METHOD FOR ACTIVATING A VEHICLE FUNCTION AND ASSOCIATED DEVICE

Abstract

The invention relates to a method for activating a vehicle function by means of an activation device (D) comprising two outward-facing transmitter-receivers (EM1, EM2) arranged adjacent to each other and under a surface accessible from the outside to the user. The vehicle function is activated by the detection of a sliding movement along said surface. The method comprises: the emission of waves from the two transmitter-receivers; the reception of reflected waves; and the comparison of the time-of-flight and power values ​​of the waves by each transmitter-receiver with predetermined time-of-flight and power value profiles. If the detection of two consecutive time-of-flight peaks coincides with the detection of two power value drops, then the sliding movement is detected, and the vehicle function is activated. Figure for the abstract: Fig. 1

Description

Title of the invention: METHOD FOR ACTIVATING A VEHICLE FUNCTION AND ASSOCIATED DEVICE Technical field

[0001] The present invention relates to the field of automobiles and more particularly concerns a method for activating a function of a motor vehicle and an associated device. The invention applies in particular to the function of locking and unlocking the openings of a motor vehicle. Prior art

[0002] In a motor vehicle, it is known to use presence detection devices in order to detect the presence of a hand or a foot of a user of the vehicle and thus allow the locking or unlocking of all or part of the openings of the vehicle, for example the doors or the trunk. For example, the detection of the presence of a user's hand on or in front of a door handle coupled with the recognition of an identifier of a "hands-free" access device worn by this user, allows the locking and unlocking of these openings.

[0003] To do this, when the user approaches the vehicle, communication is established on a wireless communication link between the access device, for example an electronic badge or a mobile telephone, and the detection device in order to authenticate said access device using its identifier.

[0004] For this purpose, the detection device comprises an antenna allowing the reception of the identifier sent by the access device. The detection device is connected to an electronic computer of the vehicle (ECU: English abbreviation for “Electronic Control Unit”) to which it transmits the identifier.

[0005] According to the state of the art, the access device is generally an electronic badge. The signal received by the antenna of the detection device, comprising the identifier of the access device, is emitted via RF (Radiofrequency) or LF (Low Frequency) waves.

[0006] Nowadays, however, it is increasingly common to use a mobile phone to perform authentication functions, which makes it possible to avoid using a dedicated electronic badge and thus limit the number of devices. Since most mobile phones do not have RF or LF communication means, it is known to use, for example, ultra-wideband or UWB communication (Ultra Wide Band in English) which equips most existing phones to send the device identifier in the case of a vehicle unlocking function.

[0007] The approach of the access device close to the detection device (less than 10 cm) and the recognition of the identifier received by the computer, coupled with the detection of the presence of the user's hand, allows the door to be locked or unlocked.

[0008] In order to detect the presence of the user's hand and allow the unlocking of the vehicle's openings, such a detection device comprises, in a known manner, a capacitive sensor. Generally, a capacitive sensor is dedicated to a detection zone, and according to the prior art, there is a capacitive sensor for the unlocking zone and a capacitive sensor for the locking zone, the two zones being distinct.

[0009] According to an example of capacitive measurement, such a capacitive sensor comprises a first capacitor periodically charged and discharged into a second capacitor. When the first capacitor is discharged into the second capacitor, the charges are balanced between the two capacitors.

[0010] When a hand is present on the handle or near the handle, for example less than 10 mm away, the charge level of the first capacitor increases. This results in a greater discharge of the first capacitor into the second capacitor and therefore a higher balancing level in the presence than in the absence of a hand on the handle. Such a sensor thus makes it possible to detect the intention of a user to unlock the openings of the vehicle.

[0011] However, the use of capacitive sensors has many disadvantages:

[0012] In this case, the detection of a user's approach by capacitive sensors is not robust and generates false detections.

[0013] In particular, under certain environmental conditions, when the ambient air is humid, or when there is salt on the roads, which is projected onto the metal body of the vehicle, a capacitive coupling is created between the detection zones and the metal parts of the vehicle, which prevents any detection of the presence of a user by the capacitive sensors.

[0014] In addition, raindrops or snowflakes on the door handle increase the value of the capacitance measured by the capacitive sensors, thus triggering false detections.

[0015] And finally, detection by capacitive sensors is incompatible with handles covered with metallic paint or comprising chrome-plated surfaces, the presence of metal in the handle creating a coupling with the detection zones and inhibiting the detection of the presence of a user.

[0016] While for some vehicles false detections are not desired, for other vehicles false detections are not tolerated.

[0017] This is the case for vehicles equipped with folding handles, i.e. the case of handles for which the detection of the user's presence controls the movement of a motorized handle, which when at rest is completely integrated into the door and when activated deploys and protrudes outside the door. For this type of handle, the untimely deployment or retraction of the handle due to false detection by the capacitive sensors risks hitting or pinching the user's hand.

[0018] This is also the case for vehicles equipped with electrically assisted opening, for which the unlocking detection is accompanied not only by the unlocking of the door but also by its opening. In this case, the false detections cause the door to open unexpectedly.

[0019] And finally, false detections are not tolerable for vehicles equipped with the “Safe Lock” security function, for which the locking detection not only controls the locking of the vehicle from the outside but also the locking of the vehicle from the inside (anti-theft device). In this case, false detections can cause the user to be locked inside the vehicle.

[0020] To overcome these drawbacks, it is known from the prior art to replace at least one of the capacitive sensors, for example the capacitive sensor dedicated to locking the vehicle, with a pressure detection sensor, for example an inductive sensor comprising a metal target which moves towards a coil of the sensor when the user presses on the locking or unlocking zone. The variation in inductance of the coil of the inductive sensor, linked to the approach of the target towards the coil, makes it possible to validate the detection of the user's intention to lock or unlock.

[0021] However, the integration of a UWB communication device and an inductive pressure detection sensor in the same vehicle door handle has a major drawback, as the space in the handles becomes increasingly restricted, (for the sake of the aesthetics of the handle) the mechanical integration of the components is not always possible due to lack of space and proves to be expensive.

[0022] The invention proposes a method for activating a function of a vehicle and a device, in this case for unlocking and / or locking a vehicle door, making it possible to overcome the drawbacks of the prior art. More particularly, the invention proposes an improved and modified UWB communication device for also detecting the user's pressure on a dedicated surface, presenting a saving in space and cost compared to the prior art. Statement of the invention

[0023] The invention relates to a method for activating a vehicle function, by an activation device, from “hands-free” access equipment carried by a user, the activation device comprising at least two transmitter receivers oriented towards the outside of the vehicle and capable of communicating with said equipment in ultra wide band, the method being remarkable in that the two transmitter receivers are previously placed adjacent to each other, and under a surface accessible from outside the vehicle to the user and in that the activation of the vehicle function is triggered by the detection of a sliding movement of a part of the user's body along said surface, the method comprising the following steps: a. sequential transmission of ultra-wideband waves from the two transmitters to said equipment, b. reception of reflected waves, c. comparison for a predetermined period, i. time-of-flight values ​​of the waves reflected and received by each transceiver with a predetermined time-of-flight profile, the predetermined time-of-flight profile comprising two consecutive time-of-flight peaks above a threshold time-of-flight value, each peak being detected by a different transceiver ii. power values ​​of the waves reflected and received by each transceiver with a predetermined power value profile, said predetermined power value profile comprising two consecutive drops in power values ​​below a power threshold value, each drop being detected by a different transceiver, d. if the times of detection of the two consecutive peaks of flight time coincide with the times of detection of the two drops in power values, then detection of a sliding movement of a part of the user's body along the surface, e. and activation of the vehicle function.

[0024] The invention also relates to a device for activating a vehicle function from “hands-free” access equipment carried by a user, the activation device comprising at least two transmitter-receivers oriented towards the outside of the vehicle and capable of communicating with said equipment in ultra-wide band, the device being characterized in that the two transmitter-receivers are adjacent to each other, and under a surface accessible from outside the vehicle to the user and in that the device further comprises: a. means for sequentially transmitting waves between the two transmitter-receivers and for receiving reflected waves, b. means for carrying out a first comparison, over a predetermined period, of the time-of-flight values ​​of the reflected waves received by each transceiver with a predetermined time-of-flight profile, said profile comprising two consecutive time-of-flight peaks above a time-of-flight threshold value, each peak being detected by a different transceiver, c. means for carrying out a second comparison during the predetermined duration, of the power values ​​of the reflected waves received by each transceiver with a predetermined profile of power values, said profile comprising two consecutive drops in power values ​​below a power threshold value, each drop being detected by a different transceiver, d. means for carrying out a third comparison between times of detection of flight time peaks with times of detection of drops in power values, e. means of activating the vehicle function depending on the result of the three comparisons.

[0025] The invention also relates to any computer program product comprising program code instructions for executing the steps of the method according to the above characteristics when said program is executed on a computer.

[0026] Finally, the invention applies to any motor vehicle, comprising an activation device according to the characteristics listed above. Brief description of the drawings

[0027] Other characteristics and advantages of the invention will become apparent from reading the description which follows. This is purely illustrative and must be read in conjunction with the appended drawings in which:

[0028] [Fig.l]: [Fig.l] schematically represents a motor vehicle equipped with the activation device according to the invention,

[0029] [Fig.2]: [Fig.2] schematically represents a vehicle door handle in which there are two transmitter receivers according to the invention,

[0030] [Fig.3]: 1a [Fig.3] comprises at the top of the figure, seven illustrations representing the passage of a user's finger successively in front of the first transmitter receiver then in front of the second transmitter receiver and comprises at the bottom, four graphs illustrating over time the changes in the flight times and the intensity values ​​received by each of the two transmitters according to the passage of the finger in front of the first then in front of the second transmitter receiver illustrated in the seven graphs at the top of the figure,

[0031] [Fig.4]: [Fig.4] is a schematic representation of the activation device according to the invention,

[0032] [Fig.5]: [Fig.5] is a flowchart illustrating the different stages of the process activation according to the invention. Description of the embodiments

[0033] In [Fig.l], a motor vehicle V is shown equipped with an activation device D for a vehicle function according to the invention. The activation device D comprises at least two transmitters EM1, EM2 in Ultra Wide Band ULB capable of communicating in ultra wide band with portable access equipment SD, for example a smartphone or an electronic key carried by a user U.

[0034] The activation device D further comprises a central control unit 10 electronically connected to the transmitters and receivers EM1, EM2.

[0035] This central control unit 10 makes it possible to manage the transmission and reception of data in ULB via the transceivers. This is known from the prior art and will not be detailed further here.

[0036] Ultra Wide Band ULB communication is understood to mean radiofrequency communication which is based on the transmission of pulses of very short duration, often less than a nanosecond. Thus, the bandwidth can reach very high values ​​between 250 and 500 MHz and beyond. Note that the invention also applies to any other means of communication allowing a wideband signal to be obtained, for example Wifi which uses OFDM (“Orthogonal Frequency Division Multiplex” type modulation), i.e. a method of coding digital signals by orthogonal frequency distribution in the form of multiple subcarriers.

[0037] According to the invention, the transmitters / receivers EM1, EM2 are located in a bodywork element facing the outside of the vehicle V in order to transmit towards the outside of the vehicle V on the side where the user approaches the vehicle V. According to the invention, the transmitters / receivers EM, EM2 are adjacent to each other, in a door handle, deployable or not, in the pillar of the driver's door, in a rearview mirror, etc., that is to say in a bodywork element towards which the user can approach. The transmitters / receivers EM1, EM2 can also be included in an insert located in a window of the driver's door.This location is interesting insofar as the transmitter receiver EM1 can thus transmit either towards the interior of the vehicle or towards the exterior of the vehicle, and have two functionalities, that targeted by the present invention and a second functionality of detecting presence inside the passenger compartment of the vehicle, the window having only a very low attenuation of the ultra wide band waves when these pass through it. Preferably, but in no way limitingly, the transmitter receivers EM1, EM2 can be located in the same plane.

[0038] In the example illustrated in [Fig.2], the transmitters EM, EM2 are located in a handle P of a door 20 of a motor vehicle V. The transceivers EM1, EM2 each comprise, in a manner known per se, an antenna ATI, AT2 in ultra wide band ULB, and are located under a contact surface S of the handle P accessible to the user U. The contact surface S is oriented preferentially but in a non-limiting manner towards the outside of the vehicle V. According to the invention, the activation of the vehicle function is triggered by sliding a part of the body of the user U, for example the user's finger along this contact surface S, under which the two transceivers EM1, EM2 are located, as will be explained below.

[0039] According to the invention, the activation of a vehicle function, here the unlocking of the openings, is based on: a. on the prior authentication of the access equipment by ultra wide band or Bluetooth®, this process being known to those skilled in the art it will not be detailed further here and, b. according to the invention furthermore on the sliding of a part of the user's body along the contact surface under which the ultra wideband transmitter receivers EM1, EM2 are located, as will be detailed below.

[0040] According to the invention, the activation device D further comprises: a. Means for emitting ultra-wideband waves sequentially by the two transmitters EM1, EM2 and for receiving M1 ultra-wideband waves reflected by a part of the user's body, b. Means for carrying out a first comparison M2 during a predetermined duration AT, of the time-of-flight values ​​TOF1, TOF2 of the waves reflected and received by each transmitter receiver EM1, EM2 with a predetermined time-of-flight profile PTOf, said profile comprising two consecutive peaks Ptofi, Ptof2 of time-of-flight above a threshold time-of-flight value STOf, each peak being detected by a different transmitter receiver, c. Means for carrying out a second comparison M3 during the predetermined duration, of the power values ​​RSSI1, RSSI2 of the waves reflected and received by each transceiver EM1, EM2 with a predetermined power value profile PRSSi, said profile comprising two consecutive drops BRSsu, BRSSi2 of power values ​​below a power threshold value SRSsi, each drop being detected by a different transceiver, d. Means for carrying out a third comparison M4 between detection times t2, t3, t2', t3' of the time-of-flight peaks Ptofi, Ptof2 with detection times tl, t4, tl', t4' of the drops in power values ​​BRSsn, BrssI2, e. Means of activating M5 the vehicle function depending on the result of the three comparisons.

[0041] The reception means M1, the means for carrying out a first comparison M2, the means for carrying out a second comparison M3, the means for carrying out a third comparison M4 and the activation means M5 are preferably in the form of software included in an integrated circuit of the central control unit 10 (see [Fig.4]).

[0042] The central control unit 10 also comprises a processor 100 and a memory 101 (see [Fig.4]) in which instructions are recorded for configuring the processor to execute certain particular processes, in particular to implement the steps of the activation method, according to the embodiment as described below.

[0043] The means for sequentially transmitting ultra-wideband waves and receiving reflected ultra-wideband waves M1 comprise software processing means enabling analysis in time of flight TOF of the waves, and in power of the signal received by the access equipment, also called "RSSI" or "Received Signal Strength Indication" in English. These two parameters are known to those skilled in the art and will not be detailed further here. It is important to note for the realization of the invention, that the two transceivers EM1, EM2 transmit waves sequentially in quasi-simultaneity, that is to say with a very short delay separating the transmissions of the two transceivers EM1, EM2.The simultaneity of the emissions between the two transmitter receivers EM1, EM2 is not desired because it would create disturbances between the emissions, it is therefore preferable that the transmitter receivers each emit in turn with a very short delay between them, for example less than 100 ms. This delay being very short, this allows processing and sampling of the reflected waves received by the two transmitter receivers in parallel and almost simultaneously and therefore this makes it possible to have an image of the user's gesture in front of the two transmitter receivers EM1, EM2.

[0044] The invention resides in the fact that the sliding of a user's finger along the surface S, that is to say consecutively in front of the first transmitter EM1 then in front of the second transmitter EM2 modifies the electromagnetic field emitted then received by the two antennas ATI, AT2. In this case the user's finger obstructs the waves during their emission and reception by the transmitters and receivers EM1, EM2 and lengthens their round-trip flight time. Conversely, the user's finger absorbs part of the waves emitted by the transmitters and receivers and the power of the waves reflected and received by the antennas ATI, AT2 is reduced. This indication of power received by the access equipment which is returned and communicated to the activation device, that is to say to the transmitters receivers EM1, EM2 is therefore lower than that obtained without the presence of the finger in front of the antennas ATI, AT2. By sliding his finger along the surface S, that is to say by passing his finger first in front of the first transmitter EM1, the user modifies the flight time TOF1 and the power of the reflected waves RSSI1 received by the first transmitter receiver EM1 then by passing consecutively in front of the second transmitter receiver EM2, he modifies the flight time TOF2 and the power of the reflected waves RSSI2 received by the second transmitter receiver EM2.

[0045] By measuring for a predetermined duration AT, the flight time values ​​TOF1, TOF2, and the received power values ​​RSSI1, RSSI2 by each transmitter EM1, EM2, it is therefore possible to detect the sliding movement of the finger along the surface S and therefore the intention of the user to unlock his vehicle.

[0046] For this purpose, the means for carrying out a first comparison M2 compare for each transceiver during said predetermined duration AT, the flight time TOF1, TOF2 with a flight time threshold value STof- If the flight time of each transceiver EM1, EM2 at a first instant tl, tl' is greater than this threshold value, Stof, then at a second instant following the first t2, t2' is less than the threshold value STof, this means that the finger has passed in front of the transceiver. The flight time profile PTOF then comprises two consecutive flight time peaks PTofi, Ptof2 during the predetermined duration AT corresponding to the passage of the finger in front of each transceiver (see [Fig.3]).

[0047] Similarly, the means for carrying out a second comparison M3 compare for each transceiver during said predetermined duration AT, the received power value RSSI1, RSSI2 with a received power threshold value SRSsi. If the received power value of each transceiver EM1, EM2, at a third instant t3, t3' is lower than this threshold value SRSsi, then at a fourth instant t4, t4' following the third is higher than this threshold value SRSsi, this means that the finger has passed in front of the transmitter. The intensity value profile then comprises two consecutive drops in received power values ​​BRSsu; BRSSi2, during the predetermined duration AT corresponding to the passing of the finger in front of each transceiver (see [Fig.3]).

[0048] The means for carrying out a third comparison M4 then compare, for each transmitter receiver EM1, EM2, the instants t1, t1, t2', t2' of passage of the flight time values ​​above and below the flight time threshold value STof, i.e. the instants of detection of flight time peaks PTofi, Ptof2, with the instants of passage t3, t3'; t4; t4' of the received power values ​​below then above the received power threshold value SRssi, i.e. with the instants of detection of a drop in received power values ​​BRSsn, BRSsi2- If the instants of detection of the start and end of the flight time peaks coincide with the start and end times of the drops in received power values, then it is determined that the user's finger has indeed passed successively in front of the first transceiver EM1, then in front of the second transceiver EM2 and that he intends to unlock his vehicle V.

[0049] The means for activating a vehicle function M5 then unlock the opening.

[0050] The method of activating a vehicle function, illustrated in [Fig.5] in the form of a flowchart, will now be described.

[0051] During a prior step E0, an Ultra Wide Band communication is established with the access equipment SD by the activation device D. The ULB waves are emitted by the activation device D, sequentially between the two transceivers EM1, EM2, that is to say in turn. Then in a first step E1 reflected waves are received by said device D from the access equipment SD and are processed by the activation device D.

[0052] Once the reflected waves have been received, the time of flight TOF1, TOF2 and the intensity of the signal thus received RSSI1 RSSI2 are determined by each transmitter EM1, EM2 for the waves that it has emitted.

[0053] During a second step E2, the time-of-flight values ​​TOF1, TOF2 are compared for a predetermined duration AT with a predetermined time-of-flight value profile. In this case, if it is detected by each transmitter receiver EM1, EM2 that the time-of-flight values ​​TOF1, TOF2 are at a first instant t1, t1' greater than the threshold value ST0F, then at a second instant t2, t2' less than the threshold value STof, then two consecutive time-of-flight peaks are detected, if each transmitter receiver detects a peak PTOfi, Ptof2 then the method moves to the next step.

[0054] During the third step E3 (of course the second step E2 and the third step E3 can be carried out simultaneously), the received power values ​​RSSI1, RSSI2 are compared for a predetermined duration AT with a predetermined power value profile. In this case, if it is detected by each transceiver EM1, EM2 that the received power values ​​RSSI1, RSSI2 are at a third instant t3, t3' lower than the threshold value SRSsi, then at a fourth instant t4, t4' higher than the threshold value STOF, then two consecutive drops in signal power values ​​are detected, each transceiver detecting a drop BRSSI1, BRSSI2 and the method moves on to the next step.

[0055] During a fourth step E4, it is checked whether the times of flight peak start tl, tl' and the times of start of decrease t3, t3' of received power values ​​coincide, and whether the times of end of flight peak t2, t2' and the times of end of decrease t4, t4' of received power values ​​coincide. By "coincide" is meant the fact that the peaks of flight time values ​​PTofi, Ptof2 and the decreases of values ​​of received power BRSSI1, BRSSI2 occur almost simultaneously and are detected almost simultaneously to within a time delay tolerance, i.e. for example to within a few milliseconds. This is illustrated in [Fig.3]. We see that the instants do not coincide perfectly, but that the time-of-flight peaks PTOfi, Ptof2 occur at the times when the drops in the received power value BRSsu, BRSSi2-

[0056] If the times of peak flight times coincide with the times of drop in received power, it is then considered that the user U has slid his finger along the surface S, successively in front of the first transmitter receiver EM1, then in front of the second transmitter receiver EM2 and that this voluntary gesture means that he intends to unlock the vehicle's openings.

[0057] In the fifth step E5, the openings are then unlocked.

[0058] At the bottom of [Fig.3] are represented the flight times TOF1, TOF2 and the received power values ​​RSSI1, RSSI2 for each transmitter receiver EM1, EM2 as a function of the position of the finger with respect to said transmitter receivers which is illustrated at the top of [Fig.3],

[0059] The impact of the position of the user's finger U relative to each transmitter receiver EM1, EM2 on the flight time and the received power appears clearly on the graph located at the bottom of [Fig.3].

[0060] The invention is therefore ingenious insofar as the use of two ultra-wideband antennas makes it possible to detect the user's intention to unlock his vehicle while avoiding the use of a capacitive sensor. The invention is ingenious insofar as these antennas can also be used for other functions such as detecting presence inside the passenger compartment of the vehicle and / or detecting from a distance the user's approach to his vehicle.

Claims

Claims

1. Method for activating a vehicle function, by an activation device (D), from a “hands-free” access device (SD) carried by a user (U), the activation device comprising at least two transceivers (EM1, EM2) oriented towards the outside of the vehicle and capable of communicating with said equipment in ultra wide band (ULB), the method being characterized in that the two transceivers (EM1, EM2) are previously placed adjacent to each other, and under a surface (S) accessible from outside the vehicle to the user and in that the activation of the vehicle function is triggered by the detection of a sliding movement of a part of the user's body along said surface (S), the method comprising the following steps: a. sequential transmission of ultra-wideband waves from the two transmitters and receivers (EM1, EM2) to said equipment, b. reception of reflected waves, c. comparison for a predetermined duration (AT), i. time-of-flight values ​​(TOI, TOF2) of the waves reflected and received by each transceiver (EM1, EM2) with a predetermined time-of-flight profile, the predetermined time-of-flight profile comprising two consecutive time-of-flight peaks (PTofu Ptof2) above a time-of-flight threshold value (Stof), each peak being detected by a different transceiver ii. power values ​​(RSsn, Rssn) of the waves reflected and received by each transceiver (EM1, EM2) with a predetermined power value profile, said predetermined power value profile comprising two consecutive drops in power values ​​(BRSsu, BRSSi2) below a power threshold value (SRSsi), each drop being detected by a different transceiver, d. if the detection times of the two consecutive peaks (PTOfi, P T0F2) of flight time coincide with the detection times of the two drops in power values ​​(BRSsu, BRSSi2) then

2. detection of a sliding movement of a part of the user's body along the surface (S), e. and activation of the vehicle function. Device (D) for activating a vehicle function from a “hands-free” access device (SD) carried by a user (U), the activation device comprising at least two transceivers (EM1, EM2) oriented towards the outside of the vehicle and capable of communicating with said equipment in ultra wide band (ULB), the device (D) being characterized in that the two transceivers (EM1, EM2) are adjacent to each other, and arranged under a surface (S) accessible from outside the vehicle to the user and in that the device further comprises: a. means for sequentially transmitting waves from the two transmitters and receivers (EM1, EM2) to said equipment and for receiving reflected waves, b. means for carrying out (M2) a first comparison, for a predetermined duration (AT), of the time-of-flight values ​​(TOF1, TOF2) of the reflected waves received by each transmitter-receiver (EM1, EM2) with a predetermined time-of-flight profile, said profile comprising two consecutive time-of-flight peaks (PTOFb Ptof2) above a time-of-flight threshold value (STOf), each peak being detected by a different transmitter-receiver, c. means for carrying out (M3) a second comparison during the predetermined duration (AT), of the power values ​​(RSSI1, RSSI2) of the reflected waves received by each transceiver (EM1, EM2) with a predetermined profile of power values, said profile comprising two consecutive drops in power values ​​(BRSsu, BRSSi2) below a power threshold value (SBRssi), each drop being detected by a different transceiver, d. means for carrying out (M4) a third comparison between times of detection of peaks (tl, t2, tl', t2') of flight time with times of detection of drops (t3, t4, t3', t4') of power values, e. means of activation (M5) of the vehicle function if detection times of the two consecutive peaks (PTofi, Ptof2) of flight time coincide with detection times of the two drops in power values ​​(BRSsn, BRSsi2) detecting a sliding movement of a part of the user's body along the surface (S).

3. A computer program product comprising program code instructions for executing the steps of the method according to claim 1 when said program is executed on a computer.

4. Motor vehicle (V), characterized in that it comprises an activation device (D) according to claim 2.

Images