US2202786A - Elliptic spring - Google Patents

Description

May 28, 1940. r. R. WEBER ELLIPTIC SPRING Filed May 11, 1939 Patented May 28, 1940 UNITED STATES PATENT GFFICE ELLIPTIC SPRING Application May 11, 1939, .Serial No. 272,938

4 Claims.

This invention relates to elliptic springs and more particularly to elliptic springs and auxiliary fulcrum blocks therefor adapted to shorten the effective length of the spring under predetermined load or force conditions.

An object of the present invention is to provide a full elliptic spring having resilient auxiliary fulcrum blocks engaged by the main leaves of the semi-elliptic spring sections and adapted to be compressed therebetween during deflection of the spring under increasing force to gradually shorten the effective length of the spring, thereby gradually providing additional strength to support the increased load.

A further object is to provide resilient auxiliary fulcrum blocks as aforesaid which will gradually change the effective ends of the spring during deflection of the spring due to uneven track or other reasons, without any jars or shocks due to the stiffening of the spring action, and will snub the oscillations of the spring due to such deflection.

A further object is to provide an elliptic spring having axiliary fulcrum blocks which are made of yielding material and present no hard surfaces to the main leaves of the spring which could injure the leaves and cause them to break.

Other and further objects of and advantages achieved by the present invention will be apparent from the following description of an approved embodiment thereof and the claims appended hereto.

Referring to the drawing forming a part of this application, Figure 1 is a side elevation of a full elliptic spring embodying the present invention; and Fig. 2 is a plan view of the spring of Fig. 1.

A simple elliptic spring which is strong enough and has the proper rate of deflection to support a fully loaded railway vehicle, such as a freight car, is too stiff to support the same car properly when it is empty. To overcome this characteristic of a simple elliptic spring, it has long been the practice to employ an elliptic spring having auxiliary leaves, such as the spring shown in Figs. 1-5 of patent to Edgerton et al., No. 872,226, granted November 26, 1907. In such a spring the regular leaves operate to support an empty car in the usual manner of a simple elliptic spring, but when the car is heavily loaded and additional support is needed, the spring is deflected sufficiently so that the auxiliary leaves engage each other at their ends and come into operation, providing a pair of short, stiff, heavy leaves which are amply strong to support the heavy load.

This elliptic spring employing auxiliary leaves answers the problem to a certain extent, but has itself certain other inherent undesirable characteristics which are not present in the spring of the present invention. They are namely, that the two auxiliary leaves employed add to the weight, the cost, the over-all height, and the solid height of the spring. Furthermore, there is an abrupt change in the load-supporting and deflection characteristics of the spring which is highly undesirable. That is to say, the spring has two actions; a light-load flexible support before the auxiliary leaves engage and a heavyload stiff support after they engage. As the change from one of these conditions to the other is immediate, the nature of the deflection of the spring changes very abruptly. A further disadvantage is that at some loads, as when the adjacent ends of the auxiliary leaves are slightly spaced, oscillation of the spring due to unevenness of track or other causes, during operation of the railway Vehicle, will result in the continual engaging and disengaging of the ends of the auxiliary leaves. This causes a continual changing from a light-load spring to a heavy-load spring, and each time that the auxiliary leaves. come into engagement with each other, there will be a resulting jar due to the abrupt change in the stiifness of the spring. This also occurs even where the auxiliary leaves are ordinarily in contact, if the uneven track conditions cause, 9

the auxiliary leaves to separate during deflection of the spring.

The present invention is directed to provide a spring which will deflect readily when under light loads, and yet be adapted to provide the strength. and stiifness necessary to support heavy loads, without incurring in the spring the inherent faults of the elliptic spring employing auxiliary leaves. To obtain this result an elliptic spring, which is relatively long in proportion to its weight when taking into consideration the maximum loads which it is designed to support, is employed in combination with resilient auxiliary fulcrum blocks which operate under predetermined loads to shorten the effective length of the spring, thereby stiffening the action of the spring.

It has long been known that to employ an auxiliary fulcrum block between the main leaves of an elliptic spring will, when the spring is defiected sufficiently to engage the block, change the effective ends of the spring, shortening the effective length of the spring, stiffening it and adapting it to support a heavier load. Such auxiliary fulcrum blocks are shown in combination with an elliptic spring in the patent to Potter, No. 481,971, granted September 6, 1892.

However, the auxiliary fulcrum blocks of the Potter patent are metal castings having either horizontal faces opposed to the main leaves of the spring or inclined faces. In either event, the main leaves deflect until they are almost parallel with the faces of the blocks, which is the critical point where further deflection will cause a change in the effective ends of the spring. Upon this further deflection there is an immediate change of the eflective ends of the spring. That is to say, under light loads, the ends of the spring are determined by the points of contact between the main leaves and the outer ends of the auxiliary fulcrum blocks and under heavy loads the effective ends of the spring are determined by the points of contact between the main leaves and the inner ends of the auxiliary fulcrum blocks, and. the change from the outer points of contact to the inner points of contact is immediate.

This immediate change in the eifective spring ends has undesirable eifects similar to those encountered in the use of an elliptic spring employing auxiliary leaves, namely that there is the same abrupt change from a light-load spring to a heavy-load spring. Furthermore, when the spring is deflected to the critical point, further deflection due to track unevenness will result in a jar each time the spring fulcrums at the inner edges of the auxiliary fulcrum blocks and when the spring is rapidly oscillating as it will be in service, there will be a continuous engagement and disengagement of the main leaves of the spring with the auxiliary fulcrums at the inner edges of the auxiliary fulcrum blocks, and a corresponding continuous series of jars.

A further disadvantage of the metal auxiliary fulcrum blocks of the Potter patent is that the main leaves of the elliptic spring are practically always bearing against the blocks along a single line, which overstrains the main leaves and leads to their eventual breakage. Moreover, each time the auxiliary fulcrums are engaged, which, as aforesaid, may occur in rapid succession under certain conditions, the main leaves are dealt severe blows because of the sudden engagement with the hard metal edge of the blocks, and the shock of these blows leads to the fracture of the main leaves and the eventual breakage at these points.

Coming now to the present invention, the elliptic spring I shown in the drawing is of ordinary construction except for the addition of the features of the present invention. It comprises a pair of semi-elliptic spring sections 2, each consisting of a main leaf 3 and a plurality of shorter leaves 4 secured together by a band 5. The sections 2 are connected together at their ends in the usual manner to deflect about the axes a which determine the long or main pivots of the spring, which are the points between which the spring deflects under light loads.

A pair of resilient rubber fulcrum blocks 6 is disposed between the main leaves 3, each in spaced relation equi-distant from the adjacent axis at. These blocks are rectangular in shape and are secured between the sections 2 in a vertical position so that the top and bottom outer corners l and 8 respectively are in engagement with the main leaves 3 and the top and bottom inner corners 9 and II) respectively are in spaced relation with their respective main leaves 3. These blocks, when compressed between the main leaves 3, provide auxiliary pivots for the spring, shortening the effective length of the spring, as will later more fully appear.

A plate H, which is secured to one of the sections 2, in the present instance the top section, by means of the spring band 5 thereof, extends outwardly toward the ends of the spring and is secured at each of its ends to a block 6, thereby securing the blocks against displacement.

The blocks may be secured to the plate II in any desirable manner. In the present instance the blocks are shown made in two parts I2 and I3, each rectangular in shape, the parts I2 being vulcanized to the upper adjacent surface of the plate I I and the parts l3 being similarly attached to the lower surface, each in alignment with the adjacent part l2. However, it is within the scope of the present invention to secure the resilient blocks in place in any other practical manner as for instance by securing each block 6 to the adjacent end of the elliptic spring. Furthermore, there are many methods which may be employed to secure the parts I 2 and I3 of the blocks 6 to the plate H, as for instance, by bolting them thereto. As the parts I 2 and I3 are similar in all respects, the ends of the plate I! will be in the horizontal central plane of the elliptic spring when both blocks are in engagement with both main leaves.

As aforesaid, the plate ll may be secured to either section 2, and it may be made of any metal which is suitable to be secured to the blocks. The plate ll shown in Fig. 1.is made of the same metal as the spring leaves. Its spring action is directed in the opposite direction from the spring action of its section 2 so that when the two sections 2 are disassembled, the plate H holds the blocks in engagement with its section 2. Therefore, when the spring is in operation upon a railway vehicle, if the load is light enough so that the main leaves 3 do not both engage the blocks 8, the blocks 6 will be held in engagement with the section 2 with which they are secured and will not be suspended between the sections 2 where they would be free to vibrate.

The present invention will be better understood from a brief description of the operation of the elliptic spring and auxiliary fulcrum blocks. The spring, as shown in Fig. 1, is at the position it would be compressed to by a light load, which is the load imposed on it by an empty railway vehicle at rest. Under this load the spring main leaves are engaging the corners 1 and 8 of the blocks and slightly compressing them. The effective spring ends (pivots) are at the axes a,

however, for the blocks have not been compressed sufficiently to resist the pressure exerted by the main leaves to effect a change in the effective length of the spring.

When the vehicle is being loaded at rest, the spring will be at first initially deflected and then further deflected more and more with each successive addition of load supported by it. Each further deflection will result in a further compressing of the blocks, and the blocks will offer a corresponding greater resistance to the compressing of the spring. When the blocks are compressed to a suflicient extent, they begin to act as fulcrums, bending the spring main leaves slightly at the points of engagement therewith, which starts the gradual shortening of the effective spring length. The more the blocks are compressed, as the load is increased, the more pronounced becomes this bending, and there is an accompanying less tendency of the spring to deflect about the axes a, which results in an increasing shortening of the effective spring length.

The change from operation as a long spring (with ends at the axes a) to a short spring (with effective ends on the auxiliary fulcrum blocks 6) is gradual, due to the fact that the resilient blocks are compressed gradually and consequently change the efiective length of the spring main leaves gradually. That is to say, when the main leaves start to bend at the points of engagement With the auxiliary fulcrum blocks, the spring is still operating partially with its ends at the axis a, and the effective spring ends are somewhere intermediate the axes a. and the blocks 6. The bending of the spring is proportional to the compressing of the blocks, so that during this change in the effective spring ends, the spring length is effectively becoming successively shorter and shorter during the deflection of the spring. There will be a point, of course, where the blocks will no longer further compress, and at this point the shortest effective length of the spring will finally be determined.

This gradual changing of the effective ends of the spring is important in the case ofthe loading of a standing vehicle for it provides a continually changing series of effective spring lengths, each for a different load. In the case of a vehicle, whether empty or loaded, that is running along track in service, the gradual shortening of eifective spring length is important because it provides a spring action which gradually stiffens, during oscillation of the spring, due to uneven track conditions, with each corresponding shortening of the spring length each time the spring compresses, thereby affording a strong support for the vehicle and snubbing the oscillations of the spring.

In the case of an empty vehicle supported on a spring deflected to the position shown in Fig. 1, there will be considerable vertical oscillatory movement of the spring as the vehicle runs along the track in service. This will result in the elliptic spring continually opening and increasing in height so that the blocks ii disengage the lower section 2. Each opening movement is followed, of course, by a closing movement which brings the blocks once more in engagement with the lower section 2. If the blocks were not resilient this would result in a series of jars, but as the blocks of the present invention are resilient, no such jars occur, and the blocks serve to snub the oscillatory movements of the spring, partly because of their resilient nature and partly because of their capacity to stiffen the spring action.

The deflection of the elliptic spring to which the novel auxiliary fulcrum blocks have been applied, can be divided into three parts. The first deflection will be from an unloaded spring to a spring supporting a light load, as an empty railway vehicle, which load will initially compress the blocks. The rate of this deflection in proportion to the weight of the load will be constant. The second deflection will be the deflection of the spring during the further compressing of the auxiliary fulcrum blocks, and as the effective spring ends are always changing during this compressing, the deflection will be at a gradually decreasing rate. The third deflection will be from the full compressing of the blocks to the full permissible deflection of the spring, and this deflection will have a constant rate, but it will be a lesser rate than that of the spring being deflected under a light load. It will be understood that the second and third deflections are due to increased loads or forces. Looking at this graphically, the first deflection would be represented by a straight inclined line and the third deflection would be represented by another straight line at a greater inclination, the two straight lines being connected by a smooth curve which represents the second deflection. That is to say there is no abrupt change in direction in the graph such as takes place where a rigid auxiliary fulcrum block is employed.

Finally, because of the resilient nature of the auxiliary fulcrum blocks, which provide a yielding surface to the spring, which surface must be compressed before the spring can be affected by the blocks, no harm is done to the spring because of its engagement with the blocks or because of its continuous engagement and disengagement with the blocks during oscillations of the spring. Therefore there is no danger of the auxiliary fulcrum blocks causing breakage of the spring leaves.

The blocks 6 have been described as resilient rubber blocks, but it will be understood that any resilient block having the characteristics of the blocks 6 aforedescribed may be used and the claims are intended to cover all such resilient blocks.

While there has been hereinbefore described an approved embodiment of this invention, it will be understood that many and various changes and modifications in form, arrangement of parts and details of construction thereof may be made without departing from the spirit of the inven,.

tion and that all such changes and modifications as fall within the scope of the appended claims are contemplated as a part of this invention.

The invention claimed and desired to be secured by Letters Patent is:

l. A vehicle spring of the full elliptic type comprising twooppositely disposed sections, each section including a stack of spring leaves and means at the central portion thereof holding said leaves tightly together, said sections having their main leaves innermost and connected together at the adjacent ends thereof to provide spring end pivots for maximum effective spring length, said sections being spaced apart from said ends throughout their lengths and adapted for supporting at said central portions load of the vehicle superstructure and to yieldingly resist spring compressive force applied at said central portions by flexing, said flexing increasing under forces of increasing magnitude; and two resilient blocks serving as spring pivots for minimum eifective spring length, said blocks being secured in said space substantially against bodily movement and being disposed one at each side of and in longitudinal spaced relation to said central portions, each block having opposed faces extending longitudinally of said spring in line with a plurality of leaves of each of said sections and spaced from the end pivot adjacent thereto, each of said faces being disposed opposite the main leaf adjacent thereto and operably engageable therewith, each of said blocks being thereby gradually compressed under increasing forces within predetermined limits for cooperation with the end pivot adjacent thereto during flexing of the said sections to effect flexing of said sections initially about said end pivots and 4 finally about said blocks.

section including a stack of spring leaves and means at the central portion thereof holding said leaves tightly together, said sections having their main leaves innermost and connected together at the adjacent ends thereof to provide spring end pivots for maximum effective spring length, said sections being spaced apart from said ends throughout their lengths and adapted for supporting at said central portions load of the vehicle superstructure and yieldingly resist spring compressive force applied at said central portions by flexing, said flexing increasing under forces of increasing magnitude; and two resilient blocks serving as spring pivots for minimum effective spring length, said blocks being secured in said space substantially against bodily movement and being disposed one at each side of and in longitudinal spaced relation to said central portions, each block having opposed faces extending longitudinally of said spring in line with a plurality of leaves of each of said sections and spaced from the end pivot adjacent thereto, each of said faces being disposed opposite the main leaf adjacent thereto and operably engageable therewith, each of said blocks being thereby gradually compressed under increasing forces within predetermined limits for cooperation with the end pivot adjacent thereto during flexing of said sections to effect flexing of said sections initially about said end pivots, thereafter progressively about points between each of said end pivots and the block face adjacent thereto, and finally about said blocks.

3. A vehicle spring of the full elliptic type cornprising two oppositely disposed sections, each section including a stack of spring leaves and means at the central portion thereof holding said leaves tightly together, said sections having their main leaves innermost and connected together at the adjacent ends thereof to provide spring end pivots, said sections being spaced apart from said ends throughout their lengths and adapted for supporting at said central portions load of the vehicle superstructure and to yieldingly resist spring compressive force applied at said central portions by flexing, said flexing increasing under forces of increasing magnitude; and two resilient blocks secured in said space substantially against bodily movement and being disposed one at each side of and in longitudinal spaced relation to said central portions, each block being in line with a plurality of leaves of each of said sections and spaced from the end pivot adjacent thereto and having outer and inner end faces extending transversely of said spring and opposed faces extending longitudinally of said spring, each of said opposed faces being disposed opposite the main leaf adjacent thereto and operably engageable therewith whereby each of said blocks is gradually compressed under increasing forces within predetermined limits initially at said outer end face and progressively to said inner end face for cooperation with the end pivot adjacent thereto during flexing of said sections to effect flexing of said sections initially about said end pivots for maximum effective spring length and subsequently about said blocks, first at the outer end faces thereof and progressively therefrom at points successively nearer said inner end faces for respectively successively shorter effective spring lengths, and finally at said inner end faces, providing minimum effective spring length.

4. A full elliptic spring comprising two oppositely disposed sections, each section including a stack of spring leaves and means at the central portion thereof holding said leaves tightly together, said sections having their main leaves innermost and being spaced apart from their ends throughout their lengths, said spring having a maximum effective spring length to provide maximum spring flexibility and a minimum effective spring length to provide maximum spring stiifness thereby increasing the load supporting capacity of said spring, said innermost leaves being connected together at their adja- 5 cent ends to provide spring end pivots for said maximum eifective spring length; and two resilient blocks secured in said space substantially against bodily movement and being disposed one at each side of and in longitudinal spaced relation to said central portions, each block being in line with a plurality of leaves of each of said sections and spaced from the end pivot ad jacent thereto and disposed opposite said main leaves and operably engageable therewith, each of said blocks being thereby gradually compressed under increasing loads within predetermined limits thereby cooperating with each other to serve as pivots for said minimum effective spring length,

THEODORE R. WEBER.

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