JP2005127416A - Oil pressure control device and wheel loader using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oil pressure control device, returning the stroke of a first direction control valve to the vicinity of a neutral position by the operation of a second direction control valve to stop a flow rate and give priority to the pressure oil of the second direction control valve, and a wheel loader, facilitating the operation by using the above oil pressure control device in simple constitution. <P>SOLUTION: This oil pressure control device includes: an oil pressure pump; two or more actuators; and a direction control valve for controlling the pressure oil supplied to the actuators. The oil pressure controlled device includes: the first direction control valve displaced from the neutral position by a first pilot pressure to feed pressure oil to a first actuator; a second direction control valve for feeding pressure oil to a second actuator by a second pilot pressure; and a stroke return means returning the stoke of the first direction control valve to the vicinity of the neutral position by the second pilot pressure in switching the first direction control valve to give priority to the oil pressure fed from the second direction control valve to the second actuator. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydraulic control device and a wheel loader using the same, and more particularly, a hydraulic control device that prioritizes pressure oil supply to a predetermined actuator by a directional control valve having stroke return and facilitates operation of the wheel loader. About.

  2. Description of the Related Art Conventionally, work machines mounted on work vehicles such as construction machines, industrial vehicles, and agricultural machines are driven by hydraulic control devices and their operations are controlled. As the hydraulic circuit of the hydraulic control device, a parallel circuit, a tandem circuit, a series circuit, or a circuit combining any one of them according to the use of the work vehicle is used. For example, a parallel circuit is used in a hydraulic excavator as shown in Patent Document 1.

In the hydraulic control device of Patent Document 1, a plurality of actuators are operated by a single pump via a control valve, and the control valve has a plurality of spools corresponding to the plurality of actuators, respectively. Are arranged in parallel, and each spool is provided with a pump / tank bypass circuit for bleed-off.
The control valve is provided with a spool stroke return means, and the spool stroke return means regulates the spool stroke to a predetermined position near the full stroke only when the engine speed exceeds a predetermined value, When the spool is located at a predetermined position, the pump / tank bypass oil passage is opened by a predetermined bleed-off amount, while when the spool is located at a full stroke, the pump / tank bypass oil passage is closed.
As a result, the pressure of the actuator can be increased to the relief pressure even when the amount of pump oil is low due to the low engine speed, which eliminates the power shortage during low-speed operation of the hydraulic excavator and improves workability. To do.

  Patent Document 2 has been proposed as another parallel circuit. In Patent Document 2, a plurality of directional control valves are connected in parallel to one hydraulic pump, and an actuator is connected to each directional control valve. A pressure compensation valve is provided on the inlet side of each directional control valve. Each pressure compensation valve is set at the highest load pressure among the load pressures of each actuator, and the discharge pressure oil of the hydraulic pump is flowed to multiple actuators with different load pressures. It can be distributed and supplied.

Further, the present applicant has proposed a parallel circuit as shown in Patent Document 3. Patent Document 3 includes a travel valve that joins the discharge pressure oils of a plurality of hydraulic pumps and supplies them to a travel motor, and a work implement operation valve that joins the discharge pressure oils of a plurality of hydraulic pumps and supplies them to a work implement actuator. Means for reducing the meter-in opening area of the work machine operation valve when the traveling hydraulic motor is driven is provided.
As a result, when the work implement is operated while traveling, the meter-in opening area of the work implement operation valve can be reduced, so that the load pressure of the traveling hydraulic motor can be increased even when a plurality of hydraulic pumps are merged. The load pressure can be lowered. For this reason, it is not necessary to join and separate the discharge pressure oils of a plurality of hydraulic pumps by a joining valve, the operation is simple, and straight running is possible even when the load pressure of the actuator for the work implement becomes high.

Japanese Patent No. 2779332 JP 60-11706 A Japanese Patent Laid-Open No. 10-37251 (page 3, FIG. 1)

However, in the parallel circuit of Patent Document 1, as is well known, when the discharge pressure oil of one hydraulic pump is supplied to a plurality of actuators, the pressure oil is supplied only to the actuator having a low load pressure, and the load pressure differs. It is difficult to operate the actuators simultaneously, and it is difficult to preferentially operate a predetermined actuator among a plurality of actuators.
For this reason, in Patent Document 2, a plurality of actuators are simultaneously operated at a speed corresponding to an operation amount of a directional control valve for controlling the loads regardless of loads acting on the plurality of actuators.

However, in Patent Document 2, when operating one actuator, it is necessary to operate the operation amount of one actuator to zero in order to operate other actuators with priority over one actuator. is there.
That is, it is necessary to return the operating lever of one actuator to the original and to operate the operating lever of another actuator. For this reason, since the operation involves the return operation of one operation lever and the operation of entering another operation lever, the operation is complicated, and the operation is delayed and the start of operation of other actuators is delayed. .

In a wheel loader, for example, after operating a work machine while moving forward and excavating with a bucket, operating a boom while moving backward to raise the bucket, and further operating a bucket while moving forward toward a dump or the like Sediment is discharged to the dump bed. After discharging the load on the bucket, the boom is lowered to return to the excavation position while returning the bucket to the excavation posture.
In this operation, when excavation of the earth and sand becomes difficult, the earth and sand are excavated while alternately excavating by the bucket and rising by the boom, and the earth and sand are loaded on the bucket.

Further, when the load on the bucket is released to the dump bed, the boom is stopped and the bucket is rotated to release the load while the boom is rising.
Moreover, when discharging the load of a bucket and returning to an excavation state, the bucket is rotated while lowering the boom.
At this time, if the hydraulic circuit of Patent Document 2 is used for a wheel loader, the return operation of the one operation lever (corresponding to the boom operation lever) and the entering operation of the other operation lever (corresponding to the bucket operation lever) Need to be performed. As a result, the operation becomes complicated, the entry operation is delayed, the start of operation of other actuators is delayed, and the operability and workability are not good.

In Patent Document 3, when a working machine having a small load pressure is operated while traveling, the hydraulic oil flows into the working machine and stops traveling. Therefore, the meter-in opening area of the working machine operation valve is reduced, and the hydraulic pump The pressure oil is restricted from flowing to the work machine, and the pressure of the discharge pressure oil of the hydraulic pump is increased so that the work machine can run while operating.
As a result, the work machine actuator and the traveling hydraulic motor can be operated simultaneously. Therefore, if this is used for a wheel loader, a return operation and an entry operation are required as in Patent Document 2. Further, when the boom and bucket of the wheel loader are operated with this hydraulic circuit, there is a problem that a large drive source for driving the hydraulic control device is required because the pressure of the hydraulic pressure discharged from the hydraulic pump is high.

  The present invention has been made paying attention to the above-mentioned problems. The first direction control valve is provided with a stroke return means, and the stroke return is activated by operating the second direction control valve. Is returned to the vicinity of the neutral position, the flow rate is stopped, and the hydraulic control device that gives priority to the pressure oil of the second direction control valve, and the wheel that makes the operation easy by using the hydraulic control device for the wheel loader The purpose is to provide a loader.

  In order to achieve the above object, the first invention controls a hydraulic pump, a plurality of actuators that are operated by pressure oil discharged from the hydraulic pump, and pressure oil that is operated by pilot pressure and is supplied from the hydraulic pump to the actuator. In a hydraulic control device including a directional control valve that performs a stroke, the stroke is displaced from a neutral position by a first pilot pressure, and the stroke is neutral by a second pilot pressure. The second directional control valve that is displaced from the position and supplies pressure oil to the second actuator, and is operated by the second pilot pressure when the first directional control valve is switched, and the stroke of the first directional control valve is returned to the vicinity of the neutral position. Letting the pressure oil fed from the first directional control valve to the first actuator to the pressure oil fed from the second directional control valve to the second actuator. It has a configuration having a stroke returning means for previously be.

  In the second aspect of the invention, the directional control valve is formed by either a parallel valve having an open center, a parallel valve having a closed center, or a parallel valve having a pressure compensation valve at the closed center.

  According to a third aspect of the present invention, there is provided a shuttle valve that selects a high pressure of the second pilot pressure that acts on the second directional control valve, and a first directional control that is attached to the first directional control valve and receives the second pilot pressure from the shuttle valve. Stroke return means comprising a pressure chamber for returning the stroke of the valve is provided, and the stepped ring is slidably and freely fitted in the stepped hole of the spring case, and the pressure chamber is formed between the stepped ring and the spring case. It is the structure formed by the space of the stepped part.

  According to a fourth aspect of the present invention, there is provided a shuttle valve that selects a high pressure of the second pilot pressure that acts on the second directional control valve, and a first directional control valve that operates by receiving the second pilot pressure that acts on the second directional control valve. Stroke return means comprising a pressure reducing valve for reducing the first pilot pressure acting on the pressure and returning the stroke is provided.

  In a fifth aspect of the present invention, the directional control valve is a closed center parallel valve with a pressure compensation valve, and the second directional control is performed for the pressure oil that is supplied from the first directional control valve to the first actuator by operating the stroke return means. Give priority to the pressure oil supplied from the valve to the second actuator, or actuate the pressure compensation valve to distribute the pressure oil of the hydraulic pump according to the stroke amount of the first direction control valve and the second direction control valve Or a priority circuit selection means for selecting either of them.

  According to a sixth aspect of the present invention, there is provided a boom direction control valve for controlling pressure oil to a boom cylinder that moves up and down a boom having a first direction control valve attached to a wheel loader, and a bucket having a second direction control valve attached to the boom. It comprises a wheel loader provided with a bucket direction control valve for controlling the pressure oil to the bucket cylinder that can be raised and lowered.

According to the first invention, since the stroke of the first directional control valve returns to the neutral position and the flow rate is stopped by the second pilot pressure that operates the second directional control valve, the discharge pressure oil of the hydraulic pump is controlled by the first directional control. Since the second direction control valve preferentially supplies the flow rate to the valve, the hydraulic control device can reliably operate the second actuator with a simple configuration.
According to the second aspect of the present invention, the stroke of the first directional control valve can be achieved by using either a parallel valve having an open center, a parallel valve having a closed center, or a parallel valve with pressure compensation at the closed center. Since the flow rate is supplied to the second actuator from the second directional control valve in preference to the second actuator regardless of the load of the first actuator and the second actuator. Can be operated to.

According to the third invention, the shuttle valve selects a high pressure of the second pilot pressure acting on the second directional control valve, sends the pilot pressure to the pressure chamber of the first directional control valve, and the stroke of the first directional control valve. Therefore, the stroke return means can have a simple configuration. Further, by providing the shuttle valve in the second direction control valve, the hydraulic control device can be reduced in size, and the number of pipes can be reduced to prevent oil leakage.
According to the fourth aspect of the present invention, a high second pilot pressure acting on the second directional control valve is selected by the shuttle valve, and the first directional control valve acting on the first directional control valve is operated by receiving the second pilot pressure. Since the pilot pressure is reduced and the stroke is restricted, the stroke return means can have a simple configuration.

According to the fifth invention, when the priority circuit selection means is operated and the stroke return means is deactivated, the discharge pressure oil of the hydraulic pump is distributed by the pressure compensation valve according to the stroke amount of the direction control valve. In this case, combined operation of the boom and bucket is possible when the load is light, etc., and in the case of single operation, the fine control is constant without being affected by the load, and a large excavation force can be obtained at a very low speed. This makes it possible to improve workability and excavability.
When the priority circuit selection means is not operated and the stroke return means is activated, the operation is facilitated by giving priority to the bucket in the same manner as described above. For example, a wheel loader can easily excavate hard earth and sand. Become. Also in this case, in the single operation, the fine control is made constant as described above by the pressure compensation valve, and a large excavation force can be obtained at a slow speed.

According to the sixth aspect of the invention, the first direction control valve is a boom direction control valve that controls the pressure oil to the boom cylinder that raises and lowers the boom of the wheel loader, and the second direction control valve allows the bucket to be raised and lowered. By using the bucket direction control valve for controlling the pressure oil to the cylinder, the boom direction control valve is moved up and down by the hydraulic control device described above, and then the bucket direction control valve is operated to operate the boom. The bucket can be stopped and operated with priority by an easy operation.
For this reason, the return operation of the boom direction control valve is not required as in the prior art, and the bucket can be preferentially operated by operating only the bucket direction control valve, and the operation with the wheel loader becomes easy. The bucket can be operated quickly and workability can be improved.

Embodiments of a hydraulic control device and a wheel loader using the same according to the present invention will be described below with reference to the drawings.
First, a wheel loader using the hydraulic control device of the embodiment will be described. 1 is a schematic side view of a wheel loader equipped with a hydraulic control device, FIG. 2 is an overall hydraulic circuit diagram of the hydraulic control device, FIG. 3 is a sectional view of a directional control valve for a boom constituting the hydraulic control device, and FIG. Sectional drawing of the direction control valve for buckets which comprises a hydraulic control apparatus, FIG. 5 is the schematic explaining the relationship between a pilot signal and a stroke return part. In the following, two directional control valves for the boom and the bucket are shown. The first directional control valve is the boom directional control valve, the first actuator is the boom cylinder, and the bucket relationship is the first. 2, the second direction control valve is described as a bucket direction control valve, and the second actuator is described as a bucket cylinder.

In FIG. 1, the wheel loader 1 includes a vehicle main body 3 and a work device 5 attached to the front portion of the vehicle main body 3. The vehicle body 3 includes a vehicle body 11 including a front frame 7 and a rear frame 9, a cabin 13, and the like.
The working device 5 includes a pair of left and right booms 17 pivotably supported by a pivot shaft 15 of the front frame 7 and a pair of left and right boom cylinders interposed between the front frame 7 and each boom 17 to raise and lower the boom 17. 19, a bucket 21 of a working part pivotally supported at the front end of the boom 17, a bucket cylinder 23 interposed between the front frame 7 and the bucket 21 and rotating the bucket 21.

  FIG. 2 shows a hydraulic circuit of the first hydraulic control device 31 of the first embodiment that drives the working device 5. The first hydraulic control device 31 includes a hydraulic pump 33, a tank 35, a direction control valve 37, a boom cylinder 19, a bucket cylinder 23, a pilot valve 39, a stroke return unit 40, and the like. Is supplied to the direction control valve 37 as pressure oil, and the direction control valve 37 is switched by the pilot valve 39 and supplied to the boom cylinder 19 to supply the boom 17 or to the bucket cylinder 23 to supply the bucket 21. It is operating.

The direction control valve 37 is a stack valve having at least a boom direction control valve 41 (hereinafter referred to as a boom valve 41) and a bucket direction control valve 42 (hereinafter referred to as a bucket valve 42), and a boom valve. 41 and the bucket valve 42 are formed by closed centers each having a pressure compensation valve 45 attached thereto.
In addition, the boom valve 41 and the bucket valve 42 are formed as parallel valves, with each pressure compensating valve 45 connected in parallel to the hydraulic pump 33 by a pump pipe 43.

2 and 3, the boom valve 41 is formed by a four-position switching valve, and a spool 48 is loosely and slidably fitted in a spool hole 47 a of the valve body 47.
A spring case 50 and a stepped ring 51 are attached to both ends of the valve main body 47, and a pilot chamber 52 a that receives a pilot pressure from a boom pressure reducing valve 60, which will be described later, of the pilot valve 39 by the spring case 50, the stepped ring 51 and the spool 48. , 52b are formed.

The boom pressure reducing valve 60 and the raising pilot chamber 52a are connected by a raising pilot pipe 53a, and the boom pressure reducing valve 60 and the lowering pilot chamber 52b are connected by a lowering pilot pipe 53b.
The pilot chambers 52a and 52b receive pilot pressure from the boom pressure reducing valve 60 in one side thereof, and the oil in the pilot chambers 52a and 52b on the opposite side is returned to the tank 35 via the boom pressure reducing valve 60, 48 is slid in the horizontal direction shown in the figure.

The boom valve 41 is provided with a pressure compensation valve 45, and a boom cylinder 19 and a tank 35 are connected to the boom valve 41. The boom valve 41 is switched by receiving a pilot pressure in either of the pilot chambers 52a and 52b, receives the pressure oil of the hydraulic pump 33 from the pressure compensation valve 45 to the pump port 47b, and passes through the spool 48 to raise or lower the port 47c. Feeds to the boom cylinder 19 from 47d.
The return oil from the boom cylinder 19 is received by the lowering port 47d or the raising port 47c and returned to the tank 35 from the tank ports 47e and 47f, and the boom 17 is raised and lowered from the above.

The boom valve 41 has a neutral position (N), a raised position (H), a lowered position (L), and a floating position (F). In the neutral position (N), the raising port 47c and the lowering port 47d are closed by the spool 48, and the boom cylinder 19 is stopped. In the raised position (H), the spool 48 is switched by receiving the pilot pressure in the pilot chamber 52a for raising, and is sent to the boom cylinder 19 from the raising port 47c and extended to raise the boom 17.
In the lowered position (L), the spool 48 is switched by receiving the pilot pressure in the pilot chamber 52b for lowering, and is sent from the lower port 47d to the boom cylinder 19 to be reduced to lower the boom 17. In the floating position (F), a larger pilot pressure is received in the pilot chamber 52b for lowering, the spool 48 is switched, and the raising port 47c, the lowering port 47d, the tank port 47e, and the pump port 47b are connected, and the boom cylinder 19 is connected. The boom 17 is floated by freely expanding and contracting according to an external force.

2 and 4, the bucket valve 42 is formed by a three-position switching valve, and the bucket spool 56 is loosely and slidably fitted in the spool hole 55 a of the valve body 55.
A spring case 57 is attached to both ends of the valve body 55, and a dump pilot chamber 58a and a tilt pilot chamber 58b for receiving a pilot pressure from a bucket pressure reducing valve 61 (described later) of the pilot valve 39 are formed by the spring case 57 and the spool 56. Has been.

The bucket pressure reducing valve 61 and the dump pilot chamber 58a are connected by a dump pilot pipe 59a, and the bucket pressure reducing valve 61 and the tilt pilot chamber 58b are connected by a tilt pipe 59b.
The pilot chambers 58a and 58b receive the pilot pressure from the bucket pressure reducing valve 61 inside one side, and the oil in the pilot chambers 58a and 58b on the opposite side is returned to the tank 35 through the bucket pressure reducing valve 61, and the spool 56 is slid in the horizontal direction shown in the figure.

The bucket valve 42 is provided with a pressure compensation valve 45, and a bucket cylinder 23 and a tank 35 are connected to the bucket valve 42. The bucket valve 42 is switched by receiving a pilot pressure in either of the pilot chambers 58a and 58b, receives the pressure oil of the hydraulic pump 33 from the pressure compensation valve 45 to the pump port 55b, and passes the spool 56 to the dump port 55c or tilt. It is fed from the port 55d to the bucket cylinder 23.
The return oil from the bucket cylinder 23 is received by the tilt port 55d or the dump port 55c, and returned to the tank 35 from the tank ports 55e and 55f, and the bucket 21 is rotated from the above.

Further, the bucket valve 42 has a neutral position (N), a dump position (D), and a tilt back position (T). In the neutral position (N), the dump port 55c and the tilt port 55d are closed by the spool 56, and the bucket cylinder 23 is stopped.
In the dump position (D), the spool 56 receives the pilot pressure in the dump pilot chamber 58a and is switched, and the spool 56 is fed from the dump port 55c to the bucket cylinder 23 and extended to dump the bucket 21. The tilt back position (T) is switched when the spool 56 receives the pilot pressure in the tilt pilot chamber 58b, and is supplied to the bucket cylinder 23 from the tilt port 55d to be reduced to tilt back the bucket 21.

2 and 5, the pilot valve 39 is composed of, for example, a pressure proportional pressure reducing valve having a single operating lever 39a. When the operating lever 39a is operated in the longitudinal direction of the vehicle body, the boom pressure reducing valve 60 is activated. Thus, the pilot pressure is output to the pilot chambers 52a and 52b of the boom valve 41.
When the operation lever 39a is operated in the left-right direction of the vehicle body, the bucket pressure reducing valve 61 is activated to output pilot pressure to the pilot chambers 58a, 58b of the bucket valve 42.

When the operation lever 39a is operated in an oblique direction between the front-rear direction and the left-right direction of the vehicle body, the boom pressure reducing valve 60 and the bucket pressure reducing valve 61 are operated, and the boom pressure reducing valve 60 applies the pilot pressure to the boom. The pressure reducing valve 61 for the bucket 41 outputs pilot pressure to the pilot chambers 58 a and 58 b of the bucket valve 42.
In the pilot valve 39, an operation lever may be attached to each of the boom pressure reducing valve 60 and the bucket pressure reducing valve 61, and the boom 17 and the bucket 21 may be operated separately by two operation levers.

The stroke return portion 40 is formed by a shuttle valve 63 and a return pressure chamber 65. The shuttle valve 63 is incorporated in the valve body 55 of the bucket valve 42, and the return pressure chamber 65 is a boom valve. 41 pilot rooms 52a and 52b are provided outside.
One end of the shuttle valve 63 is connected to the dump pilot chamber 58a of the bucket valve 42 through a communication hole 67a, and the other end is connected to the tilt pilot chamber 58b of the bucket valve 42 through a communication hole 67b. The pilot pressure is received through both pilot chambers 58a and 58b. The shuttle valve 63 selects the higher pilot pressure acting on both pilot chambers 58a and 58b, and feeds it to the return pressure chamber 65 from the valve body 47 of the boom valve 41 adjacent by the take-out communication hole 67c. doing.

The return pressure chamber 65 is formed by the space of the stepped portion between the stepped ring 51 and the spring case 50, in which the stepped ring 51 is slidably and freely fitted in the stepped hole 50 a of the spring case 50. . Further, the inner side of the stepped ring 51 forms pilot chambers 52 a and 52 b of the boom valve 41. The return pressure chamber 65 includes a left return pressure chamber 65a attached to the raising pilot chamber 52a and a right return pressure chamber 65b attached to the lowering pilot chamber 52b.
Both return pressure chambers 65a and 65b are connected to the shuttle valve 63 through an extraction communicating hole 67c, and receive the pilot pressure of the bucket pressure reducing valve 61 that has passed through the shuttle valve 63 to bring the spool 48 of the boom valve 41 to the neutral position. It is returning.

For example, in FIG. 3, when the boom 17 is raised, the pilot pressure of the boom pressure reducing valve 60 is supplied to the raising pilot chamber 52a, and the spool 48 of the boom valve 41 moves in the right direction in the figure against the spring. Slide to move to the raised position (H).
As the spool 48 moves, the right stepped ring 51 moves to the right in the drawing together with the right retainer 48b, and its right end abuts against the spring case 50 and stops at the raised position (H). The left stepped ring 51 receives the pilot pressure of the raising pilot chamber 52 a and stops while the right end portion 51 a is in contact with the valve body 47.
In this state, when the pilot pressure of the bucket pressure reducing valve 61 that has passed through the shuttle valve 63 acts on both return pressure chambers 65a and 65b, the left stepped ring 51 receives further pilot pressure in the left return pressure chamber 65a. The right end 51a is already in contact with the valve body 47 and remains stopped at that position.

On the other hand, in the right return pressure chamber 65b, the force due to the pilot pressure acting on the right stepped ring 51 is greater than the resultant force of the force and spring force due to the raising pilot chamber 52a. Pushes the spool 48 together with the retainer 48b to return from the raised position (H) to the neutral position (N).
As described above, when the spool 48 that operates the boom 17 is operated and the spool 48 is in the raised position (H), the lowered position (L), and the floating position (F), the bucket pressure reducing valve 61 that operates the bucket 21. Is operated, the pilot pressure of the bucket pressure reducing valve 61 passes through the check valve 63 and acts on the return pressure chamber 65 on the opposite side of the pilot chamber 52 moving the spool 48, so that the spool 48 is in the neutral position ( N). As a result, the boom 17 stops at that position, and the bucket 21 is preferentially operated.

When lowering the boom 17, when returning from the lowered position (L) to the neutral position (N), a lift port 47 c that connects the spool 48 to the bottom of the boom cylinder 19 and a tank port 47 e connected to the tank 35 are provided. Then, as shown by the dotted line in the P part of FIG. As a result, the boom 17 is lowered by its own weight, and the bucket 21 is operated by pressure oil from the hydraulic pump 33 so that the boom 17 and the bucket 21 are interlocked.
At this time, the lowering port 47d is provided with a regeneration circuit connected to the raising port 47c, and the boom 17 is quickly dropped by this regeneration circuit. The regeneration circuit is provided with a vacuum prevention valve 69, and the port 47g and the lowering port 47d are connected via the vacuum prevention valve 69, and the return oil of the boom cylinder 19 is sent to the lowering port 47d to prevent vacuum. .
As described above, the return to the neutral position of the boom 17 can be appropriately selected to return to the neutral position (N) or the vicinity of the neutral position according to the application.

Further, in the above, as shown in FIGS. 3 and 5, the stroke return portion 40 can be reduced in size by incorporating the shuttle valve 63 into the valve body 55 of the bucket valve 42.
The stroke return unit 40 includes communication holes 67a and 67b in which pilot oil from the shuttle valve 63 to the return pressure chamber 65 is opened in the valve body 55 of the bucket valve 42 and the valve body 47 of the boom valve 41, By connecting the main body 47 and the extraction communication hole 67c opened in the valve main body 55, piping can be eliminated and oil leakage can be prevented.

Next, the operation of the first hydraulic control device 31 will be described using the excavation work of the wheel loader 1.
In order to excavate the earth and sand, the operator moves the wheel loader 1 forward with the bucket 21 of the working device 5 in the ground excavation posture, and causes the bucket 21 to enter the earth and sand. When the bucket 21 enters the earth and sand, the operator operates the operation lever 39 a in the left-right direction to tilt the bucket 21 back, and fills the bucket 21 with the earth and sand.
At this time, when the bucket 21 is not operated due to the resistance of the earth and sand, the operator stops the tilt back of the bucket 21 and moves the bucket 21 upward by the boom 17 to reduce the load of the earth and sand acting on the bucket 21 and then again. The operation of tilting back the bucket 21 is repeated.

In this operation, in order to move the boom 17 upward, the operation lever 39a is operated in the front-rear direction, the pilot pressure is increased from the boom pressure reducing valve 60, and is supplied to the pilot chamber 52a. Move to (H). Thereby, the pressure oil of the hydraulic pump 33 is sent to the boom cylinder 19 from the raising port 47c, and the boom cylinder 19 is extended, and the boom 17 is raised.
When the boom 17 is raised and the load on the bucket 21 is reduced, the operator operates the operation lever 39a to the left and right tilt back side while keeping the operation lever 39a in the up-and-down direction. The bucket pressure reducing valve 61 supplies pilot pressure to the tilt pilot chamber 58b, and the bucket spool 56 is moved to the tilt back position (T) by the pilot pressure. Thereby, the pressure oil of the hydraulic pump 33 is sent to the bucket cylinder 23 from the tilt port 55d, the bucket cylinder 23 is reduced, and the bucket 21 is tilted back.

At this time, the pilot pressure sent from the bucket pressure reducing valve 61 to the tilt pilot chamber 58b is simultaneously fed to the right return pressure chamber 65b provided in the boom valve 41 via the shuttle valve 63.
The pilot pressure in the right return pressure chamber 65b presses the right stepped ring 51, pushes back the spool 48 together with the retainer 48b, and returns from the raised position (H) to the neutral position (N). As a result, the boom 17 stops at that position, and the bucket 21 preferentially operates to put earth and sand into the bucket 21.

Further, at this time, when the amount of earth and sand entering the bucket 21 is small, the tilt back of the bucket 21 is stopped, the wheel loader 1 is advanced, and earth and sand are put into the bucket 21. In order to stop the tilt back of the bucket 21, the operator performs an operation of returning the operation lever 39a to the neutral position in the left-right direction.
Accordingly, the pilot pressure sent from the bucket pressure reducing valve 61 to the tilt pilot chamber 58b is stopped, the bucket spool 56 is returned to the neutral position (N) by the spring, and the bucket cylinder 23 is stopped.

At the same time, the pilot pressure sent from the bucket pressure reducing valve 61 to the right return pressure chamber 65b of the boom valve 41 stops, and the pilot pressure in the right return pressure chamber 65b becomes zero.
As a result, the right stepped ring 51 is pushed back from the neutral position (N) to the raised position (H) together with the spool 48 and the retainer 48b by the resultant force of the pilot pressure in the raising pilot chamber 52a and the spring force.

  The spool 48 of the boom valve 41 sends the pressure oil from the hydraulic pump 33 to the boom cylinder 19 and extends it, and the boom 17 is raised. Therefore, the boom 17 can be easily operated by stopping the bucket and raising the boom 17 only by returning the operation lever 39a to the neutral position in the left-right direction. Further, when the operation lever 39a is operated in the left-right direction again at the raised position of the boom 17, the raising of the boom 17 can be stopped and the bucket 21 can be tilted back.

  As described above, the operation lever 39a can be operated with priority given to the operation of the bucket 21 by moving in the left-right direction at the raised position of the boom 17, and the bucket 21 can be operated by pushing the operation lever 39a back to the original neutral position. Can be raised and the boom 17 can be raised, the operation becomes easy and the bucket 21 can be operated quickly, and the workability can be improved.

FIG. 6 is a schematic diagram illustrating the relationship between the pilot signal and the stroke return unit in the second hydraulic control device 31A of the second embodiment.
In the first hydraulic control device 31, as shown in FIGS. 2 and 5, the stroke return portion 40 is formed by a shuttle valve 63 and a return pressure chamber 65 attached to the boom valve 41. The higher pilot pressure that activates the bucket 21 is selected and fed to the return pressure chamber 65, the spool 48 of the boom valve 41 is returned to the neutral position, the boom 17 is stopped, and the bucket 21 is Priority is given to operation.

  On the other hand, in the second hydraulic control device 31A of the second embodiment, instead of the boom valve 41, the first boom valve 41A which is a boom direction control valve without the return pressure chamber 65 is used. Boom return pressure reducing valves 70a and 70b for connecting and blocking the raising pilot chamber 52a and the lowering pilot chamber 52b of the first boom valve 41A are provided, and the boom raising pilot pressure is reduced by the boom returning pressure reducing valve 70a. The boom lowering pilot pressure is reduced by the boom return pressure reducing valve 70b.

The stroke return part 40A is formed by a shuttle valve 63 and boom return pressure reducing valves 70a and 70b, and the shuttle valve 63 is incorporated in the valve body 55 of the bucket valve 42.
One end of the shuttle valve 63 is connected to the dump pilot chamber 58a of the bucket valve 42 through a communication hole 67a, and the other end is connected to the tilt pilot chamber 58b of the bucket valve 42 through a communication hole 67b. The pilot pressure is received through both pilot chambers 58a and 58b. The shuttle valve 63 selects the higher pilot pressure acting on both pilot chambers 58a, 58b, and switches from the valve body 47A of the boom valve 41A adjacent to the take-out communication hole 67c to a bucket operation priority switching valve to be described later. It is fed to the boom return pressure reducing valves 70a, 70b via 75.

  The return pressure reducing valves 70a and 70b receive the higher pilot pressure selected by the inner shuttle valve 63 of the pilot pressure acting on both pilot chambers 58a and 58b from the bucket pressure reducing valve 61 that operates the bucket valve 42. One of the pilot chambers 52a and 52b connected to the boom pressure reducing valve 60 that operates to operate the spool 48 of the first boom valve 41A is connected to the tank 35, and the first boom valve 41A is operated. The pilot pressure from the boom pressure reducing valve 60 to the pilot chambers 52a and 52b is cut off, the pilot pressure in the pilot chambers 52a and 52b is reduced, and the spool 48 is returned to the neutral position.

  The boom return pressure reducing valves 70a and 70b are formed by pilot pressure reducing valves, operate by receiving the higher pilot pressure selected by the inner shuttle valve 63 of the pilot pressure of the bucket pressure reducing valve 61, and from the shut-off position to the connection position. Controlled. The boom return pressure reducing valve 70 a is connected to the raising pilot chamber 52 a of the boom valve 41, and the boom return pressure reducing valve 70 b is connected to the lowering pilot chamber 52 b of the boom valve 41.

In the second hydraulic control device 31A, a bucket operation priority switching valve 75 (hereinafter referred to as bucket priority switching valve) for selecting whether or not the bucket 21 is prioritized between the shuttle valve 63 and the boom return pressure reducing valves 70a and 70b. A valve 77) and a switch 77 for switching the bucket priority valve 75. When the switch 77 is attached to the grip of the operation lever 39a, the switch can be easily turned on and off.
The bucket priority valve 75 is formed by a two-position switching valve. The input port is connected to the shuttle valve 63 and the output port is connected to the boom return pressure reducing valves 70a and 70b. The higher pilot pressure selected by the inner shuttle valve 63 of the pilot pressure of the bucket pressure reducing valve 61 is supplied to the boom returning pressure reducing valves 70a and 70b, and the boom returning pressure reducing valves 70a and 70b are operated. Yes.

The bucket priority valve 75 is normally in the connection position (E) by a spring, and connects the shuttle valve 63 and the boom return pressure reducing valves 70a and 70b to operate the boom return pressure reducing valves 70a and 70b. .
As a result, when the bucket 21 is operated, the bucket priority valve 75 sends the higher pilot pressure selected by the inner shuttle valve 63 of the pilot pressure of the bucket pressure reducing valve 61 to the boom return pressure reducing valves 70a and 70b. And the boom return pressure reducing valves 70a and 70b are operated to reduce the pilot pressure in the pilot chambers 52a and 52b, the spool 48 of the first boom valve 41A is returned to the neutral position (N), and the boom 17 is stopped. At the same time, the bucket 21 is prioritized and operated.

When the switch 77 is operated, the bucket priority valve 75 switches to the shut-off position (G) against the spring and shuts off the shuttle valve 63 and the boom return pressure reducing valves 70a and 70b.
Thereby, even if the bucket 21 is operated, the bucket priority valve 75 is in the cutoff position (G), and the pilot pressure of the bucket pressure reducing valve 61 does not act on the boom return pressure reducing valves 70a and 70b. 17 and the bucket 21 can be individually operated or combined.

Next, the operation of the second hydraulic control device 31A will be described using the excavation work of the wheel loader 1, but since it is substantially the same as the first embodiment, the differences will be described.
First, the operation priority of the bucket 21 is selected without turning on the switch 77. Similarly to the above, when the bucket 21 is not operated due to the resistance of earth and sand, the boom 17 is raised, and when the load on the bucket 21 is reduced, the operation lever 39a is moved in the left-right direction while the operation lever 39a is kept in the up-and-down position. Operate to the tilt back side.
The bucket pressure reducing valve 61 feeds the pilot pressure to the tilt pilot chamber 58b to move the bucket spool 56 to the tilt back position (T) and tilt back the bucket 21. At the same time, the bucket valve 63 and the bucket Through the priority valve 75, the pilot pressure is supplied to the boom return pressure reducing valves 70a and 70b for control.

The boom return pressure reducing valves 70a and 70b operate so as to reduce the output of the boom pressure reducing valve 60, thereby lowering the raising pilot chamber 52a and the lowering pilot chamber 52b, and placing the first boom valve 41A in the neutral position. Returning to (N), the boom 17 is stopped. As a result, the boom 17 stops at that position, and the bucket 21 preferentially operates to put earth and sand into the bucket 21.
Accordingly, the boom return pressure reducing valves 70a and 70b are operated so as to perform pressure reduction when the boom 17 is operated by the boom pressure reducing valve 60 and when the bucket 21 is operated by the bucket pressure reducing valve 61. Then, the raising pilot chamber 52a and the lowering pilot chamber 52b are set to a low pressure, and similarly to the first embodiment, the first boom valve 41A is returned to the neutral position (N) by a spring, the boom 17 is stopped, The bucket 21 is operated with priority.

Next, a case where the switch 77 is turned on and the operation priority of the bucket 21 is not selected will be described.
For example, when simultaneous operation is required by the boom 17 and the bucket 21, the switch 77 is turned on to bring the bucket priority valve 75 to the cutoff position (G). As a result, the pilot pressure of the bucket pressure reducing valve 61 does not control the boom return pressure reducing valves 70a and 70b, and even when the bucket 21 is operated, the boom pressure reducing pressure valves 70a and 70b operate to reduce pressure. Disappear.
Therefore, even if the bucket 21 is operated during the operation of the boom 17, the bucket 21 does not operate preferentially, and the boom 17 and the bucket 21 can be operated at the same time, and the pressure attached to each valve. The compensation valve 45 can distribute the oil discharged from the hydraulic pump in accordance with the operation amount of the operation lever 39a.

In the case of the wheel loader 1, for example, when the earth and sand to be excavated are soft and the boom 17 and the bucket 21 can be operated simultaneously, the switch 77 is operated to set the bucket priority valve 75 to the shut-off position (G). The lever 21a can be operated in the front-rear direction and / or the left-right direction to lift the boom 17 and tilt the bucket 21 back to load earth and sand into the bucket 21.
Even when the earth and sand are hard, the switch 77 can be operated when the load becomes light during excavation, and the boom 21 can be tilted back while the boom 17 is lifted so that the boom 17 and the bucket 21 can be operated simultaneously. it can. Accordingly, even when the excavated soil is soft or hard, by operating the switch 77, the priority of the bucket 21 or the combined operation by the pressure compensation valve 45 can be performed, and the operability and workability are improved.

FIG. 7 shows a hydraulic circuit of a third hydraulic control device 31B that drives the working device 5 of the third embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.
In the first hydraulic control device 31 and the second hydraulic control device 31A, the boom valves 41 and 41A and the bucket valve 42 are formed by a parallel valve with a pressure compensation valve 45 at a closed center. A parallel circuit is formed by being connected in parallel to the hydraulic pump 33. Thus, the boom valves 41 and 41A and the bucket valve 42 control the amount of oil discharged from the hydraulic pump 33 by the pressure compensation valve 45 according to the operation amount of the operation lever 39a, so that the boom cylinder 19 and the bucket cylinder 23 Each is discharged.

On the other hand, in the third hydraulic control device 31B of the third embodiment, the second boom valve 41B and the first bucket valve 42A are closed centers not provided with only the pressure compensation valve 45 of the first embodiment. Are connected to the hydraulic pump 33 in parallel to form a parallel circuit.
Accordingly, the second boom valve 41B and the first bucket valve 42A are switched by the respective operations of the operation lever 39a, and discharge the oil discharged from the hydraulic pump 33 to the boom cylinder 19 or the bucket cylinder 23, respectively. At this time, when the boom 17 and the bucket 21 are combined and operated, the pressure oil of the hydraulic pump 33 flows to the first bucket valve 42A regardless of the load. Thereby, the bucket 21 is operated with priority over the boom 17.

  Since the operation is almost the same as that of the first embodiment, description thereof is omitted.

FIG. 8 shows a hydraulic circuit of a fourth hydraulic control device 31C that drives the working device 5 of the fourth embodiment.
The fourth hydraulic control device 31C is formed by a parallel valve having an open center, and each is connected in parallel to the hydraulic pump 33 to form a parallel circuit. As a result, the third boom valve 41C and the second bucket valve 42B are switched by the operation of the operation lever 39a to discharge the oil discharged from the hydraulic pump 33 to the boom cylinder 19 or the bucket cylinder 23 and to the boom 17 respectively. On the other hand, the bucket 21 is preferentially operated with a simple configuration.

  Since the operation is almost the same as that of the first embodiment, description thereof is omitted.

  In the above description, the directional control valve uses the boom valve 41 and the bucket valve 42, the pump side is the boom valve 41 of the first directional control valve, and the next adjacent second directional control valve. Although it was described as the valve 42 for the bucket of the valve, for example, the direction control valve is set to 3 or more, the pump side is set to the bucket valve 42 of the second direction control valve, and the remaining one is The boom valve 41 of the first directional control valve may be used.

It is the side schematic diagram of the wheel loader carrying the hydraulic control device concerning the present invention. 1 is an overall hydraulic circuit diagram of a hydraulic control device according to the present invention. (Example 1) It is sectional drawing of the direction control valve for booms which comprises the hydraulic control apparatus which concerns on this invention. (Example 1) It is sectional drawing of the direction control valve for buckets which comprises the hydraulic control apparatus which concerns on this invention. (Example 1) It is the schematic explaining the relationship between the pilot signal which concerns on this invention, and a stroke return part. (Example 1) FIG. 3 is a schematic diagram illustrating a relationship between a pilot signal and a stroke return unit in the first hydraulic control apparatus according to the present invention. (Example 2) It is a whole hydraulic circuit diagram of the 2nd hydraulic control device concerning the present invention. Example 3 It is a whole hydraulic circuit diagram of the 3rd hydraulic control device concerning the present invention. (Example 4)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wheel loader, 3 ... Vehicle main body, 5 ... Working apparatus, 17 ... Boom, 19 ... Boom cylinder (1st actuator), 21 ... Bucket, 23 ... Bucket cylinder (2nd actuator), 31, 31A, 31B, 31C DESCRIPTION OF SYMBOLS ... Hydraulic control device, 33 ... Hydraulic pump, 37 ... Direction control valve, 39 ... Pilot valve, 39a ... Operation lever, 40, 40A ... Stroke return part, 41 ... Boom direction control valve (first direction control valve), 41A ... 1st boom valve, 42 ... Bucket direction control valve (second direction control valve), 45 ... Pressure compensation valve, 60 ... Boom pressure reducing valve, 61 ... Bucket pressure reducing valve, 63 ... Shuttle valve, 65 ... Return Pressure chamber, 70a, 70b ... boom decompression valve, 75 ... bucket operation priority switching valve working device, 77 ... switch.

Claims (6)

In a hydraulic control device comprising a hydraulic pump, a plurality of actuators that are operated by pressure oil discharged from the hydraulic pump, and a directional control valve that is operated by pilot pressure and controls pressure oil supplied from the hydraulic pump to the actuator,
A first directional control valve that displaces a stroke from a neutral position by a first pilot pressure and feeds pressure oil to the first actuator;
A second directional control valve that feeds pressure oil to the second actuator when the stroke is displaced from the neutral position by the second pilot pressure;
Actuated by the second pilot pressure at the time of switching the first directional control valve, returning the stroke of the first directional control valve to the vicinity of the neutral position, and for the pressure oil fed from the first directional control valve to the first actuator, A hydraulic control device comprising stroke return means for giving priority to pressure oil supplied from the second direction control valve to the second actuator. The hydraulic control device according to claim 1, wherein
The hydraulic control apparatus having a stroke return means, wherein the direction control valve is formed by any one of a parallel valve having an open center, a parallel valve having a closed center, or a parallel valve having a pressure compensation valve at the closed center. . A shuttle valve that selects a high second pilot pressure acting on the second directional control valve;
Stroke return means provided with a pressure chamber attached to the first directional control valve and receiving the second pilot pressure from the shuttle valve to return the stroke of the first directional control valve is provided, the pressure chamber having a stepped hole in the spring case 3. A hydraulic control device according to claim 1, wherein the step ring is slidably and freely fitted in a loose manner, and is formed by a space of the step portion between the step ring and the spring case. . A shuttle valve that selects a high second pilot pressure acting on the second directional control valve;
Stroke return means comprising a pressure reducing valve that operates by receiving the second pilot pressure acting on the second directional control valve and depressurizes the first pilot pressure acting on the first directional control valve to return the stroke. The hydraulic control device according to claim 1 or 2, characterized by the above. The hydraulic control device according to claim 2, wherein
The directional control valve is a closed center parallel valve with a pressure compensation valve, and the second directional control valve to the second actuator with respect to the pressure oil fed from the first directional control valve to the first actuator by operating the stroke return means Either give priority to the pressure oil to be supplied to the pump, or actuate the pressure compensation valve to distribute the hydraulic oil of the hydraulic pump according to the stroke amount of the first direction control valve and the second direction control valve A hydraulic control device comprising priority circuit selection means for selecting A directional control valve for a boom that controls pressure oil to a boom cylinder that raises and lowers a boom attached to the wheel loader by a first directional control valve;
6. The bucket direction control valve for controlling the pressure oil to the bucket cylinder that allows the bucket attached to the boom to freely move up and down, wherein the second direction control valve comprises a bucket direction control valve. Wheel loader using any hydraulic control device.