GB2158183A

GB2158183A - Annular disc spring

Info

Publication number: GB2158183A
Application number: GB08509625A
Authority: GB
Inventors: Andreas Forster
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1984-04-28
Filing date: 1985-04-15
Publication date: 1985-11-06
Also published as: JPS60241537A; FR2563877A1; DE3415925A1; GB8509625D0

Abstract

An annular disc spring in the relaxed condition comprises a substantially frusto-conical annular disc body 11 which is formed as a body of rotation curved in axial longitudinal sectional planes. The curvature 17, Fig. 3, is concave towards the outer side of the cone and is preferably limited in the radial direction towards the margins of the annular disc body 11 by uncurved zones. The curvature may be provided in the form of a corrugation 17a, Fig. 4. The annular body 11 may have spring tongues 13,13a projecting inwardly and so constitute a diaphragm spring for a friction clutch. The diaphragm spring has a high spring force with low spring force super elevation, with comparatively slight material thickness. <IMAGE>

Description

SPECIFICATION Annular disc spring The invention relates to an annular disc spring especially a dished spring or a diaphragm spring.

From German Publication Specification No.

19 45 233 a diaphragm spring for a motor vehicle friction clutch is known the annular disc body of which has substantially frustoconical form in the relaxed condition. Spring tongues protrude radially inwards from the internal circumference of the annular disc body. Considered in axial longitudinal sectional planes the disc body has a straight rectangular cross-section.

In annular disc springs of this kind the spring characteristic is determined essentially by the ratio of the cone frustum height to the material thickness of the disc body. The spring force can be increased by an increase of the ratio. Admittedly in conventional springs it must be accepted that as the spring travel increases the spring force passes through a more or less distinct maximum and then decreases again. This force super elevation can be reduced by reduction of the ratio of cone frustum height to material thickness, which however is frequently accompanied by a reduction of the maximum force. The reduction of the ratio can be achieved in conventional diaphragm springs by increasing the material thickness. Annular disc springs of thick material however are undesired, since the long-term loadability of the spring is reduced by reason of material fatigue phenomena.Furthermore thick spring material makes the production of the annular disc spring more difficult.

It is the problem of the invention to improve an annular disc spring having an annular disc body which is substantially frustoconical in the relaxed condition, and especially a diaphragm spring with tongues protruding from the internal circumference of the disc body, in such a way that despite a reiatively great value of the ratio of cone frustum height to material thickness of the annular disc body, it displays a relatively small force super elevation.

This problem is solved in accordance with the invention in that the disc body is formed as a body of rotation curved in axial longitudinal sectional planes. This curvature, which is preferably an encircling corrugation, coaxial with the cone axis, in the annular disc body, renders possible a reduction of the material thickness with equal spring force or for equal material thickness an increase of the spring force, in comparison with conventional annular disc springs. The reduction of the material thickness increases the durability of the annular disc spring and facilitates its production.

The disc body or corrugation is preferably of concave curvature in relation to the outside of the cone frustum. This measure further increases the life of the annular disc spring. In relation to the neutral fibres of the annular disc body cross-section, this reduces tension stresses in the especially endangered marginal zones of the annular disc body, or compression stresses occur.

To reduce the loading of the marginal zones it is further advantageous if the corrugation extends at a distance from the internal circumference and from the external circumference of the disc body and/or if the disc body crosssection on both sides of the curvature or corrugation is straight in axial longitudinal sectional planes. Thus the influence of the bending stresses in the marginal zones of the annular disc body is reduced, which reduces the loading of the marginal zones and prolongs the life of the annular disc spring.

The invention is to be explained in greater detail below by reference to drawings, wherein:- Figure 1 shows a diagrammatic axial longitudinal section through a conventional diaphragm spring; Figure 2 shows a partial elevation of a diaphragm spring in accordance with the invention; Figure 3 shows an axial longitudinal section through the diaphragm spring according to Fig. 2, seen along a line Ill-Ill; Figure 4 shows an axial longitudinal section through a variant of the diaphragm spring according to Fig. 2 and Figure 5 shows a diagrammatic spring characteristic curves of diaphragm springs, showing the spring force F in dependence upon the spring travel D.

The conventional diaphragm spring as represented partially in axial longitudinal section in Fig. 1 comprises a substantially frustoconical annular disc body 1, from the internal circumference of which a plurality of tongues 3 staggered in the circumferential direction in relation to one another protrudes radially inwards substantially in the direction of the outer surface of the cone. The annular disc body 1 is a body of rotation in relation to a cone axis represented at 7. The cone frustum height of the annular disc body 1, that is the distance of the internal circumference of the annular disc body 1 from its external circumference in the direction of the cone axis 7, is designated by h in Fig. 1. The material thickness of the annular disc body 1 is designated by s.In axial longitudinal sectional planes, that is in section planes containing the cone axis 7, the annular disc body 1 has the form of an elongated straight rectangle.

The ratio h/s determines the spring characteristic of the diaphragm spring. The curve A in Fig. 5 shows the course of the spring force F in dependence upon the spring travel ffor a high value of the ratio h/s. The curve B shows the spring characteristic for a small value of h/s. According to the curve A as the spring travel increases the spring force firstly increases in order to decrease again. This spring force super elevation is substantially greater compared with curve B.

Diaphragm springs according to Fig. 1 are frequently used in motor vehicle friction clutches. In these and similar utilisation cases the spring force, after a maximum value is reached, should be as independent as possible of the spring travel, in order to prevent spring force variations when the clutch friction linings are worn. If a force super elevation according to the curve A were tolerated, the spring force could vary in an undesired manner on a variation of the spring travel by reason of the clutch wear.

For a predetermined maximum spring force in conventional diaphragm springs the material thickness s of the annular disc body 1 would have to be increased to reduce the spring force of super elevation. There are limits to the increase of the material thickness s, since the bending stresses occurring in thick annular disc bodies greatly reduce the life of the diagphragm spring. Furthermore the production expense increases if the material thickness s is increased.

The curve C in Fig. 5 shows the spring characteristic of a diaphragm spring according to the invention in which for a value of h/s similar to that of curve A the force super elevation is reduced to a value in the order of magnitude of the curve B.

Figs. 2 and 3 show details of the diaphragm spring according to the invention.

This again comprises a substantially frustoconical annular disc body 11, from the internal circumference of which tongues 1 3 protrude radially inwards. The annular disc body 11 is formed as a body of rotation in relation to a cone axis 1 5 and is curved concavely towards the outside of the cone, as represented at 17, between its internal circumference and its external circumference, seen in axial longitudinal sectional planes containing the cone axis 1 5. The curvature 1 7 encircles the cone axis 1 5 concentrically over the entire circular extent of the annular disc body 11.

Otherwise the annular disc body 11 has a constant material thickness.

When the diaphragm spring is in operation for example in a motor vehicle friction clutch, the diaphragm spring is supported in the region of its external circumference and is deformed, especially flattened out, by forces acting on the inner ends of the tongues 1 3 in the direction of the cone axis 1 5. In the elastic deformation of the annular disc body 11, bending stresses D (Fig. 2) are generated in relation to cone outer surface lines 1 9. The curvature 1 7 stiffens out the annular disc part 11 in relation to these bending stresses.

The curvature 1 7 can have any desired form, provided that it is ensured that the surface inertia moment of the annular disc body cross-section seen in an axial longitudinal sectional plane, in relation to a cone outer surface line extending through the internal circumference and the external circumference of the annular disc body 11, is greater than the rectangular annular disc body cross-section, related to a corresponding cone outer surface line, of conventional diaphragm springs.

The curvature 1 7 of the annular disc body 11 is concave, seen from the outer side of the cone. In this way tension stresses at the circumferential margins of the annular disc body 11 which would reduce the life of the diaphragm spring are diminished or converted into compression stresses.

Fig. 4 shows a variant of a diaphragm spring which differs from the diaphragm spring according to Figs. 2 and 3 essentially in the radial width of its curvature. Parts of like effect are designated in Fig. 4 by the reference numerals of Figs. 2 and 3 and with the letter a for distinction. For explanation therefore reference is made to the description of Figs. 2 and 3.

The annular disc body 11 a contains a corrugation 1 7a which is concave on the outer side of the cone and extends over the entire circular extent of the annular disc body 11 a concentrically with the cone axis 1 spa. In the direction of the cone outer surface line 1 9a, the corrugation 1 7a is adjoined on both sides by zones 21, 23 which have a rectilinear course, seen in axial longitudinal sectional planes. The zones 21, 23 of the annular disc body 11 a reduce the bending stresses in the marginal zones compared with the region of the corrugation 1 7a. The long-term loadability of the margins of the annular disc body 11 a and thus of the diaphragm spring is increased in this way.

The invention is especially suitable for diaphragm springs of motor vehicle friction disc clutches and leads to annular disc springs which, despite slight material thickness of their annular disc body, have a low force super elevation with comparatively high spring force.

Claims

1. Annular disc spring, especially diaphragm spring, the annular disc body (11; 11 a) of which in the relaxed condition is of substantially frusto-conical form, characterised in that the disc body (11; 11 a) is formed as a body of rotation curved in axial longitudinal sectional planes.

2. Annular disc spring according to Claim 1, characterised in that the disc body (1 1;11 a) is of concave curvature in relation to the outer side of the cone frustum.

3. Annular disc spring according to Claim 1 or 2, characterised in that the disc body (11 a) is provided with at least one encircling corrugation (1 7a) concentric with the cone axis (1 spa).

4. Annular disc spring according to Claim 3, characterised in that the corrugation (1 7a) extends at a distance from the internal circumference and from the external circumference of the disc body (11 a).

5. Annular disc spring according to Claim 3 or 4, characterised in that the disc body (11), seen in sectional planes containing the cone axis (1 5a) has a straight cross-sectional form on both sides of the corrugation (1 7a).

6. Annular disc spring as claimed in claim 1, substantially as described herein with reference to and as illustrated by any one of the examples shown in the accompanying drawings.