Abstract:
A disc brake return spring comprises a V-shaped spring having two spring members, with each member ending in an engagement leg. Each engagement leg is angled with respect to the spring legs in a fashion so that the spring applies a moment to the friction pad to counteract rotation that occurs about the backing plate supports. The return spring is employed in a disc brake assembly having friction pads with backing plates that are disposed on either side of a rotor for braking purposes.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Application Ser. No. 60/371,127, which was filed on Apr. 10, 2002. 

   FIELD OF THE INVENTION 
   The present invention is directed to a return spring for pads in a disc brake system and, in particular, to a return spring with engagement legs that apply a torque to maintain the pads generally parallel to the rotor when in a non-braking state. 
   BACKGROUND ART 
   In disc brake systems, it is common to employ return springs that return the disc brake pads to a rest position after braking. These springs come in a variety of shapes, including v-shapes. Typically, the ends of the springs engage the upper parts of the backing plates that support the brake, or friction pads.  FIG. 1  is a partial top view  10  of a typical disc brake assembly wherein a v-shaped spring  1  is positioned between backing plates  3  that support friction pads  5 . The v-shaped spring  1  exerts an outward force “F” on the pads  5  to urge each pad  5  away from respective outer surfaces  8  of the rotor  7 , thus preventing drag, excessive pad wear, and excessive rotor wear during the non-braking condition. 
     FIG. 2  illustrates the spring  1  in a typical installation and shows one of two opposed ears  9  that are commonly used to carry the backing plate. The ears  9  ride in a recess  12  in the mounting member  14 . Engagement legs  11  at the end of each spring member  13  engage openings  15  in the backing plates  3 . As shown in  FIG. 4 , the engagement legs  11  are perpendicular to the spring member  13 . When positioned in the opening  15  in the backing plate  3  (see  FIG. 3 ) the engagement leg  11  is generally parallel to the opposing sides of the opening  15 . 
     FIG. 5  illustrates a problem created by the return spring shown in  FIGS. 1-4 . The forces applied by the spring  13  to the upper parts of the backing plates  3  create a torque that rotates the pads about the ears  9  when the system is in a non-braking state. Thus, the plates  3  rotate about a longitudinal axis “M” of the plate (see  FIG. 2 ) that extends in a tangential direction (with respect to the brake rotor) between the ears  9 , which causes the pads  5  to assume a non-parallel configuration with respect to the rotor  7 , whereby the bottoms of the pads often contact the rotor  7  in the areas  16  resulting in uneven pad wear and excessive drag. 
   Accordingly, a need exists to reduce or eliminate the uneven wear and drag that result from the configuration shown in  FIG. 5  to increase friction pad and rotor life. The invention responds to this need by providing a uniquely configured disc brake pad return spring that applies a force urging the pads away from the rotor and also applies a twisting force that prevents the rotation about the backing plate ears normally caused by the return spring force. 
   SUMMARY OF THE INVENTION 
   It is a first object of the present invention to provide an improved disc brake pad return spring. 
   Another object of the invention is to provide a disc brake pad return spring that not only urges the pads away from the rotor in the non-braking state but also maintains a parallel alignment between the pads and the rotor. 
   Yet another object of the invention is to provide an improved disc brake assembly that utilizes the inventive disc brake return spring. 
   A further object is to provide a method of maintaining friction pads in a generally parallel orientation with respect to a rotor when in a non-braking state by inducing a first moment that opposes the moment induced in the backing plate by the return spring. 
   Other objects and advantages of the present invention will become apparent as a description thereof proceeds. 
   In satisfaction of the foregoing objects and advantages, the invention includes a disc brake pad return spring, the spring in combination with a disc brake assembly, and a method of counteracting the torque or rotation that is caused by the return spring when the brake pads are in the non-braking state. 
   The return spring of the invention is configured such that it applies a torque that counteracts the torque normally created by application of the return force to the backing plate at a location displaced from a longitudinal axis that extends between the mounting ears. The invention will be described with regard to the preferred embodiment, but it will be appreciated that other configurations are possible that will apply forces and moments equivalent to those applied by the preferred embodiment. 
   In the preferred embodiment, the return spring comprises a pair of spring members that together form a v-shape, and each spring member terminates in an engagement leg that extends at an angle to the respective spring leg such that the two legs diverge from each other. The engagement legs are received in holes in the backing plates in such a manner that the desired torque is applied to the backing plate. 
   In the preferred embodiment, the two engagement legs lie in a plane transverse to a plane containing the spring members. The engagement legs are not parallel, however, and diverge at an angle that will place the spring members in torsion and apply a desired moment to each backing plate when engaged therewith. The plane containing the engagement ends may be perpendicular to the plane containing the spring members or not. Further, the spring may be symmetrical or not. 
   The return spring also forms part of a brake pad assembly that includes a pair of friction pads mounted to a pair of backing plates, and a rotor. Each engagement leg is positioned in a respective hole in a backing plate of the assembly so that the spring legs force the friction pads away from the rotors when in a non-braking state. 
   The inventive return spring applies a torque to maintain the pair of friction pads mounted on their respective backing plates generally parallel to the rotor when in a non-braking condition. By its configuration and when in use in the brake assembly, the return spring applies a linear outward force at a top portion of backing plates. At the same time and due to the twist applied to the spring members by the angular relationship of the engagement legs, the engagement legs induce a moment at the top portion of the backing plates. This moment counteracts the moment that is induced in the backing plates ears as a result of the application of the return force at a location spaced from the axis of the support ears. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is now made to the drawings of the invention wherein: 
       FIG. 1  is a partial top view of a prior art disc brake assembly at rest; 
       FIG. 2  is a partial side view of the assembly of  FIG. 1 ; 
       FIG. 3  is a cross-sectional view along the line III-III of  FIG. 2 ; 
       FIG. 4  is an open end view of the return spring of  FIG. 1 ; 
       FIG. 5  is an end view of the assembly of  FIG. 1 ; 
       FIG. 6  is an end view of one embodiment of the return spring of the invention; 
       FIG. 7  is a perspective view of the spring of  FIG. 6 ; 
       FIG. 8  is a partial cross-sectional view of the spring of  FIG. 7  retained in a disc brake assembly; 
       FIG. 9  shows an end view of the brake assembly referred to in  FIG. 8  in the non-braking state. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention offers significant improvements in the operation of disc brake assemblies and longevity of brake components such as friction pads and rotors. Unlike many prior art disc brake assemblies, use of the inventive disc brake return spring maintains the friction pads in a generally parallel relationship with the rotor when at rest and in a non-braking state. Consequently, unwanted contact between the pads and rotors in the non-braking condition is eliminated or at least drastically reduced. 
   Referring now to  FIGS. 6-9 , one embodiment of the inventive return spring is designated by the reference numeral  20  and includes a pair of spring members  21  that are joined by a connector portion  23 . Each spring member terminates in an engagement leg  25  with a free end  27 . Each engagement leg  25  is bent outward to form an angle α as shown in  FIGS. 6 and 7 , measured in a plane containing the two engagement legs and with respect to a line perpendicular to the plane containing the two spring members  21 . It will be appreciated that the engagement legs  11  of the prior art design of  FIG. 3  are parallel, whereas those of the invention diverge. Each leg  25  and its adjacent spring member  21  lie in a plane, and the leg  25  forms an angle β in that plane (see  FIG. 7 ) that may be more than 90°. 
   The orientation of the engagement legs  25  may be defined with respect to different reference lines, such as axes “fly” and “z” shown in  FIG. 7 , or a component of the brake assembly such as the rotor surface  8  or a wall of the opening  15  in the backing plate. The angle α is defined herein as lying in the plane containing both engagement legs, e.g., the plane formed by a “y” axis perpendicular to the plane containing the spring members and “z” axis lying in both the plane containing the spring members and the plane containing the engagement legs. The angle α is measured in the y-z plane from the y-axis. The directions of the engagement legs intersect in the y-z plane, and the “y” axis extends in the direction of the bisector of the angle of intersection. Thus, if the spring is symmetrical, the angle α is one half the angle of intersection. 
     FIG. 8  is an illustration of the engagement leg  25  received in opening  15  in one of the backing plates  3 . Before being placed in the hole, the ends of the engagement legs are rotated toward each other to reduce the angles αand thereby apply a torque to each of the spring members. Thus, when engaged in the hole, the leg  25  assumes an angle α′. 
   The angle α′ is determined by the geometry of the hole and the engagement leg. If the diameter of the hole is the common 2.4 mm, the diameter of the spring member is the common 1.7 mm, and the length of the engagement leg is 5.4 mm, α′ will be about 7.4°. 
   As in the prior art design, the spring members  21  apply a force to the backing plates through the legs  25  urging the backing plates  3  and the attached friction pads  5  away from the rotor  7 . Because this force is applied at a distance from the longitudinal axis “M” formed by the ears of the backing plates, it generates a moment about that axis, tending to rotate the backing plate about the axis. The described orientation of the engagement legs  25 , however, applies as twist to the spring members such that they apply to the backing plates an opposed twisting force, or moment that counteracts the rotation of the plates about the axis “M” caused by the restoring force of the return spring. 
     FIG. 9  illustrates the advantages of the invention, wherein the friction pads  5  and plates  3  are in the at-rest state and are generally parallel to the rotor  7 . Bending the legs  25  outwardly by angle α in the rest state (i.e., the free ends  27  diverge with respect to each other in the at -rest state, see  FIGS. 6 and 7 ) causes the spring leg to act both as a spring to produce the outward linear force “F” and as a torsion spring along length “L” to induce a moment “M” (see  FIG. 9 ) to the top of the backing plate. The dimensions of the spring leg  25  and opening  15  are sized such that this moment overcomes the moment resulting from application of the spring return force to the top of the pad on the one hand and the frictional resistance to sliding of the ears on the other. Thus, the torsion applied by the legs  25  force the bottom of the pad to slide away from the rotor  7  to provide clearance between the rotor  7  and the pads  5  in the parallel orientation shown in  FIG. 9 . 
   In one design for commonly used spring materials, the angle αis about 15° so that each of the spring members is subjected to a torsion pre-load of about 8° to thereby apply the desired moment of about 1.7 in.-lbs. to each of the brake pads. This is only an illustration, however, and depends on such factors as the modulus of elasticity and spring constant of the material, and the diameter of the spring. In general, once the magnitude of the desired moment is determined and the spring material known, the required angular displacement α can be calculated. Depending on the particular materials and dimensions, the desired angle may be in the range of from 10° to 30°. 
   While the v-shaped spring is shown with a simple v-shape via the connector portion  23 , other shapes could be employed for the spring members  21 , such as a double V-shape as disclosed in JP-56-21633, or other curved shapes as would be within the skill of the art. In addition, the spring  20  can be made from any conventional spring material. Further, it can have a circular cross section, or any other cross sectional shape as would be within the skill of the art. 
   The connection between the spring and the backing plate may vary also and is not limited to the preferred engagement shown. For example, the engagement leg may be differently configured, and the backing plate could include a protrusion received in a recess in the spring, or the spring could be attached to the backing plate by another connector such as a threaded screw, or the like. 
   As such, an invention has been disclosed in terms of preferred embodiments thereof, which fulfill each and every one of the objects of the present invention as set forth above and provides new and improved disc brake return spring as well as a disc brake assembly employing the spring. 
   Of course, various changes, modifications and alterations from the teachings of the present invention may be contemplated by those skilled in the art without departing from the intended spirit and scope thereof. It is intended that the present invention only be limited by the terms of the appended claims.