JP3294863B2 - Pump control device for hydraulic transmission mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling a pump discharge amount of a hydraulic transmission mechanism.

[0002]

2. Description of the Related Art A hydraulic transmission mechanism (HST) used in a construction machine or the like is composed of a hydraulic pump driven by an engine and a hydraulic motor that rotates by receiving pump discharge oil.

As disclosed in Japanese Patent Application Laid-Open No. Sho 63-214562, while the pump discharge amount is controlled substantially in proportion to the engine speed, the discharge amount decreases when the pump load pressure exceeds a predetermined value. In this way, the pump driving horsepower, which is the product of the discharge pressure and the discharge amount, is kept at a constant value so that the engine is not overloaded.

[0004]

In order to perform such control, a regulator piston for adjusting the tilt angle of the swash plate for controlling the pump discharge amount is provided, and the hydraulic pressure guided to the left and right of the regulator piston is controlled. Feedback control is performed by a regulator.

The control regulator includes a horsepower control valve for controlling the discharge pressure from the charge pump, a differential pressure control orifice, an inching valve, a hydraulic switching valve for distributing the control pressure, and the like. Although the control hydraulic pressure is controlled, these hydraulic devices are arranged in a sub-body different from the circumstance in which the control regulator and the like are stored.

[0006] For this reason, the configuration of the control section including the control regulator is complicated, the number of parts is large, and high accuracy is required for functional parts. Was.

An object of the present invention is to simplify the structure of the pump control device and reduce the number of parts.

[0008]

According to the present invention, there is provided a regulator piston for adjusting an angle of a swash plate for controlling a discharge amount of a main pump, hydraulic chambers on left and right sides of the regulator piston,
Relative displacement within the left and right ends of the regulator piston
One end is seated on the spring seat housed in Noh and the other end is
Springs respectively arranged to be seated on the inner end of the regulator piston, and the hydraulic pressure at both ends of the regulator piston
The chambers are respectively housed in the left and right pressure chambers facing the
Can be engaged with the other end of the
Force and the other said split seated on the regulator piston
Of the regulator piston due to the balance with the
A main spool for holding and controlling the position , a hydraulic switching valve for selectively supplying a discharge pressure of a charge pump interlocked with the main pump to one of the left and right pressure chambers , and an inner end of a regulator piston slidably. A free piston that penetrates and selectively contacts the left and right main spools via the spring seat, and the pressure of the one pressure chamber according to the position of the main spool through an orifice to a hydraulic chamber on the opposite side to the other. And a guiding passage.

[0009]

When the discharge pressure of the charge pump, which varies proportionally according to the engine speed, is introduced into one of the pressure chambers via the hydraulic switching valve, the main spool is displaced while compressing the spring. In response to this, the holding pressure in the hydraulic chamber on the opposite side is generated, the regulator piston is displaced against the main spool, and the pump discharge increases. At steady (or maximum) engine speed, the pump reaches its maximum displacement.

When the pump load increases at a discharge rate corresponding to the engine speed, a reaction force that pushes the regulator piston back toward the neutral position acts, and the holding pressure of the hydraulic chamber increases. This holding pressure causes the free piston to push back the main spool and release the holding pressure in the hydraulic chamber according to the position of the main spool. For this reason, the regulator piston is displaced toward the neutral position, and the pump discharge amount is reduced.

[0011]

Embodiments of the present invention will be described below.

In FIG. 1, reference numeral 1 denotes a main pump which rotates by being driven by an engine (not shown), 2 denotes a charge pump which works in conjunction with the main pump 1, and 3 denotes a reversible rotary drive which receives oil discharged from the main pump 1. The hydraulic motors 4 and 5 are hydraulic circuits connecting the main pump 1 and the hydraulic motor 3 and constitute a hydraulic transmission mechanism (HST).

A regulator piston 10 is provided to control the tilt angle of a swash plate (not shown) for adjusting the discharge amount of the main pump 1.

As shown in FIG. 2, the regulator piston 10 connected to the swash plate arm is slidably disposed inside the pump case 11, and the holding pressure of the regulator piston 10 is selectively provided on the left and right sides. Hydraulic chamber 12 led to
A and 12B are formed. Main spools 13A and 13B are slidably housed in the pump case 11 at both ends of the regulator piston 10, respectively.

These main spools 13A and 13B are
Spring seats 14A, 14B and spring 15
A contacts the regulator piston 10 via A and 15B. In addition, the free piston 16 penetrates freely through the center of the regulator piston 10, and the free piston 1
6 comes into contact with the main spools 13A, 13B via the spring seats 14A, 14B.

A control pressure corresponding to the discharge pressure of the charge pump 2 is selectively guided to the pressure chambers 17A, 17B containing the main spools 13A, 13B via a hydraulic pressure switching valve (solenoid valve) 18.

The hydraulic chambers 12A and 12B accommodating the regulator piston 10 are connected to annular ports 19A and 19A formed around main spools 13A and 13B on opposite sides.
It communicates with 19B by passages 21A and 21B with orifices 20A and 20B interposed in the middle.

In the main spools 13A and 13B, a through hole 21 communicating with the pressure chambers 17A and 17B and an annular groove 24 draining toward the tank on the outer periphery of the spool are formed with the annular ports 19A and 19B interposed therebetween. Depending on the position of the main spools 13A, 13B, the annular ports 19A, 1
Control the pressure acting on 9B.

That is, in the retreat position where the control pressure acting on the main spools 13A and 13B is small, the annular port 1
9A and 19B are in large communication with the low-pressure annular groove 24 to reduce the pressure, whereas in the forward position the annular ports 19A and 19B
19B is communicated with the high-pressure through-hole 21 to increase the pressure, and at an intermediate position, the pressure is increased or decreased according to the degree of communication between the annular groove 24 and the through-hole 21.

Incidentally, 31A and 31B are main spools 1
This is an adjuster for regulating the retreat positions of 3A and 13B and adjusting the neutral position of the regulator piston 10.

The hydraulic switching valve 18 is provided with the pressure difference 17A,
The passages 22A and 22B communicating with the control passage 17B respectively communicate with the control passage 23 by switching.
The discharge pressure from the charge pump 2 is led to 3.

An inching spool 25 is interposed in the middle of the control passage 23, and opens a return passage 26 for releasing the control pressure to a low pressure side by rotation of the inching spool 25.
This reduces the pump discharge toward zero.

A choke 27 for temperature compensation is interposed in the control passage 23 upstream of the inching spool 25 to adjust the control pressure in accordance with the oil temperature. further,
Reference numeral 28 denotes a variable orifice for adjusting the inclination characteristics of the rotation speed and the flow rate. Hydraulic oil passes through a range equal to or higher than the set pressure of the relief valve on the upstream side. , Each of which is interposed in the middle of a passage branched from the control passage 23 and connected to the return passage 26, thereby adjusting the reference value of the control pressure introduced into the control passage 23.

The configuration is as described above. Next, the operation will be described.

The discharge pressure of the charge pump 2 rotating together with the main pump 1 rises substantially in proportion to the engine speed. The discharge oil from the charge pump 2 is sent into the control passage 23, and a part of the oil is leaked to the low pressure side by the variable orifices 28 and 29, thereby adjusting the flow characteristics of the control pressure at the time of starting and the number of revolutions.

This control pressure is guided to one of the main spools 13A and 13B via the inching spool 25 when the hydraulic switching valve 18 is switched.

The switching of the hydraulic switching valve 18 is arbitrarily determined by the operator determining whether the vehicle is moved forward or backward. If the control pressure is introduced to one pressure chamber 17A, the other pressure chamber 17B Drained to the tank side.

Then, the main spool 13A is displaced while compressing the spring 15A, and at the same time, introduces pressure from the through hole 21 to the annular port 19A. Will be introduced as At this time, the other hydraulic chamber 12
A is drained to the tank side via the annular port 19B.

For this reason, the regulator piston 10 moves to the left in the drawing while compressing the spring 15A. However, the control pressure applied to the main spool 13A causes the main spool 13A to push back the spring 15A, and the free piston 16 slidably penetrating the center of the regulator piston 10 is moved to the right hydraulic chamber 1
2B, the spring seat 14 is pressed by the holding pressure.
Move to the left until the main spool 13A contacts
In order to exert an opposing force on the displacement of the piston, the regulator piston 10 stops at a position where these are balanced.

In this manner, the regulator piston 10
Is controlled, the swash plate tilt angle of the main pump 1 changes, and the discharge flow rate changes accordingly. That is, the swash plate tilt angle increases in accordance with the control pressure (charge pump discharge pressure) applied to the main spools 13A and 13B, and the discharge flow rate increases.

On the other hand, a reaction force depending on the pump discharge pressure (pump load) acts on the swash plate in a direction to return the swash plate tilt angle to its original value, and this is a tilt moment proportional to the length of the swash plate arm. Acts in a direction to return the regulator piston 10 to the neutral position.

Since the return force of the regulator piston 10 due to this moment compresses the hydraulic chamber 12B, the holding pressure of the hydraulic chamber 12B increases due to the compression force. Therefore, the free piston 16 is further pushed to the left, and pushes back the main spool 13A. Main spool 13A
As a result, the degree of communication between the annular port 19A and the low-pressure annular groove 24 increases, and the regulator piston 10 is retracted toward the neutral position while releasing the holding pressure of the hydraulic chamber 12B.

Then, the regulator piston 10 stops at the position where these are balanced. In this way, the acting force based on the pump discharge pressure is fed back, and the discharge flow rate of the main pump 1 is controlled according to the discharge pressure.

The specific operation will be described in more detail with reference to FIG.

In the following description, each symbol has the following meaning.

P ₃ : Control pressure applied to main spool P ₅ : Holding pressure of regulator piston A: Pressure receiving area of regulator piston a: Pressure receiving area of main spool b: Pressure receiving area of free piston f: Initial load of spring k: Spring the spring constant x: displacement of the regulator piston L: arm length of the swash plate M: tilting moment (1) according to the swash plate flow control now takes control pressure P ₃ on the left side of the main spool 13A, the right hydraulic chamber regulator piston 10 is moved to the left by the holding pressure P ₅ of 12B, and stationary at a certain position x. The balance of the force acting on the main spool 13A is as follows due to the reaction force between the spring 15A and the free piston 16.

P ₃ · a = f + k · x + P ₅ · b The holding pressure P ₅ applied to the regulator piston 10 is as follows, including the reaction force based on the tilting moment acting on the regulator piston 10.

P ₅ (A−b) = f + k · x + M / L Therefore, P ₅ = (f + k · x + M / L) / (A−b) The swash plate tilting moment M is represented by the number of rotations, tilt angle, and discharge. Although it changes with pressure, the contribution ratio of the discharge pressure acting on the swash plate as the discharge reaction force of the main pump is the largest, and the discharge pressure P
(Pump load pressure).

The load pressure (the process to reach the maximum flow rate) engine speed flow control in until it reaches a steady (maximum) rotation is small, when P ₅ is almost negligible, the formula, P ₃ · a = f + k · x Therefore, the displacement amount x of the regulator piston 10 and, consequently, the pump discharge amount Q are as follows.

[0040] x = As shown in _{(P 3 · a-f)} / k α (Q) 7, when the P ₃ will change linearly with the rotational speed N, the displacement amount of the regulator piston 10 x
( ∝Q ) also changes correspondingly. However, the displacement amount of the regulator piston 10 is regulated at a constant value,
Since it does not increase any more, the maximum tilt angle is also regulated to a predetermined value.

In this manner, the displacement of the regulator piston 10 is controlled via the springs 15A and 15B in accordance with the discharge pressure P (≒ control pressure) of the charge pump 2 proportional to the engine speed N. As shown in FIG. 4, the discharge amount Q of the main pump 1 is controlled substantially in proportion to the engine speed N.

(2) Horsepower Control It is assumed that the pump load has increased during operation at the maximum rotational speed (the pump flow rate is maximum). From the above equation, P ₅
= (F + k.x + M / L) / (A-b), wherein the tilting moment M increases substantially in proportion to the pump discharge pressure P as shown in FIG.

Here, from the equation, P ₅ = (M / L) / (A−b) + (f + k · x) / (A−b), so that (M / L) / (A−b) is as a function of the discharge pressure P, when expressed on the basis of the relationship between the discharge pressure P of the P _5, as shown in FIG.

From the above equation, the displacement amount x of the regulator piston 10 is given by: x = (P ₃ .a-f-P ₅ .b) / k This x is considered in relation to the discharge pressure P. In the formula, except P ₅ is not a function of directly with the discharge pressure P, when the maximum tilt angle, and a constant in the P ₃ · a-f
Since it can be considered , x is displaced to the maximum, so
As shown in FIG. 10, after a certain pressure P ₀ , x decreases as the discharge pressure P increases as P ₅ increases.

The displacement x of the regulator piston 10 is substantially proportional to the discharge flow rate Q. Therefore, if the characteristic of this broken line is set so as to be in contact with the constant horsepower curve of the engine, the horsepower control is performed as shown in FIG. Can be.

That is, the control pressure acting on the main spools 13A and 13B, the acting force of the springs 15A and 15B,
And the change in the tilting moment due to the pump load is detected as the holding pressure of the regulator piston 10, and this is applied to the free piston 16 to cause the main spool 13A, 1
By feeding back to 3B, the pump load can be controlled to a constant value so that the generated horsepower of the engine does not exceed a constant value.

(3) Inching Control When the opening of the inching spool 25 is zero, all control pressure is directly introduced into the pressure chambers 17A and 17B of the main spools 13A and 13B, and the pump discharge flow rate is proportional to the engine speed. When the inching pedal (not shown) is operated to open the opening of the inching spool 24, the discharge oil from the charge pump 2 escapes to the return passage 26, and the control pressure decreases.

As the control pressure P3 decreases, the displacement of the main spools 13A, 13B and the regulator piston 10 decreases, and the pump discharge decreases. When fully opened, the control pressure is equal to the pressure on the lower pressure side of either the main passage 4 or 5 (equal to the charge relief set pressure for replenishing leakage in a closed circuit), and thus the regulator piston 10 is in the neutral position. And the pump discharge becomes zero.

By operating the inching pedal in this manner, the rotation of the hydraulic motor 3 can be stopped and the running of the vehicle can be stopped even though the main pump 1 (engine) is rotating. .

In this case, since the inching spool 25 is directly inserted into the control passage 23, the responsiveness of the control pressure change is good, and the responsiveness to the inching operation can be enhanced.

[0051]

According to the present invention as described above, according to the present invention, regulation
In the pressure chamber facing the hydraulic chamber at both ends of the
The holding pressure of the hydraulic chamber behind the
To adjust the position of the regulator piston.
The main spool is located at
Supply the discharge pressure of the charge pump proportionally to the pressure chamber
Control the pump discharge in proportion to the engine speed.
Controlled flow rate can be controlled. In addition, the regulator pi
Slidably through the tongue and pressed by the holding pressure of the hydraulic chamber.
Freepis to selectively contact the left and right main spools
Tons, when the pump load pressure exceeds a predetermined value
The holding pressure rises and the main sp
Pressure, reduce the holding pressure, and
The pump toward the neutral position, reducing the pump output
The pump drive horsepower, which is the product of the discharge pressure and the discharge amount
To a constant value to prevent the engine from becoming overloaded.
Controlled horsepower. And the free piston is
Slide the regulator piston freely through the left and right
Only to selectively contact the spool.
Therefore, the structure can be significantly simplified, the number of parts can be reduced, the cost can be reduced, and the reliability of operation is improved because there are few parts requiring high precision.

[Brief description of the drawings]

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

FIG. 2 is a sectional view centering on a regulator piston.

FIG. 3 is an explanatory diagram for explaining an operation principle.

FIG. 4 is a flow rate control characteristic diagram showing a relationship between a pump flow rate and a rotation speed.

FIG. 5 is a horsepower control characteristic diagram showing a relationship between a pump flow rate and a pressure.

FIG. 6 is an inching control characteristic diagram showing a relationship between a pump flow rate and an opening degree of an inching spool.

FIG. 7 is a characteristic diagram showing a relationship between a control pressure and a displacement amount of a regulator piston with respect to a pump rotation speed.

FIG. 8 is a characteristic diagram showing a relationship between a pump discharge pressure and a swash plate tilting moment.

FIG. 9 is a characteristic diagram showing a relationship between a pump discharge pressure and a holding pressure.

FIG. 10 is a characteristic diagram showing a relationship between a pump discharge pressure and a displacement amount of a regulator piston.

[Explanation of symbols]

 1 Main Pump 2 Charge Pump 3 Hydraulic Motor 10 Regulator Piston 12A Hydraulic Chamber 12B Hydraulic Chamber 13A Main Spool 13B Main Spool 15A Spring 15B Spring 16 Free Piston 17A Pressure Chamber 17B Pressure Chamber 18 Hydraulic Switching Valve 19A Annular Port 19B Annular Port 20A Orifice 20B Orifice 21A passage 21B passage 23 control passage 25 inching spool

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F16H 61/42

Claims (2)

(57) [Claims] 1. A regulator piston for adjusting the <br/> angle of the swash plate to control the discharge rate of the main pump, and the hydraulic chamber of the left and right of the regulator piston, respectively relative displacement friendly in the left and right ends of the regulator piston
One end is seated on the spring seat housed in Noh and the other end is
The springs respectively arranged to be seated on the inner end of the regulator piston, and the left and right facing the hydraulic chamber at both ends of the regulator piston
The other end of the spring seat
Can be engaged with the pressure in one pressure chamber and the regulator
The balance with the reaction force of the other spring seated on the piston
The lance holds and controls the position of the regulator piston.
That the main spool, left the right selectively supplying hydraulic switching valve discharge pressure of the charge pump in conjunction with the main pump to one of the pressure chambers, to slide freely through the inner end of the regulator piston of the main spool and the selectively abuts the free piston via the spring seat, and a passage for introducing through one another orifice to the hydraulic chamber on the opposite side the pressure of the one pressure chamber above depending on the position of the main spool A pump control device for a hydraulic transmission mechanism, comprising: 2. An inching spool interposed in a control passage for guiding the discharge pressure of a charge pump to a main spool and releasing the discharge pressure to a low pressure side in accordance with an opening degree of the charge pump.
3. The pump control device for a hydraulic transmission mechanism according to claim 1.