EP0848123B1 - A remote keyless entry system - Google Patents

Description

FIELD OF THE INVENTION
• This invention relates to the field of compact, radiofrequency (RF) transponders of the type known to be useful insystems for security and information storage, access control,entry validation and identification, and in other comparablesystems.
• Remote keyless entry systems require an interrogatorcircuit built into a road vehicle or building, for example,and a remote transponder which incorporates transmitting andreceiving circuits in a compact case that may be carried by aperson in a key, a key fob, a badge, a tag or in any similarminiaturized housing. More particularly this invention relatesto a transponder in a road vehicle or automotive remotekeyless entry and immobalization system which is functionalover an increased range in active and passive modes ofoperation. This invention further relates to a transponderwhich utilizes a secure challenge-response encryptiontechnique to provide greater security for the user.
• Compact passive low frequency transponders, using afrequency of 134.2 kilohertz (134.2 kHz), for example, forpassive entry and immobilizer functions and radio frequencyremote control transmitters, using a frequency of 433megahertz (433 MHz), for example, for use in remote keylessentry and security systems for automobiles are generallyknown. These systems allow access to the automobile withoutthe use of battery power, if the transponder is used in closeproximity to the interrogator, and allow the operator totransmit commands such as locking and unlocking doors, hoodand trunk, controlling vehicle lighting and ignition, andarming and disarming the anti-theft security system to thevehicle over greater distances. The transponders used mayemploy an interrogator-responder arrangement with an EEPROM data storage device and a small capacitor that servesas an energy accumulator, charged by the energy provided bythe radio frequency interrogation, to provide power for thetransponder. The transponder is, thus, sufficiently small tosupplement or replace a conventional vehicle door and ignitionkey. Such a transponder is disclosed by Schuermann at at. InU.S. Patent 5,053,774.
• In this context, reference is made to EP-A-0 690 190, which discloses a remotekeyless entry system with a key module and an in-vehicle lock module. The keymodule comprises a remote control transmitter using a high frequency and atransponder for receiving and transmitting low frequency signals. Upon actuation of apush button, the remote control transmitter transmits an encoded high frequencysignal to the lock module. If the lock module receives the high frequency signalproperly, it starts transmitting control signals having a frequency of 125 kH. If thekey module is within a distance of about 70 cm from the lock module, it receives thecontrol signals and responds by sending a driving signal to the lock module forlocking or unlocking the vehicle doors.
• Reference is further made to EP-A-0 767 286, which discloses a remote keylessentry and immobilization system for automotive use. The system comprises a key,which uses high frequency transmission for remote operation such as opening andclosing the door locks and low frequency transmission when the key is inserted in theignition lock of the vehicle for two way communication between the automobile andthe key. The content of the document is comprised in the state of the art according toArticle 54 (3).
• However, the transponder systems in current use generallyhave a limited operating range. Current remote controltransponder systems require battery power for proper operationand are not functional, in a passive mode, that is, whenoperated without a battery.
SUMMARY OF THE INVENTION
• The present invention provides a road vehicle remotekeyless entry system which is functional over an increasedrange in the active and passive modes of operation whileincreasing security by the use of a secure challenge-responseencryption technique.
• The present invention provides a secure roadvehicle keyless entry system comprising an in-vehiclecommunication processor and a remote transponder. Thecommunication processor and transponder communicate inparallel paths, a first path being a radio frequencytransmission from the transponder to the communicationprocessor and a second path being a low frequency, encryptedtwo way transmission between the transponder and thecommunication processor.
• The first and second paths are both used to communicatebetween the in-vehicle communication processor and thetransponder in response to a manual stimulus to the remotetransponder.
• The present invention further provides a method of vehiclekeyless entry comprising the steps ofclaim 12. The radio frequency transmissionand the low frequency, encrypted transmission can becompared by the communication processor for authenticationof the transmitted data or command before the communicationprocessor authorizes the desired operation and, if onecommunication channel is affected by interference, thesecond communication channel may be used as a backup.
• Preferably the communicationprocessor has a radio frequency receiver, a low frequencytransmitter/receiver and a controller capable of sending andreceiving signals via the low frequency transmitter/receiverand receiving signals via the radio frequency receiver. Thetransponder has a radio frequency transmitter that transmits asignal to the communication processor upon receipt of a manualstimulus and a low frequency transmitter/receiver capable ofreading the signals received from the communication processorand preparing an encrypted response for transmission to thecommunication processor. When the transponder provides anencrypted response containing the correct vehicle code tothe communication processor, the communication processorauthorizes the desired operation such as, for example,locking or unlocking the car, arming or disarming the anti-theftalarm system or the performance of vehicle relatedinitialization functions such as seat, seat belt and vehiclemirror adjustments and lighting the vehicle interior lights.
• It is further contemplated that the radio frequencyreceiver in the communication processor and the radiofrequency transmitter in the transponder may betransmitter/receivers, each capable of performing both thereceiving and transmitting functions. When radio frequencytransmitter/receivers are used, both the radio frequencycommunication and the low frequency communication betweenthe communication processor and the transponder will be twoway transmissions used to transmit data between the twodevices.
BRIEF DESCRIPTION OF DRAWINGS
• The present invention will now be further described byway of example, with reference to the accompanying drawings inwhich:
• FIG. 1 is a block schematic illustrating the functionalelements and data paths of one embodiment of the road vehiclekeyless entry system of the present invention.
• FIG. 2 is a block schematic illustrating the functionalelements and data paths of the remote transponder of thisembodiment of the invention.
• FIG. 3 is a block schematic illustrating the lowfrequency transmitter/receiver of the remote transponder ofthis embodiment of the invention.
• FIG. 4 is a block schematic illustrating modifications tothe remote transponder of the road vehicle keyless entrysystem of FIG. 1.
• FIG. 5 is a block schematic illustrating modifications tothe remote transponder of the road vehicle keyless entrysystem of FIG. 4.
• FIG. 6 is a block schematic illustrating the functionalelements and data paths of one embodiment of the writedistance expander of the remove transponder of FIG. 5.
• FIG. 7 is a block schematic illustrating the functionalelements and data paths of a second embodiment of the writedistance expander of the remote transponder of FIG. 5 and
• FIG. 8 is a block schematic illustrating a write distanceexpander.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENT
• In the road vehicle keyless entry system of the presentinvention the immobilization function, which locks the vehicleand initiates operation of the alarm system, is separate fromthe remote keyless entry function, which, for example, resetsthe alarm system and authorizes unlocking the vehicle andperformance of vehicle related initialization functions such as seat, seat belt and vehiclemirror adjustments and lighting the vehicle interior lights.
• Turning to the drawings, FIG. 1 illustrates thefunctional elements and data paths of one embodiment of theroad vehicle keyless entry system of the present invention.In this disclosure, the term road vehicle means all of thevarious types of vehicles that are operated upon the highwaysystem including, but not limited to, automobiles, trucks,vans, motorcycles, buses and motorhomes. It is intendedthat the arrangement shown in FIG. 1, and in the followingfigures, shall be interpreted as an illustrative systemconfiguration and that other possible configurations, moreadapted to the specific user needs, exist within the scopeof the disclosure herein. Further, the use of likereference numbers to identify components within the variousfigures indicates the presence of similar elements withineach of the different figures.
• The road vehicle keyless entry system, generallydesignated as 10, includes a communication processor 11 thatis located within the vehicle and a remote, miniaturizedtransponder 15. Communication processor 11 may also benamed an interrogator or called by other names indicatingits function as a unit which requests and receivesinformation from theremote transponder 15. Communicationprocessor 11 has aradio frequency receiver 12, a lowfrequency transmitter/receiver 13 and acontroller 14 whichis capable of sending and receiving signals via the lowfrequency transmitter/receiver 13 and receiving signals viatheradio frequency receiver 12.Controller 14 combinedwith low frequency transmitter/receiver 13 is preferably,a TIRIS reader, the term TIRISbeing an acronym known to those skilled in the art asdenoting certain types of devices or equipment utilizing thetransponder arrangement and TIRIS reader disclosed in Schuermann et al., U.S. Patent 5,053,774. Thetransponder15 has aradio frequency transmitter 16 that transmits asignal to communication processor 11 upon receipt of astimulus manually produced by an operator's actuation of oneof a plurality ofpush buttons 18. Whilepush buttons 18are shown for convenience, any manually operatable, pulsecreating switch such as, for example, a toggle switch or arotary switch may be used.Transponder 15 also has a lowfrequency transmitter/receiver 17 capable of reading signalsreceived from communication processor 11, preparing anencrypted response and transmitting the encrypted responseto communication processor 11.
• In the present embodiment of the invention,communication processor 11 located within the vehicle andremote transponder 15 communicate with one another to permita flow of information to initiate operations at the vehicle.Communication between the two devices is initiated by thevehicle operator who pushes abutton 18 ontransponder 15which responds by transmitting a radio frequency (RF) signalto communication processor 11 and a signal to low frequencytransmitter/receiver 17 to prepare it for interrogation bycommunication processor 11. The signal transmission, usinga rolling code for security, is a one way communication ordata transfer fromtransponder 15 to communication processor11 using a radio frequency signal of 433 megahertz (433MHz),for example, or another suitable frequency. In response tothe initial signal fromtransponder 15, communicationprocessor 11 transmits a low frequency interrogation totransponder 15 requesting identification and verification ofthe original radio frequency signal. Thus, the lowfrequency communication between the devices, using a lowfrequency signal such as, for example, 134.2 kilohertz(134.2 kHz), is a two way data exchange using the challenge-responseprinciple for authentication or verification of identity. Security of the low frequency signal ismaintained by using an encryption key which is known only tocommunication processor 11 in the vehicle andremotetransponder 15. Whentransponder 15 provides an encryptedresponse containing the correct vehicle code tocommunication processor 11 in response to the interrogation,communication processor 11 authorizes the desired operationwithin the vehicle. This use of encryption logic andinterrogation and response via the low frequency datatransmission, in addition to the rolling code used forsecurity with the radio frequency signal, greatly increasesthe security of the road vehicle keyless entry system.
• In the description above, a radio frequency transmitterand a receiver are used. It is further contemplated thatradio frequency receiver 12 in communication processor 11andradio frequency transmitter 16 intransponder 15 may betransmitter/receivers, each capable of performing both thereceiving and transmitting functions. When radio frequencytransmitter/receivers are used, both the radio frequencycommunication and the low frequency communication betweencommunication processor 11 andtransponder 15 will be twoway transmissions used to transmit data between the twodevices. This use of two way radio frequency communicationis illustrated by the solid and dotted signal lines betweenradio frequency receiver 12 andradio frequency transmitter16.
• FIG. 2 is a block schematic of the functional elementsand data paths ofremote transponder 15 of this embodimentof the invention showingradio frequency transmitter 16 andlow frequency transmitter/receiver 17. For remote securityfunctions such as, for example, turning on the interiorvehicle lights or arming or disarming the security system afunctional range of greater than 10 meters is desired. Forthis purpose,transponder 15 includesradio frequency transmitter 16 which operates at a frequency of 433megahertz (433MHz) using a rolling code for security. Thepresent transponder 15 further includes low frequencytransmitter/receiver 17 which provides a two way exchange ofdata with the communication processor 11 in the vehicleusing an encrypted signal having a frequency of 134.2kilohertz (134.2 kHz). Use of low frequencytransmitter/receiver 17 allows access to, or enables,additional features such as, for example, programming, theexchange and verification of identification and the use ofencryption logic and the transmission of various desiredcommands to the vehicle, all of which can significantlyincrease the security of the road vehicle remote keylessentry system.
• A vehicle operator provides a manual stimulus at theremote transponder 15 to initiate a command - the operatorpushes one of the plurality of switches or pushbuttons 18to indicate the action desired at the vehicle.Transponder15 includesradio frequency transmitter 16 which includescontrol logic module 29, radio frequency modulator/driver 28andrandom number generator 30. In response to theoperator's action,radio frequency transmitter 16 transmitsa signal, the desired command, toradio frequency receiver12 in communication processor 11 at the vehicle andsimultaneously transfers the command to low frequencytransmitter/receiver 17 via the serial interface. Forreceipt of this command signal, power to passive, lowfrequency transmitter/receiver 17 is provided by battery atterminal ACT on thecontrol logic module 21 and data arereceived using clock and data input ports, terminals SC andSI. In addition to thecontrol logic module 21, lowfrequency transmitter/receiver 17 includesencryption logicmodule 22,memory 23,radio frequency circuitry 24,shiftregister 25, tuned antenna, a parallel resonant circuit, 26 and charge orpower capacitor 27. Low frequencytransmitter/receiver 17 transmits the remote command to lowfrequency transmitter/receiver 13 which was switched to thereceive mode bycontroller 14 whenradio frequency receiver12 detected the carrier and command signal fromradiofrequency transmitter 16. Thus, even if external influencescreate interference with the radio frequency transmission ofthe desired command, the command may be received bycommunication processor 11 through the use of low frequencytransmission signals although the transmission range for thelow frequency signal is reduced. Authentication of thecommand may be confirmed by control processor 11transmitting a challenge to thetransponder 15 using lowfrequency transmitter/receiver 13. When the challenge isreceived by low frequency transmitter/receiver 17, theencryption logic module 22 encrypts the challenge using theencryption key stored within memory 23 (not readable) andtransfers the encrypted challenge and a serial number, whichis also stored withinmemory 23, to theradio frequencytransmitter 16. The encrypted challenge and serial number,together with the repeated command, are transmitted inparallel to communication processor 11 by bothradiofrequency transmitter 16 and low frequencytransmitter/receiver 17 as a complete response to thechallenge to authenticate the first command transmission.Controller 14 executes the command, or authorizes otherdevices to execute the command, if the correct vehicle codeor signature is received in response to the challenge. Withbidirectional communication using the low frequencytransmitter/receivers 13 and 17, the challenge-responsefeature provides greatly increased security over the rollingcode system. It is now also possible to transmit additionaldata or programming information between theremote transponder 15 and the communication processor 11 using thelow frequency transmitter/receiver 17.
• As discussed above, it is further contemplated that theradio frequency receiver 12 in communication processor 11andradio frequency transmitter 16 intransponder 15 may betransmitter/receivers, each capable of performing both thereceiving and transmitting functions. When radio frequencytransmitter/receivers are used, both the radio frequencycommunication and the low frequency communication betweencommunication processor 11 andtransponder 15 will be twoway transmissions used to transmit data between the twodevices.
• For remote keyless entry, a function or transmissionrange of at least approximately one meter (1 m) isnecessary. However, this range is difficult to reach withpassive transponders, even when the transponder has anantenna the size or a credit card. Therefore, an activefunction may be provided by the inclusion of a battery asshown in FIG. 3, a block schematic of a low frequencytransmitter/receiver 50, another embodiment of the lowfrequency transmitter/receiver 17 forremote transponder 15.
• Low frequency transmitter/receiver 50 includeslogiccontrol module 51,receiver control module 52,transmittercontrol module 53, the end ofburst detector 54, theadaptive plucklogic module 55,signal level converter 56,clock regenerator 57, divider 58,threshold detector 59,resonant circuit 60,charge capacitor 61 anddiodes 62, 63and 64 connected as shown in FIG. 3. Resonatecircuit 60has a capacitor connected in parallel with an inductor withthe value of each component selected to provide a resonantcircuit that is resonant at a radio frequency of 134.2 kilohertz (134.2 kHz). The size ofcharge capacitor 61 isselected so that the fully charged capacitor will havesufficient charge to provide the power necessary to enable the low frequency transmitter/receiver 50 to functionproperly. A capacitor sufficiently large would be, forexample, a capacitor of approximately 0.12 microfarads(0.12µf).Diodes 62, 63 and 64 are symbols for thenecessary one way function, that is, the signal is conductedin only one direction.Diodes 62, 63 and 64 are preferablySchottky diodes with low feed through voltage, if possiblein the selected semiconductor process, although they may benormal semiconductor diodes such as 1N4148 diodes or fieldeffect transistor (FET) circuits using switched gates.
• The vehicle operator initiates a command by providing amanual stimulus at the door handle of the vehicle or withremote transponder 15 - the operator operates the doorhandle or pushes one of the plurality of switches or pushbuttons 18 to indicate the action desired at the vehicle.After receipt of a radio frequency signal fromtransponder15, the communication processor 11 or interrogator transmitsa low frequency signal (134.2 kHz) to low frequencytransmitter/receiver 50 which, when received byresonantcircuit 60, provides electrical energy to chargecapacitor 61 in addition to askingtransponder 15 forconfirmation of the command or action request. The lowfrequency voltage is rectified bydiode 62 andchargescapacitor 61. The voltage level reached onchargecapacitor 61 depends upon the distance between thecommunication processor 11 and thetransponder 15 antennaswhich are typically resonance circuits having a high qualityfactor such as, for example,resonant circuit 60. Ifsufficient energy is accumulated so that the voltage oncharge capacitor 61 exceeds a certain limit such as onevolt, for example, thethreshold detector 59 switches thebattery supply voltage frombattery 65, provided at terminalVBAT, to connect the battery voltage through connections VCCto the logic circuitry of low frequency transmitter/receiver 50. Thethreshold detector 59 prevents discharge ofbattery65 whentransponder 15 is in the presence of electromagneticinterference such as, for example, if the transponder isplaced upon a television set. If the voltage limit oncharge capacitor 61 is low, the influence of theinterference will increase, but the sensitivity (the signaldetection range) will also increase. As explanedhereinafter, thethreshold detector 59 may be an active or apassive device. Increasing the sensitivity requires morestand-by current frombattery 65, with a resulting decreasein battery life. The threshold detector may also be locatedat the radio frequency signal input where higher signalamplitudes are normally available. Ifbattery 65 is notavailable, voltage is still provided to the logic circuitrybycharge capacitor 61 throughdiodes 63 and 64. Theresonant circuit 60 is separated from the integrated circuitpower supply during the reception of data, the write phase,from the communication processor 11. The signal received bytransponder 15 and the level of oscillation of theresonantcircuit 60 is usually low when the distance between thecommunication processor 11 and thetransponder 15 is great.The use ofbattery 65 to provide voltage to the circuitenables the low frequency transmitter/receiver 50 circuit toreceive and react to transmitted signals having loweramplitudes than would be possible in the passive mode ofoperation, that is, without battery power. voltage ismonitored by the end ofburst detector 54. When theamplitude of the voltage signal drops and theresonantcircuit 60 resonates with its own frequency instead of beingenhanced by the signal from communication processor 11, theend ofburst detector 54 activatesclock regenerator 57 andthe plucklogic module 55 which preferably provides peakpluck and slope control. The plucklogic module 55 enhancesoscillation whenever a voltage amplitude drop caused by the resonant circuit loss factor is detected. Pluck logic, theplucklogic module 55 and the peak detector used in plucklogic are described in U.S. Patent 5,283,529, U.S. Patent5,227,740 and U.S. Patent 5,126,745
• The provision of battery power enables the circuit tooperate properly with the reception of a lower signalamplitude than would be possible in the passive mode.Voltage amplitude drops during and after the write phase aredetected by the end ofburst detector 54 over greaterdistances because internal current sources and digitalcircuits of low frequency transmitter/receiver 50 arealready fully functional asbattery 65 provides thenecessary power rather than relying upon the signal receivedbycharge capacitor 61 to provide power, as would berequired in the passive mode of operation. The lowfrequency transmitter/receiver 50 is able to regenerate evensmall signal amplitudes which helps pluckcircuit 55 enhancethe oscillation during the free running times, during thereception of write signals and during the transmission ofresponse data. Thus, the distance over which data may bereceived bytransponder 15 using pulse width modulation issignificantly enhanced when compared to the distancepossible when a transponder operating in the passive mode isused.
• After a period for the charging ofcharge capacitor 61,communication processor 11 transmits a challenge such as,for example, a random number totransponder 15. Thischallenge is received by low frequency transmitter/receiver50 and is encrypted, using the encryption key stored in itsmemory, to become the signature of thetransponder 15. Thisgenerated signature, the encrypted random number, and theserial number oftransponder 15 are transmitted to thecommunication processor 11 by the low frequency transmitter/receiver 50 and, at the same time, transferredtoradio frequency transmitter 16 oftransponder 15 usingthe internal serial input/output interface circuitry. Whenthe internal serial input/output interface circuitry is usedwithout low frequency transmitter/receiver 13 being involvedso that no voltage is charged incapacitor 61, the activatesignal on terminal ACT of low frequency transmitter/receiver50 switches thebattery 65 voltage, provided at terminalVBAT, to connect through connections VCC to thelevelconverter 56 which maintains the correct input and outputsignal voltage levels under all voltage supply levels.
• When the end of burst, the end of the transmission fromcommunication processor 11, measured by end ofburstdetector 54 lasts for a certain time such as, for example, aperiod of 1.9 milliseconds (1.9 ms), a "timeout" or responsesignal is generated in accordance with the disclosure abovefor transmission to communication processor 11. Divider 58counts the radio frequency oscillations regenerated byclockregenerator 57 during the end of burst period to determinewhen the response or "timeout" signal is to be generated andswitches the battery voltage, terminal VBAT, to theresonantcircuit 60 to increase the transmission frequency amplitudeand, therefore, to increase the transmission readingdistance and the signal robustness against noise or otherinterference. Thus, similar to the enhanced receptiondistance, the distance over which data may be transmitted bytransponder 15 of this invention using frequency shiftkeying (FSK) is enhanced when compared to the distancepossible when a transponder operating in the passive mode isused. Theradio frequency transmitter 16 transmits thesignature and serial number with a command that thecommunication processor 11 accept the parallel low frequencyresponse as a backup and as a security check. This dualsignal, the parallel transmission of a radio frequency signal and a low frequency signal, enhances the securityagainst noise and manipulation of the command signals.
• Operation may also be enhanced by usingtransmitter/receivers as theradio frequency receiver 12 incommunication processor 11 andradio frequency transmitter16 intransponder 15. When radio frequencytransmitter/receivers are used, both the radio frequencycommunication and the low frequency communication betweencommunication processor 11 andtransponder 15 will be twoway transmissions, further enhancing the security againstnoise and manipulation of the command signals.
• The road vehiclekeyless entry system 10 may also beused to replace the ignition key of the vehicle. When thevehicle operator has entered the vehicle and wishes to startthe engine, the operator will initiate a new command processwith a manual stimulus of a push button on or near thevehicle dash board, for example. This stimulus initiates anew challenge/response phase via the low frequencytransmitter/receivers. Operation of thekeyless entrysystem 10 after receipt of the low frequency signal is asdescribed above.
• Turning now to FIG. 4, a block schematic illustratesmodifications to theremote transponder 15 of the roadvehiclekeyless entry system 10 of FIG. 1. Communicationprocessor 11 is located within the vehicle andminiaturizedtransponder 15 is a remote unit which may be carried by thevehicle operator. The apparatus and operation ofcommunication processor 11 andtransponder 15 are asdescribed in regard to FIG. 1 above except that the serialinput/output interface circuitry betweenradio frequencytransmitter 16 and low frequency transmitter/receiver 17 isreplaced by driver/demodulator circuit 19 andcoupling coil20 to provide for the contactless transfer of data betweenthe two circuits. In this embodiment, battery voltage is provided toradio frequency transmitter 16 and voltage istransferred to low frequency transmitter/receiver 17 bysignal transmission throughcoupling coil 20. Commands areinitiated by the manual stimulation of one of the pluralityofpush buttons 18 onradio frequency transmitter 16 whichtransmits the command to communication processor 11 and atthe same time transfers the command data to low frequencytransmitter/receiver 17. As described above, it iscontemplated thatradio frequency receiver 12 andradiofrequency transmitter 16 may be transmitter/receiversallowing two way radio frequency communication in additionto the two way low frequency communication. It is, thus,possible to initiate commands by manual stimulation of pushbuttons, similar to pushbuttons 18, located oncommunication processor 11. Communication processor 11would transmit the command toradio frequency transmitter16, which would then be a transmitter/receiver, and it wouldrequest data from low frequency transmitter/receiver 17 torespond to the command from communication processor 11.Solid and dotted lines are shown in FIG. 4 to illustrate thetwo way flow of information by the use of radio frequencytransmitter/receivers. The commands and data aretransferred to low frequency transmitter/receiver 17 viacoupling coil 20 which is driven by driver/demodulatorcircuit 19. The response, also viacoupling coil 20, fromlow frequency transmitter/receiver 17, the signature, serialnumber and status, are demodulated by driver/demodulatorcircuit 19 for reading byradio frequency transmitter 16.Operation of communication processor 11 andtransponder 15are otherwise as described in regard to FIG. 1 above. Thisembodiment of the invention may be especially useful if itis desired to separate the command function provided byradio frequency transmitter 16, which initiates all commandsby operation of one of thepush buttons 18, from the communication function provided by low frequencytransmitter/receiver 17, which provides two waycommunication for the transfer and verification of databetweentransponder 15 and communication processor 11.Radio frequency transmitter 16 and low frequencytransmitter/receiver 17 may, thus, be in separate compactcases, allowing separate use of a passive transponder foroperation over short distances, separate use of an active,battery powered radio frequency transponder for remotecontrol functions over greater distances and combined use ofthe passive and active transponder functions over the fulldesired operating range, thus allowing adaption of thetransponder size to the size the vehicle operator is willingto carry.
• FIG. 5 is a block schematic illustrating modificationsto the remote transponder of the road vehicle keyless entrysystem of FIG. 4. In FIG. 5 the driver/demodulator circuit19 interface of FIG. 4 is replaced or complimented by awrite distanceexpander interface circuit 19a whichcooperates withradio frequency transmitter 16 and lowfrequency transmitter/receiver 17 to provide atransponder15 that is operable at an increased distance betweentransponder 15 and communication processor 11 with lowfrequency transmitter/receiver 17 operating in the passivemode, that is without a voltage directly supplied by abattery.
• Road vehiclekeyless entry system 10 has communicationprocessor 11 andtransponder 15. The functional elementsand operation of communication processor 11 are describedabove.Transponder 15 has a low frequencytransmitter/receiver 17 that operates on a low frequencysuch as, for example, 134.2 kilohertz (134.2 kHz) to providetwo way communication, a challenge and encrypted response,with communication processor 11.Transponder 15 also has aradio frequency transmitter 16 that operates on a radiofrequency such as, for example, 433 megahertz (433 MHz).Radio frequency transmitter 16 is equipped with a batteryand the range in whichtransponder 15 can receive the lowfrequency signal is increased by write distanceexpanderinterface circuit 19a. Theradio frequency transmitter 16and low frequency transmitter/receiver 17 must be in acommon housing for operation over extended distances, butmay be separated from one another while providing basicoperations at shorter operating ranges.
• Theradio frequency transmitter 16 is typically used toprovide security functions such as, for example, lightswitching, alarm arming and disarming and similar functions.The low frequency transmitter/receiver 17 is typically usedin the passive operating mode to provide keyless entry andimmobilization functions at short range, for example atdistances less than one meter (1 m). When a request orcommand is made by the manual operation of one of aplurality ofpush buttons 18 ontransponder 15 or by amechanical switch such as the vehicle door handle, achallenge or interrogation, a random number, is transmittedfrom communication processor 11 using a ferrite or air coilantenna and pulse pause modulation at a frequency of, forexample, 134.2 kilohertz (134.2 kHz) to the low frequencytransmitter/receiver 17 oftransponder 15. Low frequencytransmitter/receiver 17 encrypts the challenge using asecret encryption key held in its memory (not readable) toproduce a signature and responds by transmitting theencrypted challenge, its signature, and the transponderserial number to the communication processor 11 using afrequency shift keying (FSK), frequency modulation, signalat a frequency of, for example, 134.2 kilohertz (134.2 kHz).If the distance between communication processor 11 andtransponder 15 is too far, this communication will fail. To achieve a greater functional range, thewrite distanceexpander 19a interface circuit is provided.
• One embodiment of thewrite distance expander 19a isshown in FIG. 6 in a block schematic illustrating theexpander's functional elements and data paths. A blockschematic is used in FIG. 7 to illustrate the functionalelements and data paths of a second embodiment of thewritedistance expander 19a.
• Write distance expander 19a interface circuit includesresonant circuit 80 which consists ofcoil 81, which alsoserves as a coupling coil, and a capacitor tuned to afrequency of 134.2 kilohertz (134.2 kHz); radiofrequencyvoltage limiter 82 with a battery charge circuit;diode 83connected to chargecapacitor 84;threshold detector 85;clock regenerator 86, an operational amplifier used as acomparator;envelope rectifier 87; end ofburst detector 88;and a 134.2 kilohertz (134.2 kHz)clock generator module 89which may, for example, be a pluck logic module or aseparate oscillator with a divider gated by activationsignal TXCT.
• Coil 81, which is, for example, a small ferrite or aircoil, is located proximate the antenna of low frequencytransmitter/receiver 17 at a position in which thecoil 81can receive the radio frequency signals from communicationprocessor 11 and the resonant circuit of low frequencytransmitter/receiver 17. Thewrite distance expander 19aresonant circuit 80 has a high quality factor to achieve aradio frequency voltage amplitude of at least about 1 to 2volts at the desired maximum reading distance between thetransponder 15 and communication processor 11. Whencommunication processor 11 transmits a challenge totransponder 15 and the distance between the two devices istoo great, the low frequency transmitter/receiver 17 willnot function properly because the challenge is not received or the signal is too weak. If the challenge is not properlyreceived by low frequency transmitter/receiver 17,encryption of the challenge is not started and no responsewill be transmitted to the communication processor 11. Thewrite distance expander 19a circuit has athreshold detector85 which detects the radio frequency voltage increase duringthe charge phase, the period in which the radio frequencysignal from communication processor 11 is used to chargecharge capacitor 84. Thethreshold detector 85 activatesthe supply voltage for the active devices and turns on thecontroller within theradio frequency transmitter 16. Thethreshold detector 85 may be an N-channel FET with low gatesource-voltage, a circuit that does not consume power aslong as the FET is not in the conductive state. Thethreshold detector 85 can also be an active device whichconsumes a certain amount of standby current from thebattery. The pulses of the PET, or of the active device,can be used to trigger a retriggerable monoflop or can beused directly to turn on the controller withinradiofrequency transmitter 16 which activates the power supply tothewrite distance expander 19a. The oscillation of thewrite distance expander is rectified bydiode 83 andfiltered bycharge capacitor 84 to provide a referencevoltage for the comparators,clock regenerator 86 and end ofburst detector 88.
• During transmission of the command and the challenge tothe low frequency transmitter/receiver 17, the radiofrequency signal is pulsed and the length of the pulsepauses are the indication for a low or a high bit. Theenvelope rectifier 87 detects the pulse pauses by rectifyingthe output of theclock regenerator 86. Theenveloperectifier 87 output signal is compared to the voltagereference level by the end ofburst detector 88 and thissignal is conducted to the controller ofradio frequency transmitter 16. The controller monitors the output from endofburst detector 88, detects the length of the pulse pausesand determines whether a low bit or a high bit is received.Threshold detector 85,envelope rectifier 87 andcomparator88 may be combined in the simplest case using a field effecttransistor (FET) with low gate/source voltage as shown inFIG. 8, an illustration of a simple write distance expander.When an encryption command is received, the challenge isreceived and stored in controller memory. The controller ofradio frequency transmitter 16 switches the voltage providedbybattery 90 to theclock regenerator 86 when the responsefrom the low frequency transmitter/receiver 17 is expectedandclock regenerator 86 amplifies and limits the radiofrequency signal oscillation and generates a digital clocksignal. This clock signal is conducted directly to thecontroller ofradio frequency transmitter 16 or to thecontroller through a digital oranalog demodulator circuit91 if the controller is not capable of demodulating thesignal. The controller checks the frequency shift keying(FSK) modulated response from the low frequencytransmitter/receiver 17 to determine whether it is valid andcomplete. The encrypted response to the challenge from thecommunication processor 11 is transmitted by the lowfrequency transmitter/receiver 17 and the response, thesignature, status and other desired information, may be sentin parallel by theradio frequency transmitter 16 to confirmand authenticate the response. When only the challenge, butno response from the low frequency transmitter/receiver 17,is detected by the controller ofradio frequency transmitter16, the controller transfers the challenge stored in memoryto the low frequency transmitter/receiver 17 using the 134.2kilohertz (134.2 kHz)clock generator 89 which may be apluck logic circuit or a gated oscillator with divider asshown in thedemodulator circuit 91. When low frequency transmitter/receiver 17 receives the challenge, it willgenerate an encrypted signature from the challenge and willtransmit the encrypted signature at a frequency of 134.2kilohertz (134.2 kHz) as the response to communicationprocessor 11. This response will also be transferred toradio frequency transmitter 16 and will be transmitted at aradio frequency of 433 megahertz (433 MHz) to communicationprocessor 11 in parallel with the low frequency transmissionof the response. The radio frequencyvoltage limitercircuit 82 necessary to protect the components can be usedto chargebattery 90. If thethreshold detector 85, and thecontroller ofradio frequency transmitter 16, detects acontinuous radio frequency signal for a long period of time,then radiofrequency voltage limiter 82 will switch thevoltage to a higher level for use to chargebattery 90.Depending upon the low frequency voltage initiated in thewrite distance expander 19a resonant circuit 81 (antennasize) and the threshold detector level sensitivity,distances of from about 1 meter (1 m) to about 2 meters (2m) betweentransponder 15 and communication processor 11 canbe bridged for remote keyless entry communications. Thisgreater or expanded signal reception distance combined withthe greater transmission distance for radio frequencyremotecontrol transmitter 16, greater than 10 meters (>10 m)allows the operator to gain access to the vehicle orauthorize other vehicle actions from a greater distance orwithout removing thetransponder 15 from the pocket.
• In addition to the described function, writedistanceexpander 19a may also be used as a low cost radio frequencymodule with receive and transmit capabilities. Such modulescould be used in transponders useful over short distances.
• In view of the foregoing description, it will be seenthat several advantages are attained by the presentinvention.
• Although the foregoing includes a description of thebest mode contemplated for carrying out the invention,various modifications could be made in the constructionsherein described and illustrated without departing from thescope of the invention. It is intended that all materialcontained in the foregoing description or shown in theaccompanying drawing should be interpreted as illustrativerather than limiting.

Claims (13)

1. A secure road vehicle keyless entry system (10) comprising an in-vehiclecommunication processor (11) and a remote transponder (15), the communicationprocessor (11) and transponder (15) communicating in parallel paths, a first pathbeing a radio frequency transmission from the transponder (15) to thecommunication processor (11) and a second path being a low frequency,encrypted two way transmission between the transponder (15) and thecommunication processor (11) where the first and second paths are both used tocommunicate between the in-vehicle communication processor (11) and thetransponder (15) in response to a manual stimulus to the remote transponder (15).
2. The secure road vehicle keyless entry system (10) of claim 1 wherein theradio frequency transmission and the low frequency transmission are comparedfor authentication of the transmitted data.
3. The secure road vehicle keyless entry system (10) of claim 1 wherein theradio frequency transmission is a two way transmission between the transponder(15) and the communication processor (11).
4. The secure road vehicle keyless entry system (10) of claim 1 furthercomprising: the communication processor (11) having a radio frequency receiver(12), a low frequency transmitter/receiver (13) and a controller (14) capable ofreading the signals sent and received by the low frequency transmitter/receiver(13); and
      the transponder (15) having a radio frequency transmitter (16) for transmittinga signal to the radio frequency receiver (12) of said communication processor (11)upon receipt of a manual stimulus and a low frequency transmitter/receiver (17) capable of reading signals received from the communication processor (11) andtransmitting an encrypted response to the communication processor (11).
5. The road vehicle keyless entry system (10) of claim 4 wherein thetransponder (15) further includes an interface circuit and a coupling coil toprovide contactless transfer of data between the radio frequency transmitter andthe low frequency transmitter/receiver.
6. The road vehicle keyless entry system (10) of claim 4 or claim 5 whereinthe radio frequency transmitter (16) of the transponder (15) and the radiofrequency receiver (12) of the communication processor (11) send and receive asignal having a frequency of 433 megahertz.
7. The road vehicle keyless entry system (10) of any of claims 4 to 6 whereinthe low frequency transmitter/receivers (17) of the transponder (15) and thecommunication processor (11) send and receive a signal having a frequency of134.2 kilohertz.
8. The road vehicle keyless entry system (10) of claim 5 wherein the manualstimulus is the manual actuation of one of a plurality of push buttons (18).
9. The road vehicle keyless entry system (10) of any of claims 4 to 8 whereinthe communication processor radio frequency receiver (12) and the transponderradio frequency transmitter (16) are radio frequency transmitter/receivers capableof two way transmissions between the communication processor (11) and thetransponder (15).
10. The road vehicle keyless entry system (10) of any of claims 4 to 9 whereinthe transponder (15) supplements or replaces the vehicle door and ignition keys,signals from the transponder (15) being received by the communication processor(11) that, after reception and verification of access codes, authorizes unlocking thevehicle and performance of vehicle related initialization functions such as seat,seat belt and vehicle mirror adjustments.
11. The road vehicle keyless entry system (10) of any of claims 5 to 9 whereinthe transponder radio frequency transmitter (16) and low frequencytransmitter/receiver (17) are in separate cases.
12. A method of vehicle keyless entry comprising the steps of:

    providing an in-vehicle communication processor (11) and a remote,miniaturized transponder (15), the communication processor (11) having a radiofrequency receiver (12), a low frequency transmitter/receiver (13) for transmittinglow frequency signals and a controller (14) for reading the signals sent andreceived by the low frequency transmitter/receiver (13) and the transponder (15)having a radio frequency transmitter (16) that transmits a signal to thecommunication processor (11) upon receipt of a manual stimulus thereat and alow frequency transmitter/receiver (17) for reading low frequency signals receivedfrom the communication processor (11) and transmitting an encrypted response tothe communication processor (11);

    providing said manual stimulus to cause said transponder (15) to send an RFsignal to said communication processor (11) and sending a low frequency signalto said low frequency transmitter/receiver (13) at said communication processor(11) in response to said manual stimulus;

    then sending a low frequency signal from said low frequencytransmitter/receiver (13) at said communication processor (11) to saidtransmitter/receiver (17) at said transponder (15) in response to at least one of saidsignals from said transponder (15) to said communication processor (11); and thensending a signal from said transponder (15) to said communication processor (11)in response to said signal from said communication processor (11) to saidtransponder (15).
13. The method of claim 12 wherein said signal from said low frequencytransmitter/receiver (13) at said communication processor (11) to said lowfrequency transmitter/receiver (17) at said transponder (15) is an encoded signal.

Images