Abstract:
A method for receiving data from and associating locations of a plurality of tire condition sensors in a vehicle comprises the step of mounting a first directional antenna in the vehicle oriented in a first direction to receive signals from an associated transmitter of at least some of said tire condition sensors. A second directional antenna is mounted in the vehicle oriented in a second direction to receive signals from an associated transmitter of others of said tire condition sensors. Signal strength of any received signals is determined, and sensor locations are determined by determining a differential signal value.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a non-provisional application that claims priority from provisional application Ser. No. 60/937,482 filed in the name of Xing Ping Lin on Jun. 28, 2007 assigned to the same assignee of the present application, and entitled METHOD AND APPARATUS FOR DETERMINING AND ASSOCIATING SENSOR LOCATION IN A TIRE PRESSURE MONITORING SYSTEM USING DUAL ANTENNAS which is hereby fully 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 the tire-based transmitter 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 associated tire locations so as to associate and display tire condition information appropriately. 
       SUMMARY OF THE INVENTION 
       [0005]    According to an example embodiment of the present invention, a method for receiving data from and associating locations of a plurality of tire condition sensors in a vehicle comprises the step of mounting a first directional antenna in the vehicle oriented in a first direction to receive signals from an associated transmitter of at least some of said tire condition sensors. A second directional antenna is mounted in the vehicle oriented in a second direction to receive signals from an associated transmitter of others of said tire condition sensors. Signal strength of any received signals is determined, and sensor locations are determined by determining a differential signal value. 
         [0006]    In accordance with another example embodiment of the present invention, an apparatus for receiving data from and associating location of a plurality of tire condition sensors in a vehicle comprises a first directional antenna oriented in a first direction in the vehicle to receive signals from an associated transmitter of at least some of said tire condition sensors. The apparatus also comprises a second directional antenna oriented in a second direction in the vehicle to receive signals from an associated transmitter of others of said tire condition sensors. A circuit determines signal strength of any received signals, and a controller determines sensor locations by determining a differential signal value. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    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: 
           [0008]      FIG. 1  is a schematic block diagram of a vehicle including an example embodiment of the present invention; 
           [0009]      FIG. 2  is a schematic block diagram of a vehicle including another example embodiment of the present invention; 
           [0010]      FIG. 3  is a circuit diagram of an antenna circuit that may be included in the embodiment of  FIG. 2 ; and 
           [0011]      FIG. 4  is a circuit diagram of another antenna circuit that may be included in the embodiment of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to  FIG. 1 , a vehicle  20 , according to an example embodiment of the present invention, includes front left tire  22 , front right tire  24 , rear left tire  26 , and rear right tire  28  at vehicle tire corner locations FL, FR, RL, and RR, respectively. 
         [0013]    Each of the tires  22 ,  24 ,  26 , and  28  includes an associated tire condition sensor  32 ,  34 ,  36 ,  38 , respectively, mounted within the tire for sensing a condition of its associated tire such as pressure, temperature, etc. Each tire condition sensor  32 ,  34 ,  36 ,  38  includes an associated transmitter (not shown) that transmits a radio frequency (“RF”) signal having at least (a) an associated unique tire identification information code and (b) measured pressure information and/or temperature information as sensed by the sensor. 
         [0014]    A vehicle-based receiver (“VBR”)  50  is mounted in the vehicle  20 . The VBR  50  is adapted to receive RF signals from the associated transmitters of the tire condition sensors  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. 
         [0015]    An electronic control unit (“ECU”)  60  is provided and is connected to the VBR  50 . The ECU  60  receives from the VBR  50  signals that include the tire identification codes and sensor information, such as sensed tire pressure and/or temperature, received from the associated RF transmitters of the tire condition sensors  32 ,  34 ,  36 ,  38 . The ECU  60  is connected to a display device  66  that displays to the vehicle operator any alert condition relating to a sensed tire condition that is out of specification. One skilled in the art will appreciate that continuous sensed data could be displayed in addition to or instead of alert condition information. 
         [0016]    For the proper display of tire condition data, whether alert condition or continuous data, the ECU  60  must learn the tire identification code associated with each tire condition sensor located within each tire at each tire position. To accomplish this learning of identification codes associated with each tire condition sensor, a differential signal strength process or method is used that eliminates the effects of sensor variations and tire variations. 
         [0017]    The VBR  50  includes a dual antenna arrangement to auto-locate or associate each of the tire condition sensors  32 ,  34 ,  36 ,  38  with a tire position. The VBR  50  may be equipped with more than two antennas. In accordance with an example embodiment, the VBR  50  includes two antennas  52  and  54 . The antenna  52  is an external antenna, and the antenna  54  is an internal antenna. Both antennas  52  and  54  could be internal antennas. To reduce the cost, the external antenna  52  may be a simple wire connected to the connector used for the power/ground and data lines connection. 
         [0018]    Because there are two antennas  52  and  54 , there are two sets of data. Each data set comprises the four signals associated with the four tire condition sensors  32 ,  34 ,  36 , and  38 . If a spare tire is provided, there will be five tire condition sensors and, therefore, five signals in each data set. With regard to the four sensor differential signal strength process or method described below, it is relatively easy to identify the tire condition sensor mounted in the spare tire because its signal will have the minimal change over the time during driving. 
         [0019]    The differential signal strength process or method of the invention uses RSSI values determined by the RSSI circuitry. In general, if the VBR  50 , including the antennas  52  and  54 , is mounted closer to one tire, e.g., tire  28 , than to the other tires, as shown in  FIG. 1 , the signal with highest RSSI value received by each of the antennas will be received from and indicate the tire condition sensor  38  in the close tire  28 . If the antennas  52  and  54  are properly oriented directional antennas, signals with lower RSSI values will be received from the tire condition sensors, e.g., sensors  34  and  36 , as shown in  FIG. 1 , toward which the antennas  52  and  54  are oriented. Signals with the lowest RSSI values will be received from the tire condition sensors that are laterally offset from the directions in which the antennas  52  and  54  are oriented, e.g., sensors  32  and  36  for antenna  52  and sensors  32  and  34  for antenna  54 . The two antennas  52  and  54  of the embodiment of  FIG. 1  are directional antennas and one antenna, e.g., antenna  52 , is oriented toward one tire condition sensor, e.g., sensor  34 , and its associated transmitter (not shown) and the other antenna, e.g., antenna  54 , is oriented toward another tire condition sensor, e.g., sensor  36 , and its associated transmitter (not shown). 
         [0020]    In accordance with the invention, both the RSSI signal values and differential RSSI signal values can be used to identify the four tire condition sensors  32 ,  34 ,  36 , and  38  and associate them with the four tire corner locations FL, FR, RL, and RR, respectively. The differential RSSI signal values (RSSI at antenna  52  minus RSSI at antenna  54 ) are particularly useful when the separation between the individual RSSI signal values is not large. The advantage of using differential RSSI signal values is that the differential RSSI signal values are independent of tire variations and sensor variations. The apparatus mounting arrangements and associated process or method described below have been shown to be useful in generally every vehicle. 
         [0021]    In the embodiment of  FIG. 1 , the tire condition sensors  34  and  38  on the right side of the vehicle  20  create a strong field on the right side due to the vehicle&#39;s metal structure, and the tire condition sensors  32  and  36  on the left side of the vehicle create a strong field on the left side due to the vehicle&#39;s metal structure. Similarly, the tire condition sensors  36  and  38  adjacent the rear of the vehicle  20  create a strong field in the rear area. Consequently, by placing the VBR  50  closer to the right rear tire  28 , but under the vehicle  20  and a short distance from the right side of the vehicle, the internal antenna  54  can be used to distinguish between the tire condition sensors  32  and  34  closer to the front of the vehicle and the tire condition sensors  36  and  38  closer to the rear of the vehicle. The external antenna  52 , which is a wire extending to the right and routed along the plastic bumper strip on the right side of the vehicle  20 , can be used to distinguish the tire condition sensors  34  and  38  on the right side of the vehicle from the tire condition sensors  32  and  36  on the left side of the vehicle. 
         [0022]    The two charts below illustrate the relative RSSI values that can be expected from the signals associated with the four different tire condition sensors  32 ,  34 ,  36 , and  38  at the two antennas  52  (Ant_Out) and  54  (Ant_In) in the embodiment of  FIG. 1 . The first chart indicates the sensors for which the relative RSSI values are given on the left side of the second chart. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ant_Out 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Ant_In 
                 FL 
                 FR 
                 FL 
                 FR 
               
               
                   
                 RL 
                 RR 
                 RL 
                 RR 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Ant_In + Ant_Out 
                 Ant_In − Ant_out 
               
             
          
           
               
                   
                 Ant_Out 
                 Antenna 
                 Ant_Out 
                 Antenna 
                 Ant_Out 
               
               
                   
                   
               
             
          
           
               
                 Ant_In 
                 1 
                 1 
                 1 
                 2 
                 Ant_In 
                 2 
                 3 
                 Ant_In 
                 0 
                 −1 
               
               
                   
                 2 
                 3 
                 1 
                 3 
                   
                 3 
                 6 
                   
                 1 
                 0 
               
               
                   
               
             
          
         
       
       
         
           
             The highest sum of the RSSI values [6] at the two antennas (Ant_In+Ant_Out) for a particular sensor determines that the sensor is positioned at the rear right (RR) tire corner location. 
             The lowest sum of the RSSI values [2] at the two antennas (Ant_In+Ant_Out) for a particular sensor in combination with the least difference between the RSSI values [0] at the two antennas (Ant_In−Ant_Out) for the sensor determines that the sensor is positioned at the front left (FL) tire corner location. 
             The second highest RSSI value [2] at antenna  52  (Ant_Out) for a particular sensor in combination with the lowest calculated difference between the RSSI values [−1] at the two antennas (Ant_In−Ant_Out) for the sensor determines that the sensor is positioned at the front right (FR) tire corner location. 
             The second highest RSSI value [2] at antenna  54  (Ant_In) for a particular sensor in combination with the highest calculated difference between the RSSI values [1] at the two antennas (Ant_In−Ant_Out) for the sensor determines that the sensor is positioned at the rear left (RL) tire corner location. 
           
         
       
     
         [0027]    With the VBR  50  placed in a generally rear right position, internal antenna  54  is under the vehicle  20  and away from any edge of the vehicle. External antenna  52  extends along the right side of the vehicle  20 . As previously mentioned, the main purpose of the internal antenna  54  is to determine the rear tire condition sensors  36  and  38 . The main purpose of the external antenna  52  is to determine the right side tire condition sensors  34  and  38 . With a wire antenna, as used for external antenna  52 , it is possible to use the same connector for both the power and data lines. No extra connector or RF connector is required. 
         [0028]    In accordance with another embodiment of the present invention,  FIG. 2  shows a closed loop antenna system in which two closed loop antennas  52 ′ and  54 ′ are used instead of the antennas  52  and  54  of the embodiment of  FIG. 1 . In other respects, the embodiment of  FIG. 2  includes the same hardware elements as the embodiment of  FIG. 1 . Referring to  FIG. 2 , the VBR or antenna assembly  50 ′ includes two internal loop antennas  52 ′ and  54 ′ that are placed substantially orthogonal to each other. The loop antennas  52 ′ and  54 ′ are small compared to the radio signal wavelength. As with the embodiment of  FIG. 1 , because there are two antennas, there are two sets of data. Each data set comprises the four signals associated with the four tire condition sensors  32 ,  34 ,  36 , and  38 . Again, if a spare tire is used, there will be five tire condition sensors and, therefore, five signals in each data set. With regard to the four sensor differential signal strength process or method described below, it is relatively easy to identify the spare tire in that its signal will have the minimum change over time during driving. 
         [0029]    The differential signal strength method or process of the invention uses RSSI values determined by the RSSI circuitry. In general, if the VBR  50 ′ is mounted closer to the one of the tires, e.g., tire  26 , as shown in  FIG. 2 , than to the other tires, the signal with highest RSSI value received by each of the antennas  52 ′ and  54 ′ will be received from and indicate the tire condition sensor  36  in the close tire  26 . If the antennas  52 ′ and  54 ′ are properly oriented directional antennas, signals with lower RSSI levels will be received from the associated transmitters (not shown) of tire condition sensors, e.g., sensors  32  and  34 , as shown in  FIG. 2 , at the end of the vehicle  20  (i.e., the front of the vehicle in  FIG. 2 ) that is opposite the end adjacent to which the tire condition sensor  36  is located. 
         [0030]    The two antennas  52 ′ and  54 ′ of the embodiment of  FIG. 2  are directional antennas and are arranged with one antenna, e.g., antenna  52 ′, oriented toward one tire condition sensor, e.g., sensor  34 , and the other antenna, e.g., antenna  54 ′, oriented toward the other tire condition sensor, e.g., sensor  32 . Thus, in effect, the null of internal loop antenna  52 ′ is presented generally toward the tire  22  and its tire condition sensor  32 , and the beam of internal loop antenna  52 ′ is oriented generally toward the tire  24  and its tire condition sensor  34 . The internal loop antenna  54 ′ is oppositely arranged. In other words, the null of internal loop antenna  54 ′ is presented generally toward the tire  24  and its tire condition sensor  34 , and the beam of internal loop antenna  54 ′ is oriented generally toward the tire  22  and its tire condition sensor  32 . 
         [0031]    In accordance with the invention, both the RSSI signal values and differential RSSI signal values (e.g., RSSI at antenna  52 ′ minus RSSI at antenna  54 ′) can be used to identify the four tire condition sensors  32 ,  34 ,  36 , and  38  and associate them with the four different tire corner locations FL, FR, RL, and RR, respectively. The advantage of using differential RSSI signal values is that the differential RSSI signal values are independent of tire variations and sensor variations. 
         [0032]    In the embodiment of  FIG. 2 , the VBR  50 ′ is mounted close to the rear left (RL) vehicle tire corner location. The beam from antenna  54 ′ is directed toward the FL vehicle tire corner location and tire condition sensor  32  and its associated transmitter (not shown). The null from antenna  54 ′ is directed toward the FR vehicle tire corner location and tire condition sensor  34 . The exact angle of the antenna  54 ′ with respect to the longitudinal axis of the vehicle  20  can be determined according to the vehicle&#39;s structure. The beam from antenna  52 ′ is directed toward the FR vehicle tire corner location and tire condition sensor  34  and its associated transmitter (not shown). The null from antenna  52 ′ is directed toward the FL vehicle tire corner location and tire condition sensor  32 . Again, the exact angle of the antenna  52 ′ with respect to the longitudinal axis of the vehicle  20  can be determined according to the vehicle&#39;s structure. 
         [0033]    From the foregoing arrangement of the antennas  52 ′ and  54 ′ relative to the tire condition sensors  32 ,  34 ,  36 , and  38 , the tire condition sensors can be identified and associated with the four different tire corner locations FL, FR, RL, and RR, respectively. Specifically, as previously described, the tire condition sensor with the highest RSSI value at each of the antennas  52 ′ and  54 ′ is determined to be at the rear left (RL) tire corner location. Alternatively, this tire condition sensor can be identified by computing the sum of the RSSI values for each tire condition sensor at each antenna and identifying the tire condition sensor with the highest sum of RSSI values at the two antennas as being at the rear left (RL) tire corner location. 
         [0034]    To identify the tire condition sensors at the front left (FL) and front right (FR) tire corner locations, the antennas  52 ′ and  54 ′ are turned on separately to identify the tire condition sensor with the next highest RSSI value at each antenna. The tire condition sensor with the next highest RSSI value at antenna  52 ′ is identified as being the tire condition sensor at the FR tire corner location. The tire condition sensor with the next highest RSSI value at antenna  54 ′ is identified as being the tire condition sensor at the FL tire corner location. If there is any ambiguity, the following differential values are computed (where, for example, FL_Ant1 means the RSSI value from the tire condition sensor presumed to be at the FL vehicle tire corner location as determined at the antenna  54 ′ (Ant1)): 
         [0000]      FL_Ant1−FL_Ant2   (1) 
         [0000]      FR_Ant1−FR_Ant2   (2) 
         [0000]      If 
         [0000]      ( FL   —   Ant 1 −FL   —   Ant 2)&gt;0 
         [0000]    then the tire condition sensor at the FL tire corner location has been properly identified. 
         [0035]    Likewise, if 
         [0000]      ( FR   —   Ant 1− FR   —   Ant 2)&lt;0 
         [0000]    then the tire condition sensor at the FR tire corner location has been properly identified. 
         [0036]    Finally, the tire condition sensor with the smallest change in RSSI value between antenna  52 ′ and antenna  54 ′ is identified as being the tire condition sensor at the RR tire corner location. 
         [0037]    As previously mentioned, there may be difficulty in identifying the tire condition sensors at the FL and FR tire corner locations. This ambiguity may result from variations in the tires  22 ,  24 ,  26  and  28  or variations in the tire condition sensors  32 ,  34 ,  36 , and  38 . To resolve such ambiguities, the differential RSSI values described above can be computed. The differential RSSI values are independent of power variations in that tire condition sensors  32 ,  34 ,  36 , and  38  and variations in the tires  22 ,  24 ,  26  and  28 , as illustrated below: 
         [0000]        X=FL   —   Ant 1 −FL   —   Ant 2,   (1) 
         [0000]        Y=FR   —   Ant 1− FR   —   Ant 2   (2) 
         [0000]        Z=X−Y    (3) 
         [0000]        Z =( FL   —   Ant 1− FL   —   Ant 2)−( FR   —   Ant 1 −FR   —   Ant 2)   (4) 
         [0000]    As previously described, the antenna 1 beam is directed toward or focused on the FL vehicle tire corner location, the antenna 2 beam is directed toward or focused on the FR vehicle tire corner location, and the antenna 2 null is presented generally toward the FL vehicle tire corner location. 
         [0038]    So 
         [0000]      ( FL   —   Ant 1 −FL   —   Ant 2)&gt;0   (5) 
         [0000]    regardless of the RSSI values of FL_Ant1 and FL_Ant2. 
         [0039]    The reverse is true for the FR vehicle tire corner location. 
         [0000]      ( FR   —   Ant 1 −FR   —   Ant 2)&lt;0   (6) 
         [0000]    regardless of the RSSI values of FR_Ant1 and FR_Ant2. 
         [0040]    So, 
         [0000]      Z&gt;0   (7) 
         [0041]    This is true regardless of sensor power variations and tire variations. Since the values X and Y determined according to equations (1) and (2), respectively, are differential values, they are independent of the sensor power number. For example, if the power of the tire condition sensor  32  at the FL vehicle tire corner location is 10 dB lower than the power of the tire condition sensor  34  at the FR vehicle tire corner location sensor, equation (1) becomes: 
         [0000]        X =( FL   —   Ant 1−10)−( FL   —   Ant 2−10)= FL   —   Ant 1− FL   —   Ant 2 
         [0000]    Thus, there is no change for X. 
         [0042]    As to Z: 
         [0000]    
       
         
           
             
               
                 
                   Z 
                   = 
                     
                    
                   
                     
                       [ 
                       
                         
                           ( 
                           
                             FL_Ant1 
                             - 
                             10 
                           
                           ) 
                         
                         - 
                         
                           ( 
                           
                             FL_Ant2 
                             - 
                             10 
                           
                           ) 
                         
                       
                       ] 
                     
                     - 
                     
                       ( 
                       
                         FR_Ant1 
                         - 
                         FR_Ant2 
                       
                       ) 
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       ( 
                       
                         FL_Ant1 
                         - 
                         FL_Ant2 
                       
                       ) 
                     
                     - 
                     
                       ( 
                       
                         FR_Ant1 
                         - 
                         FR_Ant2 
                       
                       ) 
                     
                   
                 
               
             
           
         
       
     
         [0000]    Thus, there is also no change for Z. 
         [0043]    This demonstrates that the differential RSSI values are independent of the sensor power variation. The differential RSSI values should be also independent of the tire attenuation variations. 
         [0044]    Another factor that may interfere with the identification of the tire condition sensors  32 ,  34 ,  36 , and  38  and the association of the tire condition sensors with the tire corner locations is the proximity of the antennas and the possible sharing of the same grounding structure by the antennas. With particular reference to antennas  52 ′ and  54 ′ of the embodiment of  FIG. 2 , turning on the antennas separately so that one antenna is ON while the other antenna is OFF may not be sufficient to permit each antenna to identify the tire condition sensor  34  or  32  toward which the antenna is oriented. To permit independent functioning of the antennas  52 ′ and  54 ′, it may be desirable selectively to change the impedance matching or resonating of each antenna, in turn, so that the unwanted or non-selected antenna is resonating outside of the operating frequency range of the antennas. 
         [0045]    One example arrangement for achieving such impedance switching of antennas  52 ′ and  54 ′ is shown in  FIG. 3 . In  FIG. 3 , loop antenna  52 ′ is connected to the ECU  60  and other components of the antenna circuit through two switches  70  and  72 . By opening both switches  70  and  72 , the antenna  52 ′ is electrically isolated from other electrical components. Similarly, loop antenna  54 ′ is connected to the ECU  60  and other components of the antenna circuit through two switches  74  and  76 . By opening both switches  74  and  76 , the antenna  52 ′ is electrically isolated from other electrical components. As shown, opening and closing of the switches  70 ,  72 ,  74  and  76  is controlled by the ECU  60 . A similar arrangement of switches can be used with the embodiment of  FIG. 1 . 
         [0046]    Another example arrangement for achieving impedance switching of antennas  52 ′ and  54 ′ is shown in  FIG. 4 . In  FIG. 4 , loop antenna  52 ′ is connected to the ECU  60  and other components of the antenna circuit through two controllable impedance devices  80  and  82 . By controlling both devices  80  and  82 , the antenna  52 ′ can be effectively isolated from other electrical components. Similarly, loop antenna  54 ′ is connected to the ECU  60  and other components of the antenna circuit through two controllable impedance devices  84  and  86 . By controlling both controllable impedance devices  84  and  86 , the antenna  54 ′ can be effectively isolated from other electrical components. As shown, the ECU  60  controls the controllable impedance devices  80 ,  82 ,  84  and  86  sufficiently to change the operating frequency of each antenna  52 ′ and  54 ′ selectively so that if is out of the normal operating frequency range of the antennas. A similar arrangement of controllable impedance devices can be used with the embodiment of  FIG. 1 . 
         [0047]    Although it is desirable for the loop antennas  52 ′ and  54 ′ to be oriented substantially perpendicular to each other, the present invention is not limited to that orientation. The present invention contemplates other orientations. 
         [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.