FR2879750A1 - Vehicle wheel rotation direction determining method for determining wheel`s left/right position, involves correlating angular position obtained by measuring physical unit and direction of variation of gravity to determine rotation direction - Google Patents

Abstract

The method involves emitting signals comprising information relative to variation of gravity measurement, when wheel (2) is in angular positions. A physical unit representing the angular position of the wheel during the emission of each signal, is measured. The angular position obtained by the measurement of the physical unit and direction of variation of the gravity are correlated for determining rotation direction of the wheel. An independent claim is also included for a device for determining rotation direction of a wheel of a vehicle.

Description

The present invention relates to a method for determining the meaning of

  rotation of a wheel and a device implementing this method. Such a method finds particular application for realizing the location of the wheels of a vehicle equipped with a tire pressure monitoring system.

  More and more vehicles are equipped with such a system. A pressure sensor is then placed inside each tire and each sensor communicates with at least one central unit for transmitting various information, and in particular the measured pressure. It is necessary in such a system to be able to automatically identify the location of a pressure sensor, that is to say, know each time that information is received by the central unit to which wheel this information is associated.

  Tire pressure information in a tire pressure monitoring system is generally sent from the wheel sensors to the central unit by radio waves. An antenna fixed with respect to the chassis of the vehicle receives the information and transmits it. Some tire pressure monitoring systems provide an antenna per wheel, and therefore a pressure sensor. In this case, the identification of the wheel is done by filtering. For a given antenna, the strongest received signal corresponds to the pressure sensor closest to the antenna. The location of the wheel and the associated sensor is thus in this manner.

  However, to simplify the system and make it more economical, it is better to have only one antenna. When a pressure sensor then emits information, it must be possible to determine which wheel is associated with this sensor. For a motor vehicle with four wheels, it must first be determined whether the sensor is associated with a front wheel or a rear wheel and it must be determined whether the information comes from a wheel located to the right or left of the vehicle .

  The document FR-2 774 178 proposes a method for locating and recognizing the position of the wheels on a motor vehicle. This method provides for defining for each wheel a signal signature emitted by the corresponding sensor as a function of the position of the wheel on the vehicle. Subsequently, to determine the source of a signal, the latter is compared with the stored signatures. This procedure is complex and its implementation is complicated.

  The document EP-1 172 656 discloses a sensor for determining the direction of rotation of a part such for example a wheel. This sensor comprises a first accelerometer measuring in a first direction and a second accelerometer measuring in a second direction. The accelerometers are arranged in such a way that their measurement directions are not parallel and do not coincide with the axis of rotation of the part. The direction of rotation of the part is then determined by observing the phase difference between the signals emitted by the two accelerometers. This device has the disadvantage that it is necessary to provide two accelerometers.

  This increases the cost of the sensor used.

  The present invention therefore aims to provide a method for determining the direction of rotation of a wheel. This then makes it possible to determine the right / left location of this wheel. Preferably, this method will be easy to implement and will not require the implementation of expensive means.

  For this purpose, the invention proposes a method for determining the direction of rotation of a wheel of a vehicle equipped on the one hand with an accelerometer arranged in such a way that its measurement axis is not parallel to the axis. rotation of the wheel and secondly means for transmitting a signal.

  According to the invention, this method comprises the following steps: in a first angular position of the wheel, emission of a signal comprising information relating to the variation of the measurement of the gravity effected by the accelerometer, in a second angular position of the wheel, distinct from the first position, emission of a signal comprising information relating to the variation of the measurement of the gravity effected by the accelerometer, measurement of a physical quantity representative of the angular position of the the wheel during the emission of each signal, and correlation between the angular position of the wheel obtained by measuring the physical quantity and the direction of variation of the gravity to determine the direction of rotation of the wheel.

  This method makes it possible to determine in a simple manner the direction of rotation of a wheel without having to use complex and expensive means. This method proposes in summary to emit two signals at predetermined angular positions. These signals indicate the variations of the field of gravity. By receiving two successive signals, it is not known to which angular position correspond the first and second signals. This ambiguity is raised by the measurement of a parameter depending on the angular position of the wheel. Knowing then the variations of the gravity in two known given points, one can deduce the direction of rotation of the wheel and thus the right / left location of this one (if one knows in which direction the vehicle moves).

  To obtain a better signal from the accelerometer, the measurement axis of the accelerometer is advantageously oriented tangentially to the rotation of the wheel.

  In order to better distinguish the two angular positions at which the emissions are produced, these two angular positions are preferably substantially diametrically opposite one another.

  An embodiment of the invention proposes that the emission of the signal is performed when the acceleration is zero along the axis of measurement of the accelerometer. Signal transmissions are then made when the accelerometer is substantially at the top dead center and at the bottom dead center of its trajectory.

  A method according to the invention is for example made at each start of the vehicle. In this way, it is possible to detect whether the position of the wheels has been changed.

  In the case of determining the direction of rotation of several wheels, each emitted signal advantageously comprises an identifier specific to the corresponding wheel.

  The signals transmitted are for example received by a central unit. In this case, the measured physical quantity can be the power of the signal received by this central unit. When the central unit receives the signals emitted by the four wheels of the vehicle, it can be provided that prior to the implementation of the method a calibration is performed so as to determine eight distinct power levels corresponding to two power levels for each of the four wheels. Then, the power of the received signal can be used to determine, with the aid of the stored powers, the location and the direction of rotation of the wheel corresponding to the received signal.

  Another embodiment provides that a pressure sensor is associated with the accelerometer, the measured physical quantity is the local pressure just before the emission of the signal and the emitted signal also includes information corresponding to the measured pressure.

  The present invention also relates to a device for determining the direction of rotation of a vehicle wheel, characterized in that it comprises: an accelerometer arranged on the wheel of the vehicle so that the accelerometer measures according to a distinct direction the axis of rotation of the wheel, means for determining the direction of variation of the acceleration of the gravity on the measurement axis of the accelerometer, transmitting means for transmitting a signal indicating said direction of variation; means for measuring a physical quantity representative of the angular position of the wheel during the transmission of the signal; and a central unit intended to determine the direction of rotation of the wheel as a function of the signals received and results obtained when measuring the physical quantity.

  Such a device allows the implementation of a method as described above.

  In such a device, when the wheel has a valve, then the accelerometer is preferably mounted at this valve.

  In a device as described here, the central unit comprises for example means for measuring the power of a received signal.

  A device according to the invention may further comprise a pressure sensor, and the accelerometer and the pressure sensor are for example mounted within the same housing.

  Details and advantages of the present invention will become more apparent from the following description given with reference to the accompanying diagrammatic drawings in which: FIG. 1 schematically shows an accelerometer arranged on a wheel in four positions of this wheel, and FIG. 2 shows the signal emitted by this accelerometer according to the direction of rotation of the wheel.

  Figure 1 shows very schematically a wheel 2 of a vehicle equipped with an accelerometer 4. The scale between the wheel 2 and the accelerometer 4 is not respected. In addition, four accelerometers 4 are represented on the wheel 2, whereas the latter has only one. This figure shows in fact the four main positions that can take the accelerometer 4 when the wheel 2 rotates.

  Wheel 2 is a conventional wheel of a vehicle. The latter is equipped with a tire pressure monitoring system. This wheel 2 thus also comprises a pressure sensor, not shown, associated with the accelerometer 4. These elements, as well as other electronic components, such as an RF signal transmitter (for Radio Frequency) are mounted in a housing, it itself attached to the wheel 2. Conventionally, the wheel 2 comprises a valve (not shown) allowing in particular the introduction of air into the tire. In the present embodiment, said housing (not shown in the figures) is mounted on this valve. It is understood, however, that this housing could be fixed in any appropriate place of the rim.

  The accelerometer 4 is an accelerometer of known type. Any type of accelerometer can be used here. In the present case, for reasons of cost, it is possible to choose an accelerometer measuring only in one direction, this measurement direction being symbolized in FIG. 1 in each of the positions represented by an arrow 6. Reference 6 is also used thereafter to designate the measurement direction of the accelerometer 4. This accelerometer 4 is associated here with electronic means for determining whether the result of the measurement performed by the accelerometer is increasing or decreasing. Here, for example, a derivation of the signal provided by the accelerometer 4 is carried out.

  The accelerometer 4 is mounted on the wheel 2 so that its measurement direction 6 is not coincident with the axis of rotation of the wheel 2. In the preferred embodiment shown in FIG. 1, the measurement direction 6 is tangential to the rotational movement of the wheel 2.

  For each of the four positions of the accelerometer 4 shown in Figure 1, a vertical arrow 8 represents the Earth's gravity. Note then that for the upper and lower positions of the accelerometer 4 shown, the component of the Earth's gravity on the measurement direction 6 is zero. For the position of the accelerometer shown on the left of FIG. 1, the accelerometer 4 measures the totality of the Earth's gravity and the measurement direction 6 is oriented in the same direction as the gravity while for the position of the accelerometer represented on the right of FIG. 1, the accelerometer 4 measures the totality of the earth's gravity and the measurement direction 6 is oriented in the opposite direction to the gravity. Thus, the two upper and lower positions represented by the measurement 0 are associated with the value 0, at the position represented on the left of FIG. 1 and the position represented on the right of FIG. 1 with the value -1. Between these four positions, the component of Earth's gravity varies sinusoidally in the direction of measurement.

  On each of the wheels of the vehicle under consideration, the accelerometer is mounted in the same way. For example, it is possible to provide a coding mounting system to guarantee the correct positioning of the accelerometer. Providing the mounting of the accelerometer 4 on the valve of the wheel 2 facilitates its proper orientation.

  In FIG. 1, it has been assumed that when the valve of the wheel is facing an observer, the measuring direction 6 of the accelerometer 4 is oriented tangentially with respect to the wheel 2 and towards the right when the valve is located. in low position, close to the ground.

  FIG. 2 represents the variations of the measurement of the accelerometer 4 according to whether the wheel 2 rotates in the direction indicated by the arrow 10 of FIG. 1 or in the direction indicated by the arrow 12 of FIG.

  The direction of rotation indicated by the arrow 10 corresponds to the direction of rotation of a right wheel of the vehicle when that advances (the valve is in front of the observer). In this case, the measurement made by the accelerometer varies as indicated on the top curve of FIG. 2, the progression on this curve being indicated by an arrow 10 '.

  The direction of rotation indicated by the arrow 12 corresponds to the direction of rotation of a left wheel of the vehicle when the advance. In this case, the measurement made by the accelerometer varies as indicated on the top curve of FIG. 2, the progression on this curve being indicated by an arrow 12 '.

  In FIG. 2, the points of the curves corresponding to the measurement made when the accelerometer 4 is at the top dead center are indicated by the letter A while the points of the curves corresponding to the measurement made when the accelerometer 4 is at bottom dead center are identified by the letter B. It is thus noted on the curves of Figure 2 that for a right wheel of the vehicle, when the accelerometer 4 is at the top dead center, the signal measured by this accelerometer is a decreasing signal while for the left wheel this signal is increasing. Similarly, for a right wheel of the vehicle, when the accelerometer 4 is at the bottom dead center, the signal measured by this accelerometer is an increasing signal while for the left wheel this signal is decreasing.

  In a preferred embodiment, the invention proposes, when determining the right / left position of a wheel, to emit a signal (symbolized in FIG. 2 by an arrow in the form of a flash) when the measurement carried out by the accelerometer passes through O. The emitted signal then comprises an identifier ID code corresponding to the wheel concerned and an indication, symbolized by a rising or falling arrow, indicating the direction of variation of the measurement made by the accelerometer. This last information can be coded for example on a bit.

  A central unit (not shown) receives this signal. In order for this central unit to be able to determine whether the received signal emanates from a left wheel or a right wheel, it is sufficient to determine whether the signal was transmitted when the accelerometer 4 was at the top dead center or at the bottom dead center. .

  One embodiment of the invention provides this information by analyzing the power of the signal received by the CPU. Since the obstacles (in particular metal) between the dead center A top of a wheel and the antenna of the central unit are not the same as those between the bottom dead center B of the same wheel and said antenna , the attenuation of the same signal emitted from the top dead center of a wheel and the bottom dead center of this same wheel is not the same. The power of the signal received by the central unit reflects the variation of this attenuation. Thus, depending on the power of the received signal, it is possible to determine whether the signal has been sent from a top dead center A or from a bottom dead center B. This is shown in FIG. 2 by a thicker transmission arrow in B than in FIG. in A. Different process variants can be envisaged here. For example, it is possible to determine in advance eight distinct power levels, two levels for each of the four wheels. In this way, by measuring the average power of several identical signals (same identifier and same direction of variation of the component of the gravity) received successively, it is possible to determine at which position the signals were emitted, that is to say from which wheel and also from the top dead center or the bottom dead center.

  It is also conceivable to determine the direction of rotation of a wheel, and therefore its location right / left (it is assumed here that the vehicle is moving forward), by analyzing the power of two successive signals that will have the same identifier ID but the directions of different variation. In general, the signal corresponding to the top dead center is more attenuated (therefore less powerful) than that corresponding to the bottom dead center. By comparing the two powers, it is thus possible to determine the position corresponding to each of the transmissions. Of course, for each vehicle and each wheel of this vehicle, the power variations between the emissions corresponding to the top dead centers and those corresponding to the low dead points are determined beforehand.

  It is possible to provide a learning of the different powers, or variation of power, of the signals received by the central unit during the manufacture of the vehicle. Such learning can take place during rolling tests which are generally performed at the end of the assembly line of motor vehicles.

  In the example above, the power of the received signal is used to determine if a signal has been transmitted from a bottom dead center or a top dead center of the wheel. Another physical quantity can be used to determine the position of the accelerometer during transmission.

  As indicated above, an application of the method of determining the direction of rotation of a wheel relates to the tire pressure monitoring systems. In such a case, the accelerometer 4 described above is associated, as also described, with a pressure sensor which is placed in the corresponding tire.

  In a tire of a wheel of a vehicle, when the latter rolls, the pressure is not uniform. This pressure is slightly greater at the bottom dead center, where the air is compressed due to the crash of the tire, than at the top dead center.

  The present invention then proposes to measure the pressure in the tire during the emission of the RF signal. The result of the measurement made is then joined to the transmitted signal. The central unit which receives the signal can thus determine if this signal was emitted while the sensor was at the top dead center or at the bottom dead center.

  In the present illustrative example, assume the accelerometer mounted as described above with reference to Figure 1. A first signal is emitted when the accelerometer 4 measures a zero acceleration. This accelerometer 4 is therefore at the top dead center or at the bottom dead center. Likewise, a second signal is emitted during the next zero measurement of the accelerometer. These two signals contain the same identifier ID. The first signal indicates that the measured acceleration is decreasing while the second signal indicates increasing acceleration. The signals also include a pressure indication. In this example it is assumed that the first measured pressure is less than the second. We know that the first signal was sent from the top dead center. Taking into account the decay of the accelerometer signal at top dead center, the signal curve of the accelerometer corresponds to the first curve of FIG. 2 and the direction of rotation of the wheel is that corresponding to the arrow 10. concerned wheel is therefore a right wheel.

  Those skilled in the art will readily deduce from this reasoning how to analyze the different acceleration and pressure measurement results to determine the direction of rotation of the corresponding wheel and thus also its right / left location.

  The determination of the right / left location of the wheels may for example be performed at each start of the vehicle. To be sure that the vehicle moves forward, this determination can be implemented for example only from a predetermined speed threshold.

  As can be seen from the foregoing, the present invention can be implemented with a very simple device. It is enough to associate with a pressure sensor an accelerometer measuring in a single direction. Simple electronic means used to analyze the accelerometer signal and to interpret the received signals then make it possible to determine the direction of rotation of the wheel and thus its right / left location. In addition, the implementation of the method is simple and does not require complex adjustments.

  In the method described above, signals giving information on the measurement made by the accelerometer are emitted at two distinct points, determined in advance and each corresponding to a given angular position of the wheel. To then determine the direction of rotation of the wheel, a physical quantity is measured. This physical quantity is representative of the angular position of the wheel.

  The present invention is not limited to the preferred embodiments described above by way of nonlimiting examples of method and device. It also relates to all variants within the scope of those skilled in the art within the scope of the claims below.

Claims (13)

  1. Method for determining the direction of rotation of a wheel (2) of a vehicle equipped on the one hand with an accelerometer (4) arranged in such a way that its measurement axis (6) is not parallel to the axis of rotation of the wheel (2) and secondly means for transmitting a signal, characterized in that it comprises the following steps: in a first angular position of the wheel (2), transmission a signal comprising information relating to the variation of the measurement of the gravity made by the accelerometer (4), - in a second angular position of the wheel (2), distinct from the first position, transmission of a signal comprising information relating to the variation of the measurement of gravity performed by the accelerometer (4), - measurement of a physical quantity representative of the angular position of the wheel (2) during the transmission of each signal, and correlation between the angular position of the wheel (2) obtained by the measurement of the large ur physical and the direction of variation of gravity to determine the direction of rotation of the wheel.   2. Method according to claim 1, characterized in that the measurement axis of the accelerometer 4 is oriented tangentially to the rotation of the wheel (2).   3. Method according to one of claims 1 or 2, characterized in that the emissions are carried out in two angular positions which are substantially diametrically opposite one another.   4. Method according to one of claims 1 to 3, characterized in that the emission of the signal is performed when the acceleration is zero along the axis of measurement (6) of the accelerometer.   5. Method according to one of claims 1 to 4, characterized in that it is performed at each start of the vehicle.   6. Method according to one of claims 1 to 5, characterized in that each transmitted signal also comprises an identifier (ID) specific to the corresponding wheel.   7. Method according to one of claims 1 to 6, characterized in that the transmitted signals are received by a central unit, and in that the measured physical quantity is the power of the signal received by the central unit.   8. Method according to claim 7, characterized in that the central unit receives the signals emitted by the four wheels (2) of the vehicle, in that prior to the implementation of the method a calibration is carried out so as to determine eight distinct power levels corresponding to two power levels for each of the four wheels, and in that the power of the received signal is then used to determine, with the aid of the stored powers, the location and the direction of rotation of the corresponding wheel. to the received signal.   9. Method according to one of claims 1 to 6, characterized in that a pressure sensor is associated with the accelerometer (4), in that the measured physical quantity is the local pressure just before the transmission of the signal , and in that the transmitted signal also comprises information corresponding to the measured pressure.   10. Device for determining the direction of rotation of a wheel (2) of a vehicle, characterized in that it comprises: an accelerometer (4) disposed on the wheel (2) of the vehicle so that accelerometer measuring in a direction distinct from the axis of rotation of the wheel, means for determining the direction of variation of the acceleration of the gravity on the measurement axis of the accelerometer, transmitting means for transmitting a signal indicating said direction of variation; means for measuring a physical quantity representative of the angular position of the wheel during the transmission of the signal; and a central unit intended to determine the direction of rotation of the wheel. function of the signals received and the results obtained during measurement of the physical quantity.   11. Device according to claim 10, characterized in that the wheel (2) comprises a valve, and in that the accelerometer (4) is mounted at the level of this valve.   12. Device according to one of claims 10 or 11, characterized in that the central unit comprises means for measuring the power of a received signal.   13. Device according to one of claims 10 to 12, characterized in that it further comprises a pressure sensor, and in that the accelerometer (4) and the pressure sensor are mounted within a single housing.