JPH06185093A - Front controller of wheel loader - Google Patents

Abstract

PURPOSE:To reduce the descending speed of the boom to mitigate the shocks on grounding of the bucket and also move up swiftly the boom to increase the working efficiency, by reducing the hydraulic oil flow rate or retaining it to the ordinary flow rate, when the boom moves down by the gravity and the front end of boom reaches a specified level above the ground or lower by turning a switch valve to the float position. CONSTITUTION:A boom cylinder 4 is provided with a switch valve 14 to change the flow of hydraulic oil. When the switch valve 14 is turned over to the float position F, the rod chamber of the boom cylinder 4 is connected to the bottom chamber thereof through a connection path 15. When the boom is lowered by the gravity to a specified height from the ground or lower at the front end of the boom, the flow rate of the hydraulic oil passing through the path 15 is decreased by a solenoid valve 22 and the descending speed of the boom is decreased. When the boom is lifted up higher than a specified level above the ground, the flow rate in the path 15 is retained as much as the ordinary rate. In this way, the shock of the bucket on grounding is mitigated and the working time is curtailed and further, the working efficiency can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front control device for a wheel loader, and more particularly to a front control device having a variable boom lowering speed.

[0002]

2. Description of the Related Art As this type of front control device, the one disclosed in Japanese Patent Laid-Open No. 62-33938 is known. This will be described with reference to FIG. The front loader shown in FIG. 8 has a boom 52 rotatably connected to the front part of the tractor 51 and a bucket 53 rotatably attached to the tip of the boom 52. The boom 52 includes a boom cylinder 54. Thus, it is possible to move up and down between the illustrated solid line position and the two-dot chain line position. The bucket 53 is rotatable with respect to the boom 52 by the bucket cylinder 55. The boom cylinder 54 and the bucket cylinder 55 are driven by directionally controlling the discharge oil of a work hydraulic pump (not shown) with a directional control valve.

A detection switch (not shown) is provided near the base end of the boom 52 to turn on and off according to the rotation angle of the boom 52, and the tip of the bucket 53 is shown by A and B in the figure. When located in the area, the detection switch is kept in the ON state. When the detection switch is turned on, the controller (not shown) reduces the amount of switching of the boom directional switching valve (proportional valve) to a value lower than usual to reduce the up-and-down speed of the boom 52. The impact at the time of grounding or when the boom 52 is stopped at the uppermost stage is mitigated. In this specification, such a front loader is also included in the concept of the wheel loader.

[0004]

By the way, generally, in a wheel loader, a bucket is thrust into the accumulated soil piled on the ground to scoop earth and sand, and this is repeatedly loaded into a dump truck, but the cycle time at the time of the operation is reduced. In order to shorten the length, it is necessary to move the boom 52 up and down at a speed higher than a certain level. However, in the device of FIG. 8 described above, when the bucket tip is within the areas A and B, the drive speed of the boom 52 is always lowered during both the boom lowering and the boom raising. Therefore, the work efficiency was lowered, and the metering property was not good especially for a skilled worker.

An object of the present invention is to provide a front control device for a wheel loader, which alleviates the impact when the bucket comes into contact with the ground and improves the working efficiency by rapidly moving the boom up and down.

[0006]

1 and 2 showing an embodiment, the present invention will be described. In the present invention, a boom cylinder 4 for raising and lowering a boom 2 by oil discharged from a working hydraulic pump 12 is provided. A direction switching valve 14 that switches the direction of the pressure oil guided to the boom cylinder 4 and a bucket cylinder 5 that rotates the bucket 3 connected to the tip of the boom 2 by the oil discharged from the working hydraulic pump 12 are provided. When the direction switching valve 14 is switched to the float position F, the rod chamber of the boom cylinder 4 and the bottom chamber communicate with each other through the communication passage 15, and the boom 2 descends by gravity. It
The flow rate adjusting means 22 for adjusting the flow rate of the pressure oil flowing through the communication passage 15, the float position detecting means 21 for detecting that the direction switching valve 14 has been switched to the float position F, and the tip of the boom 2 are provided. Height detecting means 7 for detecting that the ground height is below a predetermined value, and the direction switching valve 14
When it is detected that the height of the boom tip to ground is less than or equal to a predetermined value while the switch to the float position F is detected, the flow rate of the pressure oil in the communication passage 15 is reduced to be lower than usual. The control means 23 for controlling the adjusting means 22 is provided to solve the above problems. In particular, claim 2 has a first position a which is interposed in the communication passage 15 and communicates the bottom chamber of the boom cylinder 4 with the rod chamber without a throttle, and the bottom chamber and the rod chamber with a throttle. The flow rate adjusting means is constituted by the switching valve 22 that can switch to the second position b that communicates with each other, and when the switching of the direction switching valve 14 to the float position F is detected, the ground height of the boom tip is predetermined. When it is detected that the value becomes equal to or less than the value, the switching valve 22 is switched to the second position b, and at other times, the switching valve 22 is held at the first position a. According to the third aspect of the present invention, when it is detected that the ground height of the boom tip becomes equal to or lower than a predetermined value while the switching of the direction switching valve 14 to the float position is detected, the pressure oil in the communication passage 15 is released. The flow rate adjusting means 31 (FIG. 6) is controlled so as to gradually decrease the flow rate with time. Further, claim 4 comprises a command means 24 for outputting a signal for prohibiting the operation of the flow rate adjusting means, and when the prohibition signal is outputted, it is concerned with the switching position of the direction switching valve 14 and the ground height of the boom tip. The flow rate adjusting means is controlled so as not to adjust the flow rate of the pressure oil in the communication passage.

[0007]

When the direction switching valve 14 is switched to the float position F, that is, when the boom 2 descends due to gravity, if the ground height of the boom tip falls below a predetermined value,
The flow rate adjusting means 22 reduces the flow rate of the pressure oil flowing through the communication passage 15, and thereby the lowering speed of the boom 2 is reduced. Therefore, the impact when the bucket touches the ground can be alleviated. Also, in cases other than the above, the flow rate of the pressure oil in the communication passage 15 is maintained at a normal amount, so that the boom 2 can be raised and lowered quickly. In particular, when the direction switching valve 14 is switched to the float position F and the ground height of the boom tip becomes equal to or lower than a predetermined value, the switching valve 22 is set.
Is switched to the second position b, whereby the communication passage 15
The pressure oil is throttled by the throttle 22a, the flow rate is reduced, and the descending speed of the boom is reduced. Further, in claim 3, the directional control valve 1
If the ground height of the boom tip becomes equal to or lower than a predetermined value while the switch 4 is switched to the float position F, the flow rate adjusting means 31.
As a result, the flow rate in the communication passage 15 gradually decreases with time. As a result, the boom descending speed gradually decreases. Further, in claim 4, when the prohibition signal is output from the command means 24, the flow rate of the pressure oil in the communication passage is not adjusted regardless of the switching position of the direction switching valve 14 and the ground height of the boom tip. Therefore, the lowering speed of the boom 2 is not reduced.

Incidentally, in the section of means and action for solving the above-mentioned problems for explaining the constitution of the present invention, the drawings of the embodiments are used to make the present invention easy to understand. It is not limited to.

[0009]

【Example】

-First Embodiment- A first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a side view of the wheel loader WR according to the present embodiment. A pair of left and right booms 2 (only one is shown) are rotatably connected to the front portion of the vehicle body 1 in the vertical direction, and each boom 2 A bucket 3 is rotatably connected to the tip of the. Reference numeral 4 denotes a pair of boom cylinders that rotate the boom 2 (only one is shown), and 5 denotes a bucket cylinder that rotates the bucket 3 via the bell crank 6.

At the base end of the boom 2, a cam 2a is provided in the vicinity of the rotating shaft X as shown in FIG. 3, while the boom position detecting switch 7 is provided near the boom mounting portion of the vehicle body 1.
Is provided, and the switch 7 is turned on and off by the cam 2a when the boom 2 is moved up and down. That is,
While the boom 2 is descending, the ground height of its tip is h (Fig. 2).
When the cam 2a reaches, the detection switch 7 is turned on, and thereafter, the on state is maintained until the boom 2 reaches the lowermost end. Further, when the boom 2 rises from the state where the bucket 3 is in contact with the ground and the ground height of the tip of the boom 2 exceeds h, the cam 2a
Is separated from the switch 7 and the switch 7 returns to the off state.

FIG. 1 is a block diagram of a front control device of the wheel loader WR. The oil discharged from the work hydraulic pump 12 driven by the engine 11 is guided to the bucket cylinder 5 via the bucket direction switching valve 13 and to the pair of boom cylinders 4 via the boom direction switching valve 14. It is designed so that it can be eaten. The bucket directional control valve 13 is operated by a lever 13a, and a tilt position T for rotating the bucket 3 upward (tilt driving) and a dump position for rotating the bucket 3 downward (dump driving). It is possible to switch between D and a neutral position N for stopping the bucket 3.

On the other hand, the boom direction switching valve 14 includes the lever 1
4a is operated to raise the boom 2, a raising position U for raising the boom 2, a lowering position D for lowering the boom 2 by hydraulic pressure, a float position F for lowering the boom 2 by gravity, and stopping the boom 2. It is possible to switch to a neutral position N for performing the operation. At the float position F, the conduit 15a connected to the bottom chamber of the boom cylinder 4 and the conduit 15b connected to the rod chamber are communicated with each other to form a communication passage 15, and the pressure oil in the bottom chamber passes through the communication passage 15 to form a rod. By moving into the room, the boom 2 is allowed to descend due to gravity. Reference numeral 21 denotes a float position detection switch, which when the boom directional control valve 14 is switched to the float position F, is a switch control member 14b that interlocks with the spool.
Is mechanically turned on by and is kept off at other positions.

An electromagnetic switching valve (hereinafter referred to as an electromagnetic valve) 22 is provided in the pipe line 15a. This solenoid valve 22 connects the pipe line 15a without passing through the throttle 22a.
B communicating with the position (first position) via the diaphragm 22a
It can be switched to a position (second position), and the switching is performed by turning on / off the relay 23. Relay 23
The relay coil 23a that constitutes the selector switch 24 for selecting the presence / absence of flow rate adjustment control described later, the boom position detection switch 7 described above, and the float position detection switch 2
It is connectable to the battery BT via 1 and, and is excited when all of these switches are turned on. The relay switch 23b is turned on along with the excitation of the relay coil 23a, whereby the solenoid portion 22b of the switching valve 22 is excited and the solenoid valve 22 is switched from the a position to the b position. In addition, the relay switch 23 is demagnetized along with the demagnetization of the relay coil 23a.
b is turned off, whereby the solenoid portion 22b is demagnetized and the switching valve 22 returns to the a position.

A detent solenoid 25 detents the bucket directional control valve 13 operated to the tilt position T at that position, and releases the detent when the bucket 3 is driven to a predetermined posture. The predetermined posture is a posture in which the bottom surface of the bucket 3 becomes parallel to the ground when the boom 2 descends to the lowermost end.

Next, the operation of the embodiment will be described. FIG. 4 is a diagram showing an example of the earth and sand loading work by the wheel loader WR. At this time, it is assumed that the selection switch 24 is turned on. First, the wheel loader WR is moved forward from the position indicated by P1 while the boom 2 is located at the lowermost end and the bottom surface of the bucket 3 is in contact with the ground horizontally.
As shown by 2, the bucket 3 is thrust into the accumulated soil M. In this state, by operating the operation lever 13a, the bucket directional control valve 1
When 3 is switched from the neutral position N to the tilt position T, the oil discharged from the hydraulic pump 12 is guided to the bottom chamber of the bucket cylinder 5, the bucket cylinder 5 is extended and the bucket 3 is tilt-driven, and the soil in the bucket 3 is reduced. Be taken in.

In this state, the bucket directional control valve 13 is returned to the neutral position N, the wheel loader WR is moved backward, and at the same time, the boom directional control valve 14 is switched to the up position U by the operation lever 14a. As a result, the oil discharged from the hydraulic pump 12 is guided to the bottom chamber of the boom cylinder 4 via the direction switching valve 14, the conduit 15a and the electromagnetic valve 22, and the boom cylinder 4 extends and the boom 2 rises. Here, since the solenoid valve 22 is currently switched to the a position, the pressure oil flowing through the conduit 15a is not throttled regardless of the rotating position of the boom 2, and therefore the boom 2 is quickly raised. be able to.

When the wheel loader WR moves backward to the position P1, the dump truck DC is moved backward to move the wheel loader W.
The wheel loader WR is moved forward in this state. When the bucket 3 moves forward until it is located on the dump vessel DC of the dump truck DC, the bucket directional control valve 13 is switched to the dump position D to drive the bucket 3 to dump, and the soil in the bucket 3 is loaded on the dump vessel.

Next, the dump truck DC is retracted to the position shown in the figure, and then the wheel loader WR is moved forward. At the same time, the bucket direction switching valve 13 is switched to the tilt position T, and the boom direction switching valve 14 is moved to the float position F. Switch. By switching the switching valve 13 to the tilt position T, the bucket 3 performs a tilt operation. Further, by switching the switching valve 14 to the float position F, the float position detection switch 2
When 1 is turned on, a communication passage 15 that connects the bottom chamber of the boom cylinder 4 and the rod chamber is formed. Therefore, the boom 2 descends while contracting the cylinder 4 by its own weight and the weight of the bucket 3, and at this time, the pressure oil in the bottom chamber flows into the rod chamber through the communication passage 15.
Here, since the solenoid valve 22 is still switched to the a position at this point in time, the pressure oil flowing through the communication passage 15 is not throttled. Therefore, the boom 2 descends as indicated by L1 in FIG. 5 and its descending speed. Gradually increases.

On the other hand, the bucket directional control valve 13 is detented at the tilt position T by the detent solenoid 25, and when the bucket 3 is in the above-described predetermined posture, the detent is released and returns to the neutral position N. Boom 2 after that
Continues to descend due to gravity, and when the ground height at its tip reaches h (FIG. 2), the boom position detection switch 7 is turned on by the cam 2a in FIG. At this time, since the selection switch 24 and the float position detection switch 21 are already turned on, the relay coil 23a is excited when the boom position detection switch 7 is turned on, the relay switch 23b is turned on, and the solenoid portion 22b of the solenoid valve 22 is turned on. When excited, the solenoid valve 22 switches from the a position to the b position. As a result, the pressure oil flowing through the communication passage 15 is throttled by the throttle 22a, and its flow rate is reduced, so that the descending speed of the boom 2 is rapidly reduced at point P in FIG. It falls relatively slowly. Therefore, as compared with the case where the boom 2 is lowered as indicated by L3, when the bucket touches the ground (Q
The impact of point) is alleviated.

Since the bucket 3 is held in the predetermined posture as described above, it is grounded in a state where its bottom surface is parallel to the ground, that is, in a posture in which the scooping operation of earth and sand can be started immediately. In this state, the bucket 3 is thrust into the accumulated soil again, and the scooping of soil and sand and the loading of the dump truck DC are repeated in the same manner as described above.

On the other hand, if it is desired to shorten the working time even if the impact relaxation at the time of contacting the bucket is sacrificed, the selection switch 24 may be turned off. In this case, since the relay coil 23a is not excited even if the boom position detection switch 7 and the float position detection switch 21 are both turned on,
The solenoid valve 22 always holds the position a. Therefore, when the boom directional control valve 14 is at the float position F and the ground height of the boom 2 is less than or equal to h, the boom 2 is shown in FIG.
It descends at high speed as indicated by 3.

In the configuration of the above embodiment, the solenoid valve 22
Is a flow rate adjusting means, the float position detecting switch 21 is a float position detecting means, the boom position detecting switch 7 is a height detecting means, and the relay 23 is a controlling means. In the above description, the means for controlling the switching of the solenoid valve 2 is composed of hardware.
The on / off state of No. 4 may be input to the controller, and the controller may switch and control the solenoid valve according to the on / off state of each switch.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. 6 and 7. The same parts as those in FIG. 1 are designated by the same reference numerals, and different points will be mainly described. In FIG. 6, an electromagnetic proportional valve (flow rate adjusting means) 31 is provided in the pipe line 15a connected to the bottom chamber of the boom cylinder 4 instead of the switching valve 22. This solenoid proportional valve 31 has a variable throttle 31a.
And the aperture opening is changed according to the switching amount. 32 is a solenoid portion 31b of the solenoid proportional valve 31.
The controller 32 is a controller (control means) for controlling the applied voltage to the solenoid proportional valve 31 to control the switching amount. The controller 32 includes the boom position detection switch 7, the float position detection switch 21, and the selection switch 24 described above. Each is connected in parallel.

The controller 32 has a solenoid portion 31b.
The voltage applied to the diaphragm 31a is controlled as shown in FIG. 7A, and as a result, the diaphragm aperture of the diaphragm 31a changes as shown in FIG. 7B. According to this, when the boom direction switching valve 14 is switched to the float position F when the selection switch 24 is on, the applied voltage is kept at zero until the ground height of the boom 2 descending by gravity reaches h. Thus, the throttle opening of the variable throttle 31a of the switching valve 31 is held at the maximum value. Therefore, the boom 2 descends as indicated by L1 in FIG. On the other hand, when the ground height of the boom 2 reaches h, the voltage applied to the solenoid portion 31b gradually increases with time, and the diaphragm opening of the variable diaphragm 31a gradually becomes smaller. Therefore, the flow rate of the pressure oil flowing through the communication passage 15 gradually decreases, and the descending speed of the boom 2 gradually decreases as indicated by L4 in FIG.

According to this control, since the deceleration of the boom 2 at the point P in FIG. 5 is smaller than that in the first embodiment, the deceleration shock can be alleviated. Further, since the descending speed of the boom 2 immediately before reaching the point Q is smaller than that in the first embodiment, it is possible to further reduce the impact when the bucket comes into contact with the ground.

The means for detecting the height of the boom is not limited to the switch 7 and may be constituted by, for example, a rotary encoder or a proximity switch. Further, the float position detecting means is not limited to the embodiment, and for example, the lever 14
It may be configured by a switch that is turned on when a is switched to the float position. Further, the flow rate adjusting means is not limited to the solenoid valve 22 or the solenoid proportional valve 31 described above. Furthermore, as explained above with the so-called wheel loader,
The present invention can be similarly applied to the front loader shown in FIG.

[0027]

According to the present invention, when the directional valve is switched to the float position, that is, when the boom descends due to gravity, if the ground height at the tip of the boom falls below a predetermined value, the boom cylinder is lowered. Since the flow rate of the communication passage that connects the bottom chamber and the rod chamber is reduced, it is possible to reduce the descending speed of the boom immediately before the bucket touches the ground and reduce the impact when the bucket touches the ground. In other cases, the flow rate reduction control is not performed, so the boom can be raised and lowered quickly, and work efficiency and metering can be improved. Claim 3 in particular
According to the invention, when the ground height of the boom tip becomes equal to or lower than the predetermined value, the flow rate of the communication passage is gradually decreased according to time, so that the descending speed of the bucket does not decrease sharply during deceleration. It is possible to alleviate the shock and the shock when the bucket touches the ground. Further, according to the invention of claim 4, when the predetermined operation is performed, the flow rate of the pressure oil in the communication passage is maintained at a normal amount regardless of the switching position of the direction switching valve and the ground height of the boom tip. This is effective when it is desired to shorten the work time.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a hydraulic circuit and an electric circuit of a front control device for a wheel loader according to a first embodiment.

FIG. 2 is a side view of a wheel loader.

FIG. 3 is a diagram illustrating a height position detection switch and its operating principle.

FIG. 4 is a diagram showing an example of work of a wheel loader.

FIG. 5 is a diagram showing changes in the descending speed of the boom.

FIG. 6 is a diagram showing a configuration of a hydraulic circuit and an electric circuit in the second embodiment.

FIG. 7 is a time chart showing a voltage applied to the solenoid proportional valve and a change in the throttle opening degree corresponding thereto.

FIG. 8 is a side view showing a conventional front loader.

[Explanation of symbols]

 1 Vehicle Body 2 Boom 3 Bucket 4 Boom Cylinder 5 Bucket Cylinder 7 Boom Position Detection Switch 12 Work Hydraulic Pump 13 Bucket Directional Change Valve 14 Boom Directional Change Valve 15 Communication Passage 21 Float Position Detection Switch 22 Solenoid Valve 22a Throttle 23 Relay 24 Selection switch 31 Electromagnetic proportional valve 31a Variable throttle 32 Controller

Claims (4)

[Claims] 1. A boom cylinder for moving a boom up and down by oil discharged from a work hydraulic pump, a direction switching valve for switching the direction of pressure oil guided to the boom cylinder, and the boom discharged by oil discharged from the work hydraulic pump. And a bucket cylinder that rotates a bucket connected to the tip of the directional control valve, when the directional control valve is switched to the float position,
A front control device for a wheel loader configured such that a rod chamber and a bottom chamber of the boom cylinder communicate with each other through a communication passage and the boom descends due to gravity. A flow rate adjusting unit that adjusts a flow rate of pressure oil flowing through the communication passage. A float position detecting means for detecting that the direction switching valve has been switched to a float position; a height detecting means for detecting that the ground height of the boom tip is below a predetermined value; When it is detected that the ground height of the boom tip is below a predetermined value while the switching of the switching valve to the float position is detected, the flow rate of the pressure oil in the communication passage is reduced in order to reduce the flow rate. A front control device for a wheel loader, comprising: a control unit that controls an adjusting unit. 2. The flow rate adjusting means is interposed in the communication passage and communicates the bottom chamber of the boom cylinder with the rod chamber without a throttle, and the bottom chamber and the rod chamber. And a second position communicating with each other through a throttle, and the control means controls the boom tip to ground when the switching of the directional control valve to the float position is detected. The switch valve is switched to a second position when it is detected that the height is below a predetermined value, and the switch valve is held at the first position otherwise. 1. The front control device for the wheel loader according to 1. 3. The communication means, when the control unit detects that the ground height of the boom tip becomes equal to or lower than a predetermined value while the switching of the direction switching valve to the float position is detected. The front control device for the wheel loader according to claim 1, wherein the flow rate adjusting means is controlled so as to gradually reduce the flow rate of the pressure oil in the passage with time. 4. A command means for outputting a signal for prohibiting the operation of the flow rate adjusting means is provided, and the control means, when the prohibition signal is output, the switching position of the directional control valve and the ground of the boom tip. The front control device for a wheel loader according to claim 1, wherein the flow rate adjusting means is controlled so as not to adjust the flow rate of the pressure oil in the communication passage regardless of the height.