Patent Publication Number: US-2019193480-A1

Title: Sensor system for monitoring tire wear

Description:
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 sensing system based on tire-embedded tread wear sensor implementation. 
     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, being visual, the vehicle operator has to manually inspect each tire on the vehicle while it is stationary in order to find the colored indicators on the tire circumference, which is slow and inconvenient it is also difficult to do in muddy, dirty or snowy conditions. Similar problems occur when the tire employs the tie-bar type wear indicator and it can be difficult to determine the extent of wear until the tire is completely worn. It is quicker and easier for the operator to use the visual Lincolns head penny coin method. 
     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. While providing information about the extent of wear to the vehicle operator, this visual type of wear indicator suffers from the same practical operational problems mentioned above in [003]. Furthermore, the measurement is not numerical or digital so in order to derive full information from it, such as the rate of wear, the results must be transcribed into a computer or smart phone. This is slow and inconvenient for the operator. 
     A cheap and effective 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 vehicle tire and tread wear device assembly includes a tread wear indicator affixed to one or more tire tread 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 therefor. 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 view of a tire and tread wear sensor assembly; 
         FIG. 2  is a close-up front view of a tire and tread wear sensor assembly; 
         FIGS. 3A-3F  are example capacitor electrical elements suitable for use in the invention; 
         FIG. 4  is a first embodiment of a tread wear sensor; 
         FIG. 5  is a second embodiment of a tread wear sensor; 
         FIG. 6  is a schematic diagram of a vehicle having a tire and passive tread wear sensors assembly mounted on each axle that could be powered and communicated wirelessly with a vehicle hub mounted miniature RFID reader with direct power source from the vehicle; 
         FIG. 7  is a schematic diagram of a vehicle having a tire and passive tread wear sensors assembly mounted on each axle that could be powered and communicated wirelessly with a vehicle hub mounted miniature RFID reader with power source from a wireless charging transmitter that is powered by vehicle; 
         FIG. 8  is a schematic diagram of a vehicle having a tire and passive tread wear sensors assembly mounted on each axle that could be powered and communicated wirelessly with a single RFID reader with power source from the vehicle; 
         FIGS. 9A-D  illustrate alternate embodiments of capacitive sensors mounted in the tread elements. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , an example tire  10  is shown having a sidewall  12  and a radially outward tread  14 . The tread  14  as shown may further include one or more tread elements  18 , such as for example, multiple rows of tread lugs  16 . However, the tread elements  18  may also be tread blocks or tread ribs. However, the invention is not limited to a tread with tread elements  18 , and may also be used on a smooth outer tread surface having no tread elements. The tire  10  further includes an inner liner or air impervious layer  20 . Pursuant to conventional tire construction, the tire  10  is formed as a tire carcass  22  in a green tire build procedure and subsequently cured into the finished tire product. 
       FIG. 2  illustrates an enlarged view of the tread region, illustrating the tread rows  16  formed by the spaced apart tread elements  18  that are separated by circumferential grooves  17 . At least one of the tread elements  18 , and preferably multiple tread elements, are equipped with a sensor  100 , also referred herein as a “wear sensor” or “treadwear indicator.” The purpose of the sensor is to detect the progressive wearing of the tread elements  18  or the depth of a tire tread having no tread elements. One or more of the tread wear sensors  100  are mounted in the tread in order to monitor the general tread wear of the tire. By monitoring tread wear digitally, by a wireless electrical reader, the wear status of the tire and rate of wear 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  FIG. 3 , the principle by which the tread wear sensors  100  operate will be understood. Each tread wear sensor  100  includes an electrical element that is a capacitor.  FIG. 3A  illustrates a capacitor made of two opposed conductive plates that are separated by a dielectric. Thus, a thin strip of rubber or polymer  100  that has a first side  110  and a second side  120  that is either painted or printed with a large block  112 , 122  of electrically conductive paint or ink to form a capacitor, with printed lead lines  114 , 124 . One suitable ink for use in a tire is made by EMS, Inc in Delaware, Ohio and is sold under the trade name CI-2061. The ink must also be electrically conductive and flexible, and be capable of withstanding more than 50% strain both dynamic and static. In one example, the type of ink that would work is graphite ink. 
     Other examples of capacitors are shown in  FIG. 3C  a coaxial cable and pair of parallel wires as shown in  FIG. 3D . 
       FIG. 4  illustrates a first example of a tread wear sensor system  200 . The tread wear sensor includes a plurality of sensors  100  embedded in the tread elements of a tire. One or more of the tread elements have a sensor  100  that utilizes a capacitive sensor. The sensor  100  includes a rubber layer (dielectric layer) having a first conductive plate A on a first side, and a second conductive plate B on a second side. The first and second conductive plates with dielectric layer act as a capacitor. The capacitance signal indicates the remaining tread depth. Preferably, conductive ink is used to print desired area on each side of the rubber layer  100  as shown in  FIG. 3E  and  FIG. 3F  based on the required initial capacitance level that will be determined by detection sensitivity and signal noise. The capacitor configuration is not limited to a parallel-plate capacitor. Several other capacitor configurations such as coaxial, pair of parallel wires, or to parallel coplanar strips could also be used for this purpose and are shown in  FIGS. 3C  and  FIG. 3D . This type of sensor is a continuous tread wear indicator. The measured capacitance C T  has linear relationship with remained tread depth L as C T =C O  X L/L O    
     The capacitance sensor is oriented in the radial direction so that as the tread wears, the capacitance level decreases. Preferably, each of the capacitance sensors are printed or painted with electrically conductive and flexible ink, and then inserted in a sipe or groove of the tire. Alternatively, the sensors could be mounted to an outer surface of the tread block or rib. 
     More preferably, multiple capacitance sensors electrically connected to single chip RFID tag  220  to provide rib based or location based wear indication and converter chip to provide A/D conversion. The RFID tag  220  is enhanced to receive multiple data inputs.  FIG. 4  is one of one example to provide rib based wear information (5 ribs tire); 
       FIG. 5  is a second embodiment of a sensor system that is similar to the embodiment shown in  FIG. 4 , except for the following differences. Each tread element includes multiple capacitive sensors  100 . For example, tread elements  300 , 310 , 320  and  330  each have at least one capacitance sensor, preferably at least two capacitance sensors  100  and more preferably at least three capacitance sensors  100 . The tread element  340  has at least one capacitance sensor, and preferably two capacitance sensors. The capacitance sensors are in electrical communication with a passive RFID tag that preferably includes an Analog/digital converter chip. 
       FIG. 9  illustrates additional configurations of capacitance sensors arranged in tread elements.  FIG. 9A  illustrates capacitance sensors for an axially outer tread element with sensors arranged for discrete tread wear detection.  FIG. 9 b    illustrates capacitance sensors for an axially interior tread element with sensors arranged for discrete tread wear detection.  FIG. 9C  illustrates capacitance sensors for an axially outer tread element with sensors arranged for continuous tread wear detection.  FIG. 9D  illustrates capacitance sensors for an axially interior tread element with sensors arranged for continuous tread wear detection. 
     Furthermore, one or more of the capacitor based sensors  100  could also be used as aquaplaning detector. As the tire runs through the wet surface, the circuit will indicate near zero capacitance (shorted). This may provide extra safety information for vehicle operation. 
     As examples from the above described embodiments, the enhanced passive tag will integrate with at least one (may include multi-channels) A/D converter that provides power from RFID tag to sensor and converts measured signal (analog) into digital form and store it to RFID tag&#39;s memory that then transmitted to RFID reader upon requested as illustrated in  FIGS. 11 and 12 . Multiple A/D converters may be used if different types of sensors (for example, voltage and capacitance based sensor) are integrated with same RFID tag; 
     Reader Location and Power Options 
     Each reader  40  may be a small electronic receiver, electronic transceiver that could communicate with a passive RFID (RadioFrequency IDentification) tag/sensor to obtained required information; In another embodiment as shown in  FIG. 6 , there are four miniature readers  40  located at each vehicle axle, wherein the readers  40  are mounted to a protected wheel hub. Each miniature reader  40  is preferably included a mid- or long-range wireless power receiver  42  so that it would be powered wirelessly by a central vehicle mid- or long-range wireless charging transmitter  41 . The wireless charging transmitter  41  is powered by the vehicle battery and wirelessly charges each miniature reader  40  via the power receiver  42 . A rechargeable battery or supercapacitor base power storage device is preferably included with reader  40 . A low power RF reader could be implemented for this application as the reader is closed to sensors. A programable RFID reader is preferably for this application that could handle multiple tag/sensors in a tire without any hardware modification. Multiple wireless communication protocols are preferably included within the reader such as Bluetooth, Wi-Fi and/or LTE. 
     An alternative embodiment is shown in  FIG. 8  wherein there is a single RFID reader  60  that is mounted in the vehicle and is powerful enough to read the signals from the sensors. the reader  60  receives power from the vehicle battery. 
     In an alternate embodiment, the reader is at a remote location such as a drive over reader device. Alternatively, the reader may be powered by a small battery or energy harvestor embedded in the patch, or be hardwired to the vehicle battery as shown in  FIG. 7 . 
     The tread depth measurement would only need to be taken at low frequency and transmitted infrequently e.g., once a month due to the slow wear rate of tires, so power requirements would be low. The tread depth readings could be stored on a server for commercial tire management &amp; data analysis. For consumer tires, the server could send emails to consumer warning of need to replace a worn-out tire. In addition, the non-skid of all four tires on a passenger car could be monitored as well as say both shoulders of each to give info on alignment maintenance. This convenience would be even more valuable on commercial fleet vehicles where the non-skid of all 18 wheels could be monitored automatically. 
     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.