GB2208420A

GB2208420A - A resiliently deformable element for use as a buffer stop in a motor vehicle suspension

Info

Publication number: GB2208420A
Application number: GB8818313A
Authority: GB
Inventors: Carlo F Tondato
Original assignee: POLIPREN Srl
Current assignee: POLIPREN Srl
Priority date: 1987-08-07
Filing date: 1988-08-02
Publication date: 1989-03-30
Also published as: GB8818313D0; DE3826831A1; IT212299Z2; IT8753593V0

Abstract

A resiliently deformable element (3) made of a microcellular elastomeric material has an upper part (16) adapted to contact a suitable seat of the motor vehicle chassis and a lower part (19) against which a surface of the casing of a shock absorber (1) can contact. The first part (16) is delimited internally and externally by coaxial surfaces (17, 18) and the second part (19) is annular, coaxial with the first part, projects axially from it, and is delimited by inner and outer surfaces of revolution (20, 21) each of which is generated by rotating about the axis (22) of the element a segment of a curved line the centre of curvature of which is located on the same side of the line itself as that on which the said axis (22) lies. The segments are chosen so that sections through the second part (19) of the element (3) taken on planes orthogonal to the axis (22) of the element itself, have decreasing cross-sectional areas with increasing distance from the first part (16) of the element. …<IMAGE>…

Description

1 A 8 4 20 2 A RESILIENTLY DEFORMABLE ELEMENT ADAPTED TO BE USED AS A

BUFFER STOP IN A MOTOR VEHICLE SUSPENSION The present invention relates to a resiliently deformable element made of an elastomeric material having a microcellular structure adapted to be utilised as a buffer stop in a motor vehicle suspension, in particular a suspension of the McPherson type.

As is known suspensions of this type comprise, substantially, a shock absorber the casing of which is pivoted at its lower end to an axle or a half-shaft of the motor vehicle and the stem of which is pivoted to a suitable region of the motor vehicle chassis. A coil spring, coaxial with the shock absorber, is fitted between this and the motor vehicle body and has a lower end which rests on a suitable shoulder fixed to the shock absorber easing and an upper end which rests on a seat of the motor vehicle body. In suspensions of this type a resiliently deformable element is normally also fitted, the functions of which are those of constituting a buffer to stop deformation of the suspension and as a true and proper resilient element acting at least during the latter part of the deformation of the suspension.

Deformable elements of this type normally have a tubular 41 2 form and, therefore, have an axial hole into which the stem of the shock absorber is inserted: the upper end of the element rests on a suitable seat of the chassis whilst in the terminal part of the deformation movement of the suspension a surface of the casing of the shock absorber engages the lower part of such element.

It has been found that for a correct operation of suspensions of this type the overall resilient characteristic of the suspension itself, that is to say the variation of the force transmitted through it in dependence on the axial deformation thereof, must be substantially rectilinear in the first section and, in the second section, non-linear but with a rigidity increasing with increasing deformation; with a behaviour characteristic of this type there is in fact obtained a greater ride comfort and, simultaneously, a better road holding and a more marked resilient return of the suspension.

Since the first-described deformable elements constitute not only buffer stops against deformation of the suspension, but also true and proper resilient elements equivalent to the springs of the suspension itself, they exert a substantial influence on the overall characteristics of the suspension and, in particular, in i 3 the second section thereof: therefore their resilient characteristic (variation of the axial force generated by them in dependence on deformation) must be defined in a rigorous manner. To obtain an overall suspension characteristic having the first-described behaviour deformable elements with non-linear characteristics have been produced comprising a first section with a lower rigidity and a second section with a greater rigidity than that of the first section, separated by a rather marked knee; in fact only when the deformable elements have the first defined characteristic behaviour is it possible to obtain anoverall characteristic of the suspension in which the rigidity, substantially constant in the first section thereof, increases in a gradual manner.

A characteristic of this type can, however, only be obtained with deformable elements having a very complex form: there have in fact been proposed for this purpose deformable elements which have a first section in the form of a sleeve on the external surface of which are formed annular grooves of particular form, and a second part which extends from the first and which actually forms a bellows. With this arrangement two parts with differentiated rigidity are obtained, and therefore during a first part of the deformation of the suspension 4 only the second part of the deformable element reacts, which is shaped as a bellows and which has a lower rigidity, whilst in the remaining part of the deformation the part with higher rigidity reacts.

Deformable elements of the type described above have several disadvantages.

First of all, because of their complex form, these elements are difficult to construct and require complex and expensive equipment; in fact they have numerous undercuts which make removal from the forming moulds particularly difficult; further, the time required for forming these elements is particularly long.

Finally, in some regions of these elements, during deformation of the elements themselves, high stresses are generated both because of the complex stress state which is generated in the zones themselves (due to shearing, bending and compression stresses) and of the tearing effect consequent on the presence of corners, sharp variations in section, and the considerably reduced thicknesses which are necessary in some parts of the element. Consequently, the resistance of such elements to fatigue stresses is rather low and it is therefore possible for ruptures to occur in use.

The object of the present invention is that of providing a deformable element of the type first indicated, which will be free from the described disadvantages and which therefore will be constructionally very simple, which can be produced at low cost and without the use of complex equipment, and which will have a practically limitless durability.

According to the present invention there is therefore provided a resiliently deformable element made of an elastomeric material of microcellular structure adapted to be utilised as a buffer stop in a motor vehicle suspension, the said element having a tubular form with an axial hole into which the shock absorber stem is fitted, an upper end adapted to engage on a suitable seat of the motor vehicle chassis and a lower end on which a surface of the shock absorber casing rests, characterised by the fact that it comprises a first part which is internally and externally delimited by coaxial surfaces and a second part of annular form, coaxial with the first, which projects axially from it, the said second part being delimited by internal and external surfaces of revolution, each of which is generated by rotating a segment of a curved line about the axis of the element, the centres of curvature of the segments being located 3 6 with respect to the line itself on the side on which the said axis lies, the said segments of curved line being chosen in such a way that sections through the said second part of the element, taken an planes orthogonal to the axis of the element itself, have decreasing areas with increasing distance of the sections themselves from the said first part of the element; conveniently the said segments of curved line are constituted by arcs of circles.

For a better understanding of the present invention a more detailed description of it will now be given by way of example with reference to the attached drawings, in which:

Figure I schematically represents a vertical section through a suspension on which the deformable element of the invention is utilised; Figure 2 represents a detail of the section of the preceding Figure to illustrate the shape of the deformable element of the invention in a configuration in which deformation of the element itself commences; Figures 3 and 4 represent partial sections of a part of the deformable element of the invention corresponding to two different embodiments of the element itself; 1 3 7 Figure 5 represents the behaviour characteristic of the resilientdeformable element of the invention; and Figure 6 represents the behaviour characteristic of the overall suspension of Figure 1 in which the deformable element of the invention is -fitted.

The deformable element of the invention is adapted to be mounted on a motor vehicle suspension of the type such as that represented in Figure 1 (a McPherson suspension substantially comprising a shock absorber 1, a coil spring 2 coaxial with it and the deformable element itself indicated with the reference numeral 3). The lower end of the casing 4 of the shock absorber 1 is pivoted by means of a collar 5 to an axle or a half-shaft of the motor vehicle, whilst the upper end of the stem 6 of the shock absorber itself is pivoted to the motor vehicle body 1; the connection between this end and the motor vehicle body can be made in any known way and, conveniently, with the connection means illustrated in Figure 1 and comprising a nut 8 screwed onto a threaded end of the stem and an annular rubber bearing 9 interposed between a washer 10, on which the nut itself rests, and a chassis 7.

The coil spring 2 has a lower end which rests on a collar 11 fixed to the casing 4 of the shock absorber 1 and an 3 8 upper end which rests on the chassis 7 via a ring 12.

The deformable element 3 of the invention, which is of substantially tubular form, is traversed by the stem 6 of the shock absorber and has an upper end which rests on another annular rubber bearing 13, with the interposition of a cap 14. The axigl length of the deformable element 3 is chosen in such a way that its lower end is located at a certain distance from the upper surface 15 of the easing 4 of the shock absorber when the suspension is in its rest position illustrated in Figure 1.

As can be seen from Figure 2, the deformable element substantially comprises a first part 16 which is delimited internally and externally by coaxial cylindrical surfaces 17 and 18 respectively and a second part 19 of annular form, coaxial with the preceding part, which projects axially from it. The second part is delimited by an internal surface 20 and an external surface 21, both being surfaces of revolution, each of which is generated by rotating about the axis 22 of the element a segment of a curved line the centre of curvature of which is located on the same side of the line itself as that on which the axis 22 lies. Such curved line segments are conveniently constituted, as has been shown in the embodiment illustrated in Figures 4 and 1 t i J 9 5, by arcs of circles: in these Figures the reference numerals 25 and 26 have been used to indicate two arcs of circles which are used to generate, by rotating the arcs themselves about the axis 22, the internal surface 20 and the external surface 21 of the second part 19 of the element; as is seen from these Figures, the centres of curvature Cl. C 2 of the arcs 25 and 26 are located, with respect to the arcs themselves, on the same side as that on which the axis 22 lies.

Moreover, the curved line segments which are the generatrices of the internal surface 20 and the external surface 21 must be chosen in such a way that they generate the internal and external surfaces 20 and 21 with a form and disposition such that sections through the second part of the element 19, taken on planes orthogonal to the axis 22 of the element, have decreasing areas with increasing distance of the sections themselves from the first part of the element 16.

To obtain this object, when the curved line segments are constituted by arcs of circles 25 and 26, the centre of curvature C 1 of the circular arc 25 must lie on a straight line indicated t1, which is orthogonal to the axis 22 of the element and is symmetrical with respect to the end points A and B of the arc itself: in this way the internal diameters of the upper and lower end sections of the second part 19 are substantially equal to one another; these diameters have been indicated in Figures 3 and 4 with the reference letters D A and D B Moreover, the centre C 2 of the circular arc 26 which generates the external surface 21 of the second part of the element 19 is located on a second straight line t 2 which is also orthogonal to the axis 22 of the element and which is located between the straight line t 1 and the upper end of the element itself: as a consequence of the position of the centre C 2 sections through the second part of the element 19 taken on planes orthogonal to the axis 22 of the element obviously have decreasing area with an increase in the distance of the sections themselves from the first part 16 of the element.

Conveniently the radius of the arc 25, indicated R 1 in the drawings, is minor than the radius of the arc 26 indicated R 2 The embodiment of Figure 4 differs from that of Figure 3 only by the fact that the straight line t 2 on which the centre C 2 of the arc 26 is located lies beneath the section which separates the first part 16 from the second part 19 of the element, the section line of which has 1 J i 1 11 been indicated t 5 in Figure 4; in this case, conveniently, the part of the external surface 21 which lies between the sections which contain the straight lines t 2 and tst indicated 27 in Figure 4, is 5 cylindrical.

The lower end of the second part 19 of the element conveniently has a circular junction 28 between the internal and external faces.

The inner diameter, indicated D A' of the section which separates the first part 16 of the element from the second part 19 of the element is equal to the diameter of the hole 17 (Figure 2) of the first part 16. Moreover the outer diameter of the section of the second part 19 of the element which separates this from the first part 16, a diameter indicated D c in Figures 3 and 4, is less than the diameter of the lower section of the first part 16, which diameter corresponds to that of the cylindrical outer surface 18.

Conveniently, between the first and second parts there is formed an einnular groove 29 which also has an influence on the resilient behaviour of the element and which, simultaneously, serves for the fixing of an outer protective casing 30 (Figure 2).

12 The deformable element of the invention is made of an elastomeric material with a microcellular structure, that is to say one comprising closed and open cells of extremely small dimensions; conveniently this elastomeric material is a polyurethane or a rubber. The element is made by means of the usual technology for forming microcellular materials, utilising moulds able to produce the element itself.

The element of the invention is mounted on the suspension in the manner visible in Figure 1, that is to say by inserting the stem 6 of the shock absorber through the hole in the element 3 and bringing the upper end of this to rest against the annular bearing 13, with the interposition of the cap 23; the lower end of the element is, on the other hand, located at a predetermined distance from the upper annular surface 15 of the casing 4 as is clearly seen in Figure 1.

The operation of a suspension in which the deformable element is fitted is as follows.

During running of the vehicle the forces acting on an axle or a halfshaft are transmitted through the collar 5, the casing 4 of the shock absorber 2 and from this to 13 the chassis through the coil spring 2 and the stem 6 of the shock absorber itself. During the first part of the deformation of the suspension only deformation of the coil spring 2 takes place which presents a substantially linear characteristic and, therefore, the overall characteristic of the suspension is rectilinear as represented by the initial section A of the diagram of Figure 6; in this is plotted, by way of example, the variation of the force F transmitted through the suspension as a function of the deformation C of the suspension itself.

As the upper surface 15 comes into contact with the lower surface of the deformable element 3, assuming the configuration represented in Figure 2, this latter also contributes to supporting the load which acts on the suspension together with the spring 2, and therefore the overall characteristic of the suspension depends also on the characteristic of this element. In Figure 5 there has been shown this latter characteristic which, as in seen, substantially comprises two non-linear sections B and C: in the first section the rigidity of the element, whilst increasing with an increase in the deformation, is relatively low, whilst in the second section C this rigidity increases rapidly with an increase in deformation; the two sections B and C are therefore f 14 separated by a rather marked knee. This characteristic derives from the particular form of the element of the invention: in fact in the first part of the stroke only the part 19 of the element is deformed, to which corresponds the first section of the characteristic B of Figure 5: in fact the lower end of the part 19 which is of smaller cross-section is deformed first. The section C of the characteristic of Figure 5 substantially corresponds to the deformation of the first part 16 of the element. It is important to note that the tangent to the characteristic illustrated in Figure 5 which passes through the origin of the characteristic itself forms an angle indicatedW-, which is substantially equal to the angle'k of the first section of the characteristic of Figure 6: in this way the overall characteristic of the suspension illustrated in the Figure itself has a terminal section D in which the rigidity increases gradually starting from the first section A; the overall characteristic behaviour of the suspension of the type such as is illustrated in Figure 6 produces a notably comfortable ride and ensures a good road holding.

During deformation of the element 3 of the invention there are no concentrations of stresses produced in any part of the element itself; in fact, in the material of the first part 16, there are substantially only compression stresses, whilst in the second part 19 there are bending and compression stresses; because of the gradual variation of the area of the sections, the bending stresses which are encountered in this part are substantially constant. Moreover in th-is part there are no sharp corners or rapid variations in cross-section and therefore there is no appreciable tearing effect.

For these reasons it has been found that the deformable element 3 has a practically limitless life and is not subjected to fatigue rupture.

The deformable element of the invention can be made with the use of very simple equipment: the forming moulds can be produced at low cost and have a long life. Finally, since the deformable element does not have any parts with very low thickness the forming process can be effected rapidly and without particular precautions.

It is evident that modifications and variations can be introduced to the form of the deformable element which has been described without departing from the ambit of the invention.

16

Claims

CLAIMS 1. A resiliently deformable element made of an elastomeric material having a microcellular structure adapted to be used as a buffer stop in a motor vehicle suspension, the said element having a tubular form with an axial hole into which is inserted the stem of a shock absorber, an upper end adapted to rest on a suitable seat of the motor vehicle chassis and a lower end on which a surface of the shock absorber easing rests, characterised by the fact that it comprises a first part which is internally and externally delimited by coaxial surfaces and a second part of annular form coaxial with the first and which projects axially from it, the said second part being delimited by inner and outer surfaces of revolution each of which is generated by rotating about the axis of the element a segment of a curved line the centre of curvature of which is located, with respect to the line itself, on the same side as that on which the said axis lies, the said segment of curved line being chosen in such a way that sections through the said second part of the element taken on planes orthogonal to the axis of the element itself have decreasing area with an increase in the distance of the sections from the said first part of 25 the element.

1 17

2. An element according to Claim 1, characterised by the fact that the said segments of curved line are arcs of circles.

3. An element according to Claim 1 or Claim 2, characterised by the fact that the centre of the circular arc which generates the said inner surface of the said second part of the element is located substantially on a first straight line orthogonal to the said axis of the element and which is symmetrical with respect to the end points of the arc itself in such a way that the inner diameters of the upper and lower end sections of the said second part are substantially equal to one another.

4. An element according to any preceding Claim, characterised by the fact that the centre of the circular arc which generates the said outer surface of the second part of the element is located substantially on a second straight line which is orthogonal to the said axis of the element and which is located between the said first straight line and the upper end of the element itself in such a way that the sections through the said second part of the element taken on planes orthogonal to the axis itself have decreasing areas with increasing distances of the sections from the said first part of the element.

i 18

5. An element according to Claim 4 or Claim 5, characterised by the fact that the radius of the circular are which generates the said internal surface is minor than the radius of the circular arc which generates the 5 said external surface.

6. An element according to any preceding Claim, characterised by the fact that the said coaxial surfaces of the said first part of the element are cylindrical.

7. An element according to any preceding Claim, characterised by the fact that the inner diameter of the section of the said second part of the element which separates this second part from the first part is equal to the diameter of the said hole through the said first part.

8. An element according to any preceding Claim, characterized by the fact that the outer diameter of the section through the said second part of the element which separates this second part from the first part is smaller in diameter than the lowermost section through the said first part.

9. An element according to Claim 8, characterised by the fact that between the said first and second parts of i 1 1 19 the element there is formed an annular groove.

10. An element according to any preceding Claim, characterised by the fact that the said elastomeric material of microcellular structure is polyurethane.

11. An element according to any of Claims from 1 to 9, characterised by the fact that the said elastomeric material of microcellular structure is a rubber.

12. A resiliently deformable element made of an elastomeric material of microcellular structure substantially as described and illustrated in the attached drawings.

Published 1988 at The Patent Office. State House, 66 71 High Holborn, London WC1R 4TP. Further copies may be obtained from The Patent Office,