Abstract:
A tire pressure monitoring apparatus includes a valve assembly mountable in a vehicle wheel and a housing securable to the end of the valve assembly. A pressure sensor assembly is securable in the housing for monitoring tire pressure and providing an electrical signal indicative thereof. The pressure sensor assembly includes a flexible circuit board, and a battery held within a fold of the flexible circuit board, wherein the flexible circuit board is overmolded.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 61/084,055, filed Jul. 28, 2008, the entirety of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to tire pressure monitors and is more particularly directed to a method and apparatus for overmolding a tire pressure monitor. 
       BACKGROUND OF THE INVENTION 
       [0003]    It is known to attach a tire pressure monitoring (“TPM”) sensor assembly to a rim of a vehicle wheel. The TPM sensor assembly includes an electronic tire pressure sensor and a power source, such as a battery. The tire pressure sensor senses the air pressure in the tire and transmits an electronic signal, such as a radio-frequency (“RF”) signal, to an on-board vehicle receiver. The receiver evaluates the signal and provides an alarm to a vehicle occupant if the pressure in the tire is too low. A TPM sensor assembly may monitor other tire conditions such as tire temperature, etc. 
         [0004]    TPM sensor assemblies of various types are known. One particular type of TPM sensor assembly includes a housing strapped to its associated wheel. Other known TPM sensor assemblies may include the valve stem assembly itself. Such valve stem mounted TPM sensors have the sensor mounted to the end of a valve stem assembly. Such valve stem/TPM sensor assemblies may include a soft elastomeric material surrounding the valve stem that seals against an associated mounting hole in the wheel as the assembly is snapped into place. During mounting, the valve stem is pulled through a receiving hole of the wheel. Such valve stems are known in the art as snap-in valve stems. The TPM sensor of the assembly senses tire pressure and/or tire temperature and sends appropriate radio frequency information including a unique tire identification (“ID”) code, sensed tire pressure, and sensed tire temperature to a vehicle on-board receiver for information display to the vehicle operator. 
       SUMMARY OF THE INVENTION 
       [0005]    In accordance with one example embodiment of the present invention, a tire pressure monitoring apparatus is provided including a valve assembly mountable in a vehicle wheel and a housing securable to the end of the valve assembly. A pressure sensor assembly is securable in the housing for monitoring tire pressure and providing an electrical signal indicative thereof. The pressure sensor assembly includes a flexible circuit board, and a battery held within a fold of the flexible circuit board, wherein the flexible circuit board is overmolded. 
         [0006]    In accordance with another example embodiment of the present invention, a tire pressure monitoring apparatus is provided comprising a pull-through valve assembly mountable in a vehicle wheel and a housing securable to the end of the pull-through valve assembly. A pressure assembly is securable in the housing for monitoring tire pressure and providing an electrical signal indicative thereof. The pressure sensor assembly includes a flexible circuit board, and a battery held within a fold of the flexible circuit board, wherein the flexible circuit board is overmolded. 
         [0007]    In accordance with another example embodiment of the present invention, a method of manufacturing a tire pressure monitor is provided comprising the steps of folding a flexible tire pressure monitoring circuit board around a battery, overmolding the folded circuit board, attaching the overmolded circuit board to the end of a tire valve assembly, and mounting the valve assembly in a tire. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The foregoing and other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which: 
           [0009]      FIG. 1  is a schematic perspective view of a valve stem TPM sensor assembly made in accordance with one example embodiment of the present invention; 
           [0010]      FIG. 2  is a side view of the valve stem TPM assembly of  FIG. 1  mounted in a through hole of a vehicle wheel; 
           [0011]      FIG. 3  is a partially exploded view of the valve stem TPM assembly of  FIG. 1 ; 
           [0012]      FIG. 4  is a top view of a flexible circuit board in accordance with an example embodiment of the present invention showing circuitry mounted thereon; 
           [0013]      FIG. 5  is a bottom view of flexible circuit board of  FIG. 4  showing a battery mounted thereon; 
           [0014]      FIG. 6  is a side view of flexible circuit board of  FIG. 4  partially folded; 
           [0015]      FIG. 7  is a side view of flexible circuit board of  FIG. 4  fully flexed over into a folded condition; 
           [0016]      FIG. 8  is a partial sectional view of the sensor assembly showing the folded circuit board of  FIG. 7  mounted in the sensor assembly of  FIG. 1 ; and 
           [0017]      FIG. 9  is another partial sectional view of the sensor assembly showing the folded circuit board of  FIG. 7  mounted in the sensor assembly of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring to  FIG. 1 , a tire pressure monitoring device  10  includes a valve stem TPM sensor assembly  12  having an integrally connected valve mechanism  14 , and housing  18  that allows for low cost manufacturing, assembly, and installation. The valve mechanism  14  has a valve body  20  that extends along an axis A-A and connects to the housing  18 . The housing  18  provides an area for mounting monitoring, transmitting, and receiving electronics. The valve body  20  may be made from plastic, metal, or metal alloy, such as brass or any other material without departing from the spirit and scope of the claimed invention. In one example embodiment, the valve body  20  acts as a transmitting antenna for the TPM device  10 . 
         [0019]    Referring to  FIG. 2 , a mounting arrangement between the tire pressure TPM device  10  and a tire rim  24  is shown. The pressure mounting device  10  includes an inside end  26  (located inside the tire (not shown)) and an outside end  28  with respect to the tire rim  24 . The tire pressure mounting device  10  is secured to the tire rim  24  by inserting the device through a hole  27  located on the rim. The tire pressure mounting device  10  is advanced through the hole  27  until the tire rim  24  engages a cylindrical recess  30  that provides a sealing engagement between first and second shoulders  32 ,  34 , respectively. 
         [0020]    The outside portion of the wheel containing the outside end  28  is typically at atmospheric pressure and the inside portion of the wheel containing the inside end  26  (located inside the tire (not shown)) is typically maintained at a pressure greater than atmosphere. To achieve this pressure differential, fluid is transported through the valve stem TPM assembly  12  to the inside of the wheel (tire) via a fluid passage in the valve assembly (not shown) to an exit orifice (not shown) provided in the housing  18 . 
         [0021]    As mentioned, within the housing  18  are the electronics for sensing the tire conditions and for transmitting to a vehicle on-board receiver an RF signal having information related to the sensor ID, and sensed tire conditions. Referring to  FIGS. 4-7 , the electronics  42  for the TPM sensor assembly are carried on a flexible circuit board  40 . The electronics may take the form of discrete circuit components, an application specific integrated circuit (“ASIC”), a microcomputer, etc., and/or any combination thereof. As can be seen in  FIG. 4 , an integrated circuit  42  is mounted to the flexible circuit board  40 . 
         [0022]    As viewed in  FIG. 5 , a coin style battery  44  is used to supply electrical power for the TPM sensor assembly. The battery  44  has two faces, one face is the negative terminal and the other face is the positive terminal. On the opposite side of the circuit board from the mounted circuit components  42 , the battery  44  is mounted. In an unfolded condition, one terminal of the battery is electrically connected to the board  40 . To connect the other terminal of the battery so as to provide operating power to the board and, in turn, the circuit components  42 , the circuit board  40  is folded over onto the other side of the battery  44 . As seen in  FIGS. 6-9 , the flexible circuit board  40  is folded around the battery  44  so as to hold the battery  44  and provide the necessary electrical connections between the battery and the circuitry  42 . In addition, the electronic assembly, the printed circuit board assembly (“PCBA”) including the circuitry  42  and the battery  44  are overmolded to protect the circuitry from environmental conditions. 
         [0023]    The PCBA is overmolded with a first inner layer  60  of Thermoplastic Elastomer (“TPE”) and a second outer layer  70  of Nylon material so as to provide environmental protection. The thermoplastic elastomer inner layer  60  bonds to the electronic devices  40 ,  42 ,  44 , providing environmental protection as well as providing a protective layer of soft polymer so that the solder joints attaching the electronic components to the flexible circuit board  40  are not degraded through coefficient of thermal expansion miss-match. The adhesion of the TPE to the flexible circuit board  40  and its electronic components  42 ,  44  prevent moisture ingress. A hard outer layer of nylon 70 is then over molded around the TPE  60  so that further mechanical protection is provided. Since the nylon outer layer  70  establishes a chemical bond to the TPE inner layer  60 , no moisture plain is formed between the two polymer materials. The bonding of the TPE inner layer  60  and nylon outer layer  70  to the pressure sensing circuitry  42  provides for a molded pressure path  50  from the outside of the package to the pressure sensing circuitry  42 . During the overmolding process, a sensing hole  50  must be maintained to the sensor portion of the TPM circuitry  42  so that the pressure on the inside of the tire can communicate with the sensor and be monitored by the sensor circuitry. 
         [0024]    From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.