Patent Publication Number: US-6655508-B2

Title: Disc brake rotor

Description:
This is a division of application Ser. No. 09/754,688 filed on Jan. 3, 2001 now U.S. Pat. No. 6,454,058. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to disc brake rotors as used in a vehicle braking system. More particularly, the invention relates to a vehicle brake rotor that incorporates a plurality of vanes designed to reduce noise generated in the brake system. 
     BACKGROUND OF THE INVENTION 
     Noise generated during a brake application has been increasing as the size of vehicles has been decreasing. Attempts have been made to reduce the noise generated using various systems and methods. One such technique involves the use of sound adsorption coatings on the pad assembly. While such coatings have some effectiveness, the addition of the coating adds cost to the manufacture and at times, undesirable noise occurs when the thickness of the coating has not been uniform. 
     Another technique involves a disc brake pad assembly having clench tabs extending through rubber-like grommets in openings in a caliper housing leg so that the grommets are retained in the openings and the brake pad assembly is retained on the housing leg. The grommets provide a noise dampening action during braking to reduce noise. 
     Individual noise problems have been reduced through the modification of the ingredients in the composition of materials that make up a brake pad. In many of these cases, while noise may have been abated somewhat, the braking effectiveness of the system has been changed by the modification of the brake pad material. Still another technique of reducing brake noise involves affixing a ring damper about a periphery of a brake rotor in a disc brake system. The ring damper is held in place by a groove formed in the periphery of the disc and is pre-loaded against the rotor both radially and transversely. 
     The above techniques involve the reduction of noise by absorbing or masking the noise after it has been created or by adding costly complexity to the braking system. It would be advantageous to design the system to reduce the potential for the creation of noise. It has been suggested that much of brake squeal or noise is influenced by the excitation of the natural frequencies of a rotor caused by the rubbing of friction pads on a rotor surface. There is evidence that a disc brake rotor may have a dozen or more naturally occurring frequencies. While most of these are in the axial direction, others are in the torsional direction. In simulated braking applications only certain of these natural frequencies create brake noise or squeal. Every natural frequency of a vibrating system has associated with it a mode shape that describes the pattern of deformation associated with that natural frequency. In a continuous structure, the mode shape is generally accepted or described by defining the pattern of nodes (loci of points of zero deformation) on the surface of the structure. Experiments have shown that the mode shape of an annular circular plate, a shape like that of a brake rotor, includes nodal circles and diameters. Thus, a beneficial effect on brake noise should be attainable if the nodal diameter modes of an installed disc rotor are maintained at a maximum separation, thereby reducing or eliminating coupling of the nodal diameter modes in the audible frequency range. 
     A typical structure of a brake rotor includes a central disc portion that is adapted to be mounted to an axle of a vehicle as in known in the art, by fasteners. An extending portion typically connects one of a pair of rotor friction plates or cheeks to the central disc portion. An outboard plate is the portion of the rotor that includes a friction surface attached to the central disc portion adjacent to the wheel and faces outward from the vehicle body. An inboard plate faces inward toward the vehicle body. 
     A plurality of vanes extend from an inner surface of the first or outboard plate to connect a second inboard plate thereto. The vanes are typically arranged in a radial fashion about the rotor. The vanes hold the first and second plates in a parallel, side-by-side relationship. Typically, vanes have an overall regular elongate, rod, coffin or rectangular shape with a generally constant width and cross-sectional area. In other words, many current vanes start out a rectangular cross-section at one end and remain rectangular throughout the longitudinal distance of the vane at an opposite end. Similarly, a prior-art plate typically has a thickness or cross-section remaining substantially constant along the radial direction. 
     A rotor may possess a number of inherent resonance modes. In use, the rotor may generate vibrations including a mode characterized by radial (and potentially transverse and some tangential) displacement of the plates of the rotor. Further, the rotor may generate vibrations in a mode referred to as an X-mode, characterized by mainly transverse (with some radial and tangential) displacement of the plates of the rotor. A transverse modal vector is defined by one nodal diameters at the friction radius of the rotor and X order nodal diameters defined by the number of transverse antinodes. Coupling of a radial and an X-mode in a rotor results in a hybrid mode vibration. In a hybrid mode, one plate exhibits radial mode behavior and the other plate exhibits X-mode behavior. 
     It would be advantageous to provide an apparatus and method to prevent the occurrence of hybrid mode behavior in a disc brake rotor. 
     SUMMARY OF THE INVENTION 
     An aspect present invention provides a rotor for a disc brake including a pair of friction plates arranged coaxially in a parallel, spaced-apart relationship and a plurality of vanes extending between the pair of friction plates. The vanes have a proximal end, a distal end and a mid-portion extending between the proximal end and the distal end. The proximal end of a plurality of the plurality of vanes include a first width, the mid-portion including a second width, the first width being substantially greater than the second width. 
     Other aspects of the present invention provide a rotor wherein the first width of half the vanes is substantially greater than the second width. The first width of the other half of the vanes can be substantially the same as the second width. The first width of at least half the vanes can be from about 50 percent greater than the second width to about twice that of the second width. 
     In another aspect of the invention, a plurality of the plurality of vanes can include an inverted T-shaped portion adjacent the proximal end of the vanes. Half of the vanes can include an inverted T-shaped portion adjacent the proximal end of the vanes. The inverted T-shaped portion is at least 50% wider than a width of the mid-portion. The rotor may further include an angled portion located between each inverted T-shaped portion and the mid-portion. 
     An aspect of the present invention provide a method of reducing noise in a disc brake rotor including stiffening a radially inner portion of the brake rotor with a proximal portion of a plurality of vanes and reducing hybrid vibration modes in an audible frequency range. The proximal portion of the plurality of vanes can include an inverted T-shaped portion. Half of the plurality of vanes can include an inverted T-shaped portion at a proximal portion. The other half of the plurality of vanes can include a substantially constant width from a proximal portion to a distal portion of the vanes. 
     Another aspect of the present invention provides a rotor for a disc brake including means for stiffening a radially inner portion of the brake rotor with a proximal portion of a plurality of vanes and means for reducing hybrid vibration modes in an audible frequency range. The proximal portion of the plurality of vanes can include an inverted T-shaped portion. Half of the plurality of vanes can include an inverted T-shaped portion at a proximal portion. The other half of the plurality of vanes can include a substantially constant width from a proximal portion to a distal portion of the vanes. 
    
    
     The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a perspective view of an embodiment of a brake rotor of the present invention including inverted T-shaped vanes; 
     FIG. 2 illustrates an alternating arrangement of the vanes in the brake rotor of FIG. 1; 
     FIG. 3 illustrates a prior art rotor exhibiting deformation generated by a hybrid mode coupling of radial and X-modes of vibration; and 
     FIG. 4 illustrates an embodiment of the present invention exhibiting less deformation than the rotor of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 one embodiment of a brake rotor is generally shown at numeral  110 . The brake rotor  110  includes a central attachment portion  112 . An extending portion  114  is attached adjacent to the periphery  116  of the central attachment portion  112 . A first friction plate  118  (one of a pair of parallel friction plates) is depicted attached to the central attachment portion  112  by the extending portion  114 . A second friction plate (not shown), which would be oriented in a parallel, spaced apart relationship to the first plate  118  is omitted to show the structure (vanes) therebetween. A plurality of vanes  120 ,  122  is provided that extend between the plates and are arranged in a radial fashion. The vanes  120 ,  122  are radial members, each having a proximal end  124 ,  126  adjacent the extending portion  114  and a middle span or mid-portion  128 ,  130  that extends longitudinally in a radial direction to a distal end  132 ,  134 . The distal end  132 ,  134  is located adjacent the outer periphery  136  of the friction plates. 
     In one embodiment, a first and a second set of vanes  120 ,  122  are provided between the plates in an alternating arrangement. In other words, a first vane  120  is followed by an adjacent second vane  122 , which is followed by a first vane  120  and so on, around the rotor  110 . Each of the first set of vanes  120  has a generally constant width rectangular shape from proximal end  124  to distal end  132 . Each of the second vanes  122  has an inverted T-shape configuration. The inverted T-shaped portion  138  is located in the proximal end  126  of the vane  122 . The middle span  130  of the vane  122  is essentially a longitudinally extending rectangular portion. The vane  122  can include an angled portion  140  between the middle span  130  and the inverted T-shaped portion  138 . The inverted T-shaped portion  138  of the vane  122  can have a width about 50% greater than that of the middle span  130  of the vane  122 . The inverted T-shaped portion  138  of each vane  122  can have a width about twice that of the middle span  130  of the vane  122 . Also, the width of portion  138  can be made from about 50% greater to about twice that of the middle span  130  of the vane  122 . 
     Referring to FIGS. 1 and 2, in an alternating configuration about the rotor  110  are the first vanes  120  and the second vanes  122 . The first vanes  120  can lack the inverted T-shaped configuration of the proximal portion  126  of the second vanes  122 . The widened portion or inverted T-shaped portion  138  of vanes  122  can add stiffness to the inner diameter or inner periphery  137  of the rotor  110 . This configuration may provide a beneficially modified pattern of nodal resonance modes. 
     Referring to FIG. 3, a depiction of a prior art rotor is generally shown at  210 . The rotor  210  includes a central hat or disc portion  212 . An outer plate  218  is connected to the central hat portion  212 . Inner plate  219  is connected to the outer plate  218  by a plurality of conventional vanes, one of which is shown at  220 . In this illustration, the rotor  210  is shown (exaggerated) exhibiting a hybrid mode deformation including 2 nd  radial mode and 2 nd  X-mode deformation. 
     Referring to FIG. 4, an embodiment of the present invention includes a rotor depicted in a similar view as that shown in FIG.  3 . The rotor  310  includes a central hat or disc portion  312 . An outer plate  318  is connected to the central hat portion  312 . Inner plate  319  is connected to the outer plate  318  by first plurality of vanes, one of which is indicated at  320  and a second plurality of vanes  322 . The vanes  322  may include the inverted T-shaped configuration shown in FIGS. 1 and 2. Compared to the prior art rotor of FIG. 3, the rotor of the present invention (depicted in FIG. 4) exhibits less deformation, and thus a lower amplitude or amount of overall vibration. 
     As discussed above, a rotor possesses a number of nodal diameter and circle modes. Each of the nodal modes generates a different pattern of resonant rotor vibration. When the n th  nodal diameter mode (radial) converges or couples near the same frequency with the one nodal circle mode X-mode), noise is often produced. The convergence of the radial and X-modes produces a hybrid mode shape than contains a contribution from each mode shape. The character of the hybrid mode shape includes one rotor cheek or plate being a radial mode shape and the other rotor cheek being a nodal diameter/nodal circle mode shape. The radial mode content of the hybrid mode receives energy from the tangential forces of the brake linings. The radial mode couples with the nodal circle/nodal diameter mode content to produce out-of-plane motion. This is the mechanism by which the hybrid mode can cause brake noise or squeal. In operation, the inverted T-shape vane design increases the stiffness of the nodal circle/nodal diameter modes, thereby moving their frequencies higher in the spectrum than the radial modes. The inverted T-shape vanes reduces or eliminates the hybrid coupling of these modes. 
     While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.