Abstract:
A tire condition monitoring device mounted on a wheel assembly with a tire and executing wireless signaling to a vehicle body, includes an electric circuit further including a sensor detecting a condition of the tire and a wireless circuit executing wireless signaling to transmit results of detection by the sensor, a DC power supply supplying power to the electric circuit, a pair of power lines connecting the DC power supply and the electric circuit to each other, and inductor elements connected to the paired power lines respectively.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a tire condition monitoring device detecting pneumatic pressure of a tire and executing wireless signaling to transmit results of the detection to a vehicle body.  
         [0003]     2. Description of the Related Art  
         [0004]     Tire condition monitoring devices of the above-described type have conventionally been provided with an electric circuit to which electric power is supplied from a battery. The electric circuit includes a pressure sensor measuring pneumatic pressure of a tire. Results of measurement are transmitted to the vehicle body by radio. JP-A-2005-119370 discloses one of the tire condition monitoring devices of the above-described type.  
         [0005]     Vehicles have recently been sophisticated in functionality and consequently, the necessity of tire condition monitoring devices has been increased. With increase in the necessity, the tire condition monitoring device has been required to be improved in the reliability thereof with respect to signal noise.  
       SUMMARY OF THE INVENTION  
       [0006]     Therefore, an object of the present invention is to provide a tire condition monitoring device which has higher reliability with respect to signal noise.  
         [0007]     The present invention provides a tire condition monitoring device mounted on a wheel with a tire and executing wireless signaling to a vehicle body. The device comprises an electric circuit including a sensor detecting pneumatic pressure of the tire and a wireless circuit executing wireless signaling to transmit results of detection by the sensor, a DC power supply supplying power to the electric circuit, a pair of power lines connecting the DC power supply and the electric circuit to each other, and inductor elements connected to the paired power lines respectively.  
         [0008]     The paired power lines connecting the DC power supply and the electric circuit are provided with the respective inductor elements. Consequently, noise received by the DC power supply serving as an antenna can be eliminated and accordingly, reliability with respect to signal noise can be improved as compared with the conventional tire condition monitoring devices.  
         [0009]     In one form, the tire condition monitoring device further includes a circuit board having two sides. The inductor elements are mounted on either side of the circuit board and the electric circuit is mounted on both sides of the circuit board except for first portions of either one side of the circuit board right behind the inductor elements mounted on the other side of the circuit board. The paired power lines are mounted on the second portions respectively.  
         [0010]     The electric circuit is mounted on one side of the circuit board so as not to be located right behind the inductor elements mounted on the other side of the circuit board. Consequently, the electric circuit can be restrained from an adverse effect of noise produced by the inductor elements.  
         [0011]     In another form, the inductor elements comprise a pair of chip beads respectively. Consequently, high-frequency noise can be eliminated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Other objects, features and advantages of the present invention will become clear upon reviewing of the following description of the embodiment, with reference to the accompanying drawings, in which:  
         [0013]      FIG. 1  is a diagram of a vehicle provided with the tire condition monitoring device in accordance with a first embodiment of the present invention;  
         [0014]      FIG. 2  is a sectional side view of the tire condition monitoring device;  
         [0015]      FIG. 3  is a circuit diagram showing an electrical arrangement of the tire condition monitoring device;  
         [0016]      FIG. 4  is a perspective view of a button battery and a circuit board employed in the tire condition monitoring device;  
         [0017]      FIG. 5  is a circuit diagram showing an electrical arrangement of the tire condition monitoring device of a second embodiment in accordance with the present invention;  
         [0018]      FIG. 6  is a circuit diagram showing an electrical arrangement of the tire condition monitoring device of a third embodiment in accordance with the present invention; and  
         [0019]      FIG. 7  is a perspective view of chip beads. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     A first embodiment of the present invention will be described with reference to FIGS.  1  to  4 . Referring to  FIG. 1 , a tire condition monitoring device  20  of the first embodiment is shown. The tire condition monitoring device  20  is provided integrally on a tire valve  50 . Four tire condition monitoring devices  20  are fixed to four wheel assemblies  11  together with four tire valves  50  respectively though one of the wheel assemblies  11  is shown in  FIG. 1 . A tire  14  attached to each wheel assembly  11  has an inner circumferential opening closed by a rim  13  of a wheel  12 , whereupon an interior of the tire  14  is closed.  
         [0021]     The tire valve  50  is inserted through and fixed in a through hole (not shown) formed in a widthwise middle portion of the rim  13 . The tire valve  50  has a distal end extending from the rim  13  to the opposite side of the vehicle body  15 . The tire condition monitoring device  20  is provided integrally on a proximal end of the tire valve  50  and disposed in the interior of the tire  14 . The tire valve  50  includes a core in which a valve core (not shown) is provided. The valve core prevents compressed air from being discharged through the tire valve  50  and allows compressed air to be charged into the tire  14  through the tire valve  50 .  
         [0022]     Referring to  FIG. 2 , the tire condition monitoring device  20  includes a case  21  formed integrally on the proximal end of the tire valve  50 . A circuit board  22  and a button battery  30  are provided in the case  21 .  FIG. 3  shows an electric circuit  23  mounted on the circuit board  22 . The electric circuit  23  includes a communication controller  27  to which are connected a pressure sensor  24 , a temperature sensor  25 , an acceleration sensor  26  and a wireless circuit  28 . The communication controller  27  includes a ROM, a RAM and a CPU (not shown). The ROM stores data of identification numbers assigned to the tire condition monitoring devices  20  and a predetermined program.  
         [0023]     The button battery  30  has a diameter ranging from 20 to 25 mm. The button battery  30  is enclosed in a battery enclosure (not shown) provided on an inner surface of the case  21  (see  FIG. 2 ). A pair of power lines  31 A and  32 A are connected to a positive electrode  30 P and a negative electrode  30 M of the button battery  30  respectively as shown in  FIG. 4 . A pair of electrical paths  31 B and  32 B through which electric power is supplied to the electric circuit  23  are printed on the circuit board  22 . One power line  31 A has an end soldered to the electrical path  31 B, whereas the other power line  32 A has an end soldered to the electrical path  32 B, whereby a pair of power lines  31  and  32  are provided which connect the button battery  30  to the electric circuit  23 .  
         [0024]     Two choke coils  35  are connected in series to the electrical paths  31 B and  32 B of the power lines  31  and  32  respectively. More specifically, the electrical paths  31 B and  32 B are each cut in the middle and the choke coils  35  are connected to both cut ends of the electrical paths  31 B and  32 B respectively. Each choke coil  35  has a pair of terminals  35 A and  35 B inserted into terminal holes to be soldered respectively. Furthermore, the choke coils  35  are mounted on either one of two sides of the circuit board  22 . On the other hand, the electric circuit  23  is mounted on both sides of the circuit board  22  except for portions of either one side of the circuit board right behind the choke coils mounted on the other side of the circuit board. In  FIG. 4 , regions of the circuit board  22  on which the electric circuit  23  is mounted are designated by symbols R 1  and R 2  respectively.  
         [0025]     The tire condition monitoring device  20  is thus arranged as described above. A signal processor  55  as shown in  FIG. 1  is provided in the vehicle body  15  so as to be capable of receiving signals from the tire condition monitoring device  20 .  
         [0026]     The tire condition monitoring device  20  will operate as follows. The tire condition monitoring device  20  is deactivated when the vehicle is stopped. When the vehicle starts to run, the acceleration sensor  26  is subjected to a centrifugal force due to revolution of the wheel assembly  11 , thereby being activated to deliver an interrupt signal to the CPU of the communication controller  27 . Then, the communication controller  27  carries out the predetermined program stored on the ROM. More specifically, a pressure and a temperature in the tire  14  are detected by the pressure sensor  24  and the temperature sensor  25 . The wireless circuit  28  periodically executes wireless signaling to transmit the detected pressure and temperature to the signal processor  55  together with an identification number of the tire condition monitoring device  20 . The signal processor  55  provided in the vehicle body  15  includes a wireless circuit  56 , which receives radio signals transmitted by the wireless circuit  28 . A display  57  provided in a vehicle compartment then displays information about conditions of the tire (tire pressure and temperature or occurrence of abnormal condition).  
         [0027]     The tire condition monitoring device  20  inadvertently receives electromagnetic waves from a mobile telephone, a global positioning system (GPS), television or the like during running of the vehicle. The button battery  30  having the diameter ranging from 20 to 25 mm could be an antenna resonating electromagnetic wave having a frequency range of 1 to 2 GHz. In the embodiment, however, both power lines  31  and  32  are provided with the choke coils  35  respectively. Accordingly, each choke coil  35  has high impedance against high-frequency noise such as frequency range of 1 to 2 GHz, whereas impedance of each choke coil  35  is substantially zero against DC voltage fed from the button battery  30 . Consequently, only the noise received by the button battery  30  is eliminated by the choke coils  35 , whereupon electric power can stably be supplied from the button battery  30  to the electric circuit  23 . More specifically, the tire condition monitoring device  20  can improve antinoise reliability as compared with the conventional devices. Furthermore, since the electric circuit  23  is mounted separately on both sides of the circuit board  22 , the circuit board  22  can be compactified. Furthermore, the electric circuit  23  is mounted on both sides of the circuit board  22  except for first portions of either one side of the circuit board  22  located right behind or corresponding to second portions of the other side of the circuit board  22  on which the choke coils  35  are mounted. Consequently, an adverse effect of electromagnetic waves radiated from the choke coils  35  can be suppressed. Additionally, the paired power lines  31  and  32  are disposed in parallel with and close to each other as shown in  FIG. 4 . This arrangement of the power lines  31  and  32  renders production of normal mode noise more difficult.  
         [0028]      FIG. 5  illustrates a second embodiment of the invention. The second embodiment differs from the first embodiment in that a pair of capacitors  36  are parallel-connected between the power lines  31  and  32 . The choke coils  35  are connected between the capacitors  36 . The choke coils  35  and capacitors  36  constitute a normal mode choke  37 . Normal mode noise transmitted to the power lines  31  and  32  can be eliminated by the normal mode choke  37 .  
         [0029]      FIG. 6  illustrates a third embodiment of the invention. In the third embodiment, a pair of chip beads  38  are connected to the power lines  31  and  32 , instead of the paired choke coils  36  employed in the first embodiment. Each chip bead  38  comprises a rectangular parallelepiped nickel ferrite member  38 F and a silver electrode  38 S embedded in the nickel ferrite member  38 F. The silver electrode  38 S is formed into the shape of a coil wound about a lengthwise axis of each chip bead  38 . Furthermore, each chip bead  38  has both lengthwise ends provided with external electrodes  38 A and  38 B respectively. Both ends of the silver electrode  38 S are connected to the external electrodes  38 A and  38 B respectively. As the result of the above-described arrangement, each chip bead  38  has a stray capacitance ranging from 0.05 to 0.2 pF. The chip beads  38  are mounted to intermediate portions of the power lines  31 A and  32 B, and the external electrodes  38 A and  38 B of each chip bead  38  are soldered to the power lines  31 A and  32 B respectively.  
         [0030]     According to the third embodiment, the paired chip beads  38  each having a stray capacitance ranging from 0.05 to 0.2 pF are provided in the midst of the paired power lines  31  and  32 . Consequently, noise whose frequency ranges from 1 to 2 GHz can be eliminated more reliably. Furthermore, the size of the tire condition monitoring device  20  can be reduced.  
         [0031]     The present invention should not be limited by the foregoing embodiments. The following embodiments are within the technical scope of the present invention and can be practiced. Furthermore, the invention can be practiced in various modified forms without departing from the gist.  
         [0032]     (1) The DC power supply for the electric circuit  23  should not be limited to the button battery  30 . The DC power supply may be a cylindrically columnar battery, capacitor or the like.  
         [0033]     (2) Noise may be eliminated by a ferrite ring core extending through the paired power lines  31  and  32 , instead of the choke circuits  35  and the chip beads  38 . Furthermore, resistors may be connected to the pair of power lines  31  and  32  for elimination of high-frequency noise.  
         [0034]     The foregoing description and drawings are merely illustrative of the-principles of the present invention and are not to be construed in a limiting sense. Various changes and modifications will become apparent to those of ordinary skill in the art. All such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims.