JPH04173478A - Hydraulic drive unit for working vehicle - Google Patents

Abstract

PURPOSE:To enable steering at the emergency time with low-priced structure by providing an engine-driven emergency hydraulic pump together with a steering pump, and leading the discharge oil of the emergency hydaulic pump to a steering valve means when the discharge flow quantity of the steering pump is less than the specified value. CONSTITUTION:A hydraulic drive unit for a working vehicle is closed circuit- connected to a variable displacement hydraulic pump 2 driven by an engine 1, through main ducts 3a, 3b. This hydraulic drive unit is provided with a travel hydraulic motor 4 driven by the discharge oil of the pump 2, and a steering cylinder 5 driven by the discharge oil of a steering pump 7 driven by the engine 1. Pressure oil in the quantity corresponding to the operation of a steering wheel 9a is led to the steering cylinder 5 by a steering valve 9. In this case, there is provided an emergency hydraulic pump 21 connected together with the steering pump 7, to the engine 1 so as to be driven by the engine 1. The discharge oil of this emergency hydraulic pump 21 is led to a steering means P through a passage switching means 22 only when the discharge flow quantity of the pump 7 is less than the specified value.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a hydraulic drive device used in a work vehicle employing the H3T system, such as a wheel loader.

B. Conventional technology Figure 3 shows HST (Hydrostatic Tra
This figure shows a conventional example of a hydraulic drive device for a wheel loader that employs the NSmission system.

In FIG. 3, a variable displacement hydraulic pump (H3T pump) 2 driven by an engine 1 has a -pair of main pipes 3a.
, 3b, a hydraulic motor 4 is connected in a closed circuit, and the hydraulic motor 4 is rotated by the oil discharged from the hydraulic pump 2. The rotation of the hydraulic motor 4 is transmitted to the wheels 6, thereby causing the vehicle to travel. Reference numeral 7 denotes a steering pump driven by the engine 1, and its discharged oil is guided to the steering valve mechanism 9 via a pipe 41 and a check valve 8.

The steering valve mechanism 9 distributes pressure oil at a flow rate according to the rotational operation speed of the steering wheel 9a out of the oil discharged from the steering pump 7 to the rond chamber 5a or the bottom chamber 5b of the steering cylinder 5 according to the rotational direction of the steering wheel 9a. The vehicle is steered left and right by contraction of the steering cylinder 5.

Here, if the engine 1 stops for some reason while driving, the hydraulic motor 4 rotates due to the inertia of the vehicle and acts as a pump, so the hydraulic pump 2 is driven by the oil discharged from the hydraulic motor 4, and the hydraulic pump 2 The rotation of the engine 1 causes the engine 1 to be driven (this is referred to as the power recovery effect of H8T).

Therefore, the rotation of the engine 1 also drives the steering pump 7, and its discharged oil is supplied to the steering valve mechanism 9, so that until the vehicle stops, steering operations can be performed by lightly operating the steering wheel 9a.

Next, a case will be described in which the engine 1 is operating but the steering pump 7 is out of order.

Reference numeral 10 denotes a differential pressure type pressure switch that is switched based on the differential pressure across the throttle 9b of the steering valve mechanism 9. When the steering pump 7 malfunctions and its discharge flow rate becomes less than a predetermined amount, the differential pressure across the throttle 9b becomes less than a predetermined value, and the pressure switch 10 is thereby switched to position Ilb. The state of the switch 10 is input to the controller 11, and when the controller 11 detects that the switch 10 has been switched to the position, it drives the electric motor 12. The emergency hydraulic pump 13 is driven by the rotation of the motor 12, and the oil discharged from the pump 13 is guided to the steering valve mechanism 9 via the check valve 14 and the conduit 41. As a result, the steering operation can be performed by lightly operating the steering wheel 9a as in the normal state.

On the other hand, when the steering pump 7 is operating normally and its discharge flow rate is greater than or equal to the predetermined amount, the differential pressure is greater than or equal to the predetermined value, so the pressure switch 10 is at position a, and at this time the controller 11 does not drive the motor 12, that is, the hydraulic pump 13. In addition, in Figure 3, 15
．． 16 is a relief valve for setting the maximum discharge pressure of the hydraulic pump 7.13.

C9 Problem to be Solved by the Invention However, with the above configuration, in order to perform the steering operation in the same way as normal when the steering pump 7 fails, a highly durable pressure switch must be used, and the electric motor 12 and the controller 11 are required, resulting in an increase in cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide a hydraulic drive system for a work vehicle that is inexpensive and capable of performing emergency steering operations.

Means for Solving the Problem No. 93 Explained in conjunction with FIG. 1 showing an embodiment, the invention of claim 1 provides a variable displacement hydraulic pump 2 driven by an engine 1, A traveling hydraulic motor 4 connected in a closed circuit via a pair of main pipes 3a and 3b and driven by oil discharged from a variable displacement hydraulic pump 2;
a steering pump 7 driven by the engine 1;
A steering cylinder 5 that is driven by the oil discharged from the steering pump 7 to steer the vehicle, and a steering valve means that guides an amount of pressure oil to the steering cylinder 5 according to the operation of the steering wheel 9a out of the amount of oil discharged from the steering pump 7. 9 is applied to a hydraulic drive system for a working vehicle. An emergency hydraulic pump 21 is connected to and driven by the engine 1 together with the steering pump 7, and the oil discharged from the emergency hydraulic pump 21 is supplied to the steering valve means 9 only when the discharge flow rate of the steering pump 7 is less than a predetermined amount. This solves the above problem.

Further, when explained in conjunction with FIG. 2, the invention of claim 2 includes the above-mentioned variable displacement hydraulic pump 2, traveling hydraulic motor 4, steering pump 7, steering cylinder 5, steering valve means 9, steering pump 7
The present invention is applied to a hydraulic drive system for a work vehicle, which includes a charging hydraulic pump 31 that is connected to and driven by the engine 1 and supplies charging oil to a pair of main pipes 3a and 3b. When the discharge flow rate of the steering pump 7 is above a predetermined amount, the discharge oil of the charging hydraulic pump 31 is guided to the pair of main pipes 3a and 3b, and the supply to the steering valve means 9 is blocked, and the discharge flow rate of the steering pump 7 is When the amount is less than a predetermined amount, a flow path switching means 32 directs the oil discharged from the charging hydraulic pump 31 to the steering valve means 9.
and thereby solve the above problems.

E1 Effect (1) Invention of Claim 1 When the steering pump 7 malfunctions and its discharge flow rate becomes less than a predetermined amount, the flow path switching means 22 guides the discharge oil of the emergency hydraulic pump 21 to the steering valve means 9. As a result, even if a highly durable pressure switch, electric motor, or controller is not used, the steering operation can be performed in the same way as when the steering pump is out of order.

(2) Invention of Claim 2 When the steering pump 7 malfunctions and its discharge flow rate becomes less than a predetermined amount, the flow path switching means 32 guides the discharge oil of the charging hydraulic pump 31 to the steering valve means 9. As a result, as described above, the steering operation can be performed in the same way as in normal times without using a pressure switch, electric motor, or controller.

It should be noted that in the above-mentioned sections and section E, which describe the present invention in detail, figures of embodiments are used in order to make the present invention easier to understand, but the present invention is not limited to the embodiments.

F. Example 1.First embodiment- A first embodiment of the present invention will be explained with reference to FIG.

Note that the same parts as in FIG. 3 are given the same reference numerals, and only the differences will be explained.

In FIG. 1, reference numeral 21 denotes an emergency hydraulic pump connected and driven together with the hydraulic pumps 2 and 7 to the power shaft of the engine 1, and the discharge oil is supplied to the hydraulic pilot type switching valve 22.
guided by. The switching valve 22 is.

A position where the discharged oil of the hydraulic pump 21 is returned to the tank, and B where this discharged oil is guided to the pipe line 41, that is, the steering valve mechanism 9.
The throttle 9 of the steering valve mechanism 9 can be switched to the position
Switches according to the differential pressure before and after b.

That is, when the discharge flow rate of the steering pump 7 is a predetermined amount or more, the differential pressure across the throttle 9b becomes a predetermined value or more, and at this time, the switching valve 22 is maintained at the A position by the pressure of the conduit 41. When the discharge flow rate of the steering pump 7 becomes less than a predetermined amount, the differential pressure becomes less than a predetermined value, and the switching valve 22
is switched to the B position by the spring force of the spring 22a.

Next, the operation of the embodiment will be explained.

When the steering pump 7 is operating normally,
Since the discharge flow rate is above the predetermined amount, the switching valve 22 maintains the human position, and therefore the discharge oil of the hydraulic pump 21 is returned to the tank, and the absorption torque of the hydraulic pump 21 is very small. When the steering pump 7 malfunctions and its discharge flow rate becomes less than a predetermined amount, the differential pressure across the throttle 9b becomes less than a predetermined value, so the switching valve 22 is switched to position B as shown in the figure by the force of the spring. As a result, the oil discharged from the hydraulic pump 21 is guided to the steering valve mechanism 9 via the conduit 41, so that the steering operation can be performed in the same way as in normal operation by lightly operating the steering wheel 9a. Note that when the engine 1 is stopped while the vehicle is running, the power recovery effect of the H8T allows the steering operation to be performed in the same manner as when the vehicle is running normally until the vehicle stops, as described in the prior art section.

In the configuration of the above embodiment, the steering valve mechanism 9 constitutes the steering valve means, and the switching valve 22 constitutes the flow path switching means.

1.Second embodiment- A second embodiment of the present invention will be explained with reference to FIG.

Note that the same parts as in FIG. 1 are given the same reference numerals, and only the differences will be explained.

In FIG. 2, numeral 31 is a charge pump, and its discharge oil is supplied to a pipe 42 and a pair of check valves 51a and 51.
The oil is guided as charge oil to the pair of main pipes 3a and 3b via pipe 43, and also to the switching valve 32 via pipe 43. The switching valve 32 can be switched between the "A" position where it blocks the oil discharged from the charge pump 31 and the "Open" position where this discharged oil is supplied to the pipe line 41. Similar to FIG. 1), this is performed by the front and back pressure of the throttle 9a. Note that 52 is the charge pump 31
This is a relief valve that sets the maximum discharge pressure.

When the steering pump 7 is operating normally and its discharge flow rate is greater than a predetermined amount, the switching valve 32 is operated as shown in the figure.
Since the pipe 43 is blocked, the entire amount of oil discharged from the charge pump 31 is guided as charge oil to the main pipes 3a and 3b via the check valves 51a and 51b. Further, if the steering pump 7 malfunctions and its discharge flow rate becomes less than a predetermined amount, the differential pressure across the throttle 9b becomes less than a predetermined value, and the switching valve 32 is not switched to the "open" position. As a result, the oil discharged from the charge pump 31 is guided to the pipe 41 through the pipe 43, and the steering valve mechanism 9
Therefore, by lightly operating the steering wheel 9a, the steering operation can be performed in the same manner as in normal operation.

Note that in the above description, the switching valve 22 is
．． 32, but the steering pump 7
Other switching methods may be used as long as the switching is performed according to the discharge flow rate.

Effects of the G0 Invention According to the invention of claim 1, since the discharge oil of the emergency hydraulic pump is guided to the steering valve means when the discharge flow rate of the steering pump is less than a predetermined amount, the durability that was previously required is achieved. It is possible to perform steering operation in an emergency with an inexpensive configuration without using a high pressure switch, electric motor, controller, etc.

According to the second aspect of the present invention, when the discharge flow rate of the steering pump is less than a predetermined amount, the discharge oil of the conventional charging hydraulic pump is guided to the steering valve means, so that the same effect as described above can be obtained.

[Brief explanation of drawings]

FIGS. 1 and 2 show the first embodiment of the present invention. FIG. 3 is a diagram showing a hydraulic drive system for a working vehicle according to the second embodiment, and FIG. 3 is a diagram showing a conventional hydraulic drive system. 1: Engine 2: Variable displacement hydraulic pump 3a, 3
b: Main pipe 4: Hydraulic motor 5 Ni steering cylinder 7: Steering pump 9 Ni steering valve mechanism 21: Emergency pump 22, 32: Switching valve 31: Hydraulic pump for charging

Claims (1)

[Scope of Claims] 1) A variable displacement hydraulic pump driven by an engine, and a traveling pump connected to the variable displacement hydraulic pump in a closed circuit via a pair of main pipes and driven by oil discharged from the variable displacement hydraulic pump. a hydraulic motor; a steering pump driven by the engine; a steering cylinder driven by oil discharged from the steering pump to steer the vehicle; A hydraulic drive system for a working vehicle includes a steering valve means for guiding pressure oil to the steering cylinder, and an emergency hydraulic pump connected to and driven by the engine together with the steering pump; A hydraulic drive device for a work vehicle, comprising: flow path switching means for guiding the discharged oil of the emergency hydraulic pump to the steering valve means only when the oil is less than a fixed amount. 2) a variable displacement hydraulic pump driven by the engine; a traveling hydraulic motor connected in a closed circuit to the variable displacement hydraulic pump via a pair of main pipes and driven by oil discharged from the variable displacement hydraulic pump; and the engine. a steering pump driven by the steering pump; a steering cylinder driven by the oil discharged from the steering pump to steer the vehicle; A hydraulic drive system for a work vehicle, comprising: a steering valve means for guiding the steering pump to the steering pump; and a charging hydraulic pump that is connected to and driven by the engine together with the steering pump and supplies charging oil to the pair of main pipes. When the discharge flow rate is above a predetermined amount, the discharge oil of the charge hydraulic pump is guided to the pair of main pipes and the supply to the steering valve means is blocked, and when the discharge flow rate of the steering pump is less than a predetermined amount, the charge hydraulic pressure is A hydraulic drive device for a work vehicle, comprising: flow path switching means for guiding oil discharged from the pump to the steering valve means.