Abstract:
A disc brake for a vehicle wherein first and second friction member have projections thereon that are located in grooves in first and second rails of an anchor. On movement of the first and second frictions members during a brake application, the projections slide in the grooves to maintain a parallel alignment between a braking surface thereon and radial braking surfaces on a rotor and at the same time transmit reactions forces into a rotor to oppose the rotation of the rotor. Braking surfaces on the projections engage the rotor to assist in opposing the rotation of a rotor during each brake application.

Description:
This invention relates to a disc brake wherein first and second friction members each of which have projections thereon that are retained in grooves in an anchor to align engagement surfaces thereon with a rotor and to transmit reaction forces into an anchor during a brake application. 
   BACKGROUND OF THE INVENTION 
   U.S. Pat. Nos. 4,044,864; 4,219,106; 4,200,173; 4,335,806 and 5,551,537 are typical prior art disc brakes which have an anchor with support surfaces or rails therein that are spaced apart from each other to receive ears on carrier members that slide on the rails to guide first and second friction pads toward a rotor and carry reaction forces into the anchor to resist the rotation of the rotor during a brake application. While the shape of a carrier member may be different as illustrated in U.S. Pat. Nos. 5,396,972; 6,578,680 and 6,994,190 all such carrier members are normally made from steel or iron having a compatible co-efficient of friction with materials of the anchor such that during a brake applications excessive wear does not occur. Unfortunately, in some instances a slipper or sleeve member may be required to be placed between the ears and anchor to reduce wear and provide a co-efficient of friction that does not effect the movement during a brake application. In evaluating disc brakes, it is estimated that the weight of the carrier members may account for up to one percent of a disc brake and this invention discloses that the overall weight of a disc brake could be reduced by eliminating the carrier members while functioning in an equivalent manner. 
   SUMMARY OF THE INVENTION 
   The present invention discloses a disc brake wherein peripheral projections extend from the friction member, are received in guides on an anchor to align braking surfaces thereon with a rotor and directly communicate reaction forces into an anchor during a brake application. 
   In more particular detail, the disc brake has an anchor that is fixed to a housing of a vehicle with spaced apart first and second rails each of which have grooves therein to receive the projections and align a braking surfaces on the first and second friction members with first and second radial braking surfaces located on opposite sides of a rotor. The friction members are made from a semi-metallic material and the projections have a shape that corresponds to the grooves in the anchor. A caliper is connected to the anchor through pins that are attached to ears that extend from a caliper housing to align a bore and piston retained therein and arms that span the rotor with the first and second rails. In response to an operator input, pressurized fluid is presented to the bore that acts on the piston to move the first friction member toward and into engagement with the first radial braking surface on the rotor and acts on the caliper housing to pull the arms and correspondingly the second friction member toward and into engagement with the second radial braking surface of the rotor to effect a brake application. The first and second friction members move toward the rotor during a brake application with the projections sliding in the grooves in the first and second rails to maintain a desired alignment between braking surfaces on the friction members and the braking surfaces while at the same time reaction forces generated in opposing the rotation of the rotor are directly carried through the projections into the anchor. In this disc brake, the piston and arms of the caliper are made of a material having a coefficient of friction that is different than either the rotor or the friction members. Should excessive wear occur in either the piston or arms as may happen over a period of time as a result of the engagement with the friction members with the anchor, a loosely retained first shield member is placed between the piston and first friction member and loosely retained second shield member is placed between the arms and the second friction members. The shield members are preferable made of a thin sheet of steel that would protect the piston and arms from wear as a result of numerous engagements with the friction members during an expected life of a friction member. In addition, each shield has a plurality of axial tabs each of which has a length that extend toward the rotor and which are designed to engage the rotor when the thickness of a friction member is reduced to a predetermined thickness to provide an audio indication of a remaining thickness of the friction member. If desired one or all of the tabs could be rolled to hold an electronic sensor such that on engagement with the rotor an electrical circuit is closed and an indicator activated to provide a visual indication of the thickness of the friction member. 
   An object of the present invention is to provide a disc brake with peripheral projections on first and second friction members that are received in grooves in an anchor to guide the friction members into engagement with a rotor and to carry reaction forces into the anchor to oppose the rotation of the rotor during a brake application. 
   A further object of this invention is to provide a disc brake having a phenolic piston through which an actuation force is applied to a friction member with a shield to attenuate wear between the piston and a friction member through repeated engagements that would occur during a projected life of the friction member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is schematic illustration of a disc brake according to the present invention; 
       FIG. 2  is an exploded view of the component of the disc brake of  FIG. 1 ; 
       FIG. 3  is a sectional view taken along line  3 - 3  of  FIG. 1 ; 
       FIG. 4  is a sectional view taken along line  4 - 4  of  FIG. 1 ; 
       FIG. 5  is a sectional view taken along line  5 - 5  of  FIG. 4 ; 
       FIG. 6  is an enlarged view of an alternate embodiment of a portion of the shield of  FIG. 3 ; 
       FIG. 7  is a sectional view taken along line  7 - 7  of  FIG. 6 ; 
       FIG. 8  is a sectional view of the disc brake of  FIG. 5  after the friction material has worn to a predetermined thickness; 
       FIG. 9  is a sectional view of the disc brake of  FIG. 8 ; and 
       FIG. 10  is sectional view of the shield of  FIG. 7  after the friction material has worn to a predetermined thickness. 
   

   DETAILED DESCRIPTION 
   In the specification where similar components are used in more than one situation the component may be identified by a number or a same number plus depending on a relationship with other components. 
   The disc brake  10  illustrated in  FIGS. 1 ,  2 ,  3 ,  4  and  5  functions in a manner similar to disc brakes disclosed in U.S. Pat. Nos. 4,200,173 and 5,810,122 wherein an anchor or support member  12  is fixed to a knuckle  14  as disclosed in U.S. Pat. No. 5,988,761 for a brake system of a vehicle. The anchor or support member  12  for such disc brakes being distinguished by first  16  and second  18  spaced apart parallel rails and corresponding first  20  and second  22  parallel spaced apart bores and having an integral caliper  24  with a housing  26  that is separated from arms  30 ,  30 ′ by a bridge  28  that spans a rotor  50 . The caliper  24  being connected to the anchor  12  by guide pins  32 ,  32 ′ that are respectively attached to ears  36  and  38  that extend from the caliper housing  26  and the first guide pin  32  is mounted to slide in the first bore  20  and the second guide pin  32 ′ is mounted to slide in the second bore  22  in the support member  12 . With the first  20  and second  22  bores being parallel to each other, the first guide pin  32  and the second guide pin  32 ′ align face  46   a  on a first friction member  46  and face  48   a  on a second friction member  48  in a parallel relationship adjacent a first face  50   a  and a second face  50   b  on a rotor  50  that is connected to rotate with an axle of the vehicle. The housing  26  has a bore  40  in which a piston  42  is located to define an actuation chamber  44  that is supplied with pressurized fluid under the control of an operator. The first friction member  46  is connected to piston  26  while the second friction member  48  is connected to arms  30 ,  30 ′. When an operator desires to effect a brake application, pressurized fluid is supplied to an actuation chamber  44  of bore  40  that simultaneously acts on piston  42  and the bottom  41  of bore  40 , to develop an actuation force that moves face  46   a  on the first friction member  46  toward and into engagement with face  50   a  and face  48   a  on the second friction member  48  toward and into engagement with face  50   b  of rotor to create a clamping force that retards the rotation of rotor  50  to effect a brake application. The clamping force created through the engagement of face  46   a  and face  48   a  with rotor  50  causes the first  46  and second  48  friction members to rotate in a direction of the leading edge engagement such that a reaction force corresponding to the clamping force applied to retard the rotation of rotor  50  is transmitted into either rail  16  or  18  of anchor  12  depending on the rotational direction of the rotor. 
   The clamping force is a function of the area of the engagement surface of the faces  46   a  on the first friction member  46  and face  48   a  on the second friction member  48  times the input force derived from the area of piston  42  times the pressurized fluid supplied to the actuation chamber  44 . The area of the engagement surfaces of the first  46  and second  48  friction members includes the projections  47  and  49 , see  FIG. 2  and as a result provides an improvement over known disc brakes since the input force is applied over a larger area from a same level of pressurized fluid that is supplied to the actuation chamber  44 . 
   In more particular detail, the disc brake  10  is characterized in that the first rail  16  of the anchor  12  has a first groove  60  and the second rail  18  of the anchor  12  has a second groove  60 ′ therein. Each groove  60 , 60 ′ having a semi-spherical shape that extends from a first side  62  to a second side  64  of the anchor  12  and in that the first friction member  46  and the second friction member  48  each have projections  47  and  49  that are respectively mated in the first groove  60  and second groove  60 ′. Thus, the shape of the projections and grooves allows reaction forces to be transmitted in a smooth manner into the rails  16 ,  18  without damage to the friction materials. 
   The first  46  and second  48  friction members are identical and made from a semi-metallic composition of material having a mixture that is generically defined by metal particles or metal oxide fibers, elastomers and modifiers retained in a matrix by a thermosetting resin. The resulting friction member having a substantially stable coefficient of friction up to 1000 degree Fahrenheit with a desired coefficient of friction and a strength in compression of at least 40,000 psi. 
   Each friction member  46 , 48 , as best illustrated in  FIG. 2 , is further defined by having an arcuate shape with a uniform thickness with projections  47 , 49  having a semi-spherical shape corresponding to grooves  60 , 60 ′ that extend there from. 
   The piston  26  for a disc brake is normally made from a phenolic material which has a lower coefficient of friction than either the caliper  12  or the friction members  46 . In order to prevent scaring of the piston  26 , a barrier or shield  70  is placed between the piston  26  and the friction member  46 . The shield  70 , as best shown in  FIGS. 2 ,  3 ,  4  and  5  is defined by a sheet of metal having a thickness of 0.05 mm and a shape that matches the engagement surfaces  46   a , 48   a  of the friction members  46 , 48 . The shield  70  is resiliently aligned on the friction members  46 , 48  by a plurality of tabs  72 , 72 ′ . . .  72   n  that engage the sides of the friction members  46 , 48  at four points with tab  72  being located adjacent projection  47  and tab  72 ″ being located adjacent projection  49 . Tabs  72 , 72 ′ . . .  72   n  each have a length that are a function of the compressive strength of the composition of material of the matrix of the friction members  46 , 48  but most often will be from about one fourth to one third the original thickness of the friction members  46 , 48 . The end of the tabs  72 , 72 ″ engaging the rotor  50  to provide a audible noise when the thickness of the friction material is worn to that thickness and may not have sufficient strength to carry a maximum reaction force into an anchor  12 . 
   Under some circumstances either or both tab  72   a  or tab  72   a ″ may be rolled in a manner as illustrated in  FIGS. 6 and 7  so as to retain a sensor  80 ,  80 ′. Sensor  80  is held by the tab  72   a  and sensor  80 ′ would be held by  72   a ″ such that when an end  82  thereon engages rotor  50  an electrical circuit  84  is closed and an indicator light  86  is activated to provide a warning that the thickness of a friction members  46 ,  48  has been reduced to a predetermined thickness and the area of the either projection  47  or  49  could be crushed or damaged from the transmission of a maximum reaction force into anchor  12 . 
   When an operator desires to effect a brake application in a vehicle equipt with disc brake  10 , pressurized fluid is supplied to actuation chamber  44  that acts on piston  42  to move the first friction member  46  toward and into engagement with brake surface  50   a  on rotor  50  and acts on the bottom of bore  41  to pull arms  30 ,  30 ′ and the seconds friction member  48  toward and into engagement with brake surface  50   b  on rotor  50  to create a clamping force from which reaction forces are carried into anchor  12  by way of projections  47 , 47 ′ or  49 , 49 ′ depending on the direction of rotation of the rotor  50 . As the first  46  and second  48  friction members move toward the rotor  50  projections  47 ,  47 ′ and  49 ,  49 ′ axially slide in grooves  60 ,  60 ′ acutely rotate about the axis of the rotor  50  toward the anchor  12  to transmit the reaction forces into rails  20  and  22 . The reaction force is spread over the axial surface area of projections  47 ,  47 ′ or  49 ,  49 ′ depending on the rotational direction of rotor  50 . When the friction material has its original thickness as illustrated in  FIG. 5 , the reaction forces as transmitted through the projections  47 ,  47 ′,  49 ,  49 ′ is relatively low however as the thickness of the friction material decreases as a result of wear as illustrated in  FIG. 8  the surface area decreases and as a result there is a corresponding increase in the unit of force transmitted through a projection. When this increase in force reaches the crushing force or force wherein a projection  47 ,  47 ′,  49 ,  49 ′ may bend, it is necessary to replace a friction member. The tabs  72 ,  72 ′ that are located on the shield  70  are resiliently attached to a friction member  46 , 48 , have a length that is selected such that end  82  thereof engage the rotor  50  to provide a audible warning when the thickness has been reduced to the predetermined thickness or with the second embodiment of  FIG. 6  end  82  of sensor  80  contacts rotor  50  as illustrated in  FIG. 10  to closes a circuit  84  and activated light  86  to provide a visual warning of such a reduction in thickness prior to a reduction in surface area where a crushing force could impede the transmission of a reaction force into the anchor  12  during a brake application. 
   On termination of the presence of pressurized fluid supplied to chamber  44 , return seal  90  acts on piston  42  to move the first friction member  46  away from the rotor  50  to define a running clearance between faces  46   a  and surface  50   a  and face  48   a  and surface  50   b  such that rotor  50  may freely rotate. 
   It is further suggested that the projections  47 , 47 ′, 49 , 49 ′ may be coated with an anti-oxidization agent to reduce the possibility of an increase in the sliding resistance in grooves  60 , 60 ′ should the disc brake  10  be inactive for a period of time.