Patent Document

FIELD OF THE INVENTION 
     The invention relates generally to a sensing system for real-time monitoring of tire wear over its life time and, more specifically, to a method of installing a wear sensor into a tire. 
     BACKGROUND OF THE INVENTION 
     The use of tread wear indicators is not new and the use of tread wear indicators is mandated by law in many countries. A variety of such indicators are known. Once such type employs colored indicia below the tread for a visual indicator of wear. Other types use tie-bar type elements in the tread grooves. 
     The practical problem with the colored indicators of the type mentioned is that there is no way for the operator to determine the level of wear until the tire is worn. When the tire employs the tie-bar type wear indicator, it can be difficult to determine the level of wear. 
     U.S. Pat. No. 6,523,586 discloses wear indicators for a tire tread wherein, in a series, or predetermined closely located grouping, of related marks, the marks disappear as the tire is worn. While this provides continuous information to the consumer, the complexity of forming the tire is increased due to the need to form multiple different marks that appear only after a defined amount of wear. 
     A tread wear indicator which is readily integrated into a tire and which reliably measures tread wear in a manner easily monitored by a vehicle operator is, accordingly, desired and heretofore unattained. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the invention a method of installing a tread wear sensor in a tire includes configuring tread wear indicators to each include a stack of sacrificial resistive sensor elements. The stacks of resistive sensor elements are affixed to respective selected tread elements (lugs) positioned at dispersed axial locations across a tire tread region. Each stack of resistive sensor elements is oriented parallel to a ground engaging surface of a respective tread lug with each resistor sensor element at a respective sensor depth from the ground engaging surface. The sensor elements sacrificially abrade and change in resistance responsive to progressive tread wear on the tread element to the sensor depth. 
     In another aspect, the method includes measuring the resistive sensor elements of each stack for a change in resistivity; and determining a tread wear status profile based on the measured change in resistivity of the resistive sensor element in each stack. 
     According to another aspect of the invention, the method of affixing the resistive sensor elements of each tread wear indicator to a tread element includes dividing a tread lug into opposed tread element blocks by an axially extending incision; spreading the opposed tread element blocks apart; affixing a stack of resistive sensor elements to a channel-facing surface of a tread element block; and converging the tread element blocks together to eliminate the channel therebetween. The circuit including the stack of resistive sensor elements may be etched onto a substrate for insertion into the tread lug channel or, alternatively, etched to a channel-facing surface of one of the divided lug tread element blocks. 
     The method, in a further aspect of the invention, includes positioning multiple connector assemblies within the tire carcass cavity radially opposite the selected tread lugs. A needle projection from each of the connector assemblies is inserted radially outward through the tire carcass from a tire cavity side. The needle projection extends to a position opposite a respective stack of resistive sensor elements and carries conductive leads which engage and establish electrical contact with the respective stack of resistive sensor elements. 
     Definitions 
     “Groove” means an elongated void area in a tread that may extend circumferentially or laterally about the tread in a straight curved, or zigzag manner. Circumferentially and laterally extending grooves sometimes have common portions and may be sub classified as “wide”, “narrow”, or “sipe”. The slot typically is formed by steel blades inserted into a cast or machined mold or tread ring therefore. In the appended drawings, slots are illustrated by single lines because they are so narrow. A “sipe” is a groove having a width in the range from about 0.2 percent to 0.8 percent of the compensated tread width, whereas a “narrow groove” has a width in the range from about 0.8 percent to 3 percent of the compensated tread width and a “wide groove” has a width greater than 3 percent thereof. The “groove width” is equal to tread surface area occupied by a groove or groove portion, the width of which is in question, divided by the length of such groove or groove portion; thus, the groove width is its average width over its length. Grooves, as well as other voids, reduce the stiffness of tread regions in which they are located. Sipes often are used for this purpose, as are laterally extending narrow or wide grooves. Grooves may be of varying depths in a tire. The depth of a groove may vary around the circumference of the tread, or the depth of one groove may be constant but vary from the depth of another groove in the tire. If such narrow or wide groove are of substantially reduced depth as compared to wide circumferential grooves which they interconnect, they are regarded as forming “tie bars” tending to maintain a rib-like character in the tread region involved. 
     “Inner” means toward the inside of the tire and “outer” means toward its exterior. 
     “Outer” means toward the tire&#39;s exterior. 
     “Radial” and “radially” are used to mean directions radially toward or away from the axis of rotation of the tire. 
     “Tread” means a molded rubber component which, when bonded to a tire casing, includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load. The tread has a depth conventionally measured from the tread surface to the bottom of the deepest groove of the tire. 
     “Tread Element” is a protruding portion of a tread such as a lug or rib which constitutes the element that comes into contact with the road. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described by way of example and with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective front view of a tire showing the sensor location. 
         FIGS. 2A and 2B  are enlarged fragmented front views taken from  FIG. 1  showing sensor locations. 
         FIG. 3  is a graph showing sensor resistance vs. tire wear. 
         FIG. 4  is a schematic drawing of parallel resistor electrodes in tread block. 
         FIG. 5  is a perspective view of parallel resistors in a tread block. 
         FIGS. 6A through 6C  are schematic views of alternative sensor patterns showing in  FIGS. 6A and 6B  like-sized resistive elements and, in  FIG. 6C , different sized resistive elements. 
         FIGS. 7A through 7C  are schematic views of alternative stacked pattern layouts of two full sensors showing how the sensors would be etched onto an insulator layer with the contact area being formed over at 90 degrees. 
         FIGS. 8A and 8B  are schematic view showing a “Flip-Flop” layout, in which a formed finished sensor is located in a tread block. 
         FIG. 9  is a perspective view of a Flip-Flop sensor in a tread block and a plug-in connector. 
         FIG. 10  is a plan view of a thru-belt connector. 
         FIG. 11A  is a section view of a tread block showing a flip-flop sensor and thru-belt connector. 
         FIG. 11B  is a section view of a tread block showing a flip-flop sensor and a conduction chimney connector alternative embodiment. 
         FIG. 12  is a diagram of first System Architecture embodiment. 
         FIG. 13  is a diagram of second alternative System Architecture embodiment. 
         FIG. 14A  is an enlarged section view of a tread area showing sensors and thru-belt connector placed in full row of lugs. 
         FIG. 14B  is an enlarged section view of a tread area showing sensors placed on conducting adhesive strips. 
         FIGS. 15A and 15B  are perspective views of an alternative embodiment showing lug center cutting and a sensor being etched directly onto inside area of lug using liquid ink jet printing. 
         FIG. 16A  is a section view showing an ink jet pattern on a cut tread block surface. 
         FIG. 16B  is a section view showing an etched tread block inside surface and thru-belt connector in place before closing. 
         FIG. 16C  is a section view showing a finished etched sensor and connection to thru-belt connector. 
         FIG. 17A  is a perspective view of a cut tread block with etched conductor being placed directly to an inside surface. 
         FIG. 17B  is a perspective view of an etched conductor fully placed in a cut tread block. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 ,  2 A and  2 B, a representative tire assembly  10  is shown including a vehicle tire  12  having a radially outward tread  14  defined into multiple circumferential tread rows  16 . Within each of the tread rows  16  is a circumferential array of tread elements  18 , also referred to herein as tread lugs or blocks. The tire  12  further includes an internal cavity  20 . Pursuant to conventional tire construction, the tire  12  is formed as a tire carcass  22  in a green tire build procedure and subsequently cured into the finished tire product. 
       FIGS. 2A and 2B  show enlargement views of the tread region, illustrating the tread rows  16  formed by the spaced apart tread blocks  18 . At least one of the tread blocks  18 , and preferably multiple tread blocks, are equipped with a resistive sensor  24 , also referred herein as a “wear sensor” or “treadwear indicator”. As seen in the sensor configuration of  FIG. 2A , the tread lugs  18  equipped with wear sensors  24 ,  26  and  28  are lugs which lie in a co-linear axial alignment across the tread  14 . In  FIG. 2A , an alternative wear sensor architecture is depicted in which the sensors  24 ,  26 ,  28  lie in a sequential or diagonal array across the tread  14 . The purpose of the sensors  24 ,  26 ,  28  is to detect the progressive wearing of the tread lugs  18  to which the sensors are attached in order to monitor the general tread wear of the tire. By monitoring tread wear, the wear status of the tire may be ascertained. From determining the wear status of the tire, a decision on whether and when to replace the worn tire may be made. 
     With reference to  FIGS. 3 ,  4  and  5 , the principle by which the tread war sensors  24  operate will be understood. The sensors  24  are constructed having an array  30  of resistor elements. In the embodiment shown, four resistor elements R 1 , R 2 , R 3  and R 4  are shown but it will be appreciated that more or fewer resistors may be employed if desired. The resistors are positioned in parallel at differentiated radial depths along a tread block  18  to which the resistors are secured. The resistors progressively wear out as the tread block  18  wears, causing a measurable change (drop) in the measured electrical resistance R of the array  30 . When multiple tread blocks are so fitted with resistor arrays, such as two or three blocks, at different locations in the tread, the wear status of the tread at the selected tread locations may be ascertained by detecting and measuring the drop in resistance R of each array. 
     A micro-processor processes the data from the tread blocks fitted with resistor arrays. Upon application of an algorithm to the data, a tire wear estimation is made. If the tire is equipped with an in-tire tire pressure monitoring system (TPMS) which transmits tire pressure data from a TPMS pressure sensor, the TPMS system may be employed for the additional purpose of at least detecting data from the resistor sensors  24 ,  26 ,  28  and transmitting the data by radio-frequency signal to a remote receiver. 
       FIG. 3  shows a representative wear sensor  24  in a new tire lug  18  which is unworn. It will be seen that all four resistor lines R 1 , R 2 , R 3  and R 4  in array  30  are positioned in parallel and provide a cumulative resistance Rmax. For a new tire, R 0 -Rmax. The graph  32  of sensor resistance (ohms) vs. tire tread block wear (mm) illustrates the wear detection principle as the tire tread lug  18  wears. As the lug wears, resistor lines progressively wear and are eliminated. A drop in resistance R from the array  30  results. The diagram in  FIG. 3  of a used tire shows an elimination of resistors R 1  and R 2  as the lug  18  wears away. As a consequence Rt of the array  30 &lt;Rmax. Further wear on the lug will progressively eliminate resistor lines R 3  and R 4 , reducing Rt. 
       FIG. 4  is a schematic drawing of the array  30  of parallel resistor elements R 1 , R 2 , R 3  and  4  in tread block  18 .  FIG. 5  is a perspective view of the parallel resistors in the tread block  18 . The resistor elements or electrodes may be screen printed on a film substrate  38 . For example, the resistors may be on 45 micrometer thick film and silver ink recovered with carbon ink used to print the circuitry thereon by techniques common in the industry. It is further contemplated that through the use of a suitable substrate, such as Kapton® plastic material, the substrate in the wear sensor  24  will be capable of withstanding the temperatures imposed during tire cure. Consequently, it is possible through appropriate selection of materials to incorporate the resistor sensor  24  into a tread block  18  of a green tire during green tire build. As shown schematically in  FIG. 5 , the system employs a through-belt snap-in connector  34  to establish electrical connection between the wear sensor resistors and a TPMS sensor module  36 . The TPMS module  36  is designated as “TPMS+” to represent that the TPMS module  36 , in addition to measuring and transmitting pressure data from the tire cavity, may also be employed to transmit data from the wear sensor to a remote receiver. It will be noted that the TPMS +module  36  mounts to the cavity side surface of the tire carcass such as the tire inner liner. It will further be noted that the connector  34  is deployed through the tire carcass from the cavity side. The connector  34  projects through the carcass belt reinforcement  40  and includes electrical leads which establish electrical engagement with the resistor array  30  as will be explained below. 
     The resistor elements R 1 , R 2 , R 3 , R 4  constituting the array  30  may be configured in multiple patterns as reflected in  FIGS. 6A ,  6 B and  6 C. In  FIG. 6A , the resistors are arranged in a single row pattern. In  FIG. 6B , the resistors are in a double row pattern. In  FIG. 6C , the resistors are in a single row pattern in mutual differentiated sizes so that each resistor carries and may be identified by a unique resistive value (ohm). The different resistive values of elements R 1 , R 2 , R 3  and R 4  assist in identifying change in Rt as the tire lug wears and thereby the wear status of the lug  18 . 
       FIGS. 7A through 7C  are schematic views of alternative stacked pattern layouts of two full sensors.  FIG. 7A  shows a full sensor layout  52  etched to an isolation layer pattern  54 .  FIG. 7B  shows a stacked configuration in front, back, and side elevation views of the etched sensor  56  on the isolation layer  58 .  FIG. 7C  shows a configuration in which “flip-flop” contacts  60  are utilized. The contacts  60  have etched resistor sensor circuitry  62  integrated into isolation layers  64 . The contacts  60  provide connector wings  66  extending perpendicular to the plane of the isolation layer  64  and parallel to a tread block plane. The wings  66  are configured as contact pads so as to maximize the “blind” contact area available to a thru-belt snap-in connector explained following. The sensor front and rear views are shown in  FIG. 7C . 
     Referring to  FIGS. 8A and 8B , the ‘flip-flop” sensor contact  60  configuration is shown in greater detail. The wings  66  the sensor layout define a contact area formed over at 90 degrees from the body of the sensor containing the resistive array  30 . In the “flip-flop” sensor configuration  60 , the resistor array  30  extends radially (direction arrow  69  in  FIG. 9 ) within a tread lug  18 . The contact wings  66  are formed ninety degree over and position at a radially inward end of the lug  18 . The wings  66  carry a rubber conductive cap  68  bonded to an isolation layer  70 . Leads from the resistor array  30  electrically connect to the conductive cap  68 . So positioned, the wings  66  are diagonally separated and project in opposite axial directions (direction arrow  71  in  FIG. 9 ), ninety degrees over from the radially extending body of the sensor. 
     With continued reference to  FIGS. 9 ,  10  and  11 A, a plug-in needle-style connector  72  is provided to establish interconnection between a TPMS module and the lug-mounted flip-flop contacts  60  of the wear sensor  24 . The connector  72  is operative as a through-belt connector which penetrates a tire carcass from the internal cavity side to establish electrical connection with the contact pads  68  of the flip-flop wings  66 . The connector  72  includes a housing  74  having projecting wall plug-style probe fingers  76  for penetrating through the tire carcass from the cavity side. The fingers  76  are provided with an axial array of piercing arrowhead flanges beveled in an orientation which assists in achieving the intended carcass penetration. Extending into the housing  74  from the TPMS module (unshown) are leads  78 ,  80  coupled respectively to inside conductors  82 ,  84 . The inside conductors extend through a respective one of the punch-in fingers  76  to terminate at a punch-in head  85 . The length of the punch-in fingers  76  is sufficient to span the distance between the tire inside cavity and the contact pads of the lug-mounted sensor  24 . The array of arrow-head configured piercing flanges  77  extend along each of the fingers  76  to deter disengagement of the connector  72  from the tire carcass after the fingers  76  have penetrated the tire carcass and engaged with the flip-flop contact pads. 
     From  FIG. 9 , it will be appreciated that housing  72  is oriented during an attachment sequence to the tire carcass so as to align with the flip-flop contact pads  60  on the wings  66 . The distance between the penetrating fingers  76  of connector  72  is such that the fingers  76 , once suitably located and punched through the tire carcass, will encounter and engage the contacts  60  on each of the flip-flop wings  66 . The plug fingers  76  have a length approximately  3  mm. Electrical connectivity is thereby established and maintained between the contacts  60 , the inside conductors  82 ,  84  and the leads  78 ,  80  extending to a data transmitting device such as one integrated into a tire-mounted TPMS module. The flip-flop connector wings  66  serve to maximize the “blind” contact area targeted by the punch-through connector  72 . The connector  72  is added in a post-cure procedure 
     Referring to  FIGS. 11B , an alternative means of interconnectivity between wear sensor  24  and a remote data transmitting device is shown. The plug-in needle connector  72  utilizes conduction chimneys  88 ,  90  in the alternative embodiment to interconnect housing leads  82 ,  84  to appropriate flip-flop contact pads carried by contact wings  66 . The conduction chimneys  88 ,  90  are formed from anisotropic conducting adhesives that fill through-passageways punched through the tire carcass belt construction. The leads  82 ,  84  are electrically coupled to the conduction chimneys  88 ,  90  and are thereby connected to the contact pads of the wear sensor  24 . 
     A first system architecture  92  which utilizes tread wear measurement is depicted schematically in  FIG. 12 . In the system  92  the intelligence and algorithm for data processing is located out of the tire. A TPMS system may be utilized for sensor read-in and for RF data transmission from the wear sensor. Alternatively, a dedicated wear sensor input device and data transmitter device from the wear sensor may be employed if desired. The in-tire architecture  94  in the system architecture  92  includes the sensor resistor elements R 1 , R 2 , R 3 , R 4 ; the resistance/current measurement circuit; an RF-emitting antenna; an energy harvester; an energy storage capacitor; a current rectifier circuit; and a sensor read-out circuit. Transmission of resistance measurements is made by RF signal to an In-Vehicle system  96  which includes a receiver and microprocessor unit  100 . The microprocessor  100  transmits an output reflecting tire wear via the vehicle CANBUS  98  to the vehicle Electronic Control Unit (ECU). The vehicle ECU may then use the tire wear status in active safety and traction control systems such as an anti-lock brake system (ABS); an electronic stability program control system (ESP); direct traction control system (DTC); adaptive cruise control system (ACC); etc. 
     The process of wear estimating by measuring the resistance change in the resistance/current measurement circuit may be adjusted and optimized through the selection of differentiated individual sensor resistances (i.e. R 1  through R 4  have different resistances). Sensor interconnection (serial vs. parallel) may further be selected to make the measurement of resistance change in reading and algorithmic functions simplified. 
     The vehicle ECU may further output notification communication  104  to a vehicle operator. Such notification may take multiple forms such as a head up display; driver panel controls; service center information transmittal remote to the vehicle; a driver smartphone, etc. 
     An alternative system architecture  106  is shown schematically in  FIG. 13 . In the alternative system, the microprocessor  114  is incorporated as part of the in-tire  108  electronics rather than part of the in-vehicle  110  system. The microprocessor is programmed with a wear estimation algorithm that uses the resistance change within the resistance/current measurement circuit to derive tread wear status. An energy harvester is provided to power the in-tire electronics. The energy harvester may be piezo-based, electroactive polymer-based, or constitute a battery. The tread, as described previously and shown in  FIGS. 2A and 2B , has multiple tread lugs equipped with a wear sensor  24 . By monitoring and measuring the wear of multiple tread lugs situated at different locations across the tread, a general conclusion as to tread wear may be derived. The microprocessor  114  in the second embodiment analyzes data from each sensor  24  and transmits by RF signal tread wear data to an in-vehicle receiver. As with the embodiment of  FIG. 12 , the second embodiment architecture of  FIG. 13  communicates tread wear information by the vehicle CANBUS  112  to the vehicle ECU which then employs tread wear in an array of active safety and traction control systems  116 . As with the architecture embodiment of  FIG. 12 , the vehicle ECU may further output notification communication to a vehicle operator in an array of communication options  118 . Such notification may take multiple forms such as a head up display; driver panel controls; service center information transmittal remote to the vehicle; a driver smartphone, etc. 
       FIG. 14A  shows an enlarged section view of a tread area showing sensors  24  employing flip-flop configured contacts  20  attached in full row of tread lugs  18 . The thru-belt connectors  72  extend through the tire contact to engage and establish electrical contact with the contacts  60  of the sensors  24  as described previously. 
       FIG. 14B  shows by enlarged section view a tread area in which the flip-flop contacts  60  of the sensors  24  are placed on anisotropic conducting adhesive strips or tape  120 . Engagement of the thru-belt connectors (not shown) is with the anisotropic tapes  120 . 
     In  FIGS. 15A and 15B , perspective views of an alternative embodiment is shown in which the center of a tread block  18  is cut in preparation for attachment of the wear sensor by a radially extending cut line  124  into the lug  18 . The bifurcated lug  18  is separated forming a V-shaped channel  126 . A sensor half  128  is then etched directly onto inside area of lug  18  using a suitable process such as liquid ink jet printing.  FIG. 16A  shows in section view the ink jet pattern on a cut tread block surface of a left half of the block  18 . In  FIG. 16B  the plug-in needle connector  72  is inserted through the carcass from the tire cavity side as described previously, with contact probes  131 ,  133  positioned within the V-shaped channel  126  opposite terminal ends of the etched sensor circuit  62 . As shown in  FIG. 16B  by directional arrows  134 , the bifurcated block halves  130 ,  132  are then closed together to eliminate the channel  126  and bring the contact probes  131 ,  133  into contacting electrical engagement with the terminal ends of the etched circuit  128 .  FIG. 16C  shows in section the finished etched sensor and connection to the thru-belt connector. 
       FIG. 17A  is a perspective view of the cut tread block  18  receiving a separately-formed etched circuit  138  as an alternatively to etching the circuit directly to the tread lug. The etched circuit  138  is applied to a strip of suitable material such as flexible polymer film  140 . The polymer film  140  is then attached to an inside surface of the lug formed facing the cut V-shaped channel  126 . An adhesive  142  is pre-applied to the channel-facing surface of the lug  18  operative to adhere the film  140  carrying etched sensor  138  to the lug surface. The through-belt connector is then attached (not shown) in a similar manner to that shown in  FIG. 16C  to complete the circuit to tread lug sensor interconnection. The lug  18  is then closed as indicated by arrows  144 . 
     From the foregoing, it will be appreciated that the sensor  24  to a host lug  18  may be achieved in alternative procedures. The  FIGS. 16A  through C procedure etches the circuit directly to a bifurcated lug surface once the lug is separated. The  FIG. 17A  and B approach is to pre-form an etched circuit to a carrier polymer strip which is then assembled to the lug by use of an adhesive. In either assembly process, the completed resistive sensor circuit is at its intended location within the tread lug, oriented to progressively wear as the tread lug wears. The through-belt connector extends from the cavity side of the tire carcass through the belt assembly to establish and maintain a positive mechanical and electrical engagement with the sensor contact pads. A flip-flop contact configuration for the sensor operates to increase the target area and facilitates alignment of the through-belt connector probes with the target contact regions. 
     Tread wear device assembly includes a tread wear indicator affixed to one or more tire tread elements. The indicator(s) is constructed as a plurality of radially stacked sensor elements operatively configured and located to sequentially sacrificially abrade and change in electrical resistance responsive to a progressive tread wear of the tread element to which the sensor element is affixed. The sensor elements are connected by circuitry that communicates a data signal from the sensor elements to a data processor indicative of a change in resistivity of the sensor elements. The data processor receives the data signal from the sensor elements and determines a radial wear level of the tread element(s) based on the data signal. 
     One, and preferably multiple, sensors  24  are mounted to a respective tread lug in a pre-determined pattern across the tread. The resistive element(s) integrated into circuitry of sensors  24  are operatively subjected to a progressive etching induced by the tread wear of the respective tread element, whereby producing a measureable change in sensor resistivity. Each sensor  24  is targeted by a plug-in needle connector  72  operative to protrude through the tire carcass  22  from a cavity  20  side of the carcass to engage and establish an electrical contact with the sensor elements R 1  through R 4 . 
     Multiple tread wear indicators or sensors  24  are affixed over the tire tread, each indicator at a respective tread location and each mounted to a respective tread element. Each tread wear indicator  24  is constructed having radially stacked sensor elements R 1  through R 4  that sequentially sacrificially abrade and change in resistivity as the respective host tread lug progressively wears. The plug-in needle connectors  72  protrude through the carcass from a tire cavity side of the carcass and establish a positive mechanical and electrical contacting engagement with respective sensors  24  and the electrical interface contact pads thereof. Alternative architectures of the system, shown by  FIGS. 12 and 13 , evaluate the change in electrical resistance of the sensors  24  cause by tread lug wear and thereby determine the status of lug wear. Such information is communicated from the sensors  24  to a processing unit. The status of tread wear may then be used by vehicle safety and handling systems. Information concerning tread wear status may further be communicated to a vehicle operator. 
     Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.

Technology Category: b