JPH09217384A - Driving force switching device for wheel loader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the working efficiency by setting driving force (excavating force) and working speed to conditions suitable for the work of a wheel loader. SOLUTION: This device has a combining piping 18 having pumps 2, 3 driven by the same prime mover 1, which combines the discharge pressure oils of the pumps 2, 3. A wheel loader having a shift down switch 19 for shifting down a transmission gear from second speed to first speed has a selector 24 for laying one pump 3 into unload state in interlocking with the input operation of the shift down switch 19. Thus, when a operator shifts down the transmission gear from the second speed to the first speed by the input operation of the shift down switch 19, the one pump 3 is laid in the unload state, whereby a high driving force can be provided. When the unload state is released in interlocking with the operation of switching the transmission gear to neutral or backward, the following operation can be quickly performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving force switch for a wheel loader for excavating earth and sand from ground or the like, scraping raw materials, or scooping rough stones and loading them into dumps. It concerns the device.

[0002]

2. Description of the Related Art Conventionally, a wheel loader has been used for excavating earth and sand from the ground or scooping rough stones and loading them into dumps or the like. Also,
A wheel loader is also used for scraping raw materials and the like piled up in a wide range of places in a mountain shape.

[0003] Explaining the excavation work by the wheel loader as an example, the bucket provided at the front part is slightly lifted off the ground, and is driven into the earth and sand by the driving force of the tire. Scooping the excavated earth and sand into the bucket by rotating the bucket, and then carrying the earth and sand above the dump while retreating or turning while raising the boom, and moving the tip of the bucket above the dump. The dump is loaded with earth and sand by turning it downward. Therefore, in this work, it is optimal from the viewpoint of work efficiency that the boom is moved while being lifted after excavation and the equipment is set such that the boom is positioned at the upper end when loading the dump. This is the same as in the case of rough stones, because the same operation is performed to scoop up the bucket and transport it to a desired position or load it into a transport machine such as a dump truck. On the other hand, in the case of the scraping work, the scooped raw materials are repeatedly piled up on the spot.

[0004] As a driving force switching device in this type of wheel loader, there is a device as shown in a hydraulic circuit diagram of FIG. 5, and a first pump 52 and a second pump 53 driven by a prime mover 51 are provided. Is supplied to the steering switching valve 54B via the flow control valve 54A of the steering operation valve 55 to drive the steering cylinder 56, and the pressure oil discharged from the second pump 53 is supplied to the working machine operation valve. There is a configuration in which a bucket cylinder 58 and a boom cylinder 59 are supplied to the cylinder 57 to drive the bucket cylinder 58 and the boom cylinder 59. In this configuration, the discharge pressure oil of the first steering pump 52 flows to the work equipment operation valve 57 when the steering is not used, and the flow required for turning the steering is only used when the steering is not used. The flow is controlled to flow to the switching valve 54B side.

When a large working force is applied, such as when excavating earth and sand, the pressure oil pipe 6 discharged by the second pump 53
Since the pressure in 0 increases, the pressure of this pressure oil is detected, the second pump 53 is unloaded by the unload valve 61, and only the pressure oil discharged from the first pump 52 is supplied to the working machine operation valve 57. The power is supplied, the absorption horsepower of the pump is reduced, and the driving power of the wheels is increased by the power of the prime mover 51 to improve the working capacity (conventional example 1).

As a conventional technique of this type of hydraulic circuit, there is a device described in Japanese Utility Model Laid-Open No. Sho 60-75701. In this device, if the pressure of the pressure oil rises while the boom is rotated upward, it is unloaded. In order to solve the problem that the valve is unloaded and the flow rate of supply to the boom cylinder decreases, the boom rising speed slows down and work efficiency deteriorates, the pressure oil is Even if the pressure becomes high, the unload valve can be switched so as not to be in the unload state (conventional example 2).

There is also another device described in Japanese Utility Model Application Laid-Open No. 4-61154. In this device, a cutoff valve for unloading a hydraulic circuit can be easily mounted and removed, and an extra pipe is eliminated. Therefore, an additional operation valve provided with a cutoff valve is provided (conventional example 3).

Further, another conventional technique is disclosed in Japanese Patent Laid-Open No. 2-9 / 1990.
Although there is an invention described in Japanese Patent No. 1328, in this invention, 3
Two pumps are driven by the same prime mover to obtain a traveling drive force, thereby trying to optimize the traveling torque.
According to the present invention, it is possible to select whether or not the discharge oil of one pump is to be unloaded by manual operation (conventional example 4).

The prior art relating to the downshift switch of the driving force switching device according to the present application is disclosed in Japanese Patent Publication No.
There is an invention described in US Pat.
A technique is described in which a shift down switch is provided on a work implement operation lever that allows an operator to shift down a transmission gear from a second speed to a first speed at an optimum timing and with an easy operation at the time of excavating earth and sand. Have been.

[0010]

However, the hydraulic circuit of the prior art 1 does not enter the unload state unless the pressure of the hydraulic oil in the circuit becomes higher than a set value by cutting the bucket into earth and sand. In addition, the operator cannot intentionally put one pump into the unload state during work requiring high excavation force, that is, high driving force.
In addition, when the boom is rotated upward as in the loading operation, the circuit pressure increases and the second pump 53 is brought into the unload state, so that the operation speed is reduced.

Further, in the hydraulic circuit of the second conventional example, even when the boom is turned upward, the unload prohibition switch is turned on at a predetermined angle as in the first conventional example, so that the speed does not decrease during the turning. However, depending on the contents of the work, the setting of the switch for switching to unload prohibition may need to be changed. Further, in the case of this conventional example, when a large wheel driving force is required but the speed of the work machine (boom / bucket) may be low, such as when the boom is turned upward during the lifting operation, the worker is However, it is impossible to arbitrarily set the vehicle in the unloaded state even if the vehicle desires to obtain a large wheel driving force.

As described above, the operation of the wheel loader may be performed with a small driving force as in the case of a dump loading operation, but it is necessary to prohibit unloading when it is desired to work quickly. Since there are various cases in which unloading prohibition is not required when a driving force is required, is the work required to be in the unloading state only by the pressure of the pressure oil as in Conventional Example 2? It cannot be unambiguously determined.

Also, in the conventional example 3, similarly to the conventional example 2, the unloading state of the pump cannot be switched to obtain a large driving force or a high working speed according to the work content.

Further, in the above-mentioned conventional example 4, it is possible to select whether or not to use the unload valve by manual operation. However, in this conventional example 4, as described in the above-mentioned conventional example 2, even a small driving force is used. The operator needs to manually switch the valve depending on whether he wants to work quickly but is slow but needs a large driving force. In it, it is difficult to improve the work efficiency.

[0015]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the invention according to the present application provides a downshift switch for downshifting a transmission gear from a second speed to a first speed, and an operator turns on the downshift switch. By doing so, in conjunction with this operation, one of the pumps is unloaded to reduce the absorption horsepower of the pump, thereby increasing the driving force of the wheels and exerting a high excavation force. This makes it possible to improve the working efficiency by setting the driving force (digging force) and the working speed to conditions suitable for the work of the wheel loader.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to this application includes a first pump and a second pump driven by the same prime mover,
A steering circuit for supplying pump pressure oil to the steering operation valve, a work machine circuit for supplying discharge pressure oil of the second pump to the work valve operation valve, and a merging circuit for merging these circuits. A wheel loader provided with a downshift switch for downshifting the transmission gear from second gear to first gear by an on operation.
Providing a switching valve for unloading the pressure oil discharged from the pump, switching the switching valve in conjunction with the on / off operation of the downshift switch to bring the second pump into the unloaded state, and bringing the transmission gear into neutral or reverse. Control means for canceling the unload state of the switching valve in conjunction with the control.

Thus, by shifting down the transmission gear from the second speed to the first speed by the shift down switch,
Since the second pump is brought into the unloading state in conjunction with this operation, the absorbed horsepower of the pump is reduced, and the horsepower can be used as the driving force of the wheels to exert a high driving force. This second
The unloading state of the pump is interlocked with the on-operation of the shift-down switch performed by the operator requiring the wheel driving force. If the transmission gear is switched to neutral or reverse after completion of work requiring high driving force in the first speed, the unload state of the second pump is released, so that the excavated object in the bucket can be transported at a high speed. Can be stowed.

Furthermore, a first pump, a second pump and a third pump driven by the same prime mover are provided, and the discharge pressure oil of the first pump is used as a switching valve for steering, and the discharge pressure oil of the second pump is used as a flow control valve. Steering circuit for supplying to the
A work machine circuit for supplying the discharge pressure oil of the pump to the work machine operation valve; and a joining circuit for joining the circuit of the second pump and the circuit of the third pump.
In a wheel loader provided with a downshift switch for downshifting from the first speed to the first speed, a switching valve for unloading the hydraulic oil discharged from the second pump is provided in the work machine circuit, and is linked with an on operation of the downshift switch. The same applies if control means is provided for switching the switching valve to bring the second pump into the unloaded state and releasing the unloaded state of the switching valve in conjunction with the operation of shifting the transmission gear to neutral or reverse. By shifting down the transmission gear from the second speed to the first speed with the downshift switch, the second pump is unloaded in conjunction with this operation, so that the absorption horsepower of the pump decreases, and the horsepower is reduced to the driving force of the wheels. To achieve high driving force. The unloading state of the second pump is linked to the turning-on operation of the shift-down switch performed by the operator requiring the wheel driving force. Also,
If the transmission gear is switched to neutral or reverse after the work requiring a high driving force at the first speed is completed, the unloading state of the second pump is released and the excavated object in the bucket can be transported or loaded at a high speed. it can.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a hydraulic circuit diagram showing a first embodiment of the invention according to this application in a normal state, and FIG. 2 is a hydraulic circuit diagram showing an unload state of the same embodiment.

As shown, the first embodiment is of a two-pump type, in which a first pump 2 and a second pump 3 driven by a prime mover 1 are provided, and a pressure oil pipe 4 of the first pump 2 is provided. Connected to the flow control valve 5A of the steering operation valve 6,
The flow rate of the pressure oil is adjusted by the flow rate adjusting valve 5A and supplied to the steering switching valve 5B. This circuit is a steering circuit. And the switching valve for steering 5B
Is connected to a steering cylinder 8 by a pipe 7. The return pipe 9 is connected to the switching valve 5B for steering.
And is configured to return the pressure oil after driving the steering cylinder 8 to the tank T.

The pressure oil pipe 10 of the second pump 3 is connected to a check valve 11
Is connected to the working machine control valve 12 via. This circuit is a working machine circuit. And the operating valve 12 for the working machine
Are connected to a bucket cylinder 14 and a boom cylinder 16 by pipes 13 and 15. The pressure oil after driving the bucket cylinder 14 and the boom cylinder 16 and the pressure oil when not in use are configured to return to the tank T from the return pipe 17 provided in the operation valve 12 for the working machine.

The flow control valve 5A and the working machine operation valve 12 are connected by a merge pipe 18 which is a merge circuit, and when the steering is not used, the pressure oil of the first pump 2 is supplied to the flow control valve 5A. Is supplied to the working machine operating valve 12 through a junction pipe 18 so that a quick operation can be performed by a large flow rate of pressure oil.

On the other hand, in the invention according to this application, a shift gear provided in a traveling transmission G driven by the prime mover 1 via a torque converter C is used to shift down from a second speed to a first speed. A down switch 19 is provided, and a controller 20 for detecting an ON operation of the down-shift switch 19 is electrically connected by a wiring 21. The controller 20 and the transmission G
Are electrically connected to each other by the wiring 22, and the controller 20 shifts down the gear in the transmission G from the second speed to the first speed by turning on the downshift switch 19. . Note that the controller 20 is electrically connected to the signal with the forward-reverse switching lever L ₁ and the speed stage switching lever L ₂ is input.

A branch pipe 23 is provided in the pressure oil pipe 10 between the second pump 3 and the check valve 11, and a switching valve 24 is provided in the branch pipe 23. This switching valve 2
The pressure oil that has passed through 4 is configured to return to the tank T by the return pipe 25. The switching valve 24 normally closes the pipeline in the state of FIG. 1, and the pressure oil discharged from the second pump 3 does not flow to the return pipe 25 side.

The controller 20 and the switching valve 24 are electrically connected by a wiring 26.
When the shift down switch 10 is turned on, the controller 20 causes the switching valve 24 to move from the closed state of FIG.
It is configured to switch to the communication state.

According to the driving force switching device for a wheel loader according to the first embodiment configured as described above, the driving force can be switched by the following operation.

That is, in a loading operation or the like where quickness is required, as shown in FIG. 1, the pressure oil discharged from the first pump 2 and not used for steering driving (black arrow). ) And the pressure oil (white arrow) discharged from the second pump 3 are supplied to the operating valve 12 for the working machine, and the operating valve 12 for the working machine causes the bucket cylinder 14 or the boom cylinder 16 to be actuated by the high-flow pressure oil. It can be moved quickly for efficient work. Since the prime mover 1 drives the two pumps 2 and 3 at this time, the driving force of the wheels is small. The pressure oil discharged from the second pump 3 also flows to the branch pipe 23 but is blocked by the switching valve 24.

On the other hand, when performing low speed work such as excavation work, the controller 20 shifts down the transmission gear of the transmission G from the second speed to the first speed by turning on the shift down switch 19. Then, the controller 20 switches the switching valve 24 to the communication state of FIG. Therefore, the pressure oil (white arrow) discharged from the second pump 3 returns to the tank T from the return pipe 25 via the switching valve 24, and the second pump 3 enters the unload state.

Accordingly, in this state, only the pressure oil (black arrow) discharged from the first pump 2 is supplied to the working machine operation valve 12 via the flow control valve 5A and the junction pipe 18. At this time, the pressure oil in the junction pipe 18 does not flow toward the branch pipe 23 by the check valve 11.

When one of the pumps is brought into the unloading state in this manner, the absorption horsepower of the pump decreases, and the horsepower of the prime mover 1 is used as the wheel driving force, whereby the working capacity can be increased. Moreover, in the invention according to this application, the downshifting of the transmission gear and the switching of the second pump 3 to the unload state are performed simultaneously in conjunction with the downshift switch 19, so that the second pump 3 is unloaded. The wheel drive power is automatically increased without the need for special operation.

This is because, in this kind of wheel loader, when the work requiring a large driving force, the working speed is preferably low, so that the relationship between the driving force and the speed is automatically determined only by turning on the shift down switch 19. Therefore, it is possible to achieve a state that is optimally suitable.

Further, by switching the transmission gear is switched by the input operation of the shift down switch 19 from the second speed to the first speed to the neutral or reverse by the forward-reverse switching lever L _1, the signal from the lever L ₁ is the controller 2
0, the controller 20 switches the switching valve 24 from the communicating state to the closed state. That is, the unload state of the switching valve 24 is released. Accordingly, the pressurized oil of the second pump 3 is supplied from the pressurized oil pipe 10 to the operation valve 12 for the working machine, so that the quick operation of rotating the bucket or the boom can be performed by the two pumps 2 and 3. it can.

This is because, for example, when an excavated object excavated by a wheel loader is loaded into a dump,
At the time of digging, a high digging force is required at a low speed, so that the second pump 3 is unloaded at the same time as the shift down switch 19 is operated to become one pump, thereby exhibiting a high driving force. When the gears are loaded into the dump truck, the shifting gear is put into reverse, and at the same time, the unloading state of the second pump 3 is released, so that the two pumps can be used to quickly raise the boom and rotate the bucket. The entire work flow can be performed efficiently.

Further, since the work is always performed at a low speed during the lifting operation, a high driving force is exerted even when the boom is turned upward only by turning on the shift down switch 19 immediately before the bucket is bitten into the earth and sand. It becomes possible.

Next, a second embodiment of the invention according to the present application will be described with reference to a hydraulic circuit diagram in a normal state shown in FIG. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

As shown, the second embodiment is of a three-pump type, and includes a first pump 2, a second pump 3, and a third pump 30 driven by a prime mover 1. First
The pressure oil pipe 27 of the pump 2 is connected to the steering switching valve 5B of the steering operation valve 6, and the pressure oil pipe 28 of the second pump 3 is connected to the flow control valve 5A of the steering operation valve 6.
The hydraulic oil of the first pump 2 is used exclusively for steering, and the hydraulic oil of the second pump 3 is supplied with a necessary amount of hydraulic oil only when a shortage occurs in the first pump 2. And supplied to the steering switching valve 5B.
This circuit is a steering circuit. The pressure oil pipe 28 is provided with a check valve 29 for preventing pressure oil from flowing backward from the flow control valve 5A side.

The third pump 30 is connected to the working machine operating valve 12 via a pressure oil pipe 31. This circuit is a working machine circuit.

The flow control valve 5A and the operating valve 12 for work equipment are connected by a junction pipe 18. When the steering is not used, the entire pressure oil of the second pump 3 is connected to the flow control valve 5A from the junction pipe. The working oil is supplied to the working machine operating valve 12 via 18 so that a large amount of pressure oil can be used for quick work.

The other structures are the same as those described in the first embodiment.
The description is omitted because it is the same as the embodiment.

According to the driving force switching device for the wheel loader according to the second embodiment configured as described above, the driving force can be switched by the following operation.

That is, in a loading operation or the like where quickness is required, as shown in FIG. 3, the pressure oil discharged from the second pump 3 and not used for steering driving (white arrow). ) And the pressure oil (black arrow) discharged from the third pump 30 are supplied to the working machine operating valve 12, and the working machine operating valve 12 operates the bucket cylinder 14 or the boom cylinder 16 by the large flow rate of the working oil. It can be moved quickly for efficient work. At this time, since the three pumps 2, 3, and 30 are driven by the prime mover 1, the driving force of the wheels is small, but quick work can be performed. The pressure oil discharged from the second pump 3 also flows to the branch pipe 23 but is blocked by the switching valve 24.

On the other hand, when performing a low-speed operation such as an excavation operation, the controller 20 shifts down the transmission gear of the transmission G from the second speed to the first speed by turning on the shift-down switch 19. Then, the controller 20 switches the switching valve 24 to the communicating state (see FIG. 2) in conjunction with the input operation. Therefore, the pressure oil (white arrow) discharged from the second pump 3 returns to the tank T from the return pipe 25 via the switching valve 24, and the second pump 3 enters the unload state (see the white arrow in FIG. 2). ).

Accordingly, in this state, only the pressure oil (black arrow) discharged from the third pump 30 is supplied to the operation valve 12 for the working machine.

When one pump is unloaded in this way, the absorption horsepower of the pump decreases, and the horsepower of the prime mover 1 is used for the wheel driving force, thereby increasing the working capacity. Further, similarly to the first embodiment, the downshifting of the transmission gear and the switching of the second pump 3 to the unload state are simultaneously performed in conjunction with the downshift switch 19, so that the second pump 3
The wheel drive power is automatically increased without requiring any special operation for unloading the vehicle.

Therefore, in the second embodiment as well, the first
Similarly to the embodiment, the relationship between the driving force and the speed can be automatically set to a suitable state only by the ON operation of the shift-down switch 19, and the transmission gear switched to the first speed by the shift-down switch 19 can be changed. By switching to neutral or reverse, the unloading state of the switching valve 24 can be released and the buckets or booms can be quickly rotated by the pumps 3 and 30, thereby enabling the overall work flow of the wheel loader to be reduced. It can be performed efficiently.

In the first and second embodiments, the second
Although only the switching valve 24 is used as the unloading means for the pump 3, as shown in the hydraulic circuit diagram of FIG. 4, if the unloading valve 32 with the vent port and the switching valve 33 are combined, the switching valve 33 has a small capacity. An unloading means can be configured. As the unloading means, other known unloading means using an electric signal may be used, and the present invention is not limited to these configurations.

[0047]

The invention according to the present application is configured as described above, and has the following effects.

According to the driving force switching device for the wheel loader according to the first and second aspects, a high driving force can be obtained by turning the second pump into the unloaded state only by the operator turning on the downshift switch. By switching the transmission gear to neutral or reverse, the unloading state of the pump is released and quick work can be performed, so that it is possible to easily set the relationship between the driving force and the working machine speed to favorable conditions, The work flow by the wheel loader can be performed efficiently, and the overall work efficiency can be improved.

In particular, the above-described effect can be obtained in the configuration of two pumps in the first embodiment and the configuration of three pumps in the second embodiment.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing a normal state of a first embodiment of a driving force switching device for a wheel loader according to the present application.

FIG. 2 is a hydraulic circuit diagram showing the circuit of FIG. 1 in an unloaded state.

FIG. 3 is a hydraulic circuit diagram showing a normal state of a second embodiment of the driving force switching device for the wheel loader according to the present application.

FIG. 4 is a hydraulic circuit diagram showing a normal state in which another unloading means is used in the driving force switching device shown in FIG. 1;

FIG. 5 is a hydraulic circuit diagram of a conventional wheel loader.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... 1st pump 3 ... 2nd pump 4 ... Pressure oil piping 5A ... Flow control valve 5B ... Steering switching valve 6 ... Steering operation valve 7, 13, 15 ... Piping 8 ... Steering cylinder 9, 17, 25 ... Return pipe 10 ... Pressure oil pipe 11 ... Check valve 12 ... Work equipment operating valve 14 ... Bucket cylinder 16 ... Boom cylinder 18 ... Combined pipe 19 ... Shift down switch 20 ... Controller 21,22,26 ... Wiring 23 ... Branch pipe 24 ... Switching valve 27 ... Pressure oil pipe 28 ... Pressure oil pipe 29 ... Check valve 30 ... Third pump 31 ... Pressure oil pipe 32 ... Unloader valve with vent port 33 ... Switch valve T ... Tank G ... Transmission C … Torque converter L ₁ … Leverage forward / reverse switching lever L ₂ … Speed stage switching lever

Claims (2)

[Claims] A first pump and a second pump driven by the same prime mover, a steering circuit for supplying a discharge pressure oil of the first pump to a steering operation valve, and a discharge circuit of a second pump. A wheel loader comprising: a work machine circuit to be supplied to a work machine operation valve; and a merging circuit for merging these circuits, and provided with a downshift switch for downshifting the transmission gear from the second speed to the first speed by an on operation. In the working machine circuit, a switching valve for unloading the hydraulic oil discharged from the second pump is provided, and the switching valve is switched in conjunction with the ON operation of the downshift switch to bring the second pump into the unload state. A driving force switching device for a wheel loader, further comprising control means for releasing an unloaded state of the switching valve in conjunction with an operation of shifting the transmission gear to neutral or reverse. A first pump, a second pump, and a third pump driven by the same prime mover, wherein a discharge pressure oil of the first pump is used as a switching valve for steering, and a discharge pressure oil of a second pump is used as a flow regulating valve. , A working machine circuit for supplying the discharge pressure oil of the third pump to the working machine operation valve, and a merging circuit for merging the circuit of the second pump and the circuit of the third pump. A wheel loader provided with a shift-down switch for shifting down a transmission gear from a second speed to a first speed by an on-operation, wherein a switching valve for unloading pressure oil discharged from a second pump is provided in the working machine circuit. The second pump is switched to the unload state by interlocking with the operation of turning on the downshift switch, and the second pump is unloaded. The unload state of the switching valve is interlocked with the operation of shifting the transmission gear to neutral or reverse. Driving force switching device of the wheel loader, characterized in that a control means for releasing the.