Brakes – Vehicle – Railway
Reexamination Certificate
1997-10-14
2001-05-29
Graham, Matthew C. (Department: 3613)
Brakes
Vehicle
Railway
C104S259000, C188S25000B
Reexamination Certificate
active
06237726
ABSTRACT:
The invention relates to a rail brake element, in particular in connection with rail brake buffer blocks, according to the preamble of patent claim
1
.
A rail brake element of the above-identified type has become known from German 24 53 223. The clamping plates which are of an approximately C-shaped cross-section are pressed together above the rail head by means of clamping bolts. In the lower area the clamping plates include angular friction elements which are made of a suitable friction material such as bronze. The friction elements engage the bottom side and the lateral surfaces of the rail head. A so-called lining piece is supported against the rail head, which lining piece is also made of friction material and has at its upper side tapered surfaces which are engaged by the upper legs of the clamping plates. When the clamping bolts are subjected to tension forces, compression and tension forces are exerted upon the friction elements by a wedge action such that a corresponding friction force will be generated at the rail head.
Modifications of such a brake element have become known from German 834 572 or German 34 22 230.
Apart from the friction coefficient the brake action of such a rail brake element depends on the force which urges the friction elements against the rail head. This force is applied via the clamping bolt, with a double spring ring being disposed between the clamping bolt and a clamping plate. The only possibility to preset the urging force is to measure the torque for tightening the clamping bolt. However, there are no defined relationships between the measured torque and the actual urging force because the measured torque depends also on other parameters such as the friction at the clamping bolt threads or the friction between the bolt head and the spring, etc. When there will be wear of the friction element, the reduced stroke will be compensated by the helical spring. If the helical spring exhibits an unfavorable force-displacement-relationship, which is the case normally with the used helical springs, wear will result in a significantly reduced urging force.
The actual braking effect by the rail brake element is obtained by displacing the rail brake element along the rail head, for example by a buffer block which either stands upon the rails relatively loosely or is integrated in the rail brake element. However, before this will occur, stationary friction will have to be overcome, with stationary friction theoretically being at least twice as large as sliding friction, however, in practice may be much higher due to corrosion of the rail and braking parts of the rail brake element. During the initial impact phase the rail brake element acts like a rigid barrier which begins to move only after the stationary friction has been overcome. This will cause a substantial shock for the oncoming vehicle. If a plurality of rail brake elements are disposed one after the other in abutting relationship, this will result in an excessive, unacceptable value of the described stationary friction. This is why it is common practice to arrange the rail brake elements in spaced relationship so that the stationary friction of the individual rail brake elements will be overcome one after the other during a braking operation.
The problem to be solved by the invention is to provide a rail brake element, in particular in connection with rail brake buffer blocks, which overcomes the above drawbacks and exhibits a relatively small stationary friction while providing for an optimal braking effect by sliding friction.
This problem is solved by the features of patent claim
1
.
In the brake element of the invention the brake lining layer engages the rail head by means of at least one raised portion of wear-resistent material having a stationary friction coefficient smaller than said of the brake lining layer. According to one aspect of the invention the wear material may be made of plastics such as a suitable polyamide. It is of inventive significance that the raised portion has a relatively small friction coefficient and in particular provides for small stationary friction of the rail brake element. As a result only a relatively small impact force is necessary to cause the rail brake element to move during a braking operation. Due to the resulting sliding friction between the raised portion and the rail head, the wear material should be worn off during a relatively short path of movement of the rail brake element such that the brake lining layer will then engage the rail head to provide for the desired brake effect.
The height for which the raised portion extends above the actual brake lining layer may be very small. The compression resistence of the used wear material and its height are to be chosen such that extensive engagement between the brake lining layer and the rail head is avoided. Such an engagement should be obtained only by wear of the wear material.
In one embodiment of the invention the wear material may be applied to the brake lining layer so as to be continuous; however, in an alternative embodiment of the invention it may be applied so as to be disposed in spaced areas. Preferably, separate parts, preferably of plastics, are used, which parts are mounted to the brake lining in suitable manner. Application thereof and, respectively, re-application thereof after wear should be as simple as possible so as to be readily performable by servicing personal. In one embodiment of the invention the brake lining layer comprises a brake ledge which engages only the bottom side of the rail head; the brake ledge may be of an arcuate cross-section according to a further development of the invention. According to a further development of the invention block-like wear portions may be inserted in respective recesses of the brake ledge and secured therein for example by a press fit. It is particularly preferred to provide the block-like wear portion with a flange which cooperates with counterbores of bores in the brake ledge which are formed on the side facing the clamping plate. In this manner, the wear portion is retained in the bore of the brake ledge by the associated portion of the clamping plate. The convex arcuate shape of the brake ledge has furthermore the advantage that it has a defined surface engaging the rail head.
A further development of the invention provides that the clamping device is supported against the top side of the rail head via a pad of friction material and exerts a tension force upon the clamping plate. In this manner the urging force for the brake lining layer is not generated by a wedge effect as in the rail brake element of the above mentioned prior art, but exclusively by tension forces exerted upon clamping plates. The tension forces may be applied by a clamping bolt. It is much more acurate to set the brake force by applying an urging force than by generating a wedge effect as in the prior art. In an embodiment of the invention the pad cooperates with the clamping bolt which is disposed in a threaded bore of a lining ledge above which the clamping plate extends and the outside of which is connected to the clamping plates, with the pad being received in a recess of the lining ledge and a compression spring being disposed between the clamping bolt and the pad. According to a further development of the invention the compression spring may comprise a Belleville spring assembly which exhibits a favorable force-displacement-characteristic. The pad which provides for a braking action can be provided also with a raised wear portion as described above in connection with the brake lining, in order to reduce stationary friction also at this location. Preferably, in an elongated rail brake element there are provided a plurality of pads in spaced relationship, each in connection with a clamping bolt and a Belleville spring assembly.
Generating an urging force by the clamping bolt has the advantage that the urging force is proportional to the distance for which the brake element has moved. This distance may be measured in a simple manner. To this end a further de
A. Rawie GmbH & Co.
Graham Matthew C.
Vidas Arrett & Steinkraus P.A.
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