Abstract:
A method for identifying tire location including the steps of transmitting a low frequency signal at different power levels and receiving radio frequency identification signals. Tire identification and location based on low frequency power level for two tire transmitters is determined. Radio frequency signals from two different tire transmitters are received and tire identification and location are determined based on radio frequency signal strength.

Description:
RELATED APPLICATION  
       [0001]    This application claims priority from U.S. provisional patent application Ser. No. 60/800,980, filed on May 17, 2006, the subject matter of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]    The present invention is directed to a tire pressure monitoring system and, more particularly, to a method and apparatus for associating each tire based monitoring device with a tire location on the vehicle. 
       BACKGROUND OF THE INVENTION  
       [0003]    Tire pressure monitoring systems having an associated tire based pressure sensor and transmitter in each tire are known. The tire based sensor inside a tire senses the pressure of its associated tire and transmits the sensed pressure information to a vehicle mounted receiver. The vehicle mounted receiver is connected to a display that displays a warning to the vehicle operator when an under-inflated tire condition occurs. 
         [0004]    Each tire based transmitter within a tire has a unique identification code that is transmitted as part of the tire transmission signal. The vehicle based receiver can be programmed with the identification codes and the tire associated tire locations so as to associate and display improper tire condition information appropriately. 
       SUMMARY OF THE INVENTION  
       [0005]    According to an example embodiment of the present invention, a method for identifying tire location including the steps of transmitting a low frequency signal at different power levels and receiving radio frequency identification signals. Tire identification and location based on low frequency power level for two tire transmitters is determined. Radio frequency signals from two different tire transmitters are received and tire identification and location are determined based on radio frequency signal strength. 
         [0006]    In accordance with another example embodiment of the present invention, a method is provided for identifying tire transmitter location in a tire pressure monitoring system for a vehicle comprising the steps of transmitting a first low powered, low frequency signal adjacent a first tire location, monitoring for a transmitted identification return signal from said first tire location, storing said monitored identification return signal from said first tire location, and transmitting a second higher powered, low frequency signal adjacent the first tire location. The method further includes the steps of monitoring for a transmitted identification return signal from a second tire location, storing said monitored identification return signal from said second tire location, monitoring for periodic transmissions of identification signal from a third and forth tire location from the first tire location, and determining signal strength of the monitored periodic transmissions of identification signal from a third and forth tire location from the first tire location and associated tire location and signal identification of the third and forth tire location based on signal strength. 
         [0007]    In accordance with another example embodiment of the present invention, an apparatus is provided for identifying tire location including a transmitter for transmitting a low frequency signal at different power levels. A receiver receives radio frequency identification signals. A controller determines tire identification and location based on radio signal received in response to the low frequency power level signals and determines tire identification and location based on radio frequency signal strength. The transmitter and receiver may be on a single integrated circuit located at one tire location. 
         [0008]    In accordance with yet another example embodiment of the present invention, a tire pressure monitoring system for a vehicle is provided comprising a low powered transmitter mounted adjacent a first tire location for transmitting adjustable powered, low frequency signals. A monitor monitors for a transmitted identification signals from tire locations and a memory stores said monitored identification signals from said tire locations. The system further includes a circuit for determining signal strength of monitored transmissions of identification signal from the tire locations, and a controller for associating tire location in response to signal returns and signal strength of transmissions of identification signals from the tire locations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]    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: 
           [0010]      FIG. 1  is a schematic block diagram of a vehicle including an example embodiment of the present invention; 
           [0011]      FIG. 2  is a schematic block diagram of a vehicle including another example embodiment of the present invention; 
           [0012]      FIG. 3  is a schematic block diagram of a portion of the invention shown in  FIG. 2  showing the LF initiator and the vehicle based receiver in more detail; and 
           [0013]      FIG. 4  is a schematic block diagram of a vehicle including yet another example embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0014]    Referring to  FIG. 1 , a vehicle  10 , according to an example embodiment of the present invention, includes front left tire  12 , front right tire  14 , rear left tire  16 , and rear right tire  18  at vehicle tire corner locations FL, FR, RL, and RR, respectively. A single low frequency (“LF”) initiator coil  20  is placed in one of the vehicle&#39;s wheel wells at, for example, the right rear wheel well behind the right rear tire, as shown in  FIG. 1 . The position of the LF initiator  20  is such that a substantially different distance from the LF initiator  20  is achieved between two tire locations. In accordance with one example embodiment, the LF initiator coil  20  is aligned to be parallel with the rear axel  24  of the vehicle  10  connecting the two rear wheels  16 ,  18 . 
         [0015]    Each of the tires  12 ,  14 ,  16 , and  18  includes an associated tire condition sensor  22 ,  24 ,  26 ,  28 , respectively, mounted within the tire for sensing a condition of its associated tire such as pressure, temperature, etc. Each of the tires  12 ,  14 ,  16 , and  18  also includes an associated low frequency (“LF”) receiver and radio frequency (“RF”) transmitter (“LFR/RFT”)  32 ,  34 ,  36 ,  38 , respectively, connected to its associated sensor  22 ,  24 ,  26 , and  28 , respectively, and mounted within the tire. Each of the LFR/RFT circuits are adapted to respond to a received LF initiating signal and, in response thereto, transmit an RF signal having at least an associated unique tire identification information code, and any other desired information for that tire such as measured pressure and/or temperature as sensed by its associated sensor. 
         [0016]    A vehicle based receiver  50  (“VBR”) is mounted in the vehicle  10  at a location spaced near one of the front tires FL or FR and spaced from the LF initiator  20 . The RF receiver  50  is adapted to receive RF signals generated from the tire transmitters  32 ,  34 ,  36 , and  38  and includes circuitry to determine the strength of the received RF signals known as received signal strength indication (“RSSI”) circuitry. 
         [0017]    An electronic control unit (“ECU”)  60  is provided and controllably connected to the LF initiator coil  20  for controlling the transmission of LF initiation signals. The ECU not only controls the timing of the LF initiation signals but also the signal strength. Signal strength is controlled either via amplitude control or frequency control. 
         [0018]    The ECU  60  is also connected to the vehicle based receiver  50  and receives signals from the RF transmitters  32 ,  34 ,  36 ,  38  having the tire identification codes and sensor information such as sensed tire pressure and temperature. The ECU  60  is connected to a display device  66  and displays any alert condition to the vehicle operator of a sensed tire condition out of specification. One skilled in the art will appreciate that continuous sensed data could also be displayed. 
         [0019]    For the display of each tire condition data whether alert or continuous data, the ECU  60  must learn the tire identification code associated with each tire pressure monitoring system within each tire at each tire position. To accomplish this learning of identification codes associated with each tire pressure monitoring system (the sensor plus LFR/RFT) within the tire at each tire position, a combination LF and RF plus RSSI technique is used. 
         [0020]    It should be appreciated that the axis of the initiator coil  20  could be different from that shown in  FIG. 1  to allow a different pair of tire mounted sensors to respond. In accordance with the example embodiment, with the axis orientation as shown, the LF initiator  20  is controlled by the ECU  60  to provide a low power output LF signal that has a field strength sufficient that the LF receiver in the right rear tire  18  can receive the signal. In response to receiving the LF signal, the LFR/RFT circuit  38 . responds with an RF response signal that includes that tire&#39;s associated unique identification (“ID”) code and could include additional information such as tire pressure information and/or tire temperature. This RF response signal is received by the receiver  50  and processed by the ECU  60 , to verify that the “ID” code is applicable to this vehicle  10 . Since the ECU knows that it just initiated tire  18  and the code is valid for this vehicle  10 , the code it just received is the ID code corresponding for tire  18 . It then stores that code association in memory for later use. 
         [0021]    The ECU then interrogates via LF coil  20  an LF signal with a second stronger LF signal designed to be of sufficient signal strength that the LF receiver within tire  16  can receive the second LF signal. The signal strength can be increased either through amplitude or frequency. In response to receiving the LF interrogation signal, the LFR/RFT circuit  36  responds with an RF response signal that includes that tire&#39;s associated unique identification (“ID”) code and could include additional information such as tire pressure information and/or tire temperature. This RF response signal is received by the receiver  50  and processed by the ECU  60  in a similar manner, checking validity. The ECU will receive two ID signals in response to this initiation, one from tire  18  and one from tire  16 . Since it knows the ID from tire  18 , it can ignore that ID and it knows that the other ID corresponds to that of tire  16 . It then stores that code association in memory for tire  16  for later use. 
         [0022]    During normal operation of the vehicle  10 , the tire pressure monitoring. systems (sensors plus LFR/RFT) in the tires  12  and  14  will periodically transmit RF signals having their associated unique ID codes and sensed tire condition information. The vehicle based receiver  50  receives each of the RF signals so transmitted and makes a determination using its RSSI circuitry which RF signal is stronger. The ECU  60  then correlates the stronger RF signal with the transmitted ID code and stores that with the associated tire location. If the receiver  50  is closest to tire  12 , the code for closed tire corresponds to tire  12  and the other code corresponds to tire  14 . The received signal strength from the two initiated tires  16  and  18  is not utilized in the location association of tires  12  and  14 . 
         [0023]    System design requires that adequate margin be built into the system to allow for RF attenuations, and resulting RSSI changes. Such attenuations may result from component variation, but are primarily the result of tire rotation effects, vehicle modifications such as the use of different tire construction, weather, and other RF interference conditions. These attenuation variations may exceed the ranges of the RSSI circuitry capability. The vehicle mounted receiver needs to optimize receive circuit and RSSI range to give the largest received signal difference between the two tire sensor systems being located. 
         [0024]    RSSI difference optimization is possible by two methods. The first method is for the vehicle based receiver to scale the RSSI allowing measurement of values that were out of RSSI measurement range. To bring RSSI values into range, so the difference can be measured, can be accomplished by increasing or decreasing the vehicle based receiver sensitivity, depending if the RSSI value was below or above the RSSI range, respectively. After location is determined, the vehicle based receiver  50  sensitivity may be increased back to maximum value to increase the RF link margin to allow for variations due to tire rotation and RF interference desensitization. 
         [0025]    The second RSSI difference optimization method is using vehicle tire sensors that include a speed sensor, such as an accelerometer. Upon the tire&#39;s achieving a predetermined speed threshold, the RF transmitter RFT would enter a timed period in which RF signals are transmitted at a reduced signal level, but at a higher transmission rate. 
         [0026]    Referring to  FIGS. 2 and 3 , another example embodiment of the present invention is shown in which a vehicle  110  includes front left tire  112 , front right tire  114 , rear left tire  116 , and rear right tire  118  at vehicle tire corner locations FL, FR, RL, and RR, respectively. An integrated circuit  120  having a low frequency initiator (“LFI”) circuit and a vehicle based receiver (“VBR”) circuit is mounted in one of the vehicle&#39;s wheel wells at, for example, the right rear wheel well behind the right rear tire, as shown in  FIG. 2 . The position of the LFI/VBR circuit  120  is such that each vehicle tire is located a different distance there from. In accordance with this example embodiment, the LFI/VBR circuit  120  has an internal LF coil aligned to be parallel with the rear axel (not shown) of the vehicle  110  connecting the two rear wheels  116 ,  118 . 
         [0027]    Each of the tires  112 ,  114 ,  116 , and  118  includes an associated tire condition sensor  122 ,  124 ,  126 ,  128 , respectively, mounted within the tire for sensing a condition of its associated tire such as pressure, temperature, etc. Each of the tires  112 ,  114 ,  116 , and  18  also includes an associated low frequency (“LF”) receiver and radio frequency (“RF”) transmitter (“LFR/RFT”)  132 ,  134 ,  136 ,  138 , respectively, connected to its associated sensor  122 ,  124 ,  126 , and  128 , respectively, and mounted within the tire. Each of the LFR/RFT circuits are adapted to respond to a received LF initiating signal and, in response thereto, transmit an RF signal having at least an associated unique tire identification information code, and any other desired information for that tire such as measured pressure and/or temperature as sensed by its associated sensor. 
         [0028]    The vehicle based receiver circuit of the integrated circuit  120  is adapted to receive RF signals generated from the tire transmitters  132 ,  134 ,  136 , and  138  and includes received signal strength indication (“RSSI”) circuitry to determine the strength of the received RF signals. 
         [0029]    An electronic control unit (“ECU”)  160  is provided and controllably connected to the LFI/VBR circuit  120  for controlling the transmission of LF initiation signals and receipt of RF signals. The ECU not only controls the timing of the LF initiation signals but also the signal strength. Signal strength is controlled either via amplitude control or frequency control. 
         [0030]    The ECU  160  is also processes the received RF signals having the tire identification codes and sensor information such as sensed tire pressure and temperature. The ECU  160  is connected to a display device  166  and displays any alert condition to the vehicle operator of a sensed tire condition out of specification. One skilled in the art will appreciate that continuous sensed data could also be displayed. 
         [0031]    For the display of tire condition data whether alert or continuous data, the ECU  160  must learn the tire identification code associated with each tire pressure monitoring system within each tire. To accomplish this learning of identification codes associated with each tire pressure monitoring system (the sensor plus LFR/RFT) within the tire, a combination LF and RF plus RSSI technique is used. 
         [0032]      FIG. 3  shows the low frequency initiator and vehicle based receiver circuit functions of the integrated circuit  120  in more detail. The ECU  160  controls a frequency controlled oscillator having an output connected to an LF antenna  142  through a drive circuit  144 . As mentioned, the LF antenna in accordance with the example embodiment is aligned with the rear axle of the vehicle. The ECU  160  controls the gain of the drive circuit  144  via a power control arrangement  146 . Power of the LF initiation signal or interrogation signal is controlled either via amplitude control or frequency control. An RF receiver circuit  150  is connected to an RF antenna  152 . The output of the RF receiver is connected to an RSSI circuit. The output of the RSSI circuit is connected to the ECU  160 . 
         [0033]    The LF initiator circuit portion of the integrated circuit  120  is controlled by the ECU  160  to provide a low power output LF signal that has a field strength sufficient that only the LF receiver in the right rear tire  118  can receive the signal. In response to receiving the LF initiation signal, the LFR/RFT circuit  138  responds with a RF response signal that includes that tire&#39;s associated unique identification (“ID”) code and could include additional information such as tire pressure information and/or tire temperature. This RF response signal is received by the vehicle based receiver circuit portion of the integrated circuit  120  and processed by the ECU  160 . Since the ECU knows that it just initiated tire  118 , the code it just received is the ID code corresponding for tire  118 . It then stores that code in its internal memory for later use. 
         [0034]    The ECU  160  then interrogates via LFI circuit portion of the integrated circuit  120  an LF signal with a second stronger LF signal designed to be of sufficient signal strength that the LF receiver within tire  116  can receive the second LF signal. The signal strength can be increased either through amplitude or frequency. In response to receiving the LF interrogation signal, the LFR/RFT circuit  136  responds with an RF response signal that includes that tire&#39;s associated unique identification (“ID”) code and could include additional information such as tire pressure information and/or tire temperature. This RF response signal is received by the vehicle based receiver circuit of the integrated circuit  120  and processed by the ECU  160 . The ECU will receive two ID signals in response to this initiation, one from tire  118  and one from tire  116 . Since it knows the ID from tire  118 , it can ignore that ID and it knows that the other ID corresponds to that of tire  118 . It then stores that code in its internal memory for tire for later use. 
         [0035]    During normal operation of the vehicle  110 , the tire pressure monitoring systems (sensors plus LFR/RFT) in the tires  112  and  114  will periodically transmit RF signals having their associated unique ID codes and sensed tire condition information. The vehicle based receiver circuit of integrated circuit  120  receives each of the RF signals so transmitted and makes a determination using its RSSI circuitry which RF signal is stronger. The ECU  160  then correlates the stronger RF signal with the transmitted ID code and stores that with the associated tire location. If the vehicle based receiver circuit of the integrated circuit is closest to tire  114 , the code for closest tire corresponds to tire  114  and the other code corresponds to tire  112 . 
         [0036]    RSSI difference optimization is possible using vehicle tire sensors that include a speed sensor, such as an accelerometer. Upon the tire&#39;s achieving a predetermined speed threshold, the RF transmitter RFT would enter a timed period in which RF signals are transmitted at a reduced signal level, but at a higher transmission rate. 
         [0037]    Referring to  FIG. 4 , yet another example embodiment of the present invention is shown in which a vehicle  210  includes front left tire  212 , front right tire  214 , rear left tire  216 , and rear right tire  218  at vehicle tire corner locations FL, FR, RL, and RR, respectively. An integrated circuit  220  having a low frequency initiator (“LFI”) circuit and a vehicle based receiver (“VBR”) circuit is mounted in one of the vehicle&#39;s wheel wells at, for example, the right rear wheel well behind the right rear tire, as shown in  FIG. 4 . The position of the LFI/VBR circuit  220  is such that each vehicle tire is located a different distance therefrom. In accordance with this example embodiment, the LFI/VBR circuit  220  has an internal LF coil aligned to be parallel with the rear axel (not shown) of the vehicle  210  connecting the two rear wheels  216 ,  218 . 
         [0038]    Each of the tires  212 ,  214 ,  216 , and  218  includes an associated tire condition sensor  222 ,  224 ,  226 ,  228 , respectively, mounted within the tire for sensing a condition of its associated tire such as pressure, temperature, etc. Each of the tires  212 , 214 ,  216 , and  218  also includes an associated low frequency (“LF”) receiver and radio frequency (“RF”) transmitter (“LFR/RFT”)  232 ,  234 ,  236 ,  238 , respectively, connected to its associated sensor  222 ,  224 ,  226 , and  228 , respectively, and mounted within the tire. Each of the LFR/RFT circuits are adapted to respond to a received LF initiating signal and, in response thereto, transmit an RF signal having at least an associated unique tire identification information code, and any other desired information for that tire such as measured pressure and/or temperature as sensed by its associated sensor. 
         [0039]    The vehicle based receiver circuit of the integrated circuit  220  is adapted to receive RF signals generated from the tire transmitters  232 ,  234 ,  236 , and  238  and includes received signal strength indication (“RSSI”) circuitry to determine the strength of the received RF signals. 
         [0040]    An electronic control unit (“ECU”)  260  is provided and controllably connected to the LFI/VBR circuit  220  for controlling the transmission of LF initiation signals and receipt of RF signals. The ECU not only controls the timing of the LF initiation signals but also the signal strength. Signal strength is controlled either via amplitude control or frequency control. 
         [0041]    The ECU  260  is also processes the received RF signals having the tire identification codes and sensor information such as sensed tire pressure and temperature. The ECU  260  is connected to a display device  266  and displays any alert condition to the vehicle operator of a sensed tire condition out of specification. One skilled in the art will appreciate that continuous sensed data could also be displayed. 
         [0042]    For the display of tire condition data whether alert or continuous data, the ECU  260  must learn the tire identification code associated with each tire pressure monitoring system within each tire. To accomplish this learning of identification codes associated with each tire pressure monitoring system (the sensor plus LFR/RFT) within the tire, a combination LF and RF plus RSSI technique is used. 
         [0043]    The LF initiator circuit portion of the integrated circuit  220  is controlled by the ECU  260  to provide a low power output LF signal that has a field strength sufficient that only the LF receiver in the right rear tire  218  can receive the signal. In response to receiving the LF initiation signal, the LFR/RFT circuit  238  responds with a RF response signal that includes that tire&#39;s associated unique identification (“ID”) code and could include additional information such as tire pressure information and/or tire temperature. This RF response signal is received by the vehicle based receiver circuit portion of the integrated circuit  220  and processed by the ECU  260 . Since the ECU knows that it just initiated tire  118 , the code it just received is the ID code corresponding for tire  218 . It then stores that code in its internal memory for later use. 
         [0044]    The ECU  260  then interrogates via LFI circuit portion of the integrated circuit  220  an LF signal with a second stronger LF signal designed to be of sufficient signal strength that the LF receiver within tire  216  can receive the second LF signal. The signal strength can be increased either through amplitude or frequency. In response to receiving the LF interrogation signal, the LFR/RFT circuit  236  responds with an RF response signal that includes that tire&#39;s associated unique identification (“ID”) code and could include additional information such as tire pressure information and/or tire temperature. This RF response signal is received by the vehicle based receiver circuit of the integrated circuit  220  and processed by the ECU  260 . The ECU will receive two ID signals in response to this initiation, one from tire  218  and one from tire  216 . Since it knows the ID from tire  218 , it can ignore that ID and it knows that the other ID corresponds to that of tire  218 . It then stores that code in its internal memory for tire for later use. 
         [0045]    During normal operation of the vehicle  210 , the tire pressure monitoring systems (sensors plus LFR/RFT) in the tires  212  and  214  will periodically transmit RF signals having their associated unique ID codes and sensed tire condition information. The vehicle based receiver circuit of integrated circuit  220  receives each of the RF signals so transmitted and makes a determination using its RSSI circuitry which RF signal is stronger. The ECU  260  then correlates the stronger RF signal with the transmitted ID code and stores that with the associated tire location. If the vehicle based receiver circuit of the integrated circuit is closest to tire  214 , the code for closest tire corresponds to tire  214  and the other code corresponds to tire  212 . 
         [0046]    An RF blocking (“RFB”) structure  280  is provided located between the vehicle based receiver  220  and the front left tire  212  so as to reduce the amplitude of the RF transmitted signal from the RF transmitter  232  so as to make a larger difference in the two signals between the FL and FR tires as seen by the vehicle based receiver  220  circuitry RSSI. 
         [0047]    RSSI difference optimization is possible using vehicle tire sensors that include a speed sensor, such as an accelerometer. Upon the tire&#39;s achieving a predetermined speed threshold, the RF transmitter RFT would enter a timed period in which RF signals are transmitted at a reduced signal level, but at a higher transmission rate. 
         [0048]    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.