Patent Publication Number: US-2013228009-A1

Title: Brake pad wear detection system and method

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to vehicular braking systems, and more specifically, to sensor systems used to monitor brake pad and other braking components. 
     BACKGROUND 
     Automobiles, motorcycles, heavy machinery and other vehicles use friction braking to convert kinetic energy into heat. Typically, a brake pad made of a friction absorbing material is pressed against a metal rotor, or disc, attached to a rotating axle or wheel. The brake pad absorbs energy, and the vehicle experiences negative acceleration. A floating caliper moves with respect to the disc (i.e., along a line parallel to the axis of rotation of the disc). A piston on one side of the disc pushes an inner brake pad until it makes contact with the braking surface. The piston pulls a caliper body with an outer brake pad so pressure is applied to both sides of the disc. 
     The brake pads are sacrificial in that they protect the more expensive rotor. The brake pads are intended to be slowly ablated during repeated braking applications. Wear-through of the brake pads can create an emergent brake failure. The resultant metal-to-metal contact can erode expensive parts. 
     Brake pad sensors are used to inform vehicle operators of an impending wear-through. However, conventional brake pad sensor may induce noise and require replacement whenever the brakes are replaced. Such brake pad sensing systems may further require additional parts, can be time-consuming to install, and can be incompatible with original equipment manufacturer (OEM) components. 
     SUMMARY OF THE DISCLOSURE 
     In a particular embodiment, an apparatus includes a linear enclosure having an opening and a cap proximate the opening. The cap includes a cap surface. A slide bolt may be configured to move in a first direction within the linear enclosure. A shaft may be in axial alignment with the slide bolt. A biasing mechanism may bias the shaft in the first direction towards the slide bolt. Sensor circuitry may generate a first signal indicative of brake pad wear in response to movement of the shaft. 
     According to another particular embodiment, an apparatus includes a cap having a cap surface. The cap surface may be positioned proximate an opening of an enclosure partially enclosing a slide bolt that is configured to move in a first direction. A shaft may be in axial alignment with the slide bolt and may be biased in the first direction. The shaft may include a first portion that extends in the first direction relative to the cap surface and a second portion that extends in a second, opposite direction relative to the cap surface. Sensor circuitry may generate a first signal indicative of brake pad wear in response to movement of the shaft. 
     According to another particular embodiment, a method of determining brake pad wear includes positioning a cap having a cap surface proximate an opening of an enclosure. The enclosure at least partially encloses a slide bolt configured to move in a first direction. The method further may include positioning a shaft in axial alignment with the slide bolt. The shaft includes a first portion that extends in the first direction away from the cap surface and a second portion that extends in a second direction away from the cap surface and opposite the first direction. The shaft may be biased in the first direction. A first signal indicative of brake pad wear may be generated at a sensor in response to movement of the shaft. 
     An embodiment of a brake sensor does not touch the rotor and generate noise. The brake sensor may be installed in minutes without replacing the brakes. An embodiment of a brake sensor retrofits an existing brake sensor and plugs-in without additional parts. The distance between the caliper bolt and the sensor plunger increases as the brake pads wear. As a result, an embodiment of a brake sensor will not interfere with brake operation even should the brake system fails and seizes. The brake system may be reusable and may not have to be changed at every brake job. 
     These and other advantages and features that characterize the invention are set forth in the claims annexed hereto and forming a further part hereof. However, for a better understanding of the invention, and of the advantages and objectives attained through its use, reference should be made to the Drawings and to the accompanying descriptive matter in which there are described exemplary embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an embodiment of a brake pad sensor system installed in a vehicle having new brake pads; 
         FIG. 2  is a diagram of an embodiment of a brake pad sensor system installed in a vehicle having brake pads exhibiting an intermediate degree of wear; 
         FIG. 3  is a diagram of an embodiment of a brake pad sensor system installed in a vehicle having brake pads exhibiting an advanced degree of wear; and 
         FIG. 4  is a diagram of an embodiment of a brake pad sensor system having a cap that substantially encloses a sensor shaft and associated switches. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of a brake pad wear detection system combines an electrical measurement (e.g., a resistance or a voltage measurement) with another input to determine when a brake pad should be replaced. For instance, a dynamic stability control computer may receive inputs relating to at least one of vehicle speed, brake pressure, and individual wheel speed. Other inputs may include the mileage at the time new brakes are installed. An input may include how many miles are traveled before the resistance changes from zero ohms to one or multiple threshold voltages (e.g., 470 ohms). Another input may regard how many miles are traveled between the point where the threshold resistance and an open status (infinite ohms). Times and distances corresponding to the signal changes may be used along with the other inputs to count down the mileage until a next replacement. 
     Changing resistance values may correspond to a changing voltage drop across a known value, fixed resistor known to the dynamic stability control computer. In this manner, an embodiment of the brake pad wear detection system uses the resistance values to modify a voltage signal or drop that is read by the dynamic stability control computer. 
     An embodiment of the brake sensing system may include a potentiometer, Hall-effect senor, or variable resistor (e.g., instead of a fixed resistance step) to send a live measurement of the brake pad thickness. This embodiment may require fewer calculations and with reprogramming. 
       FIG. 1  shows an embodiment of a brake sensor system  100  that includes a brake caliper slide bolt  102 , or pin, configured to move in a first direction (indicated by arrow  104 ) in response to brake pad wear. More particularly, as the brake pad wears, the caliper slide bolt  102  slides within a linear enclosure, or rubber slide bolt boot  106 , towards the brake pad (not shown). A cap  108  proximate an opening may partially seal the brake caliper slide bolt  102  and the rubber slide bolt boot  106 . 
     An end of a shaft  110 , or plunger, in axial alignment with the slide bolt may contact an end of the slide bolt  102 . In a particular embodiment, the shaft  110  includes a first portion that extends in the first direction relative to a surface of the cap  108  and a second portion that extends in a second, opposite direction relative to the surface of the cap  108 . 
     A biasing mechanism  112  may bias the shaft  110  in the first direction  104 . For example a spring may bias the shaft  110  towards the slide bolt  102  in such a manner that the shaft  110  remains in substantially contact with the slide bolt  102  as the slide bolt  102  moves. 
     A sensor module  114  may include a channel to accommodate movement of the shaft  110 . For example, the sensor module  114  may comprise a hollow plastic cylindrical structure. The sensor module  114  may further include sensor circuitry configured to generate a first signal indicative of brake pad wear in response to movement of the shaft  110 . In  FIG. 1 , the sensor circuitry may include a first switch  116  and a second switch  118 . In a particular embodiment, the sensor module  114  may be attached or integral with one or more of the cap  108  and the biasing mechanism  112 . 
     The shaft  110  may include a first indicator  120  that is sensed by the sensor circuitry, which initiates generation of the first signal at the sensor circuitry. The first indicator  120  may comprise at least one of a depression and a projection that may contact-switch or otherwise activate the first switch  116 . The first and second switches  116 ,  118  of an embodiment are contact switches that are substantially aligned with one another. In another embodiment, additional switches are included and may be staggered relative to one another. Both switches  116 ,  118  may be depressed when not in contact with the indicators  120 ,  122 . More particularly, the switches  116 ,  118  may be depressed when contacting a surface of the shaft  110  that does not include a depression, as shown in  FIG. 1 . 
     As shown in later figures, the first switch  116  may raise when the first indicator  120  (e.g., depression) of the shaft  110  passes by the first switch  116  as the shaft  110  traverses towards the receding slide bolt  102 . At the same time, the second switch  118  may remain pushed down because the opposing surface of the shaft  110  is not receded at the second switch  118 . Both switches may be raised when a second indicator  122  (e.g., depression) of the shaft  110  is positioned proximate the second switch  118 . At the same time, the first switch  116  may remain in its raised position because it is proximate the first indicator  120 . As discussed herein, generation of a second signal at the sensor circuitry may be initiated when the second indicator trips the second switch  118 . 
     In the embodiment of  FIG. 1 , the cap  108  includes an aperture through which the shaft  110  is configured to travel. The cap  108  may be formed of rubber, plastic, or metal and may seal the slide bolt boot  106  and the slide bolt  102  from contaminant. The cap  108  may be attached or integral with the sensor module  114 . 
     As shown in  FIG. 1 , the slide bolt  102  may be flush with the end of the slide bolt boot  106  when an automobile has new brake pads and a caliper body  124  is moved fully outward from the centerline of the automobile. The shaft  110  may be seated in a bottom portion of the slide bolt  102 . For example, the shaft  110  may seat inside a hex shape cutout at an end of the slide bolt  102 . A spring comprising the biasing mechanism  112  may be stretched, or extended, because the shaft  110  is pushed out by the slide bolt  102 . 
     In operation, the shaft  110  may slide in the first direction, biased by the biasing mechanism  112 . The shaft  110  may be in constant contact on the end of the slide bolt  102  as the outer brake pad wears and the caliper body  124  moves inboard toward the centerline of the vehicle. The indicators  120 ,  122  on the shaft  110  may cause the two switches  116 ,  118  to open in sequence. The first switch  116  may short past a 250 ohm resistor, giving a resistance of zero ohms when the brakes are new. About one third of the way through the life of the brake pad, the first switch  116  may reach the first indicator  120  and may spring open. The reading across the second switch  118  will reach the second indicator  122  and open, cutting off any continuity across the sensor module  114 . This sequenced operation may match the factory sensor&#39;s zero ohms to 250 ohms to open signal exactly, but without having the sensor touching the rotor and causing noise. 
     Where the brake pads are completely worn out, the caliper body may have moved fully inboard on its slide pins. The spring of the sensor may be fully collapsed. The plunger may be in a position where both switches are open and infinite resistance is indicated. 
     In another embodiment, the sensor circuitry includes a potentiometer. In another or the same embodiment, sensors may be positioned on the shaft, in addition or in the alternative to being positioned within the sensor module. One skilled in the art will appreciate the illustrated depressions could alternatively be projections comprising raised portions of the shaft configured to active switches to facilitate brake wear detection. 
     Inputs (e.g., a resistance or a voltage measurement) from the sensor circuitry may be combined with another input to determine when a brake pad should be replaced. For instance, a dynamic stability control computer may receive inputs relating to at least one of vehicle speed, brake pressure, and individual wheel speed. Other inputs may include the mileage at the time new brakes are installed. An input may include how many miles are traveled before the resistance changes from zero ohms to one or multiple threshold voltages. Another input may regard how many miles are traveled between the point where the threshold resistance and an open status. Times and distances corresponding to the signal changes may be used along with the other inputs to count down the mileage until a next replacement. 
     The brake sensor of  FIG. 1  does not touch the rotor and generate noise. The brake sensor may be installed in minutes without replacing brake pads, calipers or other components. An embodiment of a brake sensor retrofits an existing brake sensor and plugs-in without additional parts. The brake sensor will not interfere with brake operation even if the brake system fails and seizes is reusable. 
       FIG. 2  shows an embodiment of a brake pad sensor system  200  installed in a vehicle having brake pads exhibiting an intermediate degree of wear. The brake pad sensor system  200  could be the brake pad sensor system  100  of  FIG. 1 , but with the slide bolt  102  and the shaft  110  having moved inboard. 
     As the slide bolt  202  and the shaft  210  move in the direction  204 , the biasing mechanism  212  may recoil, accordingly. The biasing mechanism may cause the shaft  210  to be in constant contact with the end of the slide bolt  202  as the outer brake pad wears and the caliper body  224  moves inboard toward the centerline of the vehicle. As a result of the progression of the shaft  210  within the sensor module  214 , a first depression  220  in the shaft  210  may be positioned proximate a switch  216 . The switch  216  may consequently spring open. Another switch  218  may remain closed by the substantially opposite surface of the shaft  210 . 
       FIG. 3  shows a brake sensor brake pad sensor system  300  installed in a vehicle having brake pads exhibiting a significant or a total degree of wear. The brake pad sensor system  300  could be the brake pad sensor system  200  of  FIG. 2 , but with the slide bolt  202  and the shaft  210  having moved further inboard. 
     As the shaft  310  moves within the sensor module  214 , a first depression  320  in the shaft  310  may continue to be positioned proximate a first switch  316 . The switch  316  may consequently remain sprung open. A second depression  322  of the shaft  310  may pass near a second switch  318 . The second switch  318  may spring open into the vacancy of the depression. Activation of one or more of the first and second switches  316 ,  318  may initiate generation of an electrical signal having a voltage, current, or resistive value. The electrical signal may be combined with additional inputs to indicate that a brake pad has become worn down. 
       FIG. 4  shows a brake sensor with a cap  408  substantially encapsulating a brake sensor module  414 . The cap  408  may further enclose a biasing mechanism  412  and a least a portion of a shaft  410 . The cap  408  may remain stationary, while the cap of another embodiment may move (e.g., by force provided by a biasing mechanism). 
     In operation, a particular method of determining brake pad wear using the brake pad sensor of any of  FIGS. 1-4  may include positioning a cap proximate an opening of an enclosure that partially encloses a slide bolt. For example, the cap  108  of  FIG. 1  may be positioned proximate an opening the slide bolt boot  106 . The cap may include a cap surface, and the slide bolt may be configured to move in a first direction. For instance, the cap may include a vertical sealing surface that is perpendicular to an axis of the slide bolt boot  106 . The slide bolt  302  may travel in a first direction  104  as a result of brake bad wear. 
     A shaft may be positioned in axial alignment with the slide bolt. For example, the shaft  110  may be positioned in axial alignment with the slide bolt  102  of  FIG. 1 . The shaft may include a first portion that extends in the first direction away from the cap surface and a second portion that extends in a second direction away from the cap surface. For instance, a portion of the shaft  110  of  FIG. 1  may be located left of the vertical surface of the cap  108 , and another portion of the shaft  110  may be located to the right of the cap surface. The second direction may be opposite the first direction. The shaft may be biased in the first direction. For example, the biasing mechanism  112  of  FIG. 1  may bias the shaft  110  in the direction  104 . A first signal indicative of brake pad wear may be generated at a sensor in response to movement of the shaft. For instance, the one or more of the switches  116 ,  118  of the sensor module  114  of  FIG. 1  may generate a signal that may be combined with other inputs to determine brake pad wear. 
     While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the Applicant to restrict, or any way limit the scope of the appended claims to such detail. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus, method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of Applicant&#39;s general inventive concept.