GB2544755A - Braking element - Google Patents

Abstract

The insert 4 has a body (fig.7,6) and a braking part (fig.7,8) with braking surface (fig.1,18) extending from a recess (fig.4,12) in a holder 2 to form a braking element 1, the braking surface spaced apart from a first face (fig.1,10) of the holder and the recess has walls (fig.4,20) to restrict insert movement, the braking element may be used in a braking system clamp (fig.9,88) which is arranged to retard movement along a rail (fig.9,84). Preferably the imperforate tungsten carbide insert 4 is retained in the rectangular recess using adhesive and/or by a deformed portion (fig.1,46) of the holder extending over a thinner insert edge (fig.6,30). The insert may comprise straight triangular cross section ridges 36 forming ridge peaks 40 separated by valleys 52 forming angles 50 between 70º-90º by a distance of between 1.2-2.5mm. Preferably the rectangular insert 4 is 20-30mm long by 8-16mm wide, with five to six ridges 36 and four to five valleys 52 10-20mm in length and peaks 40 with a radius of curvature of 0.10-0.16mm; the body (fig.7,6) may be 3-7mm deep. A method of making a braking element is also claimed.

Description

Braking Element

The present invention relates to a braking element, particularly to braking element comprising a holder and an insert and more particularly to a braking element for use in the emergency braking system of a lift. The invention extends to an insert for such a braking element, to a braking system including such a braking element and to a method of making such an element.

In many countries there is a legal obligation to provide a safety device in lifts to brake downward movement of the lift carriage in the event of rapid downward movement or acceleration. Many countries have proposed similar legislation to brake upward movement of the lift carriage in the event of rapid upward movement or acceleration.

Known devices for this purpose may be secured to the lift carriage. A braking system may be provided with a clamp having a braking element for gripping a brake rail external to the carriage and relative to which the carriage is expected to move. A governor is also provided, which may be responsive to the downward acceleration or speed of the lift carriage. If the acceleration or speed exceeds a predetermined value the governor actuates the braking system to cause the clamp to grip, for example, the brake rail. This can cause the lift carriage to decelerate, and come to a halt.

Known clamps for this purpose may include at least one braking element which is moved by the clamp to engage with the rail and thereby retard relative movement. It is known, for example from GB 2314070, to provide a clamping device which is self-actuating once the clamps have made contact with a rail.

The braking element of such known systems may comprise a holder which carries an insert which is secured to the holder by a removable fixing such as a screw or bolt.

According to the invention there is provided a braking element for a lift emergency braking system, the braking element comprising a holder and an insert, the insert having a body and a braking part extending from the body, the holder having a first face which includes a recess extending from an opening into the holder along a first axis, the body of the insert being arranged within the recess such that the insert extends out of the recess through the opening such that a braking surface of the braking part is spaced apart from the first face of the holder, the recess being defined by walls shaped to substantially restrict movement of the insert relative to the holder perpendicular to the first axis.

Providing the holder with a recess with walls shaped to substantially restrict, or possibly substantially prevent, movement of the insert arranged therein relative to the holder perpendicular to the first axis means that retaining the insert in the holder is greatly simplified. Previously the insert may have been fastened to the holder using a removable fixing, for example a screw, bolt or retaining pin. The holder itself may have prevented movement of the insert in a direction parallel with the anticipated braking force, but a transverse force on the insert, for example created by an uneven braking action, or otherwise, could generate a transverse force which would have to be resisted by the retaining means, the removable fixing alone. For example if the insert was retained between upper and lower shoulders in a holder by a bolt, a transverse force parallel with the shoulders could shear the bolt and thereby allow the insert to move along the shoulder and potentially fall from the holder rendering the brake element ineffective, or at least substantially less effective.

The present arrangement uses the walls of the recess to substantially restrict movement of the insert in all directions except in the direction towards the opening of the recess through which the insert extends. During a braking action the holder is moved by a part of the braking system, for example a clamp, to force the braking surface of the insert onto a rail, for example a brake rail, and so movement of the insert in this direction during a braking action is restricted by the action of the braking system. The insert is essentially sandwiched between the rail and a floor of the recess by the braking force. Since it is only during such a braking action that it might be anticipated that significant forces would be applied to the insert it is advantageous to have such forces resisted by the holder itself rather than, for example a removable fixing or an adhesive.

By shaping the holder in this way it has been found that simple retaining means can be employed to retain the insert as the fixing means alone will never be required to resist a significant force. In this way the insert may be retained in the recess using no removable fixing such as a screw or bolt. The fixing employed may be reversible, for example to allow for replacement of inserts, but may not be considered removable, for example an adhesive can be dissolved or broken and a deformation of a part of the holder can be reversed.

The first face of the holder may be substantially planar and the first axis may be substantially perpendicular to the plane of the first face. Such an arrangement provides a simple holder design which can be readily fabricated.

The body of the insert may be substantially surrounded by the walls of the recess. Although the recess could be defined by broken walls which restrict movement, but do not substantially surround the insert it may be that such an arrangement is more complex to manufacture. Substantially surrounding the insert with the walls of the recess allows substantially continuous walls to be used which may provide a stronger holder. For example the holder may be formed from a metal such as steel and a recess could readily be machined, for example milled, into a first face as desired.

The insert may be retained within the recess by any suitable means. In some embodiment the insert is retained by an adhesive or by deforming a portion of the holder over an edge portion of the insert, or by a combination of the two. In a typical arrangement for a braking element in use a force may be applied to the holder to force the braking surface of the insert onto a guide rail. This force may extend substantially along the first axis and may be substantially parallel thereto. This means that, in use, the insert may be forced into the recess and its movement relative to the holder caused by the forces resulting from that use be restricted by the braking action and the walls of the recess. In such an arrangement the insert does not need to be retained in the recess by a particularly robust means as the retaining force may need only to prevent the insert falling out of the recess prior to use.

The depth of the recess from a floor to the opening and the depth of the body of the insert may be selected such that the body and recess are generally substantially the same depth, except in parts where the body may be deliberately reduced in depth to allow the insert to be readily retained by deformation of the holder. The shape of the insert and the shape of the recess may substantially match and the size may be the same to within less than about 1 mm, or less than about 0.5 mm, or even less, to ensure that the movement of the insert within the recess is substantially restricted. In some embodiments the insert is a location fit within the insert. In other embodiments the body may be deeper than the recess or shallower than the recess.

The edge portion of the insert over which a portion of the holder may be deformed may be less deep along the first axis than a central portion of the body. This means that the depth of the recess can be minimised as the edge portions can be arranged below the first face, between the floor of the recess and the opening, enabling the holder to be easily deformed to lie over the edge portion and thereby retain the insert. The rear of the insert may be substantially planar and may substantially match the floor of the recess. Matching non-planar shapes could be used for these surfaces, but planar provides for easier manufacturing.

The insert may be substantially imperforate. Since a removable fixing such as a screw or bolt is not needed to retain the insert in the recess the insert need not include any holes. This simplifies the manufacturing of the insert and also allows an increased braking surface area for a particular insert size. The strength of the insert may also be increased by omitting holes.

The braking surface may be substantially planar, but may alternatively be shaped, textured, or otherwise non-planer to enhance the braking efficiency of the braking element. The braking surface may comprise at least one ridge. The, or each ridge, may be substantially linear and may extend substantially parallel to a ridge axis. There may be a plurality of ridges spaced apart by valleys. The ridges may include peaks which extend furthest from the body and the peaks may all be substantially linear and lie in substantially the same plane.

These ridges provide some advantages over a planar braking surface. Braking may be achieved by a combination of a “ploughing” friction and “sliding” friction. The, or each, ridge on the braking surface may extend parallel with a ridge axis which is, in use, arranged to be substantially parallel with the relative movement between the braking element and the brake rail to be gripped. In such an arrangement the ridges can act as teeth, or “negative rake cutters”.

It has been found that when braking on a new section of brake rail with such an insert, the “Average Braking Force” (ABF) is generated approximately 50% due to sliding friction and 50% due to ploughing friction. The proportion of sliding friction to ploughing friction is a function of contact angle of the leading edge of the ridges with the brake rail.

When braking repeatedly over section of brake rail the ridges plough grooves into the rail and the proportion of sliding friction to ploughing friction changes as the depth of groove increases. The groove depth increases until the ABF is entirely due to sliding friction. The geometry of the insert design, such as the number of ridges, their spacing and their shape, can be selected such that that the ABF remains substantially constant throughout this transition.

It has been found that the groove depth when the ABF is entirely due to sliding friction will occur when the contact pressure between the sides of the ridges substantially equals the yield stress of the braking material. Any further increase in groove depth thereafter may be entirely due to normal abrasive wear between the insert and brake rail, which is extremely slow.

For a braking element for use in a lift (also known as an elevator) emergency braking system a preferred geometry has been developed for use with typical brake rails. This geometry will be described below

The braking surface of the insert may include a plurality of substantially linear, substantially parallel ridges, each having a peak. The peak-to-peak offset may be between about 1.2 mm and 2.5 mm. The average angle between the walls of adjacent ridges may be between about 70 and 90°. This can be viewed as the angle from the peak to valley to peak angle. The peaks may have a radius of curvature of between 0.10 and 0.16 mm. Each may have a substantially triangular cross section comprising a rounded top, substantially flat sides and a lower part which curves into the valley floor.

The insert and recess may be substantially rectangular in shape and may be between about 20 mm to 30 mm long along the ridge axis and between about 8 mm and 16 mm wide perpendicular to the ridge axis.

The insert may comprise between three and ten ridges, more particularly six ridges and five valleys, or five ridges and four valleys, and each ridge may extend substantially continuously for a length of between about 10 mm and 20 mm. The body may be between about 3 mm and 7 mm deep.

For the substantially triangular ridge geometry discussed above the number (N) of ridges, the length of those ridges in mm (L) and the peak-to-peak width in mm (w) can be linked by the equation: N x L = Insert force / (w x yield stress) where Insert Load is the force applied to the insert against the brake rail and the yield stress is the yield stress of the material of the brake rail.

For example, for a maximum width between ridges of 1 mm, an insert load of 16000 Newtons on a brake rail with a yield stress of 250 N/mm2, the factor N x L is 64. Thus an insert with 16 ridges, each with a length of 4 mm is suitable for such insert loads (the factor of NxLof 64).

It should be noted that the depth of each ridge from the valley floor to the peak is also important. The depth should be sufficient to penetrate any surface contamination, for example dirt or oil, on the brake rail. The depth should be at least 0.05 mm, perhaps at least 0.07 mm. This is a further advantage of non-planar, and particularly ridged, braking surfaces.

The ridge height may be between about 0.5 mm and 1.5 mm and possibly between about 0.6 mm and 1.2 mm. The ridges may comprise all of the depth of the braking part, or just a portion of it.

The insert may be fabricated from tungsten carbide, for example a sintered tungsten carbide, or from any other suitable material. The material of the insert may be harder than the material from which the rail is made. The rail may be made from a metal, for example steel.

The invention also provides a braking system comprising a clamp and a rail, the rail extending along a rail axis and the clamp including a braking element coupled thereto, the braking element being as described above and the clamp arranged to force the braking element onto the rail such that movement of the clamp relative to the rail along the rail axis is retarded.

The clamping force which forces the braking element onto the rail may be substantially perpendicular to the rail axis.

As noted above, the braking surface of the insert may comprise at least one substantially linear ridge which extends parallel to a ridge axis and the braking system may be arranged such that the ridge axis and the rail axis are substantially parallel. Such an arrangement enhances the ploughing action noted previously.

The invention also provides an insert for use in the braking element described above.

The invention further provides a method for making a braking element, the braking element being as described above, the method comprising the steps of: a) providing a holder, the holder having a first face which includes a recess extending from an opening into the holder along a first axis; b) providing an insert, the insert having a body and a braking part extending from the body; c) inserting the body of the insert into the recess through the opening such that the insert extends out of the recess through the opening such that a braking surface of the braking part is spaced apart from the first face of the holder; d) retaining the insert in the recess.

The step of retaining the insert in the recess may comprise the step of applying an adhesive to the insert and/or the recess prior to the step of inserting the body of the insert.

The step of retaining the insert in the recess may additionally, or alternatively, comprise the step of deforming a portion of the holder such that deformed portion of the holder extends over an edge portion of the insert.

The invention will now be described by way of example only with reference to the following figures in which:

Figure 1 shows a cross section view from the side of a braking element comprising a holder and an insert;

Figure 2 shows a view from the front of a braking element comprising a holder and an insert;

Figure 3 shows a view from the front of a holder;

Figure 4 shows a view from the side of a holder;

Figure 5 shows a view from the front of an insert;

Figure 6 shows a view from the side of an insert;

Figure 7 shows a view from an end of an insert;

Figure 8 shows a magnified view of the braking surface of an insert;

Figure 9 shows a braking system comprising a clamp and a brake rail; and Figure 10 shows a view from the front of a different braking element comprising a holder and an insert.

Figure 1 shows a cross section view from the side of a braking element 1 for a lift emergency braking system 80 (shown in Figure 9). The braking element 1 comprises a holder 2 and an insert 4. The holder 2 will be described with reference mainly to Figures 3 and 4 and the insert will be described with reference mainly to Figures 5, 6 and 7. The insert 4 has a body 6 and a braking part 8 extending from the body 6. The holder 2 has a first face 10 which includes a recess 12 extending from an opening 14 into the holder 2 along a first axis 16 (shown in Figure 4). The body 6 of the insert 4 is arranged within the recess 12 such that the insert 4 extends out of the recess 12 through the opening 14 such that a braking surface 18 of the braking part 8 is spaced apart from the first face 10 of the holder 2. The recess 12 is defined by walls 20 shaped to substantially restrict movement of the insert 4 relative to the holder 2 perpendicular to the first axis 16.

Mounting holes 22 are provided through the holder 2 substantially perpendicular to the first axis 16 to allow the holder 2 to be coupled to a braking system 80.

Portions 46 of the holder 2 have been deformed over end portions 30 of the insert body 6 to retain the insert in the recess 12. In this case the insert 4 is fitted into the recess 12 and portions 46 of the wall 20 of the recess 12 are deformed, for example with a hammer, to overlie the end portions of the insert 4. To facilitate such an arrangement the end portions 30 of the insert may sit within the recess 12, between the opening 14 in the first face 10 and the floor 28 of the recess 12.

Figures 3 and 4 show front and side views of a holder 2 respectively. The holder 2 has a substantially planar first face 10 which is substantially rectangular in shape. The recess 12 is arranged substantially centrally within the first face 10. The recess 12 is substantially rectangular in shape. The walls 20 of the long sides 24 of the rectangular recess 12 are substantially straight, while the short sides 26 are curved into a substantially constant arc. It should be understood that the short sides 26 could include a substantially straight portion of wall 20 if required (such an embodiment is shown in Figure 10). The rounded corners of these recesses and inserts help to avoid stress concentrations and thereby reduce the risk of any failure during use.

The recess 12 extends from the opening 14 to a floor 28. The floor 28 is substantially planar and is substantially parallel to the first face 10. The walls 20 generally extend from the opening 14 to the floor 28 substantially parallel to the first axis 16.

Figures 5, 6 and 7 show front, side and end views of an insert 4 respectively. The body 6 of the insert 4 is substantially rectangular and is shaped to substantially correspond with the shape of the recess 12 into which it is to be fitted such that the walls substantially surround the insert. The body 6 includes tapered end portions 30 which extend from a base surface 32 of the body less than a central portion 34 of the body 6 extends from the base surface 32.

The braking part 8 comprises a plurality of, in this case six, substantially linear ridges 36 which extend substantially parallel with a ridge axis 38 extend from the body 6 to peaks 40 which form the braking surface 18.

The insert 4, when viewed from the front, is substantially symmetrical top to bottom (perpendicular to the ridge axis) and side to side (along the ridge axis). So that it can be installed either way round in recess 12 of the holder 2.

The ridges 36 are substantially triangular in cross section (as shown best in Figure 8). The ridges occupy a substantially central portion 42 of the insert and do not extend entirely to either end of the insert 4 in a direction along the ridge axis 38, rather the height of the ridges 36 tapers to the body 6 at ridge end portions 44.

Figure 8 shows an enlarged view of a portion of the braking part 8 of Figure 7. The braking part 8 comprises a plurality of ridges 36 which are separated by valleys 52. The ridges 36 are substantially triangular in cross section perpendicular to the ridge axis 38. The peaks 40 of the ridges 36 are rounded and the valley floors 48 are similarly rounded. The radius of curvature of the peaks 40 in this example is about 0.13 mm and the radius of curvature of the valley floors 48 is about 0.25 mm. The angle 50 between adjacent walls of the ridges 36 which define the valleys 46 is about 78°. The distance between adjacent peaks 40 is about 1.33 mm, but in a different embodiment could be 2 mm. The peak-to-peak spacing will depend on the width of the insert and the number of ridges required.

Figure 9 shows a braking system 80 comprising a clamp 82 and a rail 84. The rail 84 extends along a rail axis 86 which extends perpendicular to this view. The clamp 82 includes a braking element 1 coupled thereto. In this case the clamp 82 comrprises two braking elements 1 arranged on opposing sides of the rail 84 and coupled to the clamp by arms 88. The clamp 82 is arranged to force the braking elements 1 onto the rail 84 such that movement of the clamp 82 relative to the rail 84 along the rail axis 86 is retarded. Such clamping mechanisms are known in the art and will not be described in detail, here. The retardation, as noted above, can be by sliding friction alone, or by a combination of ploughing and sliding friction between the braking surface 18 of the insert and the rail 84.

Figure 10 shows a view from the front of a different braking element 101 comprising a holder 102 and an insert 104. The parts all function in the same way as described above, but there are only five ridges 36 on the insert 104 and the short sides 26 of the recess 12 include a straight portion 27 as mentioned above.

Although a specific example is described herein, it should be understood that modifications in detail can be made within the scope of the claims.

Claims (29)

Claims

1. A braking element for a lift emergency braking system, the braking element comprising a holder and an insert, the insert having a body and a braking part extending from the body, the holder having a first face which includes a recess extending from an opening into the holder along a first axis, the body of the insert being arranged within the recess such that the insert extends out of the recess through the opening such that a braking surface of the braking part is spaced apart from the first face of the holder, the recess being defined by walls shaped to substantially restrict movement of the insert relative to the holder perpendicular to the first axis.

2. A braking element as claimed in claim 1, in which the first face is substantially planar and the first axis is substantially perpendicular to the plane of the first face.

3. A braking element as claimed in claim 1 or claim 2, in which the body of the insert is substantially surrounded by the walls of the recess.

4. A braking element as claimed in any preceding claim, in which the insert is retained within the recess by an adhesive.

5. A braking element as claimed in any preceding claim, in which the insert is retained within the recess by a deformed portion of the holder which extends over an edge portion of the insert.

6. A braking element as claimed in claim 5, in which the edge portion of the insert over which a portion of the holder is deformed is less deep along the first axis than a central portion of the body.

7. A braking element as claimed in any preceding claim, in which the insert is substantially imperforate.

8 A braking element as claimed in any preceding claim in which the braking surface comprises at least one ridge.

9. A braking element as claimed in claim 8, in which the, or each, ridge is substantially linear and extends substantially parallel to a ridge axis.

10. A braking element as claimed in claim 9, in which there are a plurality of ridges spaced apart by valleys.

11. A braking element as claimed in claim 10, in which the ridges include peaks which extend furthest from the body and in which the peaks all lie in substantially the same plane.

12. A braking element as claimed in claim 10 or claim 11, in which the peak-to-peak offset is between 1.2 mm and 2.5 mm.

13. A braking element as claimed in any of claims 10 to 12, in which the angle from peak to valley to peak is between 70 and 90°.

14. A braking element as claimed in any of claims 10 to 13, in which the peaks have a radius of curvature of between 0.10 and 0.16 mm.

15. A braking element as claimed in any of claims 10 to 14, in which the insert and recess are substantially rectangular in shape and are between 20 to 30 mm long along the ridge axis by between 8 and 16 mm wide.

16. A braking element as claimed in claim 15, in which the insert comprises six ridges and five valleys, or five ridges and four valleys, and in which each ridge extends for a length of between 10 and 20 mm.

17. A braking element as claimed in claim 16, in which the body is between 3 and 7 mm deep.

18. A braking element as claimed in any of claims 9 to 17, in which the, or each ridge has a substantially triangular cross section substantially perpendicular to the ridge axis.

19. A braking element as claimed in any preceding claim, in which the insert is fabricated from tungsten carbide.

20. A braking system comprising a clamp and a rail, the rail extending along a rail axis and the clamp including a braking element coupled thereto, the braking element being as claimed in any preceding claim and the clamp arranged to force the braking element onto the rail such that movement of the clamp relative to the rail along the rail axis is retarded.

21. A braking system as claimed in claim 20, in which the braking surface of the insert comprises at least one substantially linear ridge which extends parallel to a ridge axis, the braking system being arranged such that the ridge axis and the rail axis are substantially parallel.

22. An insert for use in a braking element, the braking element being as claimed in any of claims 1 to 19.

23. A method for making a braking element, the braking element being as claimed in any of claims 1 to 18, the method comprising the steps of: a) providing a holder, the holder having a first face which includes a recess extending from an opening into the holder along a first axis; b) providing an insert, the insert having a body and a braking part extending from the body; c) inserting the body of the insert into the recess through the opening such that the insert extends out of the recess through the opening such that a braking surface of the braking part is spaced apart from the first face of the holder; d) retaining the insert in the recess.

24. A method as claimed in claim 23, in which the step of retaining the insert in the recess comprises the step of applying an adhesive to the insert and/or the recess prior to the step of inserting the body of the insert.

25. A method as claimed in claim 23 or claim 24, in which the step of retaining the insert in the recess comprises the step of deforming a portion of the holder such that deformed portion of the holder extends over an edge portion of the insert.

26. A braking element substantially as herein described with reference to, or as shown in, the drawings.

27. An insert substantially as herein described with reference to, or as shown in, the drawings.

28. A braking system substantially as herein described with reference to, or as shown in, the drawings.

29. A method for making a braking element substantially as herein described with reference to the drawings.