Abstract:
A brake hold down assembly for brake mechanisms has a hold down spring designed to ease spring installation and removal as well as reduce spring overstressing. Each leg of the spring has an open-ended slot therein, and the assembly also includes a retaining pin, which interfaces with the open-ended slot in each leg to lock the spring in place after installation. The spring is preferably p-shaped with a pair of opposing legs connected by an arcuate portion.

Description:
FIELD OF THE INVENTION 
     The invention is directed to a unique configuration for providing engagement between a pin and a spring, which finds particular utility as a hold-down assembly for a vehicle brake. In accordance with another feature of the invention, the spring is p-shaped to minimize overstressing of the spring during assembly and disassembly of the brake mechanism and to prevent unintended spring disengagement. 
     BACKGROUND ART 
     Various hold down devices and assemblies have been proposed to facilitate assembly and disassembly of brake mechanisms. One such assembly is designated by the reference numeral  10  in FIGS. 1A-1C. The assembly comprises a u-shaped spring  1  and a retaining pin  3 . The spring  1  has a pair of slots  5  and  7  to allow the pin  3  to pass therethrough. The slot  5  in leg  9  of the spring is elongated and recesses  13  are provided on opposite sides of the longer side of the slot  5 . A cap  15  is provided on one end of the pin  3 , and a stop  17  is provided on the other end. The stop  17  is elongate and sized to pass through the narrower dimension of the slot  5  when the pin is in a first orientation and to engage the recesses  13  when the pin is rotated to a second orientation 90 degrees from the first orientation. With the pin in the second orientation, the spring  1  and pin are locked together by reason of the spring force urging the upper leg  9  against the stop  17  at one end and against the backing plate  23  at the other. Thus, this spring assembly holds the brake shoe  21  in position against the backing plate. The brake shoe can be removed by disengaging the pin  9  from the spring  1  by compressing the spring and rotating the spring with respect to the pin to align the stop  17  with the slot  5 . 
     The prior art design shown in FIGS. 1A and 1B is not without its disadvantages. Referring to FIG. 1C, the spring  1  can be overstressed at  25  where the arcuate portion  27  joins the leg  9 . In this configuration, only the ends of the legs  9  and  12  contact each other. A substantial part of leg  9  is unsupported and vulnerable to permanent set if the pin load is too great. Further, this overstressing can also contribute to spring and brake mechanism failure. 
     Other commonly-utilized hold down assemblies have a coil spring and a retaining pin. Like the FIG. 1 assembly, these coil spring-containing assemblies require rotation of the spring or pin for disassembly. Further, the coil spring can be difficult to grab and rotate for removal. Constant removals and installations of these types of springs can also contribute to carpal tunnel syndrome in brake technicians. 
     U.S. Pat. No. 5,540,310 to Ludtke et al. shows another type of spring and pin arrangement for holding down brake components. In Ludtke et al., the spring has a u-shape similar to that shown in FIG. 1A; however, Ludtke et al. employ a slot in one leg of the spring to facilitate installation and removal of the spring. Ludtke et al. also use a well or recess to maintain engagement between the end of the pin and the spring. However, if the pin end rises up out, of the recess, the spring can disengage from the pin and compromise operation of the brake mechanism. 
     In light of the disadvantages of the prior art assemblies used in present day brake mechanisms, a need has developed to provide improved hold-down assemblies. The present invention solves this need by providing an improved brake hold down assembly that provides a positive locking mechanism and further eliminates overstressing experienced by prior art springs to minimize the possibility of permanent set or yield during spring compression. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is a brake hold down assembly employing a positive locking feature to avoid disengagement between the hold down spring and retaining pin. 
     A further object of the present invention is to provide an improved brake hold down assembly. 
     Another object of the present invention is a hold down assembly that avoids overstressing of the assembly&#39;s spring component during removal or installation. 
     Other objects and advantages of the present invention will become apparent as a description thereof proceeds. 
     In satisfaction of the objects, the invention provides a unique engagement between opposing legs of a spring, which are preferably p-shaped. The spring includes open-ended slots for receiving a retaining pin having a head shaped to cooperate uniquely with the shape of the slot. Thus, an elongate pin body has a cap at each end. At one end, the pin includes a shoulder adjacent a cap. The shoulder is wider than the pin body, but narrower than the adjacent cap. One of the opposing legs of the spring includes an opening at an inward termination of a slot that is slightly wider than the shoulder so that the shoulder can be received in the opening after the pin is slid through the slot and into the opening. When the pin has been moved through the slot and the shoulder is engaged in the opening, engagement between the shoulder and the side of the opening prevents movement of the retaining pin out of the slot and consequent disengagement of the pin from the spring. 
     A still further aspect of the invention is the combination of a p-shaped spring and the retaining pin for use in a brake mechanism. The p-shaped spring preferably has two parallel, opposed legs and an arcuate portion connecting the legs. The spring is generally p-shaped viewed from the side when the opposing legs are pressed together, which reduces overstressing of the spring during compression. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is now made to the drawings of the invention wherein: 
     FIG. 1A is a cross sectional view of part of a brake mechanism including a prior art brake hold down assembly. 
     FIG. 1B is a top view of the spring of FIG.  1 A. 
     FIG. 1C shows part of the hold down assembly of FIG. 1A in a compressed state. 
     FIG. 2 is a cross sectional view of part of a brake assembly showing one embodiment of the invention. 
     FIG. 3 is a view along the lines III—III of FIG.  2 . 
     FIG. 4 is a side view of the spring component of the assembly of FIG.  2 . 
     FIG. 5 is a top view of a free end of the spring of FIG.  4 . 
     FIG. 6 is a side view of the pin of the assembly of FIG.  2 . 
     FIG. 7 shows the assembly of FIG. 2 fully compressed. 
     FIG. 8 is a view along the lines VIII—VIII of FIG.  7 . 
     FIGS. 9A and 9B show an alternative locking arrangement for the inventive assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention offers significant advantages over prior art brake mechanism hold-down assemblies. First, the inventive assembly provides a unique, positive-locking engagement between a spring and a retaining pin, which overcomes the disadvantage of prior art designs where accidental disengagement of the spring from the pin can occur. Further, the inventive design eliminates or greatly reduces the overstressing of spring components found in prior art assemblies. 
     The spring-pin arrangement of the invention is easier to install because it can employ a lower spring rate than prior art designs. Installation does not require rotational motions by a mechanic, reducing the likelihood of exacerbating or causing carpal tunnel syndrome. Also, the possibility of creating permanent set in the spring is greatly reduced because the spring is not subjected to the large loads required to compress prior art springs. 
     While the invention may have alternative embodiments, one embodiment of the invention is depicted in FIGS. 2-8. Referring now to FIGS. 2-6, the inventive assembly is generally designated by the reference numeral  30  and includes a spring  31  and a retaining pin  33 . 
     With reference to FIGS. 2 and 4, the spring  31  preferably includes a pair of legs  35  and  37 , which are connected by an arcuate portion  39 . Each of the legs  35  and  37  has a respective slot  40  and  42 . The slots allow the retaining pin  33  to engage the spring  31  as explained in more detail below. The spring is shown in FIG. 4 in its rest state where legs  35  and  37  diverge from each other. 
     It will be appreciated that leg  37  extends from arcuate portion  39  at a small angle as shown at  44 , while leg  35  extends from the other end of portion  39  at a substantial angle, as shown at  46 . The arcuate portion  39  extends over an arc of about 270 degrees between the legs  35  and  37 , which can be contrasted with an arc of about 180 degrees in the prior art spring of FIG.  1 A. While a 270 degree arc is preferred, the arc can range from about 250-290 degrees. 
     Referring to FIGS. 2,  3 , and  6 , the retaining pin  33  of the invention includes an elongate pin body  41 , a cap  43  on one end of the body  41  and another cap  45  at the other end. Adjacent the cap  45  is a shoulder  47 . The width of the pin body  41  is designated “X”, the width of the shoulder  47  is designated “Y” and the width of the cap is designated “Z”. The width “Y” is greater than the width “X” and less than “Z”. The several widths function to retain the pin  33  in the slot in a positive locking engagement as explained below. 
     Referring now to FIGS. 2,  3 , and  5 , the slot  40  in leg  35  terminates in opening  48 , which has a width “Q” greater than the width of slot “P”. Width “Q” of opening  48  is larger than the width of shoulder  47  whereby it securely receives the shoulder  47 . 
     The width “P” of slot  40  is slightly larger than the width of the elongate pin body  41  thus allowing the pin body to slide along the slot during installation or removal of the pin when the shoulder  47  has been disengaged from the opening  48 . As shown in FIGS. 3 and 5, the slot  40  can have an enlarged or chamfered entrance at  51  to receive the pin body  41  easily during installation of the pin. 
     FIG. 2 shows the spring  31  with the pin  33  installed such that the spring is compressed. In this mode, the spring&#39;s legs  35  and  37  are held between the underside of the cap  45  of the pin  33  and a surface of a brake component plate  55 . The plate  55  shown is part of a brake shoe with the lining  57  attached to the lining substrate  59 . The spring leg  37  urges the plate  55  against the backing plate  23  with the leg  35  held in place and biased against the underside of the cap  45 . The cap  45  prevents expansion of leg  35  and is held against the force applied by the spring to leg  35  by engagement of the other cap  43  against the backing plate  61  at surface  67 . 
     The retaining pin  33  is locked in place in leg  35  by engagement between shoulder  47 , formed by a surface external to the pin, and opening  48 , formed by a surface internal to the leg and extending from the upper surface of the leg to the lower. Because the width of shoulder  47  is greater than the width of the slot  40 , i.e., “Q”&gt;“P,” the pin cannot become dislodged when the spring is in the configuration shown in FIG.  2 . 
     Although the shoulder  47  is depicted adjacent the cap  45 , it could be located on the pin body elsewhere as long as one of the legs  35  or  37  is configured to block the travel of the shoulder when the pin is biased between the cap  45  and the plate  55 . Referring to FIGS. 9A and 9B, the shoulder  47 ′ on the pin body  41 ′ could be spaced from the underside of cap  45 , and the leg  35 ′ could include protrusions  71  extending from the bottom  73  of the leg  35 ′. The slot  40 ′ would be wide large enough to accommodate the shoulder  47 ′. Compression of the leg  35 ′ as shown in FIG. 9B would allow the shoulder to slide out the slot  40 ′ in the direction “R” for disengaging the pin by moving the spring in direction “S”. If it is desirable to have the legs  35 ′ and  37  contact each other when compressed, the leg  37  could have cut outs to receive the protrusions  71 . 
     A significant advantage of the invention is the engagement between the shoulder  47  and the opening  48  in the leg  35 . This engagement prevents disengagement of the pin  33  from the spring  31  because the shoulder  47  is too large to slide through the slot  40 . The shoulder  47  is adjacent the cap  45  whereby the spring bias of the leg  35  against the cap  45  retains the shoulder  47  in the opening  48 . 
     The inventive assembly also facilitates removal of the spring  31  as well. With reference to FIGS. 7 and 8, the spring  31  can be removed by pressing the leg  35  against the leg  37 , which moves the shoulder  47  out of the opening  48  and aligns the narrower pin body  41  with the slot  40 , see FIG.  8 . Since the width “P” of the slot  40  is large enough to allow movement of the pin body  41  therein, depressing the leg  35  allows the spring  31  to be slid in the direction “D” and the pin body  41  to travel in the direction “E” out of the slots  40  and  42  of the legs  35  and  37 , respectively. Once the hold down spring  31  and retaining pin  33  are removed, the brake component can be removed and replaced. 
     Because the arcuate portion  39  includes a larger arc length than prior art designs, i.e., the leg  35  forms an angle with respect to the arcuate portion at  46  (FIG.  4 ), less stress is applied to the spring  31  in its compressed state. It will be appreciated that the spring shown in FIG. 1C is more stressed and that a permanent set can occur in such a spring. This contrasts with the inventive configuration, which reduces overstress on the spring. In the configuration illustrated in FIG. 2, the legs  35  and  37  face each other to engage along their entire lengths when fully compressed, as shown in FIG. 7, thereby preventing permanent set in the spring  31  when manipulated for spring removal or installation. The motion of legs  35  and  37  during compression also reduces the likelihood of aggravating or causing carpal tunnel syndrome because spring or pin rotation is not necessary for removal. 
     Installation of a new brake component would follow the removal procedure described above but in reverse. The pin  33 , if completely removed, would first be inserted through the opening  65  in the backing plate, and the opening  67  in the plate  55 . Then, the spring leg  35  would be compressed and the spring  31  slid onto the retaining pin  33 . The pin body  41  then slides in the slots  40  and  42 . The leg  35  would be released so that the spring is partially uncompressed whereby the shoulder  47  engages the opening  48  in the leg  35 . The spring  31  is then locked onto the pin  33  by engagement between the shoulder and the hole until the leg  35  is again depressed for spring removal. 
     It will be appreciated that the cross sectional shapes of the shoulder and opening can be non-circular. For example, the shoulder  47  could have a square or octagonal cross section with the opening  48  having a corresponding shape to assure that the shoulder interlocks in the opening when the spring expands. Likewise, although the pin body can be circular, square, rectangular, hexagonal or another shapes as would be within the skill of the artisan can be employed. 
     The spring can be made out of any material having the necessary strength and spring constant to hold down the brake component on the backing plate. Similarly, the pin can be made of any material capable of withstanding the forces applied by the spring. 
     As is evident from FIGS. 2-8, the hold down assembly is particularly adapted for brake mechanisms employing brake shoes. However, the inventive assembly can be used in any brake mechanisms that would require the need for hold down springs and retaining pins, whether they are brake shoes, pads, or other types of brake components. 
     As such, an invention has been disclosed in terms of preferred embodiments thereof which fulfills each and every one of the objects of the present invention as set forth above and provides a new and improved brake hold down assembly. It will be appreciated by those of skill in the art that the inventive engagement may find uses in other environments as well. 
     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.