Abrasion detecting probe for a brake pad

Abstract: The invention provides an abrasion detecting probe for a brake pad which does not require insert-moulding and in which production costs are low. A probe 20 is housed in base components 35 and 36, which are snap-fitted together. In this manner, the terminal 22 can be attached within the base member 21 in a precise predetermined position by the simple operation of joining the base components 35 and 36 together. Therefore, as opposed to a conventional probe, insert-moulding is not required and the probe can be manufactured simply and cheaply. A sleeve 50 may provide an audible brake wear warning.

Description: TECHNICAL FIELD The present invention relates to an abrasion detecting probe for a brake pad, the probe having a metal terminal inside a synthetic resin base member. BACKGROUND TO THE INVENTION Conventional abrasion detecting probes of this kind include the one described in the JP 6-300064. This type of abrasion detecting probe 1, shown in Figure 11 hereof, comprises a pair of electric wires D crimped to a metal terminal 2, this terminal 2 being insert-moulded inside a synthetic resin base member 3. The abrasion detecting probe 1 is fixed through a supporting backplate of a brake pad, and when the brake pad attains its abrasion limit as a result of sliding contact with a brake disc, a tip 4 of the probe 1 is worn away together with the brake pad, and the circuit between the two electric wires D is broken. However, because the abrasion detecting probe 1 described above is produced by insert-moulding, position setting of the terminal 2 inside the mould is a troublesome and time-consuming operation which does not allow costs to be reduced. Accurate positioning is essential to ensure that the abrasion limit is set precisely. An abrasion detecting probe for a brake pad in which insert-moulding is not required and in which production costs are accordingly reduced in known from EP-A-0658699 or FR-A-2 497 309, which discloses a wear detecting probe having the pre-characterizing features of claim 1. Those probes give a warning only when the electric wire in broken, and the probe has to be replaced after a signal has been given. SUMMARY OF THE INVENTION According to the invention there is provided a wear detecting probe for a vehicle brake lining having a backplate and a friction lining thereon, said probe comprising an electrically conducting member adapted for connection to an electrical circuit by input and output connections, said conducting member being housed inside an insulating body and having a bridging portion adjacent one end of said body such that, in use, a braking surface can wear away said bridging portion to separate said conducting member into two, and thereby break an electrical circuit, wherein said body comprises two or more mutually attachable components defining a cavity to house said conducting member characterized in that said body further includes a sleeve around the exterior thereof, said sleeve protruding further than said sensor body, such that sound is generated when the sleeve contacts a brake rotor. Such a construction avoids the need for insert moulding, and thus lower manufacturing costs can be achieved. The components are typically produced as precision plastic mouldings with a shape suitable for positioning and holding the conducting member with accuracy. Preferably latch means are provided to hold the body components together to avoid rattling, and to avoid separation during transport. The latch means are preferably adapted to pass through the conducting member as an aid to correct location. According to the invention the probe is surrounded by a protruding sleeve of noise generating material. Such a sleeve gives an audible warning of the approach of the pad abrasion limit. This arrangement permits the friction lining to be replaced before the conducting member is broken, and the probe itself to be inserted into the new friction lining; thus the electrical connections need not be disturbed. BRIEF DESCRIPTION OF DRAWINGS Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompanying drawings in which: Figure 1 is a side view showing a braking device of the present invention. Figure 2 is a side cross-sectional view of a backplate to which an abrasion detecting probe has been attached. Figure 3 is an exploded view of the abrasion detecting probe. Figure 4 is an exploded view showing a terminal housed within a housing of a base component. Figure 5 is an exploded view showing the base components in an attached state. Figure 6 is a diagonal view showing the abrasion detecting probe in a completed state. Figure 7 is a cross-sectional view of the abrasion detecting probe in a completed state. Figures 8-10 are similar to Figures 2, 3 and 6, and illustrates an outer sleeve for the probe according to an embodiment of the invention. Figure 11 is a diagonal view showing a prior art abrasion detecting probe. DESCRIPTION OF PREFERRED EMBODIMENT An abrasion detecting probe is described with reference to Figures. 1-7. Figure 1 shows the components of a braking device. The number 10 in Figure 1 refers to a brake disc, a pair of backplates 11 and 12 being provided on both sides thereof, brake pads 13 and 14 being provided on the backplates 11 and 12 on the sides thereof facing the disc 10. The backplates 11 and 12 are moved towards the disc 10 by a mechanism (not shown), and as a result, the brake pads 13 and 14 press against the disc 10 and frictional force halts the rotation of the disc 10. This is conventional. As shown in Figure 2, an abrasion detecting probe 20 suitable for use in the present invention is attached by being inserted into a through hole 15 formed in a backplate 12, the anterior end of the probe 20 protruding into a through hole 17 formed in the brake pad friction material 14. As shown in Figure 3, the probe 20 is provided with a conducting member or terminal 22 made of metal and located within a body or base member 21 of synthetic resin. The terminal 22 is provided with a pair of foot members 24, which form a U-shape, joined at the base by a carrier 23 which can be cut off short. The anterior end of each foot member 24 is provided with a crimping member 25 for crimping an electric wire D, each crimping member 25 comprising a protrusion 26 which extends out from the side of the foot member 24 and is folded back above the foot member 24. Core wires D1 of the electric wire D are held between the protrusion 26 and the foot member 24 and an electrical connection is established. The core wires D1 are welded to the terminal 22 in order to further strengthen the connection. Furthermore, the foot members 24 are cranked downwards (as viewed) so that the protrusions 26 of the crimping members 25 do not protrude greatly (upwards in Figure 3) relative to the terminal 22. The entire base member 21, shown in Figure 6, has a column shape in the direction of a horizontal cross-sectional, and protrudes from the base 12. A posterior portion 30, posterior relative to the direction of insertion, having step-shaped protrusions on both sides. As shown in Figure 2, stepped faces 30A of the posterior portion 30 make contact with stepped faces 15A formed in a through hole 15, thus determining the insertion position of the probe 20. Further, a groove 32 is formed on an anterior portion 31 of the base member 21 along the direction of the circumference of the outer circumference face. As shown in Figure 2, after the probe 20 is inserted into the through hole 15 of the base 12, a clip 33 is installed in the groove 32, this clip 33 being abutting against the open edge of the through hole 15 on the base 12 and thereby retaining the probe 20 in position. As shown in Figure 3, the base member 21 is divided along in the horizontal direction into a first base component 35 (the lower part of the base member 21 in Figure 3) and a second base component 36 (the upper part of the base member 21 in Figure 3). On the first base component 35, a housing 37 is formed into an attachment face 35A, this attachment face 35A joining with the second base component 36, and the housing 37 housing the terminal 22. The lower face of the housing 37 is inclined part-way along the face to correspond to the moderate crank-shape of the foot members 24, the side corresponding to the crimping members 25 being deeper. The anterior side (the lower left side in Figure 3) of the circumference face of the housing 37 is of a round shape that corresponds to the U-shaped base of the terminal 22, and the posterior side (the upper right in Figure 3) widens out on both sides in order to house the sideways-protruding portions of the crimping members 25. Further, a pair of rounded grooves 38 which pass through to the housing 37 are formed on the posterior end of the first base component 35, the electric wires D which are attached to the terminal 22 passing to the exterior of the base member 21 through these rounded grooves 38. In addition, an angular groove 39 which passes through to the housing 37 is formed on the anterior end of the first base component 35, a connecting member (or bridging portion) 27 which links the carrier 23 and the terminal 22 passing therethrough, the carrier 23 being provided externally with respect to the base member 21. A pair of position-fixing posts or protrusions 40 are provided along a length-wise direction on the first base component 35. These position-fixing protrusions 40 protrude from the base face of the first base component 35 towards the second base component 36 and, as shown in Figure 4, these position-fixing protrusions 40 are located respectively between the anterior end and the base end of the foot members 24 of the terminal 22. Further, a slit 40A is formed from the tip towards the base on each position-fixing protrusion 40. As shown in Figure 7, a pair of position-fixing apertures or holes 41 pass through the second base component 36, the position-fixing protrusions 40 being inserted through these position-fixing holes 41, and this insertion fixing the base components 35 and 36 so that they do not move. The inner circumference of each position-fixing hole 41 has a tapered face 42, this tapered face 42 becoming narrower towards the farther side from the direction of insertion of the position-fixing protrusion 40. Consequently, the position-fixing protrusions 40 change shape and become narrower in the direction in which the slits 40A are narrower. As shown in the same figure, a housing 43 is formed on the attachment face of the second base component 36, this housing 43 housing the crimping members 25 protruding from the housing 37 of the first base component 35. With the configuration as described above, the operation and effects of the present probe are explained. The probe 20 is manufactured in the following manner. The terminal 22 inside the probe 20 is manufactured by a process of punching and folding metal plate. Then, the core wires D1 of the electric wire D are crimped between the foot members 24 and the protrusions 26 provided on the crimping members 25 of the terminal 22. Then, the core wires D1 are welded to the crimping members 25. In the case of the conventional probe 1 (see Figure 8), the terminal 22 is conveyed to the injection moulding site, and the terminal 22 must be set inside the mould and then insert-moulding carried out. As stated above, this is a troublesome and time-consuming operation which does not allow costs to be reduced. However, the probe 20 can be produced in the manner described below without having to perform insert-moulding. That is, the first and second base components 35 and 36 of the probe 20 are manufactured by injection moulding separately from the terminal 22, and are conveyed to the site in which they will be attached to the terminal 22. At that site, as shown in Figure 4, the terminal 22 is housed within the housing 37 of the first base component 35, the attachment faces of the first and second base components 35 and 36 are set facing one another and are then joined together. Then, the position-fixing protrusions 40 enter the position-fixing holes 41, thus mutually fixing the position of the first and second base components 35 and 36 and attaching them so that they do not move (see Figure 5). At this juncture, the tapered faces 42 provided in the position-fixing holes 41 (see Figure 7) guide the position-fixing protrusions 40, so that the slits 40A in the tips of the position-fixing protrusions 40 change shape and become narrower and, as a result of the outward force exerted by the position-fixing protrusions 40, the circumferential faces of the position-fixing protrusions 40 and the position-fixing holes 41 fit closely together. This prevents the base components 35 and 36 from rattling. Further, the friction between the position-fixing protrusions 40 and the position-fixing holes 41 maintains the base components 35 and 36 in a joined state. Next, the carrier 23 (see Figure 5) protruding anteriorly from the base member 21 of the terminal 22 is cut off, and the attachment of the probe 20 is complete (see Figure 6). In this manner, in the probe 20, the base components 35 and 36 are joined together in a simple operation which allows the terminal 22 to be attached within the base member 21. As a result, in comparison to the conventional example in which insert-moulding is required, the probe can be manufactured simply and cheaply. The completed probe 20, as shown in Figure 2, is inserted into the through hole 15 of the base 12 of the braking device, and the clip 33 is attached to the groove 32 of the probe 20 by means of a specified tool. The probe 20 is in a fixed state in the base 12 with its tip protruding into the brake pad 14. In this state, the base components 35 and 36 are maintained reliably in a joined state by the clip 33 and the inner wall of the through hole 15, and will not separate even if shaken, etc. When the brake pad 14 attains its abrasion limit as a result of sliding contact with the disc 10 (see Figure 1), the tip of the probe 20 is worn away together with the brake pad 14, the foot members 24 are separated, and the circuit between the two electric wires D is broken, thus allowing the attainment of the abrasion limit to be detected. An embodiment of the invention is illustrated in Figs. 8-10, the same parts having common reference numerals. As illustrated a sleeve 50 surrounds the base components 35,36, and maintains them in an attached state. The sleeve 50 is a tight push fit over the components 35,36. As illustrated, the sleeve 50 projects slightly beyond the tip of the terminal 22, so that as the pad approaches the abrasion limit, the sleeve 50 rubs against the disc. A bracket 52 holds the probe in the brake pad. The sleeve is made of a material, such as metal, which will make a noise as it is worn away; in this way the driver can hear an audible signal that the abrasion limit is about to be reached. The sleeve 50 also has the advantage of preventing separation of the components 35,36 during transport from a connector manufacturing location to a brake pad installation location. Furthermore, if the brake pad is replaced when the audible warning is first heard, there is no need to replace the probe itself - the probe can simply be inserted into a replacement brake pad without any disconnection of the electrical wires. If however the tip is worn away, the electrical circuit is broken, thus enabling a signal, such as a warning light, to be indicated to the driver. The present invention is not limited to the embodiments described above with the aid of figures. For example, the possibilities described below also lie within the technical range of the present invention. In addition, the present invention may be embodied in various other ways without deviating from the scope thereof. (1) In the present embodiment, the base member 21 can be divided into two base components 35 and 36. However, the number of base components into which the base member 21 can be divided is not limited to two. (2) In the present embodiment, tapered faces 42 are formed on the inner circumference of the position-fixing holes 41. However, it may equally well be the case that tapered faces are formed on the outer circumference of the position-fixing protrusions 40. (3) The sleeve (50) may be used to hold the base components 35,36 together in the absence of an integral latch.

Claims: A wear detecting probe for a vehicle brake lining having a backplate and a friction lining thereon, said probe (20) comprising an electrically conducting member (22) adapted for connection to an electrical circuit by input and output connections (25), said conducting member (22) being housed inside an insulating body (21) and having a bridging portion (27) adjacent one end of said body such that, in use, a braking surface can wear away said bridging portion (27) to separate said conducting member (22) into two, and thereby break an electrical circuit, wherein said body (21) comprises two or more mutually attachable components (35,36) defining a cavity (37) to house said conducting member (22), said body (21) further including a sleeve (50) around the exterior thereof, characterized in that said sleeve protrudes further than said bridging portion (27) and said sensor body (21), such that sound is generated when the sleeve (50) contacts a brake rotor. A probe according to claim 1 wherein said components (35,3.6) are moulded in plastics material, and have mutually engageable position fixing means (40,41). A probe according to claim 2 wherein said position fixing means comprise an upstanding post (40) of one component (35) and an aperture (41) of another component (36). A probe according to claim 3 wherein said conducting member (22) is 'U' shaped, and said post (40) passes through the limbs of said conducting member. A probe according to claim 4 wherein said bridging portion (27) is at the base of said conducting member, and in the plane thereof. A probe according to any of claims 3-5 wherein said position fixing means comprise two posts (40) engageable in respective apertures (41), said posts (40) being aligned with the direction of fitting of said probe. A probe according to any preceding claim wherein said body (21) comprises a shoulder (30A) for engagement with said friction lining, and adapted to limit the insertion depth of said probe in said lining. A probe according to claim 7 wherein said body (21) includes a circumferential groove (32) about the fitting axis thereof, said groove being adapted to receive a circlip (33) engageable with the friction lining side of a backplate, said circlip preventing removal of said probe in use.

Inventors: ASAO KAZUHIRO, TAKANASHI HITOSHI, ASAO, KAZUHIRO, TAKANASHI, HITOSHI, Asao, Kazuhiro, c/o Sumitomo Wiring Systems, Ltd., Takanashi, Hitoshi, Sumitomo Wiring Systems, Ltd.
Applicants: SUMITOMO WIRING SYSTEMS, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1998
Main classification: F16D66
IPC codes: F16D66