Abstract:
A brake mechanism fixed to a member allowing limited reciprocal motion and providing a restorative force to the movable member in one direction of movement thereof. A brake mechanism includes a rotor fixed to and wheel about an axle axis has a caliper assembly spanning the rotor with inboard and outboard friction members supported on either side of the rotor for selectively engaging the rotor and braking the wheel. A piston is fixed to the caliper of the inboard friction member for moving the inboard friction member toward the rotor and including a piston seal which, upon removal of fluidic pressure from the cylinder, resiliently urges the inboard friction member away from the rotor. A bracket is fixed to the vehicle supports the caliper on a pair of generally cylindrical guide pins fixed to one of the anchor bracket and caliper assembly and is movable within a pair of generally cylindrical guide pin bores of the anchor bracket and caliper assembly. A pair of central cylindrical shells and an end engaging a pin shoulder to provide the restorative force and a radially outer portion of reduced rigidity such as a plurality of fins frictionally engaging the aperture.

Description:
The present invention relates to vehicle braking systems of the disc variety, and more particularly to a disc brake caliper which restores proper running clearance after a braking event for both inboard and outboard brake pads and automatically compensates for pad wear. 
     BACKGROUND OF THE INVENTION 
     The problem of maintaining a proper running clearance between braking members is an old one. For many years, drum style brake shoes were manually advanced to compensate for wear of the shoe friction surface, for example, by turning a star wheel adjustment nut. This periodic maintenance routine was frequently initiated upon the vehicle driver detecting excess brake pedal travel. Later, automatic adjusters for resetting the rest or released shoe location were developed, some requiring the vehicle to be braked while moving in reverse to reposition the shoes. With the advent of disc brakes, some systems have employed a radially deformable metal tube with a shoulder which provides a rest or retracted position for the brake pads. Excess pad travel induces radial deformation of the tube axially repositioning the shoulder along the tube and establishing a new pad retracted location. Other systems have relied on the natural resilience of piston seals to retract the brake pads and provide running clearance between the brake rotor and brake pads. In the case of floating caliper style disc bakes, the piston seal resilience adequately retracts the inboard brake pad away from the rotor after a braking event, but repositioning of the outboard pad has been somewhat unreliable. Recent attempts to achieve more uniform clearance for both inboard and outboard pads have concentrated on the interplay between the caliper guide pins and the member in which they slide. 
     For example, one embodiment in U.S. Pat. No. 5,934,416 employs a plurality of elastic annular rings recessed either in the guide pin surface or the sidewall of the hole in which the guide pin reciprocates. The annular rings engage the other member and deform without slipping during braking. Excess brake pad travel induces slippage between the members after the deformation resulting in repositioning the pin within its hole. In another embodiment, a series of axially spaced apart radially extending springs are located along the pin surface or hole sidewall and the other member has a single similar radially extending spring. During normal braking, the single spring transition between a specific pair of the other member springs, but excess pad travel causes the single spring to slip past one of the two adjacent springs and thereafter to transition between a new specific pair. Variations on these techniques are employed in other embodiments. 
     U.S. Pat. No. 6,397,983 reiterates stating a common problem in the art of brakes is that stationary brake pads often drag on a movable friction element after the braking pressure has been released. This causes excessive wear on the pads and reduces the overall performance of the vehicle. In the art of automotive and truck disc brakes, this problem is presented when the brake pad that is carried by a movable, or floating, caliper drags on the rotor after braking pressure is released. This occurs mostly because the frictional forces between the elements carrying the caliper, such as the friction between the slide pins and the walls of the bore in which they ride, prevent return of the caliper to a rest position providing a gap between the pad and the rotor after release of braking pressure. This patent suggests a mechanism for providing a clearance between a brake pad and a rotor in a sliding-pin, floating-caliper disc brake which includes a bushing that receives a sliding pin and a resilient element between the end of the pin and the end of the bushing. The bushing is a cylindrical shell with smooth inner and outer diameters for receiving the pin and engaging a bore respectively and has a reduced diameter hole in an otherwise closed end through which a reduced diameter free end portion of the pin passes. A retainer engages the free end and holds a wave washer captive between the bushing end and the free pin end. The pin reciprocates in the bushing during operation of the brakes, and the bushing moves along the bore as the brake pads wear. A large number of parts coupled with complex assembly are just one problem with this solution, thus after over one-half century, these problems remain partially unsolved and continue to plague the industry. 
     It is desirable to maintain proper running clearance for both inboard and outboard brake pads in a very simplistic and economical manner. 
     SUMMARY OF THE INVENTION 
     The present invention provides solutions to the above problems by centering the caliper over the rotor subsequent to each brake release and establishing a predetermined bilateral running clearance. The inboard and outboard running clearances may be predisposed to be the same or of different amounts. These prescribed running clearances will be maintained regardless of inner and/or outer brake shoe pad wear or lining thickness variations. Of equal importance is the maintenance of this prescribed running clearance, prior to, during, and subsequent to lateral accelerations of the caliper imposed by the vehicle during off-brake driving durations. This may greatly reduce disk thickness variation generation and resulting brake torque variation. This maintenance is uniquely accomplished by a set of caged preloaded resilient members that are directly referenced to the rotor(s inboard and outboard rubbing surfaces. This referencing and the resulting positioning provide and maintain bilateral running clearance that is usually only obtainable in a fixed head caliper design. Thus, this design provides this benefit of a fixed head caliper without the cost and associated negative performance factors associated with the fixed head design. 
     This rotor reference positioning and maintenance of bilateral running clearance is ensured to a much more substantial degree than any other known design due to the embodiment of the caged preloaded resilient members. Specifically, this caged preloaded design provides a much higher restorative force to the caliper and brake shoe pads to initialize and maintain the bilateral running clearance. This caged preload design provides immediate and higher restorative force and it is most dependent upon the resilient member preload versus its spring rate which can be more closely established at the time of assembly. This instantaneous restorative force to keep a caliper in its desired centered position is accomplished without the caliper having to deviate significantly to either side of its centered position to generate the restorative force. This design element helps preclude brake shoe pads from striking the rotor, as the restorative force intervenes before the caliper and brake shoe pads travel far enough to strike the rotor. 
     The invention comprises, in one form thereof, a brake mechanism for a vehicle wheel, which has a rotor fixed to and rotatable therewith about an axle axis. A caliper spans the rotor and supports inboard and outboard friction members or pads, one to either side of the rotor for selectively engaging the rotor and braking the wheel. One or more fluidic cylinders are fixed to the caliper having pistons fixed to the inboard friction member for moving the inboard friction member toward the rotor upon receipt of fluidic pressure. Each cylinder has a piston seal which, upon removal of fluidic pressure from the cylinder, resiliently urges the inboard friction member away from the rotor. An anchor bracket is fixed to the vehicle for slidingly supporting the caliper. At least one generally cylindrical guide pin is fixed to one of the anchor bracket and caliper assembly. As disclosed, the guide pin threadedly engages the caliper. At least one generally cylindrical guide pin bore is located within the other of the anchor bracket and caliper assembly for receiving a corresponding guide pin. A generally cylindrical resilient bushing is interposed between the guide pin and bore for slidingly receiving the guide pin and frictionally engaging the bore. The unstressed bushing outside diameter exceeds the bore inside diameter so that the bushing is under radial compression when fit within the bore whereby the bushing is diameterally preloaded to frictionally maintain the axial location of the bushing within the bore. The pin has a shoulder for holding the bushing captive between the shoulder and said one of the anchor bracket and caliper assembly and the bushing includes a resilient end portion which is axially compressed by the guide pin shoulder as the piston receives fluidic pressure for engaging the shoulder to urge the outboard pad away from the rotor upon release of fluid pressure. The bushing has a solid cylindrical shell portion with a central cylindrical aperture for receiving the guide pin and a set of resilient deformable radially outwardly extending members for engaging the bore. The bushing may also compensate for dimensional variations, such as the guide pin bore cylindrical axis being radially displaced from the guide pin cylindrical axis. 
     An advantage of the present invention is that fewer parts are required to achieve proper running clearance. As a result, the system is less expensive to manufacture than prior systems. 
     Another advantage is the composition and arrangement of components centers and secures the caliper over the rotor upon each brake release, thus inherently providing equal running clearance on each side of the rotor to the pads, while compensating for pad wear. 
     A further advantage is if the centerline of the bore of the sleeve is offset from the centerline of the outside diameter of the sleeve, accommodation of the variance of distance between the pins, due to manufacturing tolerances, may be readily accommodated without bending or preloading the pins. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section isometric view of a brake caliper assembly incorporating the invention in one form; 
         FIG. 2  is a cross-section along line  2 - 2  showing a portion of  FIG. 1  in a brake unapplied condition; 
         FIG. 2   a  is an enlarged cross-sectional view of a portion of the bushing illustrating the gap of  FIG. 2 ; 
         FIG. 3  is a cross-section along line  2 - 2  showing a portion of  FIG. 1  in a brake applied condition; 
         FIG. 3   a  is an enlarged cross-sectional view of a portion of the bushing and caliper illustrating the gap of  FIG. 3 ; 
         FIG. 4  is a cross-section along line  2 - 2  showing a portion of  FIG. 1  in a brake applied condition illustrating running clearance compensation; 
         FIG. 5  is a cross-section along line  2 - 2  showing a portion of  FIG. 1  in a brake unapplied condition following running clearance compensation; 
         FIG. 6  is an exploded cross-sectional view of the components of  FIGS. 2-5 ; 
         FIG. 7  is a bushing end view from the right end of  FIG. 6 ; 
         FIG. 8  is a cross-section along line  8 - 8  showing a portion of  FIG. 1 ; 
         FIG. 9  is also a cross-section along line  8 - 8  showing a portion of  FIG. 1 , but illustrating different pin spacing; 
         FIG. 10  is a bushing end view from the right end of  FIG. 6  illustrating one variation on the bore engaging ribs; and 
         FIG. 11  is a cross-sectional view of another variation on the bore engaging ribs on the bushing of  FIG. 6 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several drawing views. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and particularly to  FIG. 1 , there is shown, in cross-section, a brake caliper assembly  11  for spanning and selectively braking a conventional wheel supported rotor  51  and attached vehicle wheel. The caliper includes an inboard friction surface or pad  13  and an outboard pad  15  to be positioned on opposite sides of a portion of the rotor and moved into braking engagement with the rotor by an operator actuated supply of hydraulic fluid to a pair of hydraulic cylinders  17  and  19  via inlet  21 . The caliper assembly includes an anchor bracket  23  which is fixed to the vehicle, for example, by bolts passing through apertures such as  25 . A caliper portion  27  is mounted for limited travel relative to the anchor bracket  23  along guide pins  29  and  31 . The guide pins may be shoulder bolts which engage the caliper pin ear, bringing the shoulder  81  ( FIGS. 3   a  and  6 ) of the bolt in direct and permanent contact with caliper pin ear face. An annular bushing portion ( FIG. 3   a ) may be included to exclude dirt from the area of the bushing face  81 . The guide pins are illustrated threaded into the caliper as better seen in  FIGS. 2-8 , but may be fixed to either the anchor bracket or the caliper and slidable in apertures in the other. The guide pins  29  and  31  are free to slide in respective bushings  33  and  35  in bores in the anchor bracket  23 . These anchor bracket bores are sealed against dirt and moisture by flexible boots such as  37  at one end and by plugs such as  39  at the other end. When a vehicle operator commands, fluid is supplied to the cylinders  17  and  19  whose pistons urge the inboard pad  13  toward the left and downwardly as viewed in  FIG. 1  and into engagement with the inboard face of the rotor. A continued supply of fluid causes the caliper to translate right and upwardly along the bushings  33  and  35  drawing the outboard pad  15  into engagement with the outboard rotor face braking the vehicle wheel. Conventionally, inboard pad  13  is fixed to the cylinder pistons and when fluid pressure is released, the natural resilience of the piston seals  41  and  43  withdraws the piston attached inboard pad from the rotor face, but the outboard pad is not so fortunate. Restoration of running clearance for the outboard pad upon brake release is accomplished in the present invention by the interaction of the bushings  33  and  35  with the other components as illustrated in  FIGS. 2 and 3 . 
     In the brake released or unapplied condition as seem in  FIG. 2 , the left end of bushing  33  engages the caliper  27 . There is a gap (d (between the right bushing end  49  and the shoulder  45  of the guide pin  29 , however, a peripheral bushing portion  47  may engage the pin shoulder  45 , compare  FIGS. 2 and 2   a . When the brake is applied and the inboard pad  13  engages the rotor, continued piston motion induces caliper movement a distance “a” to engage the outboard brake pad  15  and rotor face, compare  FIGS. 2 and 3 . Bushing  33  may be formed as a single molded member of resilient material. The pin shoulder  45  which may have already been in contact with bushing portion  47  now compresses portion  47  the distance “d” allowing shoulder  45  to approach the bushing right end face  49  while a gap “c” forms between the bushing left end and the caliper as best seen in FIG.  3   a . When the brake is released, the resilience of bushing portion  47  forces pin  33  back toward the right returning the components to their  FIG. 2  locations and reestablishing the outboard pad running clearance. Thus far, the bushing  33  has remained fixed within the anchor bracket bore. 
     Brake pad wear will eventually allow the distance (a (to exceed the gap “d.” When this occurs, pin shoulder  45  engages bushing  33  face  49  and additional caliper travel “b” slides the bushing leftward as viewed from the location in  FIGS. 2 and 3  to the location in  FIG. 4 . Now when the fluid pressure is relieved, the resilience of bushing portion  47  reestablishes the outboard pad clearance at the new “brake adjusted” location shown in  FIG. 5 . 
     In  FIG. 6 , the components shown in  FIGS. 2-5  have been exploded away from one another to more clearly show the individual component features and to illustrate the simple assembly technique. An end view of the bushing or sleeve  33  is shown in  FIG. 7 . The bushing comprises a solid cylindrical shell portion  53  with a central cylindrical aperture  55  for slidingly receiving the guide pin  29  and a set of resilient deformable outwardly extending members such as  57  and  59  for frictionally engaging the bore  65 . As illustrated in  FIGS. 6 and 7 , the set of outwardly extending members comprise a plurality of radially extending ribs or annuluses which are axially deformed when frictionally engaging the bore, compare  FIGS. 6 and 7  where the annuluses extend radially outwardly to  FIGS. 2-5  where they are additionally skewed axially. Note the dotted lines  61  and  63  in  FIG. 6  showing that the outside diameter of the bushing exceeds the inside diameter of the anchor bracket bore  65 . Since the unstressed bushing outside diameter exceeds the bore  65  inside diameter, the bushing is radially compressed to fit within the bore providing a diameteral preload to frictionally maintain the axial location of the bushing within the bore. The bushing to bore frictional engagement may be achieved by any suitable rib or other resilient member deformable configuration. For example,  FIG. 10  illustrates the set of outwardly extending members as an axially spaced plurality of sets of radially extending fingers such as  67 ,  69  and  71  which could be axially deformed when frictionally engaging the bore with the side view appearing much the same as in  FIGS. 2-5 . The set of outwardly extending members could also comprise one or more helical ribs  73  wrapped about and extending radially outwardly from the solid shell portion  75  of  FIG. 11  and such a rib could experiencing axial deformation and/or radial compression when frictionally engaging the bore. While not illustrated, longitudinally extending ribs can also be envisioned. Regardless of the specific configuration, the fins or fingers on the sleeve or bushing provide positive location of the sleeve in the bore and provide a diametrical force preload of the sleeve inside the pin bore. This diametrical preload force is the normal force, which in conjunction with the coefficient of friction between the sleeve and the bore, provides a lateral resistive force to oppose translation of the sleeve along the bore. This resistance to movement is important in the operation of the brake in that it must exceed, by a sufficient margin, the lateral slide force of the pin in the sleeve. 
     Lateral slide force of the pin in the sleeve. 
     The sleeve  33  portrays a design at its right hand end to provide a caged preloaded resilient mechanism function which imparts a force on the pin bolt  29  which pulls the pin bolt to the right as viewed in  FIG. 6 . The right end portion of bushing  33  has reduced rigidity due to the axially collapsible region formed by a radially outwardly extending base portion  77  which blends into a radially inwardly extending free end  79  as best seen in  FIG. 2   a . This reduced rigidity end may be a complete annulus, e.g., a solid of revolution, or formed as a series of radially extending fingers as illustrated at  83 ,  85  or  87  in  FIGS. 7 and 10 . This reduced rigidity end, the radially extending fins and the solid cylindrical shell portion are preferably all one piece formed at the same time of the same molded material, for example, by an injection molding technique. 
     The brake mechanism is assembled a shown in  FIG. 6 . The bolt  29  is passed into the central hole  55  and threaded into the caliper  27 . The bushing  33  may then be introduced into the bore  65  distorting the ribs  57  and  59  both axially and radially, or the introduction of bushing  33  into the bore  65  may precede assembly of the pin to the caliper causing initial distortion of the ribs or fins in the orientation shown in  FIGS. 2-5 . In either case, when introduced into the anchor bracket bore, the bushing fins  57 ,  59  experience both shear and compression. 
     In operation, as the brake is transitioning from a brake applied condition as in  FIG. 4  to the brake unapplied condition as in  FIG. 5 , the resilient mechanism at the right bushing end imparts a force on the pin bolt  29  shoulder  45  resulting in its movement to the right, until the caliper ear face comes in contact with the end of the sleeve as in  FIGS. 2 and 5  and the subject travel of the pin bolt and caliper is thus limited. The caliper will move in this prescribe manner as long as the lateral restraint force of the sleeve to the anchor bracket sleeve bore  65  is greater than the force required to move the pin and caliper. This prescribed motion of the pin ear and thus the caliper by the same motion of both integral pin ears to the caliper body, result in moving the caliper to the right, as pictured in  FIGS. 2-6  (left and downward in  FIG. 1 ). This movement provides a prescribed running clearance of the outer brake shoe pad  15  to the rotor  51 , since the outer shoe brake pad is affixed to the outer caliper legs. This prescribed movement is predetermined by the gaps shown in  FIGS. 2 and 3 , as designed by only the difference of two dimensions: the pin bolt under head to shoulder dimension and the overall length of the sleeve. 
     As the brake is transitioning from a brake unapplied condition as in  FIG. 2  to a brake applied condition as in  FIG. 3 , the force of the brake pistons by reaction of the inner brake pad  13  against the rotor  51  causes the caliper to translate inboard or to the left in  FIGS. 2-5 . This in turn causes the pin bolt to move to the left as the resilient end portion  47  is compressed the distance “d”. This resets the conditions as described above to allow the operation of the prescribed design elements to effect a centering of the caliper over the rotor and establishment of outer brake shoe pad to rotor running clearance as described above, during a brake release. 
     If outer pad lining wear occurred during the previous brake applied duration, the subsequent apply of the brake will cause the full compression of the resilient member  47  between the underside  45  of the head of the pin bolt and the right end  49  of the sleeve. Continuing during this same brake apply and subsequent to this full compression, additional travel of the outer brake pad and caliper housing will then cause the sleeve to translate to the left a distance “b” in the anchor bracket pin bore as seen by comparing  FIGS. 3 and 4 . This will ensure that the released position of the brake housing and outer brake shoe pad will adjust for outer brake shoe pad wear, each and every brake apply, and will thus ensure a consistent running clearance of the outer brake shoe pad to the rotor regardless of outer brake shoe pad wear thickness. The often used standard feature of connecting the inner brake shoe assembly to the piston(s), so that seal resilience and retraction of the piston upon brake release would also retract the inner brake shoe pad and establish its respective running clearance to the rotor. 
     In  FIG. 8 , a pair of generally cylindrical guide pins  29  and  31  are illustrated as fixed to the caliper assembly and having generally parallel cylindrical axes  89  and  91  spaced apart a distance “e”. The axes of the anchor bracket  23  apertures or guide pin bores are, however, spaced further apart than “a”. The pair of generally cylindrical resilient bushings  33  and  35 , which are interposed between the guide pin and corresponding bores may provide compensation for the difference between the distances separating the axes. Similarly, if the guide pin separation is oversize, e.g, distance “f”, the bushings are again capable of compensation as seen in  FIG. 9 . Hence, if the centerline of the bore of the sleeve is offset from the centerline of the outside diameter of the sleeve, accommodation of the variance of distance between the pins, due to manufacturing tolerances, may be readily accommodated without bending or preloading the pins. The placement or rotation of the sleeves in their respective bores, can be made judiciously to compensate for differences in the distance between pins as shown in  FIGS. 8 and 9 . The sleeve also has the capability due to its physical design shape, and diameter preload to provide the ability to absorb and dissipate vibrational energy. This coupled with the offset centerline approach, provide the capability and advantages of a twin low diameter clearance pin caliper while maintaining low pin slide force. 
     Thus, while a preferred embodiment has been disclosed, numerous modifications will occur to those of ordinary skill in this art. Accordingly, the scope of the present invention is to be measured by the scope of the claims which follow.