Abstract:
A vibration attenuator for a disk brake lathe has two friction pads, each having a pad recess with a distal wall and a proximal wall. When the pads are placed against a brake disk, the recesses are placed over raised heads of fasteners that affix cutting tools of the lathe to adjustable tool holders. When the tool holders are moved radially outwards across the brake disk, the fastener raised heads engage the recess proximal walls and move the pads along with the cutting tools, and also serve to couple the pads with the cutting tools to dampen vibrations. Similarly, when the tool holders are moved radially inwards, the fastener raised heads engage the recess distal walls to move the pads along with the cutting tools. A U-shaped member having a tension spring extending between two legs on which the pads are mounted forcibly engages the pads with the brake disk.

Description:
FIELD OF THE INVENTION 
     The present invention is for a vibration attenuator for use with a disk brake lathe to reduce noise and vibrations resulting from machining the surfaces of a brake disk by the lathe. 
     BACKGROUND OF THE INVENTION 
     Automotive brake disks are periodically resurfaced by a disk brake lathe in order to maintain adequate operation. The disk brake lathe typically has a pair of cutting tools, each attached to a tool holder by a fastener to allow replacement when the cutting tool becomes worn. The tool holders position the cutting tools against the surfaces of the brake disk to establish a desired depth of cut, and then maintain the cutting tools in position as they are drawn across the disk surfaces while the lathe rotates the brake disk in order to machine the disk surfaces. Typically, the desired depth of cut is set at a position near the center of a radius of the disk surface while the brake disk is rotated, and the cutting tools are then moved toward the center of the brake disk to begin the machining process. The cutting tools are then moved radially outwards to resurface the brake disk. 
     Vibrations caused by the cutting action of the cutting tools on the disk surfaces need to be attenuated, both to reduce chattering of the cutting tools to assure that the resulting machined disk surfaces are sufficiently planar for proper operation, and to reduce undesirable noise in the machining environment. One approach to reducing vibrations has been the use of friction pads which are biased against the disk surfaces and engage the cutting tools, the tool holders, and/or the fasteners. 
     U.S. Pat. No. 3,710,661 teaches a vibration dampener where friction pads engage either the tool holders or the cutting tools. The friction pads are positioned and biased against the disk surfaces by a scissors-shaped spring, which in turn is pivotably mounted to a cutting head assembly of the lathe. Since the friction pads and spring are mounted to the cutting head assembly on which the tool holders are also mounted, the friction pads move with the tool holders as the cutting head assembly is moved to position the cutting tools near the center of the brake disk and to subsequently advance the cutting tools radially across the disk surfaces. The pivotable mounting allows the spring and friction pads to be pivoted away from the cutting tools to allow the cutting tools to be replaced. Having the vibration dampener attached to the cutting head assembly may make it difficult to position the friction over the disk surfaces. Furthermore, having the spring pivotably mounted can create interference problems if the vibration dampener is to be used on a lathe, such as those made by Pro-Cut International, the assignee of the present application, which has a lock knob mounted to the top of the cutting head assembly. The lock knob serves to secure the tool holders in position once the depth of cut has been set, and typically is too large to allow a spring such as employed in the &#39;661 vibration dampener to be pivoted past the lock knob. 
     U.S. Pat. No. 4,531,434 teaches a vibration attenuator which does not require that the spring be mounted to the cutting head assembly. In the &#39;434 attenuator, friction pads are provided with pins which engage either the cutting tools or the tool holders as the cutting tools are moved radially outwards, this engagement serving to move the friction pads along with the cutting tools as the brake disk is resurfaced. The friction pads are mounted on a U-shaped spring assembly which is independent of the cutting head assembly. However, it has been found that the particular geometry constraints of the &#39;434 vibration attenuator limit its effectiveness for many lathe configurations. Furthermore, the use of pins extending from the pads may limit usefulness when the clearance above the cutting tools is restricted by a brake caliper bracket associated with the brake disk. 
     To overcome the limitations of the &#39;434 vibration attenuator, U.S. Pat. No. 6,227,085 teaches a vibration attenuator where the friction pads are provided with protruding engagement nubs which engage raised heads of the fasteners used to affix the cutting tools to the tool holders when the cutting tools are moved radially outwards. In addition to serving to move the friction pads along with the cutting tools as the brake disk is resurfaced, this engagement is purported to provide superior reduction of vibrations. The &#39;085 patent reports that the particular geometry of the vibration attenuator is well suited for use with disk brake lathes sold by Pro-Cut. 
     A limitation of both the &#39;434 and &#39;085 vibration attenuators is that they only move the friction pads along with the cutting tools when the cutting tools are moved radially outwards. When the cutting tools are moved radially inwards, the pins become disengaged from the cutting tools or tool holders in the case of the &#39;434 vibration attenuator, or the engagement nubs become disengaged from the raised head of the fasteners in the case of the &#39;085 vibration attenuator. In either case, when the cutting tools are moved radially inwards, the friction pads of the vibration attenuator become disengaged and do not move with the tool holders, requiring the vibration attenuator to be repositioned. This requirement is inconvenient in situations where the cutting tools are advanced more than once across the disk surfaces. This can occur if the first pass of the cutting tools over the disk surfaces is found insufficient to provide planar disk surfaces, or if one of the disk surfaces is deeply scored by wear. In such cases, after the cutting tools have been advanced radially outwards, they are moved radially inwards and set with an increased depth of cut, then advanced again across the disk surfaces. The unidirectional limitation of the &#39;434 and &#39;085 vibration attenuators requires that the vibration attenuator be repositioned after the cutting tools are moved radially inwards, adding an additional step to the procedure. 
     U.S. Publication US 2001/0011490 is a continuation-in-part of the application which issued as the &#39;085 patent, and teaches a nub configuration which is designed for a disk brake lathe sold by Pro-Cut. The nub is configured to affirmatively hold the nub in contact with the raised head of the fastener of the cutting tool as the tool is advanced across the disk surface. The nub also contacts an angled surface on the tool holder, which is reported to move the nub into engagement with the raised head when the disk is rotated. The operation of the &#39;490 vibration attenuator is dependent on a particular configuration of the tool holders of the disk brake lathe, and thus a particular vibration attenuator would appear to be dedicated to a particular model of lathe. 
     Thus, there is a need for a vibration attenuator for disk brake lathes which overcomes the deficiencies of the above referenced devices. 
     SUMMARY OF THE INVENTION 
     The present invention is for an improved vibration attenuator for a disk brake lathe. The attenuator provides a more flexible coupling mechanism for assuring that the attenuator tracks cutting tools of the lathe in a manner appropriate to reduce the vibration of the cutting tools as they traverse disk surfaces of a brake disk. Furthermore, the tracking is bi-directional and allows the attenuator to be positioned by the action of the cutting tools without requiring that the attenuator be affixed to a cutting head assembly used for advancing the cutting tools. Similarly, the design of the attenuator is such that its advancement with the cutting tools is not dependant on the details of the geometry of the cutting head assembly, its tool holders, or the associated cutting tools. 
     The vibration attenuator of the present invention is designed for use with a disk brake lathe having a cutting head assembly which has a pair of cutting tools. Each of the cutting tools is mounted to an associated tool holder and attached thereto by a fastener. The fastener has a fastener raised head having a head sidewall and a head top. The lathe is provided with means for moving the cutting head assembly such that the tool holders traverse a path that is substantially radial with respect to the brake disk. 
     The attenuator has a pair of friction pads, each having a disk-engaging surface which, when in service, is brought into frictional contact with a disk surface of the brake disk. Each of the pads is bounded by a pad lower surface which resides between a pad proximal surface and a pad distal surface. Each of the pads contains a pad recess in the pad lower surface. The pad recess is bounded, in part, by a recess distal wall and a recess proximal wall. These recess walls initiate at the pad lower surface and terminate at a recess bottom which is spaced apart from the pad lower surface by a recess depth D, and the recess distal wall and the recess proximal wall are separated by a recess width W of sufficient size to accommodate one of the fastener raised heads. The depth D should be sufficient to assure extended contact between the recess walls and the head sidewall of the raised head, but not necessarily the head top of the raised head. In some embodiments, the recess could extend completely through the pad, but such would limit the useful life of the resulting vibration attenuator as the pads wear. 
     When the pad recess is placed over the fastener raised head, the fastener raised head engages the recess proximal wall when the cutting head assembly is moved to advance the cutting tools radially outwards across the disk surfaces. This engagement serves to move the friction pad along with the cutting tool and the tool holder associated with the fastener, as well as serving to couple the friction pad with the cutting tool to dampen vibrations. Similarly, when the cutting head assembly is moved radially inwards, the fastener raised head engages the recess distal wall to move the friction pad along with the cutting tool and the tool holder. 
     It is preferred that a setback X of the recess distal wall from the pad distal surface be provided that is sufficiently large as to maintain each of the pads in contact with its associated one of the disk surfaces when the cutting tools have reached the periphery of the disk. Preferably, the setback X should also be maintained small enough to avoid interference of the pads with a wheel hub associated with the brake disk as the cutting tools approach the wheel hub. 
     Spring means for forcibly engaging the disk-engaging surfaces of the friction pads with the disk surfaces are provided. One preferred embodiment of the spring means is to employ a U-shaped member having a pair of legs, with each of the legs mounting into the pad proximal surface of one of the pads, and having a tension spring extending between the legs. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is an isometric view of a prior art cutting head assembly of a disk brake lathe, with a vibration attenuator which forms one embodiment of the present invention installed thereover. The cutting head assembly has a pair of cutting tools, each mounted to an adjustable tool holder by a fastener having a raised head. The vibration attenuator has a pair of friction pads, each of which has a recess configured to be engaged by one of the raised heads when the cutting tool assembly is moved radially outwards or radially inwards with respect to a brake disk, shown in phantom. 
     FIG. 2 is a detail view showing one of the fasteners which affixes one of the cutting tools to one of the tool holders of the cutting head assembly shown in FIG.  1 . 
     FIG. 3 is an isometric view of the vibration attenuator shown in FIG. 1, which is shown in an inverted position to more clearly show the details of the recesses. 
     FIG. 4 is an enlarged isometric view of one of the friction pads of the vibration attenuator shown in FIGS. 1 and 3, showing further details of the recess. 
     FIG. 5 is an isometric view of a vibration attenuator which forms another embodiment of the present invention. This vibration attenuator has recesses which traverse the thickness of the pads, allowing the vibration attenuator to be positioned more readily. 
     FIGS. 6 and 7 are partial top views of the vibration attenuator shown in FIG. 5, showing how the vibration attenuator can be slid into position. When the recesses are aligned with fastener raised heads, the pads snap into engagement with the brake disk, as shown in FIG.  7 . 
     FIG. 8 is an isometric view of a vibration attenuator which forms another embodiment of the present invention that is similar to the vibration attenuator shown in FIGS. 5-7. The pads of this embodiment have guide surfaces which facilitate sliding the recesses into position with respect to the fastener raised heads. 
     FIG. 9 is a partial view showing the relationship between the depth of the recess and the height of the fastener raised head for the embodiment shown in FIG.  8 . In this embodiment, the recess depth is greater than the height of the fastener raised head, and a pad lower surface of the pad engages the cutting tool. 
     FIG. 10 is a partial view similar to that of FIG. 9, showing an alternative embodiment where the recess depth is less than the height of the fastener raised head. In this embodiment, a recess bottom engages a head top of the fastener raised head, and the pad lower surface is spaced apart from the cutting tool. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is an isometric view showing a prior art cutting head assembly  10  of a disk brake lathe (the remainder of which is not shown) such as the disk brake lathe described in U.S. Pat. No. 6,101,911 for which the present invention is suitable. A vibration attenuator  12  of the present invention is shown engaged with the cutting head assembly  10 . The cutting head assembly  10  has a pair of adjustable tool holders  14 , and FIG. 2 shows a portion of one of the tool holders  14  in greater detail. The separation between the tool holders  14  is controlled by a pair of graduated dials  16 . A pair of cutting tools  18  are attached to the tool holders  14  and are affixed thereto by fasteners  20  (one of which is shown in FIG.  2 ), each having a raised head  22  with a height H. Frequently the raised head  22  is substantially cylindrical in form, having a diameter d. The graduated dials  16  allow the cutting tools  18  to be positioned with a desired depth of cut for machining a brake disk  24  (shown in phantom). The cutting tools  18  engage disk surfaces  26  (only one of which is viewable) which are to be machined to return the brake disk  24  to its operating specification. A lock knob  28  on the cutting head assembly  10  is turned to secure the tool holders  14  in position once the cutting tools  18  have been adjusted with respect to the brake disk  24 . 
     FIG. 3 illustrates details of the vibration attenuator  12  shown in FIG.  1 . In FIG. 3, the vibration attenuator  12  is shown in an inverted position to better illustrate its structure. The vibration attenuator  12  has a pair of friction pads  30 , each of which has a disk-engaging surface  32  which makes frictional contact with one of the disk surfaces  26 . Each of the friction pads  30  is further bounded by a pad lower surface  34  which resides between a pad distal surface  36  and a pad proximal surface  38 . 
     The pad lower surfaces  34  are each provided with a pad recess  40  having a depth D and a width W sufficient to accommodate at least a portion of one of the raised heads  22 . The recess  40  is configured to accommodate the raised head  22  even after substantial wear on the disk-engaging surface  32 . The recess  40  in this embodiment is partially bounded by a recess bottom  42 , and the separation between the recess bottom  42  and the pad lower surface  34  defines the recess depth D. This recess depth D is not critical to the design; however, it should be great enough to allow sufficient contact between the raised head  22  and the recess  40  to counteract torques created when the brake disk  24  rotates, which might otherwise disengage the friction pad  30  from the raised head  22 . It is not necessary for the depth D to be as large as the height H of the raised head  22 . 
     As better shown in FIG. 4, each of the recesses  40  is also bounded, in part, by a recess proximal wall  44  and a recess distal wall  46 . The separation between the recess proximal wall  44  and the recess distal wall  46  defines the recess width W. When the raised head  22  has a diameter d, the recess width W is selected to be somewhat greater than the diameter d. The recess proximal wall  44  is engaged by one of the raised heads  22  as the cutting tools  18  are advanced radially outwards across the disk surfaces  26 . This engagement moves the friction pads  30  radially outwards with the cutting tools  18 . When the cutting tools  18  reach the extremities of the brake disk  24 , the cutting tools  18  may be drawn back to a central hub region  48  of the brake disk  24 . The friction pads  30  track the motion of the cutting tools  18 , since the recess distal walls  46  are engaged by the raised heads  22  as the cutting tools  18  are moved radially inwards. 
     The separation between the pad distal surface  36  and the recess distal wall  46  defines a setback X. The setback X must be sufficient to withstand the forces of the raised head  22  as the cutting tool  18  is drawn toward the hub region  48  of the brake disk  24 . It is preferred for the setback X to have a minimum value sufficient to maintain the pads  30  in contact with the disk surfaces  26  when the cutting tools  18  have reached and/or slightly overshot the periphery of the brake disk  24 . To achieve such, the setback X should be selected with respect to the cutting tool  18  such that, when the raised head  22  engages the recess distal wall  46 , the pad distal surface  36  extends somewhat beyond the portion of the cutting surface of the cutting tool  18  which is active in causing removal of material from the disk surface  26  as the cutting tool  18  is advanced across the brake disk  24 . 
     Similarly, the setback X should be maintained small enough to reduce the likelihood of interference of the pads  30  with a wheel hub  50  as the cutting tools  18  approach the wheel hub  50  when the brake disk  24  is being resurfaced while remaining in place on a vehicle. Such interference can be avoided in most cases by setting a practical upper limit for the setback X of about 5 mm (0.2 inches). A setback X of about 3.00 mm (0.118 inches) has been found effective for typical cutting tools  18 . For some configurations of the tool holders  14 , it may also be preferred for a lower section  52  of the pad proximal surface  38  to be sloped toward the recess  40  to reduce the likelihood of interference between the pad  30  and the tool holder  14 . 
     In the vibration attenuator  12 , spring means for forcibly engaging the disk-engaging surfaces  32  of the friction pads  30  with the disk surfaces  26  are provided by a U-shaped handle  54  having a pair of legs  56 . Each of the legs  56  passes through the proximal surface  38  of one of the friction pads  30  and is engaged in a pad passage (not shown) sized to frictionally hold the leg  56  in the friction pad  30 . A tension spring  58  is connected between the two legs  56  and is sized such that, when the pads  30  are placed on the disk surfaces  26  (as shown in FIG.  1 ), there is a compressive load applied to the brake disk  24  to create a frictional force between the friction pads  30  and the disk surfaces  26  as the brake disk  24  rotates. 
     While the recess illustrated in FIGS. 3 and 4 traverses less than the full width of the pad, the recess can traverse the full thickness of the pad. FIG. 5 is an isometric view of a vibration attenuator  100  which, like the vibration attenuator  12 , has a pair of friction pads  102  which attach to a U-shaped handle  104 . The U-shaped handle  104  has a pair of legs  106  which in turn are each embedded in one of the pads  102 . A tension spring  108  is attached to the legs  106  and causes the pads  102  to forcibly engage a brake disk  110  (as shown in FIG.  7 ). In this embodiment, each of the pads  102  is again provided with a recess  112 . However, in this embodiment the recess  112  traverses the thickness T of the pad  102 . This simplifies the fabrication of the pads  102  and also simplifies positioning the pads  102  on the disk  110  such that the recesses  112  engage fastener raised heads  114 , shown in FIGS. 6 and 7. 
     The partial top views of FIGS. 6 and 7 illustrate how having the recess  112  traverse the thickness T of the pad  102  can assist in positioning the vibration attenuator  100 . In this embodiment, the vibration attenuator  100  can be placed over the fastener raised heads  114  by separating the pads  102  such that disk-engaging surfaces  116  of the pads  102  straddle the fastener raised heads  114  as shown in FIG.  6 . As the pads  102  are advanced across the fastener raised heads  114 , the fastener raised heads  114  can enter the recesses  112  to allow the disk-engaging surfaces  116  of the pads  102  to be brought into frictional contact with the brake disk  110 , as shown in FIG.  7 . In fact, after a period of wear, the embodiment illustrated in FIGS. 1,  3  and  4  may well result in the pad recesses  40  traversing the residual thickness of the pads  30 . 
     FIG. 8 illustrates another embodiment of the invention, a vibration attenuator  200  which shares many of the features of the vibration attenuator  100  illustrated in FIGS. 5-7. The vibration attenuator  200  again has a pair of pads  202  that each has a recess  204  which traverses the thickness T of the pad  202 . In this embodiment, each pad  202  is also provided with a guide surface  206  which intersects a recess distal wall  208  of the recess  204 . The guide surfaces  206  facilitate placing the pads  202  over fastener raised heads  210  (one of which is shown in FIG. 9) using the technique discussed above and illustrated in FIGS. 6 and 7. To preserve the ability of the friction pad  202  to be moved radially inwards by the fastener raised head  210 , the guide surface  206  should be configured such that the recess distal wall  208  is spaced apart from a disk-engaging surface  212  of the pad  202  by somewhat less than the diameter d of the fastener raised head  210 . Preferably, the recess distal wall  208  is spaced apart from the disk-engaging surface  212  by less than one half the diameter d. 
     FIG. 9 is a partial side view showing one of the recesses  204  and one of the fastener raised heads  210 . In this embodiment, the recess  204  has a recess bottom  214  that is separated from a pad lower surface  216  by a recess depth D which is greater than a height H of the fastener raised head  210 . When the recess depth D is greater than the height H, the pad lower surface  216  engages a cutting tool  218  associated with the fastener raised head  210 . The recess bottom  214  is separated from a head top  220  of the fastener raised head  210 . 
     FIG. 10 is a partial side view of an alternative pad  202 ′ having a recess  204 ′ with a recess bottom  214 ′ that is separated from the pad lower surface  216  by a recess depth D which is less than the height H. With the alternative pad  202 ′, the recess bottom  214 ′ engages the head top  220  of the fastener raised head  210 , and the pad lower surface  216  is spaced apart from the cutting tool  218 . In such cases, the pad lower surface  216  need not have a substantially planar configuration as illustrated, and could be curved, faceted, or otherwise configured. The pad lower surface  216  could be configured to suit a particular configuration of tool holder. 
     While the novel features of the present invention have been described in terms of particular embodiments and preferred applications, it should be appreciated by one skilled in the art that substitution of materials and modification of details obviously can be made without departing from the spirit of the invention.