JP2002364746A - Hydraulic servo mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems on a conventional hydraulic servo mechanism provided in a hydraulic continuously variable transmission, in which a restrictor is provided at the inlet or outlet of a control circuit, although the smaller restriction bore of the restrictor having the greater effect of reducing shock, the too small restriction bore causes no flow of a control oil into the servo mechanism at a low temperature to give inconveniences including no stop of a working machine mounted on the hydraulic continuously variable transmission, which prohibits so much reduction in restriction bore and results in a limited reduction in shock of the restrictor. SOLUTION: A constant differential pressure reducer 57 for controlling the flow rate of a control oil is provided at the inlet of a servo control passage 55 as a control circuit for controlling the operation of the hydraulic servo mechanism 61.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic servo mechanism for controlling a swash plate angle of a movable swash plate in a hydraulic continuously variable transmission, and more particularly, to reducing a shock when a sudden operation is performed. Related to the configuration.

[0002]

2. Description of the Related Art Conventionally, in a hydraulic continuously variable transmission which is constituted by a hydraulic pump and a hydraulic motor, for example, in which the hydraulic pump is a variable displacement pump, the swash plate angle of a movable swash plate of the hydraulic pump is set as follows. There is a type in which the control is performed via a servo mechanism provided in a hydraulic continuously variable transmission. When such a hydraulic continuously variable transmission is mounted on a working machine, a throttle valve is provided at an inlet or an outlet of a control circuit that controls the operation of a hydraulic servo mechanism in the hydraulic continuously variable transmission,
The shock generated when the working machine is suddenly decelerated is reduced.

[0003] For example, in a hydraulic circuit of a hydraulic type continuously variable transmission shown in FIG.
2 are connected by main circuits 132R and 132L,
The main circuits 132R and 132L and the charge pump 1
Check valves 144 and 144 are interposed between the charge circuit 153 and the charge circuit 153 to which the charge pressure is applied. The charge circuit 53 includes a check valve 14.
A relief valve 154 is provided in the circuit leading to 4.144. Then, from the charge pump 151,
The servo control pressure is supplied to the hydraulic servo mechanism 161 for controlling the swash plate angle of the movable swash plate 121c of the hydraulic pump 121 through the servo control passage 155. A throttle valve 157 is provided at the entrance of the control circuit 161.

[0004]

As described above, when a throttle valve is provided at the inlet or the outlet of the control circuit of the hydraulic servo mechanism, the effect of reducing the shock is greater as the throttle diameter of the throttle valve is reduced. However, if the aperture diameter is made too small,
At low temperatures, control oil does not flow into the servo mechanism, causing problems such as the work machine not stopping. Therefore, the diameter of the throttle cannot be reduced so much, and there has been a limit to the reduction of shock at the throttle valve. In view of the above, the present invention provides a hydraulic servo mechanism provided with a shock reducing valve capable of exhibiting a shock reducing effect without causing the above-mentioned problems at low temperatures.

[0005]

The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described. That is, in claim 1, a constant differential pressure reducing valve for controlling the control oil flow rate is provided at the inlet of the control circuit for controlling the operation of the hydraulic servo mechanism.

According to a second aspect of the present invention, the constant differential pressure reducing valve is incorporated in a housing constituting a control circuit of the hydraulic servo mechanism.

According to a third aspect of the present invention, the cover member of the constant differential pressure reducing valve is also used as a cover member of the piston chamber in which the piston of the hydraulic servo mechanism is housed.

[0008]

Next, an embodiment of the present invention will be described. FIG. 1 is a side view showing a hydraulic stepless transmission having a hydraulic servo mechanism provided with a constant differential pressure reducing valve of the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is a front sectional view showing a hydraulic servo mechanism. FIG. 4 is a diagram showing a hydraulic circuit of a hydraulic continuously variable transmission equipped with a hydraulic servo mechanism provided with a constant differential pressure reducing valve, FIG. 5 is a side sectional view showing the constant differential pressure reducing valve, and FIG. FIG. 7 is a diagram showing a flow control characteristic of a constant differential pressure reducing valve, and FIG. 7 is a diagram showing a hydraulic circuit of a hydraulic continuously variable transmission equipped with a conventional hydraulic servo mechanism.

First, the hydraulic continuously variable transmission according to the present invention will be described. As shown in FIGS. 1 to 3, the hydraulic continuously variable transmission (hereinafter, referred to as HST) 10 includes a variable displacement hydraulic pump 21 and a hydraulic motor 22, and a movable swash plate of the variable displacement hydraulic pump 21. Is controlled through a hydraulic servo mechanism 61 housed in the housing 31.

The hydraulic servo mechanism 61 includes a piston chamber 70 of the hydraulic pump 21 in the housing 31 and a piston 71 housed in the piston chamber 70. A pin shaft 23 protruding from the movable swash plate of the hydraulic pump is fitted to the side surface of the piston 71, and a through hole is vertically opened at the axial center position of the piston 71, and a spool 72 is provided in the through hole. It is slidably fitted.

The piston 71 is provided with an oil passage communicating between the upper and lower portions of the piston chamber 70. The oil passage is communicated or blocked by sliding of the spool 72, and is formed above and below the piston 71. Pressure oil is supplied to the pressure chamber 70a or the lower pressure chamber 70b so that the piston 71 can slide up and down. A fitting groove 75 is provided on the outer periphery of the lower portion of the spool 72, and the fitting groove 75
One end 41 of the pin 41 as a drive pin of the spool 72
a is fitted. Further, the pin 41 is turned up and down by turning the operation lever 20 of the hydraulic servo mechanism 61 and the spool 72 is moved up and down accordingly.

As described above, the movable swash plate of the hydraulic pump 21 is rotated by vertically operating the piston 71 and the spool 72 by rotating the operation lever 20, thereby shifting the speed of the traveling HST 10. ing.

The hydraulic circuit of the HST 10 provided with the hydraulic servo mechanism 61 as described above will be described. FIG.
As shown in the figure, the hydraulic pump 21 and the hydraulic motor 22 are connected by main circuits 32R and 32L, and check valves 44 and 44 are interposed between the main circuits 32R and 32L and the charge circuit 53. I have. The charge pressure from the charge pump 51 is applied to the charge circuit 53, and when the operating oil in the main circuits 32 </ b> R and 32 </ b> L becomes insufficient, the charge circuit 53 outputs the check valve 44.
The hydraulic fluid is supplied to the main circuits 32R and 32L via the. In addition, the charge circuit 53 includes
A relief valve 54 is provided in a circuit leading to the check valves 44 to adjust the hydraulic pressure in the main circuits 32R and 32L.

A servo control pressure is supplied from the charge pump 51 to a hydraulic servo mechanism 61 for controlling the swash plate angle of the movable swash plate 21c of the hydraulic pump 21 through a servo control passage 55. The servo control pressure is supplied to the upper pressure chamber 70a or the lower pressure chamber 70b of the piston chamber 70 by sliding the spool 72 by rotating the operation lever 20, and the piston 71 is slid to move the movable swash plate. The swash plate angle of 21c is controlled. A constant differential pressure reducing valve 5 is provided at an intermediate portion of the servo control passage 55, that is, at an inlet of a control circuit of the hydraulic servo mechanism 61.
7 are provided.

Next, the constant differential pressure reducing valve 57 will be described. As shown in FIGS. 1, 2, and 5, a constant differential pressure reducing valve 5
7 is housed in the housing 31 of the HST 10 near the hydraulic servo mechanism 61. The constant differential pressure reducing valve 57 is provided with a pressure chamber 58 formed in the housing 31.
The piston 59 is slidably fitted therein, and the piston 59 is urged upward by a spring member 56 provided in the pressure chamber 58. The servo control passage 55 is set such that the charge pump 51 side of the constant differential pressure reducing valve 57 is located on the upstream side of the control passage 55a.
7, the hydraulic servo mechanism 61 is connected to the downstream control passage 55b.
It has been.

The pressure chamber 58 is divided into an upstream pressure chamber 58a and a downstream pressure chamber 58b by a piston 59. The upstream pressure chamber 58a and the downstream pressure chamber 58b are
The orifices 59a formed in the piston 59 communicate with each other. The upstream pressure chamber 58a is formed by the communication port 59b.
The communication with the upstream control passage 55a is possible, and the downstream pressure chamber 58b is in communication with the downstream control passage 55b.

The constant differential pressure reducing valve 57 thus configured
When the control oil from the charge pump 51 flows into the upstream pressure chamber 58a through the upstream control passage 55a, the control oil in the upstream pressure chamber 58a
The pressure is guided to the downstream side pressure chamber 58b through a, and supplied to the hydraulic servo mechanism 61 from the downstream side control passage 55b.

In this case, since the space between the upstream pressure chamber 58a and the downstream control passage 55b is narrowed by the orifice 59a, there is no space between the upstream pressure chamber 58a and the downstream control passage 55b. A differential pressure occurs. That is, since the control oil that has flowed into the upstream pressure chamber 58a is throttled by the orifice 59a and flows out to the downstream pressure chamber 58b, the pressure in the upstream pressure chamber 58a is lower than the pressure in the downstream pressure chamber 58b. Becomes larger.

While the pressure difference between the upstream pressure chamber 58a and the downstream pressure chamber 58b is smaller than a predetermined value, for example, as shown in FIG.
Is within the differential pressure range Pa shown in FIG.
The flow rate of the control oil flowing into the downstream pressure chamber 58b through the orifice 59a increases in proportion to the increase in the flow rate of the control oil flowing into the inside a.

However, when the pressure difference between the upstream pressure chamber 58a and the downstream pressure chamber 58b becomes larger than a certain value,
For example, when the pressure falls within the differential pressure range Pb shown in FIG. 6, the piston 59 moves downward against the urging force of the spring member 56. When the piston 59 moves downward, the communication area between the upstream control passage 55a and the communication port 59b is reduced, the amount of control oil flowing into the upstream pressure chamber 58a is reduced, and the pressure in the upstream pressure chamber 58a and the downstream pressure are reduced. Since the pressure difference between the inside of the chamber 58b is reduced, the movement of the piston 59 is stopped at a position where the pressure difference and the urging force of the spring member 56 are balanced. Thus, in the differential pressure range Pb, regardless of the flow rate of the control oil in the upstream control passage 55a, the downstream pressure chamber 58
The flow rate of the control oil flowing out to b becomes constant, and the flow rate of the control oil supplied to the hydraulic servo mechanism 61 can be made constant.

In this case, the differential pressure range Pa of the differential pressure between the upstream pressure chamber 58a and the downstream pressure chamber 58b is determined by the magnitude of the spring force of the spring member 56.
8a and the downstream pressure chamber 58b are in a differential pressure range Pb.
The flow rate F to the downstream pressure chamber 58b when the pressure is inside is determined by the diameter d of the orifice 59a formed in the piston 59. Therefore, the differential pressure ranges Pa and F can be adjusted by changing the spring force of the spring member 56 and the diameter d of the orifice 59a, respectively.

Here, a conventional HST with a hydraulic servo mechanism is used.
In this case, when the operation lever 20 of the HST is suddenly operated, for example, when the speed is rapidly decelerated, the pressure in the upper pressure chamber 70a decreases, and the upper pressure chamber 70a in the oil passage of the spool 72 communicating with the upper pressure chamber 70a. And the area of communication with
As a result, the flow speed of the control oil into the upper pressure chamber 70a increases, and the moving speed of the piston 71 and the movable swash plate 21c also increases, causing a shock to the working machine.

However, as in this example, the hydraulic servo mechanism 6
By providing a constant pressure reducing valve 57 at the inlet of the first control circuit, the differential pressure between the upstream pressure chamber 58a and the downstream pressure chamber 58b, that is, the upstream control which is the control circuit Passage 5
When the differential pressure between the pressure chamber 5a and the upper pressure chamber 70a becomes equal to or more than a predetermined value, the flow rate of the control oil flowing into the upper pressure chamber 70a by the constant differential pressure reducing valve 57 becomes constant. With this, HS
Even when the operation lever 20 of T10 is suddenly operated, the movement of the piston 71 and the movable swash plate 21c with respect to the movement of the operation lever 20 can be made slow, and the shock of the working machine can be reduced. ing. If the size of the diameter d of the orifice 59a formed in the piston 59 of the constant differential pressure reducing valve 57 is made equal to the throttle diameter of the conventionally provided throttle valve, the control oil is supplied to the servo mechanism 61 at a low temperature. A large shock reduction effect can be obtained without causing any trouble such as the work machine not stopping due to the inflow.

The constant differential pressure reducing valve 57 is a HST10
Is housed in the housing 31, there is no need to provide a dedicated housing for the constant differential pressure reducing valve 57, and the servo control passage 55 can be formed directly in the housing 30, eliminating piping members. Therefore, the shock reduction mechanism can have a simple and inexpensive configuration. Further, since the cover member above the constant pressure reducing valve 57 is also used as the piston chamber cover 70c for closing the upper part of the piston chamber 70 in the hydraulic servo mechanism 61, the cover member dedicated to the constant pressure reducing valve 57 is used. Need not be provided, and a more inexpensive configuration can be achieved.

[0025]

As described above, the present invention has the following advantages. That is, a constant differential pressure reducing valve for controlling the control oil flow rate is provided at the inlet of the control circuit for controlling the operation of the hydraulic servo mechanism. When the pressure difference between the piston and the pressure chamber for operating the hydraulic servo mechanism becomes equal to or more than a predetermined value, the flow rate of the control oil flowing into the pressure chamber can be made constant. As a result, for example, even when the operation lever of the HST for operating the hydraulic servo mechanism is suddenly operated, the movement of the piston with respect to the movement of the operation lever can be made slow, and the working machine on which the HST is mounted Can be reduced. If the size of the orifice diameter formed in the piston of the constant pressure differential pressure reducing valve is made equal to the throttle diameter of the conventional throttle valve, the control oil will not flow into the servo mechanism at low temperatures and the working machine will not work. A large shock reduction effect can be obtained without causing any troubles such as the stop of the motor.

Furthermore, the constant pressure differential pressure reducing valve is built in the housing constituting the control circuit of the hydraulic servo mechanism, so that the housing dedicated to the constant pressure differential pressure reducing valve is provided. Need not be provided, and since the servo control passage can be formed directly in the housing and the piping member can be omitted, the shock reduction mechanism can be made simple and inexpensive.

Further, the cover member of the constant pressure differential pressure reducing valve is also used as the cover member of the piston chamber in which the piston of the hydraulic servo mechanism is housed, so that it is exclusively used for the constant pressure differential pressure reducing valve. There is no need to provide a cover member, and a more inexpensive configuration can be achieved.

[Brief description of the drawings]

FIG. 1 is a side view showing a hydraulic continuously variable transmission provided with a hydraulic servo mechanism provided with a constant differential pressure reducing valve of the present invention.

FIG. 2 is a plan view of the same.

FIG. 3 is a front sectional view showing a hydraulic servo mechanism.

FIG. 4 is a diagram showing a hydraulic circuit of a hydraulic continuously variable transmission equipped with a hydraulic servo mechanism provided with a constant differential pressure reducing valve.

FIG. 5 is a side sectional view showing a constant differential pressure reducing valve.

FIG. 6 is a diagram showing a flow rate control characteristic of a constant differential pressure reducing valve.

FIG. 7 is a diagram showing a hydraulic circuit of a hydraulic stepless transmission having a conventional hydraulic servo mechanism.

[Explanation of symbols]

 Reference Signs List 10 hydraulic continuously variable transmission (HST) 20 operation lever 21 hydraulic pump 21c movable swash plate 22 hydraulic motor 31 housing 55 servo control passage 56 spring member 57 constant differential pressure reducing valve 58 pressure chamber 58a upstream pressure chamber 58b downstream Side pressure chamber 59 Piston 61 Hydraulic servo mechanism 70 Piston chamber 71 Piston 72 Spool

Claims (3)

[Claims] 1. A hydraulic servo mechanism, wherein a constant differential pressure reducing valve for controlling a control oil flow rate is provided at an inlet of a control circuit for controlling the operation of the hydraulic servo mechanism. 2. The hydraulic servo mechanism according to claim 1, wherein the constant differential pressure reducing valve is incorporated in a housing constituting a control circuit of the hydraulic servo mechanism. 3. The hydraulic servo mechanism according to claim 2, wherein a cover member of the constant differential pressure reducing valve is also used as a cover member of a piston chamber in which a piston of the hydraulic servo mechanism is housed.