Wear detection probe for a braking member

Abstract: A wear detection probe (10) for the detection of wear of a braking member (17), is mounted on the braking member and comprises a holder (11) having a folded detection wire (15) in a wiring path. The detection wire has a folded portion (15R) and two straight portions (15S) extending from the folded portion parallel to each other and in directions substantially parallel to the surface (16a) of the brake rotor (16). The apex of the folded portion (15R) of the detection wire is nearer than the straight portions (15S) to the wear surface of the holder, so that the folded portion is broken after a predetermined amount of wear. The probe is compact, and the wire (15) remains securely in position during use.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a wear detection probe for a braking member, particularly but not exclusively a braking member of a vehicle braking system, and further relates to a braking member having such a wear detection probe mounted on it and to a brake including such a braking member. Description of the Related Art A wear detection probe for detecting the degree of wear of a braking pad of a vehicle disclosed in US-A-5833033 has an electrical detection wire folded in the shape of a "U" embedded in a holder made of resin. The wear detection probe is installed on a braking pad, with the apex at the folded portion of the wire exposed and opposed to a disk rotor and with two straight line portions of the wire extending from the folded portion parallel to the axis of the disk rotor. With the progress of the wear of the braking pad, the folded portion of the detection electric wire contacts the disk rotor and is abraded. When the wear of the braking pad reaches its use limit, the folded portion is broken, enabling an electrical signal to be derived. In the wear detection probe, the two straight line portions of the wire extend to the rear side of the braking pad (opposite to the location of the disk rotor) and are connected to an external wire breakage detection circuit. Depending on the kind of vehicle, a sufficient space for electrical wiring is not available at the rear side of the braking pad. Thus, a wear detection probe 1 as shown in present Figs. 9 and 10 has been proposed but is not thought to have been publicly used. This wear detection probe 1 is installed on a braking pad 4, with two straight line portions 2Sa and 2Sb of an electrical detection wire 2 parallel with a surface 3a of a disk rotor 3 and with the one straight line portion 2Sa nearer to the disk rotor 3 than the other straight line portion 2Sb. By arranging the straight line portions 2S in this manner, the wire 2 is extended out of the holder 4 in the radial direction of the disk rotor 3. In the wear detection probe 1, with the progress of the wear of the braking pad 4, the straight line portion 2Sa nearer to the disk rotor 3 contacts the disk rotor 3 and is abraded thereby. When the wear of the braking pad 4 reaches the limit of use, as shown in Fig. 10, the straight line portion 2Sa nearer to the disk rotor 3 is broken, which event is detected by a wear detection circuit. However, in the wear detection probe 1 having the two straight line portions 2Sa and 2Sb parallel with the surface 3a of the disk rotor 3, when the radius of curvature of a folded portion 2R of the electric wire 2 is reduced, there is a risk that the electric wire 2 is broken at the folded portion 2R. Accordingly, to make the radius of curvature of the folded portion 2R comparatively large, it is necessary to space the two straight line portions 2Sa and 2Sb from each other at a large interval in an approach/withdraw direction (direction perpendicular to the surface 3a of the disk rotor 3) with respect to the disk rotor 3, which causes the wear detection probe 1 to be large. To make the wear detection probe 1 more compact, it is conceivable to arrange the two straight line portions such that the distances between them and the surface of the disk rotor are equal, so that both straight line portions are subject to abrasion by the disk rotor. However, this construction causes the hole containing the wire to become open in the shape of a groove while the wear detection probe 1 is being abraded. As a result, there is a possibility that the wire becomes loose so that the desired manner of breaking of the wire is not achieved. EP-A-0974767 describes a wear detection probe that has a folded portion in the plane of the two parallel straight portions, one of which is closer to the wear surface than the other as described above, so that the folded portion projects a predetermined distance toward the wear surface. The predetermined distance is larger than a predetermined maximum allowable height of an annular rib on a disk rotor at its outer peripheral portion. Consequently, a centre region of the disk rotor is expected to cut the folded portion before the annular rib cuts a straight portion. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a wear detection probe which is compact in a direction perpendicular to the surface of a disk rotor, and which enables reliable wear detection. According to the present invention, there is provided a wear detection probe for the detection of wear of a braking member, as set out in claim 1. As in the probe of US-A-5833033, the folded part of the detection wire in the probe of the invention is abraded by contact between the wire and the surface of the rotor and broken when the degree of wear of the braking member reaches a predetermined limit of use, thereby enabling an electrical signal indicating the wire breakage to be obtained. According to the invention there is also provided a brake comprising a rotor having a flat braking surface and a braking member, as set out in claim 5. Preferably the two straight line portions are parallel to each other. In the present invention, the two straight line portions are so disposed that the distance from the folded portion to the surface of the rotor is less than the distance from the straight line portions to the surface of the rotor. Thus, even though the spacing between the straight line portions is widened to increase the radius of curvature of the folded portion, the dimension of the path of the wire in the direction perpendicular to the surface of the rotor can be minimised, and may be equal to little more than the outer diameter of the wire. Thus a minimal space is necessary for forming the region in which the two straight line portions are wired. If both the two straight line portions were abraded by the rotor before the folded portion is broken, there is a fear that the detection wire becomes loose. However, in the invention the folded portion to be broken is nearer to the rotor than the two straight line portions. Accordingly, the folded portion can be broken without abrading the two straight line portions. To break the detection wire without any abrasion of the two straight line portions, the apex of the folded portion is preferably located at a position nearer to the rotor than the two straight line portions by the outer diameter of the detection wire or more. In this case, in the direction perpendicular to the surface of the rotor, the dimension of the space required for the two straight line portions and the folded portion may be only twice as large as the outer diameter of the detection wire. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which:- Fig. 1 is a sectional view of a wear detection probe embedded in a braking member according to a first embodiment of the present invention before an electrical detection wire is broken. Fig. 2 is a sectional view of the wear detection probe shown in Fig. 1 in which the detection wire is broken. Fig. 3 is a front view of the wear detection probe shown in Fig. 1. Fig. 4 is a rear view of the wear detection probe shown in Fig. 1. Fig. 5 is a left side view of the wear detection probe shown in Fig. 1. Fig. 6 is a plan view of the wear detection probe shown in Fig. 1. Fig. 7 is a perspective view of a braking member of another embodiment of the invention. Fig. 8 is a perspective view of the wear detection probe of the braking member of Fig. 7. Fig. 9 is a sectional view of a state before a detection electric wire is broken in a probe which is not within the scope of the invention. Fig. 10 is a sectional view of the probe of Fig. 9 showing a state in which a detection electric wire is broken. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a disk brake system for a vehicle to which a wear detection probe 10 of the embodiment of Figs. 1 to 6 is applied will be described. The disk brake has a disk rotor 16 and a pair (one of the pair only is shown) of braking members in the form of pads 17 which in use are moved to sandwich the disk rotor under load in its axial direction (vertical direction in Fig. 1) in a conventional manner which need not be described to achieve braking effect on the rotor. An installing recess or hole 14 open in a direction (for example, outward in the radial direction of the disk rotor 16) parallel with the braking surface 16a of the disk rotor (surface confronting the braking pad 17) is formed on one of the braking pads 17 to accommodate the wear detection probe 10 embodying the present invention. The wear detection probe 10 has a holder 11 made of synthetic resin and one electrical detection wire 151ocated in a wiring path which in this embodiment lies within the holder. In the description made below, the right side in Figs. 1, 2, 5 and 6 is called the front side. The holder 11 has a pair of parallel right and left straight wiring path portions 12 penetrating through it. Each straight wiring path portion 12 is circular in section. The inner diameter of each straight wiring path portion 12 is equal to or slightly larger than the outer diameter of the detection wire 15. The right and left straight wiring path portions 12 have the same height position in the vertical direction relative to the upper surface of the holder 11. The holder 11 has a folded wiring path portion 13 which is open at its front side surface. The folded wiring path portion 13 is curved upward in front view and extends from one straight wiring path portion 12 to the other straight wiring path portion 12 semicircularly. The width (difference between inner diameter and outer diameter) of the folded wiring path portion 13 is equal to the inner diameter of the straight wiring path portion 12. That is, the width of the folded wiring path portion 13 is equal to the outer diameter of the detection wire 15 or slightly larger than that. In the region from the apex or highest part 13A (part located at the centre between the two straight wiring path portions 12 in the right-to-left direction) in the folded wiring path portion 13 to the straight wiring path portion 12, the rear end surface of the folded wiring path portion 13 forms an inclined plane 13B descending downward toward the rear side in side view (see Fig. 1). When the folded wiring path portion 13 is viewed from the above, the rear end surface 13C in its highest part 13A is approximately semicircular. The length D of the highest part 13A of the folded wiring path portion 13 in the front-to-back direction is set larger than the outer diameter of the detection wire 15. The vertical positional relationship between the folded wiring path portion 13 and the straight wiring path portions 12 is such that the lower end of the highest part 13A is located on a level with the upper end of the straight wiring path portions 12. With the detection wire 15 folded double, both ends thereof are inserted into the straight wiring path portions 12 from the front of the holder 11. The straight line portions 15S of the wire 15 are tightened inside the straight wiring path portions 12. With the folded portion 15R of the wire 15 accommodated in the folded wiring path portion 13, the folded portion 15R is brought into close contact with the rear end surface of the folded wiring path portion 13 without loosening the folded portion 15R. The detection wire 15 wired in this manner is fixed to the holder 11 by suitable fixing means (not shown). The highest portion or apex of the folded portion 15R of the detection wire 15 thus installed on the holder 11 is located at a position higher than the two straight line portions 15S by the outer diameter of the detection wire 15 or by a dimension slightly larger than that. When the wear detection probe 10 is mounted on the braking pad 17 in the hole 14 thereof, the upper surface 11A of the holder 11 faces the braking surface 16a of the disk rotor 16, the two straight line portions 15S of the detection electric wire 15 are parallel to the outer, wearing surface of the pad 17 and the surface 16a (surface which contacts with the braking pad 17) of the disk rotor 16. The distance from one straight line portion 15S to the surface 16a of the disk rotor 16 is equal to the distance from the other straight line portion 15S to the surface 16a of the disk rotor 16, and the folded portion 15R is nearer to the surface 16a of the disk rotor than the two straight line portions 15S. During braking of the rotating disk rotor 16, the braking pad 17 moves together with the wear detection probe 10 toward the disk rotor, with the surfaces of the braking pad 17 and the wear detection probe 10 facing the rotor 16 parallel with each other, and contacts the surface 16a of the disk rotor with a high force. The surface of the braking pad 17 wears owing to the friction between the braking pad 17 and the surface 16a of the disk rotor. With the repetition of the braking operation, the wear of the braking pad 17 progresses. As a result, the upper side of the holder 11 is abraded by the contact with the surface 16a of the disk rotor 16. Further, the folded portion 15R of the detection wire 15 is abraded from the high side thereof (upper side in Figs. 1 and 2). When the degree of the wear of the braking pad 17 reaches the limit of use, the detection wire 15 is broken at the highest portion of the folded portion 15R. The breakage of the detection wire 15 is detected by a breakage detection circuit (not shown) connected with the detection wire 15. The highest portion of the folded portion 15R which is broken is located at a position nearer to the disk rotor 16 than the straight line portions 15S by the outer diameter of the detection wire 15. Therefore, the surface 16a of the disk rotor does not reach the straight line portions 15S before the folded portion 15R is broken. As described above, in the embodiment, the distance from the straight line portion 15S to the surface 16a of the disk rotor 16 is equal to the distance from the other straight line portion 15S to the surface 16a of the disk rotor. Thus, even though the spacing between both straight line portions 15S in the right-to-left direction is widened by increasing the radius of curvature of the folded portion 15R, in the direction perpendicular to the surface 16a of the disk rotor a distance equal to the outer diameter of the detection wire 15 is only necessary for forming the space in which the two straight line portions 15S are wired. Accordingly, it is possible to make the wear detection probe 10 compact in the direction perpendicular to the surface 16a of the disk rotor 16. If both the two straight line portions 15S were abraded by the disk rotor 16 before the folded portion 15R is broken, the straight wiring path portion 12 and the folded wiring path 13 would be open in the shape of a groove at the upward side thereof. In this case, there is a fear that the detection electric wire 15 becomes loose. However, in the embodiment, the folded portion 15R to be broken is nearer to the disk rotor 16 than the two straight line portions 15S. Accordingly, the folded portion 15R can be broken without abrading the two straight line portions 15S. To ensure the breaking of the folded portion 15R without abrading the two straight line portions 15S, the apex of the folded portion 15R is spaced at a minimum interval from the two straight line portions 15S. That is, the folded portion 15R is located at a position nearer to the disk rotor 16 than the two straight line portions 15S by the outer diameter of the detection electric wire 15. Therefore, in the direction (height direction of the wear detection probe 10) perpendicular to the surface 16a of the disk rotor, the dimension of the space for wiring the two straight line portions 15S and the folded portion 15R can be just twice as large as the outer diameter of the detection wire 15. In this respect, it is possible to make the wear detection probe 10 compact in the direction perpendicular to the surface 16a of the disk rotor. Figs. 7 and 8 show a second embodiment of the invention, more particularly a disk brake braking member 20 having a flat metal plate 21 and a brake pad 22 adhesively fixed on the metal plate 21. In use the braking member 20 is mounted in the disk brake with the top surface 23 of the pad 22 parallel to the braking face of the disk rotor (not shown). The metal plate 21 has a stepped slot 24 adjacent a recess in one side of the pad 22. A wire holder 26 of a wear detection probe 25 is received in the slot 24 so that its top surface 27 is parallel to the top surface 23 of the pad 22. The holder 26 has grooves 28 in its sides so that it slides onto the edges of the narrower portion of the slot 24. The base 30 of the holder 26 is flush with the base of the plate 21. The holder 26 has within it a wiring path 31 of the same shape as the wiring path 15S, 15R of the embodiment of Figs. 1 to 6, with an electrical detection wire (not shown in Figs. 7 and 8) lying in the wiring path in the manner shown in Figs. 1 to 6. Although in this embodiment the holder 26 is alongside the wear surface 23 of the pad, rather than embedded in the pad as in Figs. 1 to 6, the method of operation is the same. The scope of the present invention is not limited to the above-described embodiments, but the following modified embodiments are for example included. In addition to the following embodiments, the present invention can be embodied in various modes without departing from the gist of the present invention. (1) In the above-described embodiment, the folded portion is located at a position nearer than the straight line portions to the disk rotor by the outer diameter of the detection wire. But according to the present invention, the folded portion may be located at a position nearer to the disk rotor than the straight line portion by a distance greater than the outer diameter of the detection wire. (2) In the above-described embodiment, the wear detection probe is installed on the braking pad, with the straight line portions of the wire 15 parallel to the radial direction of the disk rotor. But within the present invention, the wear detection probe may be installed on the braking pad, with the straight line portion parallel to the surface of the disk rotor and oblique or perpendicular to the radial direction thereof. (3) In the above-described embodiment, the wear detection probe is used for the disk brake for a vehicle. But within the present invention, the wear detection probe may be used for a drum brake, a friction brake, and the like in vehicles and in machinery other than vehicles. (4) In the above-described embodiment, the two straight line portions extend parallel to each other in the holder. But according to the present invention, they may extend obliquely to each other in a plane parallel to the surface of the disk rotor.

Claims: A wear detection probe (10; 25) for the detection of wear of a braking member, which in use is mounted on the braking member and comprises a holder (11; 26) having a folded detection wire (15) in a wiring path, said detection wire having a folded portion (15R) and two straight portions (15S) each extending from said folded portion in a direction substantially parallel to a wear surface of said holder which is worn away in use, wherein the apex of the folded portion (15R) of said detection wire is located at a position nearer than said straight portions (15S) to said wear surface (11A; 27) of the holder by a distance at least equal to the outer diameter of the detection wire; characterised in that the two straight portions (15S) of the detection wire are disposed in a plane so that the distance from one straight portion to said wear surface (11A; 27) of the holder (11; 26) is equal to the distance from the other straight portion to said wear surface of the holder, and the folded portion (15R) lies outside the plane in which the two straight portions (15S) lie. A wear detection probe according to claim 1, wherein said two straight portions (15S) of the detection wire are parallel to each other. A wear detection probe according to claim 1 or 2, wherein the wiring path of said folded portion (15R) of the detection wire is open at a side surface of said holder. A braking member (17; 20) having an outer surface (17a; 23) which is worn away in use of the braking member and which braking member has a wear detection probe (10; 25) according to any one of claims 1 to 3 mounted on it. A brake comprising a rotor (16) and a braking member (17) according to claim 4, which when operated effects braking of the rotor by contact of said outer surface (17a; 23) thereof with a side surface (16a) of the rotor, wherein said wear detection probe is mounted on the braking member so that said straight line portions (15S) of said detection wire are substantially parallel to said side surface (16a) of said rotor and said apex of said folded portion (15R) of said detection wire is located at a position nearer than said straight portions to said side surface (16a) of the rotor by a distance at least equal to the outer diameter of the detection wire.

Inventors: TAKANASHI HITOSHI, TAKANASHI,HITOSHI, Takanashi,Hitoshi, c/o Sumitomo Wiring Systems Ltd
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 2001
Main classification: F16D66
IPC codes: F16D66