Abstract:
A wear detection probe for a braking element includes a holder with opposed front and rear ends. A portion of the holder near the front end is configured to retain a detection wire. Thus, after sufficient wear of the brake and the holder, the detection wire will be broken to produce a signal indicative of brake wear. The holder includes two arrangement grooves extending from the abradeable portion of the detection wire to the rear end of the holder. The wear detection probe further includes a rib. The extreme rear end of the rib may include a slot, and a heat shrinkable tube may surround the wires and engage partly in the slot.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wear detection probe or sensor for a brake pad. 
     2. Description of the Related Art 
     Wear detection probes are known for detecting when a brake pad of an automotive vehicle has been worn to an operating limit or to a degree that it cannot be used any longer. The known wear detection probe is shown in FIG. 5, and is identified by the numeral  1 . The prior art probe  1  includes a detection wire  3  made integral to a resin holder  2  by insert molding. The detection wire  3  extends along an arrangement path through the holder  2  from its rear end to its front end. The detection wire  3  then is formed with a fold  3 R at the front end surface of the holder  2  and extends back to the rear end. 
     The prior art wear detection probe  1  is accommodated in a brake pad  5  such that the folded portion  3 R of the detection wire  3  faces a disk rotor  4  like a brake disk. As the wear of the brake pad  5  progresses, the wear detection probe  1  is exposed to a pad surface of the disk rotor  4  and, accordingly, the folded portion  3 R of the detection wire  3  starts to abrade. When the wear of the brake pad  5  reaches its operating limit, the detection wire  3  is cut and a warning lamp (not shown) signals that the wear of the brake pad  5  has reached its operating limit. 
     The prior art wear detection probe  1  thus constructed has a problem of high production costs because the detection wire  3  is made integral to the holder  2  by insert molding. 
     In view of this problem, an object of the present invention is to reduce production costs. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided a wear detection probe for a braking element, in which a detection wire is arranged in a path which substantially folds the detection wire at the front or abrasion end of a holder and extends to the rear end of the holder. Thus, wear of the braking element to its operating limit is detected when the folded portion of the detection wire is cut by a rotor. The wear detection probe includes at least one arrangement groove formed in the holder to extend substantially from the rear end of the holder to the folded portion of the detection wire. The detection wire is fitted or inserted in the arrangement groove. The wear detection probe further includes a restricting means for preventing the detection wire from coming out of the arrangement groove. 
     Since the wear detection probe is assembled by fitting the detection wire in the arrangement groove of the singly formed holder, production costs can be reduced as compared with the prior art wear detection probe in which the holder and the detection wire are made integral to each other by insert molding. 
     According to a preferred embodiment, the arrangement groove of the path is substantially formed in the outer surface of the holder. Although the detection wire is arranged in an arrangement groove that opens to an outer surface of the holder, the restricting means prevents the detection wire from coming out of the arrangement groove. Accordingly, the detection wire remains in the arrangement groove. 
     According to a further preferred embodiment, there is provided a wear detection probe for a braking element, in which a detection wire is arranged in a path which folds the detection wire at the front end of the holder and extends to the rear end of the holder. Wear of the braking element to its operating limit is detected when the folded portion of the detection wire is cut by the rotor. The wear detection probe includes at least one arrangement groove which is formed in the outer surface of the holder. The arrangement groove extends from the rear end of the holder to the location specified for the folded portion of the detection wire. The wire is fitted in the arrangement groove(s), and a restricting means is provided for preventing the detection wire from coming out of the arrangement groove(s). 
     Preferably, two arrangement grooves are formed, and the restricting means comprises a rib projecting from the rear end surface of the holder in a position to partition two extending portions of the detection wire extending from the arrangement grooves. A slit preferably is formed in the rib and opens in the rear edge of the rib. A connecting member is fitted or fittable through or into the slit and is adapted to connect the two extending portions of the detection wire at the opposite sides of the rib. 
     The two extending portions of the detection wire extending from the arrangement grooves are engaged with the rib by fitting the connecting member in the slit. Since the slit is open in the rear edge of the rib which intersects with the outer surface of the holder, the connecting member will not be disengaged from the slit. This prevents the detection wire from coming out of the arrangement grooves. 
     Preferably, the connecting member comprises a heat shrinkable tube, a rubber tube and/or a tube made out of soft resin that is fitted or fittable at least partly on the extending portions of the detection wire corresponding to the slit. Accordingly, the detection wire easily can be prevented from coming out of the arrangement grooves. 
     The slit preferably extends at an angle different from 0° or 180°, and most preferably substantially normal to the two extending portions of the detection wire that extend from the arrangement grooves. 
     According to a further preferred embodiment, the path comprises at least one through hole for substantially communicating with two or more arrangement grooves. The through hole is arranged at an angle different from 0° or 180°, and preferably substantially normal to the arrangement grooves and/or normal to the longitudinal direction of the holder. Accordingly, since the arrangement path in which the detection wire is fitted or arranged preferably is bent, a displacement of the detection wire can be prevented securely. 
     The path may further comprises a communication groove, which is open in the upper outer surface of the holder and which communicates between the upper sides of the through holes. 
     Further preferably, the folded portion is arranged substantially parallel to the front or abrasion end of the braking element and in a direction substantially normal to an axis of rotation of the rotor. 
     Most preferably, one or more extending portions of the detection wire extending from the one or more arrangement grooves are arranged at one or more heights being which are different from portions of the detection wire which are arranged in the arrangement grooves. 
     These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a wear detection probe according to a first embodiment of the invention. 
     FIG. 2 is a section of the wear detection probe in its mounted state. 
     FIG. 3 is a rear view of the wear detection probe without a detection wire. 
     FIG. 4 is a rear view of the wear detection probe with the detection wire assembled. 
     FIG. 5 is a section of a prior art wear detection probe. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, one embodiment of the invention applied to a known disk brake of an automotive vehicle is described with reference to FIGS. 1 to  4 . This disk brake is comprised of a brake lining member B (braking element) for pressing the opposite surfaces of a disk-shaped rotor R which is integrally rotated with an unillustrated wheel. The disk brake further compromises a support member S to which the braking lining member B is fixed. The support member S and the brake lining member B are formed with mount holes Sh, Bh which are substantially aligned with each other. A wear detection probe or sensor P, according to this embodiment, is mounted or mountable in these mount holes Sh, Bh. 
     The wear detection probe P is comprised of a holder  10  and a known detection wire  20  obtained e.g. by resin-coating a metal braided wire. 
     The holder  10  is made of a heat resistant resin material and is an integral or unitary assembly of a cylindrical portion  11 , an enlarged portion  12  and a rib  13 . The enlarged portion  12  is substantially continuous with the rear end of the cylindrical portion  11  and is substantially concentric with the cylindrical portion  12 . The rib  13  preferably is in the form of a substantially rectangular plate and projects from the rear end of the enlarged portion  12 . An arrangement path for arranging the detection wire  20  is formed in the cylindrical portion  11  and the enlarged portion  12 . 
     The arrangement path includes two through holes  15 F,  15 R which extend in a direction at an angle different from 0° or 180°, preferably substantially normal to the longitudinal direction of the holder  10  at the front end of the holder  10 . A communication groove  16  is open in the (upper) outer surface of the cylindrical portion  11  and substantially communicates between the (upper) sides of the through holes  15 F,  15 R. Two arrangement grooves  17 L,  17 R are substantially open in the (lower) outer surfaces of the cylindrical portion  11  and the enlarged portion  12 . The arrangement grooves  17 L and  17 R individually extend backward from the lower openings of the through holes  15 F,  15 R, and are substantially open in the rear end surface of the enlarged portion  12 . The detection wire  20  is arranged in the right arrangement groove  17 R, the front through hole  15 F, the communication groove  16 , the rear through hole  15 R and the left arrangement groove  17 L in this order. It should be appreciated that the inner diameter and the width of the arrangement path are set substantially equal to the outer diameter of the resin coating of the detection wire  20 . 
     FIG. 2 is a section along the left arrangement groove  17 L which communicates with the rear (right in FIG. 2) through hole  15 R. The orientation of the wear detection probe P in FIG. 2 is laterally opposite from that in FIG.  1 . Accordingly, although the right arrangement groove  17 R is seen to be located more forward than the left arrangement groove  17 L in FIG. 1, the right arrangement groove  17 R cannot be seen in FIG. 2 in which the left arrangement groove  17 L is shown because it is located behind the left arrangement groove  17 L. 
     To mount the detection wire  20  in the arrangement path, the ends of the folded detection wire  20  are inserted through or into the front and rear through holes  15 F,  15 R from above the holder  10 . A portion of the detection wire  20  that comes out of the front through hole  15 F is fitted in the right arrangement groove  17 R. A portion of the detection wire  20  that comes out of the rear through hole  15 R is fitted in the left arrangement groove  17 L. The portion of the detection wire  20  located in the front through hole  15 F serves as a folded portion  20 R. When the wear of the brake lining member B reaches its operating limit, the folded portion  20 R is abraded with the front end of the cylindrical portion  11  to be consequently cut. Extending portions  20 S of the detection wire  20  are exposed from the rear ends of the arrangement grooves  17 L,  17 R and extend backwardly along the left and right surfaces of the rib  13 . The extending portions  20  are secured to an unillustrated terminal fitting and connected with an unillustrated breakage detecting circuit via a connector. Preferably, the extending portions  20 S are arranged at a height or position which is substantially different from or offset from the portions of the detection wire  20  in the arrangement grooves  17 L,  17 R. In other words, the extending portions  20 S are located below and/or above the portions of the detection wire  20  in the arrangement grooves  17 L,  17 R. 
     The wear detection probe P is mounted by a pair of mount pins  18  which project from the outer surface of the enlarged portion  12  such that the enlarged portion  12  and the rib  13  are accommodated in the mount hole Sh of the support member S and such that the cylindrical portion  11  is accommodated in the mount hole Bh of the brake lining member B. In this mounted state, the front end of the holder  10  faces the rotor R. At this time, the folded portion  20 R of the detection wire  20  extends in the vertical direction of FIG. 2 which is substantially same as the rotating direction of the rotor R or a tangential direction of the rotor R with respect to its axis of rotation. When the thickness of the brake lining member B is reduced to a specified degree as the wear thereof progresses, the front end of the wear detection probe P and the folded portion  20 R are abraded by the contact with the rotor R and, consequently, the detection wire  20  is cut. In this way, it is detected that the wear of the brake lining member B has reached its operating limit. 
     The holder  10  of this embodiment is provided with a restricting means  25  for preventing the detection wire  20  from coming out of the arrangement grooves  17 L,  17 R. This restricting means  25  preferably is comprised of the rib  13 , a slit  19  formed in the rib  13  and a heat-shrinkable tubing  26  (connecting member). 
     The rib  13  is arranged to partition the two extending portions  20 S of the detection wire  20  that extend from the arrangement grooves  17 L,  17 R. Thus the extending portions  20 S extend along opposite surfaces of the rib  13 . The slit  19  is formed to be open in the rear end of the rib  13  and extend along forward and backward or longitudinal directions. The heat-shrinkable tubing  26  is fitted to surround the two extending portions  20 S together after the detection wire  20  is arranged in the holder  10 . An end of the heat-shrinkable tubing  26  toward the holder  10  is deformed or treated to be held in the slit  19 , and the heat-shrinkable tubing  26  is heated in this state. Then, the heat-shrinkable tubing  26  is so deformed as to reduce its diameter and is adhered to both extending portions  20 S. In this way, the heat-shrinkable tubing  26  and the detection wire  20  are made substantially integral to each other. 
     In this state, the flat heat-shrinkable tubing  26  extends substantially horizontally or transversely in the slit  19  as shown in FIG.  4 . In front of the slit  19 , loose lateral movements of the two extending portions  20 S split on the opposite sides of the rib  13  are restricted by the contact with the rib  13 . Accordingly, the heat-shrinkable tubing  26  integral to the extending portions  20 S cannot laterally move to come out of the slit  19 . Loose vertical movements of the extending portions  20 S (or movements thereof substantially in the plane of the rib  13 ) are restricted by the engagement of the heat-shrinkable tubing  26  and the slit  19 . In other words, this prevents the detection wire  20  from coming down out of the arrangement grooves  17 L,  17 R. 
     Since the wear detection probe P according to this embodiment is of the type in which the detection wire  20  is fitted in the arrangement path of the singly formed holder  10 , production costs are lower than the prior art wear detection probe in which the holder and the detection wire are made integral to each other by insert molding. 
     Although the detection wire  20  merely is fitted or inserted in the arrangement grooves  17 L,  17 R which are open in the outer surface of the holder  10 , the detection wire  20  does not come out of the arrangement grooves  17 L,  17 R because the loose vertical movement of the detection wire  20  is restricted by fitting the heat-shrinkable tubing  26  integrally mounted on the detection wire  20  in the slit  19 . 
     Further, since the arrangement path in which the detection wire  20  is fitted is bent, a displacement of the detection wire  20  can be prevented securely even if a pulling force acts on only one of the two extending portions  20 S of the detection wire  20  in a backward direction. 
     Furthermore, since the two through holes  15 F,  15 R are so formed as to extend in a direction at an angle different from 0° or 180°, preferably substantially normal to the acting direction of the pulling force, the displacement of the detection wire  20  caused by the pulling force can be prevented more effectively as compared with the case where only one through hole is provided. 
     The through holes  15 F,  15 R of the arrangement path are short because they extend in a transverse direction of the holder  10 . Thus the detection wire  20  is less likely to buckle and/or get caught during the insertion as compared with a case where the through holes  15 F,  15 R extend in the longitudinal direction of the holder  10 . Further, since the arrangement grooves  17 L,  17 R extending in the longitudinal direction of the holder  10  are open in the outer surface of the holder  10 , the detection wire  20  can be fitted or arranged easily. In other words, the detection wire  20  easily can be arranged in the arrangement path. 
     The present invention is not limited to the described and illustrated embodiment, but the following embodiments are also embraced by the technical scope of the present invention as defined in the claims. 
     Although the two arrangement grooves are exposed in the outer surface of the holder in the foregoing embodiment, only one arrangement groove may be exposed in the outer surface of the holder while the other may be formed inside the holder according to the invention. 
     Although the heat-shrinkable tubing is used as a connecting member in the foregoing embodiment, a rubber tube, a tube made of a soft resin or the like may be used according to the invention. 
     Although the restricting means is comprised of the rib, the slit and the connecting member in the foregoing embodiment, it may be an other means, such as taping, to cover the arrangement grooves according to the invention. 
     Although the two arrangement grooves are both located below the slit (or at a height that is not flush with or corresponding to the slit) in the foregoing embodiment, one arrangement groove may be located below the slit while the other may be located above the slit. 
     Although the folded portion of the detection wire is accommodated in the holder in the foregoing embodiment, the invention is also applicable to a case where the folded portion of the detection wire is exposed at the front end surface of the holder. 
     Besides the preceding embodiments, a variety of other changes can be made without departing from the scope and spirit of the invention as defined in the claims.