Abstract:
A method for stimulating wheel electronics systems of single tires of at least one tire group in a motor vehicle. The wheel electronics systems are stimulated with a low frequency trigger signal, as follows: a trigger signal is emitted from an LF trigger to the wheel electronics systems of the relevant tire group at a variably adjustable first transmission field strength. Radio frequency signals are transmitted from those wheel-side wheel electronics systems, at which a sufficiently high transmission field strength of the trigger signal has arrived containing an item of trigger information, to a vehicle-side receiving unit. A determination is made of the number of RF signals received by the vehicle-side receiving unit, each containing one item of trigger information.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. § 119, of German patent application DE 10 2006 060 755, filed Dec. 21, 2006; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a method for the targeted stimulation of wheel electronics systems of tire groups. 
         [0003]    The problem here is how to stimulate wheel electronics systems in a targeted manner using an LF trigger for emission. 
         [0004]    It has become known heretofore to cause the initialization and localization of wheels of motor vehicles using a low frequency (LF) trigger. In such cases an LF trigger unit sends a signal to a wheel electronics system, which in turn sends a signal to a vehicle-side control unit by way of a radio frequency (RF) transmission. The RF signal also contains information that makes it possible to infer therefrom the position of the respective wheel electronics system and/or wheel. 
         [0005]    Localization methods are also known, for example for heavy trucks, which also require stimulation of more than one wheel electronics system with only one LF trigger. The stimulation of two wheel electronics systems of two single tires of a dual tire with only one LF trigger is of particular interest. The main problem in this case is to be certain of stimulating both wheel electronics systems of the single tires of the respective dual tires of the axle in question, while at the same time avoiding stimulation of adjacent wheel electronics systems or even the other two wheel electronics systems of the dual tire on the opposite end of the same axle. 
         [0006]    The problem has previously been resolved by using for each wheel electronics system one LF trigger with comparatively low field strength. The main disadvantage of that method is a high technical outlay, coupled with the risk that it is not guaranteed that the target wheel electronics systems will respond. In contrast thereto, with field strengths that are too high crosstalk to adjacent wheel electronics systems could not be ruled out. 
       SUMMARY OF THE INVENTION 
       [0007]    It is accordingly an object of the invention to provide a method for the targeted stimulation of wheel electronics systems of tire pressure monitoring systems for tire groups which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type and which enables a precise response from the target wheel electronics systems. 
         [0008]    With the foregoing and other objects in view there is provided, in accordance with the invention, a method for stimulating wheel electronics systems of single tires of at least one tire group of a motor vehicle, which comprises the following steps: 
         [0009]    emitting a trigger signal from an low frequency (LF) trigger to the wheel electronics systems of a relevant tire group with a variably adjustable first transmission field strength; 
         [0010]    sending radio frequency (RF) signals from the wheel electronics systems at which a sufficiently high transmission field strength of the trigger signal has been received to a vehicle-side receiving unit, the RF signals containing an item of trigger information; 
         [0011]    determining a number of RF signals received by the vehicle-side receiving unit, each containing one item of trigger information; and 
         [0012]    assigning the wheel electronics systems where a number of RF signals received by the vehicle-side receiving unit is equal to a number of wheel electronics systems of the single tires within the respective tire group. 
         [0013]    In a preferred embodiment of the invention, at a transmission field strength of the LF trigger signal for which a number of RF signals received on the vehicle side is not equal to the number of wheel electronics systems of the single tires within the respective tire group, at least one further trigger event takes place at a different transmission field strength in such a manner that with a number that is greater/less than or equal to the number of wheel electronics systems of the single tires within the respective tire group an LF trigger signal with lower/higher transmission field strength is emitted until the number of RF signals received by the vehicle-side receiving unit equals the number of wheel electronics systems of the single tires within the respective group. 
         [0014]    In a further preferred embodiment of the invention an error message is sent to the motor vehicle driver when the transmission field strength is reduced to the minimum field strength at which more than the number of wheel electronics systems within the respective tire group are determined. 
         [0015]    In a further preferred embodiment of the invention an error message is sent to the motor vehicle driver when the transmission field strength is increased to the maximum field strength at which fewer than the number of wheel electronics systems are determined within the respective tire group. 
         [0016]    In a further preferred embodiment of the invention the change in the transmission field strength is performed by means of an incremental change or a single adjustment. 
         [0017]    In a further preferred embodiment of the invention the change in the transmission field strength is performed by means of an incremental change or a single adjustment. 
         [0018]    Expediently the transmission field strength of the first triggering is equal to the transmission field strength of the last successful triggering. 
         [0019]    A further advantageous embodiment of the invention consists in actuating the LF triggers in series or in parallel. 
         [0020]    Expediently the system is provided with the number of wheel electronics systems of the single tires within the respective tire group. 
         [0021]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0022]    Although the invention is illustrated and described herein as embodied in method for the targeted stimulation of wheel electronics systems of tire groups, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0023]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0024]      FIG. 1  is a schematic plan view showing four tire groups each having two wheel electronics systems and one LF trigger; 
           [0025]      FIG. 2A  is a similar view showing four tire groups, as in  FIG. 1 , and an optimal transmission field strength of the LF trigger; 
           [0026]      FIG. 2B  is a diagram of received target radio frequency signals as a function of time; 
           [0027]      FIG. 3A  is a schematic plan view of four tire groups, as in  FIG. 1 , and a transmission field strength of the LF trigger that is too low; 
           [0028]      FIG. 3B  is a diagram without received radio frequency signals as a function of time; 
           [0029]      FIG. 4A  is a schematic plan view of four tire groups, as in  FIG. 1 , and a transmission field strength of the LF trigger that is too high; and 
           [0030]      FIG. 4B  is a diagram of received radio frequency signals as a function of time; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    Referring now to the figures of the drawing in detail, wherein the same reference numerals are used for identical or functionally equivalent elements throughout, and first to  FIG. 1  thereof, the schematic vehicle structure shows four tire groups  19 ,  20 ,  21 ,  22  to which are assigned the single tires  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8  with the corresponding wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  and each with an LF trigger  9 ,  10 ,  11 ,  12 , respectively. The tire groups  19 ,  20 ,  21 ,  22  formed for example from dual tires are correspondingly arranged at each of the axles  13  and  14 . 
         [0032]      FIG. 2A  is similar to  FIG. 1 , with an additional exemplary optimal transmission field strength  15  triggered by the LF trigger  9 . 
         [0033]      FIG. 2B  shows an exemplary diagram of received radio frequency signals RF RSSI as a function of the time t for the wheel electronics systems  1   a ,  2   a . The transmission of the RF signals was accordingly triggered by a LF trigger signal at the wheel electronics system  1   a  and  2   a . In this case the transmission field strength of the LF trigger signal was sized such that only RF signals were triggered at the wheel electronics systems  1   a ,  2   a.    
         [0034]      FIG. 3A  is similar to  FIG. 1 , with an additional exemplary transmission field strength  16  that is too low, triggered by the LF trigger  9 . 
         [0035]      FIG. 3B  shows an exemplary diagram without received radio frequency signals RF RSSI as a function of the time t. In contrast to the example from  FIG. 2B  the transmission field strength of the LF trigger signal was in this case too low to trigger an RF signal at the adjacent wheel electronics systems. 
         [0036]      FIG. 4A  is similar to  FIG. 1 , with an additional exemplary transmission field strength  17  that is too high, triggered by the LF trigger  9 . 
         [0037]      FIG. 4B  shows an exemplary diagram of received radio frequency signals RF RSSI as a function of the time t. The transmission of the RF signals was accordingly triggered by a LF trigger signal at the wheel electronics system  1   a  and  2   a . In this case the transmission field strength of the LF trigger signal was sized such that RF signals were triggered at the wheel electronics systems  1   a ,  2   a  and additionally at the wheel electronics systems  3   a ,  4   a.    
         [0038]    LF triggers  9 ,  10 ,  11 ,  12  can be used, in the method according to the invention, that have a transmission field strength that is either continuously variable or variable in several discrete steps. In this way an adjustment of the LF trigger power is possible during the operating time so that too low a power, which leads to the target wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  failing to react, can also be corrected in the same way as too high a trigger power, which leads to additional parasitically triggered wheels  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  responding. 
         [0039]    A method can be executed for example such that initially the power known to be optimal from the last driving cycle is used for triggering, while a receiver “listens” for RF telegrams that respond with the status signal “triggered.” The system expects that precisely the number of wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  of the single tires  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8  within the respective tire group  19 ,  20 ,  21 ,  22  will report themselves as having been triggered. 
         [0040]    In the present example of a heavy truck according to  FIG. 1  there are two wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  accordingly at one of each tire group  19 ,  20 ,  21 ,  22  formed by dual tires. If more than two wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  are found, the power is reduced and the trigger event is repeated. This process is repeated until only two wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  of a tire group respond and any parasitically triggered wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  are no longer reached owing to the reduced power. If fewer than two wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  respond within the respective tire group  19 ,  20 ,  21 ,  22 , the power is increased until precisely two wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  respond. 
         [0041]    The typical methods of adjustment are conceivable here such as e.g. an incremental change, a single adjustment and possibly the correction of an over-adjustment. If the wheel electronics system  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  additionally measures the received LF field strength and transmits this value back to the receiver, a proportional adjustment is also possible in order to achieve the optimum level more quickly and precisely. In addition once an optimal value has been achieved it is expediently stored so as to persist beyond the firing cycles and used as the initial value for another journey. 
         [0042]    If two wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  associated with the corresponding tire group  19 ,  20 ,  21 ,  22  do not respond even at maximum power, an error code is set. This code can either immediately or after several confirmations or in combination with further conditions lead to a system error being signaled in order to warn the driver of a system malfunction. Likewise an error code is set if more than two wheel electronics systems  1   a ,  2   a ,  3   a ,  4   a ,  5   a ,  6   a ,  7   a ,  8   a  within the corresponding tire group  19 ,  20 ,  21 ,  22  respond as having been triggered even at minimum power. 
         [0043]    Furthermore when using a plurality of LF triggers  9 ,  10 ,  11 ,  12  on heavy goods vehicles with for example a plurality of double tire pairs, a spurious signal of low strength can be sent by adjacent LF triggers  9 ,  10 ,  11 ,  12  that prevents crosstalk by the first signal to adjacent wheel positions or that impedes crosstalk by means of collision with the spurious signal. In addition the LF triggering must be based on the transmission of a data telegram e.g. a value assigned by a vehicle-side control unit, a random number, a serial number or an item of position information. The spurious signal then disrupts the transmission of the data telegram to parasitic wheel positions by means of interference, but owing to its low intensity it does not disrupt the intended triggering at the target wheels. 
         [0044]    This is achieved as a result of the core parameter “LF trigger transmission field strength” being time-variable and being controlled by a logic circuit such that optimal performance is ensured for the lifetime of the tire pressure monitoring system. 
         [0045]    The present invention is particularly suited to tire pressure monitoring systems for motor vehicles with dual tires.