Abstract:
An exemplary embodiment providing one or more improvements includes a brake cooling apparatus and method in which heat is conducted from a brake pad to a heat dissipating portion through a heat receiving portion and a heat dissipating portion dissipates the heat into a cooling medium.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority from copending U.S. patent application Ser. No. 11/439,401, filed on May 22, 2006 and U.S. Provisional Application Ser. No. 60/683,764, filed on May 24, 2005, U.S. Provisional Application Ser. No. 60/683,735, filed on May 24, 2005 and U.S. Provisional Application Ser. No. 60/711,760, filed Aug. 29, 2005, along with U.S. patent application Ser. No. 11/439,393, filed on May 22, 2006, all of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    A typical disk brake system of a vehicle includes a caliper with one or more pistons that hydraulically force brake pads toward one another and into contact with a rotor that spins relative to the caliper when the vehicle is moving. The pads have a high coefficient of friction so that when they are forced into contact with the spinning rotor during braking, the speed at which the rotor is spinning is decreased by the frictional contact between the pad and the rotor. As the rotor speed decreases, the kinetic energy of the rotor is converted into heat. Substantial amounts of heat can be generated in the brake pads. Brake pad temperatures can reach well over the melting point of aluminum, greater than about 600 degrees Celsius. Many different techniques or mechanisms are used to remove heat from the disk brake system through the rotor. An example of one mechanism is to provide an integral vent in the rotor through which ambient air moves when the rotor is spinning to cool the rotor. Prior to the present invention, heat was usually primarily removed from the brake pads through contact with the rotor, and through the brake fluid and the brake caliper via the hydraulic pistons. 
         [0003]    The lack of a good thermal sink for the brake pad can lead to significant problems in some instances. One problem that arises when brake pads get hot is a condition in which the heat from the pad is conducted through the caliper piston to the brake fluid and causes the fluid to boil. Heat conducted through the caliper piston to the brake fluid can also lead to damaged brake caliper seals or warped caliper pistons. Another problem is a condition in which the brake pads get hot enough that they vaporize on contact with the rotor. In this condition, a cushion of gas is produced between the pad and the rotor which prevents the pad from contacting the rotor. Both of the above conditions lead to a decrease in brake efficiency which is also called fade. In extreme cases, the above conditions can result in a complete failure of the brake system. 
         [0004]    Prior attempts have been made to address the problems arising from excessive heat in the brake pad and several patents have been issued which relate to cooling disk brake systems. However, these patents generally depend on the manufacture of specifically designed custom calipers or rotors that replace or modify the original equipment calipers on the vehicle. Examples of patents which require specially manufactured custom calipers are U.S. Pat. No. 5,002,160 and U.S. Pat. No. 6,446,766. 
         [0005]    The &#39;160 patent discloses a brake caliper that is specially manufactured to have a ventilation channel for ducting ambient air to a position between the brake pad backing plate and the piston of the caliper. Someone wishing to utilize the disk brake system disclosed in the &#39;160 patent for cooling their brake pads would have to replace their calipers with the calipers disclosed in the &#39;160 patent. Since the calipers are the most expensive component of the brake system, replacing the calipers with the specially manufactured calipers of the &#39;160 patent is likely to be an expensive proposition. 
         [0006]    The &#39;766 patent discloses a specially constructed brake caliper which includes a duct that is formed inside of the body of the caliper. The duct is designed to direct air to a series of specially constructed hydraulic pistons. The pistons each have a radiator element through which the air from the duct flows to dissipate heat. The &#39;766 patent is an example of a type of device which relies on a modified caliper and modified hydraulic pistons in an attempt to cool the brake pads. Specially constructing the caliper with air flow ducts adds to the complexity of the caliper and most likely also adds to the cost of manufacturing the caliper as well. In addition to the added cost of the caliper, the device described in the &#39;766 patent also requires the hydraulic pistons to have radiator elements which would also have to be specially manufactured thereby increasing the cost of the device even further. 
         [0007]    Other U.S. patents also require modified calipers in attempts to cool the brake pads in a disk brake system. What is needed is an effective disk brake pad cooling system which can be economically utilized without modifying or replacing expensive existing brake system components. 
         [0008]    The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon reading of the specification and a study of the drawings. 
       SUMMARY 
       [0009]    The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
         [0010]    In general, a brake pad cooling apparatus and method are described for use with a disk brake system for a moveable vehicle. The disk brake system has a caliper which includes a hydraulic piston for moving a brake pad into forced contact with a rotor. The rotor rotates when the vehicle is moving and forced contact between the rotor and the brake pad reduces the rate at which the rotor is rotating to slow the movement of the vehicle. The contact also generates heat in the brake pad. The cooling apparatus comprises a thermally conductive sheet for positioning into thermal communication with the brake pad. The conductive sheet includes a thermally conductive material for conducting heat away from the brake pad. The cooling apparatus also includes a heat sink which is thermally connected to the conductive sheet to allow heat to pass from the conductive sheet to the heat sink. The heat sink is positioned away from the brake pad when the conductive sheet is in thermal contact with the brake pad and the heat sink includes at least two cooling fin members for dissipating heat into the surrounding air. During operation, the heat sink receives heat from the brake pad through the conductive sheet and dissipates the heat into the surrounding air to cool the brake pad. 
         [0011]    In another embodiment, a method for cooling a brake pad in a disk brake system of a moveable vehicle is disclosed. The disk brake system has a caliper which includes a hydraulic piston for moving a brake pad into forced contact with a rotor that rotates when the vehicle is moving. The forced contact between the rotor and the brake pad reduces the rate at which the rotor is rotating to slow the movement of the vehicle and the contact generates heat in the brake pad. A thermally conductive sheet is inserted between the brake pad and the hydraulic piston to receive the heat from the brake pad. A heat sink that includes at least two cooling fin members and which is attached to the thermally conductive sheet is positioned at a location that is away from the brake pad and is generally surrounded by air. The heat sink receives heat from the brake pad through the conductive sheet and dissipates the heat to the surrounding air with the cooling fin members. 
         [0012]    In yet another embodiment, a brake pad cooling apparatus and associated method are described for use with a disk brake system for a moveable vehicle. The disk brake system has a caliper which includes a peripheral outline and has a hydraulic piston for moving a brake pad into forced contact with a rotor. The rotor rotates when the vehicle is moving and forced contact between the rotor and the brake pad reduces the rate at which the rotor is rotating to slow the movement of the vehicle. The contact also generates heat in the brake pad. A heat receiving portion of the apparatus is in thermal communication with the brake pad and a distal heat dissipating portion extending out of the peripheral outline of the caliper is in thermal communication with the heat receiving portion. The heat dissipating portion receives heat from the heat receiving portion by thermal conduction and thereafter dissipates the heat into the ambient environment. 
         [0013]    In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view of disk brake coolers according to the present disclosure installed in a caliper of a disk brake system. 
           [0015]      FIG. 2  is an enlarged perspective view of the disk brake coolers shown in  FIG. 1 . 
           [0016]      FIG. 3  is a cross section view of the disk brake coolers and caliper taken along a cross sectional line  3 - 3  shown in  FIG. 1 . 
           [0017]      FIG. 4  is a partial cut away view of the disk brake coolers and caliper shown in  FIG. 1 . 
           [0018]      FIG. 5  is a partially cut away elevation view of the disk brake coolers and caliper shown in  FIG. 1 . 
           [0019]      FIG. 6  is a perspective exploded view illustrating components of the disk brake cooler shown in  FIG. 1 . 
           [0020]      FIG. 7  is a view of another disk brake cooler according to the present disclosure installed in a caliper of a disk brake system. 
           [0021]      FIG. 8  is a cross section view of the disk brake cooler and caliper shown in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Disk brake coolers  20   a  and  20   b,  which may be referred to individually or collectively by the reference number  20 , according to the present invention are shown in  FIG. 1  installed in a disk brake caliper  24 . Caliper  24  is mounted to a chassis of a vehicle (not shown) for use as part of a disk brake system  26  that includes a rotor  28  which rotates as the vehicle moves. Brake pad assemblies  30  and  32  ( FIG. 3 ) engage rotor  28  to slow or stop the rotation of rotor  28  which then slows or stops the vehicle movement. When brake pad assemblies  30  and  32  engage and slow or stop the rotation of rotor  28 , the rotational or kinetic energy of rotor  28  and the momentum of the vehicle are converted into heat in brake pad assemblies  30  and  32  and in rotor  28 . 
         [0023]    Disk brake coolers  20 , one of which is shown in  FIG. 2 , take advantage of thermal conduction to flow heat from brake pad assemblies  30  and  32  to a position where the heat is more efficiently transferred to the atmosphere. Brake coolers  20  each include a thermally conductive sheet  34  and a heat sink  36 . Brake cooler  20   a  includes thermally conductive sheet  34   a  and heat sink  36   a,  and brake cooler  20   b  includes thermally conductive sheet  34   b  and heat sink  36   b.  Sheets  34   a  and  34   b  are integrally formed or connected to heat sinks  36   a  and  36   b,  respectively, for conducting heat between sheets  34   a  and  34   b  and heat sinks  36   a  and  36   b.    
         [0024]    When brake coolers  20   a  and  20   b  are installed in caliper  24  ( FIG. 1 ), conductive sheets  34   a  and  34   b  are in thermal contact with brake pad assemblies  30  and  32 , respectively, and heat is transferred from brake pad assemblies  30  and  32  to sheets  34   a  and  34   b,  respectively. The heat is conducted from sheet  34   a  to heat sink  36   a,  and from sheet  34   b  to heat sink  36   b.  Heat sinks  36  extend out of caliper  24 , as shown in  FIGS. 1 ,  3  and  5 , where the heat sinks  36  transfer the heat to a cooling medium, such as surrounding air or a fluid in a cooling system, thereby removing the heat from brake assemblies  30  and  32  and decreasing the temperature found in the brake assemblies. 
         [0025]    Caliper  24 , shown in  FIGS. 1 and 5 , is bolted to the vehicle suspension or other components of the vehicle chassis (not shown) through mounting holes  38  and  40 . The caliper defines a peripheral outline  42 , from which heat sinks  36  shown in  FIG. 5  extend when brake coolers  20   a  and  20   b  are installed in caliper  24 . Heat sinks  36  are positioned at least partially extending from the peripheral outline  42  to subject heat sinks  36  to greater air flow for cooling. 
         [0026]    Details of the operation of disk brake coolers  20   a  and  20   b  are discussed below along with details of the operation of disk brake system  26 . In many instances brake coolers  20   a  and  20   b  can be essentially the same as one another except for their orientation with respect to one another when installed in the caliper  24 . Caliper  24 , of disk brake system  26 , includes an inner caliper half  44  and an outer caliper half  46  which are connected together using caliper bolts  48  ( FIGS. 1 and 4 ). Guide pins  50  and  52  extend between inner and outer caliper halves  44  and  46  for restraining brake pad assemblies  30  and  32  against unwanted movement relative to caliper  24  during application of brake pad assemblies  30  and  32  to rotor  28  and during other times. Inner caliper half  44  ( FIG. 3 ) houses an inner hydraulic piston  54  which moves within the inner caliper half to force brake pad assembly  30  into contact with rotor  28 . Outer caliper half  46  houses an outer hydraulic piston  56  which moves within outer caliper half  46  to force brake pad assembly  32  into contact with rotor  28 . 
         [0027]    Inner hydraulic piston  54  is positioned in an inner cylinder bore  58  of inner caliper  44 , ( FIG. 3 ) for movement toward and away from rotor  28 . A hydraulic seal  60  creates a fluid tight seal between the outer surface of piston  54  and the inner surface of cylinder bore  58  which together define an inner fluid reservoir  62 . Outer hydraulic piston  56  is positioned in an outer cylinder bore  64  of outer caliper  46  for movement toward and away from rotor  28 . A hydraulic seal  66  creates a fluid tight seal between the outer surface of piston  56  and the inner surface of outer cylinder bore  64  which together define an outer fluid reservoir  68 . An inner dust shield  70  and outer dust shield  72  are positioned to prevent dust and other material from contacting hydraulic seals  60  and  66 , respectively. 
         [0028]    Inner and outer fluid reservoirs  62  and  68  are fluidly connected to one another with a fluid passage (not specifically shown) and the inner fluid reservoir  62  is connected to a hydraulic brake line  73  ( FIG. 1 ) through an orifice  74  ( FIGS. 3 and 5 ) in inner caliper  44 . Inner and outer fluid reservoir  62  and  68  ( FIG. 3 ), the fluid passage and the hydraulic brake line are filled with a brake fluid (not shown) and excess air is removed through a bleeder screw  76  ( FIG. 1 ). 
         [0029]    In order to move the brake assemblies into forced contact with rotor  28 , brake fluid is moved from brake line  73  into inner fluid reservoir  62  through orifice  74  and to outer fluid reservoir  68  through the fluid passage. Fluid reservoirs  62  and  68  expand to receive the increased amount of brake fluid and pistons  54  and  56  are thereby moved toward rotor  28 , which moves the brake assemblies into contact with rotor  28 . Movement of brake assemblies  30  and  32  away from rotor  28  is accomplished when hydraulic pressure is released such that brake fluid is release from fluid reservoirs  62  and  68  and fluid reservoirs  62  and  68  are contracted. Release of brake fluid from fluid reservoirs  62  and  68  causes pistons  54  and  56  to move away from rotor  28  thereby relieving the forced contact between brake assemblies  30  and  32  and rotor  28 . Inner and outer dust shields  70  and  72  contribute to the movement of pistons  54  and  56  away from rotor  28 . Although the present example is described in conjunction with a caliper having a single piston on either side of the rotor, the disk brake cooler can be used with other calipers having multiple hydraulic pistons on either side, or a single piston on one side. 
         [0030]    Brake pad assemblies  30  and  32  each include two components, a brake pad  78  and a backing plate  80 , as shown in  FIG. 3 . Brake pad assembly  30  includes brake pad  78   a  and backing plate  80   a  while brake pad assembly  32  includes brake pad  78   b  and backing plate  80   b.  Brake pads  78   a  and  78   b  are forced toward one another to contact rotor  28  with hydraulic pistons  54  and  56  ( FIG. 3 ) through backing plates  80   a  and  80   b.  Contact between pads  78  and rotor  28  causes rotor  28  to slow and also causes pads  78  and rotor  28  to heat up. Heat from pads  78   a  and  78   b  normally conducts to backing plates  80   a  and  80   b  and pistons  54  and  56 , respectively, as well as to caliper  24  and to the brake fluid, among other parts. Brake pads  78  are typically made of a combination of several materials that are able to withstand certain temperatures and which also have an abrasive surface to create the friction between pads  78  and rotor  28  when pads  78  are forced into contact with rotor  28 . Brake pads  78  are typically cast or otherwise fastened to backing plates  80 , which are used to connect brake assemblies  30  and  32  to caliper  28 . 
         [0031]    Backing plates  80  include slots or holes  82  and  84  ( FIGS. 1 and 3 ) which interact with guide pins  50  and  52  to generally constrain brake pad assemblies  30  and  32  against movement relative to caliper  24  in any direction except toward and away from one another. Other methods are also used for constraining backing plates, such as clips (not shown). When brake pads  78  are pressed against rotor  28 , a rotational force of the rotating rotor is applied to brake pad assemblies  30  and  32  from rotor  28 . Holes  82  and  84  engage pins  50  and  52  to resist this rotational force and in this way the rotational force of rotor  28  is resisted by caliper  24  when brake pads  78  are pressed against rotor  28 . Backing plates  80  are constructed of a material which is able to resist the forces at holes  82  and  84  and pins  50  and  52 . Backing plates  80  also have yield properties which resist deformation when hydraulic pistons  54  and  56  are forcing brake pads  78  into contact against rotor  28 . 
         [0032]    Brake coolers  20   a  and  20   b  shown in  FIGS. 1 and 3  are positioned with conductive sheets  34   a  and  34   b  of brake coolers  20   a  and  20   b  interposed between backing plates  80   a  and  80   b  and pistons  54  and  56 , respectively. Brake coolers  20   a  and  20   b  include guide pin slots or holes  86  ( FIGS. 2 and 5 ) which align with guide pins  50  and  52  or other mounting hardware of the brake pad assemblies when brake coolers  20   a  and  20   b  are installed in caliper  24 . Conductive sheets  34  shown in  FIG. 2  include a shape that is similar to a shape of backing plates  80 . 
         [0033]    To engage pads  78  against rotor  28  when brake coolers  20   a  and  20   b  are installed ( FIG. 3 ), pistons  54  and  56  apply pressure to backing plates  80   a  and  80   b  through conductive sheets  34   a  and  34   b,  respectively. Since considerable pressure is applied by pistons  54  and  56 , conductive sheets  34  include a high yield strength material such as stainless steel that resists deformation from the applied pressures. When positioned as shown in  FIGS. 1 and 3 , the heat from brake pads  78  is transferred through backing plates  80  to conductive sheets  34 . Therefore, the high yield material of conductive sheets  34  is also able to resist deformation at the temperatures of the heat conducted through backing plates  80 . 
         [0034]    Conductive sheets  34  conduct the heat from backing plates  80  to heat sinks  36 . In order to maximize the conduction of heat to heat sinks  36 , conductive sheets  34  include a high thermal conductivity material such as copper. Conductive sheets  34  of the present example have a thermal conductivity greater than 100 Watts/meter-Kelvin. Other materials can also be used for the conductive sheet, for example copper tungsten has high yield strength and a high thermal conductivity. 
         [0035]    When one of the conductive sheets is inserted between the backing plate and the piston, the overall distance between the piston and brake pad is increased. This makes pads  78  closer to rotor  28  when brake coolers  20   a  and  20   b  are installed than when brake coolers  20   a  and  20   b  are not installed by an amount generally equal to the thickness of conductive sheet  34 . A thicker conductive sheet generally has an ability to conduct more heat than a thinner conductive sheet of the same material. However, if the conductive sheet is too thick, then the brake pad assembly and the conductive sheet of the brake cooler will not fit between the piston and the rotor. The thickness of conductive sheets  34  are chosen to maximize the thermal cross section of the thermal path to heat sink  36  while minimizing the impact on displacing a set of new brake pad assemblies. Conductive sheets  34  of the present example are 1 millimeter thick. 
         [0036]    Heat sinks  36  receive heat from brake pad assemblies  30  and  32  through conductive sheets  34 . Heat sinks  36  shown in  FIG. 1  are positioned remotely away from brake pads  78  and externally to caliper  24  where heat sinks  36  are in contact with surrounding air flow. As is apparent from the configuration and position shown in  FIG. 1 , heat sinks  36  will not interfere with a wheel (not shown) when the wheel is attached to the vehicle. 
         [0037]    Heat sinks  36  shown in  FIGS. 1 and 2  include an arrangement of cooling fin members  88  which extend in a row. Cooling fin members  88  provide a large surface area in which to transfer heat from heat sink  36  to the surrounding air. Cooling fin members  88  shown in  FIG. 4  extend in a direction that is perpendicular to a plane defined by rotor  28 . Typically two or more cooling fin members provide surface area for dissipating heat conducted to heat sinks  36  from conductive sheets  34  when the heat sinks are exposed to air flow in the position shown in  FIG. 1 . The cooling fin members can be formed in a variety of different shapes, so long as the shape allows the fin member to dissipate heat. In addition, the cooling fin members can be arranged in the heat sink in a variety of different ways so long as the arrangement allows the fin members to dissipate heat. For example, the cooling fin members can be transverse to the plane of the rotor and need not be parallel with respect to one another. 
         [0038]    In the example shown in  FIG. 1 , heat sinks  36  are attached to conductive sheets  34  using brazing or mechanical fasteners. Since heat sinks  36  are not subject to the same pressures that conductive sheets  34  are, heat sinks  36  can be constructed of copper. In some instances the size and weight of heat sink  36  is such that high gravity force (G-force) maneuvering of the vehicle will cause stress in the connection between heat sink  36  and conductive sheet  34 . One way in which to prevent heat sink  36  from folding or otherwise deforming conductive sheet  34  in these instances is to form heat sink  36  with a shape that prevents a single linear stress point such as a curved shape  90  shown in  FIG. 2 . 
         [0039]    Installation of brake coolers  20   a  and  20   b  is fairly simple and in most instances will be similar to the installation of brake pad assemblies  30  and  32 . Once access to caliper  24  is gained, pistons  54  and  56  are moved into caliper  24  away from rotor  28  thereby creating a space between brake pad assemblies  30  and  32  and pistons  54  and  56 , respectively. Conductive sheets  34   a  and  34   b  are then inserted between brake pad assemblies  30  and  32  and pistons  54  and  56  which leaves heat sinks  36   a  and  36   b  at a position away from brake pads  78   a  and  78   b.  Conductive sheets  34  can also be inserted between brake pad assemblies  30  and  32  and pistons  54  and  56  by installing brake pad assemblies  30  and  32  after conductive sheets  34  are installed in caliper  24 . 
         [0040]    In the previous example, the brake coolers were described as an accessory to a standard brake assembly that includes the backing plate. In another example of the brake coolers, the thermally conductive sheet is utilized as the backing plate. In this instance the brake pad is permanently attached to the thermally conductive sheet and the heat sink is connected to the conductive sheet as before. Since the thermally conductive sheet replaces the backing plate, the thermally conductive sheet can have a larger thickness while still being able to be positioned between the brake pad and the piston. This configuration is also beneficial in that the larger thickness allows for relatively large amounts of thermally conductive material to conduct the heat from the brake pad to the heat sink. 
         [0041]    Another embodiment of the brake cooler is described in conjunction with  FIG. 6 . In this embodiment, conductive sheet  34  is constructed of a primary sheet  92  and a secondary sheet  94  that are secured to one another. Heat sink  36  is constructed of a thermally conductive material such as copper that is folded into a series of cooling fin members  88 . The cooling fin members  88  provide a surface area for transferring heat from heat sink  36  to cooling medium. The cooling fin members  88  shown in  FIG. 6  have a relatively large surface area for transferring heat to surrounding air. Heat sink  36  in  FIG. 6  is connected to the conductive sheet  34  by aligning heat sink  36  with alignment holes  96  and then using a braze material  98  that is heated to adhere to the heat sink  36  and the conductive sheet  34 . 
         [0042]    In the embodiment shown in  FIG. 6 , the primary sheet  92  is secured to the secondary sheet  94  using rivets  100 . The rivets  100  extend through holes  102  in the secondary sheet  94  and holes  104  in the primary sheet  92  before being expanded to physically secure the sheets  92  and  94  to one another. When the primary and secondary sheets  92  and  94  are secured to one another, the guide pin holes are formed by cooperative alignment of a primary sheet guide hole  106  and a secondary sheet guide hole  108 . 
         [0043]    The overall conductive sheet  34 , described above, is constructed using primary and secondary sheets  92  and  94  which have a complementary shape. In the instance shown in  FIG. 6 , primary sheet  92  defines a heat pickup hole  110  in which a heat pickup portion  112  of secondary sheet  94  fits. When heat pickup portion  112  is positioned in heat pickup hole  110 , the combination of heat pickup portion  112  and primary sheet  92  surrounding heat pickup hole  110  generally define a planar surface of conductive sheet  34 . Secondary sheet  94  also includes a heat sink portion  114  which is sandwiched between primary sheet  92  and heat sink  36 . A step  116  of secondary sheet  94  transitions between heat pickup portion  112  and heat sink portion  114  of secondary sheet  94 . Step  116  allows heat pickup portion  112  to be positioned in heat pickup hole  110  of primary sheet  92  and heat sink portion  114  to be positioned at the surface of the primary sheet  92 . 
         [0044]    In the embodiment shown in  FIG. 6 , secondary sheet  94  is constructed of a high thermal conductivity material, for example copper. When installed in caliper  24 , heat pickup portion  112  of secondary sheet  94  is positioned between the backing plate and the piston. Heat pickup portion  112  receives heat from the backing plate and conducts the heat to the heat sink portion  114  where the heat is then transferred to heat sink  36 . The heat sink shown in  FIG. 6  has a large surface area that is in contact with the cooling medium, which in this case is ambient air. Because of the large surface area of the heat sink, heat is transferred from the heat sink to the cooling medium in an efficient manner. Removing heat through the heat pickup portion decreases the amount of heat that reaches the piston, thereby cooling the piston and decreasing or eliminating the occurrence of the piston and the other associated components overheating and boiling the brake fluid. 
         [0045]    Also in the embodiment shown in  FIG. 6 , the primary sheet  92  is constructed of a high yield strength material such as stainless steel. When installed, in caliper  24  the primary sheet is positioned between the backing plate and the piston with the primary sheet extending substantially the entire distance across the backing plate and the piston contacting the primary sheet on opposite sides of heat pickup hole  110 . Positioned in this way, primary sheet  92  resists deformation from the compressive force applied by the piston during braking and generally prevents the piston from deforming the heat pickup portion  112  of secondary sheet  94 . A sheet of high yield strength and high thermal conductivity material, such as copper tungsten, can be substituted for the combination of the primary and secondary sheets. 
         [0046]    Yet another embodiment of the brake cooler is described in conjunction with  FIGS. 7 and 8  for use with a single piston caliper  118 . Single piston caliper  118  includes a single piston  120  ( FIG. 8 ) which moves laterally in a cylinder  122  relative to a rotor  124  to move inner and outer brake assemblies  126   a  and  126   b  toward and away from the rotor. Each of the brake assemblies shown in  FIGS. 7 and 8  includes a backing plate  128  and a brake pad  130 . A caliper body  132  of the caliper extends around rotor  124  with a caliper cross member  134  and caliper arms  136  engage the outer brake assembly  126   b.  To engage the rotor with the brake assemblies, piston  120  moves toward the caliper arms  136  which cause the brake assemblies to move toward one another and forcibly engage the rotor. Single piston caliper  118  is connected to a mounting bracket  138  of a vehicle (not shown) using mounting bolts  140  ( FIG. 7 ). 
         [0047]    Movement of piston  120  is produced by hydraulic fluid passing through an orifice  142  to and from a brake line  144 . The hydraulic fluid enters a fluid reservoir  146  ( FIG. 8 ) defined by an interior surface of cylinder  122  and exterior surface of piston  120 . A hydraulic seal  150  extends around piston  120  to contain the fluid in fluid reservoir  146  and a dust shield  152  prevents dust and other contaminants from damaging the hydraulic seal. A bleeder screw  154  is included to remove air from the fluid reservoir. 
         [0048]    The brake cooler  20  in the embodiment shown in  FIGS. 7 and 8  includes two heat sinks  156  and  158  which are connected in a spaced apart relationship with a thermally conductive sheet  160 . Heat sinks  156  and  158  each include fin members  162  for transferring heat to the surrounding atmosphere. Heat sink  156  is positioned on one side of caliper cross member  134  and heat sink  158  is positioned on another side of caliper cross member  134 . 
         [0049]    Thermally conductive sheet  160  is sandwiched between piston  120  and backing plate  128   a  of the inner brake pad assembly  126   a.  Sheet  160  includes a high yield strength material such as stainless steel that resists deformation from the applied pressures, and a high thermal conductivity material that conducts heat from the brake pad assembly to heat sinks  156  and  158 . A single heat sink may also be used with the single piston caliper, on either the forward or rearward side of caliper cross member  134 . Moreover, an additional brake cooler can be installed between brake pad assembly  126   b  and caliper arms  136  for removing heat from outer brake pad assembly  126   b.    
         [0050]    The brake coolers provide an effective mechanism for removing heat from the brake pads without having to modify the caliper or other components of the disk brake system. Since the calipers do not have to be replaced to install the brake coolers, the brake coolers are more economical than other systems which do require the replacement of calipers or other expensive components. 
         [0051]    Removal of the heat from the brake pads with the brake coolers lowers the heat level experienced by the hydraulic brake fluid, which can thereby eliminate or substantially reduce the dangerous incidence of the brake fluid boiling. The heat removal may also eliminate or reduce the incidence of heat induced damage to the pistons, seals and other components of the caliper which can also lead to brake failure. The removal of heat from the brake pads by the brake coolers is also beneficial in helping to reduce or eliminate instances where the pads are heated to the point where they vaporize on contact with the rotor. Removing heat from the brake pad can result in the temperature of the pad remaining below the point where pad vaporization occurs, thereby substantially or completely eliminating brake pad vaporization. Reducing or eliminating the occurrences of brake fluid boiling and brake pad vaporization increases brake efficiency and may improve the safety of the vehicle to which the brake coolers are attached. 
         [0052]    While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.