Y-SPRING

Abstract: To solve problems where the existing springs do not offer a good solution, at least without using associated mechanisms that increase cost and reduce reliability, a new kind of spring is hereby proposed, hereafter designates as hY-spring. The Y-spring is a leaf spring whose geometry allows for a self-limited deformation, has a chosen initial stiffness and, when the spring is compressed, tends asymptotically to infinity, while the bending moment and the maximum stress at any given section do not overtake a value defined initially as acceptable. An alternate mounting of the same spring allows it to support traction forces and act as a true constant reaction spring. The Y-spring is made of two leafs, usually both curved, rigidly joined together at one of their ends in such a way that the surfaces of both touch each other at that end. The curvature of each of the leafs has the same sign along their entire working length. The curvature and the bending modulus along each leaf are such that the only points to touch each other are the ones in the immediate vicinity of those already touching.

Description: - DESCRIPTION Y-spring Among the various uses of springs, there are some such that the chosen stiffness is a compromise, often difficult to assume due to the different service requirements. A case with such a problem is the one corresponding to the springs used in the suspension of automotive vehicles: on rough terrain, a greater stiffness would be desirable in order to avoid too much bouncing and that the end of the allowable spring displacement be attained and cause a shock, uncomfort and even damage, while a softer ride given by a lower stiffness would be desirable on smoother roads. So far. the answers to this problem are only partial ones and the more elaborate the solutions the more expensive they become, still without reaching, in general, a good compromise when the service conditions are very different, especially when fuel economy dictates a limit to weight. A solution to this problem would be a spring with as low a stiffness as desired for small displacements but increasing to infinity when displacement would approach a given limit. Another situation where the classic springs will not allow a proper solution, without the high costs of usually inefficient and cumbersome mechanisms, is found, for instance, in the thermal power stations, where main piping are supported by the so called constant reaction springs: given the fact that through such piping flow high temperature fluids, the suspension must insure the possibility of significant displacements without increasing stresses in the piping that could lead to its failure. The springs in these suspensions should have, ideally, a constant reaction, whatever the displacements are. To solve this and some other problems where, the existing springs don ' t offer a proper solution, at least without using some kind of mechanism that would increase costs and reduce reliability, hereby is presented a new kind of spring, from now on designated Y- pring. The Y-spring is a leaf spring designed in such a way that the deformation is self-limited. The Y-spring also has a given initial stiffness that, when compressed, tends asymptotically to infinity, while keeping the bending moment (and consequently the maximum stress) at any given section within a limit defined in the design as acceptable. An alternate application of the same spring allows it to support traction forces and acts as a true constant reaction spring. The Y-spring is made of two curved leafs, rigidly joined together at one of their ends in such a way that the surfaces of both touch each other at that end. The leafs length between the touching point and the points where the compression forces are to be applied - working length - is identical for the two leafs. The curvature of each of the leafs has the same sign along their entire working length. The curvature and the bending modulus along each leaf are such that the only points to touch each other are the ones in the immediate vicinity of those already touching. A specially important variant is one where the cross sections are constant along the working length, equal in both leafs and the curvature is symmetrical. In such model, illustrated in fig. 1 : a) When compression forces are applied on the free ends, the stiffness increases with the deformation, tending to infinity as the points where the forces are applied come closer. Indeed, the applied forces effect is to straighten the leafs, with a bending moment along the length increasing to the joined ends. When this bending moment reaches a value such that the initial curvature of the leafs is nullified, they come in contact, that stops any further deformation and. consequently, any further increase of the stresses in the cross sections already in contact: the value of this maximum stress may and should be chosen such that it is lower than the acceptable maximum stress for the material. Conversely, the fact that the contact length increases, reduces the arm of the bending moment due to the applied forces, so that the stiffness will increase: in the limit, "hen th ; nm approaches zero, the force needed to further increase the deformation will tei ) infi . so that it will never be attained and the maximum load the spring will support will be limited only by the surface pressure where the forces are applied. So a spring of this type will never reach its final deformation, i. e.. with such a spring, if well designed, there will be no need for stop-limits. b) Fig. 2 shows how to use the same spring in order to work as a constant reaction spring at traction. In fact, for the same reasons given in a), if the rollers (they can also be sliders or others with the same functionality) are close enough, the stresses in the cross sections between the rollers and the contact area of the leafs ( that is the h length, in the fig.) are the same and the b length the same size, regardless of the relative position of this area in the leafs, as long as there is a minimum given distance to the joined ends of the leafs. The stresses in the cross sections are the same along the contact zone and between the rollers and the free ends the applied forces do not originate first order stresses. Consequently, the spring reaction is kept constant whatever the rollers position along the working length of the leafs.

Claims: CLAIMS 1 st. Spring made of two diverging leafs, joined together at one of their ends, in such a way that the surfaces of both touch each other at that end. 2nd. Spring, according to the 1 st. claim, characterised by a geometry such that the progressing contact between the leafs does not allow for the deformation beyond an acceptable value, corresponding to values of the bending moment and the maximum stress in each section above the pre-defined acceptable maximum v alues. 3rd. Spring, according to the above claims, characterised by two leafs with an equal operating lengtii - the length ol the leafs between the contact point and the points where the external forces are applied. 4th. Spring, according to the above claims, characterised by the curvature of each of the leafs having the same sign along their entire operating length. Sth. Spring, according to the above claims, characterised by the initial curvature and the bending modulus along each leaf being such that only points in the immediate vicinity of those already in contact can get in contact themselves. 6th. Spring, according to the above claims, characterised by allowing an application in a way as to support external compression forces, as in fig. 1. responding with reactions that tend to infinity when the points where the forces are applied approach each other. 7th. Spring, according to the above claims, characterised by allowing an application in a way as to support traction forces, as in fig. 2. responding with a reaction constant without regard to the distance between the points where the forces are applied. AMENDED CLAIMS [received by the International Bureau on 20 December 1996 (20.12.96); original claims 1-6 amended; remaining claim unchanged (2 pages)] 1st. Spring made of two diverging leafs, joined together at one of their ends, in such a way that the surfaces of both touch each other at that end and provided with two rollers linked together mounted in such a way that each roller acts over one of the leafs. 2nd. Spring, according to the 1 st. claim, except that instead of the rollers there are sliders mounted in an adequate way as to provide the same function. 3rd. Spring, according to the above claims, characterised by the common end of the leafs having a geometry such that a pull force ma}' be convenientely applied. 4th. Spring, according to the above claims, characterised by the geometry of the element linking the two rollers, or the equivalent sliders, having a geometry such that a pull force may be convenientely applied. 5th. Spring, according to the above claims, characterised by having the distance between the rollers, or sliders, such that only a small gap remains between the leafs in the plane of the rollers axis. 6th. Spring, according to the above claims, characterised by cuvature of the leafs such that the reaction to the pull, when mounted accordingly to fig. 2, can be a project defined function of he distance between the points where the forces are applied. 7th. Spring, according to the above claims, characterised by allowing an application in a way as to support traction forces, as in fig. 2, responding with a reaction constant without regard to the distance between the points where the forces are applied.

Inventors: RELOGIO RIBEIRO ANTONIO MANUEL, RELOGIO RIBEIRO, ANTONIO, MANUEL
Applicants: INST SUPERIOR TECNICO, RELOGIO RIBEIRO ANTONIO MANUEL, INSTITUTO SUPERIOR TECNICO, RELOGIO RIBEIRO, ANTONIO, MANUEL
Application year: 1996
Main classification: F16F1
IPC codes: B60G17, F16F1, F16F3