Abstract:
This invention relates to a brake component having a coating material applied thereto adapted for use in a vehicle brake assembly, method for producing such a brake component, and a vehicle brake assembly including such a brake component. The brake component is selected from the group consisting of brake shoe and a brake rotor. The brake shoe includes a friction lining having an outer surface having surface irregularities and the brake rotor including an inner cylindrical braking surface having surface irregularities. The surfaces of the brake components are disposed adjacent one another and adapted to frictionally engage one another when the brake assembly is actuated. The brake component surface having the surface irregularities prevents complete contact between the adjacent surfaces of the brake components prior to any burnishing or other contact or wear of components. According to the present invention, a green static coefficient of friction between the adjacent surfaces of the brake components is increased by applying a coating material to at least a portion of the surface of one of the brake components whereby the coating material is operative to at least partially fills in at least some of the surface irregularities so as to increase a contact area between the surfaces of the brake components thereby increasing the green static coefficient of friction between the surfaces of the brake components when the brake assembly is actuated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of PCT/US02/33434, filed Oct. 21, 2002, which claims the benefit of U.S. Provisional Application Ser. No. 60/338,902, filed Oct. 22, 2001. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates in general to vehicle brake assemblies and in particular to a brake component having a coating material applied thereto for use in such a vehicle brake assembly, method for producing such a brake component, and a vehicle brake assembly including such a brake component.  
         [0003]     Most vehicles are equipped with a brake system for slowing or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile or light truck includes a disc brake assembly for each of the front wheels and either a drum brake assembly or a disc brake assembly for each of the rear wheels. In some instances, the disc brake assembly can be a “drum-in-hat” type of disc brake assembly. The brake assemblies are actuated by hydraulic or pneumatic pressure generated when an operator of the vehicle depresses a brake pedal. The structures of these drum brake assemblies and disc brake assemblies, as well as the actuators therefor, are well known in the art.  
         [0004]     A typical drum-in-hat type of disc brake assembly includes a hydraulically or pneumatically actuated disc service brake and a mechanically actuated drum-in-hat parking and emergency brake. The disc service brake includes a rotor which is secured to the wheel of the vehicle for rotation therewith. The rotor includes a pair of opposed friction plates which are selectively engaged by portions of a caliper assembly. The interior of the rotor defines a cylindrical braking surface.  
         [0005]     A caliper assembly is slidably supported by pins secured to a mounting flange. The mounting flange is secured to a non-rotatable component of the vehicle, such as the steering knuckle or the axle flange. The caliper assembly includes a pair of brake shoes which are disposed on opposite sides of the rotor. The brake shoes are operatively connected to one or more hydraulically actuated pistons for movement between a non-braking position, wherein they are spaced apart from the opposed friction plates of the rotor, and a braking position, wherein they are moved into frictional engagement with the opposed friction plates of the rotor. When the operator of the vehicle depresses the brake pedal, the piston urges the brake shoes from the non-braking position to the braking position so as to frictionally engage the friction plates of the rotor and thereby slow or stop the rotation of the associated wheel of the vehicle.  
         [0006]     The drum-in-hat parking and emergency brake includes a pair of opposed arcuate brake shoes which are supported on a backing plate for selective movement relative thereto. The backing plate is secured to the mounting flange, or alternatively, can be formed integral therewith. Each of the brake shoes has a friction lining or pad secured thereto. The brake shoes extend within the cylindrical braking surface of the rotor. To effect parking and emergency braking action, the operator of the vehicle manually pulls an actuating lever. The lever is connected to an acutation cable having a park brake cable end which, when pulled, actuates a mechanical actuating mechanism. The actuating mechanism is located adjacent one of the ends of the brake shoes and is operative to move the brake shoes outwardly apart from one another such that the friction linings frictionally engage the cylindrical braking surface of the rotor. Such frictional engagement causes slowing or stopping of the rotational movement of the rotor and, therefore, the wheel of the vehicle in a controlled manner.  
       SUMMARY OF THE INVENTION  
       [0007]     This invention relates to a brake component having a coating material applied thereto for use in a vehicle brake assembly, method for producing such a brake component, and a vehicle brake assembly including such a brake component. The brake component is selected from the group consisting of brake shoe and a brake rotor. The brake shoe includes a friction lining having an outer surface having surface irregularities and the brake rotor including an inner cylindrical braking surface having surface irregularities. The surfaces of the brake components are disposed adjacent one another and adapted to frictionally engage one another when the brake assembly is actuated. The brake component surface having the surface irregularities prevents complete contact between the adjacent surfaces of the brake components prior to any burnishing or other contact or wear of the components. According to the present invention, a green static coefficient of friction between the adjacent surfaces of the brake components is increased by applying a coating material to at least a portion of the surface of one of the brake components whereby the coating material is operative to at least partially fills in at least some of the surface irregularities so as to increase the contact area between the surfaces of the brake components thereby increasing the green static coefficient of friction between the surfaces of the brake components when the brake assembly is actuated. The method for producing the brake component of the present invention comprises the steps of: (a) providing a brake component selected from the group consisting of brake shoe and a brake rotor, the brake shoe including a friction lining having an outer surface having surface irregularities and the brake rotor including an inner cylindrical braking surface having surface irregularities; (b) applying a liquid binder material to at least a portion of one of the outer surface of the friction lining of the brake shoe and the inner cylindrical braking surface of the brake rotor; and (c) applying a coating material to at least a portion of one of the outer surface of the friction lining of the brake shoe and the inner cylindrical braking surface of the brake rotor to at least partially fill in the surface irregularities thereof and thereby increase a contact area between the outer surface of the friction lining and the inner cylindrical braking surface of the brake rotor.  
         [0008]     Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is an outboard side elevational view of a vehicle disc brake assembly constructed in accordance with this invention.  
         [0010]      FIG. 2  is an inboard side elevational view of the vehicle disc brake assembly with the bolts removed.  
         [0011]      FIG. 3  is a sectional elevational view of the vehicle disc brake assembly.  
         [0012]      FIGS. 4 and 4 A illustrate selected portions of the vehicle disc brake assembly according to a first embodiment of this invention.  
         [0013]      FIGS. 5 and 5 A illustrate selected portions of the vehicle disc brake assembly according to a second embodiment of this invention.  
         [0014]      FIGS. 6 and 6 A illustrate selected portions of the vehicle disc brake assembly according to a third embodiment of this invention.  
         [0015]      FIG. 7  illustrates a first sequence of steps for producing the brake component part for use in the vehicle disc brake assembly of this invention.  
         [0016]      FIG. 8  illustrates a second alternate sequence of steps for producing the brake component part for use in the vehicle disc brake assembly of this invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Referring now to  FIGS. 1-3 , there is illustrated a “drum-in-hat” disc brake assembly, indicated generally at  70 , in accordance with the present invention. The disc brake assembly  70  includes a hydraulically actuated disc service brake and a drum-in-hat parking and emergency brake. The type of disc brake assembly  70  can be similar to that illustrated in U.S. Pat. Nos. 5,180,037, 5,322,145, and 4,854,423 to Evans, the disclosures of these patents herein incorporated by reference. Although the present invention will be illustrated and described in conjunction with the particular drum-in-hat disc brake assembly  70  disclosed herein, it will be appreciated that this invention can be used in conjunction with other types of drum-in-hat disc brake assemblies and/or other kinds of drum brake assemblies if so desired.  
         [0018]     As shown in the drawings, the illustrated drum-in-hat disc brake assembly  70  includes a stamped metal backing plate  71 , which is generally flat and circular in shape, and a one-piece casting  72 , which is generally circular in shape. The backing plate  71  and the casting  72  are secured to a fixed, non-rotatable component of the vehicle, such as a steering knuckle (not shown) for enclosing a rotatable axle. To accomplish this, a relatively large opening  73  is formed through the central portion of the backing plate  71 , and a smaller opening  74  is formed through the central portion of the casting  72 . The openings  73  and  74  are provided to permit an outer end of the rotatable axle to extend therethrough to the driven vehicle wheel (not shown).  
         [0019]     The casting  72  includes a plurality of holes  72 A formed therethrough which are adapted to allow bolts  95  to be received therein. The bolts  95  have respective threaded ends (not shown), which are received in threaded openings (not shown) formed in the vehicle component to secure the casting  72  thereto. A plurality of relatively smaller holes (not shown) are also formed through the backing plate  71 . These smaller holes are provided to allow suitable fasteners, such as for example rivets (not shown) to extend therethrough and secure the backing plate  71  to the casting  72 . Alternatively, the backing plate  71  can be secured to the casting  72  by other means. For example, self-tapping screws (not shown) and bolts and nuts (not shown) can be used if so desired. The illustrated backing plate  71  includes an annular groove  75  formed therein, and an outer annular portion  76  which defines a shield.  
         [0020]     In the illustrated embodiment, the casting  72  includes an integrally cast abutment block  76  provided on an outer surface thereof. The abutment block  76  extends axially through an opening formed in the backing plate  71 . Also, a pair of integrally cast ears  78  and  79 , shown in  FIG. 2 , are provided on the casting  72 . Alternatively, the structure of the backing plate  71  and/or the casting  72  can be other than illustrated. For example, the backing plate  71  and the casting  72  can be cast integrally as one-piece and/or the ears  78  and  79  can be separate components and secured to the casting  72  by appropriate means.  
         [0021]     The drum-in-hat parking and emergency brake of the disc brake assembly  70  includes first and second brake shoes, indicated generally at  80  and  80 ′. Structurally, the brake shoes  80  and  80 ′ are essentially mirror images of one another, and like reference numbers are used to indicate similar parts. The brake shoes  80  and  80 ′ include respective web portions  81  and  81 ′ which are generally flat and crescent-shaped. Arcuate table portions  82  and  82 ′ are secured to the opposed outer curved surfaces of the web portions  81  and  81 ′, such as by welding. A friction lining  83  is secured to the outer arcuate surface of the table portion  82  of the brake shoe  80 , while a friction lining  83 ′ is secured to the outer arcuate surface of the table portion  82 ′ of the brake shoe  80 ′. The friction lining  83  includes an outer surface  83 A, and the friction lining  83 ′ includes an outer surface  83 A′. Openings  84  and  84 ′ are provided near the upper ends of the web portions  81  and  81 ′, respectively, of the brake shoes  80  and  80 ′. Also, openings  85  and  85 ′ are provided through the lower ends of the web portions  81  and  81 ′, respectively, of the brake shoes  80  and  80 ′, for a purpose to be discussed below.  
         [0022]     The first and second brake shoes  80  and  80 ′ are supported on the backing plate  71  by respective pivot pin and spring-clip assemblies, indicated generally at  86  and  86 ′, which are conventional in the art. As shown in  FIG. 1 , the upper ends of the web portions  81  and  81 ′ of the brake shoes  80  and  80 ′ extend into abutment with the opposed sides of the abutment block  76 .  
         [0023]     The drum-in-hat parking and emergency brake includes a first or upper coiled spring  87  and a second or lower coiled spring  88 . The upper coiled spring  87  has hooked ends which extend through the openings  84  and  84 ′ provided near the upper ends of the web portions  81  and  81 ′, respectively, so as to urge such upper ends thereof into abutment with abutment block  76 . The lower coiled spring  88  has hooked ends which extend through the openings  85  and  85 ′ formed through the lower ends of the web portions  81  and  81 ′, respectively, so as to urge the lower ends toward one another.  
         [0024]     The drum-in-hat parking and emergency brake further includes a manual adjusting mechanism  90 . The mechanism  90  is provided to compensate for thinning of the friction linings  83  and  83 ′ resulting from wear caused by repeated use of the brake assembly  70 . The illustrated adjusting mechanism  90  is conventional in the art and includes a pair of mutually threaded struts  91  and  92  having opposed slotted ends. The lower ends of the web portions  81  and  81 ′ of the brake shoes  80  and  80 ′, respectively, are received within the slotted ends of the struts  91  and  92 . A star wheel portion  91  a is formed integrally on the strut  91  or secured thereto by suitable means. An actuating lever  94  is supported between the upper ends of the web portions  81  and  81 ′ of the brake shoes  80  and  80 ′, respectively. The actuating lever  94  is connected by an actuation cable (not shown) which is conventional in the art and which is connected to a hand operated lever or similar manually operable parking and emergency brake mechanism for manually actuating the parking and emergency brake.  
         [0025]     The disc brake assembly  70  further includes an annular rotor  93  which is secured to a wheel (not shown) of the vehicle for rotation therewith. The illustrated rotor  93  includes a pair of radially extending opposed braking surfaces  93 A and  93 B, which are spaced apart from one another in a known manner, and an axially extending annular projection  93 C. The interior of the rotor  93  defines a finish machined inner cylindrical “drum” braking surface  93 D. When assembled, the brake shoes  80  and  80 ′ are disposed within the inner cylindrical braking surface  93 D. To effect parking and emergency braking action, the actuating lever  94  is pulled, causing the lever  94  to move the brake shoes  80  and  80 ′ apart from one another and into frictional engagement with the inner cylindrical braking surface  93   d  of the rotor  93  in a known manner.  
         [0026]     The hydraulically actuated service brake of the disc brake assembly  70  includes a generally C-shaped caliper  100  and an anchor plate  101 . The caliper  100  includes an inboard leg portion  102  and an outboard leg portion  103  which are interconnected by an intermediate bridge portion  104 .  
         [0027]     The illustrated anchor plate  101  includes a pair of outwardly extending arms  105  and  106 , the outboard ends thereof being interconnected by a single outer tie bar  107 . In the illustrated embodiment, the arms  105  and  106  are provided with pairs of notches  105 A and  106 A, respectively, formed therein to slidably support an inboard brake shoe  108  and an outboard brake shoe  109 , respectively. The inboard end of the arm  105  is provided with a pair of threaded apertures  105 B and  105 C, and the inboard end of the  106  is provided with a pair of threaded apertures  106 B and  106 C.  
         [0028]     The caliper  100  is slidably supported on a pair of bolts  110  secured to the anchor plate  101 . In particular, the bolts  110  extend through apertures (not shown) formed in the inboard leg  102  of the caliper  100 . The bolts  110  have respective threaded ends  110   a  which are received in the threaded apertures  105   b  and  106   b  formed in the arms  105  and  106 , respectively, of the anchor plate  101 . The bolts  110  permit the caliper  100  to slide in both the outboard direction (left when viewing  FIG. 3 ) and the inboard direction (right when viewing  FIG. 3 ). The anchor plate  100  is secured to the casting  72  by a pair of bolts  112 . The bolts  112  extend through apertures (not shown) formed in the casting  72 , and have respective threaded ends (not shown) which are received in the threaded apertures  105 C and  106 C of the arms  105  and  106 , respectively, of the anchor plate  101 .  
         [0029]     The illustrated inboard brake shoe  108  includes a backing plate  113  and a friction lining  114 . The inboard backing plate  113  includes opposed ends having circumferentially extending tabs  113 A and  113 B provided thereon, for supporting the inboard brake shoe  108  in the notches  105 A and  106 A of the arms  105  and  106 , respectively, of the anchor plate  101 . The outboard brake shoe  109  includes a backing plate  115  and a friction lining  116 . The outboard backing plate  115  includes opposed ends having circumferentially extending tabs  115 A and  115 B provided thereon, for supporting the outboard brake shoe  109  in the notches  105 A and  106 A of the arms  105  and  106  of the anchor plate  101 . Alternatively, the structure of the anchor plate  101  can be other than illustrated if so desired. The structure and operation of the drum-in-hat disc brake assembly  70  thus far described is conventional in the art.  
         [0030]     In accordance with the present invention, the outer surface  83 A and  83 A′ of the friction linings  83  and  83 ′, respectively, and/or the finish machined inner cylindrical braking surface  93 D of the rotor  93  are coated with a preselected material to increase the static coefficient of friction of the associated component part of the brake assembly. A suitable “coating” material can include iron oxide powder (Fe 2 O 3 ); aluminum oxide powder (Al 2 O 3 ); zircon powder; and calcium oxide powder (C a CO 3 ). Preferably, the powdered coating materials are a fine powdered mildly abrasive coating material having a particle size of about 5 microns or less. Alternatively, the size of the particles of the coating material can be greater than 5 microns if so desired. Also, other suitable powdered and non-powdered coating materials can be used if so desired.  
         [0031]     Preferably, in order to coat the outer surfaces  83 A and  83 A′ of the respective friction linings  83  and  83 ′ and/or the inner cylindrical braking surface  93 D of the rotor  93 , the surfaces are first coated with a liquid binder and then one of the above coating materials are applied. A suitable liquid binder can include a liquid phenolic resin and a silicate binder. Also, the liquid binder can be mixed with water or other non-binder liquids if so desired. Alternatively, the coating material can be mixed with the binder and then applied by any suitable process, such as for example, by spray, dip, blot, brush, ink-pad or roller coating processes. In addition, the coating is preferably applied of a uniform thickness to the selected surface(s) of the brake component and preferably the coating is applied to cover the entire area of such selected surface(s); however, the coating can be applied of a non-uniform thickness to the selected surface(s) and/or the coating can be applied to cover less than the entire area of such selected surface(s) can be coated if so desired.  
         [0032]     Turning now to  FIG. 7 , there is illustrated a first sequence of steps for coating the outer surfaces  83 A and  83 A′ of the respective friction linings  83  and  83 ′ and/or the inner cylindrical braking surface  93 D of the rotor  93 . As shown therein, the sequence includes the steps of: step  210 —applying a liquid binder to the selected brake component surface; step  212 —applying a coating material to the selected brake component surface already having the liquid binder applied thereto; step  214 —shaking off any excess coating material; and step  216 —allowing the coating material and the binder to dry and harden. Step  216  can be done at ambient temperature or at an elevated temperature if so desired.  
         [0033]     Turning now to  FIG. 8 , there is illustrated a second sequence of steps for coating the outer surfaces  83 A and  83 A′ of the respective friction linings  83  and  83 ′ and/or the inner cylindrical braking surface  93 D of the rotor  93 . As shown therein, the sequence includes the steps of: step  220 —mixing the coating material and the liquid binder into a slurry or paste mixture; step  222 —applying the mixture to the outer surface of the friction linings  83  and  83 ′ and/or the inner cylindrical braking surface  93   d  of the rotor  93 ; and step  224 —allowing the mixture to dry and harden. Step  222  can be accomplished by any suitable coating process, such as for example, by spraying, dipping, blotting, brushing, ink-padding or roller coating processes. Step  224  can be done at ambient temperature or at an elevated temperature if so desired.  
         [0034]     In accordance with the present invention, the “green” static coefficient of friction between the associated brake component parts is increased due to the increase of the “true contact area” between the parts so long as the selected coating material has acceptable frictional increasing properties. The term green static coefficient of friction as used herein means the static coefficient of friction between the associated new brake component parts before any burnishing or other contact/wear of the parts has occurred. The coating of the present invention is intended to function as disclosed herein until at least the friction linings are burnished and/or other contact/wear of the parts has occurred.  
         [0035]     As shown in  FIGS. 4-6 , at least one of the surfaces of the outer surfaces  83 A and  83 A′ of the friction linings  83  and  83 ′, respectively, and/or the inner cylindrical braking surface  93 D of the rotor  93  is not “true” but rather has surface irregularities or gaps therein, as will be discussed below. This means that there is not true or complete contact between the adjacent surfaces when the parking brake is applied. By coating the outer surfaces  83 A and  83 A′ of the respective friction linings  83  and  83 ′ and/or the inner cylindrical braking surface  93 D of the rotor  93  in accordance with the present invention, the true contact area between the surfaces can be increased or built-up thereby increasing the static coefficient of friction between the surfaces of these parts.  
         [0036]     In particular, as shown in the embodiment illustrated in  FIG. 4 , the outer surface  83 A of the friction lining  83  has surface irregularities or gaps, indicated generally at G 1  therein which prevent true or complete contact between the outer surface  83 A and the inner surface  93 D when the parking brake is applied. The surface irregularities G 1  on the outer surface  83 A of the friction lining  83  are typically the result of machining, such as for example, grinding or lathe turning. In accordance with this invention as shown in  FIG. 4A , the outer surface  83 A of the friction lining  83  is coated according to this invention with a suitable coating material C 1  to at least partially fill in and as illustrated, to preferably completely fill in the gaps G 1  so that the true contact area between these surfaces is increased.  
         [0037]     As shown in the embodiment illustrated in  FIG. 5 , the inner cylindrical braking surface  93 D of the rotor  93  has surface irregularities or gaps, indicated generally at G 2  therein which prevent true or complete contact between the outer surface  83 A and the inner surface  93 D when the parking brake is applied. The surface irregularities G 2  on the inner cylindrical braking surface  93 D of the rotor  93  are typically the result of machining, such as for example, grinding or lathe turning. In accordance with this invention as shown in  FIG. 5A , the inner surface  93 D of the rotor  93  is coated according to this invention with a suitable coating material C 2  to at least partially fill in and as illustrated, to preferably completely fill in the gaps G 2  so that the true contact area between these surfaces is increased.  
         [0038]     As shown in the embodiment illustrated in  FIG. 6 , the inner cylindrical braking surface  93 D of the rotor  93  has surface irregularities or gaps, indicated generally at G 3  therein and also the outer surface  83 A of the friction lining  83  has surface irregularities or gaps, indicated generally at G 4  therein which prevent true or complete contact between the outer surface  83 A and the inner surface  93 D when the parking brake is applied. (For clarity purposes, a dotted line  99  is included in  FIG. 6  to illustrate that the rotor gaps G 3  are below the line  99  and that the lining gaps G 4  are above the line  99 ). In accordance with this invention as shown in  FIG. 6A , the inner surface  93 D of the rotor  93  is coated according to this invention with a suitable coating material C 3  to at least partially fill in and as illustrated, to preferably completely fill in the gaps G 3 . And also the outer surface  83 A of the friction lining  83  is coated according to this invention with a suitable coating material C 4  to at least partially fill in and as illustrated, to preferably completely fill in the gaps G 4  so that the true contact area between these surfaces is increased.  
         [0039]     One example of a suitable coating material which can be used to coat the outer surfaces  83 A and  83 A′ of the friction linings  83  and  83 ′, respectively, and/or the inner cylindrical braking surface  93 D of the rotor  93  includes two components, namely, a liquid binder and an abrasive particle material. The liquid binder is preferably an inorganic binder comprised of water and sodium silicate (Na 2 SO 4 ). The abrasive particle material is iron oxide (Fe 2 O 3 ). The iron oxide is preferably in the range from about 70 percent pure iron oxide (raw mined) to 100 percent pure iron oxide (synthetically made). In an example of an 85 percent pure iron oxide version, the 15 percent remainder is comprised of around 9 percent silica (SiO 2 ), around 3 percent aluminum oxide (Al 2 O 3 ), around 1 percent magnesium oxide (MgO), around 0.5 percent calcium oxide (CaO), around 0.5 percent manganese (Mn), and around 1 percent moisture. The concentration ratio by weight of iron oxide to silicate in the particular coating is in the range from about 12 to 1 to about 2 to 1. Preferably, the concentration ratio by weight of iron oxide to silicate in the particular coating is in the range from about 8 to 1 to about 4 to 1. More preferably, the concentration ratio by weight of iron oxide to silicate in the particular coating is approximately 6 to 1. Also, it is believed to be preferable to increase the amount of the silicate which is used in the liquid binder because it results in a harder coating. Also, it is believed that the amount of water which is used in the liquid binder can be varied according to particular processing needs, such as for example, temperature and humidity, since the water is used primarily as a processing agent will mostly disappear in the finished product. The coating is applied to form a relatively thin layer of generally uniform thickness on the outer surfaces  83 A and  83 A′ of the friction linings  83  and  83 ′, respectively, and/or the inner cylindrical braking surface  93 D of the rotor  93 . The thin layer of coating has a generally uniform thickness in the range from about 0.0001 inches to about 0.01 inches. Preferably, the coating has a generally uniform thickness in the range from about 0.0005 to about 0.0025 inches. More preferably, the coating has a generally uniform thickness in the range from about 0.001 to about 0.002 inches.  
         [0040]     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been described and illustrated in its preferred embodiments. However, it must be understood that the invention may be practiced otherwise than as specifically explained and illustrated without departing from the scope or spirit of the attached claims.