Abstract:
An immobiliser system for a vehicle and an immobiliser set including an immobiliser system and a switch key equipped with a transponder is provided. The immobiliser system includes:
       a native transmitter-receiver unit integrated into the vehicle, the native transmitter-receiver unit including a native antenna and being configured so as to enable a wireless communication with a transponder associated with a switch key, and   a locking device for allowing or preventing the wireless communication between the native transmitter-receiver unit and the transponder, the locking device including:
           a locking antenna arranged in the vicinity of the native antenna, and   a control unit configured to control the locking antenna in an enabled state, wherein the locking antenna does not interfere with the wireless communication between the native transmitter-receiver unit and the transponder, or in a locking state, wherein the locking antenna does interfere with the wireless communication.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an immobiliser system for a vehicle. It also relates to an immobiliser set comprising an immobiliser system and a switch key equipped with a transponder. The invention finds a particularly advantageous, but not exclusive, application in the management of a fleet of vehicles, for example for a car rental company. 
       BACKGROUND OF THE INVENTION 
       [0002]    In order to simplify the way of renting a vehicle, rental companies are largely implementing reservation systems via Internet or telephone. Such a reservation system may provide a user with an access code so as to unlock the vehicle. The access code may be entered via a keyboard placed on the outside of the vehicle or behind the windscreen. The user is so enabled to get into the vehicle, where the switch key may be left for starting the vehicle. Instead of an access code, regular users may be provided with an RFID card upon registration. The RFID card can then be “activated” on demand through the reservation system, so that when it is identified by a card reader mounted on the vehicle, it unlocks the vehicle. This reservation process shows obvious disadvantages as regards the security of the vehicle. Indeed, the switch key is left in the vehicle and an unauthorised person or a thief can break the lock of the vehicle and start the vehicle without any difficulty, even if the vehicle is equipped with a conventional immobiliser system. 
         [0003]    A conventional immobiliser system, also known as an anti-theft security system, comprises a transmitter-receiver unit and a control unit. The transmitter-receiver unit is integrated near the ignition lock of the vehicle and can transmit an electromagnetic signal to a transponder integrated in the switch key. Said electromagnetic signal powers the transponder, which returns an answer signal containing an identification code. This code is generally stored in an electronic tag, for example an RFID tag, of the transponder. It is received by the transmitter-receiver unit and processed by the control unit for checking its validity and, if appropriate, for authorising the starting of the vehicle. The identification code can be encrypted in a variety of ways. 
         [0004]    Some security systems have been developed for car rental applications. However, these security systems are not entirely satisfactory. As an example, document US 2001028295 describes an electronic key equipped with an intelligent system for receiving user “credits” from a control centre. The electronic key communicates bi-directionally with the vehicle. The latter has an electronic system in order to verify, from data contained in the electronic key, whether the user and his “credits” are valid and, if appropriate, to authorise the starting of the vehicle. However, such a system involves an electronic key containing additional functionalities. Such a customised switch key is obtained by substituting the original switch key with a dedicated switch key. One difficulty is to fit the switch key with an identification code that is accepted by the immobiliser system. In practice, the dedicated switch key is associated with the immobiliser system through an association process. This process is time consuming and generally implies the intervention of the car manufacturer. An additional drawback of this solution is that the switch keys are subjected to many shocks and can be easily damaged. Last but not least, the cost of the customised switch key is much greater in comparison with the original switch key. 
         [0005]    Document FR 2 848 951 discloses another security system developed for car rental applications. The security system comprises, in a usual manner, an immobilising transponder integrated into the vehicle, and an electronic label intended to communicate with the transponder. However, the electronic label is integrated into the vehicle far enough away from the transponder so as to prevent any direct electromagnetic coupling. A passive relay is so provided so as to enable setting up or interrupting the communication between the transponder and the electronic label. The passive relay includes a first antenna close to the transponder, a second antenna close to the electronic label, and an electrical connection equipped with a switch for connecting the two antennas. This security system is well adapted for authorising the starting of the vehicle from a remote server. However, it suffers from the need to dismantle the original key to get the electronic label. Hence, there is a risk that the original key would be damaged during its dismantling. This entails a loss of value of the vehicle for the resale. 
         [0006]    It is also known, from document U.S. Pat. No. 6,781,507, a remote starting system for a vehicle comprising a passive anti-theft security system. This remote starting system is not dedicated to a car rental application, but aims at enabling a user to remotely operate a vehicle. The system comprises a first coil arranged close to the ignition lock, a first transponder arranged in the switch key, a second transponder, similar to the first one, arranged in the vehicle close to the first coil, and a second coil wound around the second transponder. The second transponder may be used for starting the vehicle in the absence of the switch key. However, in order to maintain the functionality of the anti-theft security system, the second coil is closed via a relay. This has the effect of blocking the electromagnetic coupling between the second transponder and the first coil. When the vehicle is to be remotely started, the relay is opened, which allows the first coil to transmit a signal to the second transponder. The second transponder responds by sending an authorisation code to the first coil, thus allowing the starting of the vehicle. The invention described in document U.S. Pat. No. 6,781,507 does not alter the integrity of the anti-theft security system. However, it could not be adapted for a car rental application, insofar as it does not allow to remotely prevent the starting of the vehicle for a user in possession of the switch key. 
       SUMMARY OF THE INVENTION 
       [0007]    One aim of the invention is to alleviate at least part of the aforementioned drawbacks by proposing a security system adapted to a car rental company, whose installation is entirely reversible and does not damage the vehicle or the switch key. The invention especially aims at preventing any cable cutting or dismantling of the key. Another aim of the invention is to propose a security system with improved security. Still another aim of the invention is to propose a security system which can be driven according to access authorisation data sent from a remote server, and in particular in the context of a car rental system. 
         [0008]    At least one of the above objectives is achieved through an immobiliser system for a vehicle comprising a transmitter-receiver unit integrated in a vehicle and enabling a wireless communication with a key transponder of a switch key. The key transponder may comprise an electronic tag for allowing the transmitter-receiver unit to identify the switch key. In accordance to the invention, the immobiliser system further comprises a locking device enabling to block the wireless communication and so to prevent the identification of the key. More precisely, the object of the invention is an immobiliser system for a vehicle comprising:
       a native transmitter-receiver unit integrated into the vehicle, said transmitter-receiver unit including a native antenna and being configured so as to enable a wireless communication with a key transponder associated with a switch key,   a locking device for allowing or preventing the wireless communication between the native transmitter-receiver unit and the key transponder, said locking device comprising:
           a locking antenna arranged in the vicinity of the first antenna, and   a control unit configured to control the locking antenna in an enabled state, wherein the locking antenna does not interfere with the wireless communication between the native transmitter-receiver unit and the key transponder, or in a locking state, wherein the locking antenna does interfere with said wireless communication.   
               
 
         [0013]    The locking device may interfere with the wireless communication either by acting as an electromagnetic shield between the native transmitter-receiver unit and the key transponder, or by generating jamming signals. 
         [0014]    In a particular embodiment, the locking antenna comprises a coil having two terminal ends, and the control unit comprises a controlled switch connecting said terminal ends and a driving means for controlling the controlled switch in an open state or in a close state. The coil of the locking antenna may be configured so as to act as an electromagnetic shield between the native antenna and the transponder when the controlled switch is in the close state. 
         [0015]    The transponder may be configured so as to enable the transmission of an amplitude modulated signal to the native transmitter-receiver unit. The signal is modulated according to a modulating signal, which may characterise identification data enclosed in the transponder of the switch key. In case of an amplitude modulated signal, the control unit may be configured so as to close the controlled switch at a frequency substantially equal to a frequency of the modulating signal. The modulating signal typically shows a frequency lying in the range between about 2 kHz and about 10 kHz. 
         [0016]    The driving means for controlling the controlled switch are preferably operated through an authorisation signal. To this end, the locking device of the immobiliser system may comprise a decision unit for generating this authorisation signal. By way of example, the decision unit comprises:
       a user interface enabling a user of the vehicle to input an access authorisation datum, and   a processing unit for generating the authorisation signal as a function of the access authorisation datum.
 
In this case, the driving means of the control unit are configured to receive the authorisation signal and to control the controlled switch as a function of this authorisation signal.
       
 
         [0019]    In a particular embodiment, the control unit and the decision unit are spaced apart. This makes possible to miniaturise the control unit and to make it less visible. The control unit and the decision unit may be connected through an electrical connection or a wireless connection. In the latter case, the decision unit further comprises a wireless transmitter for transmitting the authorisation signal, and the control unit further comprises a wireless receiver for receiving the authorisation signal. 
         [0020]    The user interface of the decision unit may comprise a keypad enabling the user to enter an authorisation code, and/or a contactless card reader capable of reading an access datum stored in a user card. The authorisation code and the access datum constitute access authorisation data for the generation of the authorisation signal. The contactless card reader may be an RFID reader or an NFC reader. 
         [0021]    In a specific embodiment of the invention, the decision unit further comprises a wireless receiver able to receive an access datum from a remote server. The processing unit so generates the authorisation signal as a function of this access datum. This embodiment is particularly well suited for a car rental application, insofar as the authorisation for using a vehicle can be managed from the remote server. 
         [0022]    The locking antenna may comprise a locking coil wound around at least part of the native antenna. This configuration provides an efficient interaction of the locking antenna onto the native antenna. More particularly, the native antenna may comprise a native coil. The locking coil of the locking antenna is so wound around at least part of the native coil. 
         [0023]    By way of example, the native antenna of the native transmitter-receiver unit and the locking antenna of the locking device may be loop antennas. 
         [0024]    Another object of the invention is to provide an immobiliser set for a vehicle. The set comprises an immobiliser system according to the invention and a switch key. In a specific embodiment, the switch key includes a transponder enabling a wireless communication with the native transmitter-receiver unit of the immobiliser system. According to an important aspect of the invention, the switch key can be the original one. In other words, the switch key of the native immobiliser system does not need any modification. 
         [0025]    The invention offers the advantage of enabling to switch between a conventional mode of using the vehicle, wherein the locking device is inoperative, to an automatic rental mode, wherein the locking device is driven according to specific conditions, without the requirement of changing the switch key. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Other advantages and characteristics of the invention will become apparent on examination of the detailed description of exemplary embodiments, which are in no way limitative, and in view of the following drawings, on which: 
           [0027]      FIG. 1  schematically represents a vehicle equipped with an immobiliser system according to the prior art; 
           [0028]      FIG. 2  schematically represents a vehicle equipped with a first exemplary embodiment of an immobiliser system according to the invention; 
           [0029]      FIG. 3  represents, by a simplified block diagram, the principle elements of the immobiliser system of  FIG. 2 ; 
           [0030]      FIG. 4  represents, by a more detailed block diagram, the principle elements of the immobiliser system of  FIG. 2 ; 
           [0031]      FIG. 5  represents a second exemplary embodiment of an immobiliser system according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]    The following embodiments are described for illustrative purposes only and cannot be considered as limiting the invention to the particular forms, features, and combinations thereof. On the contrary, it should be understood that the invention should cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined in the appended claims. In particular, one can consider alternatives of the invention comprising only a selection of described features, which are described in association to other features (even if this or those selected features are isolated within a sentence comprising the other features), in case this selection of features is sufficient to confer a technical advantage or to differentiate the invention with respect to the state of prior art. The selection comprises at least one—preferably functional—feature, without structural details, or with only part of the structural details if only this part is sufficient to provide a technical advantage or to differentiate the invention with respect to the state of prior art. 
         [0033]      FIG. 1  schematically represents an interior of a vehicle equipped with an immobiliser system according to the prior art. The immobiliser system  10  comprises a transmitter-receiver unit  11 , an electronic unit  12 , and an immobilisation means, not represented. The transmitter-receiver unit  11  is arranged in the vicinity of the ignition lock  14  of the vehicle. It is configured to wirelessly communicate with a transponder  15  arranged in a switch key  16  of the vehicle, when the transponder  15  is sufficiently close to the transmitter-receiver unit  11 . This occurs in particular when the switch key  16  is inserted in the ignition lock  14 . The transponder  15  may integrate an electronic tag containing identification data, such as a code, for identifying the switch key  16 . The transponder  15  is powered by an electromagnetic field generated by the transmitter-receiver unit  11 , and responds by sending a radiofrequency signal containing the identification data. The transmitter-receiver unit  11  transmits the identification data to the electronic unit  12 , which checks for its validity. In case of valid identification data, the electronic unit  12  drives the immobilisation means for authorising the starting of the vehicle. 
         [0034]      FIGS. 2 to 4  illustrate a first embodiment of an immobiliser system according to the invention.  FIG. 2  schematically represents an interior of a vehicle equipped with this immobiliser system.  FIGS. 3 and 4  represent the principle elements of the immobiliser system, by a simplified block diagram, and by a more detailed block diagram, respectively. 
         [0035]    We first refer to  FIG. 2 . Similarly to the immobilisation system  10  of the prior art, the immobiliser system  20  according to the invention comprises a transmitter-receiver unit  11 , an electronic unit  12 , and an immobilisation means, not represented. These components are qualified as native components of the immobiliser system  20 . The native transmitter-receiver unit  11  is integrated into the vehicle, preferably in the vicinity of the ignition lock  14 . It is configured to wirelessly communicate with a transponder  15  associated with a switch key  16  of the vehicle. According to the invention, the switch key  16  can be an original key of the vehicle, that is to a say a switch key dedicated to be used with a conventional immobiliser device, as described with reference to  FIG. 1 . As can be seen on  FIG. 3 , the transponder  15  of the switch key  16  may comprise an antenna, called a key antenna  151 , and an electronic tag  152 , for example a Radio Frequency Identification (RFID) tag, or a Near Field Communication (NFC) tag. The electronic tag  152  contains identification data, such as an identification code, for identifying the switch key  16 . The transponder  15  may be arranged within the casing of the switch key  16 , or it may be attached to the key. The native transmitter-receiver unit  11  comprises an antenna, called a native antenna  111 , enabling an RF communication with the transponder  15 . The native antenna  111  is for example a loop antenna. In a particular embodiment, the transmitter-receiver unit  11  first sends a radiofrequency (RF) signal through its antenna  111  to the transponder  15 . This signal constitutes a request signal, to which the transponder  15  answers by sending an RF return signal containing the identification data. This return signal is received by the transmitter-receiver unit  11 , which transfers the identification data to the electronic unit  12 . In case of an RFID tag, the request signal normally powers the transponder  15 . The RF communication may operate at frequencies within the range between about 100 kHz and about 150 kHz. Typical values are 125 kHz, 138 kHz and 150 kHz. The electronic unit  12  processes the identification data in order to verify that the switch key  16  is authorised to start the vehicle. The verification operation may consist in comparing the identification code to a reference code stored in the electronic unit  12 . If the identification code matches with the reference code or, more generally, if the identification data are valid, the electronic unit  12  sends a start authorisation signal to the immobilising means for authorising the starting of the vehicle and, especially, the starting of the engine  31 . On the contrary, if the identification data are not valid, the start authorisation signal is not sent. Alternatively, a prohibiting signal may be sent. In any case, the electronic unit  12  must prevent the vehicle to be started. 
         [0036]    In a specific embodiment, the identification data are encrypted for the RF transmission between the transponder  15  and the native transmitter-receiver unit  11 . Any type of encryption technology can be used. By way of example, the encryption can rely on a public-key cryptographic system. In particular, the identification data can be encrypted with a private key before its transmission, and deciphered with a public key on the transmitter-receiver unit side. The identification data so constitute a digital signature and enable the authentication of the switch key  16 . 
         [0037]    The immobiliser system  20  according to the invention further comprises a locking device  21 . The locking device  21  is dedicated to allow or to prevent the RF communication between the transmitter-receiver unit  11  and the transponder  15 . It constitutes a controllable inhibiting means for this RF communication. According to a main aspect of the invention, the locking device  21  only intervenes in the RF communication between the transmitter-receiver unit  11  and the transponder  15 . It does not modify the physical configuration of the original elements of the immobiliser system  20 , that is to say the transmitter-receiver unit  11 , the electronic unit  12 , the immobilisation means, and the transponder  15 . In particular, the locking device  21  does not require to be electrically connected to an original element of the immobiliser system  20 , or to alter its integrity. The locking device  21  interferes with the RF communication. It may either generate a jamming RF signal, or inhibit the RF signals between the transmitter-receiver unit  11  and the transponder  15 . The following description considers the locking device  21  to inhibit the RF signals. Nevertheless, it is to be understood that the invention is not limited to this particular embodiment. 
         [0038]    The locking device  21  comprises an antenna, named a locking antenna  22  and a control unit  23 . The locking antenna  22  is for example a loop antenna. Such an antenna comprises a coil of turns having two terminal ends. By way of example, the coil may comprise between about 10 and about 200 turns of a copper bare wire. In a preferred embodiment, the locking antenna  22  of the locking device  21  is arranged in the close vicinity of the native antenna  111  of the transmitter-receiver unit  11 . The native antenna  111  is usually wound around the ignition lock  14  of the vehicle. The locking antenna  22  can so be wound around the native antenna  111 . In order to make the locking device  21  as discreet as possible, the locking antenna  22  may be wrapped within a special casing, resembling the original casing of the native antenna  111 . The locking device  21  would so be not visible to a thief. In case the two terminal ends of the locking antenna  22  are in a closed circuit position, the locking antenna  22  forms an electromagnetic shield between the native antenna  111  and the key antenna  151  of the transponder  15 . The phrase “electromagnetic shield” must be understood as a means for inhibiting or at least attenuating the amplitude of the electromagnetic coupling between the native transmitter-receiver unit  11  and the transponder  15 . The amplitude of the electromagnetic coupling must be attenuated enough to block the communication between the transponder  15  and the transmitter-receiver unit  11 . In a particular case, the transmitter-receiver unit  11  must be prevented from demodulating signals coming from the transponder  15 . It is to be noted that the locking antenna  22  is entirely passive, in a sense that it is not supplied with electrical power. 
         [0039]    We now refer more specifically to  FIG. 4 . The control unit  23  comprises a controlled switch  231 , and a driving means  232  for controlling the controlled switch  231  according to an authorisation signal. The controlled switch can for example be a relay, a MOSFET transistor or any other type of switch that can be controlled by a signal. The driving means  232  is for example a microcontroller. The authorisation signal for driving the controlled switch  231  may be generated in a decision unit  40 . The decision unit  40  may form part of the locking device  21 . It comprises at least an interface for inputting access authorisation data and processing means for processing these data. By way of example, the decision unit  40  comprises an RFID reader  41 , a user keypad  42 , and a microprocessor  43 . The RFID reader can be used for reading an RFID tag, and the keypad  42  for inputting an access code. In the context of a car rental system, an authorised user may be provided with an RFID card containing a user identification code and/or with the access code. These codes are processed by the microprocessor  43  for generating the authorisation signal for the driving means  232 . The microprocessor  43  may also receive access authorisation data from a remote server  44 . This server  44  may operate a car rental application for managing a fleet of vehicles. In particular, it may provide the microprocessor  43  with authorised user identification codes and/or authorised access codes. The communication between the remote server  44  and the decision unit  40  is preferably carried out via a wireless communication mode, such as for example a General Packet Radio Service (GPRS), a Universal Mobile Telecommunication System (UMTS), a Bluetooth technology or a Wi-Fi technology. To this end, the decision unit  40  comprises a transmitter-receiver unit, called a long range transmitter-receiver unit  45 . Since the decision unit  40  may only receive data, the long range transmitter-receiver unit  45  may be substituted by a simple receiver unit. 
         [0040]    In view of achieving a locking device  21  as discrete as possible, the decision unit  40  is preferably arranged away from the control unit  23 . It may for example be arranged in a housing dedicated to receive a car radio, in a glove compartment of the vehicle, or in a car trunk of the vehicle. The control unit  23  can so be made relatively small. The decision unit  40  can be connected to the control unit  23  via an electrical connection. However, a wireless communication means is preferred in order to render it invisible to a thief. Hence, the control unit  23  comprises a transmitter-receiver unit, called a short range transmitter-receiver unit  233 , and the decision unit  40  comprises an associated short range transmitter-receiver unit  46 . These transmitter-receiver units  233 ,  46  are qualified as short range in the meaning that the communication must only be enabled between two points of the interior of the vehicle. As a consequence, a wireless communication with a range of a few meters, for example between about 1 m and about 5 m, is sufficient. The wireless communication is for example carried out via a Wi-Fi technology, a Bluetooth technology or a ZigBee technology. In a simplified embodiment, the control unit  23  may comprise a receiver and the decision unit a transmitter. Such a configuration enables the authorisation signal to be transferred from the decision unit  40  to the control unit  23 . 
         [0041]    The control unit  40  can be implemented on an electronic card, for example a printed circuit board. The electronic card is called a telematic box. It can integrate other functionalities dedicated to a car rental system. By way of example, the telematic box can be used for controlling the vehicle door opening, or for recording the quantity of fuel consumed by the user, and the travelled distance. The telematic box can communicate with an on-board computer of the vehicle. 
         [0042]      FIG. 5  illustrates a second embodiment of an immobiliser system according to the invention. This second embodiment lies on the property according to which the transponder  15  of the switch key  16  transmits an RF return signal to the transmitter-receiver unit  11 , whose amplitude is modulated according to the identification data of the transponder  15 . The identification data are so embodied in a modulating signal. This signal is typically a periodic signal whose frequency lies in the range between about 2 kHz and about 10 kHz. The immobiliser system  50  shows an identical arrangement to that of the immobiliser system  20 , except that its locking device  51  comprises a different control unit. The immobiliser system  50  comprises the native components of an immobiliser system, which are an immobilisation means, not represented, a transmitter-receiver unit  11  with its native antenna  111 , and an electronic unit  12 . It also comprises a locking antenna  22 , for example a loop antenna, and a control unit  53 . The control unit  53  comprises a microcontroller  531 , a controlled switch  532 , a resistive load  533 , a bridge rectifier  534 , such as a diode bridge, and capacitive elements  535 . The control unit  53  may also comprise a short range transmitter-receiver unit  233  for communicating with a decision unit  40 . The microcontroller  531  forms a driving means for the controlled switch  532 . It integrates a modulator  5311  for generating an amplitude modulated (AM) signal at a frequency substantially equal to the frequency of the modulating signal. The AM signal drives the controlled switch  532  via a resistor  536 . The controlled switch  532  can be a MOS transistor or a bipolar transistor. It allows the two terminal ends of the locking antenna  22  to be in a short circuit configuration through the resistive load  533 . The transistor  532  can be protected via a diode  537 . The bridge rectifier  534  aims at causing the electrical current flowing in the same way at all time. The capacity of the capacitive elements  535  must be tuned in accordance with the resonant antenna to be obtained. 
         [0043]    On the contrary to the first embodiment of the immobiliser system according to the invention, which impacts the RF return signal as a whole by attenuating its overall amplitude, the second embodiment of the immobiliser system involves a time dependant attenuation of the RF return signal. This makes the perturbation more efficient and/or makes possible to miniaturise the locking antenna  22 . 
         [0044]    It should be noted that the invention is not limited to the aforementioned examples. Numerous variants may be applied to the above examples without going the scope of the invention. Moreover, different characteristics, forms, variants and alternatives of the invention may be combined with one another in various combinations provided that they are not incompatible or mutually exclusive.