Patent Abstract:
A disc brake for a motor vehicle is provided. The disc brake includes a brake disc, a brake caliper configured to straddle the brake disc, a tappet carried by the brake caliper and arranged to push a brake pad against the brake disc, and a bellows provided between the brake caliper and the tappet to seal a gap between the brake caliper and the tappet. A layer of flexible thermal insulation material may be provided between the bellows and the tappet. The layer of flexible thermal insulation material is configured to protect an outer surface of the bellows facing the brake pad from exposure to heat. Alternatively, the bellows may include a layer of flexible thermal insulation material on which an elastomer layer is formed. The layer of flexible thermal insulation material is configured to face the brake pad.

Full Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to thermal protection of disc brake components. 
     The application of a brake pad against a rotating brake disc results in the generation of very high temperatures. Although a large portion of the heat generated by the friction between the brake pad and the brake disc is dissipated by heat transfer directly from the brake disc to the air, a significant amount of heat passes from the brake pad into the structure of the brake caliper. In particular, undesirably high amounts of heat may be transferred to heat-sensitive components within the brake caliper. 
     As shown in  FIG. 1 , a typical disc brake  100  uses at least one moveable piston or tappet  110  to exert a braking force on a brake disc  120  via a brake pad  130 . The disc brake  100  may include two brake pads  130  opposed to each other on either side of the brake disc  120  (not shown). The brake caliper  140  straddles the brake disc  120 , with the brake pad  130  located between the tappet  110  and the brake disc  120 . When the brake pad  130  is in a new condition, the tappet  110  is in a fully retracted position at a maximum distance from the brake disc  120 , as shown in  FIG. 1 . In order to push the brake pad  130  against the brake disc  120 , the tappet  110  moves toward the brake disc  120 . As the brake pad  130  is used, the friction between the brake pad  130  and the brake disc  120  causes the friction material of the brake pad  130  and the brake disc  120  to wear down. As the thickness of the brake pad  130  decreases, the tappet  110  moves closer to the brake disc  120  to maintain a desired maximum clearance between the brake pad  130  and the brake disc  120  in order to minimize brake free-play. Eventually the tappet  110  reaches a fully extended position when the brake pad  130  and the brake disc  120  are in a maximum wear condition, as shown in  FIG. 2 . 
     In order to ensure the performance of the disc brake  100  over its service life, the internal caliper components must be protected from environmental influences, such as dust, chemicals, gases, and water. Typically a bellows  150  is provided to seal the annular gap between the brake caliper  140  and the tappet  110 , and to prevent dust, chemicals, gases, and water from entering the internal mechanism of the brake. The bellows  150  has a first surface  151  that is affixed to the caliper  140 , and a second surface  152  that is affixed to the tappet  110 . The first surface  151  of the bellows  150  may be directly connected to the caliper  140  or to a component outside of the caliper  140 , such as a cover plate bolted to the caliber  140  (not shown). The bellows  150  extends and retracts with the tappet  110  as the tappet  110  advances toward the brake disc  120  and returns to its rest position. In this way the bellows  150  maintains the seal between the brake caliper  140  and the tappet  110  during all operational conditions. 
     The bellows  150 , which is typically made of silicon rubber, is particularly sensitive to high temperatures. Contact between the bellows  150  and the portion of the tappet  110  immediately adjacent to the brake pad  130  (i.e. the portion of the tappet  110  reaching the highest temperatures during brake application) must be avoided, because this portion of the tappet  110  may reach temperatures that can melt or damage the rubber bellows  150 . Such contact is particularly likely when the tappet  110  is in or near the fully retracted position as shown in  FIG. 1 , when the bulk of the retracted the bellows  150  is gathered near the tappet  110 . Further, the folds of the bellows  150  do not collapse uniformly during retraction. Instead, the folds collapse stepwise, and single folds can resist the collapsing movement by remaining in an inclined position for an extended period of time. This increases the risk of contact between local areas of the bellows  150  and the tappet  110  as the tappet  110  moves away from the brake disc  120 . 
     The bellows  150  is also vulnerable to convective heat transfer from the braking process. For example, when the tappet  110  is in the fully extended position as shown in  FIG. 2 , the bellows  150  is completely unfolded, such that its full wall length is exposed to environmental attack and heat from the braking process. Further, the bellows  150  typically sees higher temperatures when the tappet  100  is fully extended (i.e. when the brake pad  130  and the brake disc  120  are in the maximum wear condition), as compared to when the brake pad  130  and the brake disc  120  are new. This is due to the reduced heat capacity of the brake disc  120  and the brake pad  130  caused by their reduced thicknesses as well as the reduced thermal insulation effect of the thinner, worn out brake pad  130 . Therefore, the bellows  150  is particularly vulnerable to thermal degradation when the tappet  110  is in the fully extended position. 
     Previous disc brake designs have included mechanisms for protecting the bellows from heat generated during the braking process. For example, the rubber bellows may be enclosed with a metallic spiral spring enclosure. However, because the metal has a high heat conductivity, the metal may melt or damage the rubber bellows upon contact. Further, it is difficult to prevent contact between the metallic enclosure and the bellows, due to the small packaging space and the uncontrollable deformation of the bellows and the metallic spring. In addition, the metallic enclosure has a poor strength of shape, especially along the lateral direction and in the fully expanded position. This can cause individual coils to skip or jam, which adversely affects the protection function of the metallic enclosure. It can also compromise the full release of the brake and cause a running clearance reduction with the risk of a hot running brake. Further, in this state it is not possible to completely retract the tappet from the brake disc to change the brake pad, due to the increased block height of the spiral spring. 
     U.S. Pat. No. 7,267,207 discloses a disc brake in which the rubber bellows are replaced with metallic bellows. However, this requires a high cost for caliper design changes, because metallic bellows are made of very thin-walled and high-grade stainless steel, and the metallic bellows are costly. In addition, relatively high forces are needed to deform the metallic bellows during extension and retraction of the tappet. 
     U.S. Publication No. 2001/0047913 discloses a disc brake that includes a pressure plate and a heat shield on the back plate of the brake pad. However, this provides limited protection against convective heat transfer, because the sides of the bellows are still exposed. Also, additional space is needed for the pressure plate and heat shield, and there is a significant additional cost to provide the pressure plate and heat shield, and their connection to the tappet. 
     U.S. Publication No. 2006/0175155 discloses a disc brake that includes an insulation disc on the tappet. The insulation disc is only effective against conductive heat transfer, and does not prevent contact between the bellows and the tappet. Also, depending on its elasticity, the insulation disc may increase the stroke demand of the brake. 
     In addition, other disc brake designs have included a heat shield that partially covers the bellows. For example, U.S. Pat. No. 4,431,090 discloses a rubber ring that deforms when impacted by the piston, U.S. Pat. No. 3,592,303 discloses an elastic heat shield that expands circumferentially as the plunger extends, and European Patent No. EP 1 972 821 B1 discloses a metallic heat shield that is inserted into an end of the bellows. However, none of these disc brake designs provides a heat shield that protects the entire exposed surface of the bellows throughout the operation of the disc brake. 
     Accordingly, there is a need for an improved disc brake in which the bellows  150  is protected against excessive heat generated during the braking process. In particular, the apparatus should advantageously protect the bellows  150  from heat throughout the entire operating range of the tappet  110 . 
     SUMMARY OF THE INVENTION 
     The present invention addresses the foregoing problems by the novel arrangement of thermal barriers between the bellows and the tappet. In a first embodiment of the present invention, a layer of flexible thermal insulation material is provided between the bellows and the tappet. The layer of flexible thermal insulation material is configured to protect an outer surface of the bellows facing the brake pad from exposure to heat. 
     The layer of flexible thermal insulation material may include a first fixed end and a second fixed end. A section between the first fixed end and the second fixed end may be configured to maintain the protection of the outer surface of the bellows as the tappet moves toward the brake disc. The section may be configured to unfold or unroll as the tappet moves toward the brake disc. 
     The flexible thermal insulation material may be a woven or knitted material. The woven or knitted material may include silica yarns, a combination of silica and fiberglass yarns, or basalt yarns. 
     The first fixed end of the layer of flexible thermal insulation material may be attached to the tappet, and the second fixed end of the layer of flexible thermal insulation material may be attached to the brake caliper. Alternatively, the first fixed end of the layer of flexible thermal insulation material may be attached to an inner circumference of the bellows, and the second fixed end of the layer of flexible thermal insulation material may be attached to an outer circumference of the bellows. 
     The section of the layer of flexible thermal insulation material between the first fixed end and the second fixed end may include a first segment adjacent to the first fixed end, wherein the first segment is provided between the bellows and the tappet in a direction of brake pad application when the tappet is in a retracted state. The section may also include a second segment adjacent to the second fixed end, wherein the second segment is provided in a space outside of an outer circumference of the bellows when the tappet is in the retracted state. 
     The disc brake with the layer of flexible thermal insulation material may be incorporated into an axle for a motor vehicle. The disc brake with the layer of flexible thermal insulation material may also be incorporated into a motor vehicle. 
     According to another embodiment of the present invention, the bellows includes a first layer of flexible thermal insulation material and a first elastomer layer formed on a first surface of the first layer of flexible thermal insulation material. A second surface of the first layer of flexible thermal insulation material opposing the first surface faces the brake pad. 
     The flexible thermal insulation material may be a woven or knitted material. The woven or knitted material may include silica yarns, a combination of silica and fiberglass yarns, or basalt yarns. The elastomer layer may include silicon rubber. 
     The bellows may also include a second layer of flexible thermal insulation material and a second elastomer layer formed on a first surface of the second layer of flexible thermal insulation material. The first elastomer layer and the second elastomer layer may be separated by an air gap. Alternatively, the first elastomer layer and the second elastomer layer may be joined by a plurality of additional elastomer layers to form a series of stacked discs. 
     The disc brake with the bellows may be incorporated into an axle for a motor vehicle. The disc brake with the bellows may also be incorporated into a motor vehicle. 
     Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a partial sectional view of a typical disc brake when the brake pad is in a new condition; 
         FIG. 2  shows a partial sectional view of the typical disc brake of  FIG. 1  when the brake pad and the brake disc are in a maximum wear condition; 
         FIG. 3  shows a partial sectional view of a disc brake with an insulation disc between the tappet and the bellows, according to an exemplary embodiment of the present invention; 
         FIG. 4  shows a partial sectional view of a disc brake with a folded insulation layer between the tappet and the bellows, according to an exemplary embodiment of the present invention; 
         FIG. 5  shows a partial sectional view of a disc brake with an insulation shell between the tappet and the bellows, according to an exemplary embodiment of the present invention; 
         FIG. 6  shows a partial sectional view of a disc brake in which the bellows is replaced with a compound material including a layer of flexible thermal insulation material on which an elastomer layer is formed, according to an exemplary embodiment of the present invention; 
         FIGS. 7A and 7B  show examples of bellows made with the compound material according to exemplary embodiments of the present invention; and 
         FIGS. 8A and 8B  show examples of disc brakes that incorporate the bellows shown in  FIGS. 7A and 7   b , respectively. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 3  shows a partial sectional view of a disc brake  100  with an insulation disc  200  between the tappet  110  and the bellows  150 , according to an exemplary embodiment of the present invention. Similar to  FIG. 1 , the tappet  110  shown in  FIG. 3  is in a fully retracted position. The insulation disc  200  is inserted into an existing air gap between the tappet  110  and the bellows  150  to prevent the bellows  150  from contacting the tappet  110 . The insulation disc  200  has an annular shape. A first end  210  of the insulation disc  200  may be a circular inner circumference that is attached to the tappet  110 . A second end  220  of the insulation disc  200  may be a circular outer circumference that extends beyond the outer circumference of the bellows  150 . The insulation disc  200  may rest on the tappet  110  and move downward with the tappet  110  to prevent the bellows  150  from contacting the tappet  110 . The second end  220  of the insulation disc  200  is not attached to the caliper  140 . 
     The insulation disc  200  is a flexible thermal insulation material, which may be a woven or knitted material. For example, the flexible thermal insulation material may be made of silica yarns, a combination of silica and fiberglass yarns, or basalt yarns. Other materials may be chosen to optimize temperature resistance and disc brake design, and to minimize cost. 
     Because the folds of the bellows  150  rest against the insulation disc  200 , preventing the bellows  150  from contacting the tappet  110 , the bellows configuration is no longer constrained by the need to shape the bellows  150  in a manner that prevents contact with the tappet  110 . The insulation disc  200  therefore permits more free deformation of the bellows  150 , allowing the length and/or diameter of the bellows  150  to be optimized to improve the functionality and service life of the bellows  150 . Further, the increased design freedom permits the space needed to install the bellows  150  to be decreased by compressing the bellows  150  in a defined manner when the tappet  110  is fully retracted without risking thermal overload of the bellows  150 . For example, the compression may be made to occur between the insulation disc  200  and the rear wall of the space for the bellows  150 . 
       FIG. 4  shows a partial sectional view of a disc brake  100  with a folded insulation layer  300  between the tappet  110  and the bellows  150 , according to another exemplary embodiment of the present invention. Similar to  FIG. 1 , the tappet  110  shown in  FIG. 4  is in a fully retracted position. The folded insulation layer  300  is a flexible thermal insulation material, which may be a woven or knitted material. For example, the flexible thermal insulation material may be made of silica yarns, a combination of silica and fiberglass yarns, or basalt yarns. Other materials may be chosen to optimize temperature resistance and disc brake design, and to minimize cost. For example, the folded insulation layer  300  may be cut out of a flat woven or knitted half-finished cloth, or cut off of a knitted hose. 
     As shown in  FIG. 4 , the folded insulation layer  300  has a first fixed end  310  and a second fixed end  320 . The first fixed end  310  may be attached to the tappet  110  and the second fixed end  320  may be attached to the caliper  140 . Alternatively, the first fixed end  310  and the second fixed end  320  may be attached to the bellows  150 . Specifically, the first fixed end  310  may be attached to the inner circumference of the bellows  150 , and the second fixed end  320  may be attached to the outer circumference of the bellows  150 . Some or all of the attachments may be made by clamping. 
     An inner portion  330  of the folded insulation layer  300  is adjacent to the first fixed end  310  of the folded insulation layer  300 . The inner portion  330  of the folded insulation layer  300  is provided between the tappet  110  and the bellows  150  in a direction of application of the brake pad  130  when the tappet  110  is in the fully retracted state. Accordingly, the inner portion  330  of the folded insulation layer  300  prevents the bellows  150  from contacting the tappet  110  when the tappet  110  is in the fully retracted state. 
     An outer portion  340  of the folded insulation layer  330  is adjacent to the second fixed end  320  of the folded insulation layer  300 . As shown in  FIG. 4 , the outer portion  340  of the folded insulation layer  300  may be folded within a space outside of an outer circumference of the bellows  150  when the tappet  110  is in the fully retracted state. Alternatively, the outer portion  340  of the folded insulation layer  300  may be rolled within a space outside of an outer circumference of the bellows  150  when the tappet  110  is in the fully retracted state. 
     When the tappet  110  extends toward the brake disc  120 , the bellows  150  expands to maintain the seal between the brake caliper  140  and the tappet  110 . For example, the outer circumference of the bellows  150  is fixed to the brake caliper  140 , and remains in place when the tappet  110  extends toward the brake disc  120 . The inner circumference of the bellows  150  may be fixed to the tappet  110 , and move toward the brake disc  120  with the tappet  110 . Accordingly, the bellows  150  unfolds in a downward direction. 
     In order to protect the entire surface area of the bellows  150  as the bellows  150  unfolds, the folded insulation layer  300  also unfolds or unrolls in a similar manner. For example, as the first fixed end  310  of the folded insulation layer  300  moves in the downward direction with the tappet  110 , the outer portion  340  of the folded insulation layer  300  gradually unfolds and leaves the space outside of the outer circumference of the bellows  150  to provide sufficient material to cover the entire surface area of the bellows  150  as the bellows  150  unfolds. Therefore, the folded insulation layer  300  protects the entire bellows  150  from heat when the tappet  110  is in the fully retracted position, the fully extended position, and any intermediate position. 
       FIG. 5  shows a partial sectional view of a disc brake  100  with an insulation shell  400  between the tappet  110  and the bellows  150 , according to another exemplary embodiment of the present invention. Similar to  FIGS. 1 and 4 , the tappet  110  shown in  FIG. 5  is in a fully retracted position. The insulation shell  400  is a flexible thermal insulation material, which may be a woven or knitted material. For example, the flexible thermal insulation material may be made of silica yarns, a combination of silica and fiberglass yarns, or basalt yarns. Other materials may be chosen to optimize temperature resistance and disc brake design, and to minimize cost. The insulation shell  400  shown in  FIG. 5  performs a similar function to the folded insulation layer  300  shown in  FIG. 4 . 
     As shown in  FIG. 5 , the insulation shell  400  has a first fixed end  410  and a second fixed end  420 . The first fixed end  410  may be attached to the tappet  110  and the second fixed end  420  may be attached to the caliper  140 . Alternatively, the first fixed end  410  may be attached to the inner circumference of the bellows  150 . Some or all of the attachments may be made by clamping. 
     An inner portion  430  of the insulation shell  400  is adjacent to the first fixed end  410  of the insulation shell  400 . The inner portion  430  of the insulation shell  400  is provided between the tappet  110  and the bellows  150  when the tappet  110  is in the fully retracted state. The inner portion  430  of the insulation shell  400  prevents the bellows  150  from contacting the tappet  110  when the tappet  110  is in the fully retracted state. 
     An outer portion  440  of the insulation shell  400  is adjacent to the second fixed end  420  of the insulation shell  400 . As shown in  FIG. 5 , the outer portion  440  of the insulation shell  400  is folded within a space outside of an outer circumference of the bellows  150  when the tappet  110  is in the fully retracted state. The insulation shell  400  may be preformed so that the outer portion  440  collapses to fill the space outside of the outer circumference of the bellows  150  when the tappet  110  is in the fully retracted state. This facilitates retraction of the tappet  110  and maximizes the available space within the disc brake  100 . 
     When the tappet  110  extends toward the brake disc  120 , the bellows  150  expands to maintain the seal between the brake caliper  140  and the tappet  110 . For example, the outer circumference of the bellows  150  is fixed to the brake caliper  140 , and remains in place when the tappet  110  extends toward the brake disc  120 . The inner circumference of the bellows  150  may be fixed to the tappet  110 , and move toward the brake disc  120  with the tappet  110 . Accordingly, the bellows  150  unfolds in a downward direction. 
     In order to protect the entire surface area of the bellows  150  as the bellows  150  unfolds, the insulation shell  400  also unfolds in a similar manner. For example, as the first fixed end  410  of the insulation shell  400  moves in the downward direction with the tappet  110 , the outer portion  440  of the insulation shell  400  gradually unfolds and leaves the space outside of the outer circumference of the bellows  150  to provide sufficient material to cover the entire surface area of the bellows  150  as the bellows  150  unfolds. Therefore, the insulation shell  400  protects the entire bellows  150  from heat when the tappet  110  is in the fully retracted position, the fully extended position, and any intermediate position. 
       FIG. 6  shows a partial sectional view of a disc brake  100  in which the bellows  500  is a compound material that includes a layer  520  of flexible thermal insulation material on which an elastomer layer  510  is formed, according to yet another exemplary embodiment of the present invention. Similar to  FIG. 1 , the tappet  110  shown in  FIG. 6  is in a fully retracted position. The layer  520  of flexible thermal insulation material is a flexible thermal insulation material, which may be a woven or knitted material. For example, the flexible thermal insulation material may be made of silica yarns, a combination of silica and fiberglass yarns, or basalt yarns. Other materials may be chosen to optimize temperature resistance and disc brake design, and to minimize cost. The elastomer layer  510  may be made of silicon rubber. 
     In the present exemplary embodiment, the layer  520  of flexible thermal insulation material is integrated with the elastomer layer  510  to form the bellows  500 . The layer  520  of flexible thermal insulation material serves as a carrier material for the elastomer layer  510 . The elastomer layer  510  may be molded or sprayed on the layer  520  of flexible thermal insulation material. The elastomer layer  510  provides a seal against dust, chemicals, gases, and water, while the layer  520  of flexible thermal insulation material provides a thermal barrier. 
     As shown in  FIG. 6 , the layer  520  of flexible thermal insulation material faces the tappet  110  and the brake pad  130 , while the elastomer layer  510  faces the internal caliper components. Like the bellows  150  shown in  FIG. 2 , when the tappet  110  extends toward the brake disc  120 , the bellows  500  expands to maintain the seal between the brake caliper  140  and the tappet  110 . For example, the outer circumference of the bellows  500  is fixed to the brake caliper  140 , and remains in place when the tappet  110  extends toward the brake disc  120 . The inner circumference of the bellows  500  may be fixed to the tappet  110 , and move toward the brake disc  120  with the tappet  110 . Accordingly, the bellows  500  shown in  FIG. 6  unfolds in a downward direction, similar to the bellows  150  shown in  FIG. 2 . 
     Because the bellows  500  includes the layer  520  of flexible thermal insulation material, the elastomer layer  510  is protected from heat as the tappet  110  extends and the bellows  500  unfolds. This is because the layer  520  of flexible thermal insulation material is always positioned between the elastomer layer  510  of the bellows  500  and the tappet  110 . Therefore, the layer  520  of flexible thermal insulation material protects the entire elastomer layer  510  of the bellows  500  from heat when the tappet  110  is in the fully retracted position, the fully extended position, and any intermediate position. 
     The bellows  500  made of the compound material can be used to replace any bellows or deformable sealing element within the disc brake  100 . For example, the bellows  500  made of the compound material could replace the guide pin bellows (not shown). The bellows  500  would be oriented such that the layer  520  of flexible thermal insulation material faces a heat source of the disc brake  100 . 
       FIGS. 7A and 7B  show examples of other configurations of bellows made with the compound material according to exemplary embodiments of the present invention. For example, as shown in  FIG. 7A , the bellows can include a first layer  600  of flexible thermal insulation material upon which a first elastomer layer  610  is formed, along with a second layer  630  of flexible thermal insulation material upon which a second elastomer layer  620  is formed. The first elastomer layer  610  and the second elastomer layer  620  face each other and are separated by an air gap  640 .  FIG. 8A  shows an exemplary embodiment of a disc brake that incorporates the bellows shown in  FIG. 7A . 
     Similarly, as shown in  FIG. 7B , the bellows can include a first layer  650  of flexible thermal insulation material upon which a first elastomer layer  660  is formed, along with a second layer  680  of flexible thermal insulation material upon which a second elastomer layer  670  is formed. The first elastomer layer  660  and the second elastomer layer  670  may be joined by a plurality of additional elastomer layers  690  to form a series of stacked discs. Each of the stacked discs shown in  FIG. 7B  has a hollow core.  FIG. 8B  shows an exemplary embodiment of a disc brake that incorporates the bellows shown in  FIG. 7B . 
     Exemplary embodiments of the present invention use a flexible thermal insulation material to protect the bellows of a disc brake from heat generated during the braking process. The insulation material may be an insulation disc that is inserted into an existing air gap between the tappet and the bellows. In another exemplary embodiment, the insulation material may be a folded or rolled insulation layer or shell that unfolds or unrolls as the tappet extends toward the brake pad. Alternatively, the bellows may be replaced by a compound material that includes the insulation material as a carrier for an elastomer layer. 
     The flexible thermal insulation material may be a woven or knitted material, which advantageously provides an adaptive and flexible shape. The flexible thermal insulation material may be made of silica yarns, a combination of silica and fiberglass yarns, or basalt yarns, each of which provides very good protection against conductive, convective, and radiative heat transfer. Using the flexible thermal insulation material to insulate the rubber bellows can significantly extend the lifetime of the bellows and prevent a failure of the bellows. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

Technology Classification (CPC): 5