Patent Publication Number: US-6705434-B1

Title: Multiple disc brake system

Description:
This application is a 371 of PCT/GB99/02415 filed Jul. 26, 1999. 
    
    
     This invention is concerned with a disc brake system, for example for a wheel of a vehicle. 
     A conventional disc brake system comprises a hub mounted on a suspension link for rotation relative thereto, the hub providing a mounting for a wheel, and a disc brake comprising a disc mounted for rotation as a unit with the hub, friction material pads arranged on opposite sides of the disc, and at least one piston and cylinder assembly operable to urge the pads into engagement with the disc, to brake the hub and hence the wheel. Conventionally, the piston and cylinder assembly is slidably mounted on a slide bolted to the suspension link of the vehicle. The disc is conventionally rigidly fixed to the hub, and wear of the pads and/or the disc is accommodated by the sliding movement of the cylinder. 
     Disc brake systems are known in which the disc rotates with the hub as a unit but can perform sliding movement on the hub. For example, see GB 1 396 503 and WO 98/25804. However, since the discs are relatively thin, they tend to tilt on the hub and affect the braking ability. Also, there is a tendency for noise to be produced by rattle of the disc against the hub. At higher disc temperatures, these problems can be particularly severe since, when there is a large temperature differential, such as 600° C., between the braking surface of the disc and the hub, the disc expands considerably, away from the hub, exacerbating the problems of tilting and rattle. These problems are addressed in WO 98/26192 in which the solution proposed is to provide a plurality of resilient force applicators which are mounted between the hub and the disc, the force applicators acting to apply radially-directed forces to the disc to control the movement thereof, the force applicators being distributed circumferentially around the hub. In the example given in WO 98/26192, the disc take system comprises two discs mounted on the same hub. One mounting means for the disc on the hub disclosed, in WO 98/26192 comprises groups of axially-extending grooves formed in the hub and teeth projecting from the discs into said grooves, the teeth being slidable along the grooves. The force applicators are in the form of leaf springs mounted on the hub in the spaces between the groups of grooves. This system requires that, at least between the groups of grooves, there is sufficient clearance between the hub and the discs to accommodate the leaf springs and flexing thereof. This clearance has the disadvantage that it increases the possibility that a disc may tilt relative to the hub, thereby adversely affecting the operation of the brake. 
     It is an object of the present invention to provide a disc brake system in which the afore-mentioned disadvantage is overcome or at least reduced. 
     The invention provides a disc brake system comprising a disc, and a hub which is arranged to rotate about an axis thereof, the system also comprising mounting means by which the disc is mounted on the hub so that the hub and the disc rotate as a unit about said axis and the disc can perform axial sliding movement on said hub, said mounting means comprising a plurality of axially-extending grooves formed in the hub and teeth projecting from the disc into said grooves, each tooth being a sliding fit in one of said grooves, the system also comprising resilient means acting to apply radial force between the disc and the hub, characterised in that said resilient means is provided by springs located in at least some of said grooves and engaging the teeth of the disc which project into those grooves to apply radial force to said teeth. 
     In a disc brake system according to the invention, the springs are accommodated in the grooves in the hub so that space for them does not have to be provided between the grooves enabling the clearance to be reduced substantially. This enables the possibility of the disc tilting on the hub to be reduced. 
     A disc brake system according to the invention may be as disclosed in WO 98/25804, except that the splined mounting means by which discs are mounted on a hub is replaced by mounting means as disclosed herein. The brake system of WO 98/25804 comprises one or more discs which are slidable on a hub under the control of leaf springs which act between the hub and the discs. The system also comprises a cylinder which is integrally formed with a suspension link and a caliper also fixed to the suspension link, the caliper having supports for friction material pads mounted thereon. 
     In a disc brake system according to the invention, the springs may be flat leaf springs as disclosed in WO 98/26192 or any other suitable type of spring. For example, the springs may be leaf springs each of which comprises at least three abutments which project transversely of the spring and engage the disc so that the abutments apply force to the disc. This arrangement has the advantage that the number of points of contact between the spring and the disc is increased thereby spreading the forces more evenly around the disc. The abutments may be provided by embossed portions of the spring. The abutments, preferably, are elongated so that each abutment remains in engagement with the disc throughout said movement of the disc on the hub. For example, said abutments may be in the form of ridges extending parallel to the axis about which the hub rotates. The leaf springs may be secured to the outer surface of the hub in a manner such that the springs extend tangentially on the hub when the disc is not mounted on the hub. Cut-outs, the holes, may be formed in the leaf springs to control the force applied by the abutments to the disc. Where the disc brake system comprises one or more further discs mounted on the hub, the leaf springs may be arranged in groups, the spring in each group being associated with each disc, at least one spring in each group being retained in position by a connection to another spring in said group. 
    
    
     There now follows a detailed description, to be read with reference to the accompanying drawings, of a disc brake system which is illustrative of the invention. 
     In the drawings: 
     FIG. 1 is an end view of the illustrative disc brake system; 
     FIG. 2 is a cross-sectional view, on a larger scale, taken on the broken line II—II in FIG. 1; 
     FIG. 3 is a perspective view, on a greatly enlarged scale, of a leaf spring of the illustrative disc brake system; and 
     FIG. 4 is a view similar to FIG. 3 but of an alternative leaf spring of the illustrative disc brake system. 
    
    
     The illustrative disc brake system  10  shown in FIGS. 1 and 2 is for a wheel (not shown) of a car. The system  10  comprises a disc  12 , a further disc  14  and a hub  15 , on which the wheel can be mounted. The hub  16  is arranged to rotate about a central axis  18  thereof. 
     The hub  16  comprises an internally splined hollow inner cylindrical portion  16   a  which is arranged to receive a drive shaft (not shown) which drives the wheel. The hub  16  also compriser an external flange  16   b  at the end of the portion  16   a . This flange  16   b  has four bolt holes  16   c  through which the wheel can be bolted to the flange  16   b  in a conventional manner. The flange  16   b  also serves to connect the portion  16   a  to an outer hollow cylindrical portion  16   d  of the hub  16 . 
     The discs  12  and  14  are identical to one another, being in the form of generally-annular cast iron or steel plates. The two discs  12  and  14  are mounted by means of mounting means of the system  10  on the cylindrical outer surface of the hub portion  16   d  so that the hub  16  and the two discs  12  and  14  rotate as a unit about the axis  18  and the discs  12  and  14  can perform axial sliding movement on said hub  16 . The mounting means comprises four grooves  20  which are formed in the outer cylindrical surface of the portion  16   d  of the hub  16  and four teeth  22  which project inwardly from each of the discs  12  and  14 . The teeth  22  enter the grooves  20  and are a sliding fit therein. However, the teeth  22  do not extend to the bottom surfaces  20   a  of the grooves  20 , there being a clearance between the bottom surfaces  20   a  and the inner surfaces  22   a  of the teeth  22 . The grooves  20  are equally-spaced circumferentially about the axis  18  and each occupies an arc of approximately 45° about the axis  18 . Between the grooves  20 , the outer surface of the hub portion  16   d  is machined to be accurately cylindrical about the axis  18 . The inner surface of each disc  12  and  14 , between the teeth  22 , is also machined to be accurately cylindrical about the axis  18  and a close fit over the cylindrical portions of the outer surface of the hub portion  16   d . The close fit of the discs  12  and  14  on the hub  16  reduces the possibility of the discs  12  and  14  tipping. 
     The system  10  also comprises four friction pads  26  (FIG. 2) for braking the discs  12  and  14  by engaging side surfaces of the discs. The friction material pads  26  are secured to three backing plates  28 , one backing plate  28   a  being between the discs  12  and  14  and the others being on opposite sides of the discs  12  and  14  to the plate  28   a . The median plate  28   a  has friction pads  26  secured to both of its faces. The brake pads  26  and the backing plates  28  are not shown in FIG.  1 . The brake pads  26  are brought into braking contact with the discs  12  and  14  by operating means (not shown) which may be similar to that described in WO 98/25804. When the brakes are applied, a movable outer friction material pad  26  is moved until the four pads  26  and the discs  12  and  14  are all in contact with one another, the discs  12  and  14  and the plate  28   a  sliding axially to accommodate this movement. 
     The system  10  also comprises resilient means acting to apply radial force between the discs,  12  and  14 , and the hub  16 . The resilient means comprises four leaf springs  32  mounted on the hub  16  and engaging the discs  12  and  14  so that the springs  32  apply radial force between each of the discs  12  and  14  and the hub  16 . The leaf springs  32  are equally distributed circumferentially around the hub  16 , each being mounted on one of the bottom surfaces  20   a  of the grooves  20 , ie the springs  32  are located in the grooves and act between the surface  20   a  and the inner surface  22   a  of the tooth  22  which enters the groove  20 . 
     One of the leaf springs  32  is shown in detail in FIG.  3 . Each spring  32  is formed from a generally rectangular piece of spring steel which is 0.25-0.3 mm thick. Each spring  32  is secured in the circumferential centre of one of the surfaces  20   a  by means of a central screw  36  which passes through a hole  32   a  in the spring  32  and enters the hub  16 . Each spring  32  extends axially on the hub  16  throughout the range of axial movement of both discs  12  and  14  so that both discs  12  and  14  are engaged by all four of the springs  32  continuously. The springs  32  act to control the sliding movement of the discs  12  and  14  on the hub  16  preventing tipping of the discs and compensating for thermal expansion effects. 
     Each spring  32  comprises four axially-extending abutments  40  which project transversely of the spring  32 . The abutments  40  are arranged with two of the abutments on each side of the hole  32   a . Two of the abutments  40  are formed at the extreme ends of the spring  32 , thereby preventing the edge of the spring  32  from engaging the tooth  22  and reducing the risk of cracking of the spring  32 . Between the two abutments  40  on each side of the hole  32   a , a rectangular hole  32   b  is cut out of the spring  32 . The hole  32   b  serves to control the force applied by the abutments  40  to the discs  12  and  14 . 
     The abutments  40  are provided by embossed portions of the spring  32  which are in the form of generally semi-circular (in transverse cross-section) ridges extending parallel to the axis  18 . The abutments  40  are elongated in the axial direction so that each abutment  40  remains in engagement with both or the discs  12  and  14  throughout the movement of the discs  12  and  14  on the hub  16 . 
     Each spring  32  is arranged to engage the discs  12  and  14  with its abutments  40  and apply force to the discs to control the movement thereof on the hub  16 . Each spring  32  is arranged so that the spring  32  extends generally tangentially of the hub  16  when the discs  12  and  14  are not mounted on the hub  16 . However, the springs  32  are deformed by the presence of the discs  12  and  14  so that each abutment  40  presses resiliently on the discs  12  and  14 . The springs  32 , thus, act to apply radially-directed forces to the discs  12  and  14 . 
     In the operation of the disc brake system  10 , the springs  32  as aforementioned control the sliding movement of the discs  12  and  14  on the hub  16 . Each spring  32  engages each disc at four points of contact, provided by the abutments  40 , thereby distributing the force applied by the spring  32  to each disc more uniformly. 
     FIG. 4 shows two leaf springs  42  which are joined together by a narrow tab  44 , the springs  42  and the tab  44  being formed from a single sheet of spring steel. The two leaf springs  42  each have a similar form to the spring  32  except that the holes  32   b  are omitted, each spring  42  having four abutments  46  which are similar to the abutments  40  of the spring  42 . However, the springs  42  are narrower than the spring  32  because each spring  42  is intended to engage only one of the discs  12  and  14 . The springs  42  are mounted on the surfaces  20   a  (as a unit connected by the tab  44 ) by means of a screw (not shown) which passes through a hole  42   a  formed in one of the springs  42 . Thus, each of the discs  12  and  14  has four of the leaf springs  42  associated therewith, the springs  42  being arranged in groups of two, one of which is mounted on the hub  16  and the other of which is retained in position by the connection, via the tab  44 , to the first-mentioned spring. As the tab  44  is narrow, the springs  42  act substantially independently. 
     In modifications of the springs  32  and  42 , the holes  32   a  and  42   a  may be omitted and the springs provided instead with self-retaining means for retaining them on the hub  16 . For example, such self-retaining means may comprise integral tabs extending from the spring over opposite ends of the hub  16  so that the springs can be clipped over the hub. In the case of the spring  32 , such tabs extend normally to the general plane of the spring from both the edges of the spring which are perpendicular to the projections  40 . In the case of the springs  42 , each of the end springs  42  in a group has one of the these tabs extending from its opposite edge to the position of the tab  44 . 
     In a further modification, the spring  32  and  42  can be formed into a non-planar form in order to determine the forces they will apply to the disc. For example, the springs can be formed into an arcuate shape such that, when the spring is mounted on the hub but before the discs are mounted on the hub, the ends of the spring are further from the hub than if the spring were planar.