GB2158899A - Rail vehicle brake - Google Patents

Abstract

A rail vehicle comprises a brake block on a brake shoe 4 pivotally mounted on a pivotally mounted hanger 14. The block is moved towards the vehicle wheel to exert braking effort by an actuator 20/22. A stay 26 is connected to the brake shoe through a lost motion system 28/30 arranged so that the retracted brake block fully clears the tyre. The actuator includes a slack adjuster which, when operated, extends rod 22 to compensate for wear, and a subsequent brake operation may cause stay to be moved to the left against frictional force provided by a spring (44, Fig. 2) biassing a washer 48 against the stay. A cam arrangement (38/40) is operated to reduce the frictional force when a new brake block is to be fitted. <IMAGE>

Description

SPECIFICATION Rail vehicle brake This invention concerns a rail vehicle brake (hereinafter called the type referred to) comprising a brake block or pad (hereinafter referred to as a block) on a brake shoe pivotably mounted at a shoe pivot on a pivotably mounted hanger, means to move the block towards a tyre of a wheel of a rail vehicle to exert braking effort thereon in a brake applied position, and means to retract the block to release said effort. Both the aforesaid means can be combined.

In a known brake of the aforesaid type, the combined effects of the jolting of the vehicle and the considerable weight of the block and shoe cause the latter to tilt about the shoe pivot so that an upper end of block rubs on the tyre when the brake is in a released state.

Thus causing excessive wear of the upper end of the block which needs renewing much sooner than would otherwise be the case.

In an effort to avoid that disadvantage friction stays have been used for several years.

The stay is pivotally connected to the brake shoe at a lower level than the shoe pivot. That pivotable connection is a round pin on the shoe disposed in a hole of the same diameter in the stay. The stay is frictionally engaged.

The intention is that as the brake is applied and released the stay moves to and fro in the frictional engagement, its pivotal connection with the shoe preventing the shoe from tilting the upper end of the block towards the tyre and so prevents the upper end of the block from rubbing on the tyre in the brake released condition. However the forces causing retraction of the shoe from brake release may not be as great as the frictional engagement of the stay, so at brake release the stay may remain in the position it is moved to by brake application and holds the lower end of the brake block rubbing against the tyre whilst the upper end is moved clear. Again this can cause undesirable excessive block wear.

In one version the stay is a second hanger pivotably connected at its lower end to the shoe, the upper end of the hanger being mounted on a pivot about which the stay can swing rubbing against applied friction material. In another version the stay is pivoted at one end to the shoe and can reciprocate substantially longitudinally against the frictional force of friction material applied against a side of the stay.

According to the invention a rail vehicle brake of the type referred to in which staying means is connected with the brake shoe through a lost motion system arranged so that the retracted brake block fully clears the tyre.

The staying means can be connected with the brake shoe through the lost motion system at a lower level than the shoe pivot.

The lost motion taken up by the system can be substantially equal the distance through which the block is retracted from the tyre to brake released position.

The lost motion system may comprise an element provided on the brake shoe or staying means and disposed between spaced abutments provided on the staying means or brake shoe, the distance between said abutments equalling the lost motion which can be taken up.

The spaced abutments may be opposite sides of an aperture. The aperture may be a slot and its opposite ends the spaced abutments. The element may be a pin.

The brake can be provided with slack adjusting means to reduce the movement of the block between brake effort exerting and brake release conditions upon detection of movement of the block between the two conditions in excess of a pre-determined amount.

The lost motion taken up may substantially equal the maximum retraction of the block from the tyre permitted by the slack adjusting means.

The staying means may be a second hanger pivoted at its upper end to the bogey or vehicle chassis which pivot is parallel to the shoe pivot, and friction means applied against said upper end to hold the second hanger in the position to which it is pivoted by application of the brake following operation of the slack adjuster. Or the staying means may be an arm mounted on the bogey or vehicle chassis to slide axially, in response to operation of the slack adjusting means, against applied frictional force intended to retain the arm in the position to which it is moved by brake application subsequent to operation of the slack adjuster.

There may be a said block on a said brake shoe pivoted on a first mentioned hanger at two different or diametrically opposed sides of the tyre periphery, the set comprising a first mentioned hanger and shoe on one side being pivotably interconnected by known pull-rod means with the set at the other side of the periphery.

The invention will now be further described by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a fragment of a rail vehicle brake formed according to the invention, shown in brake released condition; Figure 2 is a view partly in section on enlarged scale of a stay connected to the brake shoe of Fig. 1 through a lost motion system, and Figure 3 shows the brake in Fig. 1 in applied or braking effort exerting condition.

In the drawings, the rail vehicle brake is of a type known per se with the exception of a novel stay arrangement 2 connected through a lost motion system to brake shoe 4.

A rail vehicle wheel 6 has a peripheral tyre 8 against which is applied during braking a brake block 10 on the shoe, the block having a friction face of similar radius of curvature as the tyre. Towards the side of the shoe remote from the block, the shoe is pivoted at 1 2 to a lower end of a hanger or hanger arrangement 14 pivoted at its upper end at 1 6 on a bogey or vehicle chassis 18, pivots 1 2 and 1 6 being parallel.

Mounted on the chassis 1 8 is a brake actuator 20 known per se which may be fluid operated at a demand for braking to move rod 22 which pushes a nose on the back of the shoe in the direction of arrow A (Fig. 1) to apply the brake block against the tyre. When brake release is required resilient means, for example spring 24, pulls the hanger back to move the block from the tyre when the pushing force in direction A on the rod is relieved.

The resilient means may be incorporated in the actuator 20 to act on the rod 22 which may be pivotably connected to the shoe 4.

The actuator may be pivoted on the chassis 18.

The actuator 20 includes a known slack adjuster which upon detection in known manner of excess travel of the brake block between brake applied and brake released condition (due to wear of the block and/or the tyre) extends the rod 22 so that in the brake released state the distance between the friction face of the brake block and the tyre does not substantially exceed a desired pre-determined clearance x.

To ensure that at brake released condition the brake block 10 completely clears the tyre 8, the stay arrangement 2 is provided which comprises a rod 26 having at one end a slot 28 receiving a pin 30 mounted on the shoe 4. The rod also has an axial slot 32 receiving a shaft 34 passing through an aperture in a strut 36 mounted on the chassis 18. This shaft has a head constituted by a cam 38 pivoted on the rod, which cam can be rotated by a toggle or handle 40. Between the head 38 and a nut 42 is a compressed spring 44 by which discs 46 and 48 of friction material on the shaft 34 are pressed, against sides of the strut 36 and rod 26. The pin 30 and shaft 34 are both parallel with the pivot 1 2.

The slot 28 and pin 30 form a lost motion system, the distance X between end faces 28A, 28B of that slot may be substantially equal to, or slightly greater, or slightly less than distance x.

In the brake released state, the firm frictional engagement of the disc 48 with the lever 26 and the connection between the brake shoe and the lever prevent the brake shoe tilting about the pivot 1 2 to any extent which would allow upper end 1 OA of the block to touch the tyre 8. Furthermore during brake release as the shoe is moving in direction B, the pin 30 can move freely along the slot 28 from end 28A towards end 28B and thus lower end 1 0B of the brake block is not held against the tyre 8.

When the slack adjuster operates to extend the rod 22 along direction A to compensate for wear, the next time the brake is applied by the considerable force exerted by the actuator, the pin 30 may push slot end 28A to draw the lever 26 through its frictional engagement to a new position in which slot end 32A is nearer to the rod 34.

A similar arrangement or set comprising hanger 14, brake shoe 4, actuator 20 and stay arrangement 2 etc.. may be provided for applying and releasing another brake block 4 on substantially the diametrically opposite side of the tyre periphery. In this case the hanger and shoe arrangement may be connected in manner known per se by one or more pullrods extending across the vehicle wheel, in such a case only one actuator need be used.

When fitting a new brake block it is necessary to shift the lever in direction C. To make this easier, handle 40 is rotated into line with the rod 34, this rotates the cam 38 relative to the rod causing the latter to move axially to cause some unloading of the spring 44 so that the frictional force engagement of the lever 26 is reduced.

The pin 30 is at a lower level than the pivot 12.

The slot 28 can be replaced by an aperture of any shape allowing the pin to move freely between opposite ends or sides of the aperture provided those ends or sides are comparably spaced as the slot ends 28A, 28B.

Alternatively the stay arrangement 2 may be replaced by a stay arrangement in the form of a second depending hanger slotted or apertured at its lower end to form a lost motion system with the pin 30, this second hanger being pivoted at its upper end to the chassis 1 8 which upper end is in frictional engagement with one or more discs of friction material to retain the second hanger in place except after slack adjustment or when a new brake block is being fitted.

Claims (10)

1. A rail vehicle brake of the type referred to in which staying means is connected with the brake shoe through a lost motion system arranged so that the retracted brake block fully clears the tyre.

2. A rail vehicle brake according to claim 1, wherein the staying means is connected with the brake shoe through the lost motion system at a lower level than the shoe pivot.

3. A rail vehicle brake according to claim 1 or 2, wherein the lost motion taken up by the system is substantially equal to the distance through which the block is retracted from the tyre to a brake released position.

4. A rail vehicle brake according to claim 1, 2 or 3, wherein the lost motion system comprises an element provided on the brake shoe or staying means and disposed between spaced abutments provided on the staying means or brake shoe, the distance between said abutments equalling the lost motion which can be taken up.

5. A rail vehicle brake according to claim 4, wherein the spaced abutments are opposite side of an aperture through which the element extends.

6. A rail vehicle brake according to any preceding claim, wherein the brake is provided with slack adjusting means to reduce the movement of the block between brake effort exerting and brake release conditions upon detection of movement of the block between the two conditions in excess of a predetermined amount.

7. A rail vehicle brake according to claim 6, wherein the most motion taken up is substantially equal to the maximum retraction of the block from the tyre permitted by the slack adjusting means.

8. A rail vehicle brake according to claim 6 or 7, wherein the staying means is a second hanger pivoted at its upper end to the bogey or vehicle chassis which pivot is parallel to the shoe pivot, and friction means applied against said upper end to hold the second hanger in the position to which it is pivoted by application of the brake following operation of the slack adjuster.

9. A rail vehicle brake according to claim 6 or 7, wherein the staying means comprises an arm mounted on the bogey or vehicle chassis to slide axially, in response to operation of the slack adjusting means, against applied frictional force intended to retain the arm in the position to which it is moved by brake application subsequent to operation of the slack adjuster.

10. A rail vehicle brake of the type referred to substantially as hereinbefore described with reference to the accompanying drawings.