JPH05306768A - Hst hydraulic traveling driving device - Google Patents

Abstract

PURPOSE:To obtain the HST hydraulic traveling driving device, which can automatically select the inertial traveling and the HST traveling. CONSTITUTION:A bypass pipeline 21 is provided between main pipelines 3, 4 for connecting a hydraulic pump 2 to a hydraulic motor 5, and a switching valve 22 and a check valve 24 are provided on the way thereof. The switching valve 22 is switched in interlinking with a speed change switch 29 for changing a transmission 10 between a low speed stage and a high speed stage, and the switching valve 22 is positioned at the (F) position in the high speed stage side to enable the inertial traveling, and the switching valve 22 is positioned at the (R) position in the low speed stage side to fix the HST traveling. The check valve 24 is provided so as to be opened when the pressure of the main pipeline 4 as the discharge side of the hydraulic motor 5 exceeds the pressure of the main pipeline 3 at the time of forward traveling to prevent the flow-out of the discharge oil from the main pipeline 3 to the main pipeline 4 when an acceleration pedal is depressed at the time of forward traveling of a vehicle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an HST hydraulic traveling drive system used in a work vehicle such as a wheel loader.

[0002]

2. Description of the Related Art As a hydraulic traveling drive system for a work vehicle such as a wheel loader, a variable displacement hydraulic pump driven by a prime mover and a variable displacement driven by a pair of main pipes are disclosed, for example, in Japanese Utility Model Publication No. 3-12659. There is known an HST hydraulic traveling drive device including a hydraulic motor that is connected to a variable hydraulic pump in a closed circuit and is driven by oil discharged from the variable displacement hydraulic pump. In this HST hydraulic traveling drive device, the displacement of the variable displacement hydraulic pump is changed according to the number of revolutions of the prime mover by the depression of the accelerator in the driver's seat, and the number of revolutions of the hydraulic motor is changed according to the amount of pump discharge. Increase or decrease the traveling speed of the work vehicle. Further, in the drive device disclosed in this publication, the inertial traveling circuit and the H
A switch for selecting the ST travel circuit is provided, and under the condition that this switch is turned on and the accelerator pedal is not depressed for a predetermined amount or more, the inertia travel circuit is formed by connecting the pair of main pipelines to each other. The HST traveling circuit is formed by shutting off the pair of main pipelines under the condition that the pedal is stepped on a certain amount.

In such an HST hydraulic traveling drive system, when the HST traveling circuit is formed, if the accelerator pedal is loosened (in the stepping range above the predetermined amount) and the rotational speed of the prime mover is lowered, the variable displacement hydraulic pump. Discharge capacity decreases, brake pressure is generated on the discharge side of the hydraulic motor, and the vehicle decelerates. On the other hand, when the accelerator pedal is held below a predetermined amount with the switch turned on,
Since the inertial traveling circuit is formed and both ends of the hydraulic motor are communicated with each other, the inertial traveling can be performed without generating the brake pressure.

In such an HST hydraulic drive system, a mechanical transmission is connected to the output shaft of the hydraulic motor in order to extend the vehicle speed range beyond the speed adjustment range due to the change in the discharge capacity of the variable displacement hydraulic pump. However, the low speed stage suitable for work and the high speed stage suitable for traveling such as movement between sites are switched.

[0005]

By the way, in the above-described HST hydraulic traveling drive device capable of switching between inertia traveling and HST traveling, inertia traveling is selected when the transmission is on the high speed stage side, and low speed traveling is selected. It is desirable to select HST traveling on the tier side. That is, the inertial traveling is selected only when the traveling speed of the vehicle is high and the inertial energy is large, or when the driver's fatigue level is large due to the long depression of the accelerator pedal such as when moving between sites, The effect is exhibited, and rather, it is better to immediately obtain a strong braking force by loosening the accelerator pedal on the low speed side, which saves the trouble of operating the service brake one by one and improves workability.

However, in the above-described drive device, the driver needs to manually switch the dedicated switch for selecting the traveling mode to select either inertial traveling or HST traveling. It is difficult for them to decide whether or not to select inertial running, so
Even if you can select ST traveling, you can not use it effectively,
On the contrary, there was a risk that the advantages of HST traveling would be impaired.

The object of the present invention is to provide HS on the low speed stage side where the advantage of HST traveling is high, even if the driver does not make his own judgment.
An object of the present invention is to provide an HST hydraulic traveling drive device in which T traveling is automatically selected.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIG. 1 which is an embodiment. In the present invention, the variable displacement hydraulic pump 2 driven by a prime mover 1 and a pair of main pipelines 3, 3.
4 is connected to the variable displacement hydraulic pump 2 in a closed circuit, and is connected to an output shaft 5a of the hydraulic motor 5 driven by the oil discharged from the variable displacement hydraulic pump 2 and the output shaft 5a. HST hydraulic pressure provided with a speed change means 10 for changing the output speed of the engine between a low speed stage and a high speed stage, and an opening / closing means 22 for opening / closing a bypass pipe line 21 connecting a pair of main pipe lines 3 and 4. It is applied to traveling drive devices. The above-described object is to bypass the bypass conduit 21 by the opening / closing means 22 when the speed changing means 10 is on the low speed stage side.
This is achieved by providing prohibition means (26, 29) for prohibiting the opening of the.

[0009]

In the HST hydraulic traveling drive system of the present invention, when the speed changing means 10 is in the low speed stage, the opening and closing means 22 is prohibited from opening the bypass conduit 21, so that the traveling mode of the vehicle is fixed to HST traveling. It When the speed change means 10 is in the high speed stage, the bypass pipe 21 is opened and closed by the opening / closing means 22 to enable inertial traveling.

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 for making the present invention easy to understand. It is not limited to.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 is a prime mover (for example, a diesel engine) of a wheel loader according to the present embodiment, and a variable displacement hydraulic pump 2 driven by the prime mover 1 includes a hydraulic motor 5 with a pair of main pipes 3 and 4. Are connected in a closed circuit. The tilt amount of the variable displacement hydraulic pump 2 is controlled by a fixed displacement charge pump 6 that discharges pressure oil at a flow rate according to the rotation speed of the prime mover 1. That is, a part of the oil discharged from the charge pump 6 is guided to the forward / reverse switching valve 8 via the throttle 7, while the rest is directly guided to the forward / reverse switching valve 8 without passing through the throttle 7,
Further, these discharged oils are guided to the oil chambers 9a and 9b of the tilting cylinder 9 according to the switching position of the forward / reverse switching valve 8. The pressure difference between the upstream side and the downstream side of the throttle 7 changes according to the discharge amount of the charge pump 6, and the tilt cylinder 9 is driven by this pressure difference, and the tilt amount of the hydraulic pump 2 changes. Note that the switching position of the forward / reverse switching valve 8, the pressure oil discharge direction of the hydraulic pump 2, and the running direction of the wheel loader are as follows.
When the forward / reverse switching valve 8 is in the (F) position, pressure oil is discharged to the main pipe line 3 side to move the wheel loader forward, and the forward / backward switching valve 8
Is set to the (R) position, the pressure oil is discharged to the side of the main pipeline 4 so that the wheel loader moves backward.

The output shaft 5a of the hydraulic motor 5 is connected to a transmission (transmission means) 10 for changing its output speed, and the output of the transmission 10 is driven left and right via a propeller shaft 11 and an axle shaft 12. It is transmitted to the wheel 13.
As shown in FIG. 2, the transmission 10 includes two hydraulic clutches, a low speed stage side clutch 14a and a high speed stage side clutch 14b, and a transmission charge pump (shown in the figure) driven by the prime mover 1 (FIG. 1). (Not shown), and a switching valve 16 connected via a conduit 15 to the conduit 1 by the switching valve 16.
The pressure oil of No. 5 is guided to either one of the clutches 14a, 14 so that the propeller shaft 12 moves from the output shaft 5a.
The speed reduction ratio between the low speed stage and the high speed stage. That is, when the switching valve 16 is switched to the (L) position, the pressure oil in the pipeline 15 is changed to the low speed stage side clutch 1.
4a, the rotation of the output shaft 5a is caused by the low speed side gears 17, 1
When the speed reduction valve 16 is switched to the (H) position because the reduction gear ratio is increased because it is transmitted to the propeller shaft 11 via 8, the pressure oil in the pipeline 15 is transferred to the high speed stage side clutch 14b. The rotation of the output shaft 5a is guided so that the high speed side gear 1
Since it is transmitted to the propeller shaft 11 via 9 and 20, the reduction gear ratio becomes small. The switching of the switching valve 16 is performed by the operator himself switching the speed change switch provided in the driver's cab, and this speed change switch will be described later.

As shown in FIG. 1, the main pipelines 3 and 4 connecting the hydraulic motor 5 and the hydraulic pump 2 are connected by a bypass pipeline 21. In this bypass pipe 21, an on-off valve 22, a flow rate adjusting valve 23, and a flow rate adjusting valve 23 are sequentially arranged from one main pipe 4 on the discharge side of the hydraulic motor 5 toward the other main pipe 3 when moving forward.
A check valve 24 is provided. The on-off valve 22 is switched to the position (F) where the bypass line 21 is opened when the pressure of the pilot line 25 becomes higher than the set pressure of the spring 22a, and the bypass line 21 is closed in other cases (R). ) Hold in position. The switching of the opening / closing valve 22 is performed by switching the electromagnetic control valve 26 to the (A) position to open the pilot line 25 to the tank pressure, or conversely, switching it to the (B) position and setting the discharge pressure of the charge pump 6 to the pilot line 25. Controlled by what guides you. Reference numeral 27 is a slow return valve that limits the flow rate of hydraulic oil from the pilot port of the opening / closing valve 22 to the electromagnetic control valve 26.

The solenoid portion of the electromagnetic control valve 26 is connected to the power source 30 via the normally closed relay contact 28s of the relay 28 and the speed change switch 29, and these switch portions 28s,
The electromagnetic control valve 26 is switched and controlled according to the open / closed state of 29. Here, the transmission switch 29 is the transmission 10 described above.
It is provided for switching the switching valve 16 (see FIG. 2) of the transmission. When the speed change switch 29 is turned on, the transmission 10 is switched to the high speed stage side, and when the speed change switch 29 is turned off, the transmission 10 is changed. It is switched to the low speed stage side. The relay coil 28c is connected to the power source 30 via the changeover switch 31, and the normally closed relay contact 28s is opened / closed depending on the open / closed state of the changeover switch 31. The change-over switch 31 is provided in conjunction with a forward-reverse change-over switch (not shown) for changing over the forward-reverse change-over valve 8, and the forward-reverse change-over switch is changed over to the reverse side so that the forward-reverse change-over valve 8 is changed over to the (R) position. It is turned on when the forward / reverse selector switch is switched to the forward side and the forward / reverse selector valve 8 is switched to the (F) position. The change-over switch 31 may also be used as a forward / reverse change-over switch.

The check valve 24 is used for the hydraulic motor 5 when moving forward.
When the pressure in the main pipe line 4 on the discharge side exceeds the pressure in the main pipe line 3 on the suction side of the hydraulic motor 5 during forward movement, it is installed so as to be opened. As a result, the on-off valve 2
Even if 2 is switched to the (F) position, the bypass conduit 21 will not be opened unless the pressure in the main conduit 4 exceeds the pressure in the main conduit 3.

Reference numeral 33 in the drawing is a warning lamp arranged in the driver's cab, and is turned on when a drive current is supplied from the power source 30 to the solenoid portion of the electromagnetic control valve 26, and the main pipeline 4 to the main pipeline 3 side. To warn the driver that hydraulic fluid can be bypassed, that is, the HST brake will not operate when moving forward.

Next, the operation of the HST hydraulic traveling drive system having the above construction will be described. First, the operation when the transmission switch 29 is turned off and the transmission 10 is switched to the low speed stage will be described. When the speed change switch 29 is off, the drive current is not supplied from the power source 30 to the solenoid portion of the electromagnetic control valve 26, so that the electromagnetic control valve 26 is held in the (A) position, whereby the pilot line 25 of the opening / closing valve 22 is held. Is released to the tank pressure and the on-off valve 22 is held at the (R) position. Therefore, when the low speed stage is selected, the bypass pipe line 21 is always closed, and as a result, when the amount of oil discharged from the hydraulic pump 2 is decreased by loosening the accelerator pedal, the main pipe is closed. The brake pressure rises on the side of the road 4 and the HST brake operates.
The HST brake is obtained regardless of the switching position of the forward / reverse switching valve 8, that is, the traveling direction of the wheel loader. That is, the traveling mode of the wheel loader is fixed to the HST traveling mode on the low speed stage side.

On the other hand, when the transmission switch 29 is turned on and the transmission 10 is switched to the high speed stage side, the bypass conduit 21 is opened and closed depending on the open / close state of the changeover switch 31 and the operating state of the accelerator pedal. That is, when the change-over switch 31 is turned off in the state where the speed change switch 29 is turned on and the transmission 10 is switched to the high speed stage side, the normally closed relay contact 28s is closed and the power source 30 moves the electromagnetic control valve 26. Since the drive current is supplied to the solenoid,
The electromagnetic control valve 26 is switched to the (B) position, the discharge pressure of the charge pump 6 is guided to the pilot line 25, and the opening / closing valve 22 is switched to the (F) position.

When the accelerator pedal is depressed while the on-off valve 22 is held in the (F) position, the amount of oil discharged from the hydraulic pump 2 increases and the pressure in the main pipeline 3 becomes higher than that in the main pipeline 4. Therefore, the check valve 24 is closed and the main pipeline 3
The entire amount of pressure oil is supplied to the hydraulic motor 5, whereby the wheel loader is activated and accelerated. When the accelerator pedal is released with the on-off valve 22 in the (F) position, the pressure in the main pipeline 4 becomes larger than the pressure in the main pipeline 3, and the working oil in the main pipeline 4 flows into the on-off valve 22 and the flow rate. It is guided to the main pipeline 3 via the adjusting valve 23 and the check valve 24. As a result, no brake pressure is generated in the main pipeline 4, and the wheel loader runs by inertia. During this inertial running, the maximum flow rate of the bypass line 21 is limited by the flow rate adjusting valve 23, and a brake pressure is generated in the main line 4 due to the excess flow rate, so that the hydraulic motor 5 is prevented from over-rotating during downhill travel. It

When the forward / reverse switching valve 8 is switched to the (R) position with the speed change switch 29 still turned on, that is, when the wheel loader is moved backward, the forward / backward switching valve 8 is interlocked with the changeover switch. Since 31 is turned on, the normally closed relay contact 28s is opened, and the supply of the drive current from the power source 30 to the solenoid portion of the electromagnetic control valve 26 is stopped. Therefore, the electromagnetic control valve 26 is switched to the (A) position and the pilot line 25 is opened to the tank pressure, whereby the opening / closing valve 22 is switched to the (R) position and the bypass pipeline 21 is closed. Therefore, when the wheel loader is moved backward while the transmission 10 is being shifted to the high speed stage, the HST drive mode is always selected, and the HST brake is activated by loosening the accelerator pedal.

As described above, according to the HST hydraulic traveling drive system of the present embodiment, when the transmission 10 is shifted to the low speed stage side, the bypass line 21 is closed and the HST traveling mode is automatically switched. , The opening prohibition state of the bypass line 21 is released during the shift to the high speed stage.
Inertial running can be executed within a range where the advantages of running are not impaired, and the effect can be fully exerted. Further, it is not necessary for the operator to switch the switches one by one in response to the shift operation to select the traveling mode of the vehicle. Further, even when the high speed stage is selected, it is more convenient because the mode is returned to the HST traveling mode at the time of reverse traveling when the speed is low and the need for inertial traveling is low.

In the present embodiment, since the flow rate of the hydraulic oil flowing from the opening / closing valve 22 side to the electromagnetic control valve 26 side in the pilot line 25 is limited by the slow return valve 27, the opening / closing valve 22 is moved from the (F) position. The switching operation to the (R) position is performed gently. Therefore, from inertial running to HS
When switching to T running, that is, the speed change switch 2
There is no sudden increase in the pressure on the main pipe line 4 side at the time of shifting from the high speed stage to the low speed stage by turning off 9 and at the time of starting the reverse operation by switching the forward / reverse switching valve 8 to the (R) position. It has the advantage of relieving shock.

In this embodiment, since the check valve 24 is provided in the bypass pipe line 21, when the high speed stage is selected, the bypass pipe is interlocked with the operation of the accelerator pedal while keeping the open / close valve 22 in the (F) position. The road 21 can be closed and the vehicle can be started and accelerated. Therefore, it is not necessary to control the switching of the on-off valve 22 one by one according to the depression operation of the accelerator pedal. However, the present invention is not limited to the example in which the check valve 24 is provided, and the opening / closing valve 2 is operated when the accelerator pedal is depressed.
2 may be switched to the (R) position. Also, check valve 2
Instead of 4, the switching valve may be provided in the bypass line 21 in conjunction with positive and negative changes in the differential value of the depression amount of the accelerator pedal.

In the present embodiment, the electromagnetic control valve 26 is switch-controlled by the speed change switch 29 to prohibit inertial running on the low speed stage side. However, the present invention is not limited to this, and the switch 2
A controller that controls switching of the open / close valve 22 based on the open / closed state of 9 may be provided. By the way, in the example of FIG. 3, the solenoid of the on-off valve 22 is connected to the controller 40,
The bypass conduit 21 is opened and closed by changing the control signal sent from the controller 40 based on the differential value of the accelerator pedal depression amount θ sent from the potentiometer 41 and the open / closed states of the switches 29 and 31. That is, in the example of FIG. 3, the differential value of the accelerator pedal depression amount θ is negative (deceleration) when the speed change switch 29 is on (second speed) and the changeover switch 31 is off (forward).
When the controller 40 supplies the drive current to the solenoid of the on-off valve 22, the on-off valve 22
Is switched to the (F) position, so that inertial traveling is automatically selected as in the example shown in FIG.

In the above example, the changeover switch 31 is provided so that the HST traveling is automatically selected when the vehicle is moving backward even when the high speed gear is selected. However, this is omitted, and the inertia when the vehicle is moving backward when the high speed gear is selected. Of course, it may be possible to drive. In addition, in the embodiments shown in FIGS. 1 and 2, the case where the transmission 10 is a two-speed transmission is taken as an example, but the present invention can be applied to a case where the transmission 10 is configured with three or more multi-speeds. For example, in the case of a four-speed shift, the first speed and the second speed are processed as the low speed speed, the third speed and the fourth speed are processed as the high speed speed, and the like.
It suffices to divide the shift speed into two by an appropriate number and apply the shift.

In the above example, the speed change switch 29 and the electromagnetic control valve 26, or the controller 40 constitutes the prohibition means.

[0027]

As described above, the HST of the present invention is
In the hydraulic traveling drive device, opening of the bypass pipeline is prohibited by the prohibiting means when the speed changing means is in the low speed stage.
HST traveling is automatically selected on the low speed stage side where there is a high need for ST traveling. As a result, even if the driver is not familiar with the operation, it is possible to bring out the effect of inertial running without impairing the advantages of HST running, and save the driver the trouble of selecting a running mode one by one according to the shifting operation. Get burned.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of an HST hydraulic traveling drive system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a transmission in the HST hydraulic traveling drive system of FIG.

FIG. 3 is a diagram showing a circuit configuration of an HST hydraulic traveling drive system according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Prime mover 2 Variable displacement hydraulic pump 3, 4 Main pipeline 5 Hydraulic motor 10 Transmission (shift means) 21 Bypass pipeline 22 Open / close valve 26 Electromagnetic control valve 29 Shift switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Minoru Kojima Minoru 650, Kachidachi-cho, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. Tsuchiura factory

Claims (1)

[Claims] 1. A variable displacement hydraulic pump driven by a prime mover, and a hydraulic motor which is closed circuit connected to the variable displacement hydraulic pump by a pair of main pipes and is driven by oil discharged from the variable displacement hydraulic pump. And a shift means connected to the output shaft of the hydraulic motor for shifting the output speed of the output shaft between a low speed stage and a high speed stage, and a bypass pipe line connecting the pair of main pipe lines is opened and closed. In the HST hydraulic traveling drive device including an opening / closing means, a prohibiting means for prohibiting opening of the bypass pipe by the opening / closing means is provided when the speed changing means is on the low speed stage side. HST hydraulic traveling drive device.