Abstract:
A method and apparatus for bonding an active tag to a patch and assembling the patch to a tire is set forth. A patch assembly and a method for securing an electronic monitoring device having electronic and mechanical components for monitoring at least one engineering condition within a tire, comprising an rigid tag assembly encapsulating the electronic monitoring device, bonded to a vulcanized rubber patch which is secured to the inner cavity of a tire utilizing a layer of dual cure bonding rubber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application is a Divisional Application of Ser. No. 08/932,091 filed Sep. 17, 1997 now U.S. Pat. No. 5,971,046; the disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention pertains to an apparatus and a method of bonding an active tag to a patch and to a tire. More particularly, this invention sets forth a method and apparatus for encapsulating an electronic device in a rigid material, mounting the device on a vulcanized rubber patch and bonding the rubber patch to a vulcanized tire. 
     BACKGROUND OF THE INVENTION 
     It is desirable to monitor engineering conditions of tires, such as wear, internal pressure and internal temperature in order to reduce tire costs and maximize vehicle efficiency. Of course, it is advantageous to perform such monitoring in large truck tires, which are expensive. 
     Prior art methods of monitoring large truck tires have included passive integrated circuits embedded in the body of the tire, or self-powered circuits which are positioned external to the tire. The passive integrated circuits rely on inductive magnetic coupling or capacitative coupling to energize the circuit, thus providing power to the circuit from a source remote from the tire. Self-powered circuits positioned external to the tire are exposed to damage from the environment such as weather, road hazards and even vandalism. 
     Recent engineering advances have permitted the installation of monitoring devices having active integrated circuits within tires. One such device is described in U.S. Pat. No. 5,562,787 to Koch et al. entitled “Method of Monitoring Conditions of Vehicle Tires”, incorporated herein by reference, and assigned to the assignee of the present invention. These devices include an active circuit powered by a dedicated long life, miniature battery and at least one sensor for detecting, optionally storing and transmitting real time engineering conditions within the tire. Such devices are capable of being programmed to remain in an active, but dormant condition, but will switch automatically to an “awakened” condition in response to an external signal or a condition which exceeds preset limits. 
     One of the problems faced with such active devices is that they are delicate electronic devices that must operate in the harsh environment of a tire. Thus it is important to secure these devices in the tires to minimize the effect of the harsh tire environment on them, while still permitting them to be exposed to this environment to allow accurate monitoring of the engineering conditions for the life of the tire. These active devices have previously been mounted in tires by first encapsulating the device or power-containing circuit in a material which forms a rigid or semi-rigid encasement about the device, thereby inhibiting straining of the device as a result of applied stresses. Such materials have included non-foam compounds such as urethanes, epoxies, polyester-styrene resins, hard rubber compositions, and the like. The encapsulated device is then placed into a green rubber material which forms a housing or is placed in a green rubber pocket or pouch that becomes part of the tire. The encapsulated device is then permanently set within the rubber material during a subsequent vulcanizing operation. The green rubber material containing the encapsulated device may be assembled to the green tire and then vulcanized with the tire. Alternatively, the green patch containing the encapsulated device may be separately vulcanized and then affixed to a cured tire with a suitable adhesive. In either event, the delicate electronic components of the active tag are exposed to high vulcanizing temperatures which may adversely affect their performance or shorten their life. Additionally, certain components of the device, such as the pressure sensor or a thermistor must remain open to the pressurized tire cavity. The flow of rubber occurring during the vulcanization process can effect the openings to the tire cavity. As set forth in U.S. Pat. No. 5,562,787, the opening to the tire cavity can remain open during the curing operations by placement of a dowel into the opening. 
     While the methods and apparatus of U.S. Pat. No. 5,562,787 provide an acceptable method of assembling an active chip into a tire cavity, an improved method and apparatus which increases the life of the active chip in the tire is desirable. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an improved method and apparatus for assembling an active electronic monitoring device into a tire cavity is disclosed. 
     The improved method and apparatus increases the life of the electronic monitoring device by minimizing the stress, strain, cyclic fatigue, impact and vibration to which the electronic monitoring device is subjected when properly assembled into a tire. While the location of the device is an important factor in determining the life of an electronic monitoring device located within a tire, so too is the manner in which the device is installed into the tire. A method for securing within a tire an electronic monitoring device for monitoring at least one engineering condition of a tire comprises the steps of encapsulating an electronic monitoring device by placing the electronic monitoring device into a mold having a preselected configuration, the preselected configuration including at least one face having an alternating raised and recessed pattern to increase the surface area of the face. The mold is filled with an epoxy potting material so that the electronic monitoring device is encased by the epoxy. The epoxy potting material is cured to form a rigid tag assembly having a preselected configuration. However, certain electronic components comprising the electronic monitoring device, such as pressure sensors, are assembled in such a manner as to remain free from internal contamination while remaining open to the tire atmosphere as necessary. A rubber tire attachment patch having a preselected configuration is formed. The rubber patch includes a first side for interfacing with the face of the encapsulated rigid tag assembly. This first side has increased surface area, which allows for a better bond with the encapsulated tag. The first side also includes a recessed cavity surrounded by a ridge of material of sufficient height to capture the encapsulated rigid tag assembly This ridge helps to improve the bond between the rubber patch and the encapsulated rigid tag. The patch includes a second opposite side, the second side approximating the contour of the inner liner of the tire. The patch is tapered from the first side toward the second side, with the second side flaring out into a relatively thin configuration, but having a radius approaching the radius of the tire inner liner. The rubber patch is vulcanized at a preselected temperature and for a time sufficient for its vulcanization. After vulcanization, a thin layer of dual cure bonding rubber is applied to the second side of the vulcanized rubber patch. This thin layer of dual cure bonding rubber will permit the assembly of the patch assembly to the inner liner of the tire. A fluid epoxy adhesive is applied to an interface between the encapsulated tag assembly and the rubber patch. The encapsulated tag assembly is assembled into the recessed cavity on the first side of the rubber patch so that the fluid epoxy adhesive is evenly distributed across the interface and flows from the interface between the encapsulated tag assembly and the rubber patch. Of course, the increased surface area of the tag assembly allows for better bonding between the rubber patch and the encapsulated tag. The assembly or the encapsulated tag and the rubber patch is allowed to cure to form a patch assembly. The patch assembly is then assembled to the inner liner of a vulcanized tire by applying an activating cement between the dual cure bonding layer and the inner liner of the tire. This curing process permanently bonds the patch assembly to the inner liner and is diffusion-controlled. Because it is diffusion controlled, the curing must be done for a sufficient amount of time and at a sufficient temperature to allow a strong permanent bond to form. To assure that solid contact is maintained at the interface between the inner liner of the tire and the dual cure bonding layer of the patch assembly, a clamping mechanism is applied to secure the patch assembly to the inner liner during the curing process. The clamping mechanism is applied with sufficient pressure across the interface of the patch assembly and the inner liner to assure intimate contact during curing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the tire patch of the present invention. 
     FIG. 2 is a cross-sectional view of the rigid tag assembly, showing the encapsulated electronic monitoring device. 
     FIG. 3 is a cross-sectional view of the mold used to encapsulate the electronic monitoring device, producing the rigid tag assembly. 
     FIG. 4 is a perspective view of the patch assembly of the present invention. 
     FIG. 5 is a cross-sectional view of the patch assembled to the inner liner of a tire. 
     FIG. 6 is a perspective view of an alternative configuration of the tire patch of the present invention. 
     FIG. 7 is a cross-sectional view of the rigid tag assembly of FIG. 6, showing the encapsulated electronic monitoring device. 
     FIG. 8 is a perspective view of the patch assembly of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the drawings. 
     FIG. 1 shows a tire patch  10  of the present invention. The tire patch is of a preselected configuration, which as shown, is rectangular in shape. The patch may be of any other convenient configuration, but is shown as rectangular, and therefore has four edges  11 . The tire patch  10  has a first side  12  for interfacing with a face of an encapsulated tag assembly  30 , shown in FIG.  2 . The patch has a second opposite side  14  approximating the contour of an inner liner of a tire. The contour of the second side  14  preferably is radiused to have about the same radius as the tire to which it is assembled, the radius being larger for larger tires. For very large tires, such as for off-the-road tires, the radius may be eliminated altogether, so that there is no contour and the opposite side is flat, having no contour. 
     The rubber patch is vulcanized at a preselected temperature and for a time sufficient to vulcanize the patch. The patch may be rubber selected from the group consisting of Ethylene Propylene Diene Monomer (EPDM) rubber, butyl rubber, natural rubber, neoprene and mixtures thereof. One preferred embodiment is a mixture of chlorobutyl rubber and natural rubber. Another preferred embodiment is a mixture of Styrene-Butadiene rubber (SBR) and natural rubber. Typically, patches made of these rubber compositions may be cured by heating to a temperature of about 150° C. and holding at this temperature for about 30 minutes. The time and temperature may be modified as necessary to achieve sufficient curing of the patch for further assembly. 
     The first side  12  includes a recessed cavity  16  which is surrounded by a raised ridge  18  of rubbery polymer material. The recessed cavity optionally may have a roughened bottom surface to increase its surface area. The ridge  18  preferably is of the same material as the remainder of the patch. The ridge of material should be of sufficient height to capture the encapsulated rigid tag  30 . In a preferred embodiment, the ridge is about one eighth (⅛″) inch. The patch is gradually tapered from the ridge  18  of material of the first side of the patch  12 , outwardly toward the edges of the patch. 
     Affixed to the second side  14  of the vulcanized tire patch is a dual cure bonding layer  20 , which has a [first] second side (not shown) and a [second] first side  22 . This dual cure bonding layer  20  may be assembled to the patch at any time following vulcanization of the patch and prior to assembly of the patch assembly to the tire innerliner. The dual cure bonding layer  20  is permanently assembled to the patch. A non-curing cement (not shown) is applied to side  14  of the patch in order to hold the dual cure bonding layer  20  onto the patch. The non-curing cement and the dual cure bonding layer  20  are products of Patch Rubber Company. The important feature of the dual cure bonding layer  20  is that it can be chemically activated and cured, without the need for heating to an elevated temperature. The process is diffusion controlled, however, and some minimal heating will speed the curing process. The dual cure bonding layer  20  may be any material which can be activated and cured to the vulcanized rubber of the tire inner liner and the vulcanized patch. Preferably, however, the dual cure bonding rubber is natural rubber. The dual cure bonding rubber, after application of the activating cement, may cure at room temperature over a period of seventy two (72) hours. However, if more rapid curing is desired this may be accomplished by heating to 45° C. for at least twenty four hours. 
     FIG. 2 shows a cross-sectional view of the rigid tag assembly  30 , showing the encapsulated electronic monitoring device  32 . Monitoring device may be a circuit board  34  which includes electronic memory as well as a variety of sensors for monitoring engineering conditions such as, for example, pressure, temperature and distance traveled. The monitoring device is discussed in detail in U.S. Pat. No. 5,562,787, incorporated herein by reference. Mounted to the board is a power source  36 , such a battery, which permits the active monitoring of the engineering conditions, which may be stored in the electronic memory for later use. The power source provides a bulge  38  to the rigid tag assembly, although this feature is expected to become less prominent or even completely eliminated as advances in battery technology produce smaller yet more powerful batteries. The rigid tag assembly may also house an antenna, or may provide for assembly of an antenna which protrudes from the tag assembly so that the circuitry on the board can be activated for transmittal at will. 
     The circuit board including sensors, battery and optional antenna, hereinafter referred to as the electronic monitoring device, are encapsulated in a potting material  40  which solidifies into a rigid material. Referring to FIG. 3, the electronic monitoring device is placed within a mold  50  having a first half  52  and a second half  54 . At least one of the mold halves has a face with increased surface area, shown as surface  56  in the second half  54  of mold  40 . The mold is then filled with the potting material  40  in fluid form, which fills the mold and flows around the electronic monitoring device and allowed to cure, resulting in a rigid tag assembly. Any potting material having a Young&#39;s Modulus of at least 30,000 psi and which is capable of being molded around the electronic monitoring device without damaging any of the components of the device. Preferably, the potting material has a Young&#39;s Modulus of at least about 100,000 psi. Two preferred potting materials include epoxy and urethane. If desired, the curing of the potting material around the electronic device may be accelerated by preheating the mold to an elevated temperature which is above ambient, but below the temperature at which damage to the electronic monitoring device will occur. A preferred temperature is about 80° C. After the epoxy has been cured, the mold halves  52 ,  54  are separated, yielding a rigid, encapsulated tag assembly  30 . Tag assembly  30  has a bottom surface  42  having increased surface finish which is simply the impression of surface  56  from mold half  54 . 
     Rigid tag assembly  30  is assembled into the recessed cavity  16  on the first side  12  of tire patch  10  either after vulcanization of the patch or after assembly of the dual bond curing layer  20  to the patch. The patch is free of members that cover the upper surface of the electronic monitoring device. In order to permanently adhere tag assembly  30  to patch  10 , a fluid adhesive is applied to the interface between tag assembly  30  and recess  16 . This adhesive, preferably an epoxy adhesive, may be applied conveniently to surface  42  of tag assembly or to the base of recess  16 . As tag assembly  30  is pressed into recessed cavity  16 , the epoxy adhesive flows evenly along the interface between surface  42  and the base of recess  16 . The increased surface area between the base of recessed cavity  16  and surface  52  provides for additional bonding area and a stronger bond. Because the ridges around the recess are closely dimensioned to correspond to the dimensions of tag assembly  30 , excess epoxy will flow between tag assembly  30  and ridge  18 , and some epoxy may even flow out from this region. Of course, the flow of epoxy in this region will add to the strength of the assembly as the epoxy cures. While the epoxy can be allowed to cure at room temperature, the curing process can be accelerated by heating the assembly at an elevated temperature, for example a temperature of from about 75-90° C. for at least about 30 minutes. If the dual cure bonding layer  20  has not already been assembled to the second side  14  of tire patch  10 , it may be added at this time to form patch assembly  60 . 
     Referring now to FIG. 5, Patch assembly  60  was then assembled to the inner liner  75  of tire  70  such that the upper surface of the electronic monitoring device is exposed to the chamber of the tire. Activating cement was first applied to second side [ 22 ] (not shown) of dual cure bonding layer  20 . The patch assembly was then stitched to the inner liner of the vulcanized tire and the patch assembly/tire assembly was allowed to cure for a sufficient time and temperature to form a strong bond between the tire and the patch assembly. The times and temperatures utilized for this curing may be basically the same times and temperatures as previously discussed. To ensure a strong bond, the patch assembly optionally may be clamped to the tire inner liner  75 , until the curing cycle is completed. 
     FIG. 6 shows an alternative configuration of a tire patch  110  of the present invention. The tire patch  110  is of a preselected configuration, which as shown, is round in shape. The tire patch  110  has a first side  112  for interfacing with a face of an encapsulated tag assembly  130 , shown in cross-section in FIG.  7 . First side  112  includes a recessed cavity  116 , which in this alternative configuration is formed by a cylindrical rigid insert  117  molded into the rubber patch. Preferably cylindrical insert  117  is a rigid plastic material, such as nylon, epoxy or a rigid composite material such as glass-filled polyamide or glass-filled epoxy, but also may be a metal, as long as the metal does not interfere with the electronic functions and operation of tag assembly  130 . Cylindrical rigid insert  117  is surrounded by a ridge  118  of rubbery material. The ridge preferably is of the same material as the remainder of the patch and should be of sufficient height to permanently hold cylindrical insert  117  in place following curing. In a preferred embodiment shown in FIGS. 6 and 7, the ridge  118  is the same height as cylindrical insert  117 . The patch is gradually tapered from the ridge  118  of material of the first side of the patch outwardly toward the edges of the patch. Recessed cavity  116  may have a roughened bottom surface to increase its surface area, as previously described, or alternatively may be smooth and made from the same material as the cylindrical insert. The patch has a second opposite side  114  which may approximate the contour of an inner liner of a tire. The contour of the second side  114  preferably is radiused to have about the same radius as the tire to which it is assembled, the radius being larger for larger tires. For very large tires, such as for off-the-road tires, the radius may be eliminated altogether, so that there is no contour and the opposite side  114  is flat, having no contour. Tire patch  110  including cylindrical rigid insert  117  is cured prior to insertion of rigid tag assembly  130  to form a round patch assembly. 
     Rigid tag assembly  130 , which includes the encapsulated electronic monitoring device and has the same components as previously described, is essentially identical to rigid tag assembly  30  except for its profile, being round or circular instead of rectangular. Round rigid tag assembly  130  is permanently bonded to the round patch assembly by inserting rigid tag assembly  130  into cylindrical insert  117 , as shown in FIG. 8, after applying an epoxy adhesive such as a Fusor system manufactured by Lord Corp. of Erie Pa. to the interface between the rigid tag assembly  130  and the cylindrical insert  117 . Of course, the epoxy adhesive also may conveniently be applied to the interface between the bottom of cavity  116 , whether it is a roughened surface or made of the same or similar material as cylindrical insert  117 . As the rigid tag assembly  130  is inserted into cylindrical insert  117 , excess epoxy flows out from the interface, which must be removed before it cures. Cylindrical insert  117  only must be of sufficient height so that after curing of the epoxy, there is sufficient bonding strength between the insert  117  and tag assembly  130  to assure no separation. Although the rigid tag assembly  130  may be of the same height as cylindrical insert  117 , as shown in the preferred embodiment, it also may be lower or higher than cylindrical insert  117  upon assembly. If tag assembly  130  is higher than the cylindrical insert  117 , then insert  117  has a lower profile than the rigid tag assembly  130  so that the outer periphery of the rigid tag assembly  130  extends above the outer periphery of the cylindrical insert  117 , thereby reducing the overall amount of material required for tire patch  110 . 
     Patch assembly  160  formed by assembling rigid tag assembly  130  into tire patch  110  is bonded to a tire using the same materials and methods described above for Patch assembly  60 . 
     Patch assemblies manufactured and assembled to a tire inner liner in the manner described above have run through tests equivalent to 100,000 miles, and have remained fully bonded to the tire. 
     While in accordance with the patent statutes, the best mode and preferred embodiment has been set forth above, the scope of the invention is not limited thereto, but rather by the scope of the attached claims.