JP2017125353A - Loading apparatus for wheel loader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a loading apparatus in which a tilt angle of a bucket is stabilized.SOLUTION: A loading apparatus for a wheel loader comprises a linking mechanism which is so designed that a criterion point of a bucket moves in parallel with the ground. It comprises a tilt stopper working state detecting part 23 detecting a tilt stopper working state of the bucket, a communication/shutoff valve 17 witching a lift cylinder bottom room side oil path 13A for supplying pressurized oil to a lift cylinder bottom room 13a and a tilt cylinder rod room side oil path 14B for supplying pressurized oil to a tilt cylinder rod room 14b between a communication position where they are communicated each other and a shutoff position where they are shutoff, and a controlling part 22 switching the communication/shutoff valve 17 to the communication position when at least the tilt stopper sensor 23 detects the tilt stopper working state.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a cargo handling device for a wheel loader.

  The wheel loader is used not only for bucket work but also fork work. The characteristics of the tilt angle of the bucket or fork with respect to the extension of the lift cylinder are required to be different between the bucket work and the fork work. Patent Document 1 discloses an invention for controlling the tilt angle according to the angle of the boom.

JP 2010-265639 A

  In the invention described in Patent Document 1, since the tilt angle is controlled according to the boom angle (lift angle), the tilt angle of the bucket is not stable.

The wheel loader loading / unloading device according to the first aspect of the present invention includes a link mechanism 9 in which a reference point of the attachment 8 moves in parallel to the ground when the attachment 8 attached to the tip of the lift arm 10 is moved up and down. When pressure oil is supplied to the lift cylinder bottom chamber 13a and the lift cylinder rod chamber 13b, the pressure oil is applied to the lift cylinder 13 that lifts and lowers the attachment 8 via the lift arm 10, and the tilt cylinder bottom chamber 14a and the tilt cylinder rod chamber 14b. A tilt cylinder 14 that tilts the attachment 8 when supplied is provided.
The cargo handling device includes a tilt stopper operating state detector 23 that detects that the attachment 8 is in the tilt stopper operating state, a lift cylinder bottom chamber side oil passage 13A that supplies pressure oil to the lift cylinder bottom chamber 13a, and a tilt cylinder. Tilt cylinder bottom chamber side oil passage 14A for supplying pressure oil to the bottom chamber 14a is switched between a communication position for communicating with each other and a shut-off position for shutting off, that is, a switching valve, and at least a tilt stopper operating state detection. When the part 23 detects the tilt stopper operating state, the control part 22 (22a) which switches the 1st communication / shut-off valve 17 to a communication position is provided.
In addition, in order to make an understanding of an invention easy, the code | symbol of embodiment is attached | subjected and demonstrated, but it is only a reference and this invention is not limited to embodiment by this.

  According to the present invention, by connecting the lift cylinder rod chamber and the tilt cylinder rod chamber, the tilt cylinder is extended with the extension of the lift cylinder, so that the tilt angle of the bucket is stabilized.

The figure which shows the external appearance of the wheel loader 1 The figure which shows the outline | summary of the internal structure of the wheel loader 1. The figure which shows the structure of the link mechanism 9 The figure which shows the attachment angle characteristic when not operating the communication valve The figure which shows the change of the attachment angle characteristic with the presence or absence of operation of the communication valve The figure which shows the hydraulic circuit of the wheel loader 1 Flow chart showing operation of controller 22 Diagram explaining an operation example The figure which shows the attachment position of the tilt stopper sensor in a modification The figure which shows the hydraulic circuit of the wheel loader 1 in 2nd Embodiment of this invention. The figure which shows the hydraulic circuit of the wheel loader 1 in 3rd Embodiment of this invention. 12A is a diagram showing the configuration of the bottom chamber communication / shutoff valve 42, and FIG. 12B is a diagram showing the configuration of the rod chamber communication / shutoff valve 43. The figure explaining the effect peculiar to 3rd Embodiment of this invention.

(First embodiment)
The first embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 is a diagram illustrating an appearance of the wheel loader 1, and FIG. 2 is a diagram illustrating a hydraulic device of the wheel loader 1.
The wheel loader 1 includes a front frame 2, a rear frame 3, a cab 4 attached to the rear frame 3, a front attachment 100 driven by the cargo handling device 5, a traveling device 6, and a power source for the cargo handling device 5 and the traveling device 6. A prime mover 7 is provided.

  The front frame 2 and the rear frame 3 are pin-coupled in the vertical axis direction near the center of the vehicle body and bent by two steering cylinders (not shown). The front attachment 100 includes a bucket 8 and a link mechanism 9 that operates the bucket 8 and is attached to the front frame 2.

  The traveling device 6 is operated by a handle 25 provided in the cab 4 and drives the front tire 29a and the rear tire 29b to cause the wheel loader 1 to travel. The traveling device 6 includes a handle 25 provided in the cab 4 shown in FIG. 1, a steering valve (not shown), and a steering cylinder (not shown) for steering the wheel loader 1. When the steering valve is driven by the steering operation of the handle 25 and the steering cylinder expands and contracts, the front frame 2 and the rear frame 3 rotate relative to each other and the wheel loader 1 changes its direction (reverses).

  Further, the traveling device 6 includes a transmission 26, front and rear propeller shafts 27a and 27b, front and rear axles 28a and 28b, and front and rear tires 29a and 29b in order to generate a traveling driving force. The driving force from the prime mover 7 is transmitted to the transmission 26. The transmission 26 transmits the driving force from the prime mover 7 to the front axle 28a via the front propeller shaft 27a and to the rear axle 28b via the rear propeller shaft 27b. The wheel loader 1 travels when the front tire 29a rotates by the driving force of the front axle 28a and the rear tire 29b rotates by the driving force of the rear axle 28b.

  The cargo handling device 5 includes a hydraulic circuit 200 described with reference to FIG. 6 and a tilt stopper sensor 23. When the lift operation pilot valve 20 is operated by the lift lever operation, the lift spool of the control valve 15 is switched and controlled. The oil discharged from the main pump 18 is controlled by the lift spool of the control valve 15 and supplied to the lift cylinder 13 so that the lift cylinder 13 expands and contracts. When the tilt operation pilot valve 20 is operated by operating the tilt lever, the tilt spool of the control valve 15 is controlled to be switched. The oil discharged from the main pump 18 is controlled by the tilt spool of the control valve 15 and supplied to the tilt cylinder 14, and the tilt cylinder 14 expands and contracts.

A configuration related to the operation of the bucket 8 will be described with reference to FIGS. 1 and 3.
FIG. 3 is a diagram illustrating a configuration of the link mechanism 9. The link mechanism 9 includes a lift arm 10, a bell crank 11, and a push rod 12.
The lift arm 10 has a rear end portion pin-coupled to the front frame 2 and a bucket 8 pin-coupled to the front end portion. Two lift cylinders 13 are provided between a lower side near the center of the lift arm 10 and a lift cylinder bracket 2 b provided on the front frame 2. The lift arm 10 rotates up and down with respect to the front frame 2 by expansion and contraction of the two lift cylinders 13.
A bell crank bracket 10a is provided near the center of the lift arm 10, and the bell crank 11 is pin-coupled to the bell crank bracket 10a. A tilt cylinder 14 is provided between the upper portion of the bell crank 11 and the tilt cylinder bracket 2 a provided on the front frame 2. The lower part of the bell crank 11 and the bucket 8 are pin-coupled by a push rod 12. The bucket 8 is tilted or dumped by the expansion and contraction of the tilt cylinder 14.

There is a tilt stopper 10b (see FIG. 3B) as a raised protrusion on the upper part near the tip of the lift arm 10, and when the bucket 8 is tilted, the wall surface of the bucket 8 comes into contact with the tilt stopper 10b. The structure does not tilt any further. Hereinafter, a state in which the wall surface of the bucket 8 is in contact with the tilt stopper 10b is referred to as a “tilt stopper operating state”.
The bell crank bracket 10a is provided with a tilt stopper sensor 23, that is, a proximity sensor. The bell crank 11 is provided with a tilt stopper detection bar 24. In the “tilt stopper operating state”, the tilt stopper sensor bar 24 comes close to the detecting portion of the tilt stopper sensor 23, and a signal indicating the “tilt stopper operating state” is output from the tilt stopper sensor 23.

  In the wheel loader in the first embodiment, the link mechanism 9 is designed with emphasis on operability when using a fork as an attachment. This operability will be described with reference to the tilt angle characteristic with respect to the lift angle shown in FIG. 4, that is, the attachment angle characteristic.

  In this specification, “lift angle” and “tilt angle” are defined and used as follows. That is, an angle formed by a line segment connecting a connection point between the lift arm 10 and the frame 2 and a connection point between the lift arm 10 and the bucket 8 is defined as a “lift angle”. The sign of the lift angle is positive when the lift arm 10 is raised. Further, an angle formed by a straight line portion on the bottom surface of the bucket 8 and a horizontal line is defined as a “tilt angle”. The tilt angle is evaluated as an absolute value and not a negative value. However, when the wheel loader 1 attaches a fork as an attachment, an angle formed by a straight line portion on the bottom surface of the fork and a horizontal line is defined as a “tilt angle”.

  The tilt angle in the above-described tilt stopper operating state is determined according to the lift angle depending on the dimensions and mounting positions of the element members constituting the link mechanism 9.

In the wheel loader of the embodiment, when the operator operates only the lift lever and the lift cylinder 13 operates, the tilt angle of the bucket 8 changes even if the tilt lever operation is not performed. The reason is as follows.
When the lift arm 10 is operated by the operation of the lift cylinder 13, the angle of the bell crank 11 with respect to the lift arm 10 is changed, and the push rod 12 and the bucket 8 are also operated in conjunction therewith. The tilt cylinder 14 is provided between the tilt cylinder bracket 2 a and the bell crank 11, and the positional relationship between the lift arm 10, that is, the bell crank 11 and the front frame 2 is changed by a lift operation. By such a mechanism of the link mechanism 9, there is a range in which the posture of the bucket 8 greatly changes in the dumping direction when the lift arm 10 is raised.

When the wheel loader 1 to which the fork is attached performs fork work, the change of the tilt angle associated with the lift arm 10 ascending preferably has characteristics as described below. In the fork work, the lift arm 10 is lifted from a posture in which the fork is set horizontally, but it is preferable that the lift arm 10 is slightly tilted at an initial stage and then kept substantially horizontal.
When the wheel loader 1 to which the bucket is attached performs the bucket operation, it is desirable that the tilt angle changes as the lift arm 10 rises as described below. That is, when the lift arm 10 starts to rise, the tilt angle of the bucket 8 temporarily increases, and when the lift arm 10 continues to rise, the tilt angle ranges from about 50 degrees to about 60 degrees, and has a substantially constant angle. It is good to keep.
The attachment angle characteristic will be described with reference to FIGS.

  FIG. 4 is a diagram illustrating attachment angle characteristics (hereinafter referred to as “characteristics”) L1 to L4. Characteristics L2 and L4 are attachment angle characteristics in the wheel loader 1 suitable for fork work according to the present embodiment. The characteristics L1 and L3 are attachment angle characteristics of a bucket dedicated machine shown as a comparison target, that is, a wheel loader having a linkage size suitable for bucket work. Each of the characteristics L1 to L4 represents a change in tilt angle when only the lift cylinder 13 is operated in a state where the tilt cylinder length is constant, that is, in a state where the tilt cylinder 14 is not operated. That is, it is a characteristic of the tilt angle with respect to the lift angle.

  The difference between the characteristic L1 and the characteristic L3 and the difference between the characteristic L2 and the characteristic L4 are tilt angles before the lift cylinder 13 is operated. The characteristics L1 and L2 represent changes in the tilt angle when the tilt stopper is operated with the bucket 8 lowered to the vicinity of the ground, and then only the lift cylinder 13 is operated to raise the bucket 8. Characteristics L3 and L4 represent changes in the tilt angle when the tilt angle is about 0 degrees with the bucket 8 lowered to the vicinity of the ground, and then only the lift cylinder 13 is operated to raise the bucket 8.

A characteristic L1 in FIG. 4 is an attachment angle characteristic of the bucket dedicated machine, and is a characteristic suitable for bucket work. When the lift angle changes from around −30 degrees to the plus side, the tilt angle tends to increase. The tilt angle increases when the lift arm is lifted to raise the bucket loaded with excavated earth and sand. That is, earth and sand are prevented from falling from the bucket when the bucket is raised.
On the other hand, when the bucket work is performed with the wheel loader of the embodiment equipped with the link mechanism 9 preferable for the fork work, particularly when the work for raising the bucket loaded with earth and sand is largely tilted, special control is performed. When the process is not performed, the attachment angle characteristic is L2. In the characteristic L2, the bucket 8 is greatly operated to the dump side in the initial process in which the lift angle rises from around −30 degrees, and there is a possibility that earth and sand may spill out from the bucket 8.
On the other hand, a characteristic L4 in FIG. 4 is a characteristic suitable for fork work of the wheel loader of the embodiment in which the link mechanism 9 is mounted. This characteristic L4 is a characteristic in which the tilt angle tends to increase slightly when the lift angle changes from around −30 degrees to the plus side, and thereafter the tilt angle varies little even if the lift angle changes. When raising the load placed on the fork, the load can be raised in parallel.

  As described above, the wheel loader according to the embodiment includes the link mechanism 9 that changes the posture in the case of the attachment angle characteristic that places importance on the fork work. That is, it has attachment angle characteristics as indicated by characteristics L2 and L4 in FIG. As described above, when the bucket operation is performed using the link mechanism 9 having such an attachment angle characteristic, as shown by the characteristic L2, the tilt angle is reduced as the lift arm is raised, and the bucket is not intended to be dumped. There is a risk of spilling from the bucket.

  Realizing both the attachment angle characteristic suitable for bucket work and the attachment angle characteristic suitable for fork work only by devising the structure of the link mechanism requires a complicated mechanism and is not realistic. In the wheel loader of the first embodiment designed so that the attachment angle characteristics suitable for the fork work can be obtained by measuring the dimensions and mounting positions of the element members constituting the link mechanism 9, the operator's operation status is determined, in other words, the lift The operation status of the arm, the bucket, and the like is discriminated, and control for obtaining an attachment angle characteristic so that earth and sand are not spilled from the bucket at the time of bucket operation is performed by control described later.

FIG. 5 is a diagram illustrating a change in the attachment angle characteristic depending on whether or not the communication valve is operated. In the characteristic L2A for which the control is effective, the tilt angle greatly increases as the bucket 8 rises, that is, the lift angle increases, and the tilt angle becomes maximum when the lift angle is θ2. When the lift angle further increases from θ2, the tilt angle starts to decrease and converges to about 55 degrees. As apparent from the comparison between the characteristic L2 and the characteristic L2A in FIG. 5, the tilt angle is increased by enabling the control, and an attachment angle characteristic suitable for bucket work is obtained.
As will be described in detail later, the tilt cylinder 14 extends as the lift angle increases from θ1 to θ2, and when the lift angle reaches θ2, the tilt cylinder 14 reaches its maximum extension. Further, when the lift angle is θ2 to θ3, the tilt cylinder 14 remains at its maximum extension.
On the other hand, the characteristic L2 in which the control is invalid is not an attachment angle characteristic suitable for bucket work because the tilt angle decreases as the bucket 8 rises, that is, the lift angle increases.

Hereinafter, a description will be given of a hydraulic circuit incorporating control for preventing earth and sand from spilling from the bucket during the bucket operation in the wheel loader provided with the link mechanism 9 having an attachment angle characteristic preferable for fork operation.
The link mechanism 9 having an attachment angle characteristic preferable for fork work is that when the bucket 8 attached to the tip of the lift arm 10 is moved up and down, a reference point (point, surface, line) of the bucket 8 is relative to the ground. A link mechanism designed to move in parallel as much as possible.
Invalidation / validity of the control is realized by performing communication / blocking control of the supply / discharge oil passage to the lift cylinder 13 and the supply / discharge oil passage to the tilt cylinder 14 as described later. Further, when the control is invalid, the attachment angle characteristic is suitable for fork work, and when the control is valid, the attachment angle characteristic is suitable for bucket work.

(Hydraulic circuit)
FIG. 6 is a hydraulic circuit 200 of the wheel loader 1 showing some components in FIG.
The lift spool 30 is a center pilot type hydraulic pilot switching valve that takes three positions. When the lift spool 30 is in the neutral position, the pressure oil discharged from the main pump 18 is bypassed to the tilt spool 31. The lift spool 30 is switched by the pilot hydraulic pressure from the lift operation pilot valve 20a.

The lift cylinder 13 includes a lift cylinder bottom chamber 13a into which pressure oil is introduced, and a lift cylinder rod chamber 13b.
When the lift spool 30 is switched to the left position in the figure, the pressure oil discharged from the main pump 18 is supplied to the bottom chamber 13a of the lift cylinder 13 via the lift cylinder bottom chamber side oil passage 13A, and the lift cylinder 13 extends. When the lift spool 30 is switched to the right position in the drawing, the pressure oil discharged from the main pump 18 is supplied to the rod chamber 13b of the lift cylinder 13 via the lift cylinder rod chamber side oil passage 13B. Degenerate.

The tilt spool 31 is a center pilot type hydraulic pilot switching valve that takes three positions. When the tilt spool 31 is in the neutral position, the pressure oil discharged from the main pump 18 is returned to the tank 21. The tilt spool 31 is switched by the pilot hydraulic pressure from the tilt operation pilot valve 20b.
The tilt cylinder 14 includes a tilt cylinder bottom chamber 14a into which pressure oil is introduced and a tilt cylinder rod chamber 14b.
When the tilt spool 31 is switched to the left position in the drawing, the pressure oil discharged from the main pump 18 is supplied to the bottom chamber 14a of the tilt cylinder 14 via the tilt cylinder bottom chamber side oil passage 14A, and the tilt cylinder 14 Expands. When the tilt spool 31 is switched to the right position in the drawing, the pressure oil discharged from the main pump 18 is supplied to the rod chamber 14b of the tilt cylinder 14 via the tilt cylinder rod chamber side oil passage 14B, and the tilt cylinder 14 is supplied. Degenerate.

  The pressure output from the lift operation pilot valve 20a is the operation pressure for lifting and lowering the lift arm, and the pressure output from the tilt operation pilot valve 20b is the tilt operation pressure and the dump operation pressure.

  The operation pressure for raising the lift arm (hereinafter referred to as “lift arm raising operation pressure”) is measured by the pressure sensor 16a, and the tilt operation pressure and the dump operation pressure are measured by the pressure sensor 16b. The pressure measured by the pressure sensors 16 a and 16 b is output to the controller 22. However, the tilt operation pressure and the dump operation pressure are selected by the shuttle valve 33 and output to the pressure sensor 16b. Hereinafter, the tilt operation pressure and the dump operation pressure measured by the pressure sensor 16b are referred to as “tilt / dump operation pressure”.

The pressure oil supplied from the main pump 18 to the lift cylinder 13 and the tilt cylinder 14 is limited to a predetermined pressure or less by the main relief valve 34.
When the lift arm 10 is lowered in the tilt stopper operating state, an excessive pressure is applied to the tilt cylinder 14, and an overload relief valve 35 is provided to prevent this. The overload relief valve 35 is provided between the tilt cylinder bottom chamber 14 a and the tilt spool 31. When the tilt cylinder bottom chamber 14a exceeds a predetermined pressure, the pressure oil is returned from the overload relief valve 35 provided in the control valve 15 to the tank. At this time, hydraulic oil is supplied from the makeup valve 36 to the tilt cylinder rod chamber 14b in order to prevent the pressure in the tilt cylinder rod chamber 14b from abruptly decreasing and cavitation (generation of bubbles). .

  The configuration of the hydraulic circuit 200 described so far is the same as the configuration of the circuit used in the conventional wheel loader. Next, a configuration unique to the present embodiment will be described. Although the wheel loader according to the present embodiment is a wheel loader that employs a link mechanism having an attachment angle characteristic suitable for fork work, the wheel loader performs operation control so as to prevent a phenomenon that earth and sand are spilled from the bucket in a predetermined operation state of the bucket work. Is.

  The hydraulic circuit 200 according to the present embodiment includes a lift cylinder bottom chamber side / rod chamber side oil passages 13A and 13B for supplying and discharging oil to the lift cylinder 13, and a tilt cylinder for supplying and discharging oil to the tilt cylinder 14. The first communication / shutoff valve 17 interposed in the oil passage connecting the bottom chamber side / rod chamber side oil passages 14A and 14B, the lift lever operation pilot pressure sensor 16a for detecting the lift lever operation, and the tilt lever Tilt lever operation pilot pressure sensor 16b for detecting the operation, the tilt stopper sensor 23 described above, the output of the tilt stopper sensor 23 and the pressure of the operation pilot pressure sensors 16a and 16b are received and the first communication / shutoff valve 17 is switched. And a controller 22 for controlling.

The first communication / shutoff valve 17 is an electromagnetic two-position switching valve that can be switched between a closed position and an open position.
In the closed position, the lift cylinder bottom chamber side oil passage 13A connected to the lift cylinder bottom chamber 13a, the lift cylinder rod chamber side oil passage 13B connected to the lift cylinder rod chamber 13b, and the tilt cylinder bottom chamber 14a are connected. The tilt cylinder bottom chamber side oil passage 14A and the tilt cylinder rod chamber side oil passage 14B connected to the tilt cylinder rod chamber 14b are blocked.

When the first communication / shut-off valve 17 is switched to the closed position, the attachment angle characteristic by the lift lever operation or the tilt lever operation is a characteristic suitable for fork work.
In the open position, the lift cylinder bottom chamber side oil passage 13A connected to the bottom chamber 13a of the lift cylinder 13 and the tilt cylinder bottom chamber side oil passage 14A connected to the bottom chamber 14a of the tilt cylinder 14 communicate with each other. The lift cylinder rod chamber side oil passage 13B connected to the 13 rod chambers 13b and the tilt cylinder rod chamber side oil passage 14B connected to the rod chamber 14b of the tilt cylinder 14 communicate with each other.
When the first communication / shutoff valve 17 is switched to the open position, the attachment angle characteristic by the lift lever operation is switched from the default setting characteristic to another characteristic. The characteristic after switching is a characteristic suitable for bucket work in the embodiment.

(Hydraulic circuit operation)
When the lift arm raising operation is performed by the lift operation pilot valve 20a, the control pressure on one end of the lift spool 30 of the control valve 15 on the left side in the drawing increases. Then, the lift spool 30 moves to the right side, and the pressure oil from the main pump 18 is supplied to the lift cylinder bottom chamber 13a. At this time, the controller 22 determines that each operation has been performed when the lift arm raising operation pressure and the tilt / dump operation pressure obtained by the operation pilot pressure sensors 16a and 16b exceed a predetermined threshold. At the same time, the controller 22 determines whether or not the tilt stopper 10b is in an operating state based on a signal from the tilt stopper sensor 23. When the controller 22 determines that only the lift arm raising operation has been performed and the tilt stopper 10b is in the activated state, the controller 22 outputs a command to switch the first communication / shutoff valve 17 to the second position, that is, the open position.

  At this time, the pressure oil supplied to the lift cylinder bottom chamber 13a is also supplied to the tilt cylinder bottom chamber 14a, and a thrust in the extending direction is generated in the tilt cylinder 14. As shown in the attachment angle characteristic L2, the posture of the bucket 8 tends to change toward the dump side as the lift angle increases, but the tilt cylinder 14 is extended by the aforementioned thrust, and the tilt stopper operating state is maintained. The oil discharged from the rod side by the extension of the tilt cylinder 14 passes through the first communication / shutoff valve 17 and the control valve 15 and returns to the tank 21.

If the lift arm raising operation is continued as it is, the tilt cylinder 14 reaches the maximum extension, and only the lift cylinder 13 continues to extend, whereby the tilt stopper 10b shifts to the inoperative state.
As a result, the signal from the tilt stopper sensor 23 changes to an inoperative state, and the command output from the controller 22 to the first communication / shutoff valve 17 is changed to a command value for switching to the first position, that is, the closed position.

  Even when the tilt / dump operation is performed while the first communication / shutoff valve 17 is controlled to the second position, that is, the open position, and the tilt / dump operation pressure exceeds a predetermined threshold, the controller 22 also performs the first operation. The command output to the communication / shutoff valve 17 is changed to a command value for switching to the first position, that is, the closed position. When the first communication / shutoff valve 17 is switched to the first position, the lift cylinder bottom chamber side oil passage 13A and the tilt cylinder bottom chamber side oil passage 14A are shut off, and the lift cylinder 13 and the tilt cylinder 14 are operated independently. It becomes possible to do.

(Controller flowchart)
The operation of the controller 22 will be described using a flowchart.
FIG. 7 is a flowchart showing the operation of the program executed in the controller 22. The execution subject of each step described below is the CPU of the controller 22. The controller 22 operates a program described below every predetermined time, for example, every 0.1 second.

In step S101, the output of the tilt stopper sensor 23 is read, and the process proceeds to step S102.
In step S102, it is determined whether or not the read output of the tilt stopper sensor 23 is equal to or greater than a predetermined threshold value. For example, when the output of the tilt stopper sensor 23 is represented by a voltage, it is determined whether or not the input voltage is equal to or higher than a predetermined voltage. If it is determined that the output of the tilt stopper sensor 23 is greater than or equal to the threshold value, it is recognized that the tilt stopper is operating, and the process proceeds to step S104. If it is determined that the output of the tilt stopper sensor 23 is less than the threshold value, the tilt stopper operation is performed. It recognizes that it is not in a state and proceeds to step S103.

In step S103, an operation command to the first position, that is, the closed position is output to the first communication / shutoff valve 17, and the program whose operation is represented by FIG. 7 is terminated. The state proceeding to step S103 is a case where an attachment angle characteristic suitable for fork work is selected.
In step S104, the pressure output from the pressure sensor 16a, that is, the lift arm raising operation pressure is read, and the process proceeds to step S105.

In step S105, it is determined whether or not the lift arm raising operation pressure is equal to or higher than a predetermined threshold, that is, whether or not a lift raising operation is being performed. When it is determined that the lift arm raising operation pressure is less than the predetermined threshold, that is, when it is recognized that the lift arm is not operated, the process proceeds to step S106. Recognizing the raising operation, the process proceeds to step S103.
In step S106, the pressure output from the pressure sensor 16b, that is, the tilt / dump operation pressure is read, and the process proceeds to step S105.

In step S107, it is determined whether or not the tilt / dump operation pressure is greater than or equal to a predetermined threshold, that is, whether or not the tilt / dump operation is being performed. When it is determined that the tilt / dump operation pressure is greater than or equal to the predetermined threshold, the process proceeds to step S108, and when it is determined that the tilt / dump operation pressure is less than the predetermined threshold, the process proceeds to step S103.
In step S108, an operation command to the second position, that is, the open position is output to the first communication / shutoff valve 17, and the program whose operation is represented by FIG. 7 is terminated. The state that proceeds to step S108 is a case where a lift operation and a bucket operation are performed so as to obtain an attachment angle characteristic suitable for bucket work.
Note that the predetermined threshold values used in steps S102, S105, and S107 are individual values.

(Operation example)
An example of operation when the wheel loader 1 excavates earth and sand and raises the lift arm 10 to the highest lift height will be described.
FIG. 8 is a diagram for explaining an operation example when the wheel loader 1 excavates earth and sand and raises the lift arm 10 to the highest lift height. In FIG. 8, the bucket 8 and the link mechanism 9 of the wheel loader 1 are indicated by solid lines, and the front tire 29a is indicated by a two-dot chain line. The following description will be made with reference to the attachment angle characteristic shown in FIG. 5 and the flowchart shown in FIG.

The operator sets the tilt angle of the bucket 8 to about 0 degrees, that is, horizontally with the ground before the excavation target sediment, and further sets the blade edge of the bucket 8 near the ground. As shown in FIG. 8B, the wheel loader 1 travels in this state and enters the earth and sand.
When the bucket 8 bites into the earth and sand, an operation of raising the lift arm 10 is performed while the bucket 8 is tilted by reducing the traveling driving force, and the earth and sand are scooped into the bucket 8. At this time, since the tilt stopper 10b is not yet operated (step S102: NO in FIG. 7), the first communication / shutoff valve 17 is maintained at the first position.

  Subsequently, a combined operation of tilt and lift arm raising is performed until the bucket 8 is in the tilt stopper operating state. When the bucket 8 is in the tilt stopper operating state, the operator stops the tilt and lift arm raising operation, and transports the earth and sand in the traveling operation as shown in FIG. In the state immediately before the operator stops the tilt and lift arm raising operation, the output of the tilt stopper sensor exceeds the threshold (step S102: YES in FIG. 7), but it is determined that the tilt / dump operation pressure is greater than the threshold. (Step S107 in FIG. 7: NO). The controller continues to output the first position command to the first communication / shutoff valve 17.

  When the wheel loader 1 reaches a place where the earth and sand are released, the operator performs a single operation of raising the lift arm and prepares for earth release. At this time, the tilt stopper 10b is in an operating state (step S102: YES), the lift arm raising operation pressure is equal to or higher than the threshold (step S105: YES), and the tilt / dump operation pressure is less than a predetermined value (step S107: YES), the controller 22 outputs a switching command to the second position, that is, the open position, to the first communication / shutoff valve 17 (step S108). Accordingly, although the operator only performs the lift arm raising operation, the pressure oil is also supplied to the tilt cylinder bottom chamber 14 a via the first communication / shutoff valve 17, and thrust is generated in the tilt cylinder 14. However, immediately after the first communication / shutoff valve 17 is switched to the second position, the lift cylinder 13 cannot be extended because the tilt stopper is in operation. This state is a state where the lift angle in FIG. 5 is θ1.

Thereafter, when the lift arm raising operation by the operator is continued, the lift cylinder 13 is extended and the tilt cylinder 14 is also extended. This state is a state where the lift angles in FIG. 5 are θ1 to θ2.
This state is also a state indicated by a solid line in FIG. As a comparative example, a broken line in FIG. 8C shows a state where the first communication / shutoff valve 17 does not change from the first position or when the first communication / shutoff valve 17 is not provided. From the comparison between the dotted line and the solid line shown in FIG. 8C, it can be seen that the tilt angle is large and the earth and sand scooped up by the bucket 8 is less likely to spill.

If the lift arm raising operation is further continued from the state shown in FIG. 8C, the tilt cylinder 14 reaches the maximum extension. This state is a state where the lift angle in FIG. 5 is θ2.
If the lift raising operation is further continued, the lift cylinder 13 extends but the tilt cylinder 14 cannot extend any further, so that the bucket 8 slightly changes to the dump side, and the tilt stopper 10b is deactivated. In other words, the tilt stopper is in an operating state when the lift angle is θ1 to θ2, but is not in the tilt stopper operating state when the lift angle is θ2 to θ3.
When the lift angle exceeds θ2, the output value of the tilt stopper sensor 10b becomes smaller than the threshold value (FIG. 5, step S102: NO), so the first communication / shutoff valve 17 is switched to the first position by the controller 22 (FIG. 5). 5, Step S103).

If the lift arm raising operation is further continued, the lift arm 10 reaches the maximum extension and the lift angle becomes θ3. This state is a state indicated by a solid line in FIG. As a comparative example, the broken line in FIG. 8D shows a state where the first communication / shutoff valve 17 does not change from the first position or when the first communication / shutoff valve 17 is not provided. By comparing the dotted line and the solid line shown in FIG. 8D, even when the lift angle is the maximum, the tilt angle is increased by the action of the first communication / shutoff valve 17, and the earth and sand scooped by the bucket 8 is difficult to spill. You can see that
The attachment angle characteristic L2A shown in FIG. 5 has a larger tilt angle over the entire lift angle than the comparative example L2. That is, when the lift arm is raised to release the earth and sand, the bucket tilt angle can be increased, and the effect of preventing spillage of earth and sand and the effect of stabilizing the vehicle body can be obtained.

According to the embodiment described above, the following operational effects can be obtained.
(1) The load handling device 5 of the wheel loader 1 includes a link mechanism 9 in which a reference point of the bucket 8 moves in parallel to the ground when the bucket 8 attached to the tip of the lift arm 10 is moved up and down, and a lift cylinder bottom. When pressure oil is supplied to the chamber 13a and the lift cylinder rod chamber 13b, the pressure oil is supplied to the lift cylinder 13 that raises and lowers the bucket 8 via the lift arm 10, and the tilt cylinder bottom chamber 14a and the tilt cylinder rod chamber 14b. And a tilt cylinder 14 for tilting the bucket 8. The tilt stopper sensor 23 detects that the bucket 8 is in the tilt stopper operating state, and the pressure oil is supplied to the lift cylinder bottom chamber side oil passage 13A and the tilt cylinder rod chamber 14b for supplying the pressure oil to the lift cylinder bottom chamber 13a. When the switching valve, that is, the first series / shutoff valve 17 and at least the tilt stopper sensor 23 that detect the tilt stopper operating state are switched to the communication position that communicates with the communicating position of the tilt cylinder rod chamber side oil passage 14B to be supplied and the shut-off position that shuts off. And a controller (control unit) 22 that switches the first series / shutoff valve 17 to the communication position.

  In the wheel loader 1 configured as described above, when the operator performs an operation to raise the bucket 8 in the tilt stopper operating state, that is, when the operator performs a lift arm raising operation, the wheel loader 1 is introduced into the lift cylinder rod chamber 13b. A part of the pressure oil is introduced into the tilt cylinder rod chamber 14b. At this time, due to the thrust in the extending direction of the tilt cylinder 14, the bucket 8 is raised while the tilt stopper is in an operating state. Therefore, the tilt angle of the bucket 8 is stable and does not fluctuate.

(2) In the wheel loader of the first embodiment, the first series / shut-off valve 17 is an electromagnetic switching valve, and the controller 22 as the control unit determines the tilt stopper operating state based on the detection signal from the tilt stopper sensor 23. When the lift arm raising operation is detected by the detection signal from the lift arm operation pressure sensor 16a and the tilt / dump non-operation is detected by the detection signal from the tilt / dump operation pressure sensor 16b, the communication / The shut-off valve 17 is switched to the communication position.
Thus, when the tilt stopper is activated, when the lift arm 10 is raised without performing the tilting operation of the bucket 8, a part of the pressure oil supplied to the lift cylinder bottom chamber 13a is tilt cylinder bottom chamber. 14b is also supplied, and the bucket 8 maintains the tilt stopper operating state, so that the bucket 8 moves up in contact with the tilt stopper 10b, so that the posture of the bucket 8 is stabilized and the sediment from the bucket 8 is not dropped. Is prevented.

(3) The tilt stopper operating state detector, that is, the tilt stopper sensor 23 detects the tilt angle of the bucket 8 based on the positional relationship between two predetermined locations in the link mechanism 9, that is, the positional relationship between the bell crank bracket 10a and the bell crank 11. To do.
Therefore, the tilt angle of the bucket 8 can be measured with high sensitivity by appropriately selecting two locations for detecting the tilt angle of the bucket 8 according to the configuration of the link mechanism 9. Also, a plurality of combinations can be selected for the two locations for detecting the tilt angle, and can be selected from the viewpoints of ease of maintenance, resistance to changes in temperature, resistance to contamination, and the like.

(Modification 1)
In the first embodiment, the tilt stopper sensor 23 is provided in the bell crank bracket 10a, and the tilt stopper detection bar 24 is provided in the bell crank 11. However, the mounting positions of the tilt stopper sensor 23 and the tilt stopper detection bar 24 are not limited to this. The tilt stopper sensor 23 and the tilt stopper detection bar 24 may be attached at any position in the link mechanism 9 so that the tilt stopper operating state can be detected.
Further, the tilt stopper sensor 23 is not limited to the proximity sensor, and may be a distance meter.

(Modification 2)
In the first embodiment, the tilt stopper sensor 23 detects the tilt stopper operating state by detecting the tilt stopper detection bar 24 provided in the bell crank 11. However, the tilt stopper sensor 23 may detect the detection target provided in the bucket 8 to detect the tilt stopper operating state, or the tilt stopper sensor 23 may be provided other than the bell crank bracket 10a.
For example, the tilt stopper sensor 23 may be a laser distance meter, and may be provided on the bell crank 11 to measure the distance to an obstacle in a predetermined direction.

  FIG. 9 is a diagram illustrating an example in which the tilt stopper sensor 23a measures the distance from the bucket. FIG. 9A is a diagram showing the mounting position of the tilt stopper sensor 23a. The tilt stopper sensor 23a measures the distance to the obstacle in the direction indicated by the arrow. FIG. 9B is a diagram showing a tilt stopper operating state. When the controller 22 receiving the output of the tilt stopper sensor 23a detects that the distance to the obstacle output from the tilt stopper sensor 23a matches the distance to the bucket 8 measured in advance, the controller 22 determines that the tilt stopper is in an operating state. To do.

According to Modification 2 described above, the following operational effects can be obtained.
(1) The tilt stopper operating state detector, that is, the tilt stopper sensor 23 detects the tilt angle of the bucket based on the positional relationship between a predetermined location in the link mechanism 9 and the bucket 8.
Therefore, the tilt angle can be detected directly.

(Modification 3)
In the first embodiment, the controller 22 determines whether or not the tilt stopper is operating based on the output of the tilt stopper sensor 23. However, the controller 22 may determine whether or not the tilt stopper is in an operating state based on the operating states of the lift cylinder 13 and the tilt cylinder 14.
The tilt angle of the bucket 8 can be calculated from the lengths of the lift cylinder 13 and the tilt cylinder 14 and the structure and dimensions of the link mechanism 9. Therefore, if the structure and dimensions of the link mechanism 9 are known, the controller 22 can determine whether or not the bucket 8 is in the tilt stopper operating state based on the lengths of the lift cylinder 13 and the tilt cylinder 14. Therefore, for example, it is possible to determine whether or not the bucket 8 is in the tilt stopper operating state with the following configuration.

  The lift cylinder 13 and the tilt cylinder 14 are provided with sensors for detecting the lengths of the respective rods, and the expansion / contraction positions of the rods are output to the controller 22 as electric signals. The controller 22 is previously input with the structure and dimensions of the link mechanism 9. The controller 22 determines whether or not the bucket 8 is in the tilt stopper operating state based on the electrical signals input from the lift cylinder 13 and the tilt cylinder 14 and the structure and dimensions of the link mechanism 9.

According to Modification 3 described above, the following operational effects are obtained.
(1) The tilt stopper operating state detection unit, that is, the tilt stopper sensor 23 detects the tilt angle of the bucket based on the operations of the lift cylinder 13 and the tilt cylinder 14.
Therefore, it is not necessary to install a sensor in the link mechanism 9 or the bucket 8, and the configuration of the wheel loader can be simplified.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIG. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and different points will be mainly described. Points that are not particularly described are the same as in the first embodiment. This embodiment differs from the first embodiment mainly in that the signal input to the controller is only the output signal of the tilt stopper.

(Constitution)
FIG. 10 is a diagram illustrating a hydraulic circuit 200a according to the second embodiment.
The hydraulic circuit 200a includes a controller 22a instead of the controller 22 of the first embodiment, but does not include the pressure sensors 16a and 16b of the first embodiment.
The hydraulic circuit 200 a includes a second communication / shutoff valve 40 and a bucket operation detection valve 41. The second communication / shutoff valve 40 includes a lift cylinder bottom chamber side oil passage 13A and a lift cylinder rod chamber side oil passage 13B, and a tilt cylinder bottom chamber side oil passage 14A and a tilt cylinder rod chamber side oil passage 14B. It is installed in series with the first communication / shutoff valve 17. The second communication / shutoff valve 40 is normally switched to the closed position by a spring. When the lift arm raising operation pressure becomes equal to or higher than the spring pressure, the lift arm is switched to the open position.

  The bucket operation detection valve 41 is normally switched to the first position by a spring, and at this time, the pilot port on the spring pressure side of the second communication / shutoff valve 40 is connected to the tank pressure. The bucket operation detection valve 41 is switched to the second position when the tilt operation pressure / dump operation pressure becomes equal to or higher than the spring pressure. When switched to the second position, the discharge pressure of the pilot pump 19 is introduced into the pilot port on the spring pressure side of the second communication / shutoff valve 40.

(Operation)
When the lift arm raising operation pressure is output from the lift operation pilot valve 20a, the control pressure on one end of the lift spool 30 of the control valve 15 on the left side in the drawing increases. Then, the lift spool 30 moves to the right side in the figure, and the pressure oil from the main pump 18 is supplied to the lift cylinder bottom chamber 13a.
The lift arm raising operation pressure also acts on one end of the second communication / shutoff valve 40, the right side in the figure. At this time, if the bucket operation is not performed, the left side in the figure, which is the other end of the second communication / shutoff valve 40, is the tank pressure. Therefore, if the lift arm raising operation pressure exceeds a predetermined pressure, the second communication / The shut-off valve 40 switches to the second position.

Based on the signal from the tilt stopper sensor 23, the controller 22a determines whether or not the bucket 8 is in the tilt stopper operating state. If the controller 8a determines that the bucket 8 is in the tilt stopper operating state, the controller 22a turns the first communication / shutoff valve 17 on. Command to switch to 2 position.
Accordingly, when the lift arm raising operation is performed, the lift arm raising operation pressure exceeds a predetermined pressure, the bucket operation is not performed, and the bucket 8 is in the tilt stopper operating state, the following processing is performed. . That is, the pressure oil supplied to the lift cylinder bottom chamber 13a is also supplied to the tilt cylinder bottom chamber 14a, and the tilt cylinder 14 generates a thrust in the extending direction.
For this reason, the bucket 8 whose posture is to be changed to the dump side due to the increase in the lift angle is kept in the tilt stopper operating state. The oil discharged from the rod chamber by the extension of the tilt cylinder 14 returns to the tank 21 through the first communication / shutoff valve 17, the second communication / shutoff valve 40, and the control valve 15. If the lift arm raising operation is continued as it is, the tilt cylinder 14 reaches the maximum extension and shifts to a bucket posture that is not in the tilt stopper operating state.

  As a result, the signal from the tilt stopper sensor 23 changes to the non-tilt stopper operating state that is not the tilt stopper operating state, and the command output from the controller 22a to the first communication / shutoff valve 17 is switched to the first position, that is, the closed position. It is changed to the command value. When the tilt / dump operation (bucket operation) is performed and the tilt / dump operation pressure exceeds a predetermined threshold, the discharge pressure of the pilot pump 19 is output as the outlet pressure of the bucket operation detection valve 41, and the second communication is performed. / The shut-off valve 40 switches to the first position, that is, the closed position. When at least one of the first communication / shutoff valve 17 or the second communication / shutoff valve 40 is switched to the first position, the communication path between the lift cylinder 13 and the tilt cylinder 14 is shut off, and each is operated independently.

According to this 2nd Embodiment, in addition to the effect in 1st Embodiment, there exist the following effects.
(1) The wheel loader of the second embodiment includes lift cylinder supply / discharge oil passages 13A and 13B that supply pressure oil to the lift cylinder bottom chamber 13a and the lift cylinder rod chamber 13b, and the tilt cylinder bottom chamber 14a and the tilt cylinder rod chamber. Between the tilt cylinder supply / discharge oil passages 14A and 14B for supplying pressure oil to 14b, the first communication / shutoff valve 17 is arranged in series, and the lift cylinder bottom chamber side oil passage 13A and the tilt cylinder bottom chamber side oil passage 14A are arranged. Is provided with a second communication / shutoff valve 40 which is a second switching valve that can be switched between a communication position that communicates with each other and a shutoff position that shuts off. The second communication / shutoff valve 40 is configured to supply and discharge the lift cylinder when the condition that the operation for raising the lift arm 10 is performed and the operation for tilting and dumping the bucket 8 is not performed. When the conditions are not satisfied when the passages 13A, 13B and the tilt cylinder supply / discharge oil passages 14A, 14B are switched to each other, the lift cylinder supply / discharge oil passages 13A, 13B and the tilt cylinder supply / discharge oil passages 14A, 14B are switched. It switches to the blocking position that shuts off.

  When a signal for detecting the tilt stopper operating state is input from the tilt stopper sensor 23, the controller 22a switches the first communication / shutoff valve 17 to the communication position. When the second communication / shut-off valve 40 is switched to the communication position by the lift operation pressure accompanying the lift operation, a part of the pressure oil supplied to the lift cylinder bottom chamber 13a is supplied to the tilt cylinder bottom chamber 14a. Therefore, the same effect as that of the first embodiment can be obtained, and further, it is detected that the tilt stopper is in operation, and the first communication / shutoff valve 17 is switched by an electric signal, but the lift operation is detected by hydraulic pressure. did. Therefore, the reliability is slightly higher than that of the controller 22.

(2) The wheel loader according to the second embodiment switches to the tilt / dump operation detection position when an operation for tilting or dumping the bucket 8 is detected, and at the tilt / dump non-operation detection position when the operation is not detected. A third switching valve that switches, that is, a bucket operation detection valve 41 is further provided. When the bucket operation detection valve 41 is switched to the tilt / dump non-operation detection position, the second communication / shutoff valve 40 is switched to the communication position by the lift arm operation pressure generated by the operation of raising the lift arm 10, and the bucket operation is performed. When the detection valve 41 switches to the tilt / dump operation detection position, the second communication / shut-off valve 40 is held at the shut-off position even if lift arm operation pressure is generated.
Since the second communication / shutoff valve 40 and the bucket operation detection valve 41 operate by hydraulic pressure, the reliability is higher than the controller 22 that operates electrically based on the outputs of the pressure sensors 16a and 16b.

(Third embodiment)
A third embodiment of the present invention will be described with reference to FIGS. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and different points will be mainly described. Points that are not particularly described are the same as in the first embodiment. This embodiment is different from the first embodiment mainly in that the communication valve is provided separately for the bottom chamber connection and the rod chamber connection.

(Constitution)
FIG. 11 is a diagram illustrating a hydraulic circuit 200b according to the third embodiment.
The hydraulic circuit 200b includes a bottom chamber communication / shutoff valve 42 and a rod chamber communication / shutoff valve 43 instead of the first communication / shutoff valve 17 in the first embodiment. The hydraulic circuit 200 b further includes a bucket operation detection valve 41 and a communication valve operating pressure selection valve 44. The hydraulic circuit 200 b includes a controller 22 b instead of the controller 22. The hydraulic circuit 200b does not include the pressure sensors 16a and 16b included in the hydraulic circuit 200 in the first embodiment. The configurations of the bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 will be described with reference to FIG.
FIG. 12A is a diagram showing the configuration of the bottom chamber communication / shutoff valve 42, and FIG. 12B is a diagram showing the configuration of the rod chamber communication / shutoff valve 43.

  The bottom chamber communication / shutoff valve 42 switches the communication state between the lift cylinder bottom chamber 13a and the tilt cylinder bottom chamber 14a. The rod chamber communication / shutoff valve 43 switches the communication state between the lift cylinder rod chamber 13b and the tilt cylinder rod chamber 14b. The bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 are both 2-position 6-port hydraulic pilot switching valves. The bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 are both switched by the outlet pressure of the bucket operation detection valve 41 and the communication valve operating pressure selection valve 44.

  The bottom chamber communication / shutoff valve 42 has a bottom chamber oil passage 42b that connects the lift cylinder bottom chamber 13a to a hydraulic pressure source at the shut-off position, and pressurizes the lift cylinder bottom chamber 13a and the tilt cylinder bottom chamber 14a at the communication position. A bottom chamber side lift / tilt communication oil passage 42c connected to the oil source is provided. The bottom chamber side lift / tilt communication oil passage 42c has a bottom chamber check valve 42a that does not allow the pressure oil in the lift cylinder bottom chamber 13a to flow back to the tilt cylinder bottom chamber 14a.

  The rod chamber communication / shutoff valve 43 has a rod chamber oil passage 43b that connects the lift cylinder rod chamber 13b to a hydraulic pressure source at the shut-off position, and pressurizes the lift cylinder rod chamber 13b and the tilt cylinder rod chamber 14b at the communication position. It has a rod chamber side lift / tilt communication oil passage 43c connected to the oil source. The rod chamber side lift / tilt communication oil passage 43c includes a rod chamber check valve 43a that does not allow the pressure oil in the lift cylinder rod chamber 13b to flow back to the tilt cylinder rod chamber 14b.

  The first position of the bottom chamber communication / shutoff valve 42 connects the secondary side flow path 38 of the lift spool 30 to the lift cylinder bottom chamber 13a, and blocks communication between the lift cylinder bottom chamber 13a and the tilt cylinder bottom chamber 14a. . The second position of the bottom chamber communication / shutoff valve 42 is such that the bottom chamber check valve 42a blocks the flow of pressure oil from the lift cylinder bottom chamber 13a, while the lift spool 30 is connected to the lift cylinder bottom chamber 13a and the tilt cylinder bottom chamber 14a. This is the position to supply the pressure oil adjusted in. That is, the second position is a communication position where the lift cylinder bottom chamber 13a and the tilt cylinder bottom chamber 14a communicate with each other.

  The first position of the rod chamber communication / shut-off valve 43 connects the secondary side of the lift spool 30 to the lift cylinder rod chamber 13b and blocks communication between the lift cylinder rod chamber 13b and the tilt cylinder rod chamber 14b. The second position of the rod chamber communication / shutoff valve 43 is adjusted by the lift spool 30 to the lift cylinder rod chamber 13b and the tilt cylinder rod chamber 14b while blocking the flow of pressure oil into the lift cylinder rod chamber 13b by the check valve 43a. Supply the compressed oil.

  The bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 are either opened or closed by comparing the sum of the outlet pressure of the bucket operation detection valve 41 and the spring pressure with the outlet pressure of the communication valve operating pressure selection valve 44. Switch to the communication position. When the outlet pressure of the communication valve operating pressure selection valve 44 exceeds a predetermined pressure (the sum of the outlet pressure of the bucket operation detection valve 41 and the spring pressure) and the outlet pressure of the bucket operation detection valve 41 is the tank pressure, the communication position is reached. Switch. In the communication position, the pressure oil supplied to the lift cylinder bottom chamber 13a is also supplied to the tilt cylinder bottom chamber 14a.

  The communication valve operating pressure selection valve 44 is an electromagnetic switching valve that selects either the tank pressure or the lift arm raising operation pressure as the outlet pressure, and the selection is switched by the controller 22b. When the controller 22b determines the tilt stopper operating state based on the output voltage of the tilt stopper sensor 23 as described above, the communication valve operating pressure selection valve 44 is controlled to be switched so that the lift arm raising operation pressure is output. When the controller 22b does not determine the tilt stopper operating state, the communication valve operating pressure selection valve 44 is controlled to be switched so that the tank pressure is output.

  The bucket operation detection valve 41 is a hydraulic pilot type switching valve that selects either tank pressure or pilot relief pressure as the outlet pressure. The bucket operation detection valve 41 outputs a pilot relief pressure when the tilt / dump operation pressure exceeds a predetermined pressure, and outputs a tank pressure in other cases.

(Operation)
When the operator moves the lift operation pilot valve 20 a to the left side in the drawing and performs a lift arm raising operation, this operation pressure acts on the lift spool 30 of the control valve 15 and the communication valve operating pressure selection valve 44.
In the lift spool 30, the control pressure on the left side in the drawing increases by a lift arm raising operation. Then, the lift spool 30 moves to the right side in the figure, and the pressure oil from the main pump 18 reaches the bottom chamber communication / shutoff valve 42. At this time, in the case of tilt / dump non-operation, tank pressure is applied to the pilot port on the left side of the bottom chamber communication / shutoff valve 42 in the figure. On the other hand, when the tilt stopper operation state is not detected, the controller 22b performs control to hold the communication valve operating pressure selection valve 44 at the initial position, and the outlet pressure of the communication valve operation pressure selection valve 44 is the tank pressure. is there. Therefore, when the tilt / dump is not operated and the tilt stopper is not operated, the pressure oil from the lift spool 30 is supplied to the lift cylinder bottom chamber 13a via the bottom chamber communication / shutoff valve 42.

  If the controller 22b determines that the tilt stopper is in an operating state when the lift arm raising operation is being performed, the controller 22b sends the lift arm raising operation pressure to the outlet valve pressure with respect to the communication valve operating pressure selection valve 44. Command to switch to the position to be selected. Then, the lift arm raising operation pressure acts on the pilot ports on the right side of the bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 in the drawing. At this time, if no bucket operation is performed, the pilot ports on the left side of the bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 are at tank pressure. Therefore, when the lift arm raising operation pressure exceeds a predetermined pressure, the bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 are switched to the second communication position, and the main pump 18 accompanying the lift arm raising operation. From the lift cylinder bottom chamber 13a and the tilt cylinder bottom chamber 14a.

  That is, the pressure oil supplied to the lift cylinder bottom chamber 13a is also supplied to the tilt cylinder bottom chamber 14a, and the tilt cylinder 14 generates a thrust in the extending direction. As a result, the bucket 8 whose posture is about to change to the dump side maintains the tilt stopper operating state. The oil discharged from the rod side by the extension of the tilt cylinder 14 returns to the tank 21 through the bottom chamber communication / shutoff valve 42, the rod chamber communication / shutoff valve 43, and the control valve 15. If the lift arm raising operation is continued as it is, the posture of the bucket 8 becomes a posture that is not in the tilt stopper operating state.

  As a result, the signal from the tilt stopper sensor 23 changes to the tilt stopper inactive state, and the command output from the controller 22b to the communication valve operating pressure selection valve 44 is changed to a command value for switching to the tank pressure selection position. When the tilt / dump operation is performed and the tilt / dump operation pressure exceeds a predetermined threshold, the pilot relief pressure is output as the outlet pressure of the bucket operation detection valve 41, and the bottom chamber communication / shutoff valve 42 and the rod chamber are output. The communication / shutoff valve 43 is switched to the first position, that is, the closed position. When the bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 are switched to the first position, the lift cylinder 13 and the tilt cylinder 14 are shut off from each other, and each is operated independently.

According to this 3rd Embodiment, in addition to the effect in 1st Embodiment, there exist the following effects.
(1) The cargo handling device 5 of the wheel loader 1 according to the third embodiment includes a tilt stopper sensor 23 that detects that the bucket 8 is in the tilt stopper operating state, and a lift cylinder bottom that supplies pressure oil to the lift cylinder bottom chamber 13a. A fourth switching valve, that is, a bottom chamber communication / switched between a communication position for communicating the tilt cylinder bottom chamber side oil path 14A for supplying pressure oil to the chamber side oil path 13A and the tilt cylinder bottom chamber 14a and a blocking position for blocking. A communication position that connects the shutoff valve 42 to the lift cylinder rod chamber side oil passage 13B that supplies pressure oil to the lift cylinder rod chamber 13b and the tilt cylinder rod chamber side oil passage 14B that supplies pressure oil to the tilt cylinder rod chamber 14b; A fifth switching valve that is switched to the blocking position for blocking, that is, the rod chamber communication / blocking valve 43 is provided.
Further, when an operation for tilting or dumping the bucket 8 is detected, the operation is switched to the tilt / dump operation detection position, and if the operation is not detected, the bucket operation detection valve 41 and the lift arm 10 are switched to the tilt / dump non-operation detection position. It further includes an electromagnetic switching valve 44 that switches to one of a lift arm raising operation pressure selection position for selecting a lift arm raising operation pressure generated by the raising operation and a tank pressure selection position for selecting a tank pressure. When the control unit 22b detects that the tilt stopper operating state detection unit 23 detects the tilt stopper operating state, the electromagnetic switching valve 44 is switched to the lift arm raising operation pressure selection position. The switching valve 44 is switched to the tank pressure selection position. When the control unit 22b detects the tilt stopper operating state, the bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff are performed by the lift arm operation pressure generated by the operation of raising the lift arm 10 when the bucket is not operated. The valve 43 is switched to the communication position.

  Also in the wheel loader handling apparatus of the third embodiment, it is possible to achieve the same effects as the actions and effects obtained by the cargo handling apparatus of the first embodiment. Further, similarly to the second embodiment, since it includes an electromagnetic switching valve 44, a hydraulic pilot switching bucket operation detection valve 41, a bottom chamber communication / shutoff valve 42, and a rod chamber communication / shutoff valve 43, Reliability is improved as compared with the cargo handling device of the first embodiment.

(2) The bottom chamber communication / shutoff valve 42 of the cargo handling device 5 of the wheel loader 1 according to the third embodiment has a bottom chamber oil passage 42b that connects the lift cylinder bottom chamber 13a to a hydraulic pressure source at the shutoff position. At the position, there is a bottom chamber side lift / tilt communication oil passage 42c that connects the lift cylinder bottom chamber 13a and the tilt cylinder bottom chamber 14a to a pressure oil source. The rod chamber communication / shutoff valve 43 has a rod chamber oil passage 43b for connecting the lift cylinder rod chamber 13a to a hydraulic pressure source at the shut-off position, and presses the lift cylinder rod chamber 13b and the tilt cylinder rod chamber 14b at the communication position. It has a rod chamber side lift / tilt communication oil passage 43c connected to the oil source.
The bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 include a pressure selected by an electromagnetic switching valve 44 and a bucket operation detection valve 41 at a tilt / dump operation detection position or a tilt / dump non-operation detection position. It switches according to the output pressure when switched to. The bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 are switched to the communication position when the pressure selected by the switching valve 44 is higher than the output pressure of the bucket operation detection valve 41.
Since the bottom chamber communication / shutoff valve 42, the rod chamber communication / shutoff valve 43, and the bucket operation detection valve 41 are hydraulically operated, the first and second embodiments operate electrically based on the outputs of the pressure sensors 16a and 16b. More reliable than the form handling equipment.

(3) In the cargo handling device 5 of the wheel loader 1 according to the third embodiment, the bottom chamber side lift / tilt communication oil passage and the rod chamber side lift / tilt communication oil passage are respectively connected from the lift cylinder bottom chamber 13a to the tilt cylinder bottom chamber 14a. A bottom chamber check valve 42a for preventing the pressure oil from flowing into the cylinder, and a rod chamber check valve 43a for preventing the pressure oil in the lift cylinder rod chamber 13b from flowing back to the tilt cylinder rod chamber 14b.
Such check valves 42b and 43b for preventing backflow prevent the pressure oil in the lift cylinder bottom chamber 13a and the lift cylinder rod chamber 13b from flowing back to the tilt cylinder bottom chamber 14a and the tilt cylinder rod chamber 14b, which is undesirable. Can prevent the lift arm 10 from falling.
Furthermore, it has an effect peculiar to 3rd Embodiment demonstrated below.

(Effects peculiar to the third embodiment)
FIG. 13 is a diagram for explaining effects peculiar to the third embodiment.
When the first communication / shutoff valve 17 is fixed at the communication position, which is the second position, in the first and second embodiments, as shown in FIG. 13, between the bottom chambers of the lift cylinder 13 and the tilt cylinder 14, the rod chamber The space is always in communication. Furthermore, when the holding pressure of the lift cylinder 13 is higher than the holding pressure of the tilt cylinder 14 in a state where the tilt stopper is not operated, the hydraulic oil flows from the bottom chamber of the lift cylinder 13 into the bottom chamber of the tilt cylinder 14 and the bucket 8 tilts. Then, the lift arm 10 is lowered. The unexpected movement of the lift arm 10 is stopped when the holding pressures of the lift cylinder 13 and the tilt cylinder 14 are the same or when the tilt stopper 10b is activated, that is, the tilt stopper is activated.
On the other hand, in the third embodiment, since the check valves are provided in the communication valves 42 and 43, the bottom chamber communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 are fixed at the communication position which is the second position. Even so, since the hydraulic oil does not flow out from the bottom chambers of the lift cylinder 13 and the tilt cylinder 14, the situation as in the first and second embodiments does not occur. Furthermore, since the bottom arm communication / shutoff valve 42 and the rod chamber communication / shutoff valve 43 cannot be lifted by the lift arm when the second position is fixed, the driver can quickly know the occurrence of the malfunction.

The above-described embodiments and modifications may be combined.
Although various embodiments and modifications have been described above, the present invention is not limited to these contents. Other embodiments conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Wheel loader 8 ... Bucket 9 ... Link mechanism 13 ... Lift cylinder 13a ... Lift cylinder bottom chamber 13b ... Lift cylinder rod chamber 13A ... Lift cylinder bottom chamber side oil passage 13B ... Lift cylinder rod chamber side oil passage 14 ... Tilt cylinder 14a ... Tilt cylinder bottom chamber 14b ... Tilt cylinder rod chamber 14A ... Tilt cylinder bottom chamber side oil passage 14B ... Tilt cylinder rod chamber side oil passage 17 ... First communication / shutoff valve (switching valve)
22, 22a, 22b ... Controller 23 ... Tilt stopper sensor (tilt stopper operating state detector)
40: Second communication / shutoff valve (second switching valve)
41 ... Bucket operation detection valve (third switching valve)
42 ... Bottom chamber communication / shutoff valve (switching valve, fourth switching valve)
42a ... Bottom chamber check valve 42b ... Bottom chamber oil passage 42c ... Bottom chamber side lift / tilt communication oil passage 43 ... Rod chamber communication / shutoff valve (fifth switching valve)
43a ... Rod chamber check valve 43b ... Rod chamber oil passage 43c ... Rod chamber side lift / tilt communication oil passage 44 ... Communication valve operating pressure selection valve

Claims (10)

A link mechanism in which the reference point of the attachment moves parallel to the ground when the attachment attached to the tip of the lift arm is moved up and down;
A lift cylinder that lifts and lowers the attachment via the lift arm when pressure oil is supplied to the lift cylinder bottom chamber and the lift cylinder rod chamber;
A load handling device in a wheel loader comprising a tilt cylinder that tilts the attachment when pressure oil is supplied to a tilt cylinder bottom chamber and a tilt cylinder rod chamber,
A tilt stopper operating state detector for detecting that the attachment is in a tilt stopper operating state;
The lift cylinder bottom chamber side oil passage for supplying pressure oil to the lift cylinder bottom chamber and the tilt cylinder bottom chamber side oil passage for supplying pressure oil to the tilt cylinder bottom chamber are connected to a communication position for communication with each other and a blocking position for blocking each other. A switching valve to be switched;
A wheel loader loading / unloading apparatus comprising: a control unit that switches the switching valve to the communication position when at least the tilt stopper operating state detection unit detects the tilt stopper operating state. In the wheel loader cargo handling device according to claim 1,
A lift arm operation detector that detects an operation of raising the lift arm;
An attachment operation detection unit that detects an operation of tilting or dumping the attachment;
The switching valve is an electromagnetic switching valve;
The control unit is configured such that the tilt stopper operation state detection unit detects the tilt stopper operation state, the lift arm operation detection unit detects a lift operation of the lift arm, and the attachment operation detection unit A wheel loader loading / unloading device that switches the switching valve to the communication position when an attachment tilt or dump operation is not detected. In the wheel loader cargo handling device according to claim 2,
Between a lift cylinder supply / discharge oil passage for supplying pressure oil to the lift cylinder bottom chamber and the lift cylinder rod chamber, and a tilt cylinder supply / discharge oil passage for supplying pressure oil to the tilt cylinder bottom chamber and the tilt cylinder rod chamber And a second switching valve that is arranged in series with the switching valve and that is switched between a communication position that communicates the lift cylinder bottom chamber side oil passage and the tilt cylinder bottom chamber side oil passage and a blocking position that shuts off.
The second switching valve is configured to supply and discharge the lift cylinder when a condition that an operation for raising the lift arm is performed and an operation for tilting or dumping the attachment is not performed is established. When the above condition is not satisfied, the lift cylinder supply / discharge oil passage and the tilt cylinder supply / discharge oil passage are switched to a shut-off position. A wheel loader cargo handling device characterized by being replaced. In the wheel loader cargo handling device according to claim 3,
When an operation for tilting or dumping the attachment is detected, it is further switched to a tilt / dump operation detection position, and when the operation is not detected, a hydraulic pilot-type third switching valve is further switched to the tilt / dump non-operation detection position. And
When the third switching valve is switched to the tilt / dump non-operation detection position, the second switching valve is switched to the communication position by the lift arm operation pressure generated by the operation of raising the lift arm, When the third switching valve is switched to the tilt / dump operation detection position, the second switching valve is held at the shut-off position even when the lift arm operation pressure is generated. apparatus. The wheel loader cargo handling device according to claim 1,
The switching valve is disconnected from a communication position that communicates a lift cylinder bottom chamber side oil passage that supplies pressure oil to the lift cylinder bottom chamber and a tilt cylinder bottom chamber side oil passage that supplies pressure oil to the tilt cylinder bottom chamber. A hydraulic pilot-type fourth switching valve that is switched to the shut-off position;
The lift cylinder rod chamber side oil passage that supplies pressure oil to the lift cylinder rod chamber and the tilt cylinder rod chamber side oil passage that supplies pressure oil to the tilt cylinder rod chamber are switched between a communicating position and a blocking position that shuts off. A hydraulic pilot operated fifth switching valve;

A hydraulic pilot-type third switching valve that switches to a tilt / dump operation detection position when an operation for tilting or dumping the attachment is detected, and switches to a tilt / dump non-operation detection position when the operation is not detected;
An electromagnetic switching valve that switches to one of a lift arm raising operation pressure selection position for selecting a lift arm raising operation pressure generated by an operation for raising the lift arm and a tank pressure selection position for selecting a tank pressure; In addition,
When the controller detects the tilt stopper operating state, the tilt stopper operating state detection unit switches the electromagnetic switching valve to the lift arm raising operation pressure selection position, and does not detect the tilt stopper operating state. Switching the electromagnetic switching valve to the tank pressure selection position;
When the control unit detects the tilt stopper operating state, the fourth switching valve and the fifth switching valve are switched to the communication position by the lift arm operation pressure generated by the operation of raising the lift arm. A wheel loader cargo handling device characterized by being replaced. In the wheel loader cargo handling device according to claim 5,
The fourth switching valve has a bottom chamber oil passage that connects the lift cylinder bottom chamber to a hydraulic pressure source at the shut-off position, and pressurizes the lift cylinder bottom chamber and the tilt cylinder bottom chamber at the shut-off position. It has a bottom chamber side lift / tilt communication oil passage connected to the oil source,
The fifth switching valve has a rod chamber oil passage that connects the lift cylinder rod chamber to a hydraulic pressure source at the shut-off position, and pressurizes the lift cylinder rod chamber and the tilt cylinder rod chamber at the shut-off position. It has a rod chamber side lift / tilt communication oil passage connected to the oil source,
The fourth switching valve and the fifth switching valve are a pressure selected by the electromagnetic switching valve, and the third switching valve is at the tilt / dump operation detection position or the tilt / dump non-operation. Switching according to the output pressure when switched to the detection position, and switching to the communication position when the pressure selected by the switching valve is higher than the output pressure of the third switching valve. Wheel loader handling equipment. In the wheel loader cargo handling device according to claim 6,
The bottom chamber side lift / tilt communication oil passage and the rod chamber side lift / tilt communication oil passage are respectively a bottom chamber check valve for preventing the flow of pressure oil from the lift cylinder bottom chamber to the tilt cylinder bottom chamber, and A load handling device for a wheel loader, comprising: a rod chamber check valve that does not allow the pressure oil in the lift cylinder rod chamber to flow backward to the tilt cylinder rod chamber. In the wheel loader cargo handling device according to claim 1,
The wheel loader cargo handling device, wherein the tilt stopper operating state detection unit detects a tilt angle of the attachment based on a positional relationship between two predetermined positions in the link mechanism. In the wheel loader cargo handling device according to claim 1,
The wheel loader cargo handling apparatus, wherein the tilt stopper operating state detection unit detects a tilt angle of the attachment based on a positional relationship between the attachment and a predetermined position in the link mechanism. In the wheel loader cargo handling device according to claim 1,
The wheel loader cargo handling device, wherein the tilt stopper operating state detection unit detects a tilt angle of the attachment based on operations of the lift cylinder and the tilt cylinder.

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