JPH0754993A - Hst hydraulic running drive device - Google Patents

Abstract

PURPOSE:To reduce the burden of a service brake by furnishing a flow control means to lower the allowable rate of flow in a bypass line below the discharge amount of a hydraulic motor when a brake pedal is stamped. CONSTITUTION:When a mode switch 35 is put on and a brake pedal 15 is stamped during the inertial run, the throttle amount of a variable throttle valve 40 increases in accordance with the amount of stamping, and the allowable rate of flow in a bypass line 20 sinks lower than the discharge amount of a hydraulic motor 5. Therefore, the discharge oil of the hydraulic motor 5 flowing into the bypass line 20 through a main line 4 receives the throttling action of the valve 40. In response to this throttling action, a brake pressure rises on the discharge side of the hydraulic motor 5 so that its rotation is braked, and the burden of a service brake 14 is decreased. The max. value of the brake pressure on the discharge side of the hydraulic motor 5 is limited by a crossover load relief valve 42.

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 an apparatus of this type, for example,
As disclosed in Japanese Patent No. 12659, a variable displacement hydraulic pump driven by a prime mover and a traveling hydraulic motor are connected in a closed circuit by a pair of main pipelines, and a bypass pipeline is connected to the pair of main pipelines. Is provided, and HST traveling or inertia traveling can be selected by switching the opening / closing valve that opens / closes the bypass pipe. Where HST
Traveling refers to a state in which the bypass pipeline is blocked and the rotational speed of the hydraulic motor is changed according to changes in the discharge amount of the hydraulic pump to increase or decrease the traveling speed of the vehicle.Inertial travel refers to the bypass pipeline. A state in which the hydraulic motor is released and the pressure generated on the discharge side of the hydraulic motor is released to the suction side of the hydraulic motor to rotate the hydraulic motor by inertia regardless of the discharge amount of the hydraulic pump. Here, the advantage of inertial traveling is that the same acceleration / deceleration feeling as a passenger car equipped with a torque converter can be obtained during high-speed traveling when moving between sites, and it excavates by rushing into an object like a wheel loader. In a vehicle that performs the above, it is possible to loosen the accelerator pedal and rush into an object by inertia.

[0003]

However, the above-described device has a disadvantage that the hydraulic brake, which is an advantage of HST traveling, is lost due to selection of inertia traveling. That is, HS
In T travel, when the accelerator pedal is loosened, a closing pressure is generated on the discharge side of the hydraulic motor, and a large braking force acts on the vehicle. However, during inertial running, even if the accelerator pedal is loosened, the closing pressure does not occur on the discharge side of the hydraulic motor.Therefore, in order to decelerate the vehicle, depress the brake pedal in the driver's seat to operate between the hydraulic motor and the wheels. It is necessary to operate the service brake provided in the power transmission system of. Therefore, the burden of the service brake is extremely heavy.

An object of the present invention is to provide an HST hydraulic traveling drive system which can reduce the burden on the service brake while taking advantage of the advantage of inertia traveling.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIG. 1 showing an embodiment. In the present invention, a variable displacement hydraulic pump 2 driven by a prime mover 1 and a pair of main pipe lines 3 and 4 are used. A hydraulic circuit 5 connected to the displacement type hydraulic pump 2 in a closed circuit and driven by oil discharged from the variable displacement hydraulic pump 2, a bypass line 20 connecting a pair of main lines 3 and 4, and a vehicle brake. The present invention is applied to an HST hydraulic traveling drive system including a speed reducing unit 14 that decelerates a vehicle in response to an operation of a pedal 15. Then, the above-mentioned object is achieved by providing the flow rate control means 40 for lowering the allowable flow rate of the bypass pipeline 20 below the discharge rate of the hydraulic motor 5 when the brake pedal 15 is operated.

[0006]

When the brake pedal 15 is operated during the inertia running by guiding the discharge pressure of the hydraulic motor 5 from the bypass line 20 to the suction side of the hydraulic motor 5, the bypass line 20 is operated.
Permissible flow rate is lower than the discharge amount of the hydraulic motor 5. For this reason, a throttle action is generated in the bypass pipeline 20, brake pressure rises on the discharge side of the hydraulic motor 5, and rotation of the hydraulic motor 5 is braked.

Incidentally, in the section of means and action for solving the above 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.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, reference numeral 1 denotes a prime mover (for example, a diesel engine) of a wheel loader, and a variable displacement hydraulic pump 2 driven by the prime mover 1 is connected to a variable displacement hydraulic motor 5 by a pair of main pipe lines 3 and 4 in a closed circuit. Has been done. The displacement amount of the variable displacement hydraulic pump 2 is determined by the prime mover 1
It is controlled by a fixed-capacity type charge pump 6 that discharges a pressure oil at a flow rate according to the number of rotations. 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, and These discharged oils are guided to the oil chambers 9a and 9b of the tilt 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.

The relationship between the switching position of the forward / reverse switching valve 8, the pressure oil discharge direction of the hydraulic pump 2 and the traveling direction of the wheel loader is shown by an arrow F in the figure when the forward / reverse switching valve 8 is in the F position. When hydraulic pressure is discharged from the hydraulic pump 2 to the main pipeline 3 to move the wheel loader forward, and when the forward / reverse switching valve 8 is in the R position, the hydraulic fluid is discharged from the hydraulic pump 2 to the main pipeline 4 as indicated by an arrow R in the figure. It is discharged and the wheel loader moves backward. The forward / reverse selector valve 8 is switched by a forward / rearward selector switch (not shown) in the cab.

The output shaft 5a of the hydraulic motor 5 is connected to a transmission 10 for changing its output speed.
Output is propeller shaft 11 and axle shaft 12
Is transmitted to the left and right drive wheels 13 via. Transmission 10
Is to selectively connect two hydraulic clutches to switch the meshing of gears attached to these hydraulic clutches between a high speed stage and a low speed stage. The switching of the hydraulic clutch is instructed by a speed change switch (not shown) provided in the driver's cab. Axle shaft 12
A hydraulic service brake 14 is attached to the attachment portion of the wheel 13 and the wheel 13. This service brake 14
It is connected to a brake circuit 16 that generates pressure according to the amount of depression of the brake pedal 15 at the driver's seat, and brakes the rotation of the wheels 13 with a force corresponding to the amount of depression of the brake pedal 15.

A bypass line 20 is provided between the main lines 3 and 4 connecting the hydraulic motor 5 and the hydraulic pump 2.
A poppet valve 30 that opens and closes the bypass pipeline 20 and a variable throttle valve 40 that adjusts the flow rate of the bypass pipeline 20 are connected to the bypass pipeline 20. Poppet valve 30
Means that the pressure Pa, Pb of the main pipelines 3, 4 guided through the bypass pipeline 20 pushes up the valve body 31, and the spring 32
When the resultant force of the pressing force of the valve body 31 by the valve and the pressing force of the valve body 31 by the pilot pressure Pc introduced through the switching valve 33 is exceeded, the valve body 31 is separated from the valve seat 34 to open the bypass conduit 20. , Otherwise, the valve body 31 is replaced by the valve seat 3
4, and the bypass line 20 is closed.

The switching valve 33 is switched and controlled in accordance with the on / off state of a mode selection switch 35 provided in the driver's seat. When the HST traveling is selected, the mode selection switch 35 is turned off and the switching valve 33 is held at the A position. As a result, the higher pressure of the pressures Pa and Pb in the main pipelines 3 and 4 is selected by the high pressure selection valve 36 and the pilot pressure P
The valve body 31 is guided to the poppet valve 30 as c, and the valve body 31 is constantly pressed against the valve seat 34 regardless of the discharge pressure of the hydraulic pump 2 or the discharge pressure of the hydraulic motor 5 to prevent passage of pressure oil in the bypass conduit 20. . On the other hand, when the inertia traveling is selected, the mode selection switch 35 is turned on and the switching valve 33 is held at the B position. As a result, the pressure Pa of the main pipeline 3 is guided as the pilot pressure Pc of the poppet valve 30 via the pilot pipeline 37, and the pressure Pb of the main pipeline 4 is the pressure Pa of the main pipeline 3.
When the pressure exceeds a predetermined value, the poppet valve 31 is opened to allow the passage of the pressure oil in the bypass line 20. Here, the reason why the pilot pipe line 37 is connected between the main pipe line 3 and the variable throttle valve 40 is to avoid pressure fluctuation due to the throttle action of the variable throttle valve 40.

The switching valve 33 is forcibly held in the A position when the vehicle is moving backward. When the switching valve 33 is in the B position during reverse, the accelerator pedal is depressed to operate the main pipe 3,
The pressures Pa and Pb of 4 become Pa <Pb, and the hydraulic pump 2
This is because the discharge pressure of circulates from the bypass line 20 to the suction side of the hydraulic pump 2 and becomes impossible to reverse. Therefore,
In the device of this embodiment, inertial traveling can be selected only when the vehicle is moving forward. The poppet valve 30, the switching valve 33, and the high-pressure selection valve 36 are unitized, and a combination thereof forms a single logic valve 38.

The variable throttle valve 40 is connected to the brake pedal 15 via a link 41, and its throttle amount changes according to the depression amount of the brake pedal 15. That is, as the depression amount of the brake pedal 15 increases, the throttle amount of the variable throttle valve 40 increases, in other words, the opening area of the variable throttle valve 40 decreases, and the allowable flow rate of the bypass conduit 20 decreases accordingly. . The throttle amount of the variable throttle valve 40 when the brake pedal 15 is not operated is set to the bypass line 20.
The allowable flow rate is set to be substantially equal to the discharge amount when the hydraulic motor 5 is rotated at the maximum allowable rotation speed.
This is to prevent over-rotation of the hydraulic motor 5 due to inertial traveling such as when descending a slope. In addition, 42 is the main pipeline 3,4
It is a crossover load relief valve that limits the maximum pressure of.

In the HST hydraulic traveling drive system having the above construction, when the mode selection switch 35 is turned on and deceleration is required during inertia traveling and the brake pedal 15 is depressed, the operation amount is changed according to the operation amount. Variable throttle valve 40
And the allowable flow rate of the bypass pipe 20 becomes lower than the discharge rate of the hydraulic motor 5. Therefore, the discharge oil of the hydraulic motor 5 flowing into the bypass pipe 20 via the main pipe 4 is subjected to the throttling action of the variable throttle valve 40, and the brake pressure rises on the discharge side of the hydraulic motor 5 in response to this throttling action. The rotation of the hydraulic motor 5 is braked. As a result, the load on the service brake 14 is reduced, and the life of consumable parts such as brake shoes is increased. Further, since the braking force is increased, the braking distance can be expected to be shortened. The maximum value of the brake pressure on the discharge side of the hydraulic motor 5 is limited by the crossover load relief valve 42.

In the correspondence between the above embodiment and the claims,
The service brake 14 constitutes a speed reduction means, and the variable throttle valve 40 constitutes a flow rate control means. The flow rate control means is not limited to the variable throttle valve, and any means capable of variably adjusting the flow rate may be used. The operation amount of the brake pedal may be converted into a current value or a voltage value for detection, and the set value of the flow control valve may be electrically changed according to the detection result.

[0017]

As described above, according to the present invention,
If the brake pedal is operated during inertial running, the throttle action will occur in the bypass pipe line and the brake pressure will rise on the discharge side of the hydraulic motor.Therefore, the load on the deceleration means for decelerating the vehicle in response to the operation of the brake pedal will be burdened. Is reduced, and the life of consumable parts such as brake shoes provided in the speed reduction means is improved. It is expected that the braking distance will be shortened by increasing the braking force.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of an embodiment of the present invention.

[Explanation of symbols] 1 prime mover 2 variable displacement hydraulic pump 3,4 main line 5 hydraulic motor 14 service brake 15 brake pedal 20 bypass line 30 poppet valve 40 variable throttle valve

Claims (1)

[Claims] 1. A variable displacement hydraulic pump driven by a prime mover, and a hydraulic motor driven by discharge oil from the variable displacement hydraulic pump, which is closed circuit connected to the variable displacement hydraulic pump by a pair of main pipes. And a bypass line connecting the pair of main pipe lines, and a deceleration means for decelerating the vehicle in response to an operation of the brake pedal of the vehicle, wherein the brake pedal is operated. In this case, the HST hydraulic travel drive device is provided with a flow rate control means for reducing the allowable flow rate of the bypass pipe line to be lower than the discharge amount of the hydraulic motor.