MXPA99006182A - Improved disk brake assembly - Google Patents

Abstract

An annular disk brake assembly (10) having a housing (12) mounted to a vehicle and a rotor disk (32) mounted to a wheel (W) of the vehicle. Annular brake pads (20 and 52) extend parallel to the rotor disk (32) within the housing and are mounted thereto with at least one brake pad (20, 52) being movable axially by means of an oil applied bladder (56) mounted to the housing (12) and moving the first brake pad (52) axially against the disk brake. The rotor disk (32) is adapted to slide axially to engage the second brake pad (20) when pressure is applied to the rotor disk (32) by means of the first brake pad (52) and the bladder (56).

Description

IMPROVED DISC BRAKE ASSEMBLY TECHNICAL FIELD The present invention relates to disc brakes and more particularly to improvements of large contact area disc brakes for vehicles.

BACKGROUND ART The disc brake of the present invention is a disc brake of the type described in U.S. Patent 5,330,034 issued July 19, 1994 and US RE 35055 published October 10, 1995, which relate to to full annular disc brakes for larger vehicles such as trucks. The concept of the complete annular disc brake is now proposed for automobiles and light trucks and the present invention relates to a structure of a complete annular disc brake for such vehicles. There are obvious advantages to having a complete annular disposition of friction pads that make contact with an annular disc on both sides of the disc. The distribution of braking or thermal energy is directly related to the thermal resistance associated with both sides of the interface where the heat is generated. In a complete annular brake there is a large area to distribute the braking energy more efficiently. It has also been found that the vibrations between the internal and external pads are the main causes for the squealing of the brake. The analysis of the vibration response is of considerable importance in the design of brakes that may be subject to dynamic disturbances. Under certain situations, vibrations can cause large displacements and severe stresses in the brake. The speed of a vibratory system in general, proportional to its frequency and therefore a viscous damping force increases with the frequency of the vibration. The forces that resist a movement also arise from dry friction along a non-lubricated surface. It is usually assumed that it is a force of constant magnitude but opposite to the direction of movement. In addition to the forces of air resistance and external friction, damping forces also arise due to imperfect elasticity or internal friction, called violent damping, with the body. The magnitude of such force is independent of the frequency although it is proportional to the amplitude of the vibration or to the displacement. In a brake system, the dynamic load produces stresses and stresses, the magnitude and distribution of which will depend not only on the usual parameters previously found but also on the speed of propagation of the voltage waves through the material of which it is composed the system. This last consideration, although it is very important when loads are applied at high speeds, can often be disregarded when the speed of load application is slow. Since the dynamic load is considered to be the transfer of energy from one system to another, the concept of configuration (voltage energy) is an index of resistance to failure that is important. One of the important concepts is that the member's energy absorption capacity, that is, the resistance to failure, is the function of the volume of material available, in contrast to the resistance to failure under static load, which is a function of cross section area or section module. One of the main problems in adapting the technology of a complete annular brake system of the type described in the aforementioned patents is the consideration of weight and cost. It would not be realistic, no matter what the advantages, to assume that a new complete annular brake system would be accepted in the market at a price substantially higher than that of current disc brakes. In addition, any increase in weight compromises fuel consumption.

Description of the Invention It is an object of the invention to provide a brake system, especially for automobiles, which has improved heat distribution properties, and reduces the occurrence of wear. It is a further purpose of the present invention to provide a brake system that reduces the low frequency brake grinding. It is a further purpose of the present invention to provide an annular disc brake system where maximum brake performance is obtained. A construction in accordance with the present invention comprises a disk brake assembly for a vehicle wheel wherein the wheel includes a hub rotatably supported on an axle in the vehicle, the disk brake assembly comprises a housing mounted to the vehicle and at least one annular rotor disk inside the housing and means mounting the disk to the wheel. The rotor disk has at least one first radial flat friction surface and the housing includes a first annular brake shoe provided adjacent the first flat friction surface of the disk and moving axially towards and away from the first surface of the disk. friction. Means are provided to prevent the first brake shoe from rotating with the disc. The housing also includes an annular radial wall parallel to the first brake shoe, and an expansible bag of annular fluid extends between the first annular brake shoe and the radial wall, so that upon expansion of the bag the first Brake shoe moves axially to frictionally engage the friction surface of the disk, means for decoupling the first brake shoe from frictional contact with the rotor disk to the release of fluid from the expandable bag.

In a more specific embodiment of the present invention the radial disk is provided with a second annular friction surface, parallel to the first and on an opposite side of the rotor disk wherein the first and second friction discs have different radii, and one second annular brake shoe adjacent to the second annular friction disk where the squeal of the brake will be reduced.

In an even more specific embodiment of the present invention, the means for retaining the first brake shoe includes a brake shoe backing plate having an annular periphery and the housing includes a concentric wall having an internal surface radially adjacent to the brake shoe. periphery of the first brake shoe insofar as the internal surface of the concentric wall and the periphery of the first brake shoe have interdigital elements engageable that allow the axial movement of the first brake shoe relative to the concentric wall while avoiding the peripheral movement of the first brake shoe relative to the concentric wall of the housing. In an even more specific embodiment of the present invention, the means for uncoupling the first brake shoe from the first friction surface of the rotor disc is at least a rotary seal provided between adjacent axially generated surfaces of the annular radial wall of the housing and the first brake shoe. The features of the present invention can also be used for large trucks.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in detail with reference to the accompanying drawings in which: Fig. 1 is an exploded fragmentary perspective view of a disc brake embodiment according to the present invention; Fig. 2 is a fragmentary radial cross section taken through the assembled disk brake; Fig. 3 is a radial cross section similar to Fig. 2 although it includes additional elements; Fig. 4a and 4b are elongated fragmentary cross sections taken along the same section as Fig. 3 but showing the elements in a different operative position; Fig. 5 is a fragmentary radial cross section similar to FIG. 3 but showing another modality; Fig. 6 is a fragmentary perspective view partly in cross section, of another embodiment of the present invention; Figs. 7a and 7b are elongated fragmentary radial cross sections of the embodiment of Fig. 6 showing certain elements in different operative positions; Fig. 8 is a fragmentary perspective view, partly in cross section, of the embodiment shown in Figs. 6 and 7; Fig. 9 is an exploded fragmentary perspective view of yet another embodiment of the present invention; and Fig. 10 is a fragmentary elongated radial cross-section of the embodiment shown in Fig. 9.

Mode for Carrying Out the Invention Referring to the drawings, and more particularly to the Figs. 1 to 4, there is illustrated a disc brake assembly 10 for a car, having a housing in the form of a shell 12. The housing has a cylindrical wall with a corrugated inner surface 16 having cavities 16a and ribs 16b. The housing 12 includes a radial annular wall 18 providing an annular pad pad pad liner 20. The ribs 16b are relatively flat and represent cavities in the outer surface 17 as well as the ribs 17a corresponding to cavities 16a. The cylindrical wall 14 also includes a radial flange 15. The housing 12 also includes an annular radial wall 22 to which is mounted a cylindrical corrugated flange adapted to fit within the corrugated inner surface 16 of the wall 14 and is retained therein. by the flange 15. The ribs 24a of the corrugated flange 24 fit into the cavities 16a of the surface 16 while the cavities 24b correspond to the ribs 16b of the housing wall 14. Therefore, the housing 12 will be locked against the circumferential movements relative to the radial wall 22. The radial wall 22 has a hub portion 26 that can be bolted to a flange on an axis (not shown) of the vehicle. The radial wall 22 also includes an annular radial flat wall portion 28 and a cylindrical flange 30 as shown in Fig. 2. A meshed retainer 70 is provided in the receiving wall 14 in order to lock the housing 12 against the axial movement relative to the radial wall 22. The retainer 70 protrudes inwardly to engage the edge of the flange 24. An annular rotor disc 32 includes flat friction surfaces 34 and 36 and an indircular annular flange 38 having a surface internal corrugated concentric 40 with ribs 40a and cavities 40b. A hub adapter 42 includes a radial wall portion 44 adapted to be mounted to a vehicle wheel (not shown in the embodiment of Fig. 8) and an indian corrugated cylindrical wall 46. The wall 46 has ribs 46a and cavities 46b which are adapted to fit within the inner surface 40 of the inner flange 40 of the flange 38 of the rotor disc 32. Thus, the rotor disk 32 will be locked against rotational movement relative to the hub adapter 42 which is axially slidable in the same. Since the adapter 42 is mounted on a vehicle wheel the rotor disk 32 will rotate with the wheel. The rotor disc is ventilated and therefore has radially extending ventilation passages 48 communicating with the openings 49 in the housing wall 14. As shown in Figs. 1, 2 and 3, there is the axial opening 48a which intersects the radial openings 48 to ensure that as much air as possible passes through the rotor disk 32.

A brake shoe 50 includes brake linings 52 and a back plate. The brake shoe 50 includes a corrugated peripheral edge 51 which engages the inner surface 16 of the cylindrical wall 14. Thus, the brake shoe can slide axially although it is retained against rotary movement relative to the housing 12. An annular bag 56 is provided between the wall 28 and the back wall 54. When the fluid such as oil is fed into the bag 56 it will expand, moving the brake shoe 50 axially towards the friction surface 36 of the rotor disk 32. The rotor disc 32 will also slide axially in the hub 42, in response to the force exerted by the bag 56, and the radial friction surface 34 will come into frictional contact with the brake linings 20. Therefore, when it is necessary to apply the brakes, the bag 56 expands. However, to release the brakes the oil is allowed to drain from the bag 56, thereby releasing the axial force in the brake shoe 50, allowing the disk rotor 32 to freely rotate within the housing 12. Referring now to Figs. 3, 4a and 4b, the bearing seals 62, 64 will be described. A pair of bearing seals 62 are located in the present embodiment, on the outer surface of the corrugated wall 46 of the hub adapter 42 and are formed to the contour of the corrugated surface. The pairs of circumferentially extending grooves 46c, 46d are defined in a wall 46 for receiving the bearing seals 62a and 62b respectively. As shown in fig. 3, the pair of bearing seals 62a and 62b are pre-compressed when they are inserted between the hub 42 and the flange 38 of the rotor disc 32. The retainer ring 63 may be provided to hold the seal 62a in place. The seal 62b is retained by the groove 65 formed in the wall 46. The retainer ring 63 is formed with the convexly curved surface 63b to hold the seal 62a and control the deformation of the seal 62a as will be described. Likewise, the groove 65 is also formed with the convexly curved surface 65b for controlling the deformation of the seal 62b. When the rotor disk 32 slides in the hub adapter 42, as previously described, the bearing seals 62a and 62b will deform in the direction of the path of the rotor disk 32, as illustrated by the arrow in the Fig. 4b, when the force is exerted by the bellows 56 on the brake shoe 50. When the brakes are released, the bearing seals 62a, 62b will be restored due to the energy stored therein, and will return to the shape as shown. in Fig. 4a, thereby moving the rotor disk 32 and thereby removing the friction surface 34 away from the brake pad 20. The bearing seals 62a and 62b can be selected to provide the correct amount of clearance to prevent entrainment that may occur when the rotor disc 32 remains in contact with the friction pad 20. It is important that only a slight clearance can be provided in order to avoid undue pedal movement. In the same way, the bearing seal 64 which is located in the circumferential groove 30a in the flange 30 which engages the flange of the support plate 54 in the brake shoe, and which will act to return the brake shoe 50 away from the friction surface 36 of the rotor disk 32 when the fluid is drained from the bellows, in order to eliminate dragging of the brakes. The sliding contact 66 in the housing 14 seals the brake shoe against debris and dust. Referring now to Fig. 5 shows a modification to the brakes of the present invention. The elements that in fig. 5 are similar to those in Figs. 1 to 4 have been changed to hundreds. More specifically, the housing 1 12 is a shell having a cylindrical wall 1 14 which now includes a smooth indic cylindrical portion 155 adjacent to the corrugated portion 1 16. Likewise, the radial wall 122 has a smooth cylindrical wall portion 160 adjacent the corrugated peripheral wall 124. Thus, when the radial wall 122 is received within the shell or housing 1 12 the smooth wall portion 160 of the radial wall 122 will fit in the smooth cylindrical wall portion 155 of the housing 1 12. A shoulder 155a is formed between the corrugated wall portion 1 14 and the smooth wall portion 155 which acts as a stop for the radial wall 122 having complementary peripheral surfaces, which is between the corrugated portion 124 and the smooth portion 160. This will eliminate the need for the indentations 70 as shown in the embodiment of Figs. 1 to 4. The cross section of Fig. 5 is taken through the radial wall 122 exactly in the position where the shift openings 170 and 172 are for the bag 156. Referring again to FIG. 1, the wall 28 is adapted to receive the tension sensor 60. Those strain sensors 60 may be of the type known under the trademark MULTI DYN in U.S. Patent Application No. 5,522,270 issued June 4, 1996 to THOMSON-CSF. The tension sensor 60 can provide valuable information on the braking efficiencies and wear of the brake shoes. The tension sensor 60 extends in some tangential manner to the wall 28 and can, therefore, monitor the torsion that is applied between the hub 26 and the cylindrical flange 30 of the crosshead 22. With the information that can be obtained from the voltage sensor 60, the temperature of the brakes that can be monitored by means of suitable microprocessors. For example, when the brakes are applied, the pressure is known, and if the heat should increase, the torsion will be reduced. The increased temperature of the brakes will normally indicate the deterioration or malfunction of the brake. Other criteria can also be determined logically from the known pressure, and the torque information provided by the voltage sensor 60.

A further embodiment of the present invention is described in Figs. 6 to 8. The reference numbers in these figures designate elements corresponding to similar elements corresponding to similar elements in the embodiment of Figs. 1 to 4, have been changed to 200. The disc brake 210 is shown mounted to the hub H of a wheel W (Fig. 8). Therefore, the hub adapter 242 is mounted to the hub H by means of bolts. The hub adapter 242 includes a corrugated wall 246 (Figs 6, 7a and 7b) including ribs 246a and cavities 246b that engage the corrugated inner surface 240 of the flange 238 which is an integral part of the rotor disk 232. Fig. 6 illustrates the different elements of this embodiment although without the rotor disk 232. The rotor disk 232 is illustrated in Figs. 7a, 7b and 8. As previously described, the rotor disk 232 is constrained against circumferential rotation relative to the hub adapter 242 although the rotor disk 232 can slide axially relative to the hub adapter 242. The flange 238 is entangled along each edge thereof to receive the bearing seal housings 263 and 265 respectively. Each bearing seal housing 263 and 265 is made of thin-wall embossing and is formed as an annular channel having a lateral width that is greater than the diameter of the bearing seals 262a or 262b respectively. The channel area is represented by numeral 263b and 265b in Figs. 7a and 7b. The roughness portion of the channel forms a ramp that is inclined downwards from left to right in Figs. 7a and 7b. Therefore, when the rotor disk 232 is slid from right to left to engage the brake shoe represented by the brake pad 220, the flange 238 and the bearing seal housings 263 and 265 will move to the left from the position shown in Fig. 7a to the position shown in Fig. 7b. Observing the position of the bearing seals 262a and 262b, in Fig. 7b, it could be recognized that the bearing seals are somehow twisted by the ramps of the channels 263 and 265. Thus, the bearing seals have stored energy which can overcome the forces applied to the rotor disks 232 by the bag 256 when the fluid is released from the bag 256, as will be described. Therefore, the bearing seals 262a and 262b will draw the disk rotor away from the brake pad 220 to a position shown in FIG. 7a. The bearing seals 262a and 262b will slide on the surface 246 in order to compensate for wear on the brake pad 220. The bearing seals 262a and 262b also serve as a suspension for damping vibrations between the rotor disk 232 and the rotor. mallet adapter 242. In the present embodiment, the housing shell 212 represented by the indium cylinder wall 214 and the radial wall 218 is a thin-wall embossing. A skirt 218a is formed at the inner edge of the wall 218 to allow the brake pad 220 including a support wall 221 to be adjusted in position within the housing as shown in Figs. 7a and 7b. The shell 212 can be assembled from the left end side of Figs. 7a and 7b, with portion 255 extending over and concentric with the cylindrical wall portion 224 of the radial wall 222. A cover 283 that can be hinged in two parts encircles the elongated neck portion formed by the extension 255 and has a radial skirt at each edge thereof to form a channel for locking the wall 224 of the wall radial 222 inside the housing 212. FIG. 6 shows how the two-part lid 283 with short extensions 283a and 283b overlap each other. A coupling member 284 extends over the joint thus formed by the ends of the hinged cover 283. The coupling member 284 includes openings 286 through which the pins 288 can pass. Those pins are formed and pass in an area coincident with the cavities in the lid 283. The bag 256 is shown here with the U-shaped membrane 256a having leg portions that are inserted into the slots 276 and 278 within the radial wall 222. Reinforcement rings 280 and 282 are also placed in these grooves to prevent membrane 256a from expanding radially. The brake shoe 250 including the brake pad 252 and the support plate 254, has a T-shaped configuration with the leg of the T 251 that folds back from the membrane 256a to form an M, as shown in Figs. 7a and 7b. Therefore, when fluid such as oil is injected through inlet 272 as shown in FIG. 7a, the bag 256 will expand in the axial direction as shown in FIG. 7b. An additional flange 230 (corresponding to the flange 30 in FIGS. 1 to 4) is also inserted into the slot 278 although it extends axially from the radial wall 222 to support a bearing seal 264. The support plate 254 is provided with a channel-shaped slot 257 having the same construction as the one described with respect to channels 263 and 265 therein. Therefore, when the bag 256 expands, the brake shoe 250 moves to the left in the drawings of Figs. 7a and 7b, applying an axial force against the rotor disk 232 by means of the brake pad 252, which frictionally engages the friction surface 236, and further presses against the rotor disk 232 so that the friction surface 234 the brake pad 220 is engaged. Once the oil is released from the bag 256, the bearing seal 264 has been compressed in some manner as shown in Fig. 7b, which overcomes the reduced axial force, retracting from that the brake shoe 250 from the friction surface 236 of the rotor disk 232. Simultaneously, the bearing seals 262a and 262b will retract the rotor disk 232 from the frictional engagement with the brake pad 220. A sliding contact 268 is shown mounted to support plate 254 to prevent debris from entering the bearing seal area 264. Similar sliding contacts (see sliding contact 66 in FIG. 3) can be provided in other practical locations such as between the support plate 254 and the cylindrical housing wall 214. A further embodiment is shown in Figs. 9 and 10. Reference numbers corresponding to elements corresponding to elements shown in the embodiment of Figs. 1 to 4 have been changed to 300. The rotor disk 332 has friction surfaces 234 and 236 at different radial distances from the axis of rotation of the rotor disk. As seen in Fig. 10 more clearly, the opposing friction surfaces 334 and 336 are alternating. The corresponding brake pads 320 and 352 are also constructed to correspond to the radially altered friction surfaces 334 and 336. The accommodating wall 314 is formed accordingly in order to accommodate this difference in radius. It has been found that the amplitude and difference in amplitude of the vibration of the pads such as the pads 20 and 52 in the embodiment of Figs. 1 to 4 where the main factors that contribute to the generation of brake squeal. It has been found that the grinding of the brake is the result of the self-induced vibration phenomenon of the different parts. Under certain situations, vibrations can cause large displacements and severe stresses in the brake. The speed of a vibratory system is, in general, proportional to its frequency and improves a viscous stamping force that increases with the frequency of vibration.

It has been found that by having the brake pads 320 and 352 as the corresponding annular friction surfaces 334 and 336 on the rotor disc 332 at different radii, those vibrations are at different frequencies and therefore reduce the opportunities for harmonic currents that help reduce the brake squeal and the stresses that can occur in the disc brake.

Claims (9)

1. A disc brake assembly for a vehicle wheel wherein the wheel includes a hub rotatably supported to an axle on the vehicle, the disk brake assembly comprising a housing mounted to the vehicle and at least one annular rotor disk within of the housing and means mounting the disk to the wheel, the disk having at least one first radial flat friction surface and the housing including a first annular brake shoe provided adjacent the first friction surface of the disk and the shoe brake which is movable axially towards and away from the first friction surface, means provided for restricting the rotation of the first shoe with the disk, the housing including an annular radial wall parallel to the first brake shoe, and a first bag of expandable fluid between the first annular brake shoe and the radial wall, so that to the expansion of the ball the first brake shoe moves axially until Frictionally coupling the first friction surface of the disc, and means for coupling the first brake shoe from the frictional contact with the first frictional surface of the rotor disc to the release of the fluid from the bag.

2. A disc brake assembly as defined in claim 1, wherein the means for restraining the first brake shoe from rotation with the rotor disc comprise providing the housing with a centric wall having a inner surface radially adjacent to the periphery of the first brake shoe, providing the inner surface of the concentric wall and the periphery of the first brake shoe with engageable interdigital elements that allow axial movement of the first brake shoe relative to the concentric wall surface, although avoids the circumferential movement of the first brake shoe relative to the concentric wall of the housing.

3. A disc brake assembly as defined in claim 2, wherein the interdigital elements include a plurality of ribs that extend axially and are circumferentially spaced on the inner surface of the concentric wall that engages with the corresponding cavities in the periphery of the first brake shoe.

4. A disc brake assembly as defined in claim 2, wherein the housing further includes an annular radial skirt that hangs from the concentric wall located on the opposite side of the rotor disk from the first brake shoe, and A second brake shoe is provided on the annular skirt that confronts a second friction surface on the rotor disc.

5. A disc brake assembly as defined in claim 2, wherein the means for decoupling the first friction surface of the rotor disk are at least one bearing seal provided between an axially generated surface of the rotor shoe. brake and a cylindrical surface axially generated from the first radial wall of the housing extending parallel to and adjacent to the axially generated surface of the brake shoe so that the bearing seal can store energy when the force is applied to the brake shoe for frictionally coupling the frictional surface of the rotor disk by means of the expandable fluid bag and whereby the stored energy is sufficient to retract the brake shoe from the first friction surface of the rotor disk when the fluid is released from the rotor. expandable bag.

6. A disc brake assembly as defined in claim 4, wherein the means mounting the rotor disk to the wheel comprises a hub adapter adapted to be mounted for rotation with the wheel, the hub adapter. which includes a cylindrical external surface, the rotor disc that includes a central opening defined by an internal cylindrical surface, and interdigital elements are provided on the external surface of the hub adapter and the internal cylindrical surface of the rotor disc, whereby said interdigital elements couple to allow the rotor disk to slide axially into the hub adapter but without restricting the disk of rotor against the rotating circumferential movement relative to the hub adapter, and at least one bearing seal is located between the outer cylindrical surface of the hub adapter and the inner indic surface of the rotor disc and positioned so that when the Broken disc r is moved axially against the second brake shoe under the axial force that is applied by the fluid inside the expandable bag, the bearing seal is deformed to conserve energy so that when the fluid is released from the bag expandable, the energy retained in the bearing seal will be effective to decouple the second friction surface Ion of the rotor disc from the second brake shoe. A disc brake assembly as defined in claim 6, wherein there are two bearing seals spaced axially between the inner cylindrical surface of the rotor disk and the outer cylindrical surface of the hub adapter. A disc brake assembly as defined in claim 7, wherein the bearing seals are provided in channels formed in the outer cylindrical surface of the hub adapter. 9. A disc brake assembly as defined in claim 5, wherein the first radial wall of the housing includes an indian cylindrical flange extending toward the rotor disk and the first brake shoe includes a support plate that it has a cylindrical portion and a bearing seal is mounted in a groove on the flange and engages the cylindrical wall portion of the support plate. 1. A disc brake assembly as defined in claim 7, wherein the rotor disc includes a flange defining the internal cylindrical surface and an axially spaced pair of slots are provided in the flange and the flange channels. bearing seal are provided in the groove in the flange to receive the bearing seals, wherein each channel includes a portion of roughness having a sloping surface that decreases in depth from one side of the channel to the other and the axial extension which is greater that the axial extension of the bearing seal so that the bearing seal can be compressed as the rotor disk is moved towards the second brake pad, and the bearing seal engages the outer cylindrical surface of the hub adapter. A disc brake assembly as defined in claim 5, wherein the first brake shoe includes a bearing plate and the bearing plate defines a cylindrical surface opposite the radial cylindrical surface defined by the first radial wall, and a groove is defined in the cylindrical surface of the bearing plate to receive the bearing seal, the groove having a radial extension greater than that of the radial extension of the bearing seal, and a roughness portion of the groove has a inclined wall configuration to provide compression to the bearing seal when the brake shoe moves towards the rotor disk. A disc brake assembly as defined in claim 1, wherein the bag is a closed annular shell of elastic material and extends between the first radial wall of the housing and the first brake shoe. A disc brake assembly as defined in claim 1, wherein the bag includes an elongated annular membrane of resilient flexible material having parallel edges that are sealingly coupled to the first radial wall of the housing so that the bag it is formed between the membrane and the first radial wall. 14. A disc brake assembly as defined in claim 13, wherein the first brake shoe includes a support plate and the support plate has a cross section in the shape of a T with the leg of the T extending axially away from the rotor disc and engaging the membrane forming the bag, so that the cross section of the membrane has an M shape in the cross section. A disc brake assembly as defined in claim 13, wherein the first radial wall of the housing is provided with a pair of radially spaced circumferential grooves, and the ends of the membrane are received in respective grooves for sealed engagement with Wall. 16. A disc brake assembly as defined in claim 4, wherein the first and second annular friction surfaces on the rotor disc have alternating radii and the first and second annular brake shoes are located at different radii that correspond to the respective spokes of the first and second friction coupling surfaces. 1

7. A disc brake assembly for a vehicle wheel in which the wheel includes a hub rotatably supported on a vehicle axle, the disc brake assembly comprising a housing mounted to the vehicle and at least one annular rotor disk inside the housing and means mounting the rotor disk to the hub, the disk has at least one first annular flat friction surface on one side and near the periphery of the disk at a first half radius and a second plane radial annular friction surface on the other side of the disk, parallel to the first friction surface, although at a mean radius smaller than the first half radius, the housing including a first brake shoe adapted to engage the first friction surface and a second brake shoe adapted to engage the second friction surface, whereby the alternating friction surfaces and the brake shoes are effective to dampen the vibrations of l brake assembly. SUMMARY An annular disc brake assembly (10) having a housing (12) mounted to a vehicle and a rotor disk (32) mounted to a wheel (W) of the vehicle. Annular brake pads (20 and 52) extend parallel to the rotor disc (32) inside the housing and are mounted thereto with at least one brake tab (20, 52) that moves axially by means of a bag with oil (56) mounted on the housing (12) and moving the first brake pad (52) axially against the disc brake. The rotor disk (32) is adapted to slide axially to engage the second brake pad (20) when the pressure is applied to the rotor disk (32) by means of the first brake pad (52) and the bag (56).