GB2174475A

GB2174475A - A spring return system for a reciprocating component

Info

Publication number: GB2174475A
Application number: GB08511400A
Authority: GB
Inventors: Maurice Tardy; Andre Rousset
Original assignee: Bennes Marrel SA
Current assignee: Bennes Marrel SA
Priority date: 1984-03-13
Filing date: 1985-05-03
Publication date: 1986-11-05
Also published as: GB8511400D0; GB2174475B

Abstract

A spring 7 returns a hydraulic distributing slide 4 to the central position shown. The spring is compressed between the base flanges 8, 9 of two cup-shaped rings 10, 11 without being in contact with conical zones thereof. Each of the bottoms 15 of the rings only engages in frictional contact on the associated cylindrical centring portion 28, 29 of the slide, with which it loses contact immediately movement starts. The arrangement ensures that friction forces, which would disturb the delicate balance between the spring force and the pilot pressure acting on the slide, are kept to a minimum. <IMAGE>

Description

SPECIFICATION A spring return system for a component able to move reciprocally The present invention relates to a device with a spring return, able to operate with minimal frictional losses, to activate a component able to move reciprocally. This system is applied particularly, though not exclusively, to the return of a slide of the kind used on hydraulic distributors, mainly on circuits controlling jacks, valves, pumps or hydraulic motors etc. Such hydraulic circuits are used on machine tools, on workshop equipment, in the aeronautical industry and in various branches of industry.

There are known hydraulic distributors of the type in which a slide has, at one end, two cupshaped rings between which a helical spring is compressed. Each of these two rings bears on a fixed wall in the stator. The slide is able to move in either direction on each side of a central position to which the spring returns it automatically when the assembly is released from control.

In practice, it will be seen that friction arises during the movement, on the one hand between the spring and the rings, and on the other hand between the rings and the corresponding zones of the slide. This friction may lead to the appearance of high spots, which may be particularly inconvenient in the case of a distributor of which the slide has its axial movement controlled by a variable pilot pressure. In fact, at any moment, the axial position of the slide is defined by the balance of two opposing forces, namely on the one hand the thrust at that moment of the spring, and on the other hand the force exercised by the pilot pressure. When the pilot pressure is itself variable, the variable thrust force which it gives rise to is at any moment compared to the resistance force of the spring, and it will be seen that the balance may be distorted if friction resistances appear.

The present invention is intended to alleviate these disadvantages, by achieving a spring return system having minimal frictional losses throughout the operational travel of the movable component, distributing slide or other device.

According to this invention, a spring return system for a component capable of reciprocal movement comprises a coil spring confined endwise between substantially cup-shaped rings mounted on a reduced diameter portion of the component, each ring being arranged to engage a respective shoulder on the component, characterised in that clearance is provided between the internal surface of each ring and the unreduced diameter portions of the component and between the external surface of each ring and the internal surfaces of the major portion of the coils of the spring to reduce and minimise frictional contact therebetween.

Preferably, the spring return system comprises two cup-shaped rings, fitted in opposition to the same end of the movable component, the bottom of the cup of each ring being provided with a central aperture engaged around a zone of smaller diameter of the movable component so as to bear on a shoulder of the latter, a helical spring being arranged around the movable component and the two rings so as to be compressed between the flanges of these rings, and it is characterised in that:: -on the one hand, each ring comprises a body in the external shape of a truncated cone which enlarges in the direction of its flange bearing on the stator, the flange being attached to the funnelshaped truncated part by a zone which is a cylinder of revolution; - on the other hand, the zone of the movable component located between the bottoms of the two rings is of a smaller diameter than that of the central aperture in the bottom of each ring.

According to another characteristic of the invention, each of the two shoulders of the movable component is attached to its reduced section by a short cylindrical zone of revolution, of which the axial length is equal to the thickness of the bottom of the corresponding ring.

According to another characteristic of the invention, each truncated zone of the body of the rings is attached to the associated end flange by a cylindrical zone of revolution, of which the axial length is closely equal to the diameter of the metal wire which constitutes the helical spring.

A preferred embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figure 1 is a view in axial section showing the return end of a hydraulic distributor slide activated by a variable pilot pressure, the assembly being shown in the central rest position.

Figure 2 is a similar view with the distributor slide displaced to the right, compressing its return spring.

There is shown in the drawings a hydraulic distributor of which the stator 1 terminates, at one end, by a fixed casing 2, into which the recall end 3 of a distributor slide 4 projects in the known way.

The movements of the slide 4 in one direction or the other (Figure 1, arrows 5 and 6) to each side of the neutral position shown in Figure 1 are controlled by known methods, not shown, principally by a pilot pressure of variable value.

The return of the slide 4 to the neutral position shown in Figure 1 is ensured by a helical spring 7, compressed between the base flanges 8 and 9 of the two rings 10 and 11 which are fitted in opposition around the reduced section 12 of the end 3 of the slide 4, between two shoulders 13 and 14 on the latter.

The ring 10 has the shape of a cup of revolution of which the transverse bottom 15 is drilled with a circular central opening 16 which bears on the shoulder 13.

According to the invention, the bottom 15 is connected to the base flange 8 by a portion in the shape of a truncated cone of revolution 17 which widens up to a portion, which is a cylinder of revolution, which extends it up to the flange 8.

Similarly, the transverse bottom 19 of the ring 11 is drilled with a circular opening 20 connected by a funnel-shaped truncated zone 21 to a cylindrical zone of revolution 22 which is attached to the flange 9.

The helical spring 7 is compressed between the two flanges 8 and 9 of which the bottoms 15 and 19 are thus held in contact with the shoulders 13 and 14 when the spring is in the neutral centre position (Figure 1).

The diameter 23 of the metal wire constituting the spring 7 is closely equal to the axial length 24 of each of the two cylindrical zones 18 and 22.

In addition, the central reduced section 12 is a cylinder of revolution with a diameter 25 smaller than the diameter of the openings 16 and 20. This central section 12 is connected on each side to a funnel-shaped truncated zone 26, 27, which in turn connects to a centring cylinder of revolution, respectively 28, 29, at the centre of each shoulder 13, 14.

The axial length 30 of each centring cylinder 28, 29, is closely equal to the thickness of the bottom 15, 19, of the corresponding ring 10, 11.

Finally, the assembly of the spring 7 and the rings 10 and 11 is fitted with a large diametrical clearance within the fixed cap or casing 2.

The operation is as follows: When the means of control, not shown displaces the distributing slide 4 towards the right (arrow 5, Figure 2), this slide is immobilised in the position of balance between the opposing forces due on the one hand to the control pressure and on the other hand to the reaction of the spring 7, then compressed to a greater or lesser extent. As regards the components in movement, it will be seen from Figure 2 that there is clearance between these components. As for the support ring 11, which loses contact with the end 3 of the slide 4, there is only frictional contact at the beginning of the travel of this ring on the centring cylinder 29. The length 30 of this cylinder being small, it is, in addition, calculated so that the friction will cease, that is to say that the ring 11 will no longer be in contact with the slide 4, as soon as the zone of control of the fluid passing through the distributor 1, 4 is reached.

In addition, only the last spiral of each of the two ends of the spring 7 is in contact with the corresponding cylindrical centring zone 18, 22; the other parts of the spring do not rub in any way on the rest of the body of the rings, with which they are not in contact, because of the conical shape of the zones 17 and 21.

Claims

1. A spring return system for a component capable of reciprocal movement comprising a coil spring confined endwise between substantially cup-shaped rings mounted on a reduced diameter portion of the component, each ring being arranged to engage a respective shoulder on the component, characterised in that clearance is provided between the internal surface of each ring and the unreduced diameter portions of the component and between the external surface of each ring and the internal surfaces of the major portion of the coils of the spring to reduce and minimise frictional contact therebetween.

2. A spring return system for a component able to move reciprocally, comprising two rings in the shape of cups fitted in opposition to the same end of the movable component, the bottom of the cup of each ring being provided with a central drilling engaged around a zone of the movable component so as to bear on a shoulder thereof, a helical spring being arranged around the movable component and the two rings so as to be compressed between the flanges of these rings characterised in that:: - on the one hand, each ring comprises a body with the external shape of a truncated zone which widens in the direction of its flange bearing on the stator, a flange to which the funnel-shaped conical section is attached by a cylindrical zone of revolution; - on the other hand, the zone of the movable component, situated between the bottoms of the two rings, is of a diameter smaller than that of the central drilling of the bottom of each ring.

3. A spring return system according to Claim 2, characterised in that each of the two shoulders of the movable component is attached to the reduced section by a short cylindrical zone of revolution of which the axial length is equal to the thickness of the bottom of the corresponding ring.

4. A spring return system according to Claim 2 or Claim 3, characterised in that each conical zone of the body of the rings is attached to the associated end flange by a cylindrical zone of revolution of which the axial length is closely equal to the diameter of the metal wire constituting the helical spring.

5. A spring return system constructed, arranged and adapted to operate substantially as hereinbefore described, with reference to, and as illustrated by the accompanying drawings.