WO2010079179A1 - Method for determining the movement state of a vehicle - Google Patents

Abstract

The invention relates to a method for determining the movement state of a vehicle either parked or in motion, wherein said method operates in a given speed range of the vehicle and includes the following steps: providing, in at least one wheel of the vehicle, a device including at least one magnetic sensor with a maximum sensitivity axis; measuring, at the terminals of the sensor, a signal S1 representative of the time variations of the magnetic flux; applying a digital filtering of the signal S1 by the sliding average of a given number of consecutive acquisition points of the signal S1; determining the sliding average of the signal S1 thus filtered; comparing said sliding average to a transition threshold between an immobile state and a mobile state of the vehicle; and determining the movement state of the vehicle. A second method for carrying out the above is available if at least two sensors are available. The integral or the sum of the product of signals S1 and S2 is compared with a defined threshold at regular intervals.

Description

 METHOD AND DEVICE FOR DETERMINING THE DISPLACEMENT CONDITION OF A VEHICLE

Field of the invention

The invention relates to a method for determining the state of movement of a vehicle, when stopping or taxiing. It also relates to a system for determining the state of movement of a vehicle, when stopped or while driving.

Technological background

More and more motor vehicles have, for security purposes, monitoring systems comprising sensors mounted on each of the wheels of the vehicle, dedicated to the measurement of parameters such as pressure or temperature of the tires of the wheels, and intended to inform the driver of any abnormal variation of the measured parameter.

These monitoring systems usually comprise a sensor placed in each wheel with a microprocessor and a radio frequency transmitter, and a central unit for receiving the signals emitted by the transmitters, with a computer integrating a radio frequency receiver connected to an antenna. .

Conventionally, such monitoring systems comprise a displacement sensor adapted to be mounted with the measurement sensor. This sensor is intended to provide information corresponding to the state of movement of the vehicle, namely stopping or rolling of the latter.

Such information is very useful for distinguishing two types of operation of the monitoring systems. These two types are distinguished in particular by the frequency of transmission of the signals from the measurement sensors towards the central unit.

In addition, it is desirable that the transmission frequency is reduced in the operating mode corresponding to the stopping of the vehicle, to reduce the consumption of the system in general and more particularly the wear of the batteries supplying the onboard microprocessors. This reduction in the emission frequency also contributes to reducing pollution of the environment surrounding the vehicle, and consequently the risk of interferences between vehicles in the vicinity.

[0007] Conventionally, the displacement sensors used may take the form of unreliable and expensive rotation sensors (in English "roll switch"), or accelerometers comprising, for example, strain gages of the deformable beam type; these devices are very current consuming and also expensive.

The present invention aims to overcome these drawbacks and is intended to provide a method and a device for determining the state of movement, at a standstill or while driving, of a vehicle without requiring the use of a sensor. conventional displacement, and therefore without the disadvantages associated with the presence of said sensors.

EP 1 669 221 A1 discloses an autonomous device intended to be carried by a wheel to locate the right or left position of the wheel in a vehicle comprising:

- two magnetic sensors with axes of maximum sensitivity;

means for measuring a signal at the terminals of each of the magnetic sensors, capable of delivering two periodic signals out of phase with each other and representative of each of the temporal variations of magnetic flux detected by the magnetic sensors during the rotation of the wheel; and

- A calculation unit programmed to determine, from the phase shift between the two periodic signals, the direction of rotation of the wheel.

Knowing the direction of rotation of the wheel allows to deduce, the direction of movement of the vehicle being known elsewhere, the right or left location of the wheel.

This device is such that the axes of maximum sensitivity of the two magnetic sensors are intended to be placed in the tire and wheel assembly in a secant plane relative to the axis of rotation of the tire and wheel assembly, and offset relative to each other in this secant plane, a predetermined angle.

The two sensors of this device detect the global magnetic field surrounding them, composed of the Earth's magnetic field plus the environmental magnetic field vehicle. This vehicle environmental magnetic field is the resultant of a set of vehicle fields created by the presence of electrical or magnetic equipment embedded in the vehicle as well as by the metal parts close to wheel arches such as brake calipers and connecting elements. on the ground.

However, there are points of the Earth and directions of movement of the vehicle for which the contribution of the Earth's magnetic field measured by the two sensors of the previous device becomes negligible relative to the contribution of the environmental magnetic field.

The document EP 1 669 222 describes a device and a method for determining the state of displacement of a vehicle for delivering a signal representative of the variations of the values of the magnetic field detected by at least one sensor, and to provide information concerning the state of mobility of the vehicle, namely while driving or at a standstill. This device does not take into account the noise and signal disturbances that are found both at a standstill and during taxiing, and which often make it very difficult to detect a phase or transition zone between a state and stopping and a moving state of the vehicle.

Another object of the invention is to provide a method of detecting a change of state of movement of a vehicle that is both fast and accurate.

[0016] Finally, another object of the invention is to provide a method of detecting a change in the state of displacement of a vehicle which takes into account the noise related to the signals and which allows a detection level of a large reliability. Description of the invention

For this purpose, according to a first embodiment, the invention provides a method for determining the state of displacement, at a standstill or while driving, of a vehicle, said method operating in a range of speeds. vehicle data and comprising the following steps:

in at least one wheel of the vehicle, a device comprising at least one magnetic sensor with a maximum sensitivity axis;

- Measuring across the magnetic sensor signal S 1 representative of temporal variations of magnetic flux; applying a digital filtering of the signal Sl by moving average over a number of successive acquisition points of the signal Sl given; said number of successive acquisition points of the given signal S1 being at least three and being at most less than the number of measurement points of the signal S1 during a wheel revolution at the maximum speed of said given operating speed range; determining the sliding average of the signal S1 thus filtered;

comparing this sliding average with a threshold of transition between a stationary state and a mobile state of the vehicle; and

- determine the state of movement of the vehicle.

This method uses simple means to implement, is inexpensive and provides a high level of reliability. It has the advantage of being able to be used when only one sensor is available. This method effectively filters signal noises and disturbances, allowing reliable detection of the transition threshold between a stationary and mobile state of a monitored vehicle. It can be easily activated or deactivated as needed.

The fact that the number of successive acquisition points of the signal Sl used to perform the sliding average of the signal S 1 is strictly less than the number of measurement points of the signal S 1 during a wheel revolution at the maximum speed of the operating range of the process ensures that when the vehicle is in operation Sliding average motion of the signal Sl follows the evolution of this signal while filtering the noise at higher frequencies.

According to a second embodiment, the invention provides a method for determining the state of displacement, at a standstill or while driving, of a vehicle, said method operating in a given speed range of the vehicle and comprising the following steps:

placing in at least one wheel of the vehicle a device comprising at least two magnetic sensors each with an axis of maximum sensitivity;

- Measuring across the magnetic sensors signals S1 and S2 representative of the temporal variations of magnetic flux;

calculate the integral of the product of signals S1 and S2;

comparing the sum obtained to a transition threshold between a stationary state and a mobile state of the vehicle; and

- determine the state of movement of the vehicle. This low cost process is easily implemented and provides a high level of reliability. The calculations used allow a clear distinction between a stationary and mobile state of a monitored vehicle.

Advantageously, the transition threshold is adjusted as a function of the minimum speed of the given vehicle speed range. This range of vehicle speeds corresponds to the demands of car manufacturers. Usually, this range corresponds to an operation of the detection method of 20 to 120 Km / h. The link with the speed can be easily obtained from the amplitude of the signal.

To enhance the robustness of the assembly, one can add in the vehicle near a wheel equipped with a device, a magnetic field generator, such as a magnet.

It can also enhance the magnetization of one of the metal parts of the vehicle, near a wheel equipped with a device. Advantageously, there are two magnetic sensors in each device at different azimuths and in similar positions relative to the axis of rotation of the wheel.

By "similar" means substantially superposable positions by rotation about the axis of rotation of the wheel. The positions of the two axes of maximum sensitivity may, however, not be strictly superimposable in particular due to the manufacturing dispersions of the devices and their implementation in the tire and wheel assembly. The magnitude of the offsets allowed by this vocabulary of "similar" is a few degrees of inclination relative to each other.

In cases where more than one sensor is used, the two magnetic sensors are intended to be arranged at different azimuths. As a result, the signals from the two sensors will be related not only to their rotation in the Earth's magnetic field but also to the fact that they successively see the same local magnetic field.

Advantageously, each device comprises a filter element adapted to eliminate the components of the two signals of frequencies less than or equal to a given frequency.

The contribution due to the Earth's magnetic field is periodic and frequency identical to that of the rotation of the wheel. On the other hand, the signals coming from the magnetic dipoles of the vehicle (local field) are more localized; their major frequency components can thus be greater than twice the rotation frequency of the tire and wheel assembly. As a result, the filtering element introduced into the device greatly reduces the contribution to the signals related to the earth's magnetic field, which allows robust exploitation of the signals related to the environmental magnetic field.

As previously described in EP 1 669 221, the signals measured at the terminals of each sensor have a phase shift between them. But the signals analyzed are mainly related to the contribution of the environmental magnetic field of the vehicle and not the Earth's magnetic field and this phase shift is mainly related to the temporal amplitude of the circumferential offset of azimuths between the two sensors.

The filter element may be a filter having a highpass type cutoff frequency greater than the rotation frequency of the tire.

Such a filter may be an adaptive filter, depending on the speed of rotation of the wheel.

The adaptive filter can be looped back to the amplitude of the analyzed signal. This loopback mode has the advantage of being easier to implement than a loopback on the frequency of rotation of the wheel.

According to a particularly simple and economical embodiment, the filtering element comprises a high-pass type cutoff frequency greater than the target operating frequency range of the device. For example, for passenger tires of usual dimensions and for a target operating range of 20 to 120 km / h, the frequency range of rotation is then of the order of 3 to 17 Hz and the filter must have a cutoff frequency greater than 17 Hz.

The filtering element also preferably comprises a low-pass type filter of the order of 100 to 200 Hz. This low-pass filter makes it possible to reduce the noise of the analyzed signals.

[0036] Advantageously, the two magnetic sensors are intended to be placed on the wheel at substantially the same distance from the axis of rotation of the assembly.

This allows the two coils to be sensitive to flux variations of the same environmental field.

The two magnetic sensors may have their two axes of maximum sensitivity combined or be intended to be placed in the wheel with their axes of maximum sensitivity oriented circumferentially. In these two very similar embodiments, thanks to the presence of the filter element, the signals after filtering are mainly related to the components of the environmental magnetic field normal to the axial direction. These embodiments may be particularly useful in certain vehicle configurations.

According to a preferred embodiment, the two magnetic sensors are intended to be placed in the tire and wheel assembly so that the two axes of maximum sensitivity are oriented parallel to the axis of rotation of the wheel.

The fact of orienting the two axes of maximum sensitivity of the two magnetic sensors parallel to the axis of rotation implies that regardless of the orientation of the Earth's magnetic field, this field has virtually no influence on the amplitude. signals measured at the terminals of the two magnetic sensors. The amplitude of the signals is then solely related to the environmental field surrounding the device.

Preferably, the circumferential distance between the centers of the two magnetic sensors is between 1 and 8 cm. A distance of less than 1 cm no longer makes it possible to determine with sufficient precision the phase difference between the two signals with the usual acquisition frequencies and a distance greater than 8 cm makes it difficult to integrate the two magnetic sensors in a single housing.

The devices may in particular be adapted to be fixed on an inflation valve of the wheel.

The invention also provides a system for determining the state of displacement, when stopped or while driving, of a vehicle, comprising:

for each wheel, a device comprising: at least one magnetic sensor with a maximum sensitivity axis;

Measurement means at the terminals of the magnetic sensor of a signal Sl representative of the temporal variations of magnetic flux; A computing unit capable of supplying stationary vehicle information or rolling vehicle information according to the characteristics of said signal;

• an emitter ;

- in the vehicle, a central unit with a receiver and a processing unit.

This system is characterized in that the computing unit of each device is adapted to implement the previously described method to determine the state of movement of the vehicle.

Preferably, the magnetic sensor of a device has its axis of maximum sensitivity arranged parallel to the axis of rotation of the wheel.

The invention also provides a system for determining the state of displacement, when stopped or while driving, of a vehicle, comprising:

- for each wheel, a device comprising:

• two magnetic sensors with axes of maximum sensitivity;

Measuring means at the terminals of each of the magnetic signal sensors S1 and S2 representative of the temporal variations of magnetic flux;

• a computing unit, able to provide a stationary vehicle information or a vehicle information while driving according to the characteristics of said signals;

• an emitter ; - in the vehicle, a central unit with a receiver and a processing unit.

This system is characterized in that the two magnetic sensors of a device are arranged at distinct azimuths and similar positions relative to the axis of rotation of the wheel, in that the computing unit of each device is able to calculate the integral of the product of signals S1 and S2; comparing the sum obtained with a transition threshold between a stationary state and a mobile state of said vehicle to determine the state of displacement of the vehicle. Brief description of the drawings

The invention will be better understood thanks to the description of the drawings according to which:

- Figure 1 shows schematically a perspective view of a wheel of the prior art, equipped with a sensor system integral with the inflation valve;

- Figure 2 shows schematically a sectional view of a wheel of the prior art equipped with a sensor system integral with the inflation valve;

- Figure 3 schematically shows a perspective view of an inflation valve and a housing integral with the valve for receiving sensors; FIG. 4 schematically represents a view from above of a vehicle equipped with devices according to the invention;

- Figure 5 schematically shows a side view of a wheel equipped with a device according to the invention, mounted on the right side of a vehicle;

- Figure 6 schematically shows a side view of a wheel equipped with a device according to the invention, mounted on the left side of a vehicle;

FIG. 7 represents the axial component of the residual point magnetic field measured on a vehicle rear axle;

- Figures 8 and 9 each show a block diagram of an exemplary device according to the invention; FIG. 10 shows the signals S1 and S2, the result of S1 * S2 and the sum of S1 * S2, for a stationary vehicle; and

FIG. 11 shows the signals S1 and S2, the result of S1 * S2 and the sum of S1 * S2, for a vehicle traveling at low speed.

These figures illustrate the embodiment of a device in which the magnetic sensors have their directions of maximum sensitivity oriented axially, but also apply to other embodiments claimed. They are given for a purely illustrative purpose and have no limiting character. Description of embodiments

In what follows, the term "wheel" means a set consisting of a wheel in the particular sense with its disk and its rim and a tire mounted on the rim of the wheel.

Figure 1 shows a perspective view of a wheel 20 of the prior art, equipped with an inflation valve 30 and a housing 40 for receiving sensors. For the sake of clarity, the tire is not shown.

FIG. 2 represents a sectional view of another wheel 20 of the prior art, comprising a rim 22, a disk 24, a tire 10. This wheel is equipped with an inflation valve 30 and a housing 40 provided for receiving sensors. The trace of the median plane 50 of the tire, that of the circumferential or tangential direction X at the housing 40 as well as that of the axis of rotation YY 'of the wheel are also represented.

Figure 3 schematically shows a perspective view of an inflation valve 30 and a housing 40 integral with the valve and for receiving sensors; such a housing is known, for example, from EP 1 106 397. It can be adapted to receive a device 70 according to the invention.

FIG. 4 schematically represents a view from above of a vehicle 80 whose wheels 91 to 94 are equipped with devices according to the invention comprising, depending on the embodiment, one or two magnetic sensors sensitive to the environmental magnetic field. vehicle, and, in the case of the embodiment with two sensors, the latter being arranged so that their axes are parallel and circumferentially offset.

[0056] Figure 5 shows a wheel 91 mounted on the front position of the right side of the vehicle 80 which advances in the direction 120, indicated by an arrow. A device 70 according to the invention is mounted in a housing 40 and fixed on the assembly 91. The device comprises two magnetic sensors 131 and 132 sensitive to the environmental magnetic field vehicle P. Each magnetic sensor comprises a coil with a soft iron core. The two coils 131 and 132 are arranged with their two axes, respectively 141 and 142, oriented parallel to the axis of rotation of the tire and wheel assembly YY '. The two coils are thus sensitive substantially only to the component according to YY 'or axial component of the environmental magnetic field vehicle PY. The two axes 141 and 142 are also circumferentially offset, that is to say in the direction XX ', by a distance d. The corresponding azimuth offset α is illustrated in FIG. 6. The phase shift is related to the angle α (α), corresponding to the angle formed by the two centers of the coils with respect to the axis of rotation. For example, an offset of 2 cm from a circumference of 100 cm represents an angle of 2/100 * 360 ° = 7.2 °.

Each coil is a passive magnetic sensor that produces a signal proportional to the variation of the magnetic flux that passes through the Faraday-Lenz law. The signal generated by each coil is ampler as the magnetic flux variations through the coil are stronger and faster: its amplitude also depends on the rotational speed of the coil.

FIG. 6 shows a wheel 93 mounted on the front position of the left side of the vehicle 80 which advances in the direction 120. The same device according to the invention is mounted in a housing 40 and fixed in the same way on the together 93.

Figure 7 shows the component oriented along the YY 'axis of the environmental magnetic field vehicle measured with a magnetometer fixed on the rim of a wheel. This curve is measured in the case of a rear axle of a BMW 323i vehicle.

The magnetometer is attached to the rim of the wheel in a position very close to that of a device attached to the valve of this wheel. It can be seen that the vehicle environmental field for the rear axle of this particular vehicle and appreciated at the level of a box attached to an inflation valve has a peak-to-peak amplitude of the order of 9 μT.

Figure 8 shows a first block diagram of the device 70 according to the invention. For measuring and processing the potential difference across each coil 131, 132, the device comprises an amplification module 42 and a shaping module 44 including a filter having a high-pass cutoff frequency equal to 19 Hz and a comparator. The device further comprises a computing unit 46 to which is directed the shaped signal.

The computing unit may perform several treatments successively or alternatively, as described below.

The signal must be decrypted in order to obtain an indication of a movement of the vehicle, even at low speed. A suitably processed signal allows, with a threshold value, to distinguish an area in which the vehicle is considered stationary, and an area in which the vehicle is considered moving.

FIG. 10 illustrates an example of signals S1 and S2 obtained by sensors 37 and 38 when the vehicle is stationary. This figure makes it possible to observe that, when the vehicle is stopped, the signals S1 and S2 are random, of normal distributions and often substantially centered around the value 0. If the value is not centered on the 0, it is then possible to apply a filter or any other solution to eliminate the offset.

Once the vehicle in motion, the magnetic field variations during the rotation of the wheel show signals of similar shape slightly out of phase and no longer random. Thus, when stopped, as the signals are random, they oscillate in a disordered manner around zero. As soon as one rolls, their oscillation becomes structured around zero. As a result, a simple average calculation of the signals does not make it possible to distinguish the two cases, since a zero value is obtained for the two situations.

The computing unit 46 makes it possible to carry out two approaches, according to two main embodiments. The first embodiment implements adaptive filtering. According to this mode, a sliding average is determined on a few points, for example 3 or 10 points or more, the acquisition frequency of the signals Sl being of the order of 270 points per second. This average acts as a low pass filter. We can then easily determine whether or not the vehicle is traveling at a low speed, comparing the values found to a predefined threshold.

The number of successive acquisition points of the signal Sl to perform the sliding average of the signal Sl is at least three and is at most less than the number of measurement points of the signal S 1 during a wheel spin at the speed maximum of the operating speed range of the process.

By way of example, for a target operating range of 20 to 120 Km / h, a rotation frequency of a wheel at 120 Km / h of 17 Hz and a signal acquisition frequency Sl of 270 Hz, the maximum number of points given is less than 270/17 ie 15.9; in this example, the given number of points can be between 3 and 15.

It is also possible to extend the speed range of the vehicle to cover the entire range of possible speeds, in particular by reducing the number of points of the sliding average.

Thus, according to this first mode, by applying a low pass filter, the high frequencies related to noise are attenuated. When stopped, the signal is almost zero. In motion, even at low speed, the signal becomes structured, in connection with the rotation. Depending on the type of vehicle and the configuration of the equipment used, it is easy to determine the number of points required and set a threshold value to delimit the two zones. A threshold crossing indicates that the vehicle is moving. Preferably, for greater certainty, the threshold crossing is validated only if the latter is exceeded a given number of times, in a given time. This avoids the cases of crossing due to external disturbances or a non-significant displacement of the vehicle.

According to this embodiment, when the vehicle reaches a higher speed, the sliding average acting only on a few points, it follows the signal and remains above the transition threshold. The advantage inherent in this embodiment is related to the fact that it can be used with a single sensor.

If there are at least two sensors, a second embodiment is provided. According to this second mode, the computing unit 46 determines the integral of the product of the signals S1 and S2 of the two sensors:

M = Σ S1 * S2

The result M obtained is compared to a predefined threshold. This threshold is based on the vehicle and the configuration of the equipment used.

Figure 10 shows an example of evolution of the sum of S1 * S2 at the stop of the vehicle. Randomly negative and positive signed values remain low. Thus, M has order values of magnitude 10 ² . In this example, if a transition threshold of 250 or 300 is provided, the value of M is always lower than the threshold.

On the other hand, as soon as the vehicle is in motion, as shown in FIG. 11, the signals S1 and S2 become coherent. The sum of the products of S1 * S2 increases regularly, since the signals S1 and S2 are of the same sign. According to this example, M has order values 10 ³ , a factor 10 with respect to FIG. 10, with the vehicle stationary.

It is observed that the threshold value of 250 or 300 is quickly crossed, indicating a displacement of the vehicle.

A calculation is preferably carried out at regular intervals, for example every second. If the value of M persists beyond the prescribed threshold for a given time, the vehicle is declared in motion. This avoids possible errors related to parasites during the start of the vehicle.

The precise and rapid determination of the state of displacement of the vehicle allows efficient and effective management of the equipment used, particularly from the energy point of view. In fact, the periods of stopping the vehicle are used to reduce or even interrupt the supply of components that are not required. This device is suitable for passenger tires of standard dimensions with an operating range between 20 and 120 Km / h. For these tires, the corresponding operating frequency range is 3 to 17 Hz. cut on the order of 20 Hz, with a filter adapted to the conditions of the vehicle effectively suppresses the influence of signals of frequency equal to the rotation frequency and thus the parasitic influence of the Earth's magnetic field.

The strengthening of the local magnetic field is easy to perform and is very effective. It can also be done by reinforcing the magnetism of one of the metal parts of the vehicle floor connection, near the wheel well.

FIG. 9 shows a variant of the device 70. In this variant, the shaping module 44 comprises an adaptive filter comprising a variable high-pass cut-off frequency as a function of the rotational speed of the assembly. pneumatic and wheel. A loop 48 connects the computing unit 46 to the signal shaping module 44 to indicate that the adaptive filter takes into account the speed determined by the measurement unit. Preferably, the shaping module is looped back to the amplitude of the signal, this amplitude is directly a function of the speed. It is therefore very easy to determine the rotational speed from the measured amplitude.

The information is transmitted by radio to a central unit embedded in the vehicle. The central unit retains this information for a given time, usually of the order of 15 minutes.

According to the second embodiment, in the case where two sensors are provided, the device 70 also makes it possible, from the analysis of the sign of the phase shift between the two signals S1 and S2, to determine the direction of rotation of the the wheel and deduce from this direction of rotation and the direction of movement of the vehicle, determined by any other method known per se, the right or left position of the tire and corresponding wheel assembly. Preferably, the calculation unit of the device according to the invention determines the sign of the phase shift between the two signals from the two coils by intercorrelation of these two signals.

In order to reliably operate in a method for determining the location of a wheel, the device according to the invention is fixed on the same side of the wheel relative to the vehicle for all sets. at 94 whose positioning must be determined. It does not matter whether it is always the outside or always the inside of the vehicle, provided it is always the same side. Attaching the device to an inflation valve is a particularly simple way of ensuring that all devices are on the outside of the vehicle.

The direction of movement is an important parameter for identifying the left or right location of the wheels: a reversal of the direction causes an inversion of the phase shift of the signals of the two coils 131 and 132. The determination of the direction of the movement can be using a known device (for example, the EP 0 760 299 ball device), using existing signals in the vehicle (reversing lamp supply) or from the speed of the vehicle (which can be determined from the frequency of the signals measured by each of the two coils 131 and 132): by deactivating the determination of the location when the speed is below a certain limit (for example, 30 Km / h ), it is certain that the vehicle is moving forward when the determination is made. The methods described in this document thus make it possible not only to determine the side of the vehicle on which a wheel is located but also the precise position before or after the vehicle.

The method and the device according to the invention are particularly useful for use with the spare wheel of the vehicles. When this is not used, the method and the device according to the invention are not likely to cause false indications of movement of the vehicle, like certain types of devices of the prior art, for example piezoelectric systems. too sensitive to the vibrations of the vehicle. Indeed, the spare wheel not used is not rotating, even when the vehicle moves, unlike the other wheels of the vehicle: the absence of rotation avoids signal variations that could lead to threshold crossing. When used, the spare wheel, like the other wheels of the vehicle, to detect the state of movement of the vehicle.

Finally, thanks to the device, it is possible to locate the location of the newly installed spare wheel, as described above.

The invention is not limited to the examples described and shown and various modifications can be made without departing from the scope defined by the appended claims.

Claims

A method for determining the state of motion, when stopped or while driving, of a vehicle, said method operating in a given speed range of the vehicle and comprising the following steps: in at least one wheel of the vehicle, a device comprising at least one magnetic sensor with a maximum sensitivity axis; - Measuring across the magnetic sensor signal S 1 representative of temporal variations of magnetic flux; applying a digital filtering of the signal Sl by moving average over a number of successive acquisition points of the signal Sl given; said number of successive acquisition points of the given signal S1 being at least three and being at most less than the number of measurement points of the signal S1 during a wheel revolution at the maximum speed of said given operating speed range; determining the sliding average of the signal S1 thus filtered; comparing this sliding average with a threshold of transition between a stationary state and a mobile state of the vehicle; and - determine the state of movement of the vehicle. 2. A method of determining the state of displacement, when stopping or rolling, of a vehicle, said method operating in a given speed range of the vehicle and comprising the following steps: placing in at least one wheel of the vehicle a device comprising at least two magnetic sensors each with an axis of maximum sensitivity; - Measuring across the magnetic sensors signals S1 and S2 representative of the temporal variations of magnetic flux; calculate the integral of the product of signals S1 and S2; comparing the sum obtained to a transition threshold between a stationary state and a mobile state of the vehicle; and - determine the state of movement of the vehicle. 3. Method according to any one of claims 1 and 2, wherein is carried out an adjustment of the transition threshold as a function of the minimum speed of said given speed range of the vehicle. 4. Method according to any one of claims 1 to 3, wherein is added in the vehicle, near a wheel equipped with a device, a magnetic field generator. 5. Method according to any one of claims 1 to 3, wherein reinforcing the magnetization of one of the metal parts of the vehicle, close to a wheel equipped with a device. 6. Method according to any one of claims 1 to 5, wherein there is in each device two magnetic sensors at different azimuths and in similar positions relative to the axis of rotation of the wheel. 7. The method of claim 6, wherein the circumferential distance between the centers of the two magnetic sensors is between 1 and 8 cm. 8. Method according to one of claims 6 and 7, wherein the two magnetic sensors have their axes of maximum sensitivity substantially circumferentially oriented. 9. Method according to any one of claims 6 to 8, wherein the two magnetic sensors have their axes of maximum sensitivity substantially oriented parallel to the axis of rotation of the wheel. 10. System for determining the state of motion, when stopped or while driving, of a vehicle, comprising: for each wheel, a device comprising: At least one magnetic sensor with a maximum sensitivity axis; Measurement means at the terminals of the magnetic sensor of a signal Sl representative of the temporal variations of magnetic flux; A computing unit capable of supplying stationary vehicle information or rolling vehicle information according to the characteristics of said signal; " an emitter ; in the vehicle, a central unit with a receiver and a processing unit; characterized in that the computing unit of each device is adapted to implement the method according to any one of claims 1 and 3 to 5 to determine the state of displacement of the vehicle. 11. System according to claim 10, wherein the magnetic sensor of the device has its axis of maximum sensitivity arranged parallel to the axis of rotation of the wheel. 12. System for determining the state of displacement, when stopped or while driving, of a vehicle, comprising: - for each wheel, a device comprising: • two magnetic sensors with axes of maximum sensitivity; Measuring means at the terminals of each of the magnetic signal sensors S1 and S2 representative of the temporal variations of magnetic flux; • a computing unit, able to provide a stationary vehicle information or a vehicle information while driving according to the characteristics of said signals; • an emitter ; in the vehicle, a central unit with a receiver and a processing unit; characterized in that the two magnetic sensors of a device are arranged at distinct azimuths and similar positions relative to the axis of rotation of the wheel, in that the computing unit of each device is able to calculate the integral of the product signals S1 and S2 and to compare the sum obtained at a transition threshold between a stationary state and a mobile state of said vehicle to determine the state of displacement of the vehicle.