EP2143080A1

EP2143080A1 - Method for detecting an identification object in a vehicle

Info

Publication number: EP2143080A1
Application number: EP07858043A
Authority: EP
Inventors: Eric Leconte; Stephane Violleau
Original assignee: Valeo Securite Habitacle SAS
Current assignee: Valeo Comfort and Driving Assistance SAS
Priority date: 2006-12-22
Filing date: 2007-12-21
Publication date: 2010-01-13
Anticipated expiration: 2027-12-21
Also published as: WO2008077929A1; FR2910751B1; FR2910751A1; ES2440254T3; US20090315682A1; EP2143080B1; US8773240B2

Abstract

The invention relates to a method for detecting an identification object in an area (ZO) around an antenna device. The invention is characterised in that it comprises the following steps in which: a calibration signal (S_CAL) is emitted in the direction of the antenna device in order to determine a control power (PR); a functional signal (S_FONC) corresponding to the control power (PR) is emitted in the direction of the antenna device, such that the antenna device emits a pre-determined magnetic field; the magnetic field (Br) received by the identification object, corresponding to the emitted magnetic field, is measured and compared with a nominal magnetic field (B0); and, depending on the result of said comparison, it is determined if the identification object is located inside the area (ZO) around the antenna device. The invention is suitable for motor vehicles.

Description

METHOD OF DETECTING AN IDENTIFICATION OBJECT

IN A VEHICLE

Field of the invention

The present invention relates to a method for detecting an identification object in an area around an antenna device (s) and a detection system implementing the detection method.

It finds a particular application for a motor vehicle equipped with a hands-free detection system.

State of the art

According to a known state of the art, there is a method of detecting an object of identification such as a badge which acts as a receiver-transmitter to know if it is inside or outside of the passenger compartment of the vehicle. If the badge is inside the vehicle, the user is allowed to start the vehicle.

The detection of the badge is based on a magnetic field emitted from a constant power from a voltage regulation of the antenna device.

Such a solution has the disadvantage of being difficult to implement.

Indeed, the antenna device being supplied with voltage by the vehicle battery voltage, at each variation of this voltage (due to different actions such as a vehicle start, or an engine stop, etc.), it is necessary to readjust to allow the antenna device to transmit at a constant power.

Object of the invention The object of the invention is therefore more particularly to enable detection of an identifying object with a simpler solution.

It therefore proposes a method of detecting an identification object in an area around an antenna device (s), characterized in that it comprises the steps of:

- output a calibration signal to the antenna device (s) to determine a setting power,

- transmitting a functional signal towards the antenna device (s) corresponding to the adjustment power so that the antenna device (s) emits a determined magnetic field,

measuring the magnetic field received by the identification object corresponding to the emitted magnetic field and comparing it with a nominal magnetic field, determining whether the identification object is in the zone around the antenna device (s) according to this comparison.

Thus, as will be seen in detail below, there will be a detection of an identifying object through the calibration of the antenna device (s) and a comparison with a nominal magnetic field without the need for voltage regulation.

According to non-limiting embodiments, the method according to the invention has the following additional features.

- The calibration signal is not intelligible by the identification object. This allows the identification object to quickly receive the functional signal thereafter.

The process comprises a further step according to which: when sending the calibration signal, a current flowing in the antenna device is measured, and

the measured current is compared with an initial current so as to determine the adjustment power. Thus, the calibration signal depends on a current measurement that is simple to implement.

- A power is set with a given duty cycle voltage. This regulation is simple to implement. In addition, this makes it possible to compensate for variations in the supply voltage of the antenna device (s).

- The voltage is a symmetrical signal. This makes it possible to suppress the even-numbered harmonics in the measured current signal and thus obtain a more accurate measurement of the current.

- The duty ratio is 1/3. This makes it possible to suppress the multiple harmonics of three in the measured current signal and thus obtain a more accurate measurement of the current.

- The voltage is generated by means of a power stage with full-bridge or half-bridge control. This allows for a greater range of currents.

- The calibration signal is triggered according to a particular event. This makes it possible to regularly have an updated calibration signal and therefore subsequently a regular and accurate measurement of the magnetic field emitted by the antenna device (s).

According to a first variant, the particular event is a vehicle access. This makes it possible to take into account the variations in the magnetic field emitted due to external events such as temperature variations. According to a second variant, the particular event is a battery voltage variation. This makes it possible to take into account these variations in the calibration.

- The method comprises an additional initial step of writing a fixed threshold value in the identification object. This makes it possible to obtain a fixed reception field from which the identification object can receive signals from the antenna device (s) and communicate with an associated control device.

- The fixed threshold value is a function of a nominal magnetic field. This allows the identification object to respond to a signal transmitted from the antenna device (s) when it is in the area corresponding to the nominal magnetic field. .

- The area around the antenna device (s) is defined by the nominal magnetic field.

- The area around the antenna device (s) corresponds to a vehicle interior. Thus, it is determined whether the identification object is in the passenger compartment of the vehicle to allow a start of the vehicle.

According to a second object, the invention relates to a system for detecting an identification object in an area around an antenna device (s), comprising a control device, an antenna device (s) and an identification object, characterized in that: - the control device is able to:

- output a calibration signal to the antenna device (s) to determine a setting power, - issue a functional signal to the antenna device (s) corresponding to the adjustment power so that the device antenna (s) emits a determined magnetic field, determining whether the identification object is in the area around the antenna device according to a comparison made between the magnetic field received by the identification object and a nominal magnetic field, The object of identification is able to measure the received magnetic field corresponding to the emitted magnetic field and to compare it with the nominal magnetic field.

According to a third object, the invention relates to an antenna device (s) adapted to cooperate with an identification object, characterized in that it is able to:

receive a calibration signal corresponding to a determined initial power,

receiving a functional signal corresponding to a setting power determined so as to emit a determined magnetic field, and

- Transmit the functional signal to the identification object, the latter receiving a magnetic field depending on the magnetic field emitted by the antenna device (s).

According to a fourth object, the invention relates to a control device adapted to cooperate with an antenna device (s) and with an identification object, characterized in that it comprises a signal transmitter for:

- output a calibration signal to the antenna device (s) to determine a setting power, and

- Transmit a functional signal to the antenna device (s) corresponding to the set power determined so that the antenna device (s) emits a specific magnetic field.

According to a non-limiting embodiment, the control device further comprises a signal receiver for receiving a response from the identification object according to a comparison made between a received magnetic field and a nominal magnetic field.

According to a non-limiting embodiment, the comparison is performed by the identification object.

According to a fifth object, the invention relates to a motor vehicle comprising a passenger compartment in which is arranged a control device according to any one of the preceding characteristics, an antenna device (s) characterized according to any one of the preceding characteristics, the two devices being able to cooperate with an identification object.

Brief description of the figures

Other features and advantages of the present invention will be better understood from the description with reference to the drawings, given as non-limiting examples, among which:

- Figure 1 is a top view of a vehicle with a detection system implementing the method according to a non-limiting embodiment of the invention;

- Figure 2 is a representative diagram of a reception of an identification object detected by the method according to a non-limiting embodiment of the invention;

FIG. 3 is another representation of this threshold threshold for receiving an identification object detected by the method according to a non-limiting embodiment of the invention; - Figure 4 is a diagram of a non-limiting embodiment of the method according to a non-limiting embodiment of the invention;

- Figure 5 is a non-limiting mode of a communication used between an identification object and an antenna device in the context of the method of Figure 4; FIG. 6 represents a frequency spectrum of a current flowing in an antenna device and measured as part of the method of FIG. 4;

FIG. 7 represents a first embodiment of a voltage signal applied to the antenna device in the context of the method of FIG.

Figure 4 and an associated current frequency spectrum;

FIG. 8 represents a second embodiment of a voltage signal applied to the antenna device in the context of the method of FIG. 4 and an associated frequency of current spectrum; FIG. 9 represents a third embodiment of a voltage signal applied to the antenna device in the context of the method of FIG. 4 and an associated current frequency spectrum;

FIG. 10 represents a magnetic field in space whose component corresponds to a magnetic field emitted as part of the method of FIG. 4;

FIG. 11 represents an explanatory cycle-current diagram diagram of certain steps performed by the method according to FIG. 4;

FIG. 12 represents a non-limiting embodiment of a detection system implementing the method of FIG. 4; FIG. 13 represents a non-limiting embodiment of a power stage included in the detection system of FIG. 12;

FIG. 14 represents a nonlimiting example of a voltage signal generated by the power stage of FIG. 13 and an associated current frequency spectrum; and - Figure 15 is a diagram showing ranges of currents used in the process of Figure 4.

DETAILED DESCRIPTION OF NON-ITERITIVE EMBODIMENTS OF THE INVENTION FIG. 1 shows a vehicle V equipped with a signal transmission-reception device DER for controlling an antenna device A, and the antenna device A comprising, in a nonlimiting example, a plurality of antennas, here so-called external antennas AX and so-called internal antennas AI, all these antennas cooperating with a receiver-transmitter ID, all forming a detection system described below.

In the nonlimiting example of the Figure, five external antennas AX are shown, four AXl, AX2, AX3 and AX4 are located outside the passenger compartment VH of the vehicle V, here on the door handles, and an AX5 in the VC's rear bumper. In addition, two internal antennas AI1, AI2 are located in the passenger compartment VH, here at the front and rear of the vehicle. Each antenna is powered by low-frequency alternating current by the DER transceiver and emits a Be magnetic field, named Bel for indoor antennas and BeX for external antennas.

By means of their respective emitted magnetic field B, the external antennas AX make it possible to detect whether the receiver-transmitter ID is located near the vehicle V, in a nonlimiting example at a distance of less than 1.5 mm, whereas the antennas AI interiors detect whether the receiver-transmitter ID is in the passenger compartment VH of the vehicle.

The receiver-transmitter ID, in this application, is in a non-limiting example, an identification object ID carried by a user of the vehicle V, for example a badge, a key, a keyfob called "keyfob" etc. The example of the identification badge will be taken as an example in the following description.

Using the alternating current, the antennas A communicate with the ID badge by transmitting data by emitting a low frequency signal BF and the ID badge responds by emitting an RF radio frequency signal. In a non-limiting example, the low frequency signal BF is around 125 kHz and the radio frequency RF signal is around 433 MHz. We can go down to 2OkHz for the low frequency signal BF or go to GigaHz for the RF radio frequency signal according to the frequency bands available for different countries (315MHz for Asia, 868Mhz for some European countries or 915MHz in America etc.). Depending on the response, the antennas A determine whether the badge ID is allowed to open the doors of the vehicle, or whether it is allowed to start the vehicle. Note that in a non-limiting example, for the badge ID is allowed to open the doors, the user must for example touch a doorknob. For this purpose, the handles include appropriate detectors. The external antennas AX make it possible to determine a first zone of communication with the badge ID to authorize a vehicle access. This zone is defined by the magnetic field emitted by said antennas. External AX antennas must therefore guarantee at least a minimum distance from which the ID badge is authorized to access the vehicle. The internal antennas AI make it possible to determine a second zone ZO for communication with the badge ID to authorize a start. This zone is defined by the magnetic field emitted by the internal antennas. The internal antennas AI must therefore guarantee a fixed zone from which the ID badge is authorized to start the vehicle, this zone being the passenger compartment VH of the vehicle V.

Note that in practice, the magnetic field emitted by these indoor antennas AI has a greater coverage than the passenger compartment VH but is limited by the metal carcass of the passenger compartment VH of the vehicle V and overflows through the openings of the windows.

The detection of the ID badge in the second zone ZO is based on the fact that the badge is initialized with a fixed threshold value SO according to a received magnetic field BO called nominal field. Without limitation, this fixed threshold value SO is a power PO corresponding to the nominal field BO. It will be recalled that a magnetic field received Br by the badge ID is a function of the emitted magnetic field Be of the antenna device A, the latter defining the zone ZO around it representative of its magnetic field Be, which has also been called a zone Communication. FIG. 2 illustrates the position of the badge ID with respect to an antenna A of the antenna device as a function of the magnetic field Be of this antenna A and therefore of the corresponding received magnetic field Br.

It can be seen that the further the ID badge is located far from an antenna A emitting a magnetic field emitted Be, the lower the magnetic field received Br corresponding is weak. When the ID badge is at the same location as the antenna A, the received magnetic field Br is theoretically equal to the emitted magnetic field Be.

The nominal magnetic field BO therefore corresponds to the nominal communication zone ZO in which an ID badge can communicate with an antenna A and the transmission-reception device DER.

When the ID badge is outside this zone ZO (the magnetic field received Br is less than the nominal magnetic field received BO), the ID badge does not respond to the signals sent by the antenna device A or sends an RF response radio voluntarily wrong. This means that it is located outside the passenger compartment VH of the vehicle. In the opposite case, it responds by emitting an RF radio frequency signal. It should be noted that this nominal magnetic field BO is set so as to avoid the parasitic magnetic fields Bb originating from the radio disturbances as illustrated in FIG. 2 and its value is greater than the value of the parasitic magnetic fields.

Figure 3 illustrates an example of positioning the ID badge with respect to an indoor antenna AI1.

The antenna AI1 emits a magnetic field Be at a power of 15 Watts. The fixed threshold value SO is set at PO = 5 Watts. The ID badge, when in the ID1 position, receives a magnetic field BrI whose power Pl is 4.5 Watts and therefore less than the fixed threshold SO; so it's outside of the zone ZO defined by the threshold SO will therefore not communicate with the antenna AI1 and the transmission-reception device DER.

The ID badge, when in the ID2 position, receives a magnetic field Br2 whose power P2 is 5.5 Watts and therefore greater than the fixed threshold SO; it is therefore located in the ZO communication zone and will therefore communicate with the antenna AI1 and the transmission-reception device DER.

Thus, the method of detecting the ID badge to know if it is in the communication zone ZO of an antenna, in particular an internal antenna AI, is carried out in the following manner as illustrated in FIG. 4.

In an initial step 0), during the manufacture of the ID badge, the fixed threshold value SO is written in a memory of the ID tag, for example a rewritable type EEPROM memory.

Then, when using the ID badge and the antenna device A, that is to say in operating mode,

In a first step 1), a calibrating signal S CAL, also called a calibration frame, is sent in the direction of the antenna device A at an initial power PI determined for determining an adjustment power PR for the antenna device A. such signaling is illustrated in Figure 5.

In a non-limiting embodiment, the calibration signal S CAL is triggered according to a particular event. In a non-limiting example, the particular event is a vehicle access. Indeed, a vehicle access is representative of a change in the environment of the antenna device A, a variation of temperatures (due for example to different seasons), which influences the antenna device components and consequently causes a variation of its impedance Z and thus of its magnetic field emitted Be. In another nonlimiting example, the particular event is a variation of supply voltage, here the battery voltage Ubat (which may vary after an engine start or engine stop for example). This makes it possible to take into account these variations in the calibration, these variations affecting the current flowing in the antenna device. These variations of battery voltages are thus compensated, since in this case the current Irm is measured after a battery voltage variation.

The purpose of this step is therefore to take into account the variations of the impedance Z of the antenna device A in the determination of the magnetic field emitted by the antenna device A and consequently in the determination of a power of PR setting to be applied to the antenna device A.

This takes into account the impedance variations Z that appear during the use of the antenna device (s) in the vehicle, so during its operation.

It will be noted that the calibration signal S C AL is unintelligible by the identification object ID. Thus, although the identification object ID receives it, it does not respond to this signal S CAL. This avoids the badge an additional activation-deactivation period to receive this signal. Thus, the ID badge will receive faster data included in the S_FONC functional signal that it will receive thereafter.

Thus, in a first substep la), an initial power is determined

PI, to send the calibration signal S CAL.

The initial power PI is obtained by means of a calibration voltage UC of initial duty cycle α1 corresponding to a theoretical initial current Ith.

It will be noted that this theoretical initial current Ith is determined experimentally by vehicle tests. Its value varies according to the type of vehicle V. In a non-limiting embodiment, this voltage is square. This avoids energy dissipation in the power stage for applying the voltage described below. Indeed, there is a heat energy consumption only during transitions phases unlike a typical sinusoidal voltage where consumption is significantly higher. . This stage of power does not heat too much.

In a second substep Ib), when sending the calibration signal S CAL, the actual current Irm flowing in the antenna device A is measured. In fact, although an initial power PI corresponding to at the theoretical initial current Ith, because of the impedance Zr of the antenna device A, the current flowing in said device is in practice not equal to the theoretical initial current Ith. The measurement of the current Irm flowing in the antenna device A can be carried out in a simple manner by a peak amplitude detector C described below. This current Irm is an alternating current whose frequency spectrum comprises harmonics h. In FIG. 6, the harmonics of rank 1 to 5 are represented in a simplified and nonlimiting example.

In a nonlimiting embodiment, the antenna device A is tuned to the transmission frequency (the frequency being for example 125 kHz). This makes it possible to emit a larger magnetic field in amplitude at the transmission frequency, and to have a bandpass filter FL. The bandpass filter FL thus makes it possible to reduce the amplitude of the harmonics h (except for the harmonic of rank 1).

Indeed, on transmission, on the side of the antenna device A, the value of the current Irm flowing in the antenna device A is equal to the sum of the harmonics h which are present in the passband of the filter included in the Antenna device A. Depending on the selectivity of the filter, all harmonics will be available if the filter is broadband as shown in FL1 in FIG. 6, or only a part of the harmonics if the filter is narrow band such as represented in FL2 in Figure 6. At the emission therefore, the value of the emitted field Be is a function of this current Irm with harmonics h.

At the reception, on the ID badge side, the value of the current Irm which is taken into account is equal only to the harmonic hl of rank 1 called fundamental. Indeed, the received magnetic field Br (and consequently the fixed threshold value SO) corresponds to the magnetic field emitted Be at the fundamental value only and not at the sum of the harmonics.

It is therefore necessary to precisely determine the power emitted on the harmonic hl of rank 1 to enable emitting a transmitted magnetic field Be corresponding precisely to the nominal field BO and thus to the fixed threshold SO of the ID badge. It is therefore necessary to measure the current Irm so as to eliminate as much as possible the harmonics other than the fundamental h 1.

This is done by means of the initial cycle duty UC calibration voltage α1 which makes it possible to obtain the initial power PL

When the calibration voltage UC is any square signal, all the harmonics of the measured current Irm may be present as illustrated in Figure 6.

In a first non-limiting embodiment, the calibration voltage UC is a symmetrical voltage. As can be seen in Figure 7, in this case the even-order harmonics of the measured current Irm have been suppressed. As can be seen, the voltage UC is symmetrical with respect to the point PT. The symmetrical CPU voltage will make it possible to obtain precise generation and precise measurement of the initial power PI corresponding to the harmonic hl of rank 1 by suppressing parasitic currents due to other harmonics.

Indeed, during a frequency representation, a harmonic of rank n is represented by the term a _n cosnωt + b _n sinnωt. The voltage UC is an odd function, ie f (-x) = -f (x), its development in Fourier series therefore only includes sine terms, the coefficients a _n being zero.

So, knowing that Cn = j J f (x) e ^"Jnωx dx and Cn = ₂ (an-jbn) we get Cn = j (2E / πn) sin (nπαl) .sin (n (π / 2)) and bn = (4E / πn) .sin (nπα1) .sin (n (π / 2))

with ω = 2π / T, with T the period and E the amplitude of the supply voltage Ubat of the antenna device.

The Fourier series corresponding to the symmetrical voltage signal UC is therefore equal to: f (x) = Σ (4E / πn) .sin (nπα1) .sin (n (π / 2)). Sin nωx, where n = 1, ..., ∞ either

f (χ) = Σ (4E / (π (2p + 1))) sin ((2p + 1) πα1) .sin ((2p + 1) (π / 2)). sin (2p + 1) ωx , with p = 0, ..., ∞ which gives the spectrum with the harmonics in Figure 7.

The value of the fundamental hl is given by: hl = (4E / π) .sin παl. sin ωx

Moreover, it will be noted that the fact of having a square voltage avoids energy dissipation in the transistors of the power stage P. In fact, there is a heat energy consumption only during the transition phases, unlike a typical sinusoidal voltage where the consumption is significantly higher. This power stage P does not heat too much. It will be noted that the value of the adjustable duty cycle α1 makes it possible to adjust the value of the initial power PL

Thus, the symmetrical square voltage makes it possible, on the one hand, to adjust the initial power transmitted PI to a desired value corresponding to the desired communication zone ZO (and thus to accurately generate the transmitted power PI) and on the other hand to obtain an accurate measurement of the actual transmitted power PI corresponding to the effective received power of the ID badge because the harmonics of even rank are suppressed.

In a second nonlimiting embodiment, the calibration voltage UC comprises a duty cycle of 1/3 which corresponds to an offset of π / 3 of the voltage signal UC. As can be seen in Figure 8, in this case the multiple rank harmonics 3 of the measured current Irm have been suppressed.

Note that the two embodiments can be combined. In this case, as can be seen in Figure 9, there remains only harmonics of rank 1 and 5, the latter being negligible.

Thus, a precise measurement of the current Irm flowing in the antenna device A is obtained. The measured current Irm is therefore in this case representative of the amplitude of the fundamental of the emitted magnetic field.

Therefore, it is possible to deduce the initial power transmitted PI (and thus the emitted magnetic field Be) by the antenna device A corresponding precisely to the received power Pr, knowing that the emitted magnetic field Be is proportional to the measured current Irm.

It will be recalled that, in a manner known to those skilled in the art, a magnetic field B comprises three components in an orthogonal space x, y, z as illustrated in FIG. 10 which are as follows.

B _μ = (Ae Im / 2πd ³ ) * cos θ, B _θ = (Ae Im / 4πd ³ ) * sin θ, and

Bφ = 0. with Ae the effective surface of an antenna through which the magnetic field B, d the distance which allows a measurement of the magnetic field B from the center of the antenna.

It is also recalled that Ae = N _w * A * μ _rod with N _w the number of turns in the antenna _, A the cross section of the ferrite of the turns, and μ _rod the apparent permeability of the ferrite.

It should be noted that the calibration voltage UC can be obtained by means of an H-bridge power stage P with full bridge control described below.

In a third substep Ic), the measured current Irm is compared to the theoretical initial current Ith. The difference will make it possible to determine the real impedance Zr of the antenna device A and consequently to determine the adjustment power PR to be applied to the antenna device A.

It will be recalled that to obtain a zone ZO around the antenna device A corresponding to the passenger compartment of the vehicle VH, a transmitted field Be is determined corresponding to a power PR. This field that we want to obtain whose value is known therefore corresponds to a known current Iv. To supply the antenna device A with this known and desired current Iv, it is necessary to adjust the power PR of said antenna device taking into account its impedance Zr. The adjustment power PR is adjusted by means of a functional voltage UF of adjustment duty cycle α2.

In a fourth sub-step Id), a duty cycle α2 is thus determined.

The calculation of the duty ratio α2 is deduced in the following manner. We have Irm = (Ubat * sin (αlπ)) / Zr, where Zr = (Ubat * sin (αl π)) / Irm and Iv = (Ubat sin (α2 π)) / Zr where sin (α2π) = (Zr * Iv) / Ubat = (Ubat * sin (αlπ) * Iv) / (Iτm * Ubat)

= sin (αl π) * (Iv / Irm) where α2 = (1 / π) * Arcsin (sin (αlπ) * (Iv / Irm)) [1]

It may be noted that in practice, in the calculation [1] of the duty ratio α2, the actual impedance Zr of the antenna device A no longer intervenes.

In a first nonlimiting embodiment, the adjustment duty ratio α2 is calculated by means of a microprocessor of the transmission-reception device DER described below.

In a second simpler and faster embodiment, the duty cycle α2 is defined based on a pre-filled correspondence table (not shown) using the formula sin (αl π) / sin (α2 π) = Irm / Iv [2]. In this table, at each difference between the measured current Irm flowing in the antenna device during the sending of a calibration signal S CAL and the theoretical current Ith, the corresponding cyclic adjustment ratio α2 is recovered in the table. to a desired functional current Iv which takes into account the variations of the impedance Zr of the antenna device A. Such a table is as follows:

With IvI, Iv2, Iv3, etc., the different values of the desired current Iv, Irml, Irm2, Irm3, etc., the various values of the measured current Irm flowing in the antenna device A and α21 π _... α2 ₂₁ . ..α2 ₃₁ etc. ... the different corresponding duty cycle values. The application of the formula [1] or again The choice of the adjustment duty cycle α2 in this correspondence table is equivalent to using a curve CZ representative of the actual impedance Zr to determine the duty cycle α2 to be applied to the device. antennas A, as illustrated in the diagram of Figure 11 in a non-limiting example.

The abscissa is represented by the cyclic ratio α and the ordinate by the current I. As can be seen, for a theoretical initial current Ith, an initial duty cycle voltage α1 is applied. The correspondence between this initial cyclic ratio α1 and the theoretical initial current Ith lies on a curve CZth representative of the theoretical impedance Zth of the antenna device A. The actual current Irm flowing in the device is measured at this initial duty cycle α1 . The correspondence between this cyclic ratio α1 and the actual measured current Irm is situated on a curve representative of the real impedance Zr of the antenna device A. Two curves maximum CZrmax and minimum CZrmin of this real impedance Zr are represented. In the example, we took the curve CZmax corresponding to the maximum of the real impedance Zrmax. Finally, for the desired current Iv, the corresponding adjustment cyclic ratio α2 is determined by taking the curve of the real impedance Zr, here CZrmax and making a projection on the abscissa axis.

The adjustment duty cycle α 2 has thus been found to apply the desired functional voltage UF to obtain a desired power PR in the antenna device A. It will be noted that the functional voltage UF can be obtained by means of a stage of FIG. H-bridge power P with full-bridge and half-bridge control described later.

This first calibration step 1) therefore corresponds to a self-calibration of the SYS detection system to determine the adjustment power PR. Indeed, no external measuring device is necessary for this calibration.

Moreover, this auto-calibration is dynamic because it is launched during the operation of the antenna device (s), and not during its development of the antenna device (s) in the factory for example.

In a second step 2), after having sent the calibration signal S CAL, a functional signal S FONC is thus sent, also called a functional frame, in the direction of the antenna device A, as illustrated in FIG.

FIG. 5, to the adjustment power PR determined above so that the antenna device A emits a determined magnetic field Be corresponding to the desired zone ZO and more particularly to the passenger compartment VH in the example taken from the vehicle application.

In a third step 3), the received magnetic field Br is measured by the identification object ID corresponding to the transmitted magnetic field Be of the antenna device A. This measurement is carried out by means of a measurement device of the type RSSI d an amplifier ("Received Signal Strength Indication") well known to those skilled in the art included in the identification object ID.

In a fourth step 4), the received magnetic field Br is compared with the nominal magnetic field BO. This comparison is performed in the identification object ID.

In a fifth step 5), it is determined whether the ID badge is in the zone ZO around the antenna device A according to this comparison. Thus, the ID badge is in the zone ZO around the antenna device A, and therefore inside the passenger compartment VH vehicle, if the magnetic field received Br is greater than the nominal magnetic field BO. The badge ID therefore returns an affirmative response REPOK to a DC control device of the transmission-reception device DER, as illustrated in FIG. 5. The latter therefore authorizes a vehicle start-up for example. On the other hand, the badge ID is located outside the zone ZO, and therefore outside the cockpit VH vehicle, if the magnetic field received Br is less than nominal magnetic field BO. In this case, either the ID badge returns no response, it acts as if it has not received the functional signal S FONC from the antenna device A, or it sends a negative response REPNOK to the DC control device, as illustrated in Figure 5. The latter therefore prohibits any vehicle start for example.

In another variant, whether inside or outside the zone ZO, the badge ID systematically sends a response REP including the result of the comparison.

The method that has been described is implemented by a SYS detection system illustrated in a non-limiting embodiment in FIG. 12 and comprising

a DER transceiver device comprising:

a DC control device, a power stage P,

a device for measuring current C,

a receiver RE of signals for, in particular, receiving a response REPOK, REPNOK of the identification badge ID as a function of the comparison made between the magnetic field received Br and the nominal magnetic field BO.

the antenna device A, and

- a receiver-transmitter, here, the identification badge ID.

Note that according to a non-limiting embodiment, all the elements of the transceiver device DER are on the same electronic card. This allows a faster and more reliable dialogue between these different elements. On the contrary, when these elements are separated, the communication links connecting them can be more easily disturbed and the flow rates of these links can be lower. The identification badge ID is known to those skilled in the art, it is not described here.

The other elements are described in more detail below.

"The antenna device A.

In a first nonlimiting embodiment, the antenna device A is composed of a circuit RL. The latter requires amplifying the supply voltage of the antenna device to allow appropriate magnetic field emission. In a second nonlimiting embodiment, the antenna device A is composed of an RLC circuit. The latter makes it possible from the supply voltage of the antenna device A, which is here the battery voltage Ubat of the vehicle V, to directly amplify the current I flowing in the antenna device A to enable a field emission. magnetic field, without using voltage control unlike the first embodiment. It is therefore a simpler solution to implement to obtain amplification. This RLC circuit also acts as a bandpass filter as seen previously.

• The DC control device includes:

an emitter EM of signals for, in particular:

- send the calibration signals S CAL towards the antenna device A,

- send the functional signals S FONC towards the antenna device A,

transmitting control signals towards the power stage P to supply the supply voltage Ubat to the antenna device A,

a comparator CMP of current Irm, Ith, and a CALC calculation element (for example a microprocessor or an ASIC) making it possible in particular to adapt the cyclic ratios α1 and α2 of the UC and functional calibration voltages UF.

In a non-limiting embodiment, the control device DC may furthermore comprise: the receiver RE of signals for, in particular, receiving a response REPOK, REPNOK of the identification badge ID as a function of the comparison made between the magnetic field received Br and the nominal magnetic field BO.

• The P power stage.

It provides the calibration voltage UC for adjusting the initial power PI and the functional voltage UF for adjusting the setting power PR of the antenna device A.

In a non-limiting embodiment, the power stage P is H-bridge with full-bridge or half-bridge control. It is illustrated in FIG. 13. It comprises in particular four switches S1 to S4. These switches are in a nonlimiting example of the MOSFET transistors.

In order to provide a voltage, the power stage P operates as a full bridge in the following manner. The example is taken for a symmetrical voltage as shown in Figure 7.

- Between intervals tO-tl and t2-t3, either all switches are open, switches S2 and S4 are closed, or switches S1 and S3 are closed, the others being open. The UC voltage is zero.

- Between the interval tl-t2, the switches S1-S4 are closed, the others being open. The UC voltage is positive.

- Between the interval t3-t4, the switches S2-S3 are closed, the others being open. The UC voltage is negative. The two diagonals of the bridge are controlled by two control signals delayed relative to each other by half a period thus making it possible to obtain symmetry.

When the power stage P operates in complete bridge, the obtained voltage makes it possible to obtain a first range of currents Gl = [111 - 112].

The power stage P operates in the following half-bridge manner as illustrated in the example of Figure 14. It will be noted that the switch S4 is always closed. Between the intervals t0-t1 and t2-t3, the other three switches S1-S2-S3 are open, or the switch S2 is closed, the other two S1-S3 being open. UC / UF voltage is zero.

Between the interval t1-t2, the switch S1 is closed, the other two S2-S3 being open. The UC / UF voltage is positive. Or the switch S2 is closed, the other two S1-S3 being open. UC / UF voltage is negative.

When the power stage P operates half bridge, the obtained voltage provides a second range of currents G2 = [121-122] smaller than the first range and in particular twice as small.

Thus, the power stage P is used to obtain the initial power PI via the calibration voltage UC but also the adjustment power PR via the functional voltage UF.

Thus, according to the desired current Iv that one wants to obtain, one uses the power stage P in complete bridge (large range of currents G1) or half-bridge (small range of currents G2).

This makes it possible to obtain a magnetic field Be via the antenna device A regulated according to the desired type of vehicle. In fact, for example for family-type vehicles, a complete bridge will be used to provide a magnetic field emitted Be corresponding to a zone ZO delimiting the passenger compartment VH of this family vehicle, whereas for cut-off vehicles of which the cockpit is smaller, we will use a half bridge to provide a magnetic field emitted Be corresponding to this different and smaller cabin. Thus, thanks to this full-bridge or half-bridge operation, there is a field coverage adapted according to the type of vehicle without changing the RLC circuit in the antenna device A and therefore without having to adapt the resistance R of this circuit. The control device DC will be just programmed according to the vehicle type V to operate the power stage P adequately.

Moreover, it will be noted that for the same vehicle it may also be necessary to have a wide range of currents, for example in the case where there is a large variation of the battery voltage Ubat of the vehicle. Indeed, the adjustment power PR necessary to send the S_FONC functional signals is a function of this battery voltage and the impedance of the antenna device Zr. In order to compensate for the variations of the battery voltage Ubat, the adjustment duty cycle α2 is adjusted appropriately. For example, for a high battery voltage, the power stage P is operated half-bridge, while for a low battery voltage, it is operated full bridge. In order to obtain a continuous range between the two ranges of currents G1 and G2, in a non-limiting embodiment, the duty ratio α2 is in the range [1/6 - 1/2]. This is illustrated in Figure 15 showing a duty cycle-current diagram. On the abscissa is represented the cyclic ratio α, ordinate the current I. On the ordinate, we can see the respective limits 111, 112 and 121, 122 of the two scales G1 and G2. When the cyclic ratio α2 varies in the interval [1/6 - 1/2], we can see that when one operates half-bridge 1 / 2H, one is on the curve CG2 of the second range of current G2. On the other hand, when operating with full bridge H, it is on the curve CG1 of the first range G1. Finally, it can be seen that when switching from half-bridge to full-bridge operation, the range G2 to G1 is continuously changed, that is to say without any jump in current values I. In another embodiment, if the duty ratio α2 varies in the interval [1/6 - α max '] with α max' less than 1/2, as illustrated in FIG. 15, it can be seen that there has a jump in current values when moving from the half-bridge to the full bridge. In this case, some current values can not be taken into account to determine the power of the antenna device A. These are those in the range 122 'and 122 hatched. In the latter mode, to ensure continuity, take the lower limit αmin of the interval less than 1/6.

• The current measuring device C.

In a first embodiment, the current measuring device is a peak amplitude detector. This is a simple way to measure the current. It makes it possible to measure the maximum amplitude of the current, which is sufficient because the disturbing harmonics have been suppressed by the symmetrical control and the duty cycle of 1/3. Thus, this measure will give the value of the fundamental of this current. It is conventionally composed of a diode and a capacitor as shown in Figure 12.

It sends the value of the measured current Im to the calculation member CALC as illustrated in FIG. 12. Of course, other means for measuring the current can be used.

For example, the current measuring device C may be a digital sampling device or else a device which performs a rectification of current and then an average of the rectified current.

It will be noted that the antenna device A comprises one or more antennas. In the nonlimiting example described, it comprises a plurality of antennas as seen above. In this practical case, for each antenna of the antenna device A, the current is regulated in the antenna to obtain a nominal magnetic field BO associated and corresponding to the zone ZO of communication between the badge ID and the antenna. Thus, the ID badge comprises a plurality of fixed threshold value SO, associated with each antenna of the antenna device A.

Note that the example taken has been described with an indoor antenna. It will of course be possible to apply the method to an external antenna if necessary.

Moreover, it should be noted that the examples were taken with an antenna device A transmitting low frequency signals and an identification object ID transmitting radio frequency signals, but of course other examples can be taken with signal transmissions. at other frequencies.

Thus, the invention has the following advantages:

It makes it possible to control the value of the magnetic field emitted by the antenna device A by regulating the power at emission, which makes it possible to obtain a fixed threshold for the identification object and is simpler to manage than it is to manage. a variable threshold for said object;

- By programming the identification object ID with a determined fixed threshold, this makes it possible to avoid radio disturbances and therefore parasitic magnetic fields; Moreover, this threshold is fixed for all the vehicles, which makes it possible to have a universal identification object ID that functions with all the vehicles, the communication area ZO being adapted only by the transmission power Pe and therefore by the current I flowing in the antenna device A; - The power is regulated by means of a duty cycle control which is less expensive than a voltage regulation with fixed duty cycle;

- The duty cycle regulation is based on the current which is more efficient and accurate than a setting according to the battery voltage because the variations of the impedance Zr of the antenna device A are compensated contrary to a solution that would perform a regulation of the supply voltage Ubat; - The symmetrical H-bridge control makes it possible not to emit the even harmonics and consequently to reduce electromagnetic compatibility problems called EMC;

- The symmetrical calibration command with a duty cycle of 1/3 allows precise measurement of the current with a simple measuring device such as the peak amplitude detector;

- Control with a square voltage prevents the transistors of the power stage from overheating;

It makes it possible to obtain a wide range of currents if necessary, for the same vehicle or for different vehicles, without having to adapt the circuit of the antenna device A;

- The calibration step, which makes it possible to determine an adjustment power in order to determine the value of the magnetic field emitted by the antenna device (s), is dynamic because it is done during the operation of the antenna device (s). );

- The dynamic calibration step requires no additional external measuring device, unlike static calibration steps which are done upstream, ie during the mounting of an antenna device (s) ( that is to say during its development) in a vehicle (thus even before the production and sale of the vehicle);

It makes it possible to control the value of the magnetic field emitted by the antenna device when it is used in a vehicle by taking into account the variations of the impedance of the antenna device so as to obtain a fixed threshold for the object of identification; these impedance variations occurring during the use of the antenna device (s);

- The detection system comprising the antenna device (s) and the identification object makes it possible to perform an auto-calibration of antenna device (s) without external measuring device. Of course, the invention is not limited to the described application of the motor vehicle, but can be used in all applications involving a low frequency antenna and an identification object such as a home automation application for example.

Claims

claims

1. A method for detecting an identification object (ID) in a zone (ZO) around an antenna device (s) (A), characterized in that it comprises the steps of:

- transmitting a calibration signal (S CAL) to the antenna device (s) (A) to determine an adjustment power (PR),

- transmitting a functional signal (S FONC) in the direction of the antenna device (s) (A) corresponding to the adjustment power (PR) so that the antenna device (s) emits a determined magnetic field (Be) ,

- measuring the received magnetic field (Br) by the identification object (ID) corresponding to the transmitted magnetic field and comparing it with a nominal magnetic field (BO), - determining whether the identification object (ID) is located in the area around the antenna device (s) (A) based on this comparison.

2. Detection method according to claim 1, characterized in that the calibration signal (S C AL) is unintelligible by the identification object (ID).

3. Detection method according to any one of the preceding claims, characterized in that it comprises a further step in which: - when sending the calibration signal (S_CAL), a current (Irm) circulating in the antenna device (s) (E), and - the measured current (Irm) is compared with an initial current (Ith) so as to determine the adjustment power (PR).

4. Detection method according to any one of the preceding claims, characterized in that a power (PI, PR) is set with a voltage (UC, UF) given cyclic ratio (α1, α2).

5. Detection method according to the preceding claim, characterized in that the voltage (UC) is a symmetrical signal.

6. Detection method according to one of claims 4 or 5, characterized in that the duty cycle (αl) is equal to 1/3.

7. Detection method according to any one of claims 4 to 6, characterized in that the voltage (UC, UF) is generated by means of a power stage (P) with full-bridge or half-bridge control .

8. Detection method according to any one of the preceding claims, characterized in that the calibration signal (S_CAL) is triggered according to a particular event.

9. Detection method according to the preceding claim, characterized in that the particular event is a vehicle access.

10. Detection method according to claim 8, characterized in that the particular event is a variation of battery voltage.

11. Detection method according to any one of the preceding claims, characterized in that it comprises an additional initial step of writing a fixed threshold value (SO) in the identification object (ID).

12. The detection method according to the preceding claim, characterized in that the fixed threshold value (SO) is a function of the nominal magnetic field (BO).

13. Detection method according to any one of the preceding claims, characterized in that the area (ZO) around the antenna device (s) is defined by the nominal magnetic field (BO).

14. The detection method according to any one of the preceding claims, characterized in that the area around the antenna device (s) (A) corresponds to a passenger compartment (VH) vehicle.

15. System for detecting (SYS) an identification object (ID) in a zone (ZO) around an antenna device (s) (A), comprising a control device (DC), a device antenna (s) (A) and an identification object (ID), characterized in that:

the control device (DC) is able to:

determining whether the identification object (ID) is in the area around the antenna device (A) as a function of a comparison made between the magnetic field received (Br) by the object of identification (ID) and a nominal magnetic field (BO),

the identification object (ID) is able to measure the received magnetic field (Br) corresponding to the emitted magnetic field (Be) and to compare it with the nominal magnetic field.

16. Antenna device (s) (A) adapted to cooperate with an identification object

(ID), characterized in that it is suitable for:

- receive a calibration signal (SC AL) corresponding to a determined initial power (PI), receiving a functional signal (S FONC) corresponding to a determined adjustment power (PR) so as to emit a determined magnetic field (Be), and

- Transmit the functional signal (S FONC) to the identification object (ID), the latter receiving a magnetic field (Br) function of the magnetic field emitted (Be) by the antenna device (s) (A).

17. Control device (DC) adapted to cooperate with an antenna device (s) (A) and with an identification object (ID), characterized in that it comprises a signal transmitter (EM) for: - output a calibration signal (SC AL) to the antenna device (s) (A) to determine a control power (PR), and - output a functional signal (S FONC) to the antenna device (s) (A) corresponding to the determined setting power (PR) so that the antenna device (s) (A) emits a determined magnetic field (Be).

18. Control device (DC) according to the preceding claim, characterized in that it further comprises a signal receiver (RE) for receiving a response (REP) of the identification object (ID) as a function of a comparison made between a received magnetic field (Br) and a nominal magnetic field (BO).

19. Control device (DC) according to one of the preceding claims 17 or 18, characterized in that the comparison is performed by the identification object (ID).

Vehicle (V) comprising a passenger compartment (VH) in which is disposed a control device (DC) according to one of the claims.

17 to 19, an antenna device (s) (A) according to claim 16, the two devices (DC, A) being adapted to cooperate with an identification object (ID).