reduced to the minimum capacity V1, thereby performing a cutoff function to reduce the relief loss.

Further, when the second electromagnetic switching valve 25 is excited to switch to the b position, and the control pressure of the control pump 5 is applied to the pilot hydraulic pressure section 8a, the spring 8d is moved through the third piston 8h. Since the setting force is increased, the spool 8s is pushed in the opposite direction to the arrow of FIG. Therefore, since the opening of the first throttle portion 8e is enlarged and the opening of the second throttle portion 8f is reduced, the output pressure Pc of the cutoff valve 8 of the output oil chamber b increases to the maximum. Turn off the cutoff function.

The operation of this embodiment will be described by Table 1.

(I) In the case of performing ordinary excavation work without performing the hanging operation, when the hawk like mode switch 23 is turned off, the controller 26 does not input the hawk like mode signal of the hawk like mode switch 23. And the first electronic switching valve 24 and the second electronic switching valve 25 are operated irrespective of the operation of other actuators such as the boom lever 21 and the bucket lever. Therefore, since the pilot hydraulic pressure section 14b of the relief valve 14 is connected to the tank 12 via the a position of the first electromagnetic switching valve 24, the set pressure of the relief valve 14 is usually set to the set pressure ( P1) It is. Therefore, since no pressure is applied to other actuators more than necessary, problems such as oil leakage are prevented and durability is improved. In addition, since the pilot hydraulic pressure section 8a of the cutoff valve 8 is connected to the tank 12 via the a position of the second electromagnetic switching valve 25, the cutoff function of the cutoff valve 8 is operated. As a result, the pump capacity V decreases when the discharge oil of the variable displacement pump 1 reliefs, similarly to the conventional techniques shown in FIGS. 7 and 8, thereby saving energy of the driving force of the variable displacement pump 1. can do.

(II) When the hanging operation is performed, when the hawk lever 21 is turned up while the like mode mode switch 23 is turned on, the controller 26 is coupled with the lift detection signal of the lift detection sensor 22. When the like mode signal of the like mode switch 23 is input, and other actuators, such as a bucket lever, are neutral, the 1st electromagnetic switching valve 24 and the 2nd electromagnetic switching valve 25 are excited. Therefore, since the pilot hydraulic pressure section 14b of the relief valve 14 is connected to the control pump 5 via the b position of the first electromagnetic switching valve 24, the set pressure of the relief valve 14 is normally set pressure. The pressure is increased from P1 to the high set pressure P2 (P1 <P2). In addition, since the pilot hydraulic pressure section 8a of the cutoff valve 8 is connected to the control pump 5 via the b position of the second electromagnetic switching valve 25, the cutoff function of the cutoff valve 8 is released. Therefore, as shown in Fig. 4, the ability to suspend the set pressure of the relief valve 14 by the amount of pressure P2-P1 increases, and at the same time, the cutoff function is canceled, so that the pump capacity of the variable displacement pump 1 ( By V) increased (V2-V1), the working speed increases, and the work efficiency of hanging the load can be improved.

In addition, the controller 26 detects an operation of the bucket cylinder or the like from the other operation sensor 27 when inputting the raising detection signal of the raising detection sensor 22 and the turning mode signal of the likeness mode switch 23. When the detection signal is inputted, the first electronic switching valve 24 and the second electronic switching valve 25 are elemented. Therefore, it becomes the same as the operation | movement at the time of turning off the every like mode switch 23 of said (I). On the other hand, when the detection signal of the operation of the bucket cylinder or the like is turned off, the first electronic switching valve 24 and the second electronic switching valve 25 are automatically excited again, so that the set pressure of the relief valve 14 is increased. As the capacity to suspend by minutes increases, the cut-off function is released and the pump capacity V of the variable displacement pump 1 increases, so that the working speed increases and the work efficiency of suspending load is improved.

In this way, the switching of the set pressure of the relief valve 14 and the switching of the cutoff function and the release of the cutoff valve 8 are automatically performed, thereby improving the operation and operation efficiency of the operator.

In addition, as shown in FIG. 5, the rate of change when switching between the normal set pressure P1 of the relief valve 14 and the high set pressure P2 which has been boosted is reduced by the first throttle 28. Similarly, since the pressure change rate of the pilot hydraulic pressure section 8a when switching to the cutoff function operation of the cutoff valve 8 and its release is reduced by the second throttle 29, the discharge capacity of the variable displacement pump 1 The change in (V) is relaxed. Therefore, the impact on the hydraulic circuit, and thus the whole construction machine, is alleviated, so that the durability of the construction machine is improved.

In addition, although the 1st throttle 28 and the 2nd throttle 29 were provided in this embodiment, it is not limited to this, The 1st electromagnetic switching valve 24 and the 2nd electromagnetic switching valve ( 25) The signal output to the circuit may be smoothly changed.

In addition, although the relief valve 14 was made into two stage switching, it is not limited to this, It is possible to make an operator switch to three or more stages according to working conditions.

6, the structure of 2nd Embodiment is demonstrated.

In the first embodiment shown in FIG. 1, the pilot pressure receiving portion 14b of the relief valve 14 is switched to the control pump 5 and the tank 12 by the first electromagnetic switching valve 24, and the discharge pipe path ( Although the setting of the maximum discharge pressure of 1a) was switched, in this embodiment, two relief valves different in set pressure from the discharge line 1a of the variable displacement pump 1 via the first electronic switching valve 24A, That is, the normal set pressure relief valve 14A and the high set pressure relief valve 14B are connected. Other configurations are the same as in the first embodiment, and thus description thereof is omitted.

The operation and effects of the present embodiment will be described.

As in the first embodiment shown in FIG. 1, when the first electromagnetic switching valve 24A is demagnetized, it is switched to the a position, and the discharge conduit 1a is normally connected to the set pressure relief valve 14A. When the valve 24A is excited, it is switched to the b position, and the discharge conduit 1a is connected to the high set pressure relief valve 14B so that the maximum discharge pressure of the discharge conduit 1a is boosted. Other operations and effects are the same as in the first embodiment, and thus description thereof is omitted.

As described above, when the work machine other than the boom is operated in the like mode, even when the boom raising operation is performed, the maximum discharge pressure of the work machine circuit is set to the normal set pressure and at the relief set pressure vicinity. Since the cut-off control, the energy saving of the drive energy of the variable displacement pump 1 can be reduced, and the work pressure circuits other than the boom can be reduced.

When the boom raising operation and the operation of other work machines other than the boom are simultaneously performed in the hawk resiliency mode as described above, when the operation of other work machines is stopped, that is, when the boom is alone lifting operation, The pressure is set to a high set pressure and the cutoff controller function is released (stopped). By this,

(1) Improvement of work ability by increasing boom hanging capacity and working speed

(2) Improve workability of raising boom alone

(3) Improve operator's operability by automatic switching

Remarkable effects, such as can be obtained.

In addition, although the lifting detection sensor 22 detects the raising operation of the boom lever in the said embodiment, this invention is not limited to this, For example, when raising the boom direction switching valve 2 as a pilot type, it raises. You may detect based on the side pilot pressure. The same applies to the other operation sensor 27.

In addition, a hawk-like mode switch may be provided in the boom lever 21, or may be provided in the operation panel of a driver's seat.

As described above, according to the first aspect of the present invention, the controller outputs a command to the relief valve control means when the lift detection signal is inputted from the lift detection sensor, and the wake mode signal is input from the fly-like mode switch. By raising the set pressure of the relief valve, a command is output to the cutoff valve control means to release the cutoff function of the cutoff valve. Therefore, the ability to suspend the set pressure of the relief valve by the increased pressure increases, and at the same time, the cutoff function is released to increase the working speed by the increase in the pump capacity of the variable displacement pump. In addition, when the operation of raising and lowering the predetermined actuator alone (for example, raising the boom of the hydraulic excavator) is automatically raised and the cutoff function is released, there is no need to operate the switch every time the operator increases the hanging ability. Therefore, it is possible to improve the work efficiency and operability of a work that requires the power and speed of the work machine at the same time, for example, to carry a load, to raise a tree stump, or to raise a stone.

Further, according to the second invention of the present invention, when the controller inputs an operation signal from another operation sensor of an actuator other than a predetermined actuator, the controller outputs a command to the relief valve control means to reset the set pressure of the relief valve that has been boosted. It returns to the original state, returns to a normal setting pressure, outputs a command to a cutoff valve control means, and returns the cutoff function of a cutoff valve. Therefore, since the relief valve is normally set at the time of a complex operation such as during normal excavation, the pressure is not applied to other actuators more than necessary, so that problems such as oil leakage are prevented and durability is improved. In addition, when the cutoff function is restored and the discharge oil of the variable displacement pump is released, the pump capacity is reduced and driving horsepower is reduced, thereby reducing energy consumption such as fuel consumption of the engine.

Further, according to the third invention of the present invention, the rate of change when the set pressure of the relief valve is switched to the normal set pressure or the elevated high set pressure is reduced by the first buffer means, and the cutoff function and the cutoff function of the cutoff valve The rate of change with respect to the time of the control pressure to switch to the release is reduced by the second buffer means. Therefore, the impact at the time of the pressure change in the hydraulic circuit is reduced, so that the impact on each hydraulic machine, and moreover, the construction machine as a whole, is alleviated and the durability of the device is improved.

Claims (3)

The variable displacement pump is connected to an actuator for driving a corresponding work machine through a plurality of directional valves, and a relief valve for setting the maximum discharge pressure is connected to the discharge line of the variable displacement pump. In the hydraulic circuit of a construction machine, when the discharge pressure is close to the set pressure of the relief valve, the discharge amount of the variable displacement pump is gradually reduced to cut-off the capacity of the variable displacement pump through a cutoff valve that minimizes the discharge amount. The set pressure of the relief valve 14, the lift detection sensor 22 which detects that the predetermined actuator 3 has been operated toward the lifting load of the hanging actuator 3, and the relief valve 14 Relief valve control means 24 that can be freely set to a normal set pressure and a high set pressure higher than the normal set pressure, and cut-off valve control means 25 that can freely switch the cutoff valve 8 to cutoff operation and cutoff operation release. and, When the likelihood mode signal is input from the likelihood mode switch 23, and the liftup detection signal is input from the lift detection sensor 22, a command is output to the relief valve control means 24 to set the relief valve 14. And a controller (26) for boosting the pressure and outputting a command to the cutoff valve control means (25) to release the cutoff function of the cutoff valve (8). 2. The other operation sensor 27 according to claim 1, further comprising another operation sensor 27 for detecting that an actuator other than the predetermined actuator 3 has been operated, and the controller 26 inputs a detection signal from the other operation sensor 27. At this time, a command is output to the relief valve control means 24 to return the high set pressure of the relief valve 14 which has been boosted to the normal set pressure, and at the same time, a command is output to the cutoff valve control means 25 to cut off the valve ( 8) The hydraulic circuit of the construction machine, characterized in that to return the cut-off function. 3. The switch according to claim 1 or 2, wherein the first shock absorbing means (28) for reducing the rate of change of the set pressure by the relief valve (14) over time and the cutoff function and the cutoff function of the cutoff valve (8) are switched. And a second buffer means (29) for reducing the rate of change of the control pressure over time.