JP5429195B2 - Electronic key system - Google Patents

Description

  The present invention relates to an electronic key system in which an in-vehicle device mounted on a vehicle and a portable device carried by a user perform at least wireless communication for collation.

  Conventionally, it consists of an in-vehicle transceiver and one or more portable transceivers. When the in-vehicle transceiver transmits a request signal and one of the portable transceivers receives the request signal, an answer is received in response to the request signal. There is an electronic key system that locks / unlocks an automobile door when a signal is transmitted and an on-vehicle transceiver receives an answer signal (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 2003-13644

  In the electronic key system as described above, it is assumed that collation of the portable device is established in a situation where the owner of the portable device is located in the detection area of the vehicle side device.

  However, in the electronic key system as described above, if the request signal from the vehicle side device is illegally copied using a repeater or the like, the holder of the portable device is not located in the detection area of the vehicle side device. However, it is possible that the collation of the portable device may be established against the will of the portable device owner. If collation of portable devices is established in this way, there is a problem that the possibility of vehicle theft becomes high.

  In the system described in Patent Document 1, the in-vehicle transmitter / receiver has a time to measure the time from when the request signal is transmitted to when the answer signal is received, and when the answer signal is received, Only when the measured time value is within the preset effective time value, it is recognized as a normal answer signal, and locking / unlocking of the automobile door, etc. is executed. With such a configuration, it is possible to prevent collation of the portable device against the intention of the owner even if the holder of the portable device is not located in the detection area of the vehicle side device.

  However, in the system as described in the above-mentioned Patent Document 1, if the delay due to the repeater or the like is small compared to the time required for collation and the collation of the portable device is established within the effective time value, unauthorized access Cannot be prevented. In addition, since the portable transceiver transmits a response signal every time it receives a request signal from the in-vehicle transceiver, there is a problem that the answer signal is easily analyzed and the confidentiality is low.

  The present invention has been made in view of the above problems, and an object thereof is to prevent unauthorized access and improve confidentiality.

  To achieve the above object, the invention according to claim 1 is an electronic key system in which an in-vehicle device mounted on a vehicle and a portable device carried by a user perform at least wireless communication for verification, The in-vehicle device includes a transmission antenna that transmits an AM modulated wave obtained by AM-modulating a signal including command data, and the portable device includes a reception antenna that receives an AM modulated wave transmitted via the transmission antenna, and a reception antenna. Detecting circuit for detecting the AM modulated wave received in this manner, and fraud determining means for determining whether the AM modulated wave received via the receiving antenna is illegal based on the falling speed of the output waveform of the detector circuit And the response signal corresponding to the command data to the in-vehicle device when it is determined by the fraud determination means that the AM modulated wave received via the receiving antenna is not illegal. A response signal transmitting means for prohibiting transmission of a response signal corresponding to command data to the in-vehicle device when the AM modulation wave transmitted and received via the receiving antenna by the fraud determining means is determined to be illegal; It is characterized by having.

  According to such a configuration, the portable device determines whether or not the AM modulated wave received via the reception antenna is illegal based on the falling speed of the output waveform of the detection circuit, and sets the reception antenna to When it is determined that the AM modulated wave received via the reception device is not illegal, the response signal corresponding to the command data is transmitted to the in-vehicle device, and the AM modulated wave received via the reception antenna is invalid. If it is determined, transmission of a response signal corresponding to command data to the in-vehicle device is prohibited, so that unauthorized access can be prevented and confidentiality can be improved.

  As described in the second aspect, the fraud determination means includes a first comparator whose input terminal is connected to the output terminal of the detection circuit, and a second comparator whose input terminal is connected to the input terminal of the detection circuit. And determining that there is an illegal bit when the number of pulses of the signal output from the second comparator exceeds the reference value after the fall of the signal output from the first comparator. It can be determined that the AM modulated wave is illegal.

  The invention according to claim 3 is characterized in that the fraud determination means determines whether or not the AM modulated wave is illegal based on the number of bits of the received data and the ratio of the number of illegal bits. It is said.

  According to such a configuration, it is determined whether or not the AM modulation wave is illegal based on the number of bits of the received data and the ratio of the number of illegal bits. It is possible to prevent an AM modulated wave from being determined to be illegal by only one bit determined to be an illegal bit.

  According to a fourth aspect of the present invention, the portable device includes notifying means for notifying the user of the abnormality, and the AM modulated wave received via the receiving antenna by the fraud determining means is illegal. When the determination is made, it is characterized in that it includes notification control means for informing the notification means that an illegal AM modulated wave has been received.

  According to such a configuration, when it is determined that the AM modulated wave received via the receiving antenna is illegal, it is notified that the illegal AM modulated wave has been received. Recognize that unauthorized access has been received.

  In addition, as in the fifth aspect of the invention, the portable device includes a determination unit that determines whether or not the AM modulated wave received via the reception antenna is a command to itself, and the notification control unit includes the determination unit. When it is determined that the AM modulated wave received via the receiving antenna is a command to itself, the notifying means can be informed that an illegal AM modulated wave has been received.

  According to a sixth aspect of the present invention, the in-vehicle device includes attenuating means for rapidly attenuating the AM modulated wave so that the falling speed of the AM modulated wave transmitted via the transmission antenna is less than the reference value. It is characterized by that.

  According to such a configuration, the in-vehicle device rapidly attenuates the AM modulated wave so that the falling speed of the AM modulated wave transmitted via the transmission antenna becomes less than the reference value. It can be made difficult to be determined to be fraudulent.

  Specifically, as in the invention described in claim 7, after the transition from the non-modulation period of the AM modulated wave to the modulation period to the transmitting antenna, the inverted signal having a phase opposite to that of the non-modulation period for a predetermined period. Is output so that the falling speed of the AM modulated wave transmitted via the transmission antenna is less than the reference value.

It is a figure showing the whole electronic key system composition concerning one embodiment of the present invention. It is a figure for demonstrating the signal waveform output to the transmission antenna in the case of an absence of an inverted signal, and an inverted signal. It is a figure for demonstrating the waveform of the AM modulation wave transmitted from a transmission antenna, when there is an inverted signal and when there is no inverted signal. It is a figure which shows the circuit structure of LF receiving part of a portable device. It is a figure for demonstrating the input waveform of an envelope detector, an output waveform, the waveform of the signal A, and the waveform of the signal B. FIG. It is the C section enlarged view in FIG. It is a flowchart of control IC of a portable machine. It is a flowchart of control IC of a portable machine. It is a figure for demonstrating the waveform at the time of receiving the LF band AM modulation wave relayed using the repeater with a portable device.

  FIG. 1 shows the overall configuration of an electronic key system according to an embodiment of the present invention. The electronic key system includes an in-vehicle device 1 mounted on a vehicle and a portable device 2. This electronic key system has a function (so-called smart entry function) for performing control such as door locking and unlocking when a regular portable device possessed by a vehicle user enters a wireless communication area around the vehicle. In addition, it also has a function (so-called remote keyless entry function) for executing control such as door locking / unlocking in response to a button operation on a portable device.

  The in-vehicle device 1 includes an ECU 10, an LF transmission unit 11, a UHF reception unit 12, an engine switch 15, a door antenna 16, an indoor antenna 17, an in-trunk antenna 18, and an out-trunk antenna 19.

  ECU10 is comprised as a computer provided with CPU, memory, I / O, etc., CPU implements various processes according to the program memorize | stored in memory.

  The LF transmission unit 11 transmits a radio signal to the portable device 2 using radio waves in the LF band. The radio signal transmitted from the LF transmitter 11 reaches only within a limited communication area via the door antenna 16, the indoor antenna 17, the trunk antenna 18, and the trunk antenna 19 at four locations. It is supposed to be. The UHF receiving unit 12 receives a radio signal transmitted from the portable device 2 using radio waves in the UHF band.

  The engine switch 15 is a switch operated by the user when starting the engine. When the operation of the engine switch 15 is detected by a signal from the engine switch 15, the ECU 10 is permitted to start the engine. If the engine start is permitted, an engine start signal is transmitted from the ECU 10 to the engine control system.

  On the other hand, the portable device 2 includes a control IC 20, an LF reception unit 21, a UHF transmission unit 22, a reception antenna 23, a transmission antenna 24, push switches 25 and 26, a display 27, a buzzer 28, and a vibrator 29.

  The receiving antenna 23 is for receiving LF band radio waves transmitted from the in-vehicle device 1. The LF receiver 21 detects the radio wave received via the receiving antenna 23 and outputs it to the control IC 20.

  The UHF transmission unit 22 modulates a signal input from the control IC 20 and outputs the modulated signal to the transmission antenna 24. The transmission antenna 24 wirelessly transmits a radio wave in the UHF band corresponding to the signal input from the UHF transmission unit 22.

  The push switches 25 and 26 are mainly prepared as a trigger key for using the remote keyless entry function. When a one-push operation is performed, the push switch 25 is locked by the door. The door of the switch 26 is unlocked.

  The display device 27 includes a display unit configured by LEDs and the like, and displays the display unit in accordance with a signal input from the control IC 20. The buzzer 28 outputs a buzzer sound according to a signal input from the control IC 20. The vibrator 29 has a motor (not shown) for generating vibration, and generates vibration by rotating the motor in accordance with a signal input from the control IC 20.

  The control IC 20 is configured as a computer including a CPU, a memory, an I / O, and the like, and the CPU performs various processes according to programs stored in the memory.

  Next, an outline of the smart entry function will be described. Each part of the in-vehicle device 1 is controlled and operated by the ECU 10, and under the control, the LF transmitter 11 periodically transmits a transmission request signal. In addition, each unit of the portable device 2 operates under the control of the control IC 20, and when the portable device 2 enters the wireless communication area where the transmission request signal from the LF transmission unit 11 can be received, the transmission request signal is transmitted to the LF. The receiving unit 21 receives it.

  Between the LF transmitter 11 and the LF receiver 21, signal transmission using LF band radio waves is performed. This is to limit the detection area of the portable device 2 to the periphery of the vehicle. In particular, by performing signal transmission from the door antenna 16, indoor antenna 17, trunk antenna 18, trunk outside antenna 19, etc., the detection area can be limited to the vicinity of the door, indoors, inside the trunk, and outside the trunk. When the portable device 2 is detected, for example, when the portable device 2 is left behind in a room or a trunk, the portable device 2 can be prevented from being closed.

  When the LF receiver 21 receives a transmission request signal from the in-vehicle device 1, the UHF transmitter 22 transmits a response signal including a code unique to the vehicle corresponding to the portable device 2. Then, on the in-vehicle device 1 side, the UHF receiver 12 receives a response signal from the portable device 2. Note that transmission of a transmission request signal from the in-vehicle device 1 and transmission of a response signal from the portable device 2 are performed in units of frames.

  Between the UHF transmitter 22 and the UHF receiver 12, signal transmission using radio waves in the UHF band is performed. This is because even if the output level of the portable device 2 is relatively weak, a corresponding communication distance can be obtained, and the response signal can be more reliably transmitted to the in-vehicle device 1 side.

  When the UHF receiver 12 receives the response signal from the portable device 2, the ECU 10 on the in-vehicle device 1 side checks whether the code included in the response signal matches the code stored in the ECU 10 If the determination is made and they match, the door is allowed to be unlocked.

  By the way, when ECU10 in this vehicle-mounted apparatus 1 transmits the radio wave of LF band by which AM modulation was carried out from each antenna 16-19 via LF receiving part 11, in order to make the fall of AM modulation wave steep, After outputting a transmission signal to each of the antennas 16 to 19, an inverted signal obtained by inverting the phase by 180 degrees is continuously output for a predetermined period.

  That is, after shifting from the non-modulation period of the AM modulated wave to the modulation period, an inverted signal having a phase opposite to that of the non-modulation period is output for a predetermined period, and transmitted via the antennas 16 to 19. The AM modulated wave is rapidly attenuated.

  FIG. 2 shows signal waveforms output to the antennas 16 to 19 when there is no inverted signal and when there is an inverted signal. As shown in the figure, when there is an inverted signal, the inverted signal is output for a certain period after the burst disappears. It should be noted that the period during which this inverted signal is output is set to an appropriate value in accordance with the Q value of each antenna 16-19.

  FIG. 3 shows waveforms of AM modulated waves transmitted from the antennas 16 to 19 when there is an inverted signal and when there is no inverted signal. As shown in the figure, it can be seen that the fall of the AM modulated wave transmitted from each of the antennas 16 to 19 is steeper when the inverted signal is present than when the inverted signal is absent.

  The LF receiver 21 in the portable device 2 includes an envelope detector that detects an LF band AM-modulated wave received by the receiving antenna 23, and receives the signal based on the falling speed of the output waveform of the envelope detector. When it is determined that the AM modulated wave is illegal, transmission of a response signal to the in-vehicle device 1 is prohibited, and when it is determined that the received AM modulated wave is not illegal, A response signal is transmitted.

  FIG. 4 shows a circuit configuration of the LF receiver 21 of the portable device 2. The portable device 2 in this embodiment includes an envelope detector 21a and comparators 21b and 21c.

  The envelope detector 21 a performs envelope detection of the electric signal input from the receiving antenna 23 and outputs a detection signal to the control IC 20. The envelope detector 21a in the present embodiment is configured so that the falling speed of the output waveform is not as slow as possible.

  The input terminal of the comparator 21b is connected to the output terminal of the envelope detector 21a, and the input terminal of the comparator 21c is connected to the input terminal of the envelope detector 21a.

  The comparator 21b outputs a high-level signal when the voltage of the output signal of the envelope detector 21a becomes equal to or higher than a predetermined threshold value, and when the voltage of the output signal of the envelope detector 21a becomes lower than a predetermined threshold value. Outputs a low level signal.

  The comparator 21c outputs a high-level signal when the voltage of the input signal of the envelope detector 21a becomes equal to or higher than a predetermined threshold, and when the voltage of the input signal of the envelope detector 21a becomes lower than a predetermined threshold. Outputs a low level signal.

  The control IC 20 detects an illegal bit by counting the number of pulses of the signal output from the comparator 21c after the signal output from the comparator 21b falls.

  FIG. 5 shows an input waveform of the envelope detector 21a, an output waveform of the envelope detector 21a, an output waveform of the comparator 21b (denoted as signal A in the drawing), and an output waveform of the comparator 21c (indicated by signal B in the drawing). )). The input waveform and output waveform of the envelope detector 21a have the relationship shown in the figure.

  FIG. 6 is an enlarged view of a portion C in FIG. The control IC 20 in the present embodiment detects illegal bits by counting the number of rising edges of the signal B after the falling of the signal A, and the ratio of the number of illegal bits to the received bits in the frame is greater than or equal to a reference value. Whether or not the received AM modulated wave is illegal is determined based on whether or not the received AM modulated wave is illegal.

  FIG. 7 shows a flowchart of this process. When the AM modulated wave transmitted from the in-vehicle device 1 is received by the receiving antenna 23 and an electric signal is input from the receiving antenna 23 to the LF receiving unit 21, a wakeup request signal is input from the LF receiving unit 21 to the control IC 20. It has become so. The control IC 20 periodically performs the process shown in FIG. Here, it is assumed that the control IC 20 is in a sleep state.

  First, it is determined whether or not a wakeup request signal is input from the LF receiver 21 (S100).

  Here, when the wakeup request signal is not input, the determination of S100 is repeated. When the wakeup request signal is input, the determination of S100 is YES, and then the sleep state is canceled and the state shifts to the wakeup state. At the same time, the clock supply to the UHF transmitter 22 is started (S104). In addition, time measurement by a timer is started (S106).

  Next, it is determined whether or not there is an electrical signal input from the LF receiver 21 (S108). Here, when an electric signal is not input from the LF receiver 21, the determination in S108 is NO, and then it is determined whether the time is up (S110). Here, the time-up means that the measurement time after starting the time measurement by the timer in S106 exceeds a predetermined reference time.

  If an electric signal is not input from the LF receiver 21 before the measurement time after starting the time measurement by the timer in S106 exceeds a predetermined reference time, the determination in S108 is NO, and the determination in S110 is It becomes YES, and it shifts to the sleep state and stops supplying the clock to the UHF transmission unit 22 (S124), and ends this processing.

  If an electrical signal is input from the LF receiver 21 before the measurement time after starting the time measurement by the timer in S106 exceeds a predetermined reference time, the determination in S108 is YES, and S200 The illegal bit detection process is executed.

  FIG. 8 shows a flowchart of the illegal bit detection process. In this illegal bit detection process, first, 0 is substituted into the count value of “illegal bit” (S201).

  Next, it is determined whether or not the waveform of the signal A, that is, the output waveform of the comparator 21b has fallen (S202). If the waveform of the signal A has not fallen, the determination in S202 is repeated. If the waveform of the signal A falls, the determination in S202 becomes YES, and then 0 is substituted for the count value of the counter “Count”. At the same time, a timer is started (S204). If the timer has already been started, the timer is restarted.

  Next, it is determined whether the waveform of the signal B, that is, the output waveform of the comparator 21c has risen (S206). If the waveform of the signal B has not risen, the process returns to S202, and when the waveform of the signal B rises, the counter “Count” is counted up. That is, the count value of the counter “Count” is incremented by one.

  Next, it is determined whether or not the count value of the counter “Count” is larger than a predetermined determination value (S210). When the falling speed of the output waveform of the envelope detector 21a is fast, the count value of the counter “Count” is equal to or less than the determination value, so the determination in S210 is NO, and conversely, the output of the envelope detector 21a When the waveform falling speed is slow, the count value of the counter “Count” is larger than the determination value, and thus the determination in S210 is YES.

  Here, when the falling speed of the output waveform of the envelope detector 21a is fast, the count value of the counter “Count” is equal to or less than the determination value, so the determination in S210 is NO and then a time-out has occurred, or Then, it is determined whether or not the waveform of the signal A has risen (S214). Note that the timeout means that the measurement time of the timer exceeds a predetermined reference time.

  If the time-out has not occurred and the waveform of the signal A has not risen, the determination in S214 is NO and the process returns to S206.

  Further, for example, when the LF band AM modulated wave from the in-vehicle device 1 is relayed using the repeater and the falling speed of the output waveform of the envelope detector 21a is slow, the count value of the counter “Count” Is larger than the determination value, the determination in S210 is YES, and then the count value of “illegal bit” is incremented by one (S212), and it is determined whether or not the reception of the frame data is completed (S212). S216).

  If the reception of frame data has not ended, the determination in S216 is NO, and the process returns to S202. When the reception of frame data is ended, the determination in S216 becomes YES, and the process returns to S112 in FIG.

  As described above, in the illegal bit determination process, after the waveform of the signal A falls, the signal B waveform is timed out or until the signal A waveform rises, the signal B waveform counts the number of rises. It is determined whether or not is larger than a predetermined determination value. When it is determined that the count value is larger than the determination value, the count value of “illegal bit” increases by one. Such processing is repeated until reception of frame data is completed. That is, the number of illegal bits in the data frame can be specified as a count value of “illegal bit”.

  Returning to the explanation of FIG. 7, next, based on whether the ratio of the number of illegal bits to the number of received bits is larger than a specified value, whether or not the received AM modulated wave is illegal, that is, illegal It is determined whether or not a proper access has been received (S112). The number of received bits can be specified as the number of bits in the data frame.

  Here, when the number of illegal bits with respect to the number of received bits is equal to or less than the specified value, the determination in S112 is NO, and a response signal corresponding to the command data included in the transmission request signal is transmitted via the UHF transmission unit 24 (S114). . If the transmission request signal is a collation command for a collation request, it is determined whether or not it is a command to itself, and if it is a command to itself, a response signal including a unique code (identification information) Send. Next, the timer is restarted (S116), and the process returns to S108.

  If the ratio of the number of illegal bits to the number of received bits is larger than the specified value and it is determined that there are illegal bits, the determination in S112 is YES, and then the command data included in the received transmission request signal is sent to itself. It is determined whether or not the command is included (S118).

  Here, when the command data included in the received transmission request signal includes a command to itself as in the case of a collation request, the determination in S118 is YES and informs the user that an illegal AM modulated wave has been received. (S120). Specifically, a display indicating that an illegal AM modulated wave has been received is displayed on the display unit of the display unit 27 for a certain period of time, and a buzzer sound for notifying that there is an abnormality is output from the buzzer 28. The vibrator 29 is driven to generate vibration, and the process proceeds to S124.

  If the command data included in the received transmission request signal does not include the command to itself, the determination in S118 is NO, and the process proceeds to S124 without notifying the user that it is abnormal.

  In S124, the process shifts to the sleep state, and the clock supply to the UHF transmission unit 22 is stopped (S124), and this process ends.

  FIG. 9 shows the waveform of the AM modulated wave received by the portable device 2 when the LF band AM-modulated radio wave from the in-vehicle device 1 is not relayed using the repeater, and the in-vehicle device 1 using the repeater. 6 shows a waveform of an AM modulated wave received by the portable device 2 when an LF band AM modulated radio wave is relayed. Each waveform in the figure is an input waveform of the LF receiver 21 shown in FIG.

  The waveform of the received AM modulated wave of the portable device 2 when the LF band AM modulated wave from the in-vehicle device 1 is relayed using the repeater is the received AM of the portable device 2 when not relayed using the repeater. Compared to the waveform of the modulated wave, the waveform falling speed is slower. As described above, when the LF band AM modulated wave from the in-vehicle device 1 is relayed using the repeater, the falling of the waveform is blunted by the repeater and the falling speed of the waveform is slowed down. The received AM modulated wave is illegal, that is, it is determined that an unauthorized access has been received, and transmission of a response signal is prohibited. Although the repeater is configured using an antenna having a low Q value, it is possible to reduce the dullness of the falling of the waveform by the repeater. It is practically difficult to illegally duplicate the request signal from the vehicle side device by using a repeater or the like so that the owner of the machine is not aware.

  According to the configuration described above, the portable device determines whether or not the AM modulated wave received via the receiving antenna is illegal based on the falling speed of the output waveform of the detection circuit, and passes through the receiving antenna. If it is determined that the received AM modulated wave is not illegal, a response signal corresponding to the command data included in the transmission request signal is transmitted to the in-vehicle device, and the AM modulated wave received via the receiving antenna is transmitted. If it is determined to be unauthorized, transmission of a response signal to the in-vehicle device is prohibited, so that unauthorized access can be prevented and confidentiality can be improved.

  A signal output from the first comparator, the first comparator having an input terminal connected to the output terminal of the detection circuit and a second comparator having an input terminal connected to the input terminal of the detection circuit. It is possible to determine whether or not the received AM modulated wave is illegal by counting the number of pulses of the signal output from the second comparator after the fall of.

  Whether or not the received AM modulated wave is illegal based on the ratio of the number of bits of the received data and the number of illegal bits in which the number of pulses of the signal output from the second comparator exceeds the reference value. Therefore, for example, it is possible to prevent the received AM modulated wave from being determined to be illegal even if there is only one bit determined to be incorrect due to the influence of ambient noise or the like. can do.

  In addition, when it is determined that the AM modulated wave received via the receiving antenna is illegal, the user is notified that the unauthorized AM modulated wave has been received. I can recognize that.

  Further, the portable device determines whether or not the AM modulated wave received via the receiving antenna is a command to itself, and determines that the AM modulated wave received via the receiving antenna is a command to itself. If an incorrect bit is received, it will be notified that an illegal bit has been received, so that it is avoided that the user is misreported when a command from another vehicle, that is, a command to another portable device is relayed. Can do.

  In addition, the in-vehicle device attenuates the AM modulated wave so that the falling speed of the AM modulated wave transmitted via the transmission antenna is less than the reference value, so that the AM modulated wave that is not relayed is illegal. It can be made difficult to be determined.

  Specifically, after outputting an AM modulated wave to be transmitted to the transmission antenna, an inverted signal of an opposite phase is continuously output to the transmission antenna for a predetermined period, that is, from the non-modulation period of the AM modulated wave to the modulation period. The falling speed of the AM modulated wave transmitted via the transmission antenna is less than the reference value by outputting an inverted signal having a phase opposite to that of the previous non-modulation period for a predetermined period after the transition to Can be.

  In addition, this invention is not limited to the said embodiment, Based on the meaning of this invention, it can implement with a various form.

  For example, in the above-described embodiment, when the ECU 10 in the in-vehicle device 1 transmits the LF band AM modulated wave from each of the antennas 16 to 19 via the LF receiver 11, the fall of the LF band AM modulated wave is steep. In order to achieve this, the AM modulated wave to be transmitted to each of the antennas 16 to 19 is output, and then the inverted signal with the phase inverted by 180 degrees is continuously output for a predetermined period. There is no need to output an inverted signal.

  Further, in the above embodiment, the ECU 10 in the in-vehicle device 1 outputs the AM modulated wave to be transmitted to each of the antennas 16 to 19 and then inverts the waveform that has been output so far by 180 degrees for a predetermined period. The inverted signal is continuously output so that the fall of the AM modulation wave when transmitting the LF band AM modulation wave from each of the antennas 16 to 19 is made steep. However, the present invention is limited to such a configuration. For example, a switch that forcibly connects each connection point of each antenna 16 to 19 and the LF transmitter 11 to GND is provided, and an AM modulated wave to be transmitted to each antenna 16 to 19 is output, and then the switch Is turned on to forcibly connect the connection points of the antennas 16 to 19 and the LF transmitter 11 to the GND, so that an AM modulated wave in the LF band is transmitted from each of the antennas 16 to 19. It may be a steep fall of the AM modulated wave at the time that.

  Moreover, in the said embodiment, although the detection circuit was comprised by the envelope detector, it is not limited to an envelope detector.

  In the above embodiment, the first comparator includes a first comparator whose input terminal is connected to the output terminal of the detection circuit, and a second comparator whose input terminal is connected to the input terminal of the detection circuit. After the fall of the signal output from the second comparator, the number of pulses of the signal output from the second comparator is counted to determine whether or not the received AM modulated wave is illegal. For example, the amount of change per time in the detection output waveform of the detection circuit is detected, and the received AM modulated wave is invalid based on whether the amount of change per time is greater than or equal to a reference value. It may be determined whether or not.

  The correspondence relationship between the configuration of the above embodiment and the configuration of the claims will be described. S200, S112, comparators 21b, 21c correspond to fraud determination means, S114 corresponds to response signal transmission means, and display device 27, the buzzer 28, and the vibrator 29 correspond to notification means, S120 corresponds to notification control means, S118 corresponds to determination means, and the AM modulation that the ECU 10 transmits to each of the antennas 16 to 19 via the LF receiver 11 After outputting the wave, the process of outputting the inverted signal of the opposite phase for a predetermined period corresponds to the attenuation means.

DESCRIPTION OF SYMBOLS 1 In-vehicle apparatus 2 Portable machine 10 ECU
11 LF transmitter 12 UHF receiver 15 Engine switch 16 Door antenna 17 Indoor antenna 18 Trunk antenna 19 Trunk antenna 20 Control IC
21 LF receiver 21a Envelope detector 21b, 21c Comparator 22 UHF transmitter 23 Receive antenna 24 Transmit antenna 25, 26 Push switch 27 Display 28 Buzzer 29 Vibrator

Claims (7)

An in-vehicle device mounted on a vehicle and a portable device carried by a user are electronic key systems that perform at least wireless communication for verification,
The in-vehicle device is
A transmission antenna that transmits an AM-modulated wave obtained by AM-modulating a signal including command data;
The portable device is
A receiving antenna for receiving the AM modulated wave transmitted via the transmitting antenna;
A detection circuit for detecting the AM modulated wave received via the reception antenna;
Comprising fraud determination means for determining whether or not the AM modulated wave received via the receiving antenna is fraudulent based on the falling speed of the output waveform of the detection circuit;
When it is determined by the fraud determination means that the AM modulated wave received via the receiving antenna is not illegal, a response signal corresponding to the command data is transmitted to the in-vehicle device, and the fraud determination means Response signal transmitting means for prohibiting transmission of a response signal corresponding to the command data to the in-vehicle device when it is determined that the AM modulated wave received via the receiving antenna is illegal. An electronic key system characterized by that. The fraud determination means includes
A first comparator having an input terminal connected to the output terminal of the detection circuit;
A second comparator having an input terminal connected to the input terminal of the detection circuit,
By determining that there is an illegal bit when the number of pulses of the signal output from the second comparator exceeds a reference value after the fall of the signal output from the first comparator, the AM modulated wave The electronic key system according to claim 1, wherein the electronic key system is determined to be illegal.   The said fraud determination means determines whether or not the AM modulated wave is fraudulent based on the number of bits of received data and the ratio of the number of fraudulent bits. Electronic key system. The portable device is
A notification means for notifying a user;
A notification control means for informing the notification means that an unauthorized AM modulated wave has been received, when the unauthorized modulation means determines that the AM modulated wave received via the receiving antenna is unauthorized; The electronic key system according to any one of claims 1 to 3, further comprising: The portable device is
Determination means for determining whether the command data received via the receiving antenna is a command to itself;
When the determination unit determines that the command data received via the reception antenna is a command to itself, the notification control unit causes the notification unit to notify that an illegal AM modulated wave has been received. The electronic key system according to claim 4.   The on-vehicle device includes attenuation means for rapidly attenuating the AM modulated wave so that a falling speed of the AM modulated wave transmitted via the transmission antenna is less than the reference value. Item 6. The electronic key system according to any one of Items 1 to 5.   The attenuating means outputs an inverted signal having a phase opposite to that of the non-modulation period for a predetermined period after transition from the non-modulation period of the AM modulated wave to the modulation period. Electronic key system as described.

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