WO2010043357A1

WO2010043357A1 - Method and device for remote control of an operable roof of a vehicle

Info

Publication number: WO2010043357A1
Application number: PCT/EP2009/007315
Authority: WO
Inventors: Alain Brillon; Thierry Raspaud
Original assignee: Continental Automotive France
Priority date: 2008-10-14
Filing date: 2009-10-12
Publication date: 2010-04-22
Also published as: FR2937074B1; FR2937074A1

Abstract

The method of remote control of the opening of an operable roof of a vehicle comprises: ‑ a step (101) in which a remote-control key, movable relative to the vehicle, transmits a first radio signal termed the wake-up signal; ‑ a recurring step (103) in which a transmitter-receiver on board the vehicle transmits a second signal, termed the confirmation signal, in response to the reception by the equipment of the wake-up signal, this confirmation signal being transmitted without modulation; ‑ a step in which the remote control monitors to see whether it is in an authorization zone when it receives the confirmation signal, in which monitoring the remote control measures the electromagnetic field E in the frequency domain of the confirmation signal, at least during the assumed transmission of this confirmation signal, and the measured field is compared with a threshold value S; ‑ a step (104) in which the remote control transmits a third radio signal, termed the correct-distance signal, when the remote control has validated that it is in the range of the confirmation signal; and - a step (105) in which the operable roof is opened in response to the reception by the transmitter-receiver on board the vehicle of the correct-distance signal.

Description

Method and device for remote control of vehicle roof oryrant

The invention relates to the general field of remote control means of vehicle openings, and, more specifically, of automobile sunroof.

In the case of vehicles with a sunroof, it is more and more commonly desired by users, who most often have handsfree key remote controls, to be able to remotely control before entering the vehicle. opening of said sunroof, so as, for example, to lower the temperature in the passenger compartment.

To do this, their key has a sunroof remote control button, and the vehicle has a transceiver paired with the key so as to recognize only the commands from the key of the legitimate user.

These hands-free key devices generally use a detection technique of a beacon, the key, transponder type, near the vehicle. These key-tags emit in the radio frequency band an authentication message in response to a message in the low frequency band transmitted by the vehicle. With respect to these sunroof remote controls, the regulations stipulate that the user must be within six meters of his vehicle in order to operate his remote control. This regulatory provision makes it necessary to be able to estimate with a certain precision the distance between the user and the vehicle.

At the same time, it is clear that for reasons of comfort and efficiency, the coverage area of the remote control must be sufficient, for example of the order of three meters.

A known solution comprises, when actuating the remote control by the user, a transmission by the badge of a wake-up signal in radiofrequency band

(433 MHz). This show has a range of a few meters to a few tens of meters. In response, the vehicle transmits a coded signal at low frequency (around 125

KHz), whose range is therefore reduced in practice to a maximum of a few meters. The badge then emits a correct distance signal if this confirmation signal is received, which can only happen if the badge is near the vehicle. Finally, the vehicle starts opening the roof in response to detecting the correct distance signal.

As we see, it is therefore the badge that detects its proximity to the vehicle and triggers the actual opening of the roof.

In practice, the use of LF low frequencies around 125 KHz by the vehicle transmitter constitutes a strong limit to the detection distance of the key. Indeed, with a transmitter with a power of 15 watts, the maximum detection distance is of the order of 2.5 meters, and each doubling of power of the transmitter increases the detection distance by only 10%. Both for reasons of power consumption and equipment costs or legislation on the maximum powers emitted in LF, it is not possible to exceed a power of about 30 watts for the transmitter especially as some countries limit power at lower values.

The present invention therefore first object to allow use of the remote control at a greater distance from the vehicle. According to another object of the invention, this range increase of the remote control is obtained without increasing the power of the transmitter, and economically. For this purpose, the invention is directed to a method for remote control of opening of a vehicle sunroof, comprising:

a step of transmission by a remote control key, mobile with respect to the vehicle, of a first radio signal, said wake-up signal;

a step of recurrent transmission by a transceiver on board the vehicle of a second signal, said confirmation signal, in response to the reception by the equipment of the wake-up signal;

- A standby step by the remote key to determine if it is in an authorization area A, when said remote key receives the confirmation signal; a step of transmitting by the remote control key a third radio signal, called a correct distance signal, when the remote control key has detected the confirmation signal;

a step of opening the sunroof, in response to the reception by the equipment on board of the vehicle of the correct distance signal; characterized in that

the confirmation signal is transmitted without modulation, ie in CW (Continuous Wave) mode,

the standby step by the remote control key to determine if it is in the authorization area A comprises a measurement of a radio field E1 by the remote control in the frequency domain of the confirmation signal, at least during the assumed transmission of this confirmation signal, and a comparison of the measured field with a threshold value S.

It is understood that it is easier to detect the field level in the frequency band of the confirmation signal, than the content of the signal itself. Consequently, this detection of a field level, without seeking to know if this field characterizes a signal or not, makes it possible to gain 50 centimeters to one meter compared to the prior art, without substantial modification of the transceiver or from tag. Vis-à-vis the previous range of 2 to 2.5 meters, the gain is important.

The choice of the detection of the field level above a predetermined minimum value is facilitated by the use of a signal transmitted without modulation (continuous wave (CW)). Preferably, the wake-up signal is repeatedly transmitted in the form of an RF frame, the confirmation signal is issued in a recurrent manner, slaved to the RF frame of the wake-up signal, each confirmation signal being transmitted for a predetermined duration, so that immediately offset from wake-up signals. According to a preferred embodiment, the confirmation signal is emitted by the vehicle in the low frequency band LF, around 125 KHz.

The correct distance signal is preferably also issued recurrently in the form of an RF frame of correct distance, and comprises an identification code of the remote key and a correct distance code, this code being previously stored in a data processor. of the vehicle.

In order to avoid ambient noise LF which could disturb the distance measurement, the step of detecting the confirmation signal preferably also comprises a measurement of the radioelectric field E2 by the beacon in the frequency domain of the confirmation signal, before or after the transmission of this confirmation signal, and a differential signal / noise measurement.

The measurement of the field before or after the signal CW and its comparison with the measurement during the emission of the signal CW makes it possible to determine an amplitude differential, and to extract a field measurement freed from the background noise, the value of which, when it is greater than a predetermined value S, characterizes a good reception of the confirmation signal. This arrangement improves the detection in the case of very noisy environments.

According to an advantageous implementation, the method further comprises a step of counting by the onboard transceiver the elapsed time T between the start of reception of the wakeup signal and the beginning of reception of the correct distance signal, a step of comparison between this elapsed time T and a previously chosen duration, and a step of stopping the transmission of the confirmation signal, if the elapsed time T is greater than the previously chosen duration.

Advantageously, the method further comprises a step of transmission by the onboard transceiver of a completed opening signal, this signal being transmitted in non-modulation mode (Continuous Wave).

The invention aims, in a second aspect, at a vehicle roof opening remote control device comprising a transceiver on board the vehicle. vehicle, capable of transmitting a detectable confirmation signal over a range of a few meters, by one or more mobile transponder-type transponder remotes paired with the vehicle, able to receive the signals transmitted by the onboard transceiver and to transmit at least two types of signals: - a wake-up signal,

a correct distance signal, in response to the reception of a confirmation signal, characterized in that the confirmation signal, when it is transmitted, is a signal without modulation, in non-modulation mode (Continuous Wave) and in that each remote control comprises means for measuring the intensity of the radioelectric field E emitted by the transceiver in the frequency domain of the confirmation signal, and means for comparing the measured intensity with a threshold value S.

The description and the drawings of a particular embodiment of the invention will make it possible to better understand the aims and advantages of the invention. It is clear that this description is given by way of example, and is not limiting in nature. In the drawings:

• Figure 1 schematically illustrates a top view of a vehicle and its detection zones;

FIGS. 2a and 2b are chronograms of the method according to the invention, in the normal case and in a particular case;

FIG. 3 is a diagram illustrating the logic of the method according to the invention.

The invention is intended to be used for a vehicle 1, in the present embodiment of a motor vehicle, said vehicle 1 having a sunroof 10 with a controllable electric opening mechanism of conventional type and not described right here.

In the present example illustrated in Figure 1, the vehicle 1 is assumed to have a transceiver 2, associated with a data processor 5, embedded in the vehicle 1, and on the other hand, one or more 3-type remote control keys communicating with this transceiver 2. It should be noted that such means are generally present in vehicles comprising a locking system - unlocking openings, key-free hands. These vehicles then constitute an advantageous case of implementation of the invention.

The data processor 5 is connected to the electric opening mechanism of the sunroof 10 which it can therefore control the opening or closing according to, on the one hand, the data received from various sensors, for example but not limited to, the on-board transceiver 2, door opening sensors, a status sensor of the sunroof, and, on the other hand, its programmed logic.

The onboard transceiver 2, of conventional type known to those skilled in the art, uses, in accordance with standards and practices, a frequency band around 125 KHz (LF band, low frequencies) and has a range of a few meters because of its power, typically 15 watts in the present example. It is known that a signal emitted in this frequency band creates a radio field whose amplitude decreases rapidly and regularly with the distance.

According to the invention, the on-board transceiver 2 is adapted to transmit recursively in LF (Continuous Wave) mode a confirmation signal, the frame of which, in the present non-limiting example, is regular and determined for a second time. period Δt previously chosen.

In the example described here, and for economy of means, the keys also act as sunroof remote control, but the method would remain mainly unchanged with remote control devices independent keys. These key-remotes 3 are paired with the vehicle 1 in a conventional manner, and typically by storing an identification code in a memory within the key 3, and sending this identification code when it is activated or automatically on request of the on-board transceiver 2, this identification code is then received and verified by the data processor 5 of the vehicle 1. In the following "legitimate user" is called a user 4 carrying a key - remote control 3 paired with the vehicle 1.

Conventionally, each key-remote control 3 is a pocket device, thin, transponder beacon type, this beacon transmitting radio signals either on command of the carrier, or depending on the signals received. The specific technique of the remote control key 3 and the electronics embedded in the vehicle 1 are outside the scope of the invention. The pairing technique of the remote key 3 and the vehicle 1, is also known and not described in detail here.

These key-remotes 3 conventionally use frequencies in the radio band, around 433 MHz, with a range of a few meters to a few tens of meters. It is clear that other frequency bands for both the remote control keys 3 and the onboard transceiver 2 could be used without modifying the principle of the invention.

In its remote control function of the sunroof 10 of the vehicle 1, a remote control key 3 comprises a remote control actuating button (not shown in the figure), and is adapted to emit, recurrently, at least two types of signals. :

a wake-up signal when the user 4 presses the button sunroof remote control,

a correct distance signal, in response to the reception of a confirmation signal sent by the onboard transceiver 2.

According to the invention, each key-remote control is also able to carry out measurements of the radio-frequency field strength in the frequency range of the confirmation signals, in the present example embodiment around 125 kHz, at the antenna level. of the remote control key 3, and comparisons of these measurements with at least one threshold value S stored in the remote key 3.

The measurement of the intensity of the radioelectric field is carried out by conventional means, the details of which are outside the scope of the present invention. Such means are in fact generally intrinsic to the locking devices - unlocking key-type openings open hands.

Similarly, the comparison of the radio-frequency field measurements and the threshold value is carried out by means known to those skilled in the art, for example processor or dedicated component.

The method according to the invention, illustrated by the timing diagram of FIG. 2a and the diagram of FIG. 3, is concerned with the case where the legitimate user 4 is outside the vehicle 1, mobile with respect to him, and at a distance initially large, for example ten meters, and approaches the vehicle 1. When the user 4, mobile relative to the vehicle 1, actuates the button of his remote key 3, the method comprises a first step 101 transmission by said remote control key 3, of a first radio signal, said wake-up signal, in the RF radio frequency band, this signal comprising an identification code of the remote control key 3. This alarm signal is repeatedly emitted so as to form a control RF frame of conventional type.

In the embodiment described here, and as shown in FIG. 2a, this alarm signal is emitted at regular intervals when the remote control button is pressed, each wake-up signal being transmitted for a predetermined duration Δt1.

Upon receipt of this wake-up signal by the on-board transceiver 2, after verification by the data processor 5 of the vehicle 1 in a step 102 that the remote key 3 is paired with the vehicle 1, by example by comparing the received identification code with a list of authorized codes stored in a memory of the data processor 5, the onboard transceiver 2 transmits in a step 103 a second signal, said confirmation, in response to the reception by the onboard transceiver 2 of the wake-up signal.

This confirmation signal is issued recurrently, controlled by the RF control frame, each confirmation signal being transmitted for a duration Δt2 predetermined. It is understood that if the wake-up signal is emitted regularly, the confirmation signal is consequently also issued regularly.

In the present example, as seen in FIG. 2a, the emission of the confirmation signal forms a frame that is immediately shifted in time with respect to the wake-up signal transmissions. This confirmation signal frame is transmitted for a predetermined duration, for example about ten seconds. This makes it possible, on the one hand, to reduce the energy consumption of the onboard transceiver 2, and on the other hand, not to take into account requests for the opening of the sunroof that are not followed by the actual arrival. of user 4 in the immediate vicinity of the vehicle. The confirmation signal is issued in low frequency band LF, around

125 KHz, and here in mode without modulation (Continuous Wave), ie without modulation, in continuous frequency and amplitude.

It therefore forms a confirmation LF frame whose detection range by a remote key 3 is essentially determined by the power of the onboard transceiver 2. It is assumed here this power limited to about 15 watts, which leads in practice a range of detection range A of confirmation of 2.5 to 3 meters radius for the LF frame, beyond which its amplitude is lower than the background electromagnetic noise prevailing for example in urban areas or in car parks. It is clear that the choice of the radio frequency band RF for the key-remote control 3 brings a range of detection of the alarm signal, by the vehicle, substantially greater than the detection range of the confirmation signal, by the key-remote control , which is desirable in the context of the invention.

The remote control key 3 performs, at recurrent intervals, in a manner slaved to the frame of the wake-up signal, from the moment when the remote control button has been actuated, a measurement of the radio-frequency field E1 in the frequency domain of the confirmation signal. This radio-frequency field measurement E1 is carried out at the times during which the vehicle 1 is supposed to emit the confirmation signal, in practice a given delay after a transmission of the frame of the wake-up signal. It is simply a matter of measuring the intensity of the radio field in the frequency band used by the confirmation signal, and not of looking for:

- to detect if it is really a signal or,

- to determine a content of a signal.

This radio-frequency field measurement E1, or an average of several successive measurements, is then compared with a threshold value S previously memorized in the remote key 3 and characterizing a level of radio background noise.

As long as the user 4 carrying the remote key 3 remains out of the confirmation zone A, his remote key 3 does not measure, in the frequency band confirmation signal, field E1 greater than the threshold value S.

On the other hand, as soon as the user 2 approaches the vehicle 1 sufficiently and enters the range A of the confirmation signal, the radio-frequency value E1 measured by the remote control key 3 becomes greater than the threshold value. S characteristic of a typical background noise. In this step 103, the remote key 3 thus confirms its presence in the range of the confirmation signal, without the need to decode a signal, which would require a reception of a higher signal level.

In this case, the remote key 3 considers itself to be close to the vehicle 1, and it then transmits in a step 104 a third radio signal, said correct distance signal. This correct distance signal, still issued recurrently in the form of an RF distance frame, comprises, for example, simply the identification code of the remote control key 3 and a correct distance code, this code being previously stored in the remote control processor. data 5 of the vehicle 1. It should be noted that this emission of the correct distance signal by the remote control key 3 is performed without intervention on the part of the user 4, but is automatic when it is at a distance the distance is determined by measuring the radio field in the frequency band used by the confirmation signal, as has been seen.

When the remote key 3 transmits this correct distance signal, the range of its transmitter is such that the onboard transceiver 2 is almost certain to detect it. After a new pairing check of the remote key 3, the processor 5 causes in a step 105 then the opening of the sunroof.

Thus, after the alarm signal is transmitted by the key, then the transmission of the confirmation signal by the vehicle and the emission of the correct distance signal from the key causes the opening of the roof. The sequence of signals triggering the opening of the roof is shown in Figure 2a by a dashed line for information.

Optionally, the onboard transceiver 2 then emits a closed opening signal 106 for a few seconds, and for example until confirmation of the opening of one of the exits of the vehicle by a conventional opening sensor, this signal is also sent in non-modulation mode (Continuous Wave).

It should be noted that the correct distance test by the remote control key 3 is done during the entire duration of opening of the roof, and therefore in this case until reception of the opening signal completed or at this reception plus a duration a few seconds previously chosen. Indeed, in order to protect the vehicle against intrusions, it is desirable to take into account the case, illustrated in Figure 2b, of a user 4 entered and then out of the range area A of the transceiver embedded 2, ie the case where the sunroof has already been partially opened but where the user then moves away from his vehicle.

As has been seen, the remote control key 3 continues the radio field measurements E1 even after sending the correct reception signal. If the measured radioelectric field E1 becomes less than a threshold value S 'for a duration greater than a predetermined duration T', for example about ten seconds, it is because the user has emerged durably from the range A detection of the confirmation or opening signal transmitted by the onboard transceiver 2. In this case, the remote key 3 emits a cancellation signal. Its range in radio frequency band 433 MHz, being much higher than that of the transceiver 2, this signal will most likely be received by said onboard transceiver 2. The vehicle processor then orders the stop roof opening.

After a second delay T "without further reception by the transceiver 2 embeds a correct distance signal from the remote key 3, which corresponds to the case where the user 4 is not just temporarily out of the signal detection range area A, but is likely to have a lasting effect, the vehicle processor orders the re-closing of the sunroof, and then the onboard transceiver 2 stops transmitting the confirmation signal FIG. 2b illustrates this case, with a delay T "zero, the non-reception of the correct distance signal causing the immediate stopping of the emission of the confirmation signal. The triggering of the stop of the opening of the sunroof is shown in Figure 2b, for illustrative purposes, by a dotted line connecting the lack of correct distance signal and the stop opening the roof.

The scope of the present invention is not limited to the details of the above embodiments considered by way of example, but instead extends to modifications within the scope of those skilled in the art.

In a preferred variant, the remote control key 3 performs, on the one hand, radio-frequency field measurements E1 at the times during which the confirmation signal is sent, ie immediately after each transmission of the wake-up signal by this same signal. key-remote control 3, and, secondly, radio-frequency field measurements E2 at times during which the confirmation signal is not transmitted, ie after a delay Δt3 greater than the delay Δt2 of transmission of the signal of confirmation, after each transmission of the wake-up signal.

In this variant, the radio-frequency field measurement E2 determines the ambient noise, and serves as a threshold value. This is particularly interesting for taking into account very different radio environments, for example an urban environment with very strong radio background noise, and a rural environment whose background noise is significantly lower. The measurement difference E1-E2 makes it possible to determine whether the key has reached the range area A of the onboard transceiver 2.

It is understood that as long as the remote key 3 is at a great distance, much greater than the range of the onboard transceiver 2, the field corresponding to the confirmation signal is much lower than the background noise, and the value of E1 will be close to E2, and in practice randomly higher or lower than the value of E2. The average of E1-E2 will then be close to zero over a statistically significant number of measurements (a few tens). On the other hand, when the remote control key 3 approaches the onboard transceiver 2, the value E1 will more and more often be greater than the value E2, until it becomes substantially permanently higher than the value of the bound field. at background noise E2.

In a first implementation, the remote key 3 calculates an average of the difference E1-E2. As soon as this average is greater than a certain percentage of E2, the remote control key transmits the correct reception signal. In another implementation, the test can also be done between the average E1-E2 and a value equal to two (or n) times the standard deviation measured for the values of E1-E2. Any other standard type statistical test can also be used. In a similar variant, the threshold value S is not fixed, but can be modified over time according to the intensity of the signal or previously measured signals.

In a variant relating to the first step 101 of the method, when the user 4 presses the remote control button, the remote control key 3 transmits the wake-up signal in the form of a frame for a duration greater than the duration of the pressing said remote control button. In this case, the remote key 3 prolongs the emission of a previously chosen duration, sufficient for a user who moves at walking speed to cover a few meters, and for example four or five seconds.

The purpose here is that the onboard transceiver 2 can, despite the background noise and the signal reverberations, receive the control message of a user 4 who briefly actuates his remote control at a relatively large distance from his vehicle. This is clearly beyond the range of the transceiver 2, and even beyond the maximum regulatory distance of six meters. In this variant, the effective opening of the sunroof takes place, as in the description above, only when the user 4 enters the range zone A of the transceiver 2, here about 2.5 meters .

In yet another variant, the pressing of the remote control button takes place only if this support is of longer duration than a minimum duration previously chosen, for example a half-second, to avoid unwanted inadvertent support.

Similarly, in another variant, the transmission of the awakening signal by the remote control key ceases if the duration of the pressing of the remote control button is greater than a maximum duration, for example 10 seconds, to avoid cases where the remote control button is blocked in support, for example in a pocket of the user 4, probably involuntarily.

Complementarily, still in this case, the remote control key 3 then emits, in place of the wake up signal, a fourth signal, called cancellation. Upon receipt of this cancellation signal, the onboard transceiver 2 ceases the transmission of the confirmation signal. The opening procedure of the sunroof is then interrupted. It is necessary to restart it that the user 2 re-presses on his remote control button.

In another variant, also intended for protecting the vehicle against intrusions, the onboard transceiver 2 counts the elapsed time T between the start of reception of the wake-up signal and the start of reception of the correct distance signal. In this case, if this elapsed time T is greater than a previously chosen duration, typically twenty seconds, ie the user has not entered the zone of the immediate vicinity of the vehicle after 20 seconds, it is assumed that either the first wake up signal received was wrong or that the user 4 will no longer approach his vehicle in the immediate future, whatever the reason. The vehicle processor then stops the transmission of the confirmation signal, which interrupts the opening procedure of the sunroof.

Throughout the foregoing description, a valid distance validation has been described by measuring the radio field corresponding to the confirmation signal. This does not preclude further conventional decoding of said confirmation signal, even if this decoding can take place only when the user and the key-remote 3 will be in practice fifty centimeters to one meter closer to the embedded transceiver 2. This conventional decoding allows for example the remote key 3 to validate the identity of the vehicle, or to receive information.

Claims

A method of remote control opening sunroof (10) of vehicle (1), comprising:

- A step (101) of emission by a remote control key (3), movable relative to the vehicle, a first radio signal, said wake-up signal; a step (102) of recurrent transmission by a transceiver (2) on board the vehicle of a second signal, said confirmation, in response to the reception by the equipment of the wake-up signal;

a standby step (103) by the remote control key (3) to determine whether it is in an authorization zone A, when said remote control (3) receives the confirmation signal;

a step (104) of transmission by the remote control key (3) of a third radio signal, called the correct distance signal, when the remote control key (3) has detected the confirmation signal;

a step (105) for opening the sunroof, in response to the reception by the equipment on board of the vehicle of the correct distance signal; characterized in that

the confirmation signal is transmitted without modulation, ie in mode without CW (Continuous Wave) modulation,

the standby step (103) by the remote control key (3) to determine whether it is in the authorization area A comprises a measurement of a radio field E1 by the remote control key (3) in the frequency domain of the confirmation signal, at least during the supposed transmission of this confirmation signal, and a comparison of the measured field with a threshold value S.

2. Method according to claim 1, characterized in that the wake-up signal is issued repeatedly in the form of RF frame, the confirmation signal is transmitted in a controlled manner to the RF frame of the wake-up signal, each confirmation signal being transmitted for a predetermined time Δt2, immediately offset from the wake up signals.

3. Method according to any one of the preceding claims, characterized in that the confirmation signal is emitted in low frequency band LF, around

125 KHz.

4. Method according to any one of the preceding claims, characterized in that the correct distance signal is issued recurrently in the form of an RF frame of correct distance, and comprises an identification code of the remote control key (3). and a correct distance code, this code being previously stored in a data processor (5) of the vehicle (1).

5. Method according to any one of the preceding claims, characterized in that in the step (103) validation by the remote control (3) to determine if it is in the authorization area A, the threshold value S is established. according to a radio field measurement E2 at times during which the confirmation signal is not transmitted.

6. Method according to any one of the preceding claims, characterized in that it further comprises:

A step of counting by the onboard transceiver (2) the elapsed time T between the start of reception of the wake-up signal and the beginning of reception of the correct distance signal,

A comparison step between this elapsed time T and a previously chosen duration,

And a step of stopping the transmission of the confirmation signal, if the elapsed time T is greater than the previously chosen duration.

7. Method according to any one of the preceding claims, characterized in that it further comprises a step (106) of transmission by the onboard transceiver (2) of a complete opening signal, this signal being transmitted in non-modulation (Continuous Wave) mode.

8. A vehicle roof opening remote control device, comprising an onboard transceiver (2), on board the vehicle (1), able to emit a detectable confirmation signal over a range of a few meters by a or a plurality of mobile transponder-type transponders (3) paired with the vehicle (1), able to receive the signals transmitted by the onboard transceiver (2) and to emit at least two types of signals: • a wake-up signal,

A correct distance signal, in response to the reception of a confirmation signal, characterized in that the confirmation signal, when transmitted, is a CW signal (Continuous Wave), and in that each remote control (3) comprises means for measuring the intensity of the radioelectric field E transmitted by the onboard transceiver (2) in the frequency domain of the confirmation signal, and means for comparing the intensity measured with a threshold value S.

9. Device according to claim 8, characterized in that the onboard transceiver (2) uses low frequencies LF around 125 kHz.

10. Device according to any one of claims 8 to 9, characterized in that the remotes (3) use frequencies in the radio band, around 433 MHz.