Abstract:
An easily insertable and removable brake pad abrasion detector is provided by forming a recess in the rear surface of the pad, a hole in the pad backing plate communicating with the recess, a sleeve in the hole having inwardly projecting one-way pawls and a probe having a circumferential shoulder engaged by the pawls when inserted. The small diameter part of the probe may have an elliptical cross-section so that the pawls may be disengaged by merely turning the probe.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to structures for mounting a brake pad abrasion detector. 
     The insertion of a detector (or a so-called probe) at the pad abrasion limit position has been employed in order to detect the abrasion of a brake pad or a lining for many years. There have been proposed a variety of probe mounting structures. 
     However, among the conventional probe mounting structures, only a few structures permit the simple mounting of the probe as required. For instance, a structure is available in which a threaded hole is formed in the backing plate or in the probe holding member, and the probe is screwed into the threaded hole. However, this conventional structure is disadvantageous in that the machining is rather troublesome, and the probe is liable to be displaced owing to the vibration. In order to prevent the displacement of the probe, it is necessary to provide a special stopper. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide a mounting structure which is simple in construction, and with which a probe can be readily mounted when required. 
     Another object of the invention is to provide a mounting structure with which a probe can be removed if required. 
     These and other objects are achieved according to the present invention by providing a sleeve holding member having inwardly biased projections in a through hole in the pad backing plate which communicates with a blind hole in the rear surface of the pad. The probe is provided with a shoulder that is engaged by the projections when inserted into the holding member. The shoulder may be formed at the junction of two different diameter sections or by providing flat surfaces on the sides of the lower portion. In the former case, it is possible to form the smaller diameter portion with an elliptical cross-section having a major axis at least as long as the larger diameter portion so that the projections may be disengaged by rotating the probe, thus facilitating removal. In such a case, a variety of techniques are illustrated for preventing interference between the projections and through hole when the probe is rotated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention will now be described with reference to the drawings, in which: 
     FIG. 1 is a sectional view showing a mounting structure according to this invention; 
     FIG. 2 is a perspective view showing a probe holding member; 
     FIG. 3 is a perspective view showing one example of a probe which may be used in the present invention; 
     FIG. 4 is a perspective view showing a second example of a probe which may be used in the present invention; 
     FIG. 5 is a perspective view showing a third example of a probe which may be used in the present invention; 
     FIG. 6 is a cross-sectional diagrammatic view showing the probe illustrated in FIG. 5 mounted in a probe holding member; 
     FIG. 7 is a sectional view showing a second example of a mounting structure which may be used in the present invention; 
     FIG. 8 is a sectional view showing a third example of a mounting structure which may be used in the present invention; 
     FIG. 9 is a sectional view showing a fourth example of a mounting structure which may be used in the present invention; 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 1, a blind hole 2 is formed in a brake pad 1. A through hole 4 communicating with the blind hole 2 is formed in a backing plate 3. A probe holding member 10 is inserted into the holes 4 and 2 and a probe 20 is held by the probe holding member 10. 
     As shown in FIG. 2, the probe holding member 10 comprises a cylinder 11 made of an elastic material, and a flange 12 provided on the top of the cylinder 11. A pair of opposite no-return pawls 13 are formed in the wall of the cylinder 11 in the axial direction. Each of the no-return pawls 13 is inclined toward the central axis of the cylinder and the elasticity of the material gives a no-return effect to the pawls. 
     In order to fixedly secure the probe holding member 10 to the brake pad, during the manufacture of the brake pad the holding member 10 is inserted into the through hole 4 of the backing plate 3 in advance, and then the pad 1 is molded under pressure onto the backing plate so that the pad and backing plate form one unit. As a result, the flange 12 of the holding member 10 is held between the pad 1 and the plate 3 as shown in FIG. 1. 
     The aforementioned probe 20 is made up of a head section 21 and a leg section 22 as shown in FIG. 3. A shoulder 23 is formed between the two sections 21 and 22. If the probe 20 is inserted into the holding member 10 in such a manner that the head section 21 is first inserted therein, the no-return pawls 13 and 13 are engaged with the shoulder 23 of the probe to fixedly hold the latter, as shown in FIG. 1. 
     In the probe shown in FIG. 3, the shoulder 23 of the probe 20 is formed by making the diameter of the leg section smaller than that of the head section 21, and accordingly the shoulder 23 is provided along the entire circumference of the probe 20. However, a shoulder may be formed by providing flat surfaces 24 in the leg section 22 in the axial direction as is shown in FIG. 4. In this case, as the substantially flat ends of the no-return pawls 13 are abutted against the flat surfaces 24, it is also possible to prevent the rotation of the probe 20. 
     Furthermore, if the leg section 22 of the probe 22 is formed in such a manner that its section is elliptic and its major axis is equal to the diameter of the head section 21 as shown in FIGS. 5 and 6, then after the probe 20 is inserted into the holding member 10 and is affixed to the pad assembly, it can be removed therefrom. More specifically, under the condition that, as shown in FIG. 6, the shoulders 23 of the probe are engaged with the no-return pawls 13 of the holding member, the probe is turned. Then, since the section of the leg section 22 of the probe is elliptic as was described above, the pawls 13 are gradually pushed outwards. Finally, the distance between the pawls 13 is increased to the diameter of the head section 21 by the major axis as indicated by the chain line in FIG. 6, and therefore the probe can be removed from the holding member 10 merely by pulling it. 
     In this case it should be noted that, if the no-return pawl 13 is flat, its both edges are positioned outside the cylinder 11 of the holding member. However, if the diameter of the through hole 4 of the backing plate 3 is made equal to the outside diameter of the cylinder 11 as in the case of FIG. 1, then it is impossible to further move the no-return pawls 13 apart from each other because the movement is obstructed by the through hole 4. In order to eliminate this difficulty, the following method may be employed. That is, as shown in FIG. 7, the diameter of the lower portion, from the vicinity of the no-return pawls 13 to the lower end, of the cylinder 11 of the holding member 10 is made smaller so that there is provided a gap between the lower portion and the through hole 4 of the backing plate 3. Alternatively, a recess 5 may be provided along the peripheral portion of the end of the through hole 4 as shown in FIG. 8, or the holding member may be so designed that the no-return pawls 13 are exposed outside the through hole 4 as shown in FIG. 9. Furthermore, it is apparent that the holding member 10 as described above may be applied to the probes shown in FIGS. 3 and 4. 
     In addition, a collar 25 may be provided on the end of the leg section of the probe as shown in FIG. 7. In this case, as the vertical movement of the probe is positively prevented and it is possible to fixedly secure the probe in the pad assembly. It is obvious that such a collar may be also provided for the probe shown in FIGS. 3 or 4. 
     According to this invention, the probe can be fixedly secured merely by depressing it. Accordingly, the abrasion detector can be mounted on the brake assembly at any time when required, and in this case the probe can be held in place with the simple structure. 
     When the detector becomes out of order, it can be readily removed for replacement. Thus, the present invention has a variety of merits.