Abstract:
A method for determining an installation location of a wheel sensor on a wheel of a motor vehicle, wherein the method includes the steps of sampling a transverse acceleration signal of the wheel sensor, comparing the received transverse acceleration signal with a transverse acceleration signal of the motor vehicle, and determining that the wheel sensor is located on a steerable axle of the motor vehicle if the transverse acceleration signals differ from one another.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Patent Application No. 10 2013 107 828.1, filed Jul. 23, 2013, which is incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a wheel sensor for use on a motor vehicle. In particular, the invention relates to determining on which of the wheels of a motor vehicle a predetermined wheel sensor is mounted. 
     BACKGROUND OF THE INVENTION 
     A motor vehicle comprises a plurality of wheels on which wheel sensors are mounted. Each wheel sensor can sample, for example, an air pressure of a tire which is mounted on the wheel. The sampled information is usually transmitted from the wheel to the motor vehicle by means of a wireless transmission link. Since the wheel sensors can be exchanged or interchanged, for example, during servicing work on the wheels or tires, it is necessary occasionally to carry out reassignment between a wheel sensor and an installation location. The term installation location is meant here to refer to the designation of a wheel of the motor vehicle, for example “front left” or “rear right”. 
     WO 2012/035121 A1, which is incorporated by reference herein, presents a tire monitoring system in which each tire is assigned a transverse acceleration sensor. 
     U.S. Pat. No. 7,860,634 B2, which is incorporated by reference herein, presents a method for determining the location of tires in which each tire is assigned an acceleration sensor. In this context, directional information of a transverse acceleration signal of the acceleration sensor is evaluated in order to determine whether the wheel is on the right or on the left. 
     DE 10 2005 057 305 A1, which is incorporated by reference herein, presents a device for a tire pressure monitoring system in which each wheel is assigned a sensor device for sensing steering movements of the assigned wheel. The sensor device determines here a transverse acceleration of the wheel assigned thereto. From a comparison of the sensor signals with one another it is possible to determine whether a wheel is on the front axle or on the rear axle. 
     In addition it is known to position a receiver for the wireless transmission of the information of the wheel sensors in such a way that the transmission path to one of the axles is shorter than to the other axle. On the basis of the level of a reception signal it is then possible to infer the axle on which a transmitting wheel sensor is mounted. However, unexpected reflections of the wireless signals can bring about an incorrect assignment. 
     In yet a further embodiment, pulses from rotational speed sensors of all the wheels are counted during the transmission time of a wheel sensor. The position of the transmitting wheel sensor is determined on the basis of the counting result. This method is problematic, inter alia, because a relatively large number of signals have to be transmitted by a bus system of the motor vehicle, which can lead to transit time problems. 
     SUMMARY OF THE INVENTION 
     A method according to aspects of the invention for determining an installation location of a wheel sensor on a wheel of a motor vehicle comprises steps of sampling a transverse acceleration signal of the wheel sensor, of comparing the received transverse acceleration signal with a transverse acceleration signal of the motor vehicle, and of determining that the wheel sensor is located on a steerable axle of the motor vehicle if the transverse acceleration signals differ from one another. 
     If a wheel on the steerable axle is turned, a transverse acceleration acting on the wheel comprises a first component which acts in the direction of travel and a second component which acts transversely with respect thereto. The transverse acceleration of the steered wheel is therefore smaller during the cornering than the transverse acceleration of the motor vehicle. A simple and reliable assignment of a wheel sensor or a transverse acceleration signal received by the wheel sensor to an axle of the motor vehicle can be carried out on the basis of this knowledge. 
     In a preferred embodiment, it is also determined that the wheel sensor is located on a nonsteerable axle of the motor vehicle if the transverse acceleration signals correspond to one another. As a result, wheel sensors on the motor vehicle can be unambiguously assigned to a steerable or nonsteerable axle. 
     Specifically, the motor vehicle can comprise a steerable front axle and a nonsteerable rear axle. In this case, it is possible to determine that the wheel sensor is located on the front axle if the transverse acceleration signals differ from one another, and on the rear axle if the transverse acceleration signals correspond to one another. Wheel sensors of a customary motor vehicle can therefore be examined easily and reliably with respect to their installation location on the motor vehicle. 
     In one preferred embodiment it is determined that the transverse acceleration signals correspond to one another if they differ from one another by less than a predetermined amount. The predetermined amount can be specified as an absolute value or as a relative value, for example as a percentage value. Incorrect assignment of a wheel sensor to an axle can therefore be avoided. 
     The transverse acceleration signal of the motor vehicle is preferably made available by a vehicle movement dynamics control system. The vehicle movement dynamics control system can comprise, for example, an electronic stability program, an anti-lock brake system, a traction control system, an electronic braking force distribution system, a brake assistance system or an electronic brake system. As a result, a reliable and precise value for the transverse acceleration of the motor vehicle can easily be used. 
     It is preferably determined that the motor vehicle is traveling through a bend. As a result it is possible to ensure that a transverse acceleration is acting on the motor vehicle, which transverse acceleration permits the transverse acceleration signals to be differentiated. In one variant, it is also possible to specify a specific degree of cornering which has to be exceeded before the determination specified above is carried out. The degree can relate, for example, to a bend radius, a transverse acceleration of the motor vehicle or a difference in rotational speed between wheels on the same axle. 
     In a further preferred embodiment, in addition a rotational direction of the wheel assigned to the wheel sensor is determined on the basis of a longitudinal acceleration signal of said wheel sensor, and a right-hand or left-hand installation side on the motor vehicle is determined on the basis of the rotational direction. The installation position of the wheel sensor can therefore be easily narrowed down to one of, for example, four wheels of the motor vehicle. 
     A wheel sensor according to aspects of the invention for carrying out the described method is configured for mounting on a wheel of a motor vehicle and comprises a transverse acceleration sensor for determining an acceleration which runs perpendicularly with respect to a rotational plane of the wheel. The acceleration forces acting in the transverse direction of the wheel can therefore be made available for the described method. 
     In one particularly preferred embodiment, the wheel sensor comprises a pressure sensor for sensing an air pressure of a tire mounted on the wheel. A sensed tire air pressure can therefore easily be transmitted, in particular in a wireless fashion, to a processing device of the motor vehicle which can carry out an assignment of the sampled tire air pressure on the basis of the transverse acceleration signal of the wheel sensor. It is therefore easily possible to relate an adaptation of the tire air pressure or the outputting of a warning, if the tire air pressure is too high or too low, to the correct tire or to the correct wheel. 
     A computer program product according to aspects of the invention comprises program code means for carrying out the method described above when the computer program product runs on a processing device or is stored on a computer-readable data carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in more detail with respect to the appended figures, of which: 
         FIG. 1  illustrates a motor vehicle with tire sensors; 
         FIG. 2  illustrates transverse accelerations on the motor vehicle in  FIG. 1 , and 
         FIG. 3  illustrates a flow chart of a method for determining installation locations of wheel sensors on the motor vehicle in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a system  100  which comprises a motor vehicle  105  and a measuring device  110 . The motor vehicle  105  comprises a front axle  115  which is steerable, and a rear axle  120  which is nonsteerable. A left-hand front wheel  125  with a first wheel sensor  130  and a right-hand front wheel  135  with a second wheel sensor  140  are mounted on the front axle  115 . A left-hand rear wheel  145  with a third wheel sensor  150  and a right-hand rear wheel  155  with a fourth wheel sensor  160  are mounted on the rear axle  120 . The wheel sensors  130 ,  140 ,  150  and  160  are usually mounted on a rim or a valve on the respective wheel  125 ,  135 ,  145 ,  155 . In this context, the wheel sensors  130 ,  140 ,  150  and  160  are preferably configured to determine an air pressure of a tire  165  which is mounted on the respective wheel  125 ,  135 ,  145  or  155 . 
     Information of the wheel sensors  130 ,  140 ,  150  and  160  are preferably transmitted in a wireless fashion to a receiver  170 . The receiver  170  is connected to a processing device  175  which is preferably connected to a vehicle movement dynamics control system  185  via an interface  180 , for example via a CAN bus. The processing device  175  and the vehicle movement dynamics control system  185  can also be embodied integrated with one another. The vehicle movement dynamics control system  185  makes available a transverse acceleration signal which indicates an acceleration of the motor vehicle  105  transverse with respect to its direction of travel. The wheel sensors  130 ,  140 ,  150  and  160  are configured to determine a transverse acceleration which runs perpendicularly with respect to a plane of rotation of the respectively assigned wheel  125 ,  135 ,  145  and  155 . The processing device  175  is also configured to assign a wheel sensor  130 ,  140 ,  150 ,  160  to a wheel  125 ,  135 ,  145 ,  155  on the basis of a comparison of the different transverse accelerations determined. If a tire air pressure is transmitted together with the respective transverse acceleration to the receiver  170 , it is possible in this way to assign the tire air pressure to the correct wheel  125 ,  135 ,  145  or  155  or to the tire  165  mounted thereon. 
       FIG. 2  shows transverse accelerations on the motor vehicle  105  in  FIG. 1  during travel through a bend. In this context, a bend to the left is assumed by way of example. Due to centrifugal forces and centripetal forces counteracting the latter, a first transverse acceleration  205  acts on the motor vehicle  105 , it being possible to determine said transverse acceleration  205  in particular by means of the vehicle movement dynamics control system  185 . The wheel sensors  150  and  160  are mounted on wheels  145  and  155  whose rotational planes run parallel to a longitudinal axis  215  of the motor vehicle. Accordingly, the first transverse acceleration  205  also acts on the wheel sensors  150  and  160  in the transverse direction. 
     However, the wheel sensors  130  and  140  are mounted on wheels whose rotational planes during cornering enclose a predetermined steering angle different from zero with the longitudinal axis  215 . The second transverse acceleration  210  acting in the transverse direction of the wheel sensors  130  and  140  therefore reflects only part of the first transverse acceleration  205 . According to the triangular inequation the second transverse acceleration  210  is smaller than the first transverse acceleration  205 . The wheel sensors  130 ,  140 , on which the smaller second transverse acceleration  210  acts in the transverse direction, can therefore be assigned to the steerable front axle  115 , while the wheel sensors  150 ,  160 , on which the larger first transverse acceleration  205  acts in the transverse direction, can be assigned to the nonsteerable axle  120 . 
       FIG. 3  shows a flowchart of a method  300  for determining installation locations of wheel sensors  130 ,  140 ,  150  and  160  on the motor vehicle  105  in  FIG. 1 . The method  300  is configured, in particular, to be run on the processing device  175 . 
     In a first step  305 , transverse accelerations are received by one or more sensors  130 ,  140 ,  150  and  160 . In an optional step  310  it is possible to determine whether the motor vehicle  105  is moving and, if appropriate, whether this movement, for example in the form of a speed, is greater than a predetermined threshold value. If the motor vehicle  105  is not moving sufficiently, the method  300  branches back to the step  305  and can run through again. 
     Otherwise, in a step  315  the first transverse acceleration  205  is received by means of the interface  180 , specifically preferably by the vehicle movement dynamics control system  185 . Before or after this it is also possible in a step  320  to determine whether the motor vehicle  105  is traveling through a bend. It is possible to infer travel through a bend, for example, if a steering angle of the front wheels  125  and  135  which are mounted on the steerable axle  115  is greater than a predetermined threshold value. Alternatively, it is possible to infer travel through a bend if the first transverse acceleration  205  exceeds a predetermined threshold value. In yet a further embodiment, travel through a bend can also be determined if the transverse acceleration values which are received by the wheel sensors  130 ,  140 ,  150  or  160  individually or collectively exceed a predetermined threshold value. By adapting the respective threshold value it is possible to predefine how severe the cornering movement of the motor vehicle  105  has to be in order to infer a bend. If a bend is not present, the method  300  branches back to the step  305  and can run through again. 
     Otherwise, a difference between the respectively determined transverse acceleration  205  or  210  and the first transverse acceleration  205  is formed in a step  325  for each of the wheel sensors  130 ,  140 ,  150  and  160  from which information was received. In a step  330  it is then determined for each of the wheel sensors  130 ,  140 ,  150  and  160  whether the transverse acceleration  205 ,  210  determined essentially corresponds to the second transverse acceleration  210  or undershoots it. In this context it is possible to provide a further threshold value by which the transverse acceleration  205 ,  210  which is determined by the wheel sensor  130 ,  140 ,  150  or  160  must differ from the second transverse acceleration  210  in order to be considered to differ significantly. If there is a difference which exceeds the threshold value, in a step  335  it is determined that the respective wheel sensor  130 ,  140 ,  150 ,  160  is located on one of the wheels  125 ,  135  of the steerable axle  115 . Otherwise, in a step  340  it is determined that said respective wheel sensor is located on a wheel  145 ,  155  of the nonsteerable rear axle  120 . 
     LIST OF REFERENCE NUMBERS 
     
         
           100  System 
           105  Motor vehicle 
           110  Measuring device 
           115  Front axle (steerable) 
           120  Rear axle (nonsteerable) 
           125  Left-hand front wheel 
           130  First wheel sensor 
           135  Right-hand front wheel 
           140  Second wheel sensor 
           145  Left-hand rear wheel 
           150  Third wheel sensor 
           155  Right-hand rear wheel 
           160  Fourth wheel sensor 
           165  Tire 
           170  Receiver 
           175  Processing device 
           180  Interface 
           185  Vehicle movement dynamics control system 
           205  First transverse acceleration 
           210  Second transverse acceleration 
           215  Longitudinal axis 
           300  Method 
           305  Reception of transverse accelerations from sensors 
           310  optional.: Motor vehicle moving? Faster than threshold value? 
           315  Reception of transverse acceleration from ESP 
           320  Determine bend (e.g. steering angle/ESP transverse acceleration&gt;threshold value/received transverse accelerations) 
           325  Determine differences between received and ESP transverse accelerations 
           330  Difference&gt;threshold value? 
           335  Steerable axle (front axle) 
           340  Nonsteerable axle (rear axle) 
           345  optional.: determine rotational direction→vehicle side