Abstract:
A drum brake includes a spider having an anchor with as-cast recesses and anchor seats machined within the as-cast recesses. The as-cast recesses provide clearance for a shaft of a cutting tool during machining of the anchor seats. First and second brake shoes are pivotally supported by the anchor. Each brake shoe has a convex web portion positioned in communication with one of the anchor seats to transfer braking loads to the spider.

Description:
BACKGROUND 
       [0001]    The present disclosure generally relates to vehicle drum brake assemblies and drum-in-hat disc brake assemblies. More particularly, the present disclosure relates to a brake shoe to anchor interface. 
         [0002]    Nearly all motor vehicles are equipped with a brake system for slowing or stopping the vehicle in a controlled manner. The brake system may include a number of disc brake assemblies, a number of drum brake assemblies or a combination of the two types. Some vehicles are equipped with a brake assembly called a “drum-in-hat” disc brake assembly that includes a disc brake portion and a drum brake portion. Many brake assemblies are actuated by hydraulic or pneumatic pressure. Other brake assemblies or portions of the brake assembly may be actuated through the use of linkage mechanisms having a force applied by the hand or foot of the vehicle operator. 
         [0003]    Typical drum-in-hat disc brake assemblies include a hydraulically actuated disc service brake and a mechanically actuated drum-in-hat parking brake. The disc service brake includes a rotor secured for rotation with the wheel of the vehicle. The rotor includes a pair of opposed surfaces which are frictionally engaged by disc brake pads. A caliper assembly applies force to disc brake pads to cause engagement with the braking surfaces of the disc. 
         [0004]    The drum-in-hat parking brake includes a pair of opposed arcuate brake shoes that are supported on a backing plate. The shoes are selectively engageable with a cylindrical braking surface formed in a hat portion of the rotor. A manually operated actuation mechanism applies a force to one or both of the brake shoes to engage the brake shoes with the drum. 
         [0005]    Certain drum brakes include a pinned shoe design that includes a round post fixed to the backing plate. The anchor end of the shoe includes a concave portion engaging the round post. Other brake assemblies include a cast knuckle or adaptor having a machined anchor portion limiting the need for a separate steel post. Some of the brake designs having machined castings include a rounded anchor end that simulates the external surfaces of two round steel posts. Each brake shoe has an end with a concave portion that mates with the convex shape of the anchor support. Unfortunately, machining this type of anchor support requires the use of a relatively expensive CNC machining center or the use of a special cam follower because the rounded external surfaces have offset centers. The machining process is time consuming and expensive. 
         [0006]    Another anchor support design includes a brake shoe contacting anchor interface formed as a flat surface. While this design is relatively easy to manufacture, the brake shoes are no longer pinned to the backing plate to rotate about a predetermined axis. On the contrary, the brake shoes are free to translate relative to the backing plate and also the drum axis of rotation. Brake drag has been noted on many vehicles using this type of shoe anchor design because the brake shoes frequently move due to gravitational forces or road load input causing the brake shoes to rub against the drum surface. This condition may lead to poor vehicle mileage, early parking brake shoe lining wear and a degradation of parking brake performance. 
         [0007]    Other brake designs incorporate machined cast anchor supports having concave surfaces. A concave anchor seat is machined to match a convex rounded anchor end of a brake shoe. This type of anchor support may be relatively easily machined and does not require a CNC machining center. However, a depth of the concave anchor seat is limited by the geometry of the cutter. Specifically, the cutter includes a cutting portion having an outer diameter and a shaft supporting the cutting portion which typically has a smaller diameter. The diameter of the cutting portion and the diameter of the shaft define a maximum depth of cut allowable because the shaft must remain clear of the edge of the anchor support during the machining operation otherwise tool failure may occur. This machining concern results in a relatively shallow anchor seat. If the anchor seat is insufficiently recessed into the anchor support, the forces transferred to the anchor support from the shoe during braking may be undesirably concentrated against the edge of the anchor slot. High stresses result which may lead to anchor deformation, cracking and potential fracture. 
       SUMMARY 
       [0008]    A drum brake includes a spider having an anchor with as-cast recesses and anchor seats machined within the as-cast recesses. The as-cast recesses provide clearance for a shaft of a cutting tool during machining of the anchor seats. First and second brake shoes are pivotally supported by the anchor. Each brake shoe has a convex web portion positioned in communication with one of the anchor seats to transfer braking loads to the spider. 
         [0009]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
     
       DRAWINGS 
         [0010]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0011]      FIG. 1  is a partial perspective view of a drum-in-hat disc brake assembly according to the principles of the present disclosure; 
           [0012]      FIG. 2  is an exploded perspective view of the brake shown in  FIG. 1 ; 
           [0013]      FIG. 3  is a partial fragmentary perspective view of a spider component of the brake assembly depicted in  FIGS. 1 and 2  along with an exemplary cutting tool; 
           [0014]      FIG. 4  is a fragmentary plan view of a portion of the spider; and 
           [0015]      FIG. 5  is a cross-sectional view of the brake assembly taken along line  5 - 5  as shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0017]      FIGS. 1 and 2  depict a portion of a drum-in-hat disc brake assembly identified at reference number  10 . The drum-in-hat disc brake assembly  10 , hereinafter referred to as brake assembly  10 , includes a hydraulically or pneumatically actuated disc surface brake (not shown) and a drum-in-hat parking brake. Although the description and illustrations relate to a particular vehicle drum-in-hat disc brake assembly, it will be appreciated that the present disclosure may be used in connection with other drum-in-hat disc brake assemblies and other drum brake assemblies associated with service brake applications as well. 
         [0018]      FIGS. 1 and 2  depict brake assembly  10  including a spider  12 , a backing plate  14 , a first brake shoe assembly  16 , a second brake shoe assembly  18 , a link assembly  20  and an adjuster assembly  22 . Spider  12  is depicted as a one-piece casting adapted to be secured to a non-rotatable component of the vehicle, such as an axle flange or a steering knuckle (not shown). Spider  12  includes a relatively large aperture  24  extending therethrough and a plurality of bores  26  circumferentially spaced apart around aperture  24 . Aperture  24  is sized and shaped to pilot on a portion of the axle and permit another portion of the axle to extend therethrough toward the vehicle wheel (not shown). Fasteners  28  are positioned within bores  26  to secure spider  12  to the associated vehicle component. 
         [0019]    Spider  12  also includes a pair of outwardly extending ears  30  and an anchor  32 . Ears  30  are provided with apertures  34  extending therethrough. Suitable fasteners (not shown) are positioned in apertures  34  to attach a disc brake caliper assembly (not shown) to spider  12 . 
         [0020]    Anchor  32  is shown integrally cast with spider  12  protruding in an outboard axial direction from the remainder of spider  12 . As is most clearly depicted in  FIG. 3 , anchor  32  includes a number of “as-cast” surfaces and a pair of opposed seats  40  and  40 ′ machined therein. In the illustrated brake assembly, seats  40  and  40 ′ are substantially identical to one another. Accordingly, like numerals will be used to identify similar elements. Seat  40  includes a pair of opposed side surfaces  42  and  44  as well as a bottom surface  46 . Side surfaces  42  and  44  extend substantially parallel to one another and perpendicular to an axis of drum rotation  48 . Bottom surface  46  is substantially arcuately shaped and extends substantially perpendicularly between side surfaces  42  and  44 . In the embodiment depicted in  FIGS. 3 and 4 , bottom surface  46  is shaped as an arc having a center  49 . 
         [0021]    The as-cast surfaces of anchor  32  include an inner surface  50 , an outer surface  52  and side walls  54  and  56  extending axially outboard from a substantially planar surface  58  formed on spider  12 . Anchor  32  includes an end face  60  extending substantially parallel to planar surface  58 . Side walls  54  and  56  extend at an angle from surface  58  such that anchor  32  defines a footprint on surface  58  having a greater surface area than end face  60 . In addition, inner surface  50  and outer surface  52  are substantially arcuately shaped where inner surface  50  extends an arc length less than outer surface  52 . 
         [0022]    Recesses  62  are also formed during the casting process of spider  12 . Recesses  62  are defined by arcuately shaped scallops  64  axially inwardly extending from end face  60  and terminating at a land  66 . Scallops  64  and land  66  are as-cast surfaces and remain in this condition throughout the finishing processes, including machining, of spider  12  and use of brake assembly  10 . Scallops  64  are shaped to provide clearance for a shaft  70  of an exemplary cutter  72  shown in  FIG. 4 . Cutter  72  includes a cutting portion  74  that is axially translated along an axis  76  to form seats  40 . The curved shape of bottom surface  46  corresponds to the outer diameter of cutting portion  74 . By forming anchor  32  with recesses  62  during a casting or forging process, machining seats  40  is greatly simplified. In particular, only a relatively small amount of material needs to be removed during a cutter plunge. Furthermore, the tooling required to perform a cutter plunge along a single axis of travel is very simple and inexpensive compared to computer numerically controlled machines operable to move cutters along multiple axes. 
         [0023]    Spider  12  also includes a plurality of bosses  80  axially extending in an outboard direction from surface  58 . Each of bosses  80  includes an internally threaded bore  82  extending therethrough. Threaded fasteners  84  extend through apertures  86  formed in backing plate  14  and threadingly engage bores  82  to mount backing plate  14  to spider  12 . Backing plate  14  is shown as a stamped sheet metal structure having a relatively large central opening  90  which permits an outer end of the axle or steering knuckle to extend therethrough to support a wheel (not shown). 
         [0024]    Backing plate  14  also includes a first generally slotted opening  92 , a second generally slotted opening  94  and a third generally slotted opening  96 . First slotted opening  92  is shaped and positioned to allow anchor  32  to extend therethrough. Second slotted opening  94  is sized and positioned to allow link assembly  20  to extend therethrough. Third slotted opening  96  is positioned and sized to allow access to adjuster assembly  22  and adjust the parking brake while the brake assembly is in assembled condition. Backing plate  14  further includes a plurality of rest pads  100  and a plurality of openings  102 . Openings  102  are adapted to receive pins  104 . Pins  104  extend through openings  102  and backing plate  14  as well as apertures  106 ,  108  extending through first brake shoe assembly  16  and second brake shoe assembly  18 , respectively. Pins  104  have outer ends shaped to be secured to spring and clip assemblies  110  to secure brake shoe assemblies  16  and  18  to backing plate  14 . 
         [0025]    First brake shoe assembly  16  and second brake shoe assembly  18  are substantially similar to one another. Accordingly, like reference numerals will be used to indicate similar features. First brake shoe assembly  16  and second brake assembly  18  include webs  120  and  120 ′ which are generally planar sheets of steel having a crescent shape. Generally arcuate-shaped tables  122  and  122 ′ are secured to outer curved surfaces of webs  120  and  120 ′ via a process such as welding. Lining blocks  124  and  124 ′ are secured to outer surfaces  126  and  126 ′ of tables  122  and  122 ′. Lining blocks  124  and  124 ′ may be adhesively bonded, or secured to the tables  122  and  122 ′ via mechanical fasteners such rivets or bolts. Each of tables  122  and  122 ′ include a plurality of upset portions  128  and  128 ′ positioned on each inboard and outboard edge of tables  122  and  122 ′. The upset portions located on the inboard edge of tables  122  and  122 ′ are positioned to slide along pads  100  formed on backing plate  14 . 
         [0026]    Brake shoe webs  120  and  120 ′ include a first end  130  and  130 ′ having a dog  132  and  132 ′ formed thereon. The dogs  132  and  132 ′ are sized and positioned to mate with portions of adjuster assembly  22 . A first spring  134  includes hooks  135  and  135 ′ extending through apertures  136  and  136 ′ to bias first brake shoe assembly  16  and second brake shoe assembly  18  toward their retracted positions. Spring  134  engages a toothed portion  138  of adjuster assembly  22  to maintain the adjusted position of the brake assembly. Brake shoe webs  120  and  120 ′ include second ends  140  and  140 ′. Notches  142  and  142 ′ are formed in second ends  140  and  140 ′ to receive link assembly  20 . A second return spring  144  includes ends  145  and  145 ′ extending through apertures  146  and  146 ′ extending through webs  120  and  120 ′. Second return spring  144  applies a load to each of first and second brake shoe assemblies  16  and  18  drawing the brake shoes toward their retracted position. Furthermore, webs  120 ,  120 ′ include lobes  150  and  150 ′ positioned within seats  40  of spider  12 . Convexly shaped surfaces  152  and  152 ′ are formed on the distal ends of lobes  150  and  150 ′. When brake assembly  10  is not being actuated to transmit torque, convex surfaces  152  and  152 ′ engage bottom surfaces  46  and  46 ′, respectively, of anchor  32  to properly position first brake shoe assembly  16  and second brake shoe assembly  18  relative to the drum (not shown). 
         [0027]    Link assembly  20  is a parking brake actuator operable to apply forces to second ends  140  and  140 ′ of first and second brake shoe assemblies  16  and  18 . Link assembly  20  includes a lever arm  154  rotatably coupled to a cross bar  156  by a pin  158 . A cable or another linkage device (not shown) is used to provide an input force to lever arm  154  and apply the parking brake. The following description will relate to brake operation during a clockwise direction of drum rotation when viewed from a position outboard of brake assembly  10  as depicted in  FIG. 1 . In operation, the parking brake is applied by applying a force to link assembly  20 . Link assembly  20  applies forces to second ends  140  and  140 ′ of first brake shoe assembly  16  and second brake shoe assembly  18 . Based on the rotation of the drum, and engagement of lining block  124 ′ with the drum, second brake shoe assembly  18  tends to rotate clockwise in the same direction as the brake drum. First end  130 ′ of second brake shoe assembly  18  applies a load to adjuster assembly  22 . The load is transferred to first end  130  of first brake shoe assembly  16 . Lining block  124  of first brake shoe assembly  16  frictionally engages the drum and is also rotated in a clockwise direction. Due to the self-energizing nature of the brake shoes and the duo-servo arrangement, convex surface  152  of first brake shoe assembly  16  is driven into contact with bottom surface  46  of anchor  32 . At this time, convex surface  152 ′ is not engaged with bottom surface  46 ′ while convex surface  152 ′ transfers a relatively large load to anchor  32 . 
         [0028]    Anchor  32  reacts the load from first brake shoe assembly  16  without structural incident due to the relatively deep plunge of cutter  72  and resulting arc length of bottom surface  46 . More specifically, the resultant force acting on anchor  32  during braking passes through second end  140  of first brake shoe assembly  16  acting along a line “R”. The force enters anchor  32  at a location offset from an edge  160  defined by the intersection of bottom surface  46  and outer surface  52  of anchor  32 . A structurally robust design results. One skilled in the art will appreciate that when the drum rotates in the opposite or counterclockwise direction, convex surface  152  is spaced apart from anchor  32  while convex surface  152 ′ is driven into engagement with bottom surface  46 ′. 
         [0029]    Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without department from the spirit and scope of the invention as defined in the following claims.