JP7084889B2 - Construction machinery - Google Patents

Description

The present invention relates to a construction machine such as a hydraulic excavator, and more particularly to a construction machine having a blade at the front portion of a lower traveling body and performing a jack-up operation of lifting the main body by the blade.

The hydraulic drive system provided in a construction machine such as a hydraulic excavator is provided with a main relief valve that limits the maximum discharge pressure so that the discharge pressure of the main pump does not become higher than a predetermined pressure. In Patent Document 1, the main relief valve is configured as a variable relief valve, and when the operation lever of the traveling operation device is operated, the set pressure of the main relief valve is increased from the first value to the second value. A technique for increasing the output torque of a traveling motor during a traveling operation to improve the running performance is described. Further, in Patent Document 1, when the operating lever of the operating device other than the traveling motor is operated, the boosting of the set pressure of the main relief valve is released to prevent the load of the actuator other than the traveling motor from increasing.

Jitsukaisho 62-21163 Gazette

Some construction machines such as hydraulic excavators are equipped with a blade at the front of the lower traveling body. In such a construction machine, soil removal work and leveling work can be performed by running while contacting the blade with the ground. Further, the blade is used not only for soil removal work and leveling work, but also for jacking up the main body when servicing the undercarriage or cleaning the crawler.

By the way, the jack-up operation performed by using the blade is an operation of bringing the blade into contact with the ground, extending the jack-up cylinder, and lifting the main body. In some cases, the front working machine is also used to lift the main body in front of and behind the main body to jack up. When performing such a jack-up operation, it is necessary for the jack-up cylinder to generate a thrust sufficient to lift the main body, and for that purpose, it is necessary to increase the size of the jack-up cylinder, which increases the cost.

In order to reduce the size of the jack-up cylinder and obtain a large thrust, as described in Patent Document 1, the set pressure of the main relief valve may be increased during the jack-up operation. However, the prior art described in Patent Document 1 raises the set pressure of the main relief valve during traveling operation, increases the output torque of the traveling motor, and when an operating device other than traveling is operated, the main relief valve It is a technique to release the boost of the set pressure, and it is not possible to increase the set pressure of the main relief valve during the jack-up operation.

An object of the present invention is to reduce the size of a blade cylinder in a construction machine having a blade at the front of a lower traveling body so that the thrust required for the jack-up operation can be generated during the jack-up operation performed by using the blade. It is to provide construction machinery that can reduce costs.

In order to achieve the above object, the present invention has a lower traveling body having a blade in the front portion, a main body having an upper rotating body rotatably mounted on the lower traveling body, and a front portion of the upper rotating body. It has a front working machine and a hydraulic drive device mounted so as to be able to stand up and down, and the hydraulic drive device is driven by a hydraulic pump driven by a prime mover and pressure oil discharged from the hydraulic pump, and the lower portion thereof. A plurality of actuators for driving the traveling body, the upper swing body, the front working machine and the blade, a plurality of flow control valves for controlling the flow of pressure oil supplied from the hydraulic pump to the plurality of actuators, and the above. Operation for switching between multiple flow control valves Multiple operating devices that generate pilot pressure are connected to the oil supply path of the hydraulic pump, and the set pressure is switched between the normal setting and the high pressure setting higher than this normal setting. In a construction machine including a main relief valve configured as a possible variable relief valve, a jack-up detection device for detecting a jack-up operation in which the blade is driven in a downward direction and the blade lifts the main body, and the jack-up. A relief valve control device for switching the set pressure of the main relief valve from the normal setting to the high pressure setting when the jack-up operation is detected by the detection device is provided , and the plurality of actuators drive the lower traveling body. The plurality of flow control valves include a traveling motor for driving and a blade cylinder for driving the blade, and the plurality of flow control valves are a traveling flow control valve for controlling the driving of the traveling motor and a blade for controlling the driving of the blade cylinder. The plurality of operating devices include a traveling operation device for generating a traveling operation pilot pressure for switching the traveling flow control valve, and the flow control valve for the blade. Blade operation includes an operation device for the blade to generate pilot pressure.
The blade cylinder is a hydraulic cylinder that operates in the extension direction when pressure oil is supplied to the bottom side to drive the blade in the downward direction to perform the jack-up operation, and the jack-up detection device is the blade. A first pressure sensor for detecting the operation pilot pressure for lowering the blade and a second pressure sensor for detecting the travel operation pilot pressure generated by the travel operation device among the operation pilot pressures generated by the operation device for traveling. The relief valve control device sets the main relief valve when the first pressure sensor detects the operating pilot pressure for lowering the blade and the second pressure sensor does not detect the traveling operating pilot pressure. The pressure shall be switched from the normal setting to the high pressure setting .
Further, in order to achieve the above object, the present invention comprises a lower traveling body having a blade in the front portion, a main body having an upper rotating body rotatably mounted on the lower traveling body, and the upper rotating body. It has a front work machine mounted on the front portion so as to be able to look up and down, and a hydraulic drive device. The hydraulic drive device is driven by a hydraulic pump driven by a prime mover and pressure oil discharged from the hydraulic pump. A plurality of actuators for driving the lower traveling body, the upper swivel body, the front working machine and the blade, and a plurality of flow control valves for controlling the flow of pressure oil supplied from the hydraulic pump to the plurality of actuators. , Multiple operating devices that generate operating pilot pressure to switch between the plurality of flow control valves, and a high pressure setting where the set pressure is set to a normal setting and a higher pressure setting than this normal setting, which is connected to the pressure oil supply path of the hydraulic pump. In a construction machine including a main relief valve configured as a variable relief valve that can be switched to, a jack-up detection device for detecting a jack-up operation in which the blade is driven in a downward direction and the main body is lifted by the blade, and the above-mentioned A relief valve control device for switching the set pressure of the main relief valve from the normal setting to the high pressure setting when the jack-up operation is detected by the jack-up detection device is provided, and the plurality of actuators are the lower traveling body. The plurality of flow control valves include a traveling motor for driving the traveling motor and a blade cylinder for driving the blade, and the plurality of flow control valves control the traveling flow control valve for controlling the driving of the traveling motor and the driving of the blade cylinder. The plurality of operating devices include a traveling operation device for generating a traveling operation pilot pressure for switching the traveling flow control valve, and the traveling operating device including a flow control valve for the blade, and the flow control valve for the blade. Blade operation for switching Including an operating device for the blade that generates a pilot pressure, the blade cylinder operates in the extension direction when pressure oil is supplied to the bottom side to drive the blade in the lower direction. The hydraulic cylinder that performs the jack-up operation, and the jack-up detection device is
It has a first pressure sensor that detects the operation pilot pressure for lowering the blade among the operation blade operation pilot pressures generated by the operation device for the blade, and a second pressure sensor that detects the pressure on the bottom side of the blade cylinder. In the relief valve control device, the operation pilot pressure for lowering the blade is detected by the first pressure sensor, and the pressure on the bottom side of the blade cylinder detected by the second pressure sensor is higher than a predetermined threshold value. Occasionally, the set pressure of the main relief valve is switched from the normal setting to the high pressure setting.

According to the present invention, in a construction machine provided with a blade at the front of the lower traveling body, it is possible to generate the thrust required for the jack-up operation during the jack-up operation performed by using the blade, and the blade cylinder is made smaller. The cost can be reduced.

Also, when the main body is lifted in front of and behind the main body by using the blade lowering and the front working machine together, even if the jack up operation by the front working machine (boom lowering) is performed at the same time as the jack up operation by the blade lowering, the jack by the blade lowering is performed. Since the up operation is detected and the set pressure of the main relief valve is switched from the normal setting to the high pressure setting, the high pressure setting of the set pressure of the main relief valve is maintained, and good jack-up performance can be maintained.

Furthermore, during the combined operation of traveling and blades, the set pressure of the main relief valve remains at the normal setting, the maximum discharge pressure of the hydraulic pump does not increase, and an increase in the load acting on the lower traveling body should be avoided. Can be done.

It is a figure which shows the appearance of a hydraulic excavator. It is a figure which shows the hydraulic drive device provided in the hydraulic excavator of the 1st Embodiment of this invention. It is a flowchart which shows the detail of the function of a controller. It is a figure which shows the hydraulic drive device provided in the hydraulic excavator of the 2nd Embodiment of this invention. It is a flowchart which shows the detail of the function of a controller. It is a figure which shows the state which the main body of a hydraulic excavator is jacked up by a front work machine and a blade.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Hydraulic excavator>
First, a hydraulic excavator will be described as an example of the construction machine of the present invention.

FIG. 1 is a diagram showing the appearance of a hydraulic excavator.

In FIG. 1, hydraulic excavators, which are well known as work machines, include a main body 310 having a lower traveling body 300 having a blade 304 and an upper rotating body 301 rotatably mounted on the lower traveling body 300, and an upper turning body. The front working machine 302 is provided on the front portion of the body 301 so as to be vertically mounted, and the front working machine 302 is composed of a boom 306, an arm 307, and a bucket 308.

The lower traveling body 300 travels by driving the left and right tracks 300a and 300b by the traveling motors 5 and 6. The blade 304 is attached to the central frame of the lower traveling body 300, and moves up and down by expanding and contracting the blade cylinder 8. The upper swivel body 301 can be swiveled on the lower traveling body 300 by the swivel motor 7. A swing post 303 is attached to the front portion of the upper swing body 301, and a front working machine 302 is attached to the swing post 303 so as to be able to move up and down. The swing post 303 can rotate horizontally with respect to the upper swing body 301 by expanding and contracting the swing cylinder 9 (see FIG. 2). The boom 306, arm 307, and bucket 308 of the front working machine 302 can rotate in the vertical direction by expanding and contracting the boom cylinder 10, the arm cylinder 11, and the bucket cylinder 12.

<First Embodiment>
FIG. 2 is a diagram showing a hydraulic drive device provided in the hydraulic excavator according to the first embodiment of the present invention.

~ Basic configuration ~
First, the basic configuration of the hydraulic drive device according to the present embodiment will be described.

The hydraulic drive device in the present embodiment includes an engine 1 which is a prime mover, a main hydraulic pump (hereinafter referred to as a main pump) 2 driven by the engine 1, and a pilot driven by the engine 1 in conjunction with the main pump 2. Left and right traveling motors 5, 6, swivel motors 7, and blades, which are a plurality of actuators 5, 6, 7, 8, 9, 10, 11, and 12 driven by the pump 3 and the hydraulic oil discharged from the main pump 2. It includes a cylinder 8, a swing cylinder 9, a boom cylinder 10, an arm cylinder 11, a bucket cylinder 12, and a control valve 4. The hydraulic excavator according to this embodiment is, for example, a hydraulic mini excavator.

The control valve 4 is connected to the pressure oil supply path 2a of the main pump 2, and has a plurality of valve sections 13, 14, 15, 16, which control the direction and flow rate of the pressure oil supplied from the main pump 2 to each actuator. Signal by selecting 17, 18, 19, 20 and the highest load pressure (hereinafter referred to as the maximum load pressure) PLmax among the load pressures of a plurality of actuators 5, 6, 7, 8, 9, 10, 11 and 12. Connect to a plurality of shuttle valves 22a, 22b, 22c, 22d, 22e, 22f, 22g to be output to the oil passage 21 and a pressure oil supply passage 4a in the control valve 4 connected to the pressure oil supply passage 2a of the main pump 2. It is connected to the main relief valve 100 that limits the maximum discharge pressure (maximum pump pressure) of the main pump 2 and the pilot hydraulic source 33 (described later), and the pressures of the pressure oil supply passage 4a and the signal oil passage 21 are used as the signal pressure. The differential pressure pressure reducing valve 24, which is input and outputs the differential pressure PLS between the discharge pressure (pump pressure) Pd of the main pump 2 and the maximum load pressure PLmax as an absolute pressure, is connected to the pressure oil supply path 4a and is connected to the pressure oil supply path. The pressures of 4a and the signal oil passage 21 are input as the signal pressure, and when the differential pressure PLS between the pump pressure Pd and the maximum load pressure PLmax exceeds a certain constant value set by the spring 25a, the discharge flow rate of the main pump 2 is increased. It has an unload valve 25 that returns a part to the tank T and keeps the differential pressure PLS below a certain value set by the spring 25a. The outlet side of the unload valve 25 and the main relief valve 100 is connected to the tank oil passage 29 in the valve, and is connected to the tank T via the oil passage 29.

The valve section 13 is composed of a flow control valve 26a for traveling to the left and a pressure compensation valve 27a, the valve section 14 is composed of a flow control valve 26b and a pressure compensation valve 27b for traveling to the right, and the valve section 15 is for turning. The valve section 16 is composed of a flow control valve 26d for blades and a pressure compensation valve 27d, and the valve section 17 is composed of a flow control valve 26e for swing and pressure compensation. The valve section 18 is composed of a flow control valve 26f for a boom and a pressure compensating valve 27f, and the valve section 19 is composed of a flow control valve 26g for an arm and a pressure compensating valve 27g. Section 20 is composed of a flow control valve 26h for a bucket and a pressure compensating valve 27h.

The flow rate control valves 26a to 26h control the direction and flow rate of the pressure oil supplied from the main pump 2 to the actuators 5 to 12, respectively, and the pressure compensation valves 27a to 27h are the front-rear differential pressures of the flow rate control valves 26a to 26h. To control each. The pressure compensating valves 27a to 27h are pressure compensating valves of a type that do not fully close at the stroke end in the opening area decreasing direction (left direction in the drawing).

The pressure compensating valves 27a to 27h have valve opening side pressure receiving portions 28a, 28b, 28c, 28d, 28e, 28f, 28g, 28h for setting a target differential pressure, and the pressure receiving portions 28a to 28h are differential pressure pressure reducing valves. The output pressure of 24 is derived, and the target compensation differential pressure is set by the absolute pressure of the differential pressure PLS between the hydraulic pump pressure Pd and the maximum load pressure PLmax (hereinafter referred to as absolute pressure PLS). By controlling the front-rear differential pressure of the flow control valves 26a to 26h to the same absolute pressure PLS in this way, the front-rear differential pressure of the flow control valves 26a to 26h is the highest as the hydraulic pump pressure Pd for the pressure compensation valves 27a to 27h. It is controlled so as to be equal to the absolute pressure PLS with the load pressure PLmax. As a result, at the time of combined operation in which a plurality of actuators are driven at the same time, the discharge flow rate of the main pump 2 is distributed according to the opening area ratio of the flow rate control valves 26a to 26h regardless of the magnitude of the load pressure of the actuators 5 to 12. Combined operability can be ensured. Further, when the discharge flow rate of the main pump 2 becomes a saturation state less than the required flow rate, the absolute pressure PLS decreases according to the degree of supply shortage, and the pressure compensation valves 27a to 27h are controlled accordingly. Since the differential pressure between the front and rear flow control valves 26a to 26h decreases at the same rate and the passing flow rate of the flow rate control valves 26a to 26h decreases at the same rate, this also depends on the opening area ratio of the flow rate control valves 26a to 26h. The discharge flow rate of the main pump 2 can be distributed to ensure combined operability.

Further, the hydraulic drive device is connected to the pressure oil supply path 3a of the pilot pump 3 and outputs the absolute pressure according to the discharge flow rate of the pilot pump 3 and the engine rotation speed detection valve 30 and the downstream of the engine rotation speed detection valve 30. A pilot hydraulic source 33, which is connected to the side and has a pilot relief valve 32 that keeps the pressure of the pilot oil passage 31 constant, and generates a pilot primary pressure based on the oil discharged from the pilot pump 3, and a pilot oil passage 31. The operation pilot pressure (pilot secondary pressure) a, b, c, d, e, f, which is connected and for operating the flow control valves 26a to 26h using the pressure of the pilot hydraulic source 33 (pilot primary pressure) as the main pressure, It is equipped with operating devices 34a, 34b, 34c, 34d, 34e, 34f, 34g, 34h for generating g, h, i, j, k, l, m, n, o, p. The operating devices 34a and 34b are operating devices for traveling, the operating device 34c is an operating device for turning, the operating device 34d is an operating device for blades, and the operating device 34e is an operating device for swinging. The operation device 34f is an operation device for a boom, the operation device 34g is an operation assumption for an arm, and the operation device 34h is an operation device for a bucket.

The engine rotation speed detection valve 30 is connected in parallel to the throttle element (fixed throttle portion) 30f provided in the oil passage connecting the pressure oil supply passage 3a of the pilot pump 3 to the pilot oil passage 31 and the throttle element 30f. It has a flow rate detection valve 30a and a differential pressure pressure reducing valve 30b. The input side of the flow rate detection valve 30a is connected to the pressure oil supply path 3a of the pilot pump 3, and the output side of the flow rate detection valve 30a is connected to the pilot oil passage 31. The flow rate detection valve 30a has a variable throttle portion 30c that increases the opening area as the passing flow rate increases, and the discharged oil of the pilot pump 3 passes through both the throttle element 30f and the variable throttle portion 30c of the flow rate detection valve 30a. And flows to the pilot oil passage 31 side. At this time, a front-rear differential pressure that increases as the passing flow rate increases is generated in the throttle element 30f and the variable throttle portion 30c of the flow rate detection valve 30a, and the differential pressure pressure reducing valve 30b outputs the front-rear differential pressure as an absolute pressure Pa. do. Since the discharge flow rate of the pilot pump 3 changes depending on the rotation speed of the engine 1, the discharge flow rate of the pilot pump 3 can be detected by detecting the front-rear differential pressure of the throttle element 30f and the variable throttle portion 30c, and the engine 1 can be detected. The number of revolutions can be detected. Further, the variable throttle portion 30c increases the opening area as the passing flow rate increases (as the front-rear differential pressure increases), so that the degree of increase in the front-rear differential pressure becomes gradual as the passing flow rate increases. It is configured as follows.

The main pump 2 is a variable displacement hydraulic pump, and includes a pump control device 35 for controlling the tilt angle (capacity) thereof. The pump control device 35 includes a pump torque control unit 35A and an LS control unit 35B.

The pump torque control unit 35A has a torque control tilting actuator 35a, and the torque control tilting actuator 35a of the main pump 2 reduces the tilt angle (capacity) of the main pump 2 when the discharge pressure of the main pump 2 increases. The swash plate (variable capacity member) 2s is driven, and the input torque of the main pump 2 is limited so as not to exceed the preset maximum torque. As a result, the horsepower consumed by the main pump 2 is limited, and the engine 1 is prevented from stopping (engine stall) due to an overload.

The LS control unit 35B has an LS control valve 35b and an LS control tilting actuator 35c.

The LS control valve 35b has opposed pressure receiving portions 35d and 35e, and the absolute pressure PGR generated by the differential pressure reducing valve 30b of the engine rotation speed detection valve 30 via the oil passage 40 is used for load sensing control in the pressure receiving portion 35d. Absolute pressure PLS (differential pressure PLS between the discharge pressure Pd of the main pump 2 and the maximum load pressure PLmax) generated by the differential pressure pressure reducing valve 24 is guided to the pressure receiving portion 35e as the target differential pressure (target LS differential pressure). It is derived as a feedback differential pressure. The LS control valve 35b guides the pressure of the pilot hydraulic source 33 to the LS control tilting actuator 35c when the absolute pressure PLS becomes higher than the absolute pressure PGR (PLS> PGR), and when the absolute pressure PLS becomes lower than the absolute pressure PGR. (PLS <PGR), the LS control tilting actuator 35c is communicated with the tank T. The LS-controlled tilt actuator 35c drives the swash plate 2s of the main pump 2 so that the tilt angle of the main pump 2 decreases when the pressure of the pilot hydraulic source 33 is guided, and when it communicates with the tank T, the main pump 2 The swash plate 2s of the main pump 2 is driven so that the tilt angle of the main pump 2 is increased. As a result, the tilt angle (capacity) of the main pump 2 is controlled so that the discharge pressure Pd of the main pump 2 is higher than the maximum load pressure PLmax by the absolute pressure PGR (target differential pressure).

Here, since the absolute pressure PGR is a value that changes according to the engine speed, the absolute pressure PGR is used as the target differential pressure for load sensing control, and the target compensation differential pressure of the pressure compensation valves 27a to 27h is used for the main pump 2. By setting the absolute pressure PLS, which is the differential pressure between the discharge pressure Pd and the maximum load pressure PLmax, the actuator speed can be controlled according to the engine speed.

The set pressure of the spring 25a of the unload valve 25 is the absolute pressure PGR (target differential pressure of load sensing control) generated by the differential pressure pressure reducing valve 30b of the engine rotation speed detection valve 30 when the engine 1 is at the rated maximum rotation speed. ) Is set to be slightly higher.

-Operation of basic configuration-
First, the operation of the basic configuration of the hydraulic drive device of the present embodiment will be described.

<When all operating levers are neutral>
When the operating levers of all the operating devices 34a to 34h are in the neutral position, all the flow control valves 26a to 26h are in the neutral position, and pressure oil is not supplied to the actuators 5 to 12. When the flow control valves 26a to 26h are in the neutral position, the maximum load pressure PLmax detected by the shuttle valves 22a to 22g is the tank pressure.

The oil discharged from the main pump 2 is supplied to the pressure oil supply passages 2a and 4a, and the pressure in the pressure oil supply passages 2a and 4a rises. An unload valve 25 is provided in the pressure oil supply path 4a, and in the unload valve 25, the pressure of the pressure oil supply path 2a is equal to or higher than the set pressure of the spring 25a than the maximum load pressure PLmax (tank pressure in this case). When it becomes high, the pressure oil in the pressure oil supply path 2a is returned to the tank in an open state, and the increase in the pressure in the pressure oil supply path 2a is restricted. As a result, the discharge pressure of the main pump 2 is controlled to the minimum pressure Pmin.

The differential pressure pressure reducing valve 24 outputs the differential pressure PLS of the discharge pressure Pd of the main pump 2 and the maximum load pressure PLmax (in this case, the tank pressure) as an absolute pressure. The output pressure of the engine rotation speed detection valve 30 and the output pressure of the differential pressure pressure reducing valve 24 are guided to the LS control valve 35b of the LS control unit 35B of the main pump 2, and the discharge pressure of the main pump 2 rises. When the output pressure of the differential pressure pressure reducing valve 24 becomes larger than the output pressure of the engine rotation speed detection valve 30, the LS control valve 35b switches to the position on the right side in the drawing, and the pressure of the pilot hydraulic source 33 is applied to the LS control tilting actuator 35c. It is guided and controlled so that the tilt angle of the main pump 2 becomes small. However, since the main pump 2 is provided with a stopper (not shown) that defines the minimum tilt angle, the main pump 2 is held at the minimum tilt angle qmin defined by the stopper, and the minimum flow rate is reached. Discharge Qmin.
-When the operation lever is operated-
When an operation lever of an arbitrary driven member, for example, an operation device 34d for a blade is operated, the flow control valve 26d for the blade is switched, pressure oil is supplied to the blade cylinder 8, and the blade cylinder 8 is driven. ..

The flow rate flowing through the flow control valve 26d is determined by the opening area of the meter-in throttle of the flow control valve 26d and the front-rear differential pressure of the meter-in throttle. Since the pressure is controlled to be equal, the flow rate flowing through the flow rate control valve 26d (hence, the drive speed of the blade cylinder 8) is controlled according to the operation amount of the operation lever.

On the other hand, the load pressure of the blade cylinder 8 is detected as the maximum load pressure by the shuttle valves 22a to 22g, and is transmitted to the differential pressure pressure reducing valve 24 and the unload valve 25.

When the load pressure of the blade cylinder 8 is guided to the unload valve 25 as the maximum load pressure, the cracking pressure of the unload valve 25 (the pressure at which the unload valve 25 starts to open) rises accordingly, and the pressure oil supply path 2a When the pressure is transiently higher than the maximum load pressure by the set pressure of the spring 25a or more, the unload valve 25 is opened to return the pressure oil in the pressure oil supply path 4a to the tank. This limits the pressure of the pressure oil supply paths 2a and 4a from rising above the set pressure of the spring 25a from the maximum load pressure PLmax.

When the blade cylinder 8 starts to move, the pressure in the pressure oil supply paths 2a and 4a temporarily drops. At this time, the difference between the pressure of the pressure oil supply path 2a and the load pressure of the blade cylinder 8 is output as the output pressure of the differential pressure pressure reducing valve 24, so that the output pressure of the differential pressure pressure reducing valve 24 decreases.

The output pressure of the engine rotation speed detection valve 30 and the output pressure of the differential pressure pressure reducing valve 24 are guided to the LS control valve 35b of the LS control unit 35B of the main pump 2, and the output pressure of the differential pressure pressure reducing valve 24 is measured. When the pressure drops below the output pressure of the engine rotation speed detection valve 30, the LS control valve 35b switches to the position on the left side of the drawing, and the LS control tilting actuator 35c is communicated with the tank T to fill the LS control tilting actuator 35c pressure oil. The tilt angle of the main pump 2 is controlled to increase, and the discharge flow rate of the main pump 2 increases. This increase in the discharge flow rate of the main pump 2 continues until the output pressure of the differential pressure pressure reducing valve 24 becomes equal to the output pressure of the engine speed detection valve 30. By these series of operations, the discharge pressure of the main pump 2 (pressure of the pressure oil supply paths 2a and 4a) is controlled to be higher than the maximum load pressure PLmax by the output pressure (target differential pressure) of the engine rotation speed detection valve 30. Then, so-called load sensing control is performed, in which the flow rate required by the flow rate control valve 26d for the blade is supplied to the blade cylinder 8.

When an operation lever other than the operation lever of the blade operation device 34d, for example, the operation lever of the boom operation lever device 34f is operated, the boom cylinder 10 is similarly driven.

When the operation device 34d for the blade and the operation devices 34a and 34b for traveling are operated with the intention of removing soil or leveling work by the operation device of two or more driven members, for example, the blade 304, the blade is used. The flow rate control valve 26d and the flow rate control valves 26a and 26b for traveling are switched, pressure oil is supplied to the blade cylinder 8 and the traveling motors 5 and 6, and the blade cylinder 8 and the traveling motors 5 and 6 are driven.

The higher of the load pressures of the blade cylinder 8 and the traveling motors 5 and 6 is detected as the maximum load pressure PLmax by the shuttle valves 22a to 22g, and is transmitted to the differential pressure pressure reducing valve 24 and the unload valve 25.

The operation when the maximum load pressure PLmax detected by the shuttle valves 22a to 22g is guided to the unload valve 25 is the same as when the blade cylinder 8 is driven independently, and the operation is the same as when the blade cylinder 8 is driven independently, and the maximum load pressure PLmax is increased. The cracking pressure of the unload valve 25 rises, and the pressure of the pressure oil supply paths 2a and 4a is restricted from rising above the set pressure of the spring 25a above the maximum load pressure PLmax.

Further, the output pressure of the engine rotation speed detection valve 30 and the output pressure of the differential pressure pressure reducing valve 24 are guided to the LS control valve 35b of the LS control unit 35B of the main pump 2, and the blade cylinder 8 is driven independently. The discharge pressure of the main pump 2 (pressure of the pressure oil supply paths 2a and 4a) is controlled to be higher than the maximum load pressure PLmax by the output pressure (target differential pressure) of the engine rotation speed detection valve 30. The so-called load sensing control is performed, in which the flow rate required by the flow rate control valves 26f and 26g is supplied to the blade cylinder 8 and the traveling motors 5 and 6.

The output pressure of the differential pressure pressure reducing valve 24 is guided to the pressure compensating valves 27a to 27h as the target compensating differential pressure, and the pressure compensating valves 27a, 27b, 27d apply the front-rear differential pressure of the flow control valves 26a, 26b, 26d. It is controlled so as to be equal to the differential pressure between the discharge pressure of the main pump 2 and the maximum load pressure PLmax. As a result, regardless of the magnitude of the load pressure of the blade cylinder 8 and the traveling motors 5 and 6, the blade cylinder 8 and the traveling motors 5 and 6 have a ratio corresponding to the opening area of the meter-in throttle portion of the flow control valves 26b, 26c and 26d. Pressure oil can be supplied.

At this time, if the discharge flow rate of the main pump 2 is in a saturation state that is less than the flow rate required by the flow control valves 26a, 26b, 26d, the output pressure of the differential pressure pressure reducing valve 24 (main pump) is adjusted according to the degree of saturation. The differential pressure between the discharge pressure of 2 and the maximum load pressure PLmax) decreases, and the target compensation differential pressure of the pressure compensating valves 27a to 27h also decreases accordingly. It can be redistributed to the ratio of the flow rates required by 26b and 26d.

~ Characteristic composition ~
Next, the characteristic configuration of the hydraulic drive device according to the present embodiment will be described.

In the hydraulic drive device according to the present embodiment, the main relief valve 100 is configured as a variable relief valve in which the set pressure can be switched between a normal setting and a high pressure setting higher than this normal setting, and the main relief valve 100 boosts the pressure. It has a pressure receiving unit 100a that switches the set pressure from the normal setting to the high pressure setting when the signal pressure is derived.

Further, the hydraulic drive device according to the present embodiment is an operation for the blade as a jack-up detection device for detecting a jack-up operation (see FIG. 6) in which the blade 304 is driven in the downward direction and the main body 310 is lifted by the blade 304. The pressure sensor 201 (first pressure sensor) that detects the operation pilot pressure g for lowering the blade among the operation pilot pressures g and h generated by the device 34d, and the travel operation pilot pressure a generated by the operation devices 34a and 34b for traveling. It has a pressure sensor 202 (second pressure sensor) that detects, b, c, and d.

Here, shuttle valves 44a, 44b, 44c are connected to the pilot oil passages of the operation device 34a for left travel and the operation device 23b for right travel in a tournament system, and the pressure sensor 202 is connected to the uppermost shuttle valve 44c. It is connected so that the pressure sensor 202 can detect the operating pilot pressures a, b, c, d for left and right traveling. In the following, the operation pilot pressure detected by the pressure sensor 202 is represented by the reference numeral abcd.

Further, the hydraulic drive device according to the present embodiment has a closed position and an open position, and when the closed position is switched to the open position, the pilot primary pressure of the pilot hydraulic source 33 is used as the boost signal pressure as the main relief valve 100. It is provided with an electromagnetic switching valve 101 that leads to the pressure receiving unit 100a of the above, and a controller 200 that switches the electromagnetic switching valve 101 from the closed position to the open position when the jack-up operation is detected by the jack-up detection devices (pressure sensors 201 and 202). ing.

The electromagnetic switching valve 101 and the controller 200 serve as a relief valve control device that switches the set pressure of the main relief valve 100 from the normal setting to the high pressure setting when the jack-up operation is detected by the jack-up detection devices (pressure sensors 201 and 202). Function. Further, in the present embodiment, in the relief valve control device (electromagnetic switching valve 101 and controller 200), the blade lowering operation pilot pressure g is detected by the pressure sensor 201 (first pressure sensor), and the pressure sensor 202 (first pressure sensor). 2 When the traveling operation pilot pressures a, b, c, and d are not detected by the pressure sensor), the set pressure of the main relief valve 100 is switched from the normal setting to the high pressure setting.

~ Jack up operation ~
The blade 304 is used not only when performing soil removal work and leveling work, but also when performing a jack-up operation for lifting the main body 310 when maintaining the undercarriage of the lower traveling body 300 or when cleaning the tracks 300a and 300b. Is also used.

FIG. 6 is a diagram showing a state in which the main body 310 of the hydraulic excavator is jacked up by the front working machine 302 and the blade 304. In this jack-up operation, the upper swing body 301 is rotated 180 degrees, the front part of the main body 310 is lifted by the front working machine 302, and the rear part of the main body 310 is lifted by the blade 304. This jack-up operation is performed as follows.

First, the operator operates the operating lever of the turning operation device 34c to rotate the upper turning body 301 by 180 degrees, and positions the front working machine 302 on the opposite side of the blade 304. Next, the operator operates the operating lever of the operating device 34d for the blade in the blade lowering direction, switches the flow control valve 26d for the blade to the position in the blade lowering direction, and drives the blade cylinder 8 in the extending direction to drive the blade. The 304 is driven in the downward direction to raise the front portion of the lower traveling body 300 from the ground. When the front part of the lower traveling body 300 is lifted to the intended height, the operator returns the operating lever of the operating device 34d for the blade to the neutral position, returns the flow control valve 26d for the blade to the neutral position, and returns the lower traveling body 300 to the neutral position. Stop at that height. Next, the operator operates the operation lever of the boom operating device 34f in the boom lowering direction, switches the flow rate control valve 26f for the boom to the position in the boom lowering direction, and drives the boom cylinder 10 in the contraction direction to drive the boom. The 306 is driven in the downward direction to raise the rear portion of the lower traveling body 300 from the ground. When the rear part of the lower traveling body 300 is lifted to the intended height, the operator returns the operating lever of the operating device 34f for the boom to the neutral position, returns the flow control valve 26f for the boom to the neutral position, and returns the lower traveling body 300 to the neutral position. Stop the rear at that height. Further, depending on the situation, a jack-up operation by lowering the blade and a jack-up operation by lowering the boom may be performed at the same time. By performing such a jack-up operation for lowering the blade and a jack-up operation for lowering the boom, the main body 310 can be lifted to a desired height, and the jack-up posture as shown in FIG. 6 can be obtained.

When the jack-up operation by lowering the blade and the jack-up operation by lowering the boom are alternately performed, the jack-up operation of lowering the boom may be performed first. Further, instead of using the blade lowering and the boom lowering together, one side (only the front side or the rear side only) of the main body 310 may be jacked up only by lowering the blade or lowering the boom.

~ Controller 200 ~
Next, the details of the function of the controller 200 will be described with reference to the flowchart shown in FIG.

Signals from the pressure sensors 201 and 202 are input to the controller 200.

First, the controller 200 determines whether or not the blade lowering operation pilot pressure g detected by the pressure sensor 201 is equal to or higher than a preset predetermined threshold value Pa based on the signal from the pressure sensor 201 (step S100). .. The threshold value Pa is a value for determining whether or not the operation lever of the operation device 34d for the blade is sufficiently operated in the lowering direction of the blade 304 and the blade cylinder 8 feature is driven. The threshold value Pa is, for example, a jack-up operation. It is set to a value of 30 to 50% of the maximum operating pilot pressure, which is the minimum value of the operating pilot pressure range at the time of operation. When the operation pilot pressure g is equal to or higher than the threshold value Pa, it is determined that the blade cylinder 8 is driven in the downward direction and the jack-up operation may be performed, and the process proceeds to the next process. When the operation pilot pressure g is not equal to or higher than the threshold value Pa, it is determined that the blade cylinder 8 is not driven, or even if it is driven, there is no possibility that the jack-up operation is performed, and the determination in step S100 is repeated.

When the determination is affirmed in step S100, the controller 200 determines whether or not the operating pilot pressure abcd detected by the pressure sensor 202 is equal to or less than a predetermined threshold value Pmin set in advance based on the signal from the pressure sensor 202. (Step S110). The threshold value Pmin is a value for determining whether or not the operating levers of the traveling operating devices 34a and 34b are in the neutral position, and the threshold value Pmin is the maximum pressure range (tank pressure) when the operating lever is in the neutral position. Set to a value. When the operation pilot pressure abcd is equal to or less than the threshold value Pmin, it is determined that the traveling motors 5 and 6 are not driven, and the process proceeds to the next process. When the operation pilot pressure abcd is not equal to or less than the threshold value Pmin, it is determined that the traveling motors 5 and 6 are driven and traveling, and the process of step S110 is repeated.

When the determination is affirmed in step S110, the controller 200 determines that the blade cylinder 8 is currently driven in the downward direction and is not running, and the jack-up operation is being performed (that is, the jack-up operation is performed). Detected), an electric signal E is output to the electromagnetic switching valve 101, and the electromagnetic switching valve 101 is switched from the closed position to the open position (step S120). As a result, the pilot primary pressure of the pilot hydraulic pressure source 33 is guided to the pressure receiving portion 100a of the main relief valve 100 as a boost signal pressure, and the set pressure of the main relief valve 100 switches from the normal setting to the high pressure setting.

Next, the controller 200 determines whether or not the blade lowering operation pilot pressure g detected by the pressure sensor 201 is equal to or less than the threshold value Pmin (step S130). The threshold value Pmin is the same as the threshold value Pmin used in the determination in step S110, and when the operation pilot pressure g for lowering the blade is not equal to or less than the threshold value Pmin, it is determined that the jack-up operation is continuing, and the process of step S130 is performed. repeat. When the operation pilot pressure g for lowering the blade is equal to or less than the threshold value Pmin, it is determined that the operation lever of the operation device 34d for the blade is returned to the neutral position and the jack-up operation is completed, and the electric signal E to the electromagnetic switching valve 101 is transmitted. The output is stopped and the electromagnetic switching valve 101 is switched from the open position to the closed position (step S140). As a result, the pilot primary pressure (boost signal pressure) of the pilot hydraulic pressure source 33 guided to the pressure receiving portion 100a of the main relief valve 100 is cut off, and the set pressure of the main relief valve 100 returns from the high pressure setting to the normal setting.

~ Characteristic operation ~
When performing the jack-up operation as described above, the operator operates the operating lever of the operating device 34d for the blade in the blade lowering direction and operates the operating lever of the operating device 34f for the boom in the boom lowering direction. Either the operating lever of the operating device 34d for the blade or the operating lever of the operating device 34f for the boom is operated in the blade lowering direction or the boom lowering direction. However, in the jack-up operation, the operator does not operate the operating levers of the traveling operating devices 34a and 34b. In such a jack-up operation, when the operator operates the operating lever of the operating device 34d for the blade in the blade lowering direction, the controller 200 lowers the blade detected by the pressure sensor 201 in steps S100 and S110 of FIG. In order to determine that the operation pilot pressure g of the above is equal to or more than the threshold Pa and the operation pilot pressure abcd of traveling detected by the pressure sensor 202 is equal to or less than the threshold Pmin, an electric signal E is output to the electromagnetic switching valve 101 in step S120. , The electromagnetic switching valve 101 is switched from the closed position to the open position. As a result, the pilot primary pressure of the pilot hydraulic pressure source 33 is guided to the pressure receiving portion 100a of the main relief valve 100 as a boost signal pressure, and the set pressure of the main relief valve 100 switches from the normal setting to the high pressure setting.

The thrust F of the blade cylinder 8 is expressed by the following equation.

F = PA
F: Thrust P: Pressure on the bottom side of the blade cylinder 8 A: Cylinder cross-sectional area on the bottom side of the blade cylinder 8 Therefore, the set pressure of the main relief valve 100 is switched from the normal setting to the high pressure setting, so that the hydraulic pump 2 The maximum discharge pressure increases, and the thrust F of the blade cylinder 8 increases.

Here, when performing a jack-up operation by lowering the blade, a large thrust is required to lift the main body 310 from the ground. At that time, the pressure on the bottom side of the blade cylinder 8 becomes high pressure, and the pressure rises to the set pressure of the main relief valve 100 depending on the posture of the main body 310 and the inclination of the ground.

In the present embodiment, the thrust F of the blade cylinder 8 increases as described above when the jack-up operation is performed by lowering the blade. Therefore, even if the size of the blade cylinder 8 is reduced and the size is reduced, the thrust required for the jack-up operation can be generated.

On the other hand, when performing soil removal work using the blade 304, the operator operates the operation levers of the traveling operation devices 34a and 34b to switch the traveling flow rate control valves 26a and 26b, and switches the traveling motors 5 and 6. Drive. Therefore, even if the operator performs the blade lowering operation, the controller 200 determines in step S110 of FIG. 3 that the traveling operation pilot pressure abcd detected by the pressure sensor 202 is not equal to or less than the threshold value Pmin. The switching valve 101 does not switch to the open position, and the set pressure of the main relief valve 100 is maintained at the normal setting. As a result, the maximum pressure of the pressure oil supplied to the traveling motors 5 and 6 does not increase, and the increase in the load of the traveling motors 5 and 6 can be suppressed.

In the jack-up operation performed by the boom lowering operation among the jack-up operations, the electromagnetic switching valve 101 does not switch to the open position, and the set pressure of the main relief valve 100 does not switch to the high pressure setting. However, since the boom cylinder 10 is a hydraulic actuator that drives the boom 306 to perform work such as excavation, it is inherently a large specification, and jacks up even if the set pressure of the main relief valve 100 remains at the normal setting. It is possible to generate the thrust required for operation.

~ Effect ~
As described above, according to the present embodiment, when the blade 304 is driven in the downward direction to perform the jack-up operation, the set pressure of the main relief valve 100 is switched from the normal setting to the high pressure setting, and the maximum of the hydraulic pump 2 is reached. The discharge pressure increases, and the thrust of the blade cylinder 8 increases. As a result, even if the size of the blade cylinder 8 is reduced, the thrust required for the jack-up operation can be generated during the jack-up operation, and the blade cylinder can be made smaller to reduce the cost.

Further, even if the jack-up operation by lowering the blade and the jack-up operation by lowering the boom are performed at the same time, the high pressure setting of the set pressure of the main relief valve 100 is maintained, so that the thrust of the blade cylinder 8 does not decrease, which is good. Jack-up performance can be maintained.

Further, during the combined operation of traveling and the blade, the set pressure of the main relief valve 100 remains at the normal setting, the maximum discharge pressure of the hydraulic pump 2 does not increase, and the load acting on the traveling motors 5 and 6 increases. Can be avoided.

Further, by providing the electromagnetic switching valve 101 and switching the electromagnetic switching valve 101 from the closed position to the open position, the pilot primary pressure of the pilot hydraulic pressure source 33 is guided to the pressure receiving portion 100a of the main relief valve 100 as the boost signal pressure, and the main relief is provided. Since the set pressure of the valve 100 is switched from the normal setting to the high pressure setting, switching to the high pressure setting may be insufficient due to insufficient pressure as in the case of guiding the operation pilot pressure g for lowering the blade as the boost signal pressure. It can be avoided and can be reliably switched to the high pressure setting with good response, and good jack-up operability can be ensured.
<Second embodiment>
FIG. 4 is a diagram showing a hydraulic drive device provided in the y hydraulic excavator according to the second embodiment of the present invention.

In FIG. 4, the same members as those of the hydraulic drive device according to the first embodiment shown in FIG. 2 are designated by the same reference numerals. In this embodiment, the jack-up operation is detected not by the operating pilot pressure of traveling but by the pressure on the bottom side of the blade cylinder 8.

The hydraulic drive device according to the present embodiment is an operation pilot generated by the operation device 34d for the blade as a jack-up detection device for detecting the jack-up operation in which the blade 304 is driven in the downward direction and the main body 310 is lifted by the blade 304. The blade cylinder 8 is provided with a pressure sensor 201 (first pressure sensor) for detecting the operation pilot pressure g for lowering the blade among the pressures g and h, and instead of the pressure sensor 202 provided in the first embodiment. It is equipped with a pressure sensor 203 (second pressure sensor) that detects the pressure on the bottom side.

Further, the hydraulic drive device according to the present embodiment includes a controller 200A that switches the electromagnetic switching valve 101 from the closed position to the open position when the jack-up operation is detected by the jack-up detection devices (pressure sensors 201 and 203). ing.

The electromagnetic switching valve 101 and the controller 200A serve as a relief valve control device that switches the set pressure of the main relief valve 100 from the normal setting to the high pressure setting when the jack-up operation is detected by the jack-up detection devices (pressure sensors 201 and 203). Function. Further, in the present embodiment, in the relief valve control device (electromagnetic switching valve 101 and controller 200), the blade lowering operation pilot pressure g is detected by the pressure sensor 201 (first pressure sensor), and the pressure sensor 203 (third). 2 When the pressure on the bottom side of the blade cylinder 8 detected by the pressure sensor) is higher than the predetermined threshold value Pb (described later), the set pressure of the main relief valve 100 is switched from the normal setting to the high pressure setting. Other configurations of the hydraulic drive device are the same as those of the first embodiment.

Hereinafter, the details of the functions of the controller 200A will be described with reference to the flowchart shown in FIG. In FIG. 5, the same reference numerals are given to the steps that perform the same processing as the processing of the flowchart shown in FIG. 3, and the description is simplified.

Signals from the pressure sensors 201 and 203 are input to the controller 200A.

First, the controller 200A determines whether or not the blade lowering operation pilot pressure g detected by the pressure sensor 201 is equal to or higher than a preset predetermined threshold Pa based on the signal from the pressure sensor 201 (step S100). When the operation pilot pressure g is equal to or higher than the threshold value Pa, it is determined that the blade cylinder 8 is driven in the downward direction and the jack-up operation may be performed, and the process proceeds to the next process.

Next, the controller 200 determines whether or not the pressure on the bottom side of the blade cylinder 8 detected by the pressure sensor 203 is equal to or higher than a preset predetermined threshold value Pb based on the signal from the pressure sensor 203 (step S150). .. As for the threshold value Pb, is the operation in the lowering direction of the blade 304 a jack-up operation when the operating lever of the operating device 34d for the blade is operated in the lowering direction of the blade 304 and the blade cylinder 8 is driven in the extending direction? It is a value for determining whether or not, and the threshold value Pb is set to a value slightly lower than the pressure generated on the bottom side of the blade cylinder 8 when the jack-up operation is performed using the blade 304. When the pressure on the bottom side of the blade cylinder 8 is equal to or higher than the threshold value Pb, it is determined that the jack-up operation is being performed, and the process proceeds to the next process. When the pressure on the bottom side of the blade cylinder 8 is not equal to or higher than the threshold value Pb, it is determined that the jack-up operation has not been performed, and the process of step S150 is repeated.

When the determination is affirmed in step S150, the controller 200 determines that the blade cylinder 8 is currently driven in the downward direction and the jack-up operation is being performed (that is, the jack-up operation is detected), and the electromagnetic wave is detected. An electric signal E is output to the switching valve 101 to switch the electromagnetic switching valve 101 from the closed position to the open position (step S120). As a result, the pilot primary pressure of the pilot hydraulic pressure source 33 is guided to the pressure receiving portion 100a of the main relief valve 100 as a boost signal pressure, and the set pressure of the main relief valve 100 switches from the normal setting to the high pressure setting.

Subsequent processing of steps S130 and S140 is the same as that of the first embodiment.
~ Effect ~
Also in the present embodiment configured as described above, when the blade 304 is driven in the downward direction to perform the jack-up operation, the set pressure of the main relief valve 100 is switched from the normal setting to the high pressure setting, and the maximum of the hydraulic pump 2 is reached. The discharge pressure increases, and the thrust of the blade cylinder 8 increases. As a result, even if the size of the blade cylinder 8 is reduced, the thrust required for the jack-up operation can be generated during the jack-up operation, and the blade cylinder can be made smaller to reduce the cost.

Further, as in the first embodiment, even if the jack-up operation by lowering the blade and the jack-up operation by lowering the boom are performed at the same time, the thrust of the blade cylinder 8 does not decrease and good jack-up performance is maintained. Further, during the combined operation of traveling and the blade, the set pressure of the main relief valve 100 remains at the normal setting, and it is possible to avoid an increase in the load acting on the traveling motors 5 and 6.

~ Other ~
In the above embodiment, the load sensing control hydraulic circuit is used as the hydraulic drive device, but the same effect can be obtained by adopting the same configuration in the center bypass type open type hydraulic circuit. Be done.

Further, although the electromagnetic switching valve 101 is provided and the set pressure of the main relief valve 100 is switched between the normal setting and the high pressure setting, the operation pilot pressure g for lowering the blade is directly guided to the pressure receiving portion 100a of the main relief valve 100. , The set pressure of the main relief valve 100 may be switched between the normal setting and the high pressure setting, or the electromagnetic switching valve 101 is changed to the hydraulic switching valve, and the operation pilot pressure g for lowering the blade is guided to this hydraulic switching valve to hydraulic pressure. The switching valve may be switched from the closed position to the open position, and the set pressure of the main relief valve 100 may be switched between the normal setting and the high pressure setting.

1 E engine (motor)
2 Main pump (hydraulic pump)
3 Pilot pump 4a Pressure oil supply path 5 to 12 Actuator 5, 6 Travel motor 8 Blade cylinder 26a to 26h Flow control valve 26a, 26b Flow control valve for traveling 26d Flow control valve for blade 33 Pilot hydraulic source 34a, 34b Travel Operation device for 34d Blade operation device 100 Main relief valve 100a Pressure receiving unit 101 Electromagnetic switching valve (relief valve control device)
200 controller (relief valve control device)
200A controller (relief valve control device)
201 Pressure sensor (1st pressure sensor; jack-up detection device)
202 Pressure sensor (second pressure sensor; jack-up detection device)
203 Pressure sensor (second pressure sensor; jack-up detection device)
300 Lower traveling body 301 Upper rotating body 302 Front working machine 304 Blade 306 Boom 307 Arm 308 Bucket 310 Main body a, b, c, d Traveling operation pilot pressure g Blade lowering operation pilot pressure

Claims (3)

A main body having a lower traveling body having a blade in the front portion and an upper rotating body rotatably mounted on the lower traveling body, and a front working machine mounted on the front portion of the upper rotating body so as to be able to stand up and down. Has a hydraulic drive and
The hydraulic drive device is
A hydraulic pump driven by a prime mover and
A plurality of actuators driven by the pressure oil discharged from the hydraulic pump to drive the lower traveling body, the upper swivel body, the front working machine, and the blades.
A plurality of flow control valves that control the flow of pressure oil supplied from the hydraulic pump to the plurality of actuators, and
A plurality of operating devices for generating an operating pilot pressure for switching the plurality of flow control valves, and a plurality of operating devices.
In a construction machine provided with a main relief valve connected to the pressure oil supply path of the hydraulic pump and configured as a variable relief valve in which the set pressure can be switched between a normal setting and a higher pressure setting than this normal setting.
A jack-up detection device that detects a jack-up operation in which the blade is driven in the downward direction and lifts the main body by the blade.
A relief valve control device for switching the set pressure of the main relief valve from the normal setting to the high pressure setting when the jack-up operation is detected by the jack-up detection device is provided .
The plurality of actuators include a traveling motor for driving the lower traveling body and a blade cylinder for driving the blade.
The plurality of flow rate control valves include a flow rate control valve for traveling that controls driving of the traveling motor and a flow rate control valve for blades that controls driving of the blade cylinder.
The plurality of operating devices generate a traveling operation device for generating a traveling operation pilot pressure for switching the flow rate control valve for traveling and a blade operating pilot pressure for switching the flow rate control valve for the blade. Including operating equipment for blades
The blade cylinder is a hydraulic cylinder that operates in the extension direction when pressure oil is supplied to the bottom side, drives the blade in the lower direction, and performs the jack-up operation.
The jack-up detection device is
A first pressure sensor that detects the operating pilot pressure for lowering the blade among the operating pilot pressures generated by the operating device for the blade.
It has a second pressure sensor that detects the traveling operation pilot pressure generated by the traveling operating device.
The relief valve control device is
When the operation pilot pressure for lowering the blade is detected by the first pressure sensor and the traveling operation pilot pressure is not detected by the second pressure sensor, the set pressure of the main relief valve is changed from the normal setting to the high pressure setting. A construction machine characterized by switching . A main body having a lower traveling body having a blade in the front portion and an upper rotating body rotatably mounted on the lower traveling body, and a front working machine mounted on the front portion of the upper rotating body so as to be able to stand up and down. Has a hydraulic drive and
The hydraulic drive device is
A hydraulic pump driven by a prime mover and
A plurality of actuators driven by the pressure oil discharged from the hydraulic pump to drive the lower traveling body, the upper swivel body, the front working machine, and the blades.
A plurality of flow control valves that control the flow of pressure oil supplied from the hydraulic pump to the plurality of actuators, and
A plurality of operating devices for generating an operating pilot pressure for switching the plurality of flow control valves, and a plurality of operating devices.
In a construction machine provided with a main relief valve connected to the pressure oil supply path of the hydraulic pump and configured as a variable relief valve in which the set pressure can be switched between a normal setting and a higher pressure setting than this normal setting.
A jack-up detection device that detects a jack-up operation in which the blade is driven in the downward direction and lifts the main body by the blade.
A relief valve control device for switching the set pressure of the main relief valve from the normal setting to the high pressure setting when the jack-up operation is detected by the jack-up detection device is provided.
The plurality of actuators include a traveling motor for driving the lower traveling body and a blade cylinder for driving the blade.
The plurality of flow rate control valves include a flow rate control valve for traveling that controls driving of the traveling motor and a flow rate control valve for blades that controls driving of the blade cylinder.
The plurality of operating devices generate a traveling operation device for generating a traveling operation pilot pressure for switching the flow rate control valve for traveling and a blade operating pilot pressure for switching the flow rate control valve for the blade. Including operating equipment for blades
The blade cylinder is a hydraulic cylinder that operates in the extension direction to drive the blade in the downward direction when pressure oil is supplied to the bottom side to perform the jack-up operation.
The jack-up detection device is
A first pressure sensor that detects the operating pilot pressure for lowering the blade among the operating blade operating pilot pressures generated by the operating device for the blade.
It has a second pressure sensor that detects the pressure on the bottom side of the blade cylinder.
The relief valve control device is
The main relief valve is set when the operation pilot pressure for lowering the blade is detected by the first pressure sensor and the pressure on the bottom side of the blade cylinder detected by the second pressure sensor is higher than a predetermined threshold value. A construction machine characterized in that the pressure is switched from the normal setting to the high pressure setting. In the construction machine according to claim 1 or 2 .
The hydraulic drive system further comprises a pilot hydraulic source that produces a pilot primary pressure based on the oil discharged from the pilot pump driven by the prime mover.
The main relief valve has a pressure receiving unit that switches the set pressure from the normal setting to the high pressure setting when a boost signal pressure is induced.
The relief valve control device is
An electromagnetic switching valve that has a closed position and an open position and guides the pilot primary pressure as the boost signal pressure to the pressure receiving portion of the main relief valve when the closed position is switched to the open position.
A construction machine comprising a controller for switching the electromagnetic switching valve from the closed position to the open position when the jack-up operation is detected by the jack-up detection device.

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