GB2343926A

GB2343926A - Wiper for a friction element of a vehicle brake

Info

Publication number: GB2343926A
Application number: GB9925583A
Authority: GB
Inventors: Xaver Wirth
Original assignee: Knorr Bremse Systeme fuer Schienenfahrzeuge GmbH
Current assignee: Knorr Bremse Systeme fuer Schienenfahrzeuge GmbH
Priority date: 1998-10-28
Filing date: 1999-10-28
Publication date: 2000-05-24
Anticipated expiration: 2019-10-28
Also published as: DE19849790C2; GB9925583D0; DE19849790A1; GB2343926B

Abstract

To avoid the reduction of coefficient of friction between a friction element 1 of a vehicle brake, in particular a rail vehicle brake, and an element 2 to be braked as a result of dampness of the components named, the friction element 1 is provided with grooves 5 in each of which a wiper 6 is located. The wiper may take various forms, and, in one example, is constituted by a plate 9" with projecting blades 11 which define chambers 10, 19 for collecting moisture.

Description

2343926 Wiper for a friction element of a vehicle brake and brake lining

equipped therewith The present invention relates to a wiper for a friction element of a vehicle brake, for example a rail vehicle brake, and a brake lining for a friction brake of a vehicle, for example a rail vehicle.

The coefficient of friction between a friction element of a vehicle brake and an element to be braked depends in particular on the dampness of these components. The friction element consists of a porous material which absorbs water to a degree dependent on the weather. In this way, the physical coefficient of friction between the friction element and the component to be braked is reduced compared with the coefficient of friction of dry components. In the case of a rail vehicle brake this means that the coefficient of friction between the brake lining (friction element) and the brake disc (element to be braked) is reduced.

The coefficient of friction is further reduced if a so-called aquaplaning effect occurs between the friction element and the component to be braked, which can lead to floating of the friction element during the braking procedure. This takes place in particular with low surface pressures and leads to a physical coefficient of friction close to zero.

Both the water absorption of the friction element material and the aquaplaning effect can lead to unacceptable extensions of the stopping distance.

To avoid the aforementioned problems it is known to provide friction elements of materials which are as insensitive to moisture as possible. However, today there is the paradoxical situation that materials for friction elements with good coefficients of friction and a good contact pattern in dry conditions are unacceptably sensitive to moisture, whereas friction elements with rather unfavourable wear values and coefficient of friction characteristics or with a tendency to form hot spots in the dry state as a result of a poor contact pattern are more likely to be insensitive to moisture. Therefore, friction elements provided as brake linings for rail vehicles are tested according to specifications of the Union International des Chemins de Fer (UIC) in order to reveal an inadequate coefficient of friction performance in the event of dampness and/or moisture. However, this involves considerable technical and organizational expenditure.

Furthermore, it is known to counter the moisture problem with a particular geometrical form of the friction element. For example, DE 89 05 731 Ul describes a brake lining for partial lining disc brakes of, in particular, rail vehicles, which is constructed in one or more parts and is approximately kidney-shaped and optionally is secured by a dovetail guide on a lining carrier, with the adjusting surfaces present at both ends of a brake lining being divided into several straight partial surfaces which extend over the entire engagement region of the brake lining and which form an angle of less than 90' to the friction surface of the brake disc. The known brake lining has the disadvantage that an increase in the coefficient of friction is only achieved with complete re-equipping of the rail vehicle brake. Subsequent retrofitting of brake linings which are already in position with a device which increases the coefficient of friction is therefore not possible.

DE-OS 1 430 869 discloses a motor vehicle disc brake in which a fairly large number of water drainage holes or suchlike are distributed approximately evenly over the friction surfaces. Here also retrofitting is not possible. Furthermore, the water drainage holes penetrate the friction surface completely, with the result that the latter tends towards cracking and is subject to increased wear. In addition, friction surface is lost.

Finally, EP-0 443 360 Bi describes a brake lining for partial lining disc brakes with a brake disc, in particular of rail vehicles, in which water drainage devices are provided opposite the rear side, on the front side which is provided for contacting the brake disc of the disc brake for which purpose the brake lining is provided with a number of apertures. The apertures are spaced apart from each other, extend from the front side of the brake lining-continuously as far as its rear side and are suitable for the uptake and removal of friction-inhibiting contamination such as water, ice, abrasive dust or suchlike. This brake lining is constructed in one or more parts and approximately in the shape of a circular ring segment., The apertures are positioned such that at least 301 of arbitrary circles drawn on the front side of the brake lining would cut or contact at least one of the apertures provided. There is a maximum degree of overlap of the apertures of 15001, in which any conceivable circle contacts or cuts at least one aperture so that each drop of water occurring on any circle is supplied to an aperture. Alternatively, the ratio of the surface of the openings of the aperture on the front side of the brake lining to the entire front side surface including the surface of the openings of the apertures is between 2:100 (minimum) and 35:100 (maximum), or any arbitrary circle on the front side of the brake lining cuts or contacts at least one aperture and a maximum of five apertures per 150 mm of its length.

The apertures penetrate the friction body completely so that the latter also tends towards cracking and is subject to increased wear. A further disadvantage consists in that an increased coefficient of friction is only achieved if a completely new brake lining is used on the rail vehicle. A subsequent equipping of already present brake linings is therefore not possible with this device either.

In contrast, it is desirable to create a device for increasing the coefficient of friction between a friction element of a vehicle brake and an element to be braked also with humid, wet, damp or suchlike weather, which leads to less cracking and reduced wear of the friction element.

To this end, the invention provides a wiper for a friction element of a vehicle brake, e.g. a rail vehicle brake, comprising of at least one web. The wiper (and also the web) is preferably elongated.

A wiper in accordance with the invention can be used in an advantageous manner with known friction elements, in particular brake linings according to UIC specifications or circular ring sector brake linings, without changes in terms of their cracking behaviour or wear. Therefore, it is possible to use the wiper in accordance with the invention in grooves already present, in particular press grooves, of a brake lining or between two partial linings of a brake lining.

Here, the wiper in accordance with the invention may be secured by positive engagement and/or by the use of force (for example, spring force) and/or by a frictional engagement, e.g. by way of press fitting.

Alternatively or additionally, the wiper can be bonded to an outer side of the friction element or into a groove.

A wiper in accordance with the invention may have the further advantage that with appropriate installation in a friction element constructed as brake lining it operates in both directions of rotation of the element to be braked (in particular a disc brake).

This applies not only directly after the installation of the wiper into the friction element, but also with wear which is already advanced. The wiper continues its action until the wear of the friction element has reached its limit. In this event, the element to be braked is neither impaired in its action nor damaged.

This is in particular because the wiper rests with lower pressure on the element to be braked.

A wiper in accordance with the invention may be fitted to the friction elements in an advantageous manner in the course of a retrofitting procedure.

As a result of its simple assembly, a wiper in accordance with the invention may be manufactured from rod profiles. Advantageously, it is therefore suitable for all brake lining sizes.

Advantageously, a wiper in accordance with the invention can have spring elements which abut the grooves in the friction element so that the wiper in accordance with the invention is under initial stress (pre-stressed) and sprung into position.

Advantageous developments of the invention are evident from the features of the subclaims.

In a further advantageous embodiment, the previously described wiper may be provided not as a separate component but integrated in a brake lining for a friction brake of a vehicle, in particular a rail vehicle. The advantages described above are also available with this construction.

As a result of its accommodation in a groove of the brake lining in accordance with the invention, the wiper is protected against external influences such as_ inexpert handling, falling rocks or suchlike. Thus, it can be advantageously used reliably for a long time.

Further features and advantages of embodiments of a wiper and brake lining in accordance with the invention are apparent from the drawings which are presented by way of example and in which:

Figure 1 shows a circular segment brake lining with two wipers each of which is in accordance with the invention.

Figure 2 is a perspective view of one of the wipers in accordance with the invention, shown in Figure 1.

Figure 3 shows an alternative embodiment of the wiper in accordance with the invention, inserted in a brake lining. 15 Figure 4 shows a further alternative embodiment of the wiper in accordance with the invention, inserted in a brake lining.

Figure 5 shows a further alternative embodiment of the wiper in accordance with the invention, inserted in a brake lining.

Figure 6 shows a further alternative embodiment of the wiper in accordance with the invention, inserted in a brake lining.

Figure 7 shows a further alternative embodiment of the wiper in accordance with the invention, inserted in a brake lining.

Figure 8 shows a further alternative embodiment of the wiper in accordance with the invention, inserted in a brake lining. 35 Figure 9 shows a further alternative embodiment of the wiper in accordance with the invention, inserted in a brake lining.

Figure 10 shows a sectional longitudinal part of the wiper shown in Figure 8.

Figure 1 shows a friction element 1 in the form of a circular-sector brake lining. The friction element 1 is part of a disc brake system for a rail vehicle, the system not being shown in more detail. To brake the rail vehicle or to keep the rail vehicle in the braked state, the friction element 1 is placed against an element 2 to be braked. In the example shown here, the element 2 to be braked, which is only shown partially by means of a broken line, is a brake disc. Between the friction element 1 and the element 2 to be braked there is a water front 3, the flow direction of which is shown by way of example by means of arrows 4 in Figure 1. The water front 3 can consist of rain water, dew, ice, melt water or the suchlike and can contain abrasive dust and other friction-inhibiting contamination.

The friction element 1 has two grooves 5 which are spaced apart from each other and extend radially over its width. A wiper 6 is introduced into each groove 5 respectively. When a braking procedure takes place, the water front 3 flows in the direction 4 as far as the upper wiper 6 shown in Figure 1. The water front 3 is intercepted and diverted by the wiper 6, which extends over the entire width of the friction element 1 and substantially at right angles to the flow direction 4, until the water front 3 flows out of the space between the friction element 1 and the element 2 to be braked in an exit (outflow) direction 7. In this way, the part of the friction element 1 which is located below the upper wiper 6 is free of the water front 3 and the contamination contained therein.

For the case in which not all of the water following the water front 3 is diverted by the upper wiper 6 in Figure 1 in the exit direction 7, a second S wiper 6, the lower one in Figure 1, is provided. The second wiper is located in a second groove 5 which likewise extends over the entire width of the friction element 1 and substantially at right angles to the water front 3. Here also, because the wiper 6 extends radially over the entire width of the friction element 1, the water front 3 is intercepted and is diverted in the outflow direction 8 due to gravity.

The friction element 1 shown in Figure 1 is constructed symmetrically in relation to its midline H.

The upper wiper 6 in Figure 1 is aligned in relation to the midline H at an angle a different to 0', in this case 200. The lower wiper in Figure 1 is aligned in relation to the midline H likewise at an angle P different to 0, whereby, in the example shown here, the angle is smaller than the angle a. In a preferred embodiment the angles a and P are of the same size. In general, the midline H coincides with a radial direction of the brake disc (which is the element 2 to be braked), as do the wipers.

2S The wiper 6 shown in Figure 1 is shown again in Figure 2 with a perspective view. In this example the wiper 6 is constructed as a web 9 which has a rectangular cross section. The web 9 consists of a rubber or a duroplastic-like material and can be manufactured, for example, by injection moulding or extrusion moulding. Other cross sectional forms and/or materials, for example foam metal, can of course also be provided.

Figure 3 is a sectional view of an alternative embodiment of the wiper 6 which is located in the friction element 1. In this case, the web 9 is constructed in a V-shape in profile. The limbs of the web 9 abut the groove 5 in such a way that a chamber 10 is formed between them. The water intercepted by the wiper 6 can be diverted, in this chamber 10 as has already been explained with reference to Figure 1. The web 9 constructed in a V-shape can also be prepared from a rubber or a duroplastic-like material. As a result of the elasticity of these materials the wiper 6 shown in Figure 3 is sprung within the groove 5, so that it cannot fall out of the friction element 1.

Figure 4 shows a further embodiment of the wiper in accordance with the invention. The wiper G, shown here also has a web 91 which, however, has a reduced width compared with the web 9 shown in Figure 2. Six blades (or plates) 11 project from the web 91 in a slatted manner, the plates extending over the entire length of the web 91 and therefore the entire width of the friction element 1. The four left or inner plates 11 shown in Figure 4 abut the upper wall 12 of the groove 5. On the other hand, the outermost two right plates 11 shown in Figure 4 have free ends. Due to the inclined position of the plates 11 in relation to the element 2 (not shown here) to be braked, two of them always abut the surface of the element to be braked.

Here a plurality of chambers 10 are formed by the web 91, the plates 11, the wall 12 and the element 2 to be braked. Some of the chambers are open to the outside of the web and groove.

On the side opposite the plates 11, the web 91 has six holding projections 13 which abut the lower wall 14 of the groove 5. The holding projections 13 are formed in the shape of teeth and prevent the wiper 61 from falling out of the friction element 1, aided by the elasticity of the plates 11 manufactured from a rubber or duroplastic-like material. The embodiment of the wiper 61, shown here, can have a web 91 consisting of metal or plastics. In Figure 4 it can be seen that the holding projections 13 can be constructed to be substantially smaller than the blades or plates 11.

Figure 5 likewise shows a wiper 611, the web of which has blades (or plates) 11. However, in contrast with the wiper 6 shown in Figure 4, these are provided on both sides of the web 911. Here also chambers 10 are formed by the web 911, the plates 11, the upper wall 12 and the element 2 to be braked, the chambers being located above the web 911 in Figure 5.

In contrast with the embodiment shown in Figure 4, the wiper 611 shown in Figure 5 also has chambers 15 below the web 911, which chambers are constructed by the web 911, the lower wall 14 and the element 2 to be braked.

If the element 2 to be braked shown in Figure 5, rotates downwards in the movement direction 16, the water front 3 flows along the flow direction 4 into the chamber 10. From there the water, as shown in Figure 1, is diverted due to gravity, namely in one exit direction 7 if the wiper 611 shown in Figure 5 is the upper wiper 6 shown in Figure 1, or in the other exit direction 8 if the wiper 611 shown in Figure 5 is the lower wiper G shown in Figure 1.

If the movement direction of the element 2 to be braked changes into the opposite movement direction 17, a further water front 18 flows into the chamber 19 which is to be found in the area located below the web 911. The water also flows out of the chamber 19 as described previously.

Thus, the wipers 6 and 61, shown in Figure 2, Figure 3 and Figure 5 can be described as double-action wipers 6 because they can wipe away the water in both movement directions 16 and 17 of the element 2 to be braked. On the other hand, the wiper 61 shown in Figure 4 is a single-action wiper 6 because it diverts only water flowing in at the top in Figure 4. By inserting the wiper 61 shown in Figure 4 into the upper groove 5 shown in Figure 1, the water flowing in the flow direction 4 is diverted. To be able to divert also water flowing from the bottom to the top in Figure 1, a wiper G, shown in Figure 4 is rotated such that the chambers 10 open in the direction of the corresponding flow. In this way, the reliable function of the wiper 6 in accordance with the invention is also achieved with a single-action wiper 61. The wiper 611 constructed as double-action wiper 6 can of course also be inserted into the friction element 1 corresponding to Figure 1.

There is no danger of an obstruction of the chambers 10 and 19 caused by contamination, abrasive dust or suchlike because the water flowing in them has a rinsing effect. Furthermore, it is to be considered that the individual chambers 10 and 19 are sealed from each other.

Friction elements 1 used for braking purposes are subject to great wear. An appropriate wear limit 20 for a disc brake system used in rail vehicles is shown in Figure 5 by the reference symbol 20. Thus, the wear advances in the friction element 1 (here brake disc 1) from right to left in Figure S. It is evident that the function of the wiper 611 is maintained despite wear of the friction element 1 because the web 911 and the plates 11 projecting from it also wear out, whereby in Figure 5, extending from right to left, new plates 10 and 19 are progressively opened. This is also the case with the wipers 6 and 61 shown in Figures 3 and 4.

Figure 6 shows another embodiment of a wiper in accordance with the invention. The wiper 6"' has a rectangularly constructed (L-shaped) web 9"', with one limb of the web 9 abutting the lower wall 14 of the groove 5, and its other limb being provided at right angles thereto at the side opposite the element 2 to be braked, and reaching as far as the upper wall 12 of the groove 5. Plates 11 project from both limbs of the web 9"' in such a way that a wiper 6 acting on one side is produced. This wiper also has a chamber 10 through which water flowing in the flow direction 4 can be diverted.

As is evident from Figure 6, the groove 5 does not essentially have to be constructed in a wedge shape.

Rather, a groove 5 which is rectangular in cross section can also be provided in the friction element.

Figure 7 shows another embodiment of a wiper 6 in accordance with the invention. The wiper 6... is located in a groove 5 which is rectangular in cross section, is with a web 9 now being provided which is formed in a zigzag shape and abuts the lower wall 14 of the groove 5. The wiper 6... furthermore has a web 21 symmetrical to the web 9"', which web 21 abuts the upper wall 12 of the groove 5. By way of the zigzag shape of the two webs 9"' and 21 a number of chambers 10 are likewise formed, through which water flowing in in the flow direction 4 and in the flow direction 18 can be diverted.

Figure 8 shows a further embodiment of the wiper G in accordance with the invention. Here, the web 9"' of the wiper 6"' is constructed as a U-profile, from the limbs of which, which abut the upper wall 12 and the lower wall 14 of the groove 5, plates 11 project in such a way that in turn a number of chambers 10 are formed.

The wipers 6"' shown in Figures 6 to 8 also act on two sides. For this purpose, the plates 11 or webs 9 and 21 are arranged inclined in relation to the side of the element 2 to be braked, against which element the friction element 1 comes to rest.

Finally, a last embodiment of the wiper 6 in accordance with the invention is shown in Figure 9.

The web 9"" of the wiper 6"" is also constructed to be substantially U-shaped in this case. However, in this exemplary embodiment the limbs of the wiper 6"" are constructed to be inclined in relation to its midline M in such a way that the distance between the free ends of the wiper 6"", which are shown on the right in Figure 9, is shorter than the width of the web 9"" at the side of the wiper 6"" which is opposite the element (not shown) to be braked. Here also, the limbs of the wiper 6.... directly abut the upper wall 12 and the lower wall 14 of the friction element 1, with the free ends of the two limbs projecting a little beyond the groove 5. Between the web 9.... and the floor of the groove 5 shown on the left in Figure 9 a spring element 22 is provided. By means of the spring element the wiper 6"" is sprung or prestressed against the upper wall 12 and the lower wall 14 of the groove 5. The spring element 22 acting as pressure spring can be inserted as a separate component between the groove and the wiper 6"".

Figure 10 gives a longitudinal view of a part of the wiper 6.... shown in Figure 9. In the exemplary embodiment shown here, not only is one spring element 22 provided, but additional spring elements 221 and 2211, all of which can have the same dimensions or different dimensions. The distance between the individual spring elements 22, 22' and 2211 can be provided evenly or unevenly over the length of the friction element 1.

The spring elements 22, 221 and 2211 are formed as tongues which, from the web 9"", abut the floor of the groove 5. The spring elements 22, 22' and 22" are - advantageously partially pressed out of the web 9"" so that they are formed integratively on the web 9"". Of course, other formations of the spring elements 22, 221 and 2211 are possible, in particular in the form of beads (not shown) which project from the web 9... and abut the floor of the groove 5.

As already previously explained, the wipers 6, 61, 611, 6"' and 6"" can consist of a heat-resistant plastics material or rubber. However, metal may also be used for the wipers 6, 61, 611, 6"' and 6.... in accordance with the invention. In any case, the selected materials are preferably heat-resistant and flexible, so that the webs 9, 91, 911, 9... and 9"" and the plates 11 abut the element 2 to be braked and/or the groove 5, whereby a good contact between the wipers 6, 61, 611, 6"' and 6"", the groove 5 and the element 2 to be braked is ensured.

This applies even more if the wiper 6, 61, 611, 6... and 6"" is used under initial stress by prestressing, for example by spring forces, because in this way the elastically designed webs 9, 91, 911, 9"' and 9.... and the plates 11 are also under initial stress and, acting as expanding springs, prevent the wiper 6, 61, 611, 6... and 6"" from falling out.

It is evident that the wiper in accordance with the invention can be used not only with disc brake systems, but also with block brake systems, drum brake systems or suchlike.

List of reference symbols 1 friction element 2 element to be braked 3 water front 4 flow direction groove 6, 61, 611, 6"', 6"" wiper 7 outflow direction 8 outflow direction 9, 9 9 9111, 9111, web chamber 11 blades 12 upper wall 13 holding projections 14 lower wall chamber 1G movement direction 17 movement direction 18 flow direction 19 chamber limiting extent of the wear 21 web 22, 221, 2211 spring element H, M midline 0(, angle

Claims

Claims

1. A wiper (6, 6 1, 611, 6111, 6"") for a friction element (1) of a vehicle brake, comprising at least one web (9, 91, 911, 9111, 911", 21).

2. A wiper (6, 61, 611, 6111, 6"") according to claim 1, wherein at least one blade (11) projects from the web (9, 9 It 911, 9111, 91111, 2 1) 3. A wiper (6, 61, 611f 6111, 6"") according to claim 1 or 2f wherein the web (.9, 91, 9111 9111, 911"r 21) has at least one holding projection (13).

4- A wiper (6, 6', 611, 6"', 6) according to any one of claims 1 to 3, wherein the web (9, 9 1, 911, 9111, 9"", 21) Is substantially U-shaped or V-shaped in cross section.

5. A wiper (6, 61, 6 11 1 61" 1 6"") according to any one of claims 1 to 3, wherein the web (9, 911 911, 9111, 9 1 21) has a zigzag cross section.

6. A wiper (6, 6 1, 611, 6111, 6") according to any one of claims 2 to s, wherein the blades (11) on the web (9, 9 ', 911, 91", 91111 r 21) are arranged symmetrically, preferably to either side of the web.

7. A wiper (6, 6-, 6-1, 6"', 6"") according to any one of claims 2 to 6, wherein the web or webs (9, 91, 911, 9,,,, 9"", 21) and/or the blades (11) form chambers (10, 19) at least one of which is preferably open to the outside of the wiper.

8. A wiper (6, 61, 611, 6"11 6"") according to claim 7, wherein the chambers (10, 19) are separated from each other.

9. A wiper (6, 61, 611, 6"', G"") according to any one of claims 1 to 8, wherein the length of the wiper (6) corresponds to at least the width of the friction element (1). 5 10. A wiper (6, 61, 611, 611f, 6"') according to any one of claims 1 to 9, wherein at least one spring element (22, 221, 2211) is provided.

11. A wiper (G, 6 1, 611, 6111f 611") according to claim 10, wherein the spring element (22, 221, 2211) is constructed integrally on the web (9, 91, 911,.9"', -9"") 12. A brake lining for a friction brake of a vehicle 15 wherein a wiper (6, 61, 611, 6"', 6"") according to any one of claims 1 to 11 is fitted to the brake lining. 13. A brake lining according to claim 12, wherein the wiper (6, 61, 611, 6"', 6"") is fitted in a groove (5). 20 14. A brake lining according to claim 13, wherein the wiper (6, 61, 611, 6"', 6"") abuts the groove (5) on all sides thereof. 25 1S. A brake lining according to any one of claims 12 to 14, wherein the wiper (6, 61, 611, 6"', 6"") projects beyond the brake lining on the side facing an element (2) to he braked. 30 16. A brake lining according to any one of claims 12 to 15, wherein the blades (11) of the wiper (6, 6F, 611, 61", 6"") are arranged at an angle with respect to theelement (2) to be braked and preferably project towards the element (2) to be braked whereby at least one open 35 chamber is formed.

17. A brake lining according to any one of claims 12 to 16, wherein at least one wiper (6, 61, 611, 6111, 6f"v) is fitted to the side of the brake lining on which a water front (3) strikes the brake lining. 5 18. A brake lining according to any one of claims 12 to 17, wherein at least one wiper (6, 61 f 611, 6111, 61111) is aligned at an angle (a,) different to 00 with respect to the midline (H) of the friction element (1) 10 19. A brake lining according to any one of claims 12 to 18, wherein a spring element (22, 221, 2211) is provided between the wiper (6, 61, 611, 611f, 6"") and the groove (5). 15 20. A brake lining according to claim 19, wherein the spring element (22, 221, 2211) is constructed integrally on the web (9, 91, 911, 9"', 911", 21).

21. A brake lining or a wiper substantially according to any one of the embodiments thereof described with reference to Figures 1 to 10 of the accompanying drawings.