JP5391215B2 - Electronic key system - Google Patents

Description

  The present invention relates to an electronic key system.

  Conventionally, in an electronic key system, locking and unlocking of a vehicle door, engine starting, etc. are permitted through wireless communication between the electronic key and the vehicle. For example, the vehicle includes an in-vehicle antenna that transmits a request signal to an in-vehicle communication area and an out-of-vehicle antenna that transmits a request signal to an out-of-vehicle communication area around the vehicle. When the electronic key that has entered any communication area receives the request signal, it transmits a response signal including its own ID code. The vehicle receives a response signal to the request signal transmitted through the antenna outside the vehicle, and permits the locking and unlocking of the vehicle door when the ID code included therein is verified. On the other hand, the vehicle receives a response signal to the request signal transmitted through the in-vehicle antenna, and permits the engine to start when collation of the ID code included therein is established.

  In recent years, there is a concern about unauthorized communication in which an electronic key that exists far away using a repeater that relays radio waves (request signal, response signal) is disguised as if it exists outside the vehicle interior. Unauthorized communication using this repeater may cause unlocking of the vehicle door or engine start. Therefore, for example, as disclosed in Patent Document 1, a security measure against unauthorized communication using a repeater is considered.

JP 2006-118886 A

  The present applicant is considering preventing unauthorized communication using a repeater by changing the signal strength of a radio signal transmitted and received between the vehicle and the electronic key. For example, as shown to Fig.6 (a), the transmission antenna 101 provided in a vehicle transmits 1st radio signal S1 from which signal strength differs, and 2nd radio signal S2 in order. The electronic key 102 detects received signal strength RSSI (Receive Signal Strength Indication) of both signals S1 and S2 from the transmitting antenna 101. Here, the repeater does not imitate the signal strength of the radio signal. That is, the repeater transmits both signals S1 and S2 to the electronic key 102 with the same signal strength even if both signals S1 and S2 having different RSSIs are received. Therefore, when a repeater exists between the transmission antenna 101 and the electronic key 102, there is almost no difference in RSSI between the two radio signals S1 and S2. At this time, it is determined that the communication is unauthorized using the repeater, and unlocking of the vehicle door and starting of the engine are not permitted.

  On the other hand, as shown in FIG. 6B, when there is no repeater between the transmission antenna 101 and the electronic key 102, there is a difference in RSSI between the two radio signals S <b> 1 and S <b> 2 according to the position of the electronic key 102. When the RSSI difference is equal to or greater than the threshold value, it is determined that the communication is not unauthorized using a repeater, and unlocking of the vehicle door is permitted.

  Here, the RSSI that the electronic key 102 can detect is limited. That is, as shown in FIG. 6B, although the RSSI in the certain range A can be detected, the RSSI exceeding the certain range A cannot be detected. Therefore, for example, when the electronic key 102 is present at a position P1 close to the transmission antenna 101, the RSSIs of both the radio signals S1 and S2 are the same at the maximum value in the certain range A. For this reason, there is a possibility that it is determined that the communication is illegal using the repeater even though the RSSI between the radio signals S1 and S2 is not different and the communication is not unauthorized using the repeater.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an electronic key system that can more accurately determine whether or not the communication is unauthorized using a repeater. is there.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
According to the first aspect of the present invention, in the electronic key system in which control of the controlled object is executed through a wireless signal transmitted and received between the controlled object and the electronic key, the controlled object or the electronic key is a first wireless signal. , And a transmitter that transmits a second radio signal having a signal strength lower than that of the first radio signal, and a radio that is provided in the electronic key or the control target and transmitted from the control target or the electronic key A detection unit that detects a signal strength of a signal, and a difference in signal strength between the two radio signals that is provided in the control target or the electronic key and is recognized through the detection unit is a signal of the two radio signals to be transmitted. A determination unit that determines whether or not a threshold value set based on a difference in strength is exceeded, wherein the control object or the electronic key has a difference in signal strength between the two radio signals through the determination unit. The second radio signal in a state in which the execution of the control of the control target is permitted when it is determined to exceed the threshold value, and the execution of the control of the control target is prohibited when it is determined to be less than or equal to the threshold value. A new radio signal having a weaker signal strength is transmitted, and the new radio signal is used as the second radio signal in the same manner as described above, the determination unit determines that the difference in signal strength between the two radio signals is the threshold value. The gist is that the control object or the electronic key permits or prohibits execution of the control of the control object based on the determination.

  According to the configuration, a plurality of radio signals having different signal strengths are transmitted. In the case of unauthorized communication using a repeater, the difference in signal strength between these signals is below a threshold value. This is because the repeater does not imitate the signal strength of the radio signal, and therefore, when the repeater is used, the difference in signal strength of each radio signal transmitted from the repeater approximates zero.

  Further, as the distance between the electronic key and the control target decreases, the signal strength of the radio signal detected through the detection unit increases. However, there is an upper limit on the signal strength that can be detected by the detection unit. However, when the electronic key and the control target are close to each other, even if radio signals having different signal strengths are transmitted, the signal strengths of both radio signals are transmitted through the detection unit. The difference may not be detected.

  As described above, when the difference in signal strength between the two radio signals detected through the detection unit is equal to or less than the threshold value, the communication is not necessarily unauthorized communication using the repeater, and the electronic key and the control target are approached. There is a possibility. Therefore, when the difference between the signal strengths of the two radio signals is equal to or less than the threshold value, the electronic key or the control target is in a state in which execution of control of the control target is prohibited, A new radio signal having a signal strength lower than that of the signal is transmitted. When the electronic key and the controlled object are close to each other rather than unauthorized communication using a repeater, the signal strength of the new radio signal is less than the upper limit of the signal strength that can be detected by the detection unit. A difference occurs in the signal strength of the radio signal. When this difference exceeds the threshold value, control of the controlled object is permitted. As a result, it is possible to more accurately determine whether the communication is unauthorized using the repeater.

  According to a second aspect of the present invention, in the electronic key system according to the first aspect, when the control object or the electronic key transmits the new wireless signal as the second wireless signal, the determination unit When it is determined that the difference between the signal strengths of the two radio signals exceeds the threshold value, the signal strength of the determined second radio signal is stored, and the next time between the electronic key and the control target is stored. The gist is that the signal strength of the second radio signal transmitted at the time of communication is the stored signal strength.

  According to this configuration, when it is determined that the difference between the signal strength of the new radio signal transmitted as the second radio signal and the signal strength of the first radio signal exceeds the threshold value, the next time At the time of communication, the second radio signal is transmitted from the beginning with the signal strength of the new radio signal. As a result, the number of times of transmission of the second radio signal and the number of times of determination whether or not the difference in signal strength exceeds the threshold value are reduced. Therefore, when unauthorized communication using a repeater is not performed, execution of control is permitted more quickly.

  According to a third aspect of the present invention, in the electronic key system according to the first or second aspect, the control object or the electronic key is a signal intensity of the new radio signal as the second radio signal by the detection unit. The gist is to determine a state in which the execution of the control of the control object is prohibited when it is not detected that the communication is unauthorized communication using a repeater.

  Each time the difference in signal strength is less than or equal to the threshold value, a new radio signal having a signal strength lower than that of the previously transmitted second radio signal is transmitted as the second radio signal. That is, the signal strength of the second radio signal (new radio signal) is weakened at every transmission. Here, the repeater has a lower limit of received signal strength at which a radio signal can be relayed. When the received signal strength of the second radio signal falls below this lower limit, the repeater does not relay the second radio signal. In this case, the signal intensity of the second radio signal is not detected by the detection unit. Therefore, with this, it can be determined that the execution of the control of the control target is prohibited, assuming that the communication is unauthorized using the repeater.

  According to the present invention, in an electronic key system, it is possible to more accurately determine whether or not the communication is unauthorized using a repeater.

The block diagram of an electronic key system. The timing chart which shows RSSI and transmission timing of various signals. The top view of the vehicle which showed transmission areas, such as a signal for measurement. (A)-(c) is a signal diagram which showed RSSI of each signal for a measurement. (A) is a flowchart which shows the process sequence of the electronic key control part 11, (b) is a flowchart which shows the process sequence of the vehicle-mounted control part 21. (A) is the top view which showed the position of the electronic key with respect to the antenna of a vehicle, (b) is a graph which shows the change of RSSI according to the position of the electronic key.

Hereinafter, an electronic key system according to the present invention will be described with reference to FIGS.
As shown in FIG. 1, the electronic key system 1 includes an electronic key 10 possessed by a user and an in-vehicle device 20 provided in the vehicle 2. Mutual communication is performed between the electronic key 10 and the in-vehicle device 20, and locking / unlocking of the vehicle door and starting of the engine are permitted on the condition that the mutual communication is established outside and inside the vehicle.

<Electronic key>
The electronic key 10 includes an electronic key control unit 11, an LF reception unit 12, and a UHF transmission unit 13.

  The electronic key control unit 11 is configured by a computer unit and includes a nonvolatile memory 11a. An ID code unique to the electronic key 10 is stored in the memory 11a.

  As shown in FIG. 2, the LF receiver 12 continuously receives a wake signal Swk and a first measurement signal Srs1, and a wake signal Swk and a second measurement signal Srs2 from the vehicle through the reception antenna 12a. Receive. Then, the LF receiver 12 demodulates these signals into pulse signals and outputs them to the electronic key controller 11. The wake signal Swk and the measurement signals Srs1 and Srs2 are LF (Low Frequency) band radio signals.

  Further, as shown in FIG. 1, the LF receiver 12 is provided with an RSSI detection circuit 16. The RSSI detection circuit 16 detects the RSSI of the radio signal received through the reception antenna 12 a and outputs the detection result to the electronic key control unit 11.

  When the electronic key control unit 11 recognizes each wake signal Swk, the RSSI detection circuit 16 recognizes the RSSI of each of the measurement signals Srs1 and Srs2 input thereafter. When the electronic key control unit 11 recognizes the second wake signal Swk and the second measurement signal Srs2, the electronic key control unit 11 generates an ack signal Sac and outputs it to the UHF transmission unit 13. The UHF transmission unit 13 modulates the ACK signal Sac and transmits it as a UHF (Ultra High Frequency) band radio signal via its own transmission antenna 13a.

As shown in FIG. 2, a challenge signal Scc is transmitted from the in-vehicle device 20 in response to the ACK signal Sac.
When the LF receiving unit 12 receives the challenge signal Scc via the receiving antenna 12a, the LF receiving unit 12 demodulates the challenge signal Scc into a pulse signal and outputs it to the electronic key control unit 11. When the challenge signal Scc is input from the LF receiving unit 12, the electronic key control unit 11 recognizes the challenge code included in the challenge signal Scc. Then, the electronic key control unit 11 generates a response code by encrypting the challenge code.

  The electronic key control unit 11 generates a response signal Sre including the generated response code and RSSI of both measurement signals Srs1 and Srs2 as RSSI information, and outputs this signal to the UHF transmission unit 13. The UHF transmission unit 13 modulates the response signal Sre and transmits the response signal Sre as a UHF band radio signal via the transmission antenna 13a.

  In addition, as shown in FIG. 2, when confirmation that the vehicle side is not unauthorized communication using a repeater cannot be obtained, the wake signal Swk and the third measurement signal are transmitted from the in-vehicle device 20 to the response signal Sre. Srs3 is transmitted.

When the electronic key control unit 11 recognizes the wake signal Swk, the electronic key control unit 11 recognizes the RSSI of the third measurement signal Srs3 input thereafter through the RSSI detection circuit 16. Then, the electronic key control unit 11 generates an RSSI information signal Sri including the RSSI of the third measurement signal Srs3 and outputs this signal to the UHF transmission unit 13. The UHF transmitter 13 modulates the RSSI information signal Sri, and transmits the RSSI information signal Sri as a UHF band radio signal via the transmission antenna 13a.
<In-vehicle device>
As shown in FIG. 1, the in-vehicle device 20 includes an in-vehicle control unit 21, an in-vehicle transmission unit 22, an in-vehicle transmission unit 23, and an in-vehicle reception unit 24. In addition, a lock switch 36, an engine switch 33, a door lock device 34, and an engine device 35 are electrically connected to the in-vehicle control unit 21.

  As shown in an enlarged manner in the circle of FIG. 3, the vehicle outside transmission unit 22 is built in the outside door handle 4 of the vehicle door. The lock switch 36 is provided on the outer surface of the outside door handle 4 and outputs an operation signal to that effect to the in-vehicle control unit 21 when pressed by the user.

  The in-vehicle receiving unit 24 is provided substantially in the center of the vehicle interior. Further, two in-vehicle transmission units 23 are provided along the vertical direction in FIG. Furthermore, the engine switch 33 is provided in the vicinity of the driver's seat, and outputs an operation signal to that effect to the in-vehicle control unit 21 when pressed by the user. Further, the door lock device 34 automatically locks and unlocks the vehicle door when the vehicle door is closed.

  The in-vehicle control unit 21 is configured by a computer unit and includes a nonvolatile memory 21a. In the memory 21a, the same ID code as the ID code stored in the electronic key 10 is stored.

  When the in-vehicle control unit 21 recognizes that the lock switch 36 has been operated, the in-vehicle control unit 21 sequentially generates the wake signal Swk, the first measurement signal Srs1, the wake signal Swk, and the second measurement signal Srs2, and generates them. Output to the transmitter 22.

  When the wake signal Swk and the first measurement signal Srs1, and the wake signal Swk and the second measurement signal Srs2 are continuously input from the in-vehicle control unit 21, the outside-vehicle transmission unit 22 modulates them sequentially. Then, the outside transmission unit 22 transmits the modulated signals as LF band radio signals via its transmission antenna 22a. Here, the first measurement signal Srs1 corresponds to a first radio signal, and the second measurement signal Srs2 corresponds to a second radio signal. Further, the second radio signal is not always the second measurement signal Srs2, and may be a 2 + n measurement signal Srs2 + n (n is a natural number), which will be described in detail later. These measurement signals have different signal strengths. The memory 21a stores the signal strength of the second radio signal (measurement signal) in an updatable manner. Based on the signal strength stored in the memory 21a, each measurement signal having a different signal strength can be wirelessly transmitted. In the initial state, the second radio signal is the second measurement signal Srs2, and the signal strength of the second measurement signal Srs2 is stored in the memory 21a.

  As shown in FIG. 2, the signal strength of the first measurement signal Srs1 is set to be stronger than the signal strength of the second measurement signal Srs2. Therefore, the areas where the first measurement signal Srs1 and the second measurement signal Srs2 are transmitted are different. Specifically, as shown in FIG. 3, the first measurement signal Srs1 is transmitted to a first transmission area 31 formed in a semicircular shape outside each outside door. The second measurement signal Srs2 is transmitted to the second transmission area 32 that has the same shape as the first transmission area 31 and is included therein.

As shown in FIG. 2, the ACK signal Sac is returned from the electronic key 10 that has received the second wake signal Swk and the second measurement signal Srs2.
The in-vehicle receiving unit 24 receives the ACK signal Sac through the receiving antenna 24a. Then, the in-vehicle receiving unit 24 demodulates the ACK signal Sac into a pulse signal and outputs it to the in-vehicle control unit 21.

  When the in-vehicle control unit 21 recognizes the ACK signal Sac, the in-vehicle control unit 21 generates a challenge signal Scc including a challenge code and outputs it to the outside transmission unit 22. At this time, the in-vehicle control unit 21 generates a response code by encrypting the challenge code. The encryption key used for this encryption is the same for the electronic key 10 and the in-vehicle device 20. When the challenge signal Scc is input from the in-vehicle control unit 21, the vehicle outside transmission unit 22 modulates the challenge signal Scc and transmits the modulated signal via its own transmission antenna 22a.

As shown in FIG. 2, a response signal Sre is returned from the electronic key 10 in response to the challenge signal Scc.
The in-vehicle receiving unit 24 receives the response signal Sre from the electronic key 10 via the receiving antenna 24a. Then, the in-vehicle receiver 24 demodulates the response signal Sre into a pulse signal and outputs it to the in-vehicle controller 21.

  The in-vehicle control unit 21 recognizes the ID code included in the response signal Sre, the response code, and the RSSI of both measurement signals Srs1 and Srs2, which are RSSI information. The vehicle-mounted control unit 21 collates the response code generated by itself with the response code included in the response signal Sre (response collation). Moreover, the vehicle-mounted control part 21 collates with the ID code contained in the response signal Sre, and the ID code memorize | stored in the memory 21a (ID code collation). When the in-vehicle control unit 21 determines that the response verification and the ID code verification have been established, the difference ΔRs between the RSSI of the first measurement signal Srs1 recognized based on the RSSI information and the RSSI of the second measurement signal Srs2 is determined. It is determined whether or not the threshold value Th is exceeded.

  As shown in FIG. 4A, the in-vehicle control unit 21 determines that communication with the electronic key 10 is not illegal using a repeater when the difference ΔRs between the RSSIs exceeds the threshold Th. Then, the locking / unlocking state of the vehicle door is switched through the door lock device 34.

  Here, when the difference ΔRs between the two RSSIs is equal to or smaller than the threshold value Th, there is a possibility of unauthorized communication using a repeater and a possibility that the electronic key 10 is approaching the transmission antenna 22a. . The reason for this has been described above in “Problems to be Solved by the Invention”, and thus the description thereof will be omitted. In the present invention, when the difference ΔRs between the RSSIs is equal to or less than the threshold value Th, it is possible to determine which of the above two possibilities.

  Specifically, when the difference ΔRs between the RSSIs is equal to or smaller than the threshold Th, the in-vehicle control unit 21 generates the wake signal Swk and the third measurement signal Srs3 as shown in FIG. It is output to the outside transmission unit 22. The outside transmission unit 22 modulates the wake signal Swk and the third measurement signal Srs3, and transmits the modulated signal as an LF band radio signal via its own transmission antenna 22a.

  In response to the third measurement signal Srs3, the electronic key 10 returns an RSSI information signal Sri including the RSSI information of the signal. When the in-vehicle controller 21 recognizes the RSSI information signal Sri received and demodulated via the in-vehicle receiver 24, the RSSI of the third measurement signal Srs3 and the first measurement signal Srs1 included in the RSSI information signal Sri. It is determined whether or not the difference ΔRs from the RSSI exceeds a threshold value Th.

As shown in FIG. 4B, the signal strength of the third measurement signal Srs3 transmitted from the transmission antenna 22a is set to be weaker than the signal strength of the second measurement signal Srs2.
As a result, the RSSI of the first measurement signal Srs1 (corresponding to the first radio signal S1) is detected by the RSSI detection circuit 16 as shown in FIG. 6B in the “problem to be solved by the invention”. Even if the upper limit of the certain range A that can be exceeded is exceeded, the difference ΔRs between the RSSI of the third measurement signal Srs3 and the RSSI of the first measurement signal Srs1 as shown by the alternate long and short dash line in FIG. Occurs. When the in-vehicle control unit 21 determines that the difference ΔRs between the RSSI of the third measurement signal Srs3 and the RSSI of the first measurement signal Srs1 exceeds the threshold Th, it is not an unauthorized communication using a repeater. Judging. In this case, the locking / unlocking state of the vehicle door is switched through the door lock device 34 as described above. Further, when the in-vehicle control unit 21 determines that the communication is not unauthorized using the repeater, the second measurement signal stored in the memory 21a so that the second wireless signal is the third measurement signal Srs3. The signal strength of Srs2 is updated to the signal strength of the third measurement signal Srs3. Accordingly, in the next communication, the in-vehicle control unit 21 transmits the third measurement signal Srs3 instead of the second measurement signal Srs2 after the first measurement signal Srs1.

  Here, the location where the electronic key 10 is held during communication is biased for each user. For this reason, once the electronic key 10 is located at a position close to the transmission antenna 22a during communication, it is assumed that the same tendency occurs during the next communication. Therefore, by updating the second radio signal as described above, the process of transmitting the second measurement signal Srs2 during the next communication, and the difference ΔRs between the two measurement signals Srs1 and Srs2 has the threshold Th. It is possible to reduce the processing related to the determination of whether or not it exceeds.

  When the vehicle-mounted control unit 21 determines that the difference ΔRs between the RSSI of the third measurement signal Srs3 and the RSSI of the first measurement signal Srs1 is equal to or less than the threshold value Th, A measurement signal Srs4 is transmitted. The signal strength of the fourth measurement signal Srs4 is set to be weaker than the signal strength of the third measurement signal Srs3. As in the case of the third measurement signal Srs3, the RSSI of the fourth measurement signal Srs4 and the RSSI of the first measurement signal Srs1 based on the RSSI information signal Sri corresponding to the fourth measurement signal Srs4. It is determined whether or not the difference ΔRs exceeds the threshold Th. If the RSSI difference ΔRs exceeds the threshold Th, the locking / unlocking state is switched. Similarly, as shown in FIG. 4C, as long as the RSSI difference ΔRs is equal to or smaller than the threshold Th and the RSSI information signal Sri is returned, the fifth and subsequent measurement signals are also transmitted. . That is, in the case of unauthorized communication through the repeater, the 2 + n measurement signal Srs 2 + n (n is a natural number) is transmitted. The signal intensity of the (2 + n) measurement signal Srs2 + n transmitted from the transmission antenna 22a becomes weaker every transmission.

  Here, the lower limit of the RSSI that enables relaying is determined for the repeater. When the repeater receives the second + n measurement signal Srs2 + n, if the RSSI is equal to or lower than the lower limit value, the repeater cannot relay the measurement signal. Therefore, the RSSI information signal Sri is not returned from the electronic key 10 to the in-vehicle device 20 in accordance with the measurement signal.

  When it is determined that the RSSI information signal Sri is not received with respect to the transmitted measurement signal, the in-vehicle control unit 21 determines that the communication is unauthorized using the repeater. In this case, unlocking of the vehicle door is prohibited.

  In addition, when the in-vehicle control unit 21 recognizes that the engine switch 33 has been operated, the wake signal Swk and the first signal are transmitted via the in-vehicle transmission unit 23 and the transmission antenna 23a in the same manner as when the lock switch 36 is operated. The measurement signal Srs1, the wake signal Swk, and the second measurement signal Srs2 are continuously transmitted to the vehicle interior. Similarly to the above, the vehicle-mounted control unit 21 determines whether or not the response verification and ID code verification and the RSSI difference ΔRs exceed the threshold Th.

  Even in the vehicle, a situation similar to the above occurs because the distance between the transmission antenna 23a and the electronic key 10 is short. Therefore, the in-vehicle control unit 21 transmits the (2 + n) measurement signal Srs2 + n as necessary to determine whether or not the communication is unauthorized using the repeater, as described above. The in-vehicle controller 21 starts the engine through the engine device 35 when determining that the communication is not unauthorized using the repeater. On the other hand, the in-vehicle control unit 21 does not start the engine when it is determined that the communication is unauthorized using the repeater.

Next, the operation of the electronic key control unit 11 will be described with reference to the flowchart of FIG.
When receiving the wake signal Swk and the two measurement signals Srs1, Srs2, the electronic key control unit 11 recognizes the RSSI of both the measurement signals Srs1, Srs2 (S101). Then, the electronic key control unit 11 transmits an ACK signal Sac (S102). When receiving the challenge signal Scc, the electronic key control unit 11 transmits a response signal Sre (S103). Further, upon receiving the wake signal Swk and the third measurement signal Srs3, the electronic key control unit 11 recognizes the RSSI of the third measurement signal Srs3 (S104), and the RSSI information of the third measurement signal Srs3. The RSSI information signal Sri including is transmitted (S105). This is the end of the process.

  Next, the operation of the in-vehicle control unit 21 will be described with reference to the flowchart of FIG. The flowchart is started when the lock switch 36 or the engine switch 33 is operated.

  First, the in-vehicle controller 21 continuously transmits the wake signal Swk and the first measurement signal Srs1, and the wake signal Swk and the second measurement signal Srs2 (S111 and S112). The signal strength of the second measurement signal Srs2 is stored in the memory 21a. Next, when receiving the ACK signal Sac, the vehicle-mounted control unit 21 transmits a challenge signal Scc (S113). Further, when the in-vehicle control unit 21 receives the response signal Sre and determines that the response verification and the ID code verification have been established (S114), both the measurement signals Srs1, Srs2 are based on the RSSI information included in the response signal Sre. It is determined whether or not the difference ΔRs exceeds the threshold value Th (S115).

  When determining that the difference ΔRs between the two measurement signals Srs1 and Srs2 is equal to or less than the threshold value Th (NO in S115), the vehicle-mounted control unit 21 transmits the wake signal Swk and the third measurement signal Srs3 (S116). .

  The in-vehicle controller 21 determines whether or not the RSSI information signal Sri from the electronic key 10 for the third measurement signal Srs3 has been received (S117). When it is determined that the in-vehicle control unit 21 has received the RSSI information signal Sri (YES in S117), the in-vehicle control unit 21 returns to the process of step S115 and is included in the RSSI of the first measurement signal Srs1 and the RSSI information signal Sri. It is determined whether or not a difference ΔRs between the third measurement signal Srs3 and RSSI exceeds a threshold Th. Until the difference ΔRs between the two RSSIs exceeds the threshold Th (YES in S115) or the RSSI information signal Sri cannot be received (NO in S117), the processes in steps S115 to S117 are repeated. At this time, the measurement signal Srs2 + n of the Srs2 + n obtained by adding 1 to “n” for each process of step S116 is transmitted.

  When determining that the RSSI difference ΔRs between the measurement signals Srs1, Srs2 + n exceeds the threshold Th (YES in S115), the vehicle-mounted control unit 21 determines that the communication is not unauthorized using the repeater (S118). . And the vehicle-mounted control part 21 updates the signal strength of the 2nd radio | wireless signal memorize | stored in the memory 21a with the signal strength of the signal for a measurement last transmitted in step S116 (S119). When it is determined in the first step S115 that the difference ΔRs between the measurement signals Srs1 and Srs2 exceeds the threshold Th, the signal strength of the second radio signal stored in the memory 21a is the second measurement. The signal strength of the service signal Srs2 is maintained. Then, the in-vehicle control unit 21 starts the engine or unlocks the vehicle door (S120).

  On the other hand, when the in-vehicle control unit 21 cannot receive the RSSI information signal Sri (NO in S117), the in-vehicle control unit 21 determines that the communication is unauthorized using the repeater (S121). In this case, the flowchart is terminated without starting the engine or unlocking the vehicle door.

As described above, according to the embodiment described above, the following effects can be obtained.
(1) Even if the RSSI difference ΔRs between the measurement signals Srs1 and Srs2 detected through the RSSI detection circuit 16 is equal to or less than the threshold value Th, the communication is not necessarily illegal using a repeater. There is a possibility that the electronic key 10 and the transmission antennas 22a and 23a are close to each other. Therefore, when the RSSI difference ΔRs between the measurement signals Srs1 and Srs2 is equal to or less than the threshold value Th, the in-vehicle control unit 21 prohibits switching of the locking / unlocking state of the vehicle door and the like. Srs1 and a third measurement signal Srs3 having a signal intensity lower than that of the previous second measurement signal Srs2 are transmitted as the second radio signal. When the electronic key 10 and the transmission antennas 22a and 23a are close to each other, not the unauthorized communication using the repeater, the RSSI of the third measurement signal Srs3 is the upper limit of the RSSI that the RSSI detection circuit 16 can detect. As a result of the following, a difference ΔRs occurs in the RSSI of both measurement signals Srs1 and Srs3. When the difference ΔRs exceeds the threshold value Th, it is possible to switch the locking / unlocking state of the vehicle door. As a result, it is possible to more accurately determine whether the communication is unauthorized using the repeater.

  (2) When it is determined that the RSSI difference ΔRs between the third measurement signal Srs3 and the first measurement signal Srs1 exceeds the threshold Th, the third measurement signal Srs3 is used for the third measurement from the beginning at the next communication. Signal Srs3 is transmitted as the second radio signal. This eliminates the need to transmit the second measurement signal Srs2 again. Therefore, the number of transmissions of measurement signals and the number of determinations as to whether or not the RSSI difference ΔRs exceeds the threshold value Th are reduced, and if it is not unauthorized communication using a repeater, the vehicle door is more quickly Is permitted.

  (3) Every time the RSSI difference ΔRs becomes equal to or smaller than the threshold Th (NO in S115), a measurement signal having a signal strength weaker than the previously transmitted measurement signal is transmitted as the second radio signal. That is, the signal strength of the Srs2 + n measurement signal Srs2 + n transmitted in step S116 each time transmission is weakened. Here, the repeater has a lower limit of RSSI capable of relaying a radio signal. When the RSSI of the measurement signal transmitted in step S116 falls below this lower limit, the repeater does not relay the measurement signal. In this case, the RSSI of the measurement signal is not detected through the RSSI detection circuit 16, and as a result, the RSSI information signal Sri is not returned. Therefore, with this, it can be determined that the switching of the locking / unlocking state of the vehicle door is prohibited, for example, as unauthorized communication using the repeater.

In addition, the said embodiment can be implemented with the following forms which changed this suitably.
-In above-mentioned embodiment, when it is judged that the vehicle-mounted control part 21 is an unauthorized communication using a repeater (S121), you may give a warning through a buzzer etc.

  In the above embodiment, the second radio signal stored in the memory 21a has been updated in step S119. However, the process of step S119 may be omitted.

  In the above embodiment, the electronic key 10 transmits the detection result included in the response signal Sre without making any judgment on the detection result of the RSSI detection circuit 16. However, the electronic key control unit 11 may determine whether the RSSI difference ΔRs of the measurement signal exceeds the threshold Th based on the detection result of the RSSI detection circuit 16 as a determination unit (S115). The electronic key 10 includes the determination result in a wireless signal and transmits it to the in-vehicle device 20. The in-vehicle device 20 transmits the measurement signal again based on the determination result included in the wireless signal (S116), or unlocks the vehicle door or starts the engine (S120).

The RSSI detection circuit 16 in the above embodiment may be provided independently of the LF receiver 12.
In the above embodiment, each measurement signal is transmitted from the in-vehicle device 20 to the electronic key 10. However, each measurement signal may be transmitted from the electronic key 10 to the in-vehicle device 20. In this case, the RSSI detection circuit 16 is provided in the in-vehicle device 20 in the in-vehicle receiving unit 24 or independently of the in-vehicle receiving unit 24. Also in this configuration, since the RSSI of each measurement signal changes as the electronic key 10 moves, the same effect as the above embodiment can be obtained.

  In the above embodiment, each measurement signal is transmitted after the wake signal Swk. However, the transmission timing of each measurement signal is not limited to this. For example, the measurement signals Srs1 and Srs2 may be transmitted after receiving the response signal Sre. Alternatively, both measurement signals Srs1 and Srs2 may be transmitted continuously after transmitting a single wake signal Swk. Furthermore, the wake signal Swk and the measurement signal may be configured as a single signal by changing the signal strength of the wake signal Swk.

  In the above embodiment, the RSSI information is transmitted by being included in the response signal Sre. However, an RSSI information signal including only RSSI information may be transmitted separately from the response signal. Further, RSSI information may be included in the ACK signal Sac.

  In the above embodiment, the outside transmission unit 22 and the inside transmission unit 23 are provided. However, a common transmission unit inside and outside the vehicle may be provided. This transmission unit forms a transmission area inside and outside the vehicle interior.

  -You may reverse the process of step S114 and step S115 in the said embodiment. In this case, in the case of unauthorized communication using a repeater, the flowchart is ended through a NO process in step S117 without performing response verification and ID code verification.

  In the above embodiment, the in-vehicle device 20 transmits an LF band radio signal, and the electronic key 10 transmits a UHF band radio signal. However, the frequency band of the radio signal transmitted and received between the in-vehicle device 20 and the electronic key 10 is not limited to these.

  In the above embodiment, the electronic key 10 locks and unlocks the vehicle door and the like through wireless communication with the in-vehicle device 20 that is a control target. However, the control target is not limited to the in-vehicle device 20 and may be, for example, a residential door device. Even in this case, the unauthorized communication using the repeater can be prevented as in the above embodiment.

Next, the technical idea that can be grasped from the embodiment will be described together with the effects.
(A) In the electronic key system according to any one of claims 1 to 3, the detection unit is provided in the electronic key and detects signal strengths of the two radio signals from the control target. The electronic key wirelessly transmits the detection result of the detection unit, and the determination unit provided in the control target has a signal strength difference between the two wireless signals exceeding the threshold based on the received detection result. Electronic key system that determines whether or not.

According to this configuration, the determination unit is provided in the control target, so that the electronic key can be configured more compactly.
(B) In the electronic key system according to any one of claims 1 to 3 and (a), when the electronic key receives a request signal from the control target, the response signal includes its own ID code. The control object confirms the validity of the ID code included in the response signal, and when it is determined through the determination unit that the difference in signal strength between the two radio signals exceeds the threshold value, An electronic key system that permits execution of control of the control target.

  DESCRIPTION OF SYMBOLS 1 ... Electronic key system, 10 ... Electronic key, 20 ... In-vehicle apparatus (control object), 21 ... In-vehicle control part (determination part), 16 ... RSSI detection circuit (detection part).

Claims (3)

In an electronic key system in which control of the control target is executed through a wireless signal transmitted and received between the control target and the electronic key,
The control object or the electronic key includes a first wireless signal and a transmission unit that transmits a second wireless signal having a signal strength lower than that of the first wireless signal;
A detection unit that is provided in the electronic key or the control target and detects a signal intensity of a radio signal transmitted from the control target or the electronic key;
A threshold value provided on the control object or the electronic key and the difference in signal strength between the two radio signals recognized through the detection unit is set based on the difference in signal strength between the two radio signals to be transmitted A determination unit for determining whether or not
The control object or the electronic key permits execution of control of the control object when it is determined that the difference in signal strength between the two radio signals exceeds the threshold value through the determination unit, and the control object or electronic key is below the threshold value. A new radio signal having a signal strength lower than that of the second radio signal is transmitted in a state in which execution of control of the control target is prohibited when it is determined that there is,
In the same manner as described above, the new radio signal is used as the second radio signal, and the determination unit determines whether the difference in signal strength between the two radio signals exceeds the threshold value, and the control target Alternatively, the electronic key system permits or prohibits execution of the control of the control target based on the determination. The electronic key system according to claim 1.
When the control target or the electronic key transmits the new radio signal as the second radio signal, it is determined through the determination unit that the difference in signal strength between the two radio signals exceeds the threshold value. The signal strength of the determined second radio signal is stored, and the signal strength of the second radio signal transmitted during the next communication between the electronic key and the control target is stored in the stored signal strength. And electronic key system. The electronic key system according to claim 1 or 2,
The control object or the electronic key is determined to be unauthorized communication using a repeater when the detection unit cannot detect the signal strength of the new radio signal as the second radio signal. Electronic key system that confirms the state of prohibiting the execution of control.

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