Abstract:
A method to retain a minimum running clearance between the friction pads associated with a caliper of a brake and a rotor attached to a wheel of a vehicle. A bearing member associated with the wheel includes a plurality of rollers which axially move about a reference point to allow the rotor to correspondingly move and retract the friction pads of the caliper when the vehicle is subjected to centrifugal forces. This retraction of the friction pads by movement of the rotor creates a minimum running clearance between the rotor and friction pads on termination of the radial forces. A desired running clearance is reestablished during a brake application.

Description:
This invention relates to a wheel and bearing assembly whereby a minimum running clearance is retained between brake friction pads and a rotor in a brake system after a vehicle experiences centrifugal forces by utilizing a built-in end clearance in a bearing member. 
     BACKGROUND OF THE INVENTION 
     In vehicles it is a usual practice to position a wheel assembly on a bearing member located on an axle. The bearings member is designed to allow the wheel assembly to freely rotate on the axle while at the same time a rotor attached to the wheel assembly is positioned in a radial plane between friction pads of a caliper brake. A bearing member includes a plurality of rollers having a cylindrical shape or a tapered shape as disclosed in U.S. Pat. No. 5,882,123. The plurality of rollers are usually aligned in first and second rows between an outer race and an inner race. The plurality of rollers are positioned and retained in engagement with engagement surfaces on an outer race member and inner cones by trust surfaces. If the engagement with a trust surface creates too large of a retaining force on the rollers, the wheel will not rotate in a smooth manner as binding or drag occurs. Conversely, if a trust surface does not exert a sufficient retaining force on the rollers when a wheel rotates and is subjected to lateral forces it is possible to create a unstable or shimmy motion in a wheel assembly. Thus, it is desirable to position and retain the first and second rows of rollers in a bearing member in a fixed location symmetrical about a reference plane. 
     The bearings of as described above, which are currently in use for vehicles locate a wheel assembly on an axle and position a rotor with respect to friction pads of a caliper brake. In such vehicles, the rotor and friction pads of a caliper brake have a predetermined running clearance in order to prevent unwanted engagement that could produce additional resistance to rotation of the wheel. Unfortunately, vehicles do not always move in a linear and horizontal direction but are often subjected to centrifugal forces as when turning or negotiating curves. The centrifugal forces can often move a rotor attached to a wheel assembly into engagement with a corresponding friction pad in the caliper to essentially eliminate a running clearance between a friction pad and rotor. On termination of the centrifugal force and a return to linear and horizontal movement, should a vehicle now experience any vibratory force, the rotor and friction pad may momentarily engage each other in a manner whereby over a period of time the surface of the rotor is polished. It is possible for such polishing to distort the surfaces of a rotor to an extent that the coefficient of friction between the friction pads and rotor change and as a result surging may occur during a brake application. It should be noted that the polishing of a rotor as described above is limited to those instances when a vehicle travels for an extended period of time without an operator effecting a brake application as running clearances between the friction pads and rotor are automatically re-set through a brake application. 
     SUMMARY OF THE INVENTION 
     A primary object of the present invention is to provide a wheel and bearing assembly for a vehicle whereby a minimum running clearance is retained between a rotor secured to a wheel and friction pads carried by a caliper of a brake system after a vehicle encounters centrifugal forces prior to an operator effecting a brake application. 
     In more particular detail, in the present invention a bearing member is selected from a source which has a first plurality of rollers and a second plurality of rollers retained by first and second cones in a unitary outer race with preset built-in end play. The first and second cones are located on a hub of a wheel assembly with the first cone engaging a first shoulder on the hub. The hub is placed on an axle shaft of the vehicle with the second cone engaging a second shoulder on the axle shaft. The wheel assembly is secured to the axle by fasteners to hold the first and second cone members securely against the first and second shoulders. Thereafter, the unitary outer race of the bearing member is fixed to the vehicle and a rotor, which has a first peripheral face and a second peripheral face, is attached to the wheel assembly. A caliper brake is secured to the vehicle such that first and second friction disc carried by the caliper brake is aligned with the first and second peripheral faces on the rotor. The caliper brake, includes retraction structure such that a predetermined running clearance is set between the rotor and the first and second friction disc after each brake application. When the wheel assembly rotates during linear horizontal movement of the vehicle, the first plurality of rollers engage a first tapered or sloping raceway in the outer race and the second plurality of rollers engage a second tapered or sloping raceway in the outer race symmetrically with respect to a reference point such that the rotor is located in a radial plane with respect to the first and second friction disc with a desired running clearance. When the wheel assembly is subject to centrifugal forces the first and second plurality of rollers shift engagement along the first and second tapered or sloping raceways a distance corresponding to the built-in end play. This axial movement is magnified and as a result the rotor correspondingly moves friction disc to increase the running clearance a distance “y”. When the centrifugal forces terminate, the first and second plurality of rollers return to their symmetrical positions on the tapered or sloping surface on the outer race with continued horizontal linear movement of the vehicle. The first and second friction pads remain stationary and thus the movement created by the engagement with the rotor as a result the end play assures a minimum running clearance “y” is present until a brake application reestablished the desired running clearance “f”. 
     An advantage of this invention resides in the creation of a minimum running clearance “y” between a rotor and friction pads after a vehicle is subjected to centrifugal forces when a vehicle thereafter moves in a linear direction for an extended period of time prior to an operator instituting a brake application. 
     A further advantage of the brake system of this invention resides in the setting of a minimum running clearance through the selection of a bearing member having built-in end play. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a wheel and bearing assembly according to the present invention whereby a minimum running clearance is always maintained between a rotor and friction pad in a brake system; 
     FIG. 2 is an enlarged sectional view of the bearing member of FIG. 1 illustrating the relationship of the components therein with built-in end play; 
     FIG. 3 is an enlarged sectional view of the bearing member of FIG. 1 with the built-in end play magnified to illustrate the invention; 
     FIG. 4 is an enlarged sectional view of the bearing member of FIG. 1 illustrating the effect of outward centrifugal forces on the wheel assembly; 
     FIG. 4 a  is an enlarged sectional view which illustrates the resulting clearance between the rotor and friction pads as a result of the outward centrifugal forces acting on the wheel assembly as shown in FIG. 4; 
     FIG. 5 is an enlarged sectional view of the bearing member of FIG. 1 illustrating the effect of inward centrifugal forces on the wheel assembly; and 
     FIG. 5 a  is an enlarged sectional view which illustrates the resulting clearance between the rotor and friction pads as a result of the inward centrifugal forces acting on the wheel assembly as shown in FIG.  5 . 
    
    
     DETAILED DESCRIPTION 
     The wheel and bearing assembly  10  for a vehicle, shown in FIG. 1 is a schematic illustration of the present invention and includes a hub  12  retained on an axle  14 , a rotor  16 , a caliper brake  18  and a bearing member  20 . A wheel, not shown, which is attached to the hub  12  rotates when the vehicle is moving and correspondingly the rotor  16  rotates with respect to first  22  and second  24  friction pads carried by the caliper brake  18 . The caliper brake  18  is activated by hydraulic fluid being supplied to caliper brake  18  in response to an operator desiring to effect a brake application. The hydraulic fluid supplied to the caliper brake  18  moves the first  22  and second  24  friction pads into engagement with the rotor  16  to effect a brake application. When the communication of hydraulic pressure terminates, the first  22  and second  24  friction pads retract away from the rotor  16  to create a desired running clearance “x” between the face  23  on friction pad  22  and face  25  on friction pad  24  and corresponding faces  17  and  19  on rotor  16 . This clearance “x” is important as inadvertent engagement between the friction pads  22  and  24  and rotor  16  can cause polishing of faces  17  and  19  which can eventually effect the resulting coefficient of friction between these components and the smooth operation of the brake system. 
     While the running clearance “x” is automatically set after each brake application, the running clearance x can be reduced or eliminated prior to the resetting as when the components react in a different manner as a result of centrifugal force acting on the vehicle and wheel assembly. 
     In more particular detail, the present invention provides a method to attenuate the engagement of friction pads  22 ,  24  carried by caliper  18  of a brake system for a vehicle in between brake applications. The structure for achieving this method is primarily achieved through the structure of the bearing member  20 . 
     The bearing assembly  20  is best illustrated in FIGS. 1,  2  and  3  and includes a unitary outer race  50  and an inner race  52  composed of first  54  and second  56  cones. The outer race  50  and inner race  52  retain a first plurality rollers  58 , 58 ′, . . .  58   n  in a first row and second plurality rollers  60 ,  60 ′ . . .  60   n  in a second row. The first and second rows are retained or aligned between the outer race  50  and the first  54  and second  56  cones by holders or cages  61 , 61 ′. The outer race  50  has a cylindrical outer surface  62  with a plurality of projections  63  and an inner surface  64  having first  66  and second  68  tapered or sloping raceways which extend from ledge surfaces  70  and  72  adjacent ends  69  and  71 . As illustrated the first  66  and second  68  tapered or sloping raceways are symmetrically positioned with respect to a reference point  74  along the inner surface  64 . 
     Each roller in the plurality of rollers  58 , 58 ′, . . .  58   n  and  60 , 60 ′, . . . 60   n  is identical and only a single roller  58  will be described in detail. Roller  58  essentially has cylindrical shape however a peripheral apex  76  of about 0.0005 mm is located between a first end  57  and a second end  59 . The plurality of rollers are located in the cage or holder  61  to provide uniform spacing around the axle of a vehicle. 
     The first cone  54  has a first outer face  53  separated from a first inner face  55  by an outer peripheral surface  80  and an inner surface  82 . The inner surface  82  which includes a tapered or sloping raceway  84  located between a ledge or thrust surface  86  and a guide surface  88 . The tapered or sloping raceway  84  is designed to be parallel or complementary with the tapered or sloping raceway  66  in the unitary outer race  50 . Similarly, the second cone member  56  has a second outer face  97  separated from a second inner face  99  by an outer peripheral surface  90  and an inner surface  92 . The inner surface  92  which includes a tapered or sloping raceway  94  located between a ledge or thrust surface  96  and a guide surface  98 . Seals  40 , 42  are respectively located between ledges  70 , 86  and  72 , 96  to complete the bearing member  20 . 
     The end play for the first and second plurality of rollers  58 , 58 ′, . . .  58   n  and  60 , 60 ′, . . .  60   n  is determined by placing holder or cage  61  for the first plurality of rollers  58 , 58 ′, . . .  58   n  in sloping raceway  84  of cone  54  and inserted the cone  54  into the inner surface  64  of the outer race  50  until the apex  76  on the plurality of  58 , 58 ′, . . .  58   n  makes point contact with sloping raceway  66 . Thereafter, cage  61 ′ for the second plurality of rollers  60 , 60 ′, . . .  60   n  is placed in raceway  94  cone  56  and the cone  56  is inserted into the inner surface  64  of the outer race  50  until the apex  76 ′ on the plurality of  60 , 60 ′, . . .  60   n  makes point contact with sloping raceway  68 . The point contact between the apex  76  of the first plurality of rollers  58 , 58 ′, . . .  58   n  with the first sloping raceway  66  and the point of contact between apex  76 ′ of the second plurality of rollers  60 , 60 ′, . . .  60   n  with the second sloping raceway  68  defines a first linear distance “L- 1 ” while a distance between the first outer face  53  on the first cone  54  and the second outer face  97  on the second cone  56  defines a second linear distance “L- 2 ”. The second linear distance “L- 2 ” is selected such that on engagement of the inner face  55  of the first cone  54  and inner face  99  of the second cone  56  an operational end play is created between the point of contact of apex  76 , 76 ′ of the first and second plurality of rollers  58 , 58 ′, . . .  58   n ;  60 , 60 ′, . . .  60   n . Test have indicated that a set built-in end play for bearing member  20  which is equal to the first linear distance L- 1  plus a linear dimension of between 0.015 mm and 0.070 mm will be acceptable for the present invention. 
     Method of Assembly 
     The wheel and bearing assembly  10  is assembled through the following steps. A bearing member  20  having a build-in desired end play for first and second plurality of rollers  58 , 58 ′, . . .  58   n ;  60 , 60 ′, . . .  60   n  is selected from a source. The bearing member  20  is located on a hub  16  with an outer face  53  of a first cone  54  engaging a first annular shoulder  116 . Thereafter, the hub  16  is placed on an axle shaft  14  of the vehicle and outer face  97  of a second cone  56  is brought into engagement with a second shoulder  114 . A nut  214  is threaded onto axle shaft  14  to compress the first and second cones  54 , 56  against shoulders  114 , 116  and correspondingly connects hub  16  to the axle shaft  14 . The nut  214  is locked onto axle shaft  14  by a key  216  to assure that the proper retention force is maintained between the axle shaft  14  and hub  16 . Thereafter, a plurality of bolts  65  pass through corresponding openings in projections  63  of the unitary outer race  50  of the bearing member  20  and engage a stationary member  21  to fix the bearing member  10  to the vehicle. Next, a rotor  16 , having a first annular peripheral face  17  and a second annular peripheral face  19  is attached to hub  16  by wheel bolts  616 , only one is shown. Finally, a caliper brake  18  is secured to a stationary frame of the vehicle to correspondingly align and establish predetermined equal running clearances x and x′ between the first  22  and second  24  friction disc and the first  17  and second  19  peripheral faces on rotor  16 . 
     Mode of Operation 
     When the wheel and bearing assembly  10  of the present invention is located on a vehicle with a wheel attached to hub  12 , rotor  16  rotates in a plane wherein peripheral surfaces  17  and  19  are located adjacent corresponding faces  23  and  25  of the first  22  and second  24  friction pads with equal running clearances x and x′. The first and second plurality of rollers  58 , 58 ′, . . .  58   n ;  60 , 60 ′, . . .  60   n  are positioned in the outer race  50  of bearing member  20  in a manner as illustrated in FIG. 3 with apex  76 , 76 ′ for the first and second plurality of rollers  58 , 58 ′, . . .  58   n ;  60 , 60 ′, . . .  60   n  correspondingly engaging the sloping raceways  66 , 68  at points an equal distance from reference point  74  and the end play is illustrated in an exaggerated manner as clearances y and y′ between the first and second plurality of rollers  58 , 58 ′, . . .  58   n−x ;  60 , 60 ′, . . .  60   n−x  and sloping raceways  84 , 94  on the first  54  and second  56  cones. The first and second plurality of rollers  58 , 58 ′, . . .  58   n ;  60 , 60 ′, . . .  60   n  of bearing member  20  remain in this relationship as long as the vehicle is traveling in a horizontal and linear manner such that the running clearances x and x′ between the rotor  16  and friction pads  22 , 24  remain in a fixed and static condition. 
     When a vehicle is traveling in a linear manner and encounters a curve in the roadway, centrifugal forces are generated. If the centrifugal forces are great enough, the vehicle will experience an outward or inward overturning moment with respect to a roadway. The centrifugal force is resisted by the engagement of the wheels with the roadway but because of the relationship between the components of the vehicle stresses are introduced into the components and since some components are more solidly retained some components deflect more than others. 
     In a vehicle equip with the wheel and bearing assembly  10  of the present invention, the outer race  50  is fixed to the vehicle and as such remains stationary, however, the built-in end play of the bearing member  20  allows the first and second plurality of rollers  58 , 58 ′, . . .  58   n ;  60 , 60 ′, . . .  60   n  to shift in the direction of the centrifugal forces. FIG. 4 illustrates a shift of cones  54 , 56  of the bearing member  20  when radial outward centrifugal forces are experienced by a vehicle and FIG. 4 a  illustrates the resulting running clearances x−y and x′+y while FIG. 5 illustrates a shift of cones  54 , 56  of the bearing member  20  when radial inwardly centrifugal forces are experienced by a vehicle and FIG. 5 a  illustrates the resulting running clearance x+y and x′−y as rotor surfaces  17  and  19  correspondingly move the friction pads  22  and  24 . FIGS. 4 and 5 illustrate the effect of a wheel and bearing assembly  10  on opposite sides of a vehicle. The shift of the first and second plurality of rollers  58 , 58 ′, . . .  58   n ;  60 , 60 ′, . . .  60   n , in raceways  66  and  68  is limited as movement only occurs until first and second plurality of rollers  58 , 58 ′, . . .  58   n−x ;  60 , 60 ′, . . .  60   n−x  engage raceways  84 , 94 . It should be understood that the axial shift of hub  12  is magnified by the rotor  16  such that corresponding surface  17  or  19  engages face  23  or  25  to move friction pads  22  or  24  to produce the running clearances which are increased or decreased by a magnitude referred to as “y” in FIGS. 4 and 5. When the centrifugal force terminates, the first and second plurality of rollers  58 , 58 ′, . . .  58   n ;  60 , 60 ′, . . .  60   n  return to their centered positioned illustrated in FIG. 3 however, the running clearance between face  23  and surface  17  and face  25  and surface  19  will have changed as one running clearance will equal the desired running clearance plus the end play (x+y or x′+y) and the other running clearance will equal the desired running clearance less the end play (x−y or x′−y). Either way a minimum running clearance is achieved and as a result polishing of surfaces  17  and  19  is attenuated with the desired equal running clearance x,x′ being reestablished on a next brake application.