Dampered Railway Truck Friction Shoe Shim

Abstract

In a railway truck wherein friction shoes are operatively carried in wedge-shaped pockets of the bolster and are urged upwardly and outwardly by one or more control springs between the bottom of the friction shoe and the truck side frame, the invention provides for the restoration of column pressure in the spring columns that support the friction shoes by the insertion of a shim between the bottom of the friction shoe and the control springs. The insertion of the shim compensates for the loss in column pressure that results from the vertical rise of the friction shoe due to wear.

Description

This invention relates to snubbing arrangements for railway car trucks and more particularly to a particular configuration wherein friction shoes are operatively carried in pockets located at opposite sides of the bolster. Each friction shoe is resiliently mounted on a control spring that urges the friction shoe against a wear plate mounted on the upper portion of the adjacent side frame columns.

The present invention contemplates the restoration of the column pressure to the control springs, the reduced column pressure being caused by the vertical rise of the friction shoe resulting from the wearing of the friction surfaces on the shoe.

In the prior art various trucks have been proposed and a number have been placed in service wherein bolster oscillations are damped by friction devices, usually some form of friction shoe associated with the bolster for developing friction to resist its oscillations. Such arrangements have been generally successful in eliminating harmonic action of the bolster-supporting springs and the resultant harmful effect well known to those skilled in the art. However, it is commonly known that satisfactory results are obtained using the various arrangements only in the event that the friction parts, mainly the friction shoes, are not allowed to develop a condition of excessive wear; because the existence of such a condition will in turn cause the control springs associated with the respective friction parts to exert a force which is of a reduced magnitude and is out of tolerance resulting in ineffective dampening of the bolster oscillations.

It has been determined that the only practical method by which friction shoe wear can be determined is by actually measuring the wear incurred by each individual friction shoe. Since the rate of friction shoe wear is dependent on many factors, such as the type of loads carried, the type of terrain in which the car is used and even the climate in which it is used, servicing of the friction parts cannot be based on any set standard such as time or distance.

As wear occurs on the friction surfaces of the shoe the position of the shoe relative to the bolster and side frame is continuously caused to shift both vertically and horizontally. As a result of this repositioning, the force which the control spring exerts on the friction shoe is constantly being reduced. This reduction may be on the order of several hundred pounds and in some cases may even be reduced to half the initial force.

It is therefore a primary object of the present invention to provide, in a snubbed truck, a friction shoe having extended wear capabilities to be used in conjunction with a shim that may be inserted between the friction shoe and the control spring or alternatively between the control spring and the compression member of the side frame. The shim is to be so constructed as to have a thickness equal to the vertical rise of the friction shoe. The combination of the friction shoe having additional wear capabilities and the shim, which is inserted between the friction shoe and the spring, will provide for the extended life of the friction parts without the variation of column pressures in the control springs that was common in prior art arrangements.

A further object of the invention is to provide a shim having on its spring seat an offset spring positioning boss to move the spring laterally to relocate the spring axis to restore the critical relationship between slope contact area and coil spring center.

The foregoing and other objects and advantages of the invention will become apparent from the following specification and the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary side elevational view of a freight car truck partly in section embodying features of the present invention.

FIG. 2 is an exploded isometric view showing the interelation of the movable friction parts.

FIG. 3 is a detailed portion of FIG. 1 showing an elevation of the friction shoe positioned in the pocket of the bolster and shows the friction shoe in its new or unworn condition.

FIG. 4 is the same view as that shown in FIG. 3 except the friction shoe is shown in a worn condition.

FIG. 5 is the same as FIG. 4 showing the addition of a shim between the friction shoe and the control spring.

FIG. 6 is a detailed plan view showing another embodiment of the shim wherein the boss has an excentric offset.

FIG. 7 is a side view of the shim shown in FIG. 6.

Referring now to FIG. 1, a portion of a railway truck may be seen which is of conventional construction and includes a pair of spaced side frames, one of which 10 is shown. Each side frame has a compression member 12 and a tension member 14 interconnected by spaced vertical columns 16 the side of which form a window 18 (FIG. 1) substantially rectangular in slope with the upper portion 18a of the window being slightly narrower than the lower portion 18b.

It should be understood that the railway truck for the purpose of the present disclosure may be considered identical at both sides thereof and for the sake of brevity only that portion shown will be described in detail.

The window formed by the compression member 12, tension member 14 and spaced vertical columns 16 is adapted to receive the end of the bolster, generally indicated at 20. The lower surface 22 at the end of the bolster 20 is supported by a plurality of support spring groups 24 which rest at their lower ends on the side frame tension member 14. In opposite side walls 26 at each end of the bolster 20 are wedge-shaped receiving pockets 28 (FIGS. 3, 4 and 5) which open outwardly toward the side frame columns 16 and have an inclined inner wall 30 which has a width corresponding substantially to the width of the wedge-shaped friction shoe 32 positioned therein. The inclined inner wall 30 projects above the plane of the bolster top wall 34.

One wedge-shaped friction shoe 32 having extended wear capabilities is operatively carried in each pocket 28 and includes an inclined surface 36 corresponding to and frictionally engaging the inclined wall 30 of the pocket 28. The friction shoe also has a vertical surface 38 for frictionally engaging vertical wear plates 40 on the adjacent side frame columns 16.

The lower surface or spring seat 42 of the wedge-shaped friction shoe 32 is engaged by the upper end of a control spring 44 which is disposed between said friction shoe 32 and the tension member 14 of the side frame 10. The inclined inner wall 30 therefore provides an inclined thrust area equal to that of the engaged portion of the inclined surface 36 of the wedge-shaped friction shoe 32.

The wedge-shaped friction shoe 32 in a new or unworn condition (FIG. 3) is so constructed and arranged that when operatively placed in the bolster pocket 28 the control spring 44 will exert a force on the lower surface 42 of the friction shoe 32 which will urge the friction shoe 32 into frictional engagement with both the inclined surface 30 of the bolster pocket 28 and the vertical wear plates 40 located on the vertical column 16 of the side frame 10 adjacent said pocket 28. The aforementioned frictional engagement thereby produces a snubbing action on the bolster 20 intended to reduce undesirable oscillations.

Satisfactory snubbing of the bolster 20 will continue as long as the force exerted by the control spring 44 remains relatively constant. However, as the vertical and inclined friction surfaces 38 and 36 wear, the friction shoe 32 is allowed to rise in the bolster pocket 28 as illustrated in FIG. 4.

The vertical rise is caused by two factors, the first factor is the wearing of the inclined surface 36 of the shoe 32 and the inclined surface 30 of the bolster; also contributing to the vertical rise is the wear which takes place on the vertical friction surface 38 of the wedge-shaped friction shoe 32. It is the wearing of the surfaces 38, 40, 36 and 30 that cause the friction shoe to move laterally toward the vertical column 16 of the side frame 10 thereby increasing the vertical distance the shoe 32 must move before the inclined surface 36 of the friction shoe engages the inclined surface 30 of the bolster pocket 28.

As a direct result of the vertical repositioning of the friction shoe 32 the control spring 44 associated with that friction shoe 32 must increase in length in order to maintain the force on lower surface 42 of the friction shoe 32. It is this elongation of the spring 44 that causes a reduction in the column pressure of the control spring 44 which in turn hampers the snubbing of the bolster 20.

In the past it was necessary to replace the friction shoe 32 in order to restore the required column pressure necessary to insure adequate snubbing action. In many cases this meant that friction shoes were discarded that still had a substantial amount of wear remaining on the friction surfaces.

Considering that most railway cars have two trucks and each truck generally has four friction shoes it is clear that such a practice is costly in materials and labor since the effort required to replace a friction shoe is substantial.

As best seen in FIG. 5, the aforementioned problem has been overcome by inserting a shim 46, the thickness of which corresponds to the total vertical rise of the friction shoe 32, between the lower portion of the friction shoe 32 and the control spring 44 thereby restoring the proper column pressure to the control springs 44. The insertion of such a shim 46 may be done with much less effort than total shoe replacement; it also extends the useful life of the friction shoe 32.

The use of the shim 46 may be of even more effective value when used in conjunction with friction shoes 32 having extended wear characteristics in that the shoe may be used in service until the column pressure of the control spring 44 requires renewal. This would correspond preferably to the half-worn condition of the friction shoe 32 (having extended wear capabilities). After insertion of the shim 46, the friction shoe 32 could once again give useful service for a period approximately equal to the first period of use.

The maintenance procedure described above would reduce the wide range of spring pressures that would otherwise exist if the friction shoe 32 were allowed to reamin in service until totally worn out. By limiting the range through which the column pressures may vary by the utilization of a shim 46, more effective snubbing action may be maintained throughout the life of the friction parts. This improved snubbing action is accomplished without the high cost that would be associated with the complete renewal of the friction shoe 32 and its associated parts; especially when said friction shoe 32 and parts are only in a half-worn condition.

It should be understood that the shim 46 could be constructed in a number of different ways but preferably would constitute a flat plate contoured on the upper surface 48 to the shape of the friction shoe spring seat 42. The lower surface 49 of the shim 46 would be similar to the spring seat 42 of the friction shoe 32 thereby allowing the control spring 44 to seat against the lower surface 49 of the shim 46 in the same manner as it previously seated against the spring seat 42 of the friction shoe 32.

As shown in the preferred embodiment (FIG. 2), the friction shoe 32 has a positioning lug 50 cast integral on its spring seat 42, the shim 46 defines an opening 52 which allows the shim 46 to be affixed to the shoe 32. Extending from the bottom surface of the shim 46 is a positioning lug 54 to insure proper orientation of the control spring 44. The positioning lug 54 on the shim 46 is similar to the positioning lug 50 on the lower surface 42 of the friction shoe 32.

An alternative construction would be required in the event it were desired that a shim (not shown) be interposed between the lower portion of the control spring 44 and the tension member 14 of the side frame 10. In such an event, the shim would be contoured to the shape of the side frame spring seat 56.

In some applications a problem may arise due to the lateral repositioning of the friction shoe 32 resulting from wear on the vertical surface 38 of the friction shoe 32. As a result of this shift, the central axis (not shown) of the control spring is no longer aligned with the center (not shown) of the spring seat 42; instead the central axis of the control spring is shifted toward the leading edge of the shoe 32 and away from the vertical surface 38 of the friction shoe 32. In the event this shift is large enough, uneven wear of the friction surfaces 38 and 36 on the shoe 32 may occur. The uneven wear results when the shifting of the central axis of the control spring 44 is enough to cause a tipping of the friction shoe 32 thereby causing increased wear on the upper portion of the vertical surface 38 and the lower portion of the inclined surface 36 of the friction shoe 32.

Use of another embodiment of the shim 46 shown in FIGS. 5, 6 and 7 eliminates the uneven wear of the friction surfaces 38 and 36 on the friction shoe 32. As shown best in FIG. 7, the spring positioning boss 58 is offset thereby reorienting the top of the control spring 44 with the center (not shown) of the spring seat 42 on the friction shoe 32. Reorientation of the top of the control spring 44 will maintain the relationship between the slope contact area and the central axis of the control spring.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

Claims

We claim:

1. In a railway car truck including a bolster resiliently supported on a side frame having a column, friction shoe means wedgingly interposed between said bolster and said column, said friction shoe means including a lower surface having positioning means depending therefrom, and compressed spring means for urging said friction shoe means into wedging frictional engagement with said bolster and said column, the improvement residing in the interpositioning of shim means between said friction shoe means and said compressed spring means; said shim means having an upper surface and a lower surface separated by a predetermined thickness; said upper surface defining an opening contoured to mateably engage said positioning means; said lower surface of said shim means having a projection offset toward said bolster, said projection engaging and aligning said compressed spring means to vertical, thereby compensating for the horizontal shift of the friction shoe means resulting from previous wear of its column engaging area.

2. The invention according to claim 1 wherein said shim means is substantially rectangular in shape when viewed from above and said opening and said projection are axially aligned and offset from the center and equidistant from two opposing sides of said shim means.

3. The invention according to claim 1 wherein said thickness of said shim means is equal to the vertical rise of said friction shoe means resulting from the wear of said friction shoe means.