JPS5814954B2 - Direct-acting servo valve - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a servo valve used in a hydraulic control system, and particularly to a direct-acting servo valve in which a spool is directly driven by a zero-force motor.

[Prior art]

Servo valves are used to accurately control the position of cylinders, rams, etc. in hydraulic equipment using fluid pressure, but they are characterized by extremely delicate movements, such as the rolling position of a rolling mill. In order to control plate thickness accurately on the order of microns, the amount of oil supplied to the hydraulic cylinder is controlled by the servo valve to control the rolling position of the rolling mill.

In the case of rolling mills, etc., the hydraulic piping is long and the M boundary is poor, so it is inevitably extremely difficult to manage the oil used in the servo valve. Because of the strong demand for superior servo valves, it has become possible to consider the use of a direct-acting servo valve, which features a force motor that directly drives the spool, as shown in Japanese Patent Application Laid-open No. 133780/1983. It happened.

In principle, this has a small-diameter nozzle (and has a major feature of being resistant to foreign substances).

In other words, in the structure of this direct-acting servo valve, the spool that slides inside the sleeve to switch the oil path is integrally connected to the bobbin around which the coil that makes up the force motor is wound. One end of the spool, which is a fixed member installed at the same location and facing the magnet that constitutes the force motor, is held to the magnet by a coiled metal spring, and the other end of the spool is also held by a coiled metal spring. The spool is held by a stationary member, which is a fixed member, to ensure the orientation of the spool.

This is a servo valve that applies a current corresponding to an operation signal to a coil wound around a bobbin, and uses magnetic force to directly move the spool in the axial direction to operate the oil passage [Problems and analysis of conventional technology] However, this servo valve has a problem in that the response (rise) to the spool operation signal is poor.

This is because the elastic members acting on both end faces of the spool are coiled metal springs, that is, coil springs, and this coil spring exerts an uneven axial force on the end faces of the spool.
Since the resultant force of the uneven forces acts diagonally to the axis of the spool, the spool is pushed in the radial direction by the coil spring and pressed against the inner surface of the sleeve, increasing the frictional force between the spool and the sleeve. This is due to this.

In other words, since the winding end portion of the end surface of the coil spring in contact with the end surface of the sleeve is in close contact with the adjacent coil, the spring constant is higher than the portion that is not in close contact, and the spring characteristics of the coil spring in the circumferential direction are non-uniform.

Moreover, since the circumferential position of the coil spring where the spring characteristics are non-uniform changes depending on the position of the winding end of the coil spring, the direction of the reaction force due to the coil spring also varies and is difficult to predict.

Therefore, due to the non-uniformity of the spring characteristics, the resultant force of the non-uniform force exerted by the coil spring on the working surface of the spool is shifted in the radial direction with respect to the axis of the spool, and inevitably presses the spool against the sleeve. This means that a force is generated due to the bias, increasing the frictional force between the spool and the sleeve, and as a result, the response of the spool to operation signals becomes worse.

[Technical problem of the invention]

Therefore, the technical object of the present invention is to make the force applied to the end surface of the spool of a direct-acting servo valve substantially uniform over the entire working surface of the spool by means of an elastic material.

[Technical means of invention]

The technical means taken by the present invention to solve the above technical problems are as follows.

That is, 1) a rubber elastic body having an end face perpendicular to the axis is interposed between one end of the spool and the end face of the fixing member; 1i) the rubber elastic body is interposed between the end face of the spool and the fixing member; It means that it sticks to the end face of the.

[Effect of technical means]

When the coil wound around the bobbin is energized, the bobbin and spool are displaced in the axial direction while elastically deforming (stretching or compressing) the rubber elastic body, and when the energization is cut off, the spool and bobbin are made of rubber. It is returned by the elasticity (spring force) of the elastic body.

By fixing the rubber elastic body between the spool and the fixed member, the rubber elastic body is held on the same axis as the axis of the spool, and the end face of the rubber elastic body is aligned with the axis of the spool. Since the end face is perpendicular to the spool, and the axial expansion and compression are uniform all around, the force exerted on the spool end face by the rubber elastic body is almost uniform over the entire working surface. , the resultant force acts in the axial direction of the spool and does not produce a biased force in the radial direction on the spool due to the elasticity of the elastic material. Since the body is fixed, the spool can be held in the neutral position by one rubber elastic body.

Furthermore, since the rubber elastic body has internal hysteresis, which is a property of rubber itself, it has a damping effect on vibrations of the spool.

This improves the stopping characteristics of the spool.

[Embodiments of the invention]

An example illustrating a specific example of the above technical means will be described below.

The drawing is a cross-sectional view of a 3-way valve type direct-acting servo valve.
A spool 1 slides inside the sleeve 4.

The length-bore valve of this embodiment is, for example, used to input the source pressure Ps into a ram (not shown) and release it from the ram to a drain, and is intended to accurately control this.

Here, the ram pressure is shown as Pc, and the drain pressure is shown as Pd.

The spool 1 is integrally connected to a bobbin 1 having a coil 8 around which an electric wire is wound.

A displacement detector core 2 is loaded on the left end of the spool for the purpose of controlling the servo motor, and a speed detection core 9 is loaded on the right end of the bobbin 7 as necessary in case of damping adjustment.

The body 5 accommodates the sleeve 4 and provides communication between the oil passages, and the displacement detection coil 3 is also mounted opposite the core 2.

The coil 8 constituting the hose motor is inserted into the air gap of the magnetic circuit, and when a current is applied to the coil 8 provided on the bobbin 7 formed by the magnet 12, the magnetic path changes proportionally to the current. A force is generated that drives the spool 1.

Support metal fitting 10 which is the end face of bobbin 7 and magnet 12 side
In between, fU is attached to both so that a homogeneous elastic body 6 with internal damping, such as rubber, is sandwiched therebetween.

Note that the term "clamp" as used herein means that it is interposed between the bobbin 1 and the support fitting 10, and is supported so that its placement position does not shift.The left end of this rubber elastic body 6 is The right end of the bobbin 7 is connected to the support fitting 10, and in practical use, it is partially subject to seizure.

The support fitting 10 can move on the cylindrical surface of the magnet 12.
This support fitting 10 can be moved from side to side by means of a nut 11.

When setting the servo valve to the neutral state, it is sufficient to move the nut 11 left and right to find an appropriate position, and then lock the nut 11 here.

As a result, in the neutral position, no axial force acts on the homogeneous elastic body 6, and the spool 1 can be positioned approximately at the center of the sleeve 4.

From now on, the spool 1 will move based on this neutral position.

For example, rubber is most suitable as the elastic body with internal damping.

The damping effect is given by a hysteresis loop that appears between the force acting on the rubber and its displacement, and is proportional to the area of this hysteresis loop.

Hysteresis indicates the amount of internal friction in the rubber.
In metal splashes, there is practically no internal friction, so there is no hysteresis.

Since the servovalve functions as a control element of a hydraulic servo loop, it is also essential that it has as much damping as possible and good stability.

In this sense, it is extremely preferable for the servo valve supporting elastic body to have sufficient internal damping, not only from structural requirements such as favorable alignment, but also from the viewpoint of control.

As mentioned above, a homogeneous elastic body such as rubber has a large internal damping effect, so the resonance peak is small and stable, and there is no need to unnecessarily stiffen the spring constant of the elastic body.

In addition, since the spring characteristics of the elastic body are homogeneous, even if a force is applied to this elastic body, no force is generated due to deviation in the radial direction, which greatly reduces the frictional force between the spool and the sleeve. You will get it.

[Brief explanation of drawings]

The drawing is a sectional view of a direct-acting servo valve that is an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Spool, 4... Sleeve, 5... Body, 6... Rubber elastic body, 7... Bobbin, 10...
Metal fittings, 11... nuts.

Claims (1)

[Scope of Claims] 1. Direct motion in which a bobbin around which a coil is wound is attached integrally with a spool, and a control current is passed through this coil to generate electromagnetic force to drive the spool in the axial direction relative to a fixed member. In the type servo valve, a rubber elastic body having an end face perpendicular to the axis is interposed between one end face of the spool and the end face of the fixing member, and the rubber elastic body is interposed between the end face of the spool and the fixing member. A direct-acting servo valve that is fixed to the end face of the valve. 2. The direct-acting servo valve according to claim 1, wherein the fixed member is provided with a moving device for moving itself in the axial direction.