Abstract:
A pneumatic tire and monitoring device for monitoring an engineering condition of a pneumatic tire includes a pneumatic tire having a sidewall and a plurality of reinforcing cords carried in the sidewall. The monitoring device includes a sensing element that senses at least an engineering condition of a pneumatic tire and transmits the gathered data from the monitoring device to a data gathering device outside of the tire. The transmission occurs through a dipole antenna that is in communication with the sensing element. The dipole antenna is disposed substantially perpendicular to the reinforcing cords in order to maximize the probability of signal propagation through the tire sidewall.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention generally relates to monitoring devices for pneumatic tires and, more particularly, to a monitoring device having a dipole antenna used to monitor at least one engineering condition of a tire and to transmit information relating to the engineering condition to an information-gathering device positioned outside of the tire. Specifically, the present invention relates to a monitoring device having a radial dipole antenna mounted on the inside of a pneumatic tire and arranged orthogonally to the lines of electrical interference in the tire sidewall so that the probability of signal propagation through the tire sidewall is improved. 
     2. Background Information 
     It is desired in the art to monitor the conditions of a pneumatic tire while the tire is installed and in use on a vehicle. Although it is desirable to monitor engineering conditions of passenger car tires as well as truck and bus tires, it is particularly desirable to monitor the conditions of off-the-road tires because of the relatively high cost of the tires and the desire to prevent down time from a tire failure. Measuring the engineering conditions of a tire preferably occurs while the tire is in use on the off-the-road vehicle without having to remove the tire from the vehicle or specifically position the tire to take the measurements. Measuring the engineering conditions in this manner prevents the vehicle from being removed from service and thus increases the efficiency of the vehicle. Furthermore, by indicating when a tire is under-inflated, it allows prompt re-inflation to correct pressure which increases tire life providing an economic benefit. 
     Numerous types of monitoring devices are known in the art to perform these measurements. One type of monitoring device uses a passive integrated circuit imbedded within the body of the tire that is activated by a radio frequency transmission that energizes the circuit by inductive magnetic coupling. Other prior art devices used for monitoring tire conditions include self-powered circuits that are positioned external of the tire, such as at the valve stem. Other active self-powered programmable electronic devices are disclosed in U.S. Pat. Nos. 5,573,610, 5,562,787, and 5,573,611 which are assigned to the assignee of the present application. 
     Each of the active self-powered programmable electronic devices includes an antenna that is used to transmit the information gathered by the monitoring device to the information-gathering device positioned outside of the tire. One of the problems in the art is to position and configure the antenna such that the data created by the monitoring device are accurately transmitted to the information gathering device outside of the tire. In many multi-point communication systems, linearly polarized antennas are used to transmit the information gathered by the monitoring device to the information-gathering device. It is known in the art that misalignment between the sensitive access of the antennas will result in a polarization mismatch and thus a reduction in system communications efficiency. Use of linearly polarized antennas in tires that constantly change position due to wheel rotation thus create problems. It is generally desirable that one of the antennas be circumferentially polarized. It is also known in the art that transmission efficiency is reduced when a transmission must pass from one material to another material. It is thus desired to position the antenna as close to the outside of the pneumatic tire as possible in order to minimize the number of material changes that the transmission experiences. In the past, the antenna of the monitoring device generally extended into the interior chamber of the tire such that the radio waves had to first pass through the air inside the tire, through the innerliner, through the tire sidewall, and then through the air to the data gathering device. It is thus desired in the art to provide an antenna for an active, self-powered programmable electronic device that is positioned and configured to maximize the probability of signal propagation through the tire sidewall. 
     The bead ring and apex filler of the tire tend to interfere with the radially-disposed radio transmissions from the monitoring device. It has also been found that the steel reinforcing cords of the sidewall in an off-the-road tire also interfere with the signal propagation. The metal reinforcing cords create lines of electrical interference that must be considered when designing an antenna for an electronic monitoring device for a pneumatic tire. Another problem with transmitting through a tire sidewall is that the rubber of the sidewall may include carbon material that degrades the signal propagation. Another problem with transmitting through a tire sidewall is that the power that drives the transmission is limited by government radio regulations and design consideration. Electronic monitoring devices are preferably small power sources. The amount of power to drive the transmission is thus limited and the design of the antenna must consider the limited power of the monitoring device, in order to ensure a long lifetime for said device. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an objective of the present invention to provide a monitoring device and antenna configuration that maximizes the probability of signal propagation through the tire sidewall. 
     Another objective of the present invention is to provide a monitoring device and antenna configuration for a pneumatic tire that uses a -radial dipole antenna connected to an electronic monitoring device. 
     Another objective of the present invention is to provide a monitoring device and antenna configuration that orients the -radial dipole antenna orthogonally with respect to the lines of electrical interference to maximize the probability of signal propagation through the tire sidewall. 
     Another objective of the present invention is to provide a monitoring device and antenna configuration for a pneumatic tire where the radial dipole antenna is disposed closely adjacent the tire sidewall so that the signal propagates directly into the sidewall. 
     Another objective of the present invention is to provide a monitoring device and antenna configuration for a pneumatic tire that retains the antenna in a specific orientation and seals the antenna from the inside of the tire. 
     Another objective of the present invention is to provide a monitoring device and antenna configuration for a pneumatic tire that is of simple construction, that achieves the stated objectives in a simple, effective, and inexpensive manner, that solves the problems, and that satisfies the needs existing in the art. 
     These and other objectives and advantages of the present invention are obtained by a monitoring device for a pneumatic tire including at least one sensing element for sensing at least one engineering condition of the pneumatic tire; and a radial dipole antenna in electrical communication with the sensing element. 
     Other objectives and advantages of the present invention are achieved by the combination of a pneumatic tire; a monitoring device for monitoring at least one engineering condition of the pneumatic tire; the pneumatic tire having a sidewall; the monitoring device having at least one sensing element for sensing at least one engineering condition of the pneumatic tire; and a pole antenna in electrical communication with the sensing element. 
     Still other objectives and advantages of the present invention are achieved by the combination of a pneumatic tire and a monitoring device for monitoring at least one engineering condition of the pneumatic tire; the pneumatic tire having a sidewall and a plurality of reinforcing cords carried in the sidewall; a bead ring disposed in the tire sidewall; the monitoring device having at least one sensing element for sensing at least one engineering condition of the pneumatic tire; and a dipole antenna in electrical communication with the sensing element; the antenna overlying at least one of the reinforcing cords and being disposed substantially perpendicular to each of the reinforcing cords that it overlies. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of the invention, illustrative of the best mode in which applicant has contemplated applying the principles of the invention, are set forth in the following description and are shown in the drawings and are particularly and distinctly pointed out and set forth in the appended claims. 
     FIG. 1 is a sectional view of a pneumatic tire with an electronic monitoring device mounted on the innerliner of the tire; 
     FIG. 2 is a view of the monitoring device and tire sidewall taken along line  2 — 2  of FIG. 1 showing different locations for the monitoring device with antennas having different curvatures; 
     FIG. 3 is a fragmented top plan view of the monitoring device and antenna configuration of the present invention; 
     FIG. 4 is a sectional view taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is a sectional view of a first alternative embodiment of the monitoring device and antenna configuration of the present invention with the monitoring device and antenna removed from an attachment patch; 
     FIG. 6 is a sectional view of the first alternative embodiment of the monitoring device and antenna configuration with the monitoring device attached to the attachment patch and covered with a covering material; 
     FIG. 7 is a sectional view of the second alternative embodiment of the present invention; 
     FIG. 8 is a view similar to FIG. 3 showing a third alternative embodiment of the present invention; and 
     FIG. 9 is a view similar to FIGS. 3 and 8 showing a fourth alternative embodiment of the present invention. 
    
    
     Similar numbers refer to similar parts through the specification. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The first embodiment of the monitoring device and antenna combination of the present invention is depicted in FIGS. 1-4 and is indicated generally by the numeral  10 . In accordance with one of the objectives of the invention, monitoring device and antenna combination  10  includes a dipole antenna  12  that is connected to a monitoring device  14 . Dipole antenna  12  is mounted on a pneumatic tire  16  in a manner that maximizes the probability of desirable signal propagation through the tire sidewall  18 . 
     Pneumatic tire  16  includes a bead ring  20  from which sidewall  18  extends outwardly substantially radially. A package of reinforcing cords  22  extends around bead ring  20  and radially outward through sidewall  18 . Reinforcing cord package  22  may be fabricated from a variety of materials and disposed in a variety of orientations in sidewall  18 . In large, off-the-road tires, reinforcing cord package  22  may include a plurality of metal reinforcing cords  24  that each extend radially outward through sidewall  18 . Cords  24  are thus closer together adjacent bead ring  20  that at the outer radius of sidewall  18 . Tire  16  further includes an innerliner  26  positioned on the inside surface of tire  16 . Innerliner  26  may be significantly thicker in off-the-road tires than it is in passenger car tires. As is known in the art, pneumatic tire  16  is mounted on a rim and has a pressurized inner chamber when in use. Monitoring device and antenna combination  10  are disposed in this pressurized chamber as shown in FIG.  1 . 
     Monitoring device  14  may include a board  30  upon which a pair of batteries  32 , a central processing unit (CPU)  34 , and at least one sensing element  36  are mounted. Various other elements may also be positioned on board  30 . This specific configuration of monitoring device  14  is not to limit the scope of the invention as numerous monitoring device configurations will function with the present invention. Antenna  12  is in electrical communication with sensing element  36  such that the information gathered by sensing element  36  can be transmitted by antenna  12  outside of tire  16 . Components  30 ,  32 ,  34 , and  36  are all encapsulated by an encapsulation material  38  to form an encapsulated monitoring device  40 . Encapsulation material  38  provides protection to components  30 ,  32 ,  34 , and  36 . Encapsulation material  38  may be a suitable epoxy or other material that is substantially rigid after it has encapsulated the components. 
     Dipole antenna  12  includes a first antenna element  50  and a second antenna element  52  that extend away from each other. Each element  50  and  52  may be preferably fabricated from a round metal wire although different materials may be used without departing from the concepts of the invention. Dipole antennas are known in the art and may have various configurations, any of which may be used with the present invention. Each antenna element  50  and  52  is connected to and is in electrical communication with sensing element  36  by a suitable connector  54  that may be one of a variety of connectors known in the art. 
     Antenna  12  is disposed in an attachment patch  60  that is used to mount encapsulated monitoring device  40  on innerliner  26 . Attachment patch  60  includes a foot portion  62  that extends away from encapsulated monitoring device  40 . Antenna  12  is preferably located in foot portion  62 . Encapsulated monitoring device  40  is mounted on attachment patch  60  by a suitable connector, such as an adhesive that is known in the art. Similarly, attachment patch  60  is mounted on innerliner  26  by a suitable connector, such as an adhesive, that is known in the art. 
     As may be seen in FIGS. 1 and 2, antenna  12  is arranged and configured with respect to tire sidewall  18  such that antenna  12  is above bead ring  20  and substantially perpendicular or orthogonally oriented to reinforcing cords  24 . In accordance with one of the objectives of the invention, locating antenna  12  substantially perpendicularly to reinforcing cords  24  maximizes the probability of desirable signal propagation through tire sidewall  18 . When monitoring device and antenna combination  10  is used with another tire that has reinforcing cords  24  that are biased, antenna  12  is turned so that antenna  12  remains substantially perpendicular to reinforcing cords  24 . It has been found that the signal propagation pattern from radial dipole antenna  12  provides a good probability of signal propagation through sidewall  18 . 
     FIG. 2 depicts three monitoring device and antenna combination  10  locations as shown at  10 A,  10 B, and  10 C. Each combination  10 A,  10 B,and  10 C Includes an antenna  12 A,  12 B, and  12 C connected to an encapsulated monitoring device  40 A,  40 B,  40 C. The curvature of each antenna  12 A,  12 B, and  12 C matches its location with respect to sidewall  18  such that the curvature of antenna  12  is substantially equal to the radius of curvature of sidewall  18 . The dipole antenna, which is mounted to the tire at one of a plurality of radius distances defined by the sidewall, has a radius of curvature that is substantially equal to the radial distance where the dipole antenna is mounted. As such, the radius of curvature of antenna  12 A is less than the radius of curvature of antenna  12 B and both radii of curvatures for antennas  12 A and  12 B are less than the radius of curvature for antenna  12 C. By matching the radius of curvature of antenna  12 A with its location on tire sidewall  18 , each intersection of antenna  12  with a reenforcing cord  24  is substantially perpendicular or orthogonal. 
     The first alternative embodiment of the invention is depicted in FIGS. 5 and 6. The components of the first alternative embodiment are substantially the same as described above and the same numbers are used to refer to the same elements. In this embodiment, patch  60  includes a groove  70  into which antenna  12  is placed when encapsulated monitoring device  40  is attached to attachment patch  60 . Groove  70  properly positions antenna  12  with respect to attachment patch  60  so that a person installing attachment patch  60  and encapsulated monitoring device  40  will know that antenna  12  is oriented in a certain manner with respect to patch  60 . After antenna  12  is disposed within groove  70  and encapsulated monitoring device  40  is securely to attachment patch  60 , a covering material  72  is positioned over antenna  12  and groove  70  to cover antenna  12  from the inside of tire  16 . Covering material  72  also holds antenna  12  in position. Covering material  72  preferably may be an epoxy but may be other materials that are known in the art. 
     The second alternative embodiment of the invention depicted in FIG. 7 where antenna  12  is embedded within innerliner  26 . In this embodiment, antenna  12  is positioned within innerliner  26  during the fabrication of tire  16  such that antenna  12  is substantially perpendicular to reinforcing cords  24 . Tire  16  is then cured with antenna  12  which is held in innerliner  26 . Monitoring device  14  is then connected to antenna  12  at a later time by known means. 
     A third alternative configuration of the monitoring device and antenna combination of the present invention is depicted in FIG.  8  and is indicated generally by the numeral  100 . The antenna  102  of configuration  100  includes first antenna element  50  and second antenna element  52  of radial-dipole antenna  12  discussed above. Antenna  102  further includes a third antenna element  104  that is spaced from first and second antenna elements  50  and  52 . Third antenna element  104  is connected to first and second elements  50  and  52  by a pair of end elements  106  that are substantially semi-circular. In accordance with the objectives of the present invention, antenna elements  50 ,  52 , and  104  are oriented substantially perpendicular to the lines of electrical interference in sidewall  18 . 
     A fourth alternative embodiment of the monitoring device and antenna combination of the present invention is depicted in FIG.  9  and is indicated generally by the numeral  110 . Combination  110  includes substantially the same elements as combination  100  disclosed above. The only difference is that the end elements  112  of radial dipole antenna  114  are each substantially perpendicular to the end portions of antenna elements  50 ,  52  and  104 . In accordance with the objectives of the present invention, radial dipole antenna  114  is positioned to be substantially perpendicular to the lines of electrical interference in sidewall  18 . 
     Accordingly, the improved-radial dipole antenna and tire tag combination is simplified, provides an effective, safe, inexpensive, and efficient device which achieves all the enumerated objectives, provides for eliminating difficulties encountered with prior devices, and solves problems and obtains new results in the art. 
     In the foregoing description, certain terms have been used for brevity, clearness, and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirement of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed. 
     Moreover, the description and illustration of the invention is by way of example, and the scope of the invention is not limited to the exact details shown or described. 
     Having now described the features, discoveries, and principles of the invention, the manner in which the radial dipole antenna and tire tag combination is constructed and used, the characteristics of the construction, and the advantageous new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts, and combinations are set forth in the appended claims.