JPH0913428A - Traveling speed change structure of wheel loader - Google Patents

Abstract

PURPOSE: To improve the working efficiency and operability by providing a static oil pressure type continuously variable transmission with an accelerator lever, a pressure regulating mechanism, and so on, whereby at the time of working at a constant low speed, it is not necessary to continue working an accelerator pedal. CONSTITUTION: In the case of working at a constant low speed such as snow removal work, grooving work or the like, a pressure regulating mechanism 41 is operated in such a manner that the pressure of the operating oil supplied to a hydraulic cylinder 14 for changing the angle of a swash plate 9a of a hydraulic pump 9 is a low pressure side designated value. The accelerator position of an engine 8 is artificially changed by an accelerator lever 35 and fixed and held, and even if the rotating speed of the engine 8 is increased and the pressure of a charge pump 15 is increased, the pressure of the operating oil supplied to the hydraulic cylinder 14 is kept at a low pressure designated value by the regulating mechanism 41, so that a static oil pressure type continuously variable speed drive 7 is operated on the low speed side. During low-speed operation, work can be surely conducted without operating the accelerator pedal. Thus, the working performance can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed change structure for traveling in a wheel loader.

[0002]

2. Description of the Related Art Many wheel loaders are equipped with a hydrostatic continuously variable transmission for traveling. For example, as disclosed in JP-A-4-258570, an engine (see FIG. 8), the hydraulic pump of the hydrostatic continuously variable transmission (9 in FIG. 1 of the publication) and the charge pump (15 in FIG. 1 of the publication).
And a part of the hydraulic oil from the charge pump is used to drive the swash plate (9 in FIG. 1 of the above publication).
There is one configured so as to supply to a hydraulic cylinder (14 in FIG. 1 of the above publication) for changing the angle of a).

As a result, when the engine's accelerator pedal (20 in FIG. 1 of the above publication) is stepped on and the engine speed increases, the charge pump speed also increases and the working oil of the charge pump increases. The pressure also increases, and the angle of the swash plate of the hydraulic pump is changed to the high speed side by the hydraulic cylinder. On the contrary, when the accelerator pedal is released and the engine speed decreases, the charge pump speed and hydraulic oil pressure also decrease, and the hydraulic cylinder moves the angle of the swash plate of the hydraulic pump to the low speed side. Changes are being made. As described above, in the wheel loader that performs frequent acceleration / deceleration and forward / reverse switching operations by providing the configuration in which the hydrostatic continuously variable transmission is automatically shifted in conjunction with the accelerator pedal depression operation. , It has good operability.

[0004]

In the above-mentioned wheel loader, it is possible to perform a work which runs at a constant low speed, such as a snow removing work by connecting a snow removing device or a groove digging work by connecting a trainer. There is an increasing demand to make it.

In this case, if the accelerator pedal is slightly depressed, the angle of the swash plate of the hydraulic pump in the hydrostatic continuously variable transmission is changed to the low speed side. Since the number is also low, the engine may be stopped especially when the load becomes large. Further, it is tired for the worker to maintain a state where the accelerator pedal is slightly stepped on with his foot, and there is room for improvement in terms of operability. It is an object of the present invention to configure a wheel loader so that the work of traveling at a constant low speed can be reliably performed.

[0006]

The feature of the present invention resides in the following structure in the traveling speed change structure of the wheel loader as described above. It is equipped with a hydrostatic continuously variable transmission for traveling, and is configured to drive the hydraulic pump and the charge pump of the hydrostatic continuously variable transmission by the power of the engine, and part of the hydraulic oil from the charge pump is driven. The swash plate angle of the hydraulic pump is supplied to the hydraulic cylinder, and when the engine speed increases, the hydraulic cylinder from the charge pump changes the swash plate angle of the hydraulic pump to the high speed side. And an accelerator lever that can be fixedly held by artificially changing the accelerator position of the engine, and a pressure adjustment mechanism that can set and change the pressure of the hydraulic oil from the charge pump to the hydraulic cylinder arbitrarily. With.

[0007]

According to the structure of the present invention, when the work is performed at a constant low speed, the pressure of the hydraulic oil supplied from the charge pump to the hydraulic cylinder for changing the angle of the swash plate of the hydraulic pump is changed. It suffices to operate the pressure adjusting mechanism so that the pressure becomes a predetermined value on the low pressure side, and operate the accelerator position of the engine with the accelerator lever to increase the rotational speed of the engine.

When the engine speed is increased by the accelerator lever in this manner, the rotation speed of the charge pump increases and the pressure of the hydraulic oil of the charge pump also increases. Since the pressure of the hydraulic oil supplied to the low-pressure side is maintained at a predetermined value on the low-pressure side, the hydrostatic continuously variable transmission is in the state of shifting to the predetermined position on the low-speed side, and the wheel loader operates at a low constant speed. Drive in. In this case, since the engine speed is increasing, the engine will not be stopped even if the load is increased. Further, since the accelerator lever is configured to be fixedly held, the accelerator lever is held at that position even if the accelerator lever is released.

Next, when the wheel loader is used in the usual working condition, the pressure adjusting mechanism may not be operated. As a result, when the accelerator pedal is depressed to increase the engine speed, the hydraulic cylinder changes the angle of the swash plate of the hydraulic pump to the high speed side, and the accelerator pedal is released to lower the engine speed. Then, the angle of the swash plate of the hydraulic pump is changed to the low speed side by the hydraulic cylinder.

[0010]

As described above, in the traveling speed change structure of the wheel loader, it is possible to surely perform the work of traveling at a low constant speed while preventing the engine from stopping especially when the load becomes large. We were able to improve the work performance of the wheel loader. In this case, since the vehicle can travel at a constant low speed even if the accelerator lever is released, the operability is also improved.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 2, a front vehicle body 2 having a pair of left and right front wheels 1 and a rear vehicle body 4 having a pair of left and right rear wheels 3,
The front vehicle body 2 is connected so as to be swingable around the vertical axis P1.
A wheel loader is configured by including a shovel 6 via a pair of left and right arms 5 and a hitch 12 that connects various working devices (snow removing device, trainer, backhoe device, etc.) to the rear end of the rear vehicle body 4. .

This wheel loader is equipped with a hydrostatic continuously variable transmission 7 for traveling. As shown in FIG. 1, a hydrostatic continuously variable transmission 7 includes an axial plunger type hydraulic pump 9 driven by an engine 8 (forward / backward switchable and continuously variable shift operation), and an output side hydraulic motor 1.
The hydraulic pump 9 is equipped with
And a hydraulic motor 10 and a pair of oil passages 11a and 11b are connected to each other.
(See FIG. 1) A hydraulic pump 21 that supplies hydraulic oil to the like, and a charge pump 15 are driven by the engine 8.

A double-acting hydraulic cylinder 14 biased toward the neutral side by a pair of springs 14a is provided, and the hydraulic cylinder 14 is connected to a swash plate 9a of the hydraulic pump 9. The oil passage 16 from the charge pump 15 is connected to the hydraulic cylinder 14 via the filter 22, the pressure reducing valve 23, and the electromagnetically operated switching valve 18, and the oil passage 24 branched from before the pressure reducing valve 23 is the charge oil passage 17. It is connected to the. Switching valve 18
A switching lever 19 for operating the engine is provided, and the accelerator portion 8a of the engine 8 and the accelerator pedal 20 are connected via a push-pull wire 25.

A negative brake 31 is provided which is operated on the braking release side by being supplied with hydraulic oil by a spring (not shown) on the braking side, and between the filter 22 and the pressure reducing valve 23. An oil passage 32 branched from is connected to the negative brake 31 via an electromagnetically operated switching valve 33. As a result, when the engine 8 is stopped (when the charge pump 15 is stopped), the negative brake 3
When 1 is operated to the braking side and the switching valve 33 is operated to the supply position, when the engine 8 is started, the negative brake 31 is operated to the braking release side by the hydraulic oil from the charge pump 15. . And engine 8
When the switching valve 33 is operated to the oil drain position even during the operation of, the negative brake 31 is operated to the braking side.

With the above structure, when the accelerator pedal 20 is depressed, the rotation speed of the engine 8 rises, and the hydraulic pump 9 and the charge pump 1 of the hydrostatic continuously variable transmission 7 are increased.
As the rotation speed of No. 5 increases, the angle of the swash plate 9a of the hydraulic pump 9 is changed to the high speed side by the hydraulic cylinder 14, and the switching valve 18 is operated to the forward and backward positions by the switching lever 19. Change the direction of hydraulic oil and perform forward / backward switching operation. Conversely, when the accelerator pedal 20 is returned and the rotation speed of the engine 8 decreases, the rotation speeds of the hydraulic pump 9 and the charge pump 15 decrease, and the hydraulic cylinder 14 causes the swash plate 9a of the hydraulic pump 9 to move. The angle is changed to the low speed side.

As shown in FIG. 1, a hydraulic cylinder 26 for shifting the hydraulic motor 10 of the hydrostatic continuously variable transmission 7 into two high and low stages is provided, and a hydraulic cylinder 26 is provided between the switching valve 18 and the hydraulic cylinder 14. The pair of oil passages 27a and 27b are branched so that the oil passages 27a and 27b are pilot operated type selection valves 2.
8 and an electromagnetically operated low speed holding valve 29, which is connected to a pilot operated type operating valve 30 of the hydraulic cylinder 26. Forward hydraulic passage 1 in hydrostatic stepless transmission 7
The oil passage 34a branched from 1a and the oil passage 34b branched from the reverse-side oil passage 11b are connected to the hydraulic cylinder 26 via a selection valve 28, a low speed holding valve 29, and an operation valve 30.

With the structure described above, when the accelerator pedal 20 is stepped on while the switching valve 18 is in the forward position, the selection valve 28 is moved to the forward position by the hydraulic oil from the oil passage 27a (see FIG. 1). Is operated to the right side of the drawing from the state shown in (1) to move the hydraulic oil in the forward-side oil passage 11a from the oil passage 34a through the selection valve 28, the low speed holding valve 29 and the operation valve 30 to the hydraulic cylinder. 26. As a result, as the angle of the swash plate 9a of the hydraulic pump 9 is changed to the forward high speed side by the hydraulic cylinder 14 by depressing the accelerator pedal 20, the hydraulic cylinder 26 moves the hydraulic motor 10 to the low speed side. The speed is changed to the high speed side.

On the contrary, when the accelerator pedal 20 is stepped on while the switching valve 18 is being operated to the reverse position, the selection valve 28 is moved to the reverse position by the hydraulic oil from the oil passage 27b (the state shown in FIG. 1). ) To operate the oil passage 11 on the reverse side.
The hydraulic oil b is supplied from the oil passage 34b to the hydraulic cylinder 26 via the selection valve 28, the low speed holding valve 29 and the operation valve 30. As a result, the swash plate 9a of the hydraulic pump 9 is moved by the hydraulic cylinder 14 when the accelerator pedal 20 is depressed.
As the angle is changed to the reverse high speed side, the hydraulic cylinder 26 shifts the hydraulic motor 10 from the low speed side to the high speed side.

As shown in FIG. 1, an accelerator lever 35 is provided separately from the accelerator pedal 20. The operation rod 36 is inserted into the end portion of the push-pull wire 25 on the accelerator portion 8a side, and the accelerator lever 35 and the operation rod 36 are connected via the wire 37, and the accelerator lever 35 is rubbed at any operation position. A holding mechanism 38 capable of holding is provided.

With the above structure, when the accelerator lever 35 is operated to the high speed side, the operation rod 36 is slid rightward on the paper surface of FIG. 1, and the contact portion 3 of the operation rod 36 is moved.
6a allows push-pull wire 25 and accelerator portion 8
Since a is operated toward the high speed side, when the operator releases the accelerator lever 35, the holding mechanism 38 holds the accelerator lever 35 and the accelerator portion 8a at the operating position.

As a result, the accelerator portion 8a can be held at an arbitrary operating position and the vehicle can travel at a constant speed. If the accelerator pedal 20 is depressed in this state,
The accelerator portion 8a can be temporarily operated to the high speed side from the operation position where the accelerator portion 8a is held, and when the foot is released from the accelerator pedal 20, the accelerator portion 8a returns to the above-mentioned held operation position. When the deceleration pedal 40 connected to the pressure reducing valve 23 is stepped on while the accelerator portion 8a is held at an arbitrary operating position at a constant speed, the pressure of the hydraulic oil from the charge pump 15 is slightly reduced by the pressure reducing valve 23. The pressure is reduced, and the angle of the swash plate 9a of the hydraulic pump 9 is slightly changed to the low speed side. When the deceleration pedal 40 is released, the vehicle returns to the original traveling state at a constant speed.

As shown in FIG. 1, the pressure reducing valve 23 and the switching valve 18
A mechanically operated variable throttle valve 41 (corresponding to a pressure adjusting mechanism) is connected in parallel between and, and the variable throttle valve 41 is connected to the tank 42. With the above structure, when performing work at a constant low speed, the variable throttle valve 41 is set so that the pressure of the hydraulic oil supplied from the charge pump 15 to the hydraulic cylinder 14 becomes a predetermined value on the low pressure side. The engine 8 is operated to the open side, and the accelerator lever 35 is operated to the high speed side to increase the rotation speed of the engine 8.

As described above, when the rotation speed of the engine 8 is increased by the accelerator lever 35, the rotation speed of the charge pump 15 increases and the pressure of the hydraulic oil of the charge pump 15 also increases. Since the pressure of the hydraulic oil supplied to the hydraulic cylinder 14 by the valve 41 is kept at a predetermined value on the low pressure side, the angle of the swash plate 9a of the hydraulic pump 9 in the hydrostatic continuously variable transmission 7 is set to the low speed side. The wheel loader travels at a constant low speed while being held at a predetermined position. When the accelerator pedal 20 is used to freely change the angle of the swash plate 9a of the hydraulic pump 9 as described above, the variable throttle valve 41 is operated to the closed side so that the variable throttle valve 41 does not function. .

[Other Embodiments] In the structure shown in FIG. 1, the variable throttle valve 41 cannot be operated to the open side unless the accelerator lever 35 is operated to the maximum speed position, and the accelerator lever 35 is operated to the maximum speed. When operating from the position to the low speed side,
The variable throttle valve 41 may be automatically closed. Instead of the mechanically operated variable throttle valve 41, an electromagnetic proportional pressure reducing valve may be used as a pressure adjusting mechanism.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram of a hydrostatic continuously variable transmission.

[Fig. 2] Overall side view of the wheel loader

[Explanation of symbols]

 7 Hydrostatic Stepless Transmission 8 Engine 9 Hydraulic Pump 9a Hydraulic Pump Swash Plate 14 Hydraulic Cylinder 15 Charge Pump 35 Accelerator Lever 15 Charge Pump 41 Pressure Adjustment Mechanism

Claims (1)

[Claims] 1. A hydrostatic continuously variable transmission (7) for traveling, comprising a hydraulic pump (9) and a charge pump () of the hydrostatic continuously variable transmission (7) by the power of an engine (8). 15) and drives a part of the hydraulic oil from the charge pump (15) to the hydraulic pump (9).
Hydraulic cylinder (1) for changing the angle of the swash plate (9a)
4), and when the rotation speed of the engine (8) increases, the hydraulic cylinder (14) moves the hydraulic cylinder (14) from the charge pump (15) to the swash plate (9a) of the hydraulic pump (9). Is configured so as to change the angle of the engine to a high speed side, and the accelerator position of the engine (8) can be artificially changed and fixedly held, and from the charge pump (15) to the accelerator lever (35). A traveling speed changing structure for a wheel loader, comprising: a pressure adjusting mechanism (41) capable of arbitrarily setting and holding and changing the pressure of hydraulic oil to a hydraulic cylinder (14).