GB2121928A

GB2121928A - Pressure relief valve

Info

Publication number: GB2121928A
Application number: GB08315933A
Authority: GB
Inventors: Wolfgang Hohl
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1982-06-11
Filing date: 1983-06-10
Publication date: 1984-01-04
Also published as: IT8346844A1; JPH0364746B2; FR2528523B1; IT8334903V0; GB2121928B; IT1172814B; FR2528523A1; GB8315933D0; JPS58221080A; DE3222116C1; IT8346844A0

Abstract

The valve is provided with a spring loaded ball (7) acting as a closing element in a valve housing (1). A spring guide bolt (4) presses the ball (7) onto a valve seat (2) and at least three damping balls (6) of the same diameter are disposed between the spring guide bolt and the closing ball, which damping balls fill the interior of the valve housing with a small play. In order to reduce hysteresis the outer periphery (11) of the end face (10) of the spring guide bolt, on which the damping balls are disposed, lies further forwards in the valve housing, with respect to the valve port (2) on the pressure side, than the inner area of said end face. The end face may have, at least approximately, a spherical or conical curvature. <IMAGE>

Description

SPECIFICATION Directly controllec' pressure relief valve The invention relates to a directly controlled pressure relief valve with a spring-mounted ball, acting as the closing element in a valve housing, and a spring guide bolt which presses the ball onto a valve seat, at least three damping balls having the same diameter being disposed between the spring guide bolt and the closing ball, which damping balls fill the interior of the valve housing with a small play or clearance.

Pressure relief valves are used in hydraulic or pneumatic systems. They are designed to prevent a specific predetermined pressure from being exceeded. The spring-mounted ball acting as the closing element is raised from the bore if a predetermined pressure is exceeded so that the pressure medium may escape into a chamber disposed behind the ball. There is, however, the risk with pressure relief valves that they may start to vibrate and "dance" over the release aperture, leading to considerable noise development. In addition, these vibrations may lead to damage to the edges of the bore and therefore to the destruction of the pressure relief valve.

For this reason it has already been proposed, in the German Auslegeschrift 28 26 643, to use a valve in which at least three damping balls of the same diameter are disposed in the valve housing between the spring guide bolt and the closing ball.

These damping balls are disposed with a small play in the interior of the valve housing and in a simple way prevent excess axial vibration and a radial oscillation of the closing ball. This is achieved, on one hand, by providing a centering action on the closing ball and, on the other hand, as a result of the wall friction of the damping balls on the inner wall of the valve housing. A radial component of the pressure force in the damping balls is therefore produced, which is supported in each case on the valve housing. Thk'friction arising in this respect leads to a corresponding damping of the movement of the closing ball.

However, it has now been established that this known pressure relief valve is subject to a relatively high hysteresis which increases with increasing pressure. In addition, pressure adjustment does not always follow the spring tension in a strictly linear manner. The cause of this drawback lies in the wall friction of the damping balls. After opening of the pressure relief valve, the pressure must therefore be reduced again to a relatively iarge extent until the closing ball again closes the bore under the force of the spring.

There is therefore an unacceptably excessive downward drop in the pressure in the system to be controlled.

An object of the present invention is to provide a pressure relief valve of the type mentioned above, in which hysteresis is substantially eliminated and pressure adjustment follows the spring tension in a manner which is as linear as possible, whilst retaining the other known advantages of the basic arrangement.

In accordance with the invention this object is achieved by a directly controlled pressure relief valve with a spring-mounted ball acting as the closing element in a valve housing and a spring guide bolt which presses the ball onto the valve seat, at least three damping balls of the same diameter being disposed between the spring guide bolt and the closing ball, which dumping balls fill the interior of the valve housing with a small play, characterised in that the outer periphery of the end face of the spring guide bolt, on which the damping balls lie, id disposed further forward in the valve housing with respect to the valve port on the pressure side than the inner, axial area of the end face.

In the known pressure relief valve the contact surface on the spring guide bolt for the damping balls was planar and extended perpendicular to the longitudinal axis of the valve housing. As a result of these support conditions, the damping balls were subject to relatively high spreading forces which were supported on the housing wall.

As a result of the fact that the end face of the spring guide bolt forming the contact surface is embodied, in accordance with the invention, such that the outer periphery lies further forward than the inner area of the end face, the radially acting spreading forces are lower and may also be varied in accordance with the deviation of the end face from a plane surface. The lower spreading forces therefore lead to lower friction levels, as a result of which hysteresis is substantially avoided and the pressure adjustment may follow the spring tension in a strictly linear manner.

In one embodiment of the invention, the bolt end face is provided at least approximately with a ball-shaped curvature, which may be a spherical segment.

The smallest limit radius of the end face desirably corresponds to the radius of the closing ball together with the diameter of a damping ball.

With this limit radius, no horizontal spreading forces in principle occur.

A further solution of the invention consists in that the end face has at least approximately the shape of a conical envelope . This conical envelope is formed by rotation of the related tangents on the damping balls in the contact point about the longitudinal axis of the valve. In the case of simple lifting movements in the axial direction, this solution is identical to the spherical segment.

The spreading forces in the case of the cone are only modified to a somewhat greater extent in the case of an oblique opening of the closing ball, as the cone taper is always constant, whereas in the case of a sperical segment the taper is adaptable.

In the case of very small opening paths, as would arise for example if the valve of the invention is used as a servo valve, a conical envelope may also be used without any difficulty.

An embodiment of the invention is described in outline in the following with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through a pressure relief valve in accordance with the invention (with parts cut away), along the line I--I of Figure 2; and Figure 2 is a cross-section through the pressure relief valve of Figure 1 (above the damping balls).

The pressure relief valve, which is installed in a housing portion of the system to be controlled, comprises a valve housing 1 (only part of which is shown), which housing has on one side a valve port 2 at which is developed the pressure to be controlled. On the opposite side of the valve housing 1 there is an outlet port (not shown) for the removal of the pressure medium released. The connection to this outlet port is produced in a simple manner via a central inner bore 3 in a spring guide bolt 4. The spring guide bolt 4 has an enlargement in diameter 5 with and end face 10 acting as the contact surface for three (or more) damping balls 6.

The valve port 2 directed towards the pressure chamber is closed in normal conditions by a closing ball 7 acting as the closing member. A spring 8 ensures a corresponding initial tension, which spring is supported on one side on the rear side of the diameter enlargement 5 and on the other side (not shown) on the rear wall of the valve housing 1.

The three damping balls 6 are disposed in a common plane lying perpendicular to the direction of opening movement of the closing ball 7. They are of the same diameter and lie in said same plane with a small play in the interior of the valve housing 1. On the forward side, the damping balls 6 lie on the surface of the closing ball 7.

The pressure relief valve operates in the following way: As long as a predetermined pressure is not exceeded in the system to be controlled, i.e. as long as a specific pressure force in the valve port 2 is not exceeded, the closing ball 7 is pressed as the closing member on the valve port 2, under the action of the spring 8. If the predetermined pressure is exceeded, the pressure force on the closing ball 7 is greater than the spring force and the closing ball 7 is lifted from the valve seat. The pressure medium may therefore escape via the central bore 3 in the spring guide bolt 4 to the outlet port of the valve housing. The three damping balls 6 have in this respect both a damping and a centering effect on the closing ball 7.They retain the closing ball 7 on the axis of symmetry and damp the opening movement as a result of the wall friction arising betwen the damping balls and the inner wall of the valve housing.

In the known pressure relief valve, the end face of the spring guide bolt 4, i.e. the contact surface for the damping balls 6, extends in a plane manner perpendicular to the longitudinal axis (axis of opening movement of the closing ball). This plane is shown by dashed lines 9 in Figure 1. In contrast to the known pressure valve, in the present invention the end face 10 facing the valve port 2 on the pressure side is formed such that its outer periphery 11 lies, with respect to the valve port 2, further forward in the valve housing 1 than the inner axial area of the end face 10. This may be achieved in that the end face 10, as shown in Figure 1 ,forms a spherical segment (segment of enveloping sphere). This spherical shape causes, in accordance in each case with the ball radius, a reduction of the horizontal spreading forces of the damping balls 6.This is illustrated in the following with reference to the force developments shown in Figure 1.

A vertical opening force Fv which is shown by the arrow 12, is divided (by the formation of a force triangle) into three forces Fk of the same size.

Fk are the forces which are transmitted in each case from the middle point of the closing ball 7 via the middle point of a damping ball 6. The forces Fk are shown by iines 13 and 14', the line 14' being formed for the closure of the force triangle in a conventional manner by a parallel displacement of the line 14. The force Fk is further transmitted via the end face 10 of the spring guide bolt and via the friction force. In order to form a force triangle, the line 1 3 is in this respect projected as 13' into the middle point M, of a damping ball 6.

For the purpose of comparison, the force distribution in the pressure relief valve of the prior art is firstly described. The point of contact of the damping ball with the plane end face 9 takes place at B0 in the case of the prior art. In this way the force Fk is divided into a vertical and a horizontal force Fh which is shown by the dashed line 1 5.

The vertical portion of the force Fk is transmitted in the vertical direction through the point B0 and its size is represented by the dashed line 1 6. In the embodiment shown, the horizontal component Fh amounts to 36% of the opening force Fv.

In the embodiment illustrated, where the end face 10 is a spherical segment, the ball has the radius shown by the line 17. The point of contact of the damping ball 6 with the end face 10 lies at the point B. As a result of the conventional parallel displacement of the line 1 7 through the tip of the force arrow Fk (line 13'), the line 17' is produced. The horizontal component Fh resulting from this force triangle amounts to only 22% of the force Fv and is shown by the line 1 8.

The smallest limit radius for the end face 10 may also be seen from the force triangle. The smallest limit radius corresponds to the radius of the closing ball 7 together with the diameter of the damping ball 6. In this case, the radius of the spherical segment extends through the middle point Mo of the closing ball and the point of contact of the spring guide bolt 4 with the end face 10 lies at B2. As can be seen, the force Fk would be transmitted directly to the spring guide bolt 4 in this way without the occurrence of a horizontal component. If the radius of the spherical segment were to be made smaller, then in theory the damping balls 6 would move inwardly.

In accordance with the radius selected from the spherical segment, it is possible to select the percentage of the spreading force and the horizontal component Fh' which may therefore be adapted in each case to the particular case of use.

The spreading force required is in particular dependent on the througput fluid current which has to be dealt with. It was observed during tests that with, for example, a throughput of 1 3 litres/min, then up to approximately 200 bar a spreaded force of 3% can be sufficient.

The decisive factor with respect to the frictional force is obviously the surface roughness of the inner wall of the valve housing 1, although this may be taken into account accordingly.

Claims

1. A directly controlled pressure relief valve with a spring-mounted ball acting as the closing element in a valve housing and a spring guide bolt which presses the ball onto the valve seat, at least three damping balls of the same diameter being disposed between the spring guide bolt and the closing ball, which damping balls fill the interior of the valve housing with a small play, characterised in that the outer periphery of the end face of the spring guide bolt, on which the damping balls lie, is disposed further forward in the valve housing, with respect to the valve port on the pressure side, than the inner, axial area of the end face.

2. Pressure relief valve as claimed in claim 1, characterised in that the end face has, at least approximately, a ball-shaped curvature.

3. Pressure relief valve as claimed in claim 2, characterised in that the end face forms a spherical segment.

4. Pressure relief valve as claimed in claim 2 or claim 3, characterised in that the smallest limit of radius for the end face corresponds to the radius of the closing ball added to the diameter of a damping ball.

5. Pressure relief valve as claimed in claim 1, characterised in that the end face has, at least approximately, the shape of a conical envelope.

6. A pressure relief valve substantially as hereinbefore described with reference to the accompanying drawings.