US2389300A - Friction spring - Google Patents

Description

Nov. 20, 1945. E. ENDSLEY FRICTION SPRING Filed April 8, 1944 INVENT OR. L001: 6. 19/0545! a T roe/vex Patented Nov. 20, 1945 FRICTION SPRING Louis E. Endsley, Pittsburgh, Pa... assignor to The Frost Railway Supply 00., Detroit, Mich a corporation of Michigan Application April 8, 1944, Serial No. 530,139

2 Claims.

This application is a continuation-in-part of my application Serial No. 491,289 filed June 18, 1943 (Patent 2,356,662, issued August 22, 1944) and relates to friction springs of the form disclosed in said application, wherein the spring comprises a single inner helical coil and a plurality of outer coil sections each of which is so formed and assembled with the inner coil'that the turns of the outer coil sections have frictional engagement with the turns of the inner coil.

In springs of this type, commonly used on a railway car trucks, there is a tendency for the g turns of the outer coil sections to creep on the inner coil, in an axial direction. This tendency usually results from slight imperfections or inaccuracies which are difficult to avoid in springs of this character. Where three frictional outer coils are employed on an inner coil, imperfections j in the forming of the coils may cause the two I end coils to creep towards the middle coil. When end coils creep towards the ends of the; load 1 carrying coil, or towards the stop at each end of such coil. When this occurs, only two of the three coils can get in contact when compression 1 ot a the spring is released. This will depend on ,which way the middle coil happens to creep under service. In any event, the middle coil will not 7 befcrowded and overstrained.

Where-two outer friction coilsare used, it is desirabl'e' to have these two outer coils creep towards -the ends of the inner coil, or towards each stop on such coil, thus tending to move the two coils faway from each other upon release of load pres- I isure. When only twoouter friction coils are em- '.'-ployed, a greater friction is produced in a spring f oilgiven'length; therefore, creepage' of the two 'otit'er'coils towards each other does more damage, by'reason of getting in contact with one another .'atgthe center of the spring, in that the friction fcoil' turns near the middle of the spring will be Qdisjtortedradially by reason of this crowding at the'inner ends of the outer coils.

My invention has for its object the provision 'friction spring structure having along coil in frictional engagement with the turns of a pnrality of shorter coils, formed in such manner that creeping will be so controlled that the turns of the. shorter coils will return to normal no-load positions upon the removal of load from the spring; or if any creepage occurs, it willbe toward the ends of the spring assembly instead-of toward the middle thereof.

In the accompanying drawing, Fig. 1 shows the long inner coil upon which the outercoil sections are to be assembled; Fig. 2' shows a completed spring, with the inner and outer coils in assembled relation; Fig. 3 shows a modification of the structure of Fig. 2; and Fig. 4 is aperspective view of a portion of the structure of Fig. 1.

The inner coil 3 is tapered at its endmost-tums in the usual manner to provide the desired flat seating surfaces and also has stop shoulders 4 and 5 formed thereon to limit the distance which the outer coil sections 5 and I may creep toward.

the extremities of the inner coil.

The coil 3 may be formed in any suitable man- 1 ner, as by wrapping it on a mandrel, which mandrel may be tapered slightly to facilitate re-' moval of the coil therefrom. This taper usually need not he more than My in-10" of length. The;

important feature of my invention residesin forming the coil 3 along such helical-linesthat the pitch of the coil turns near the end'sof the coil gradually increases toward the ends of the coil, in the last one or two coil turns at each end of the spring, where three outer springs are employed. This increased pitch may suitably be of only .0 or .03" in each convolution as indicated in Fig. 1, where the pitch of the turns 7 adjacent to the middle of the coil are indicated by the letter "P and the increased pitch toward the ends of the coil are shown P plus .04".

Where only two outer coils are used, t e g-rad- 'uated pitch be from about the middle to the ends of the inner coil.

The outer coil sections, 8, I, and]! will'be placed "on the coil 3 by a screwing action.

By slightly increasing the pitch or the coil 3 from about the innermost end of each coil 6 and g I toward the adjacent end'of coil 3 in each in-- stance, the outer ends of the coil sections Band 1' will not have as great tensional and frictional engagement with the coil 3 as their inner ends.

Therefore, any creeping tendency of thecoils 6 and I will be toward the extremities of the coil 3, a distance limited by the stop shoulders 4 and 5, respectively? instead of the creepage being toward the middle coil 8 andperhaps crowding as P plus ,02"and and expanding it so far in radial directions that it becomes over-strained and ineiiective.

Instead of making the outer coil portion in threesectionsasshowninFigJJtcanbeiormed ofonlytwosectionsasshownatland Ilin Fig. 3 which will meet at approximately the middle of the coil 3. In such instance, the increasedpitchattheendsoitheinnercoilwill prevent crowding and over-stressing the outer coil turns at the middle of the spring,

The outer coil sections will, in either instance, be preferably so wound as to have the same taper as that of the mandrel on which the inner coil istormed.

I claim as my invention:

1. A friction spring structure comprising an inner coil and a plurality of outer coil sections asaasoo threaded on the inner coil, in end-to-end relation, the convolutions of the outer coil sections having their sides partially interposed between the sides of the convolutions of the inner coil, and a plurality of the convolutions oi the inner coil, ad-

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