Abstract:
A pressure sensing apparatus includes a pressure sensor for detecting tire pressure and generating a signal corresponding to the tire pressure, and an electrically conducting air valve seat connected to the pressure sensor for signal transmission therethrough to a transmitting antenna. The antenna has a metal cap connected to the air valve seat, at least one annual substrate defining a center coupling hole into which the cap is inserted, and at least one metal conducting wire spirally mounted in the at least one substrate around the center coupling hole. The metal conducting wire has an inner end exposed to a periphery wall of the center coupling hole of the substrate and electrically connected to the cap.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a unit of Tire Pressure Monitoring System (TPMS) and more specifically, to a tire pressure sensing apparatus installed in the tire of a vehicle for sensing the pressure of the tire and transmitting the pressure signal wirelessly. 
         [0003]    2. Description of the Related Art 
         [0004]    A typical wireless tire pressure sensing apparatus comprises a transmitter circuit coupled to each of a plurality of tires on a vehicle. The transmitter circuit is generally provided with a transmitting antenna and a pressure sensor. The pressure sensor detects the pressure of the tire and produces a corresponding pressure signal. The pressure signal is modulated into a radio frequency signal, and then transmitted to a main unit of the TPMS in the car wirelessly by the transmitting antenna. The main unit demodulates the radio frequency signal and converts the signal into a corresponding tire pressure value readable on a display panel so that the driver can monitor the tire pressure to prevent a potential accident when driving the car. However, because a tire has a metal structure, i.e. tire rim, around the periphery thereof, the metal structure provides a shielding effect that may interfere with the transmission of the radio frequency signal to be transmitted by the pressure sensing apparatus in the tire. 
         [0005]    In order to eliminate the aforesaid problem, a rod-like air valve is created for use as a transmitting antenna. Because a part of the rod-like air valve extends out of the tire after installation of the pressure sensing apparatus, the metal structure of the tire does not interfere with the transmission of the radio frequency signal produced by the pressure sensing apparatus. However, the transmitting range of the rod-like air valve is limited, and the main unit in the car can receive the radio frequency signal transmitted by the rod-like air valve only at a particular angle. Therefore, this design of pressure sensing apparatus is still not satisfactory in function. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention has been accomplished under the circumstances in view. It is one objective of the present invention to provide a pressure sensing apparatus of which the signal transmission has a wide-angle characteristic. 
         [0007]    To achieve this objective of the present invention, the pressure sensing apparatus comprises a pressure sensor for detecting tire pressure and generating a signal corresponding to the tire pressure, an air valve seat made of an electrically conducting material, electrically connected to the pressure sensor and provided with an air passage extending through two distal ends thereof, and a transmitting antenna having a cap made of a metal material and connected to the air valve seat, at least one substrate having an annular shape defining a center coupling hole coupled to the cap, and at least one metal conducting wire spirally mounted in the at least one substrate around the center coupling hole. The metal conducting wire has an inner end exposed to a periphery wall of the center coupling hole of the substrate and electrically connected to the cap. 
         [0008]    In a preferred embodiment of the present invention, the cap is fastened to one end of the air valve seat and provided with a center air hole in air communication with the air passage. A plunger is inserted through the center air hole of the cap and movable relative to the cap between a first position and a second position. A valve stem is mounted in the air passage and movable with the plunger between the first position where the valve stem blocks the air passage and the second position where the valve stem opens the air passage. 
         [0009]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0011]      FIG. 1  is a perspective view of a pressure sensing apparatus according to a preferred embodiment of the present invention; 
           [0012]      FIG. 2  is schematic drawing showing that the pressure sensing apparatus in accordance with the preferred embodiment of the present invention is installed in a tire; 
           [0013]      FIG. 3  is an exploded view in an enlarged scale of a part of the pressure sensing apparatus according to the preferred embodiment of the present invention, showing the structure of the transmitting antenna; 
           [0014]      FIG. 4  is a sectional view of the preferred embodiment of the present invention, showing that the air passage of the air valve seat of the pressure sensing apparatus is blocked; 
           [0015]      FIG. 5  is similar to  FIG. 4  but showing that the air passage is opened; 
           [0016]      FIG. 6  is a sectional view of an alternate form of the pressure sensing apparatus according to the present invention, and 
           [0017]      FIG. 7  is a perspective view of another alternate form of the pressure sensing apparatus according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Referring to  FIGS. 1-5 , a pressure sensing apparatus  10  is shown installed in a wheel rim  41  carrying a tire  40 . The tire pressure sensing apparatus  10  comprises a pressure sensor  12 , an air valve seat  14 , a transmitting antenna  16 , a valve stem  18 , a plunger  20 , a first electrically insulating member  22 , a second electrically insulating member  24 , a locknut  26 , and a cover  28 . 
         [0019]    The pressure sensor  12  is mounted inside the tire  40  to detect the inside pressure of the tire  40  and to output through its RF circuit output terminal (not shown) a radio frequency signal indicative of the inside pressure of the tire  40 . Because the pressure sensor  12  is of the known art, no further detailed description in this regard is necessary. 
         [0020]    The air valve seat  14  is a tube body made of electrically conducting material, having one end electrically connected to the RF circuit output terminal of the pressure sensor  12  and the other end extending out of a valve hole  41   a  on the wheel rim  41  and forming a free end. The air valve seat  14  has an inside air passage  141  formed through the two distal ends of the air valve seat in air communication with the inside space of the pressure sensor  12 , and an outer thread  142 . The outer thread  142  extends from the free end of the air valve seat  14  around the periphery thereof toward the other end near the pressure sensor  12 . 
         [0021]    The transmitting antenna  16  comprises a cap  161 , three substrates  162  and three metal conducting wires  163 . The cap  161  is a metal member threaded onto the outer thread  142  at the free end of the air valve seat  14 , having a center air hole  161   a  in air communication with the air passage  141  of the air valve seat  14 . The three substrates  162  are annular members arranged in a stack, each having a center coupling hole  162   a  respectively coupled to the cap  161 . The three metal conducting wires  163  are respectively spirally mounted in the three substrates  162  around the respective center coupling hole  162   a , each having an inner end  63   a  exposed on the periphery wall of the respective center coupling hole  162   a  and disposed in positive contact with the cap  161  such that the conducting wires  163  are electrically connected with the metal cap  161  for enabling the pressure signal detected by the pressure sensor  12  to be transmitted to the main unit (not shown) in the car through the air valve seat  14 , the cap  161  and the conducting wires  163 . 
         [0022]    The valve stem  18  is mounted in the air passage  141  near the free end of the air valve seat  14  and axially movable in the air passage  141  by an external force to change the closed state of the air passage  141  to the opened state for allowing external air to pass through the air passage  141  and the pressure sensor  12  to the inside of the tire  40 . 
         [0023]    The plunger  20  is inserted through the center air hole  161   a  of the cap  161 , having a contact portion  201  and a driving portion  202 . The contact portion  201  extends out of the cap  161 . The driving portion  202  is stopped against the valve stem  18 . Further, a spring member  80  is sleeved onto the driving portion  202  and stopped with its two opposite ends against the bottom edge of the contact portion  201  and the free end of the air valve seat  14  to support the plunger  20  in a first position P 1  (see  FIG. 4 ) where the contact portion  201  is kept extending out of the cap  161 . At this time, the plunger  20  simply contacts the valve stem  18  without moving the valve stem  18 , and therefore the air passage  141  is in the closed state (see  FIG. 4 ). Further, when the contact portion  201  of the plunger  20  is received an external force and moved inwardly from the aforesaid first position P 1  to a second position P 2  (see  FIG. 5 ), the valve stem  18  is moved axially in the air passage  141  by the plunger  20  to open the air passage  141  (see  FIG. 5 ). When the external force is released from the plunger  20 , the spring member  80  immediately pushes the plunger  20  backwards from the second position P 2  to the first position P 1 , and the valve stem  18  is returned, and therefore the air passage  141  is closed again. The aforesaid plunger  20  and spring member  80  can be treated as additional elements to enhance the applicability of the tire pressure sensing apparatus  10 . However, the plunger  20  and the spring members  80  can be eliminated if desired. In this case, an end cap  161 ′ is used to seal the gap (see  FIG. 6 ). After removal of the end cap  161 ′, the user can inflate the tire. 
         [0024]    The first electrically insulating member  22  and the second electrically insulating member  24  are molded from rubber and respectively wrapped about the air valve seat  14  and the junction between the air valve seat  14  and the pressure sensor  12  to isolate the air valve seat  14  from the wheel rim  41  so as to prevent change of signal transmission characteristic impedance of the air valve seat  14  due to direct contact of the metal air valve seat  14  with the metal wheel rim  41 . Further, the position of the second electrically insulating member  24  is adjustable by the locknut  26  on the outer thread  142 , i.e., the user can rotate the locknut  26  to move the second electrically insulating member  24  toward the first electrically insulating member  22 , forcing the first electrically insulating member  22  and the second electrically insulating member  24  to respectively stop against the opposite lateral walls of the wheel rim  41 . Further, a pad  25  is set between the locknut  26  and the second electrically insulating member  24  to prevent deformation of the second electrically insulating member  24  when it is squeezed by the locknut  26 . 
         [0025]    Further, the cover  28  is covered on the cap  161  over the substrates  162  to protect the substrates  162  and the metal conducting wires  163  against damage. According to the present preferred embodiment, the cover  28  is molded from plastics. 
         [0026]    By means of the aforesaid structure, the pressure sensor  12  inside the tire  40  transmits detected tire pressure signal to the air valve seat  14  when the driver is driving the car, enabling the tire pressure signal to be transmitted into the air by radio by means of the air valve seat  14  and the spiral metal conducting wires  163  on the substrates  162 . By means of the aforesaid structure, the transmitting range of the radio tire pressure signal transmitted by the tire pressure sensing apparatus  10  is much greater than the conventional designs, and the main unit in the car can accurately receive the radio tire pressure signal. Therefore, the driver knows accurately the tire pressure status when driving the car, preventing a potential danger. 
         [0027]      FIG. 7  shows that the aforesaid cover  28  can be eliminated to have the substrates  51  and three metal conducting wires  52  of the transmitting antenna  50  be exposed to the outside. 
         [0028]    Examples of the tire pressure sensing apparatus have been constructed with the features of  FIGS. 1-5 . The tire pressure sensing apparatus functions smoothly to provide all of the features discussed earlier. 
         [0029]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.