GB2108223A

GB2108223A - Friction brake

Info

Publication number: GB2108223A
Application number: GB08229088A
Authority: GB
Inventors: Sven Erik Ostberg
Original assignee: Kockums Industri AB
Current assignee: Kockums Industri AB
Priority date: 1981-10-22
Filing date: 1982-10-12
Publication date: 1983-05-11
Also published as: SE8106236L; DE3239025A1

Abstract

A friction brake comprises adjacent to as least one side of a movable brake element (11) a pivoted brake element (18) the brake surface (18b) of which can be pressed against the brake element by an operating arm (14). A latching mechanism (17, 19) alters the relative positions of the brake element and operating arm step by step as the brake surface is worn away, thus extending the life of the brake element. The arrangement is particularly suited for industrial brakes. <IMAGE>

Description

SPECIFICATION Friction brake The invention relates to a friction brake which is suited especially, but not exclusively, to use as an industrial brake, i.e. a brake for installation in stationary plants. Recently the reliability requirements for such braking arrangements have been the subject of particular attention, particularly with regard to industrial safety aspects (reliable emergency stop tripping etc).

The invention relates to a friction brake which comprises both a movable element which is to be braked and which has a brake surface, and at least one brake element interacting with the movable element and provided with a brake lining, with, on the brake lining, a brake surface which faces the brake surface on the movable element. The said movable element may consist directly of the component to be braked, for example a linearly movable sledge or similar in a machine, a railway wagon wheel etc, or of a special brake component rigidly connected to the part that is to be braked, e.g. a brake disc mounted on a shaft in such a way that it cannot rotate.The brake surface of the movable element can either, like the brake surface of the brake element, be in the form of the surface of a separate brake lining (for example in conventional disc brakes), or it may be in the form of some other surface, for example, in the case of a waggon wheel, the rolling surface ofthe wheel rim. As is known, friction brakes can be of either passive or active design. 'Passive' brakes means brakes in which the friction surfaces are normally free, and at the instant of braking are made to engage by an operating force which can be turned on and off. In active brakes the friction surfaces are constantly forced to engage with each other by a constantly acting application force, and when no braking is to be provided, the friction surfaces are kept apart by an inhibiting force capable of overcoming the application force.

In all friction brakes there is inevitably a steady wear of the friction or braking surfaces, which are arranged on special replaceable brake linings.

Known brake designs often permit only one arrangement with the brake elements in certain positions (at the 3 o'clock and 9 o'clock positions) and vibration and internal friction effects often give rise to uneven wear of the brake linings, which have to be replaced even more often than would otherwise be the case.

Each change of brake linings requires dismantling of the brake arrangement and therefore results in a stoppage of the entire installation in question.

The purpose of the present invention is to achieve a brake design which results in a very much longer life of the friction linings of the brake element, which is not effected by the mounting position and which is suitable for use on both passive and active brake constructions and to brake both rotary and linear motion.

The invention is characterised by the special features set out in the attached claims, and will now be explained in greater detail with the aid of the attached schematic drawings which relate to exam ples of embodiment, where Figures 1 and 2 show in plan view a passive disc brake according to the invention in the off and on positions, Figures 3 and 4 show an active disc brake according to the invention in the off and on positions, Figures 5-7 show a brake element from the brakes in the previous drawings at three different stages of wear, Figures 8 and 9 show, on a smaller scale, two alternative versions of the brake element, and Figures 10 and 11 show for comparison a brake according to the invention and conventional friction brake for braking a linear motion.In all the drawings, corresponding parts are designated with similar references.

According to Figures 1-4 a brake disc 11 is mounted so that it cannot rotate on a shaft 10 capable of rotating in the directions indicated by the arrow PZ, both side faces 11 c of the brake disc 11 being covered by friction or brake linings 11'. Brake disc 11 has a central part 1 1b through which shaft 10 passes and a periphery 11 a. A carrier arm 23 and a bearing journal element 15 are arranged in the region between the central part 11 band the periphery 11 a, and at a fixed distance a from side faces 1 1c. The carrier arm 23 is fixed to a carrier bar 21 rigidly mounted on the installation. A brake element 18 fitted with a friction and brake lining 18', and an operating arm 14, are supported on each bearing journal element 15 in such a way that they are free to rotate (also with respect to each other).

Brake element 18 is mechanically coupled to operating arm 14 by means of a pawl mechanism with step-by-step action which, in the example shown, comprises a gear 19 with sloping teeth 19' which is also arranged in such a way that it can rotate on bearing journal element 15 and is connected to brake element 18 in such a way that it cannot rotate, and two pawls 16, 17. The first pawl is slightly spring- loaded and is rigidly mounted on carrier bar 21. The other pawl 17 is spring-loaded and is mounted in such a way that it can rotate on operating arm 14 at a distance from bearing journal element 15 (one pawl 17 on each operating arm 14).

A traverse metal band or similar 12 with bent-up ends 1 2a is rigidly connected to the rigidly mounted carrier bar 21.

The arrangement shown in Figures 1-4 are symmetrical relative to brake disc 11 and its extension, and only one side will be described below.

Gear 19 with sloping teeth 19', the first pawl 16 and the second pawl 17, together form a pawl mechanism with step-by-step action, in which the second pawl 17 drives gear 19 in the direction of arrow A when the operating arm 14 is turned around bearing journal element 15 in the same directon, whilst, when operating arm 14 moves in the opposite direction, the first pawl 16 prevents gear 19 from resuming its former relative position with respect to operating arm 14, if its angular deflection ss' (Figure 2) minus p (Figure 1) has resulted in a greater rotary motion of the gear than the amount corresponding to one tooth interval (the operation of the brake will be described later in greater detail).

The arrangement of the parts that will be described in the following is different in the passive brake according to Figures 1 and 2, compression springs 22 are attached to the bent-up ends 12a, and inflatable elastic containers 13, for example of rubber, are fixed to carrier bar 21. The free ends 14a of the operating arms 14 are each inserted between a spring 22 and a container 13. Since operating arms 14 are free to rotate on bearing journal elements 15, the action of the springs 22 is transferred to the containers 13, and the containers are compressed.

The containers 13 may be glued at 13a.

Each container 13 is connected via a line 20a to a control valve 20 which can be operated by an operating lever 20c, and to which fluid under pressure is fed via a suppy line 20b from a source not shown, such as a compressed air compressor, or similar Brake element 18 has a special cylindrical form which is best illustrated by a cross-section according to Figure 5, in which a brake element is shown as it looks at the beginning of its period of use. A relatively thick brake lining 18', for example of fibre-reinforced friction material, is arranged around a body 18k with a central opening 15' for bearing journal. The periphery of the brake lining 18' is delimited by three different surfaces.Facing towards brake disc 11 there are two flat surfaces 18a and 18b which meet at an edge 18d and form there an angle a which is slightly greater than 1 80" so that the brake lining is equally suitable for right-handed or lefthanded installation. A cylindrical periphery 18c runs externally between the outer ends of these flat surfaces. On fitting to the brake, the opening 15' will be situated at a distance a (Figures 1, 5) from the facing side face 11' of the brake disc. However, the edge 18d is soon worn away, so that there is no contact at all with brake disc 11 when the brake is free.

In the interest of clarity, certain components such as carrier arms 23 and valve 20 are omitted in the drawings described below, Figures 2-4.

For braking - see Figure 2 - valve operating lever 20c (Figure 1) is operated so that containers 13 are inflated, which causes operating arms 14 to overcome the force of springs 22 and rotate on bearing journals 15 in the direction of the arrows A. The friction surfaces 18b of brake elements 18 come into contact with friction linings 11' of the brake disc, giving rise to braking. After a time, friction surfaces 18b begin to wear or are ground away, meaning that an ever-increasing angular deflection ss' is needed to bring the surface 1 8b into contact with the friction lining on brake disc 11. Containers 13 automatically achieve the maximum possible angular deflection every time.However, as soon as the angular deflection P'-B between the starting position and the braking position reaches an amount corresponding to a tooth interval on gear 19, the first pawl 16 moves to the next tooth, and on the return motion of operating arm 14, gear 19 is turned by the corresponding amount relative to the operating arm. The operating arms 14 run essentially parallel to each other, so that both containers 13 and springs 22 can be mounted on a common fixing device comprising metal band 12 and carrier bar 21.

Since gear 19 is rigidly connected to brake element 18, the brake element also rotates by the same amount relative to operating arm 14. According to Figure 6, friction surface 1 8b successively assumes different new positions 18', and edge 18d is transformed into a rounded surface 18d'. Figure 6 shows brake element 18 in an approximately halfconsumed condition, and the friction surface has reached position 18b". Figure 7 shows brake element 18 in the fully-consumed condition, when the friction surface has reached position 18"', and peripheral surface 18c has been reduced to a corner 18c'. It should be noted that the flat surface 18a is unaffected throughout the entire process.

The arrangement for an active brake according to Figures 3 and 4 differs from the arrangement according to Figures 1 and 2 in that the positions of containers 13 and brakes 22 are reversed. Containers 13 are fixed to the raised ends 12a, and springs 22 are attached at carrier bar 21. When containers 13 are not activated, compression springs 22 force operating arms 14 constantly to the braking position (Figure 4). To release the brake, containers 13 are activated via valve 20 (Figure 1) so that that the effect of springs 22 is overcome. Containers 13 may be riveted at 13b.

The present invention is not restricted to brakes with flat braking surfaces. Figure 8 shows a brake element 118 according to the invention, with a brake surface 118e which is matched to, i.e. curved with the same radius as, the inward-facing brake surface 111cofabrakedrum 111.

The surface 11 8a has a similar shape, and the condition that surfaces 118a and 118c must form an angle greater than 1800 means in this case, and in the case according to Figure 9, that their chords K1 and K2 must do so.

Figure 9 shows in an analogous manner a brake element 218, the surfaces 218c and 21 8a of which are matched to the outward-facing brake surface 211 c on a wheel rim 211.

Thefactthatsurfaces 118a and2l8a have the same shape as brake surfaces 1 18c and 218c results in the previously mentioned advantage that each brake element can, as required, be left-hand or right-hand mounted relative to the moving element without the need to invert the entire arrangement.

In the interest of clarity, Figures 8 and 9 do not show the other parts of the arrangement and Figure 9 does not show the chords K1 and K2.

The present invention is not restricted to braking of a rotary motion. Figure 10 shows schematically the use of a brake according to the invention to brake a movable element 311 which has a long flat brake surface 31 1c and which moves linearly in the directions of double arrow P2. Brake element 18 has a mean radius rand operating arm 14 is operated by a pull wire 13', a certain force fbeing needed to achieve a given braking effect.

In Figure, 11, which does not relate directly to the present invention, the same brake function is shown performed by means of a conventional brake block 1 with a brake lining 1 c. The block is mounted on an arm 2 pivoted at 3. Owing to the special shape of the brake lining of the arrangement shown in Figure 10 relative to the bearing journal element 15, the braking force Fis smaller than the force F' needed in the arrangement according to Figure 10 to achieve the same braking effect.

A number of modifications are possible within the framework of the invention. Springs 22 can be replaced by other constantly acting force elements and containers 13 can be replaced by other pressure medium controlled elements such as bellows, cylinder-piston assemblies etc or indeed by other force elements acting from time to time as required, including a pull wire or an electromagnet. Surfaces 18a and 18c, which are not directly involved in the work of braking, can have a shape other than that shown. Other known matching mechanisms with step-by-step action may be used. Operating arms 14 may extend in any direction at will, for example if there is no space in the direction of the extension of brake disc 11, but the arrangement shown with, essentially parallel operating arms, has the advantage of a simple design as regards the positioning of force elements of the two operating arms. It is also evident that the arrangement according to the invention may include only one brake element with associated parts, as shown in Figure 10, or several brake elements with associated parts on one side or on either side of the brake disc, for example in Figures 1-4, two additional brake elements with associated parts arranged symmetrically relative to shaft 10.

Operating arms 14 may have a crooked shape with two limbs, one limb interacting with the force elements and the other, for example at right-angles to the first, carrying pawl 17.

Claims

1. Afriction brake comprising both a movable element, which is to be braked and which has at least one brake surface, and at least one brake shoe means which has a brake lining to interact with the said brake surface, and for each brake shoe means an elongate operating arm means which has a first and a second end and pivots on a stationary bearing journal means arranged in a stationary manner opposite to and a fixed distance from the said brake surface, with two power means acting in opposite directions applying force to the operating arm means at its first end to apply and release the brake, wherein the operating arm means pivots at its second end on the said bearing journal means, the brake shoe means is mounted in such a way that it is free to rotate on the same bearing journal means as the operating arm means, and there is arranged between the operating arm means and the brake shoe means a latching mechanism with step-by-step action which from time to time rigidly connects the operating arm means with the brake shoe means and by which the rotary motion of the operating arm means around the said bearing journal means is transmitted as a rotary motion of equal magnitude to the brake shoe means, the relative positions of the operating arm means and brake shoe means being unchanged, whereby, when the said rotary motion exceeds a predetermined magnitude as a consequence of wear of the brake lining, the latching mechanism automatically brings about a change of the said relative position by one step in the direction that gives better contact between the brake lining and the brake surface.

2. A friction brake according to Claim 1, wherein the said latching mechanism includes a ratchet which can rotate on the said bearing journal means and is rigidly connected to the brake shoe means, to a first stationary and slightly spring-loaded pawl and a second spring-loaded pawl which pivots on the operating arm means at a distance from the bearing journal means.

3. A friction brake according to Claim 1 or 2, wherein the brake shoe means is surrounded by friction material.

4. A friction brake according to any one of Claims 1 to 3, wherein the brake shoe means has, on the one hand, two boundary surfaces at an angle of more than 180 to each other, one of which is the working surface of the brake lining, and on the other hand a cylindrical external peripheral surface running between the outer ends of the said boundary surfaces.

5. Afriction brake according to any one of Claims 1 to 4, wherein on either side of the movable element there is arranged a said brake surface and a said interacting brake shoe means with associated components.

6. A friction brake according to any one of Claims 1 to 5, wherein a first one of said power means is a constantly acting spring.

7. A friction brake according to any one of Claims 1 to 6, wherein a second one of said power means is a control device powered by fluid under pressure and operating from time to time.

8. A friction brake according to any one of Claims 1 to 7, wherein it includes a common fixing means on which all power means are arranged alongside each other.

9. Afriction brake according to any one of Claims 1 to 8, wherein the movable element is a conventionally rotatable brake element.

10. Afriction brake according to Claim 9, wherein the movable element is a brake disk, brake drum or wheel rim.

11. A friction brake according to any one of Claims 1 to 8, wherein the movable element is in the form of an element that can be moved linearly.

12. Afriction brake constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in, the accompanying drawings.

13. An article including a brake according to any one of Claims 1 to 12.