Abstract:
A method for monitoring tire pressure of a system is disclosed. The method includes the steps of detecting a signal other than that of an in-use tire pressure signals and in response to the detection of the signal, maintaining the proper reception of the in-use tire pressure signals by a receiver.

Description:
TECHNICAL FIELD 
     The present invention generally relates to tire pressure monitoring systems. In particular, the present invention relates to a tire pressure monitoring system that detects and reacts to a signal other than that of a signal originating from an in-use tire of the tire pressure monitoring system. 
     BACKGROUND OF THE INVENTION 
     In response to regulations implemented by the United States government, automotive manufacturers are starting to provide new vehicles with tire pressure monitoring equipment. Initiated in the year 2000, Congress passed the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act, which related to issues concerned with the operation of a vehicle with substantially under-inflated tires. Under-inflated tires can result in a tire separation/blowout, which adds to the potential for a loss of control of a vehicle. Additionally, under-inflated tires shorten tire life and increase fuel consumption. 
     Section  12  of the TREAD Act directed the Department of Transportation (DOT) to complete a rule requiring that new motor vehicles must include a warning system that indicates if tires are under-inflated. Ever further, in response to Section  12  of the TREAD Act, the National Highway Traffic Safety Administration&#39;s (NHTSA) National Center for Statistics and Analysis (NCSA) conducted the Tire Pressure Special Study (TPSS), which was designed to assess to what extent passenger vehicle operators are aware of the recommend tire pressures for their vehicles, the frequency and the means they use to measure their tire pressure, and how significantly actual measured tire pressure differs from the manufacturers recommend tire pressure. 
     As a result of the TPSS, the NHTSA favored a direct system using monitors in each wheel to determine whether tires are properly inflated so as to alert drivers when tire pressure is low. In early 2002, the NHTSA issued a regulation mandating the implementation of tire pressure monitoring systems in new vehicles beginning with the 2004 model year. Under that rule, tire pressure monitors had to warn motorists when tire pressure fell 25% or 30% below the vehicle manufacturer&#39;s recommended level. The new standard applies to passenger cars, trucks, multipurpose passenger vehicles, and buses with a gross vehicle weight rating of 10,000 pounds or less, except those vehicles with dual wheels on an axle. 
     Referring now to  FIG. 1 , a conventional tire pressure monitoring system is shown generally at  1  within a vehicle, V, shown in phantom. As seen in the Figure, a receiver  2  detects wireless tire pressure signals  3   a - 3   d  that originate from each of the four in-use tires  4   a - 4   d  located at each corner of the vehicle, V. As known in the art, each wireless tire pressure signal  3   a - 3   d  is individually recognized by the receiver  2  to properly indicate if a particular in-use tire  4   a - 4   d  is not properly inflated. Although the receiver  2  may individually recognize the inflation level of each in-use tire  4   a - 4   d , the tire pressure monitoring system  1  may be affected by a signal other than that of a signal originating from an in-use tire  4   a - 4   d , which is shown generally at  5  in  FIG. 2 . As such, the signal  5 , which is hereinafter referred to as an interfering signal  5 , may result in an incorrect reading by the receiver  2 . 
     The interfering signal  5  may be transmitted unintentionally, for example, by an in-use tire  6  operating in conjunction with a tire pressure monitoring system of a nearby vehicle, V 2 . In another situation, an operator of the vehicle, V 2 , may intentionally transmit the interfering signal  5  to the vehicle, V, in an attempt to cause the operator of the vehicle, V, to think that the in-use tires  4   a - 4   d  are losing pressure. Subsequently, the driver of the vehicle, V, may pull over on the shoulder, S, of the road to manually inspect the in-use tires  4   a - 4   d  for pressure loss. Additionally, if one of the in-use tires  4   a - 4   d  is swapped with a spare tire  4   e , which is shown located in the trunk area of the vehicle, V, the swapped-out in-use tire  4   a - 4   d  may unintentionally transmit a false signal from the trunk area of the vehicle, V, to the receiver  2  even though the tire  4   a - 4   d  is no longer loaded by the vehicle. 
     Accordingly, it is therefore desirable to provide an improved tire pressure monitoring system that detects and reacts to a signal other than that of a signal originating from an in-use tire of the tire pressure monitoring system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a plan view of a conventional tire pressure monitoring system applied to a vehicle; 
         FIG. 2  illustrates an environmental view of the tire pressure monitoring system according to one embodiment of the invention; 
         FIGS. 3A and 3B  are flow chart diagrams illustrating algorithm logic of the tire pressure monitoring system according to  FIG. 2 ; 
         FIG. 4  illustrates a plan view of a tire pressure monitoring system applied to a vehicle according to another embodiment of the invention; and 
         FIG. 5  is a flow chart diagram illustrating algorithm logic of the tire pressure monitoring system according to  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As seen in  FIGS. 3A ,  3 B and  5 , the conventional tire pressure monitoring system  1  may be modified by algorithm logic  10 ,  100  that detects and reacts to an interfering signal  5 ,  7  other than that of wireless tire pressure signals (TPS) associated with an in-use tire  4   a - 4   d . As such, any sensor data/wireless signal that appears to be foreign in nature to the algorithm  10 ,  100 , such as, for example, the signals  5 ,  7 , may be screened and rejected to ensure proper operation of the inventive systems  1   a ,  1   b . The algorithm logic  10 ,  100  may, for example, be coded in the receiver&#39;s microprocessor. 
     Referring initially to  FIG. 3A , a first algorithm  10  for screening and rejecting an interfering signal  5  is illustrated according to an embodiment. The algorithm  10  is started at step I. upon keying the vehicle, V. Although the following description is related to an active operation of the vehicle, V, (i.e., when the vehicle, V, is keyed), it will be appreciated that the algorithm  10  analyzes received tire pressure signals upon powering the receiver  2   a  with battery voltage. Accordingly, although the following description relates to a keying of the vehicle, V, tire pressure signals may be received and analyzed when the vehicle is in a keyed-off state. 
     When an interfering signal  5  is not detected by the algorithm  10 , normal operation of the system  1   a  is carried out in a continuous looping of steps  14 - 28 . However, if an interfering signal  5  is imparted to the receiver  2   a  in an intentional or unintentional manner, normal operation of the system  1   a  is ceased at step  24 , which causes the algorithm  10  to lockout the corrupting, interfering signal  5  for a determined period of time at steps  30 - 36  ( FIG. 3B ). 
     During normal operation of the algorithm  10 , the wireless tire pressure signals  3   a - 3   d  are individually processed by the microprocessor, but, for purposes of explanation in describing the flowchart shown in  FIG. 3A , the four wireless tire pressure signals  3   a - 3   d  are examined at the same time. If simultaneous examination of the wireless tire pressure signals  3   a - 3   d  is desired, the electronics and/or software of the system  1   a  may be modified accordingly. 
     Referring now to step  12 , upper and lower limits of an average signal strength envelope, which are used for comparison in the conditional test at step  24 , are set after keying the vehicle, V, at step I. The upper and lower limits that are set in step  12  may be learned, dynamic values (i.e., from the function described in steps  26  and  28 ). Essentially, the upper and lower limits are saved in memory from a previous operation of the vehicle, V. As such, the upper and lower limits may be recalled at step  12  when the vehicle, V, is keyed in a subsequent operation. Because the upper and lower limits may vary throughout the life of the vehicle, V, the algorithm  10  will operate more efficiently with recalled, learned values at step  12  rather than re-setting the algorithm  10  to operate with a broader signal strength range defined by preset upper and lower limits at the outset of keying the vehicle, V. However, if desired, pre-programmed upper and lower limit calibration may be used at the outset of the algorithm  10  in step  12  rather than applying the use of learned values from steps  26  and  28 . 
     Then, at step  14 , the wireless tire pressure signals  3   a - 3   d  are received by the receiver  2   a . Each wireless tire pressure signal  3   a - 3   d  is identified by the algorithm  10  with a specified identification (ID) that is validated at step  16 . Because surrounding vehicles may be also transmitting their own tire pressure signal IDs for their own tire pressure monitoring systems, such unintentionally-received IDs identified at step  16  are simply ignored, and the algorithm  10  is looped back to step  14 . However, if an intentional or unintentional interfering signal  5  is matched with a corrupting ID that passes the validation test at step  16 , the interfering signal  5  associated with the corrupting ID is screened in a subsequent step identified at reference numeral  24 . 
     Accordingly, if such a condition occurs, the algorithm  10  may process the interfering signal  5  with the expected tire pressure signals  3   a - 3   d  as follows starting with step  18 . At step  18 , the algorithm  10  tracks the number of signal readings for each tire pressure signal ID during a sampling period to determine if enough readings have been received so as to average the signal strength in step  26 . As such, if the expected number of signal readings during the sampling period were not received, the algorithm logic at step  20  is looped back to step  14 . However, if the expected number of signal readings were received at step  20 , the algorithm is further advanced to step  22 . 
     In step  22 , the algorithm measures the signal strength for wireless tire pressure signals  3   a - 3   d  associated with their respective IDs. Then, at step  24 , the second conditional test compares the measured signal strength for each tire pressure signal  3   a - 3   d  associated with the expected IDs against the dynamically-adjusted signal strength envelope. If the measured signal strength is within or close to the signal strength range defined by the upper and lower limits, the algorithm  10  is advanced to step  26 . Alternatively, if the measured signal strength is not close to or within the signal strength range, the interfering signal  5  associated with the expected ID may be detected and locked out by being advanced to step  30  from step  24 . Because the signal strength envelope is dynamically adjusted over the life of the vehicle, V, it is increasingly difficult for an interfering signal  5  to tamper with the operation of the system  1   a.    
     The dynamic adjustment of the signal strength envelope is performed at steps  26  and  28 , which is subsequent to the conditional test at step  24  if no lock-out period has occurred for the screened tire pressure signals. At step  26 , the measured signal strengths from step  22  are averaged to calculate an averaged signal strength value. Then, at step  28 , the envelope limits are dynamically updated in view of the averaged signal strength value calculated in step  26 . 
     According to one embodiment of the invention, step  28  may include a first calculation to determine the percentage difference of the averaged value against the upper and lower limit values. Then, the calculated percent difference is added or subtracted to the upper and lower limits. It will be appreciated that the above-described update at step  28  may be carried out by using other designs. For example, after the average value is determined, the averaged value may be compared against the upper and lower limits, and then the average value may be swapped with one of the upper and lower limits. 
     Accordingly, the illustrated algorithm logic  10  may screen and lockout an interfering signal  5  according to the conditional test at step  24 . As such, if an interfering signal  5  is imparted onto the system  1   a , the algorithm logic  10  maintains proper operation of the system  1   a . As shown in  FIG. 3B , the lockout may occur for any desirable period of time and may be incremented accordingly at step  32 . When the algorithm  10  has determined that the lockout period has ended at step  34 , the failed tire pressure signal ID(s) is unlocked at step  36  and the algorithm logic  10  returns to the beginning of the loop at step  14 . Thus, even if the interfering signal  5  maintains its presence after being unlocked at step  36 , the interfering signal  5  associated with an expected ID may be continuously locked out until it wanes. 
     Although only one conditional test is shown at step  24 , any desirable numbers of tests may be implemented in the algorithm  10  in any desirable scheme. Additionally, such additional conditional tests may be dynamic in nature as in step  24 , and may be adjusted in a similar fashion as shown in steps  26 - 28  when the upper and lower limits of the average signal strength changes during normal operation of the algorithm  10 . As such, because the conditional tests may be dynamic, the algorithm  10  lends itself to a constantly changing defense mechanism that would make it increasingly difficult for an intentional or unintentional interfering signal attack to be successfully executed. 
     Referring to  FIG. 4 , another embodiment of the invention is directed to a situation that addresses the potential for reception of an interfering signal originating from within the vehicle, V. As illustrated, a spare tire  4   e  transmits a signal  7  including a tire pressure signal ID such that the receiver  2   b  looks for five wireless tire pressure signals  3   a - 3   d , and  7  associated with five tire pressure signal IDs rather than four wireless tire pressure signals  3   a - 3   d  associated with four tire pressure signal IDs as in the embodiment described in  FIGS. 2-3B . Accordingly, the system  1   b  permits itself to monitor if one of the in-use tires  4   a - 4   d  becomes flat and is swapped with the spare tire  4   e . If the swap is not properly recognized by the receiver  2   b , the previously-designated in-use tire, which may be reconfigured to a stationary state, may result in the unintentional sending of a false signal to the receiver  2   b  from within the vehicle, V. 
     As seen in  FIG. 5 , algorithm logic  100  according to another embodiment of the invention is provided for the system  1   b  such that the receiver  2   b  automatically updates in-use and spare tire location. As similarly described above with respect to  FIGS. 3A and 3B , the system  1   b  is started at step A. Then, at step  102 , wireless tire pressure signals  3   a - 3   d  and  7  relating to tire pressure signal IDs of the in-use tires  4   a - 4   d  and spare tire  4   e  are sent to the receiver  2   b . At step  104 , the algorithm logic  100  checks to see if the wireless tire pressure signal  7  relating to the spare tire  4   e  is in a stationary state. The stationary state of any of the tires  4   a - 4   e  may be based upon any desirable transmission rate or coded message content. If it is determined that the spare tire  4   e  is in a stationary state, the algorithm logic  100  is advanced to steps  106  and  108  where flags relating to an unloaded and loaded state identifier tags are maintained for the spare and in-use tires  4   a - 4   e . After steps  106  and  108  are executed, the algorithm logic  100  is returned to the beginning of the loop at step A. 
     If the receiver  2   b  discovers that the spare tire  4   e  has been swapped with an in-use tire  4   a - 4   d , step  104  is advanced to step  110 . For the algorithm logic  100  to permit advancement to step  110 , it must be determined at step  104  that the spare tire  4   e  is no longer in a stationary state (i.e., the spare tire  4   e  is in a rotational state). If so, the spare tire  4   e  is flagged with a loaded state identifier at step  110 . Then, at step  112 , the algorithm logic  100  determines which tire  4   a - 4   d  is no longer under an in-use condition (i.e., the determined tire  4   a - 4   d  is in a stationary state). At step  114 , upon determining which tire  4   a - 4   d  is in the stationary state at step  112 , the determined tire  4   a - 4   d  is flagged with an unloaded state identifier tag. Then, at step  116 , the algorithm logic  100  swaps the spare tire pressure signal ID with the in-use tire pressure signal ID. After the IDs are properly swapped, the algorithm logic  100  is returned to the beginning of the loop at step A. 
     Accordingly, both embodiments of the invention illustrated in  FIGS. 2-5  provide a modification to conventional tire pressure monitoring systems such that the wireless in-use tire signals  3   a - 3   d  are secured by the algorithm logic  10 ,  100  without costly changes, such as signal encryption. Thus, an inexpensive method is provided and the tire pressure signal  3   a - 3   d  data may be easily maintained by the receiver  2   a ,  2   b.    
     The present invention has been described with reference to certain exemplary embodiments thereof. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the exemplary embodiments described above. This may be done without departing from the spirit of the invention. The exemplary embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is defined by the appended claims and their equivalents, rather than by the preceding description.