Abstract:
An electronic sensor for a vehicle braking system comprises an electrically conducting member housed inside an insulating body. A clip is adapted to receive the sensor and attached to a braking element of the vehicle braking system, preferably between adjacent portions of a brake lining. The clip is placed at a predetermined location such that a braking surface wears down only the brake lining without contacting the conducting member until the lining is sufficiently worn. At that time, the conducting member is separated to break an electrical circuit and provide an electronic signal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to electronic wear detection probes or sensors for vehicle braking elements.  
         [0002]     Brake lining wear sensors are well known and used in the prior art. Brake shoes and brake pads are composed of a suitable friction lining material mounted onto a metal back plate or table. The lining contacts the disc or drum, creates drag, and slow down the vehicle. Over time, the contact between the lining and the disc or drum causes the lining to wear. Thus it is desirable to provide an indication of when brake lining thickness is sufficiently worn to warrant changing of the lining.  
         [0003]     Typical electronic sensors that act as indicators are expensive and somewhat difficult to attach to brake shoes or pads. Such sensors are often molded directly into the brake lining material and therefore must be designed for use with a specific brake shoe or pad. This makes it very difficult, if not impossible, to modify a sensor manufactured for use on one vehicle braking system for use on a different vehicle braking system. It is therefore a goal of the present invention to provide a low cost lining wear sensor that easily clips on to any brake shoe or pad.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention includes a sensor comprising an electrically conducting member with a linkage portion housed inside an insulating body. The sensor is adapted for connection to a vehicle electronics system. The sensor is inserted into a clip which securely mounts on to a table of either a brake shoe or a brake pad, preferably between adjacent portions of a brake lining in the case of a brake shoe. A braking surface, either a brake drum or a brake rotor, at first wears away only the brake lining. However, the sensor is placed at a predetermined location such that the braking surface wears away the linkage portion of the conducting member to separate the conducting member into two to break an electrical circuit and provide an electronic signal when the lining is sufficiently worn.  
         [0005]     Thus the invention offers an electronic sensor that is easy to attach to both brake shoes and brake pads by way of an inexpensive clip. Further, the sensor can be used with different vehicle braking systems simply by changing the clip, thus further decreasing overall costs. If desired, it is also possible to reuse the clip with a different braking system by removing the clip from one braking system and placing it on another braking system, changing the sensor if necessary. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a perspective view of a portion of a vehicle drum brake system in accordance with a first embodiment of the present invention;  
         [0007]      FIG. 2  is a detail of  FIG. 1  showing a brake shoe table, a clip attached to the table, and a sensor received in the clip according to the present invention;  
         [0008]      FIG. 3  is a side view of  FIG. 2 ;  
         [0009]      FIG. 4  is a detail of  FIG. 2  showing the clip detached from the table and the sensor removed from the clip;  
         [0010]      FIG. 5  is a side view of  FIG. 4 ;  
         [0011]      FIG. 6  is a detail of the clip and the sensor of the present invention; and  
         [0012]      FIG. 7  shows the sensor received in a passage in the clip of the present invention.  
         [0013]      FIG. 8  is a side view showing a portion of a vehicle disc brake system in accordance with a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]      FIG. 1  shows a perspective view of a portion of a vehicle drum brake system in accordance with a first embodiment  10  of the present invention. The drum brake system includes a drum (not shown) with an inner surface (not shown) disposed about an axis of rotation A for frictionally engaging a brake lining (not shown). A pair of brake shoes  12 ,  12 ′ located adjacent the inner surface of the drum each include a backing plate comprising a table  14 ,  14 ′ and at least one brake lining segment (not shown). An actuator manipulates an S-cam  16  to move the shoes  12 ,  12 ′ into contact with the inner surface of the drum to provide a braking force, which is well known in the art.  
         [0015]     Referring to  FIG. 2 , a clip  18  receives a sensor  20  and attaches to the brake shoe table  14 , preferably between adjacent portions of the brake lining. Throughout this description, it should be understood that an additional clip  18 ′ receives an additional sensor  20 ′ in a like manner for connection to the second brake shoe table  14 ′. For ease of explanation, only one set of parts will be described. However, if desired only one sensor may be used. The sensor  20  comprises an electrically conducting member  22  housed within an insulating member  24 . The conducting member  22  includes a linkage portion  26  and is adapted for connection to a vehicle electronics system. As shown in  FIG. 3 , the top of the insulating member  24  includes a channel  28  for receiving the conducting member  22 . A pin  30  secures the conducting member  22  within the channel  28 .  
         [0016]     Turning now to  FIG. 4 , the base of the insulating member  24  includes a groove  32  for insertion into the clip  18 . The clip  18  includes a front portion  34 , a top portion  36  and a base portion  38  integrally formed with one another. The top portion  36  is formed at approximately a 90 degree angle to the front portion  34 , while the base portion  38  is formed at less than a 90 degree angle to the top portion  36 . Thus, when the clip  18  is received on the table  14 , the base portion  38  is biased away from the front portion  34 . When the two portions  34 ,  38  return to their relaxed positions, the resultant resisting force holds the clip  18  in place on the table  14  with the top portion  36  preferably flush against the table  14 . The base portion  38  preferably includes a base barb  39  at the end of the base portion  38  opposite the top portion  36  for maintaining the position of the clip  18  on the table  14 .  
         [0017]     Referring to  FIG. 5 , the front portion  34  includes a front surface  40  for receiving the sensor  20  and a back surface  42  for engaging the table  14 . The front surface  40  includes two arcuate projections  44 ,  46  surrounding an opening for retaining the sensor  20 . As best shown in  FIGS. 5-7 , the projections  44 ,  46  include chamfers  48 ,  50  and retaining tabs  52 ,  54 . The groove  32  of the base of the insulating member  24  of the sensor  20  fits between the arcuate projections  44 ,  46  beginning at the chamfered ends  48 ,  50 . The retaining tabs  52 ,  54  keep the sensor  20  in position within the clip  18 . The back surface  42  preferably contains a front barb  56 , preferably toward the end of the back surface  42  furthest from the top portion  36 . The front barb  56  helps to keep the clip  18  in place on the table  14 .  
         [0018]     When the vehicle braking system is in operation, the brake drum at first wears away only the brake lining. However, the sensor  20  is placed at a predetermined location such that the drum wears away the linkage portion  26  of the conducting member  22  to separate the conducting member  22  into two when the lining is sufficiently worn, thus breaking an electrical circuit. In the preferred embodiment, an electronic signal is generated when the circuit is broken to provide a warning that the brake lining thickness is below a predetermined thickness d, shown in  FIG. 1 . The electronic signal may be audible or visual, but is not limited thereto.  
         [0019]     In a second disclosed embodiment of the present invention, as shown in  FIG. 8 , the electronic lining wear sensor  20  is similarly used to detect wear in a vehicle disc brake system  100 . The disc brake system includes a rotor  102  with a pair of outer surfaces  104 ,  104 ′ disposed about an axis of rotation for frictionally engaging a brake lining material  110 ,  110 ′. A pair of brake pads  106 ,  106 ′, one located adjacent each outer surface of the rotor  100 , each include a backing plate  108 ,  108 ′ and at least one brake lining segment  110 ,  110 ′. An actuator moves the pads into contact with the outer surfaces of the rotor to provide a braking force, which is well known in the art. In accordance with the second embodiment, a clip  18  receives a sensor  20  and attaches to the brake pad table  110 ,  110 ′, preferably between adjacent portions of the brake lining  110 ,  110 ′ as described above. For a time, the rotor  102  wears away the lining  110 ,  110 ′ without contacting the sensor. When the lining  110 ,  110 ′ is sufficiently worn, the rotor  102  wears away the linkage portion  26  of the conducting member  22  and separates the conducting member  22  into two, breaking the electrical circuit and providing an electronic signal that the brake lining  110 ,  110 ′ is below a predetermined thickness d.  
         [0020]     Thus the invention offers an electronic sensor that is easy to attach to both brake shoes and brake pads by way of an inexpensive clip. Further, the sensor can be used with different vehicle braking systems simply by changing the clip, thus further decreasing overall costs.  
         [0021]     The preferred embodiments of the invention have been disclosed. However, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason the following claims should be studied to determine the true scope and content of this invention.