Vehicle control system and vehicle control method

Abstract

To perform appropriate vehicle control even when a portable device is approaching a transmitter of a vehicle control device.SOLUTION: A vehicle control device transmits a request signal P1 including two measurement signals different in signal intensity to a portable device. The portable device measures reception intensities RSSI(1) and RSSI(2) corresponding to respective measurement signals, and returns a response signal Q1 including the two reception intensities to the vehicle control device. When at least one of the reception intensities reaches an upper limit value Z in a measurable range, the vehicle control device transmits, to the portable device, a request signal P2 including proximity information indicating that the portable device is approaching a transmitter of the vehicle control device. When the portable device receives a request signal P2 containing proximity information, the portable device reduces the reception sensitivity to the measurement signal so that the measurement value of the reception intensity of the measurement signal does not reach an upper limit, measures the reception intensity again, and returns a response signal Q2 containing the two measured reception intensities to the vehicle control device.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control system for controlling the operation of a vehicle, and more particularly to a vehicle control system having a security function against relay attacks. [Background technology]

[0002] Vehicle control systems have been put into practical use that perform predetermined controls such as locking and unlocking vehicle doors or starting the engine based on wireless signals transmitted and received between a vehicle control device installed in a vehicle and a portable device carried by the user.

[0003] In this vehicle control system, when a user carrying a portable device operates a switch on the vehicle door handle to lock or unlock the vehicle, a request signal is sent from the vehicle control device to the portable device requesting a response. When the portable device receives this request signal, it returns a response signal including the portable device's ID to the vehicle control device. Upon receiving the response signal, the vehicle control device verifies the ID to perform authentication, and if authentication is successful, locks or unlocks the doors.

[0004] In recent years, a fraudulent act known as a relay attack has become a problem in vehicle control systems such as those described above. A relay attack is a type of fraudulent communication in which a third party other than the owner of the vehicle uses a repeater to relay a request signal sent from the vehicle control device or a response signal returned from the portable device, thereby disguising the owner's portable device, which is located far away, as if it were located near the vehicle.

[0005] 6 shows how a request signal and a response signal are relayed in a relay attack. When a third party performs an unlocking operation using a switch (not shown) on the door handle of the vehicle 30, a request signal is transmitted from the vehicle control device 10. If the portable device 50 is located far away from the vehicle 30, the request signal will not reach the portable device 50. However, if a repeater 20 is present between the vehicle 30 and the portable device 50, the request signal will be relayed by the repeater 20 and reach the portable device 50.

[0006] Therefore, the portable device 50 that receives the request signal replies with a response signal including the ID. This response signal is also relayed by the repeater 20 and received by the vehicle control device 10, and if authentication based on the ID is successful, the vehicle control device 10 outputs a control signal for unlocking the door. As a result, it becomes possible for a malicious third party to unlock the door, which may lead to crimes such as theft of the vehicle or items inside the vehicle.

[0007] Therefore, various countermeasures to prevent such relay attacks have been proposed in the past (see Patent Documents 1 to 6). For example, in Patent Document 1, two measurement signals with different signal strengths are transmitted from a vehicle control device along with a request signal, and if the difference in the reception strength of the measurement signals received by the portable device is equal to or less than a threshold, unlocking of the door is prohibited.

[0008] Specifically, as shown in FIG. 7(a), two measurement signals CW1 and CW2 are added after the data field (DATA) of a request signal and are transmitted from the vehicle control device 10. These measurement signals CW1 and CW2 are continuous waves, and measurement signal CW2 is transmitted after a certain time has passed since measurement signal CW1 was transmitted. The signal strength of measurement signal CW1 is greater than the signal strength of measurement signal CW2 (CW1>CW2). A method for varying the strength of transmitted signals is described, for example, in Patent Document 7.

[0009] FIG. 7(b) shows a response signal returned from the portable device 50 under normal circumstances when there is no relay attack. When the portable device 50 receives a request signal, it measures the reception intensities RSSI(1) and RSSI(2) of the measurement signals CW1 and CW2, respectively, and adds these values to the end of the data field (DATA) of the response signal before returning it to the vehicle control device 10. In this case, since CW1>CW2 as described above, the relationship between the reception intensities measured by the portable device 50 is RSSI(1)>RSSI(2). If the difference between these reception intensities exceeds a threshold, the vehicle control device 10 permits the door to be unlocked. FIG. 8 shows the normal transmission and reception of the measurement signals CW1 and CW2 and the reception intensities RSSI(1) and RSSI(2).

[0010] FIG. 7(c) shows a response signal returned from the portable device 50 when a relay attack is performed. In this case, the relationship between the two reception intensities measured by the portable device 50 is RSSI(1)≈RSSI(2), and there is almost no difference between the reception intensities. This is for the following reason. As shown in FIG. 9, the vehicle control device 10 transmits measurement signals CW1 and CW2 with different signal intensities. However, it is difficult for the repeater 20 to simulate the values of the signal intensities of CW1 and CW2 and the difference between them. For this reason, the signal intensities of the measurement signals CW1 and CW2 relayed from the repeater 20 to the portable device 50 are approximately the same value. Therefore, the reception intensities RSSI(1) and RSSI(2) measured by the portable device 50 are also approximately the same value. As a result, the difference between the reception intensities received by the vehicle control device 10 from the portable device 50 via the repeater 20 is below the threshold, and the vehicle control device 10 prohibits unlocking the doors.

[0011] In this way, by transmitting two measurement signals CW1 and CW2 with different signal intensities added to a request signal, fraudulent relay attacks can be prevented. However, even if a relay attack is not being performed, if the portable device 50 is located close to a transmitter included in the vehicle control device 10 when an authorized user attempts to unlock the door, the reception intensities RSSI(1) and RSSI(2) of the measurement signals received by the portable device 50 may become large, causing one or both of them to exceed the measurable range. In this case, as described below, the reception intensities exceeding the measurable range are clamped to the upper limit of the range, thereby reducing the difference between the two reception intensities measured by the portable device 50. If this difference is below a threshold, the vehicle control device 10 erroneously determines that a relay attack has been performed and prohibits unlocking the door. As a result, a problem occurs in which the door cannot be unlocked despite the operation being performed by an authorized user. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-219970 [Patent Document 2] Patent No. 6432795 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-105360 [Patent Document 4] Japanese Patent Application Publication No. 2019-68307 [Patent Document 5] Japanese Patent Application Publication No. 2018-71050 [Patent Document 6] Japanese Patent Application Publication No. 2018-62765 [Patent Document 7] Japanese Patent Application Laid-Open No. 2006-57366 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention aims to provide a vehicle control system that performs or prohibits predetermined control of a vehicle based on the reception strength of two measurement signals with different signal strengths, and that is capable of performing appropriate vehicle control even when a portable device is close to the transmitter of the vehicle control device. [Means for solving the problem]

[0014] The vehicle control system according to the present invention includes a vehicle control device that is mounted on a vehicle and performs predetermined control of the vehicle, and a portable device that is carried by a vehicle user and that wirelessly communicates with the vehicle control device. The vehicle control device generates two measurement signals with different signal strengths based on a predetermined operation being performed on the vehicle. First time A request signal is transmitted to the portable device. First time When a request signal is received, the two reception intensities corresponding to the two measurement signals are measured and the measured Two Including reception strength First time A response signal is sent back to the vehicle control device. . car Both control devices are operated from a portable device. First time When the response signal is received, it is determined whether or not one or both of the two reception intensities reaches the upper limit of the measurable range. If at least one of the two reception intensities reaches the upper limit, the portable device receives proximity information indicating that the portable device is close to a transmitter provided in the vehicle control device and two measurement signals. Second time The request signal is sent to the portable device. The portable device receives the request signal containing the proximity information. Second time When the portable device receives the request signal, it reduces the reception sensitivity to the measurement signal so that the measured reception strength of the measurement signal does not reach the upper limit. After that, the portable device measures the two reception strengths corresponding to the measurement signals again and calculates the measured reception strength. Two Including reception strength Second time A response signal is sent back to the vehicle control device. When the vehicle control device receives the second response signal, it determines whether the difference or ratio between the two reception intensities measured again by the portable device is within a predetermined range, If the difference or ratio between the two reception intensities is within a predetermined range, a predetermined control is executed on the vehicle, and if the difference or ratio between the two reception intensities is not within the predetermined range, the predetermined control is prohibited on the vehicle.

[0015] According to the vehicle control system described above, even if the portable device is close to the transmitter of the vehicle control device, the two reception intensities measured by the portable device are not clamped to an upper limit due to a decrease in the reception sensitivity of the measurement signal, and the difference between the two reception intensities is maintained at an appropriate value. This prevents the reception intensity from reaching the upper limit and allows for appropriate control of the vehicle. Furthermore, if a relay attack is actually performed, the difference between the two reception intensities will be very small, and this can be used to determine that a relay attack has occurred.

[0016] In the present invention, the vehicle control device determines whether the difference or ratio between the two reception intensities measured again by the portable device is within a predetermined range. And for the vehicle When executing a predetermined control, an unlock signal is sent to unlock the vehicle doors. Outputs , The difference or ratio between the two reception intensities is not within the specified range, and the vehicle To prohibit a specific control, use the unlock signal. Do not output This may be done.

[0017] In the present invention, The mobile phone , 1st and 2nd The device may include a receiving circuit that receives the request signal and an A / D converter that converts the analog voltage output from the receiving circuit into a digital voltage. The receiving circuit may include a coil, a capacitor, and a first resistor connected in parallel, and a series circuit of a second resistor and a switch connected in parallel with the first resistor. In this case, The mobile phone , Second time The request signal contains proximity information. If there is no , the switch is turned off, the second resistor is not connected in parallel with the first resistor, Second time The request signal contains proximity information. If there is , the switch is turned on to connect the second resistor in parallel with the first resistor, thereby reducing the receiving sensitivity to the measurement signal. [Effects of the Invention]

[0018] According to the present invention, in a vehicle control system that executes or prohibits predetermined control of a vehicle based on the reception strength of two measurement signals with different signal strengths, appropriate vehicle control can be performed even when a portable device is close to the transmitter of the vehicle control device. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a block diagram showing an example of a vehicle control system according to the present invention; [Figure 2] 3 is a flowchart showing the operation of the vehicle control system. [Figure 3] FIG. 2 is a diagram illustrating a request signal and a response signal. [Figure 4] FIG. 2 is a diagram showing the circuit of the LF receiving section of the portable device. [Figure 5] FIG. 10 is a diagram showing a measurable range of reception strength and measurement values. [Figure 6] FIG. 1 is a diagram illustrating how a request signal and a response signal are relayed in a relay attack. [Figure 7] 10A and 10B are diagrams illustrating a measurement signal added to a request signal and a reception intensity added to a response signal. [Figure 8] 10A and 10B are diagrams showing transmission and reception of measurement signals and reception intensities under normal conditions; [Figure 9] 10A and 10B are diagrams illustrating transmission and reception of measurement signals and reception strengths during a relay attack. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings, in which the same or corresponding parts are designated by the same reference numerals.

[0021] FIG. 1 shows an example of a vehicle control system according to the present invention. Only blocks related to the present invention are shown here. The vehicle control system 100 comprises a vehicle control device 10 and a portable device 50. The vehicle control device 10 is an on-board device mounted on a vehicle (a four-wheeled automobile in this example) and performs predetermined control of each part of the vehicle. The portable device 50 comprises an electronic key that is operated to lock and unlock the vehicle doors, and is carried by the vehicle user. The vehicle control device 10 and the portable device 50 are configured to communicate with each other wirelessly.

[0022] The vehicle control device 10 includes an operation unit 11 that is operated to cause the vehicle to perform a predetermined operation, a control unit 12 that is configured from a CPU, memory, etc., an LF transmission unit 13 that transmits an LF (Low Frequency) signal to the portable device 50, and a UHF reception unit 14 that receives a UHF (Ultra High Frequency) signal from the portable device 50. A request signal that requests a response from the portable device 50 is an LF signal, and a response signal returned from the portable device 50 is a UHF signal. In addition, when an operation unit 51 on the portable device 50 is operated, an operation signal transmitted from the portable device 50 is also a UHF signal.

[0023] The operation unit 11 is provided with a lock switch 11a for locking the vehicle doors and an unlock switch 11b for unlocking the vehicle doors. These switches 11a and 11b are provided on the door handles of the vehicle. The operation unit 11 is also provided with various other switches, but these are not directly related to the present invention and are therefore not shown in the drawings.

[0024] The control unit 12 has a reception strength determination unit 15, a proximity flag setting unit 16, a signal generation unit 17, an authentication unit 18, a control signal output unit 19, and a storage unit 20. The reception strength determination unit 15 determines whether or not the reception strength included in the response signal received from the portable device 50 satisfies a predetermined condition (details will be described later). The proximity flag setting unit 16 sets a proximity flag as proximity information indicating that the portable device 50 is in proximity to the LF transmission unit 13 of the vehicle control device 10 (details will be described later).

[0025] The signal generation unit 17 generates a request signal to be transmitted from the LF transmission unit 13 to the portable device 50, and a measurement signal to be added to this request signal. When the UHF reception unit 14 receives a response signal transmitted from the portable device 50, the authentication unit 18 collates the ID included in the response signal to determine whether authentication has been established. The control signal output unit 19 outputs control signals for controlling various parts of the vehicle based on the operation of the operation unit 11 of the vehicle control device 10 and the operation unit 51 of the portable device 50. The memory unit 20 stores data necessary for control, the ID of the portable device 50, etc.

[0026] The portable device 50 includes an operation unit 51 that is operated to cause the vehicle to perform a predetermined operation, a control unit 52 that is composed of a CPU, memory, etc., an LF receiving unit 53 that receives an LF signal transmitted from the vehicle control device 10, and a UHF transmitting unit 54 that transmits a UHF signal to the vehicle control device 10.

[0027] The operation unit 51 is provided with a lock switch 51a for locking the vehicle doors and an unlock switch 51b for unlocking the vehicle doors. If necessary, other switches may be provided in the operation unit 51.

[0028] The control unit 52 has a reception strength measurement unit 55, a proximity flag determination unit 56, a reception sensitivity change unit 57, a signal generation unit 58, and a storage unit 59. The reception strength measurement unit 55 measures the reception strength of each of the two measurement signals included in the request signal received from the vehicle control device 10 (details will be described later). The proximity flag determination unit 56 determines whether the proximity flag included in the received request signal is "1" or "0" (details will be described later).

[0029] The receiving sensitivity change unit 57 reduces the receiving sensitivity for the measurement signal when the request signal includes a proximity flag (details will be described later). The signal generation unit 58 generates a response signal and an operation signal to be transmitted from the UHF transmission unit 54 to the vehicle control device 10. The memory unit 59 stores data necessary for control, the ID of the portable device 50, etc.

[0031] Next, the operation of the vehicle control system 100 configured as above will be described with reference to the flowchart of FIG.

[0032] 2, the flowchart for the vehicle control device is executed by the control unit 12, and the flowchart for the portable device is executed by the control unit 52. The following describes an example of the operation for unlocking the vehicle doors.

[0033] The series of steps shown in the flowchart of Fig. 2 are initiated by operating the unlock switch 11b for unlocking the doors in the operation unit 11 of the vehicle control device 10. First, in step S1, a first request signal P1 as shown in Fig. 3(a) is generated by the signal generation unit 17. This request signal P1 includes a data area DATA, two measurement signals CW1 and CW2 with different signal intensities, and a proximity flag F. In step S1, the proximity flag setting unit 16 sets the proximity flag F to "0."

[0034] Next, in step S2, the request signal P1 is transmitted from the LF transmitter 13. The measurement signal CW2 is transmitted a certain time after the measurement signal CW1 is transmitted. The signal strength of the measurement signal CW1 is greater than the signal strength of the measurement signal CW2 (CW1>CW2).

[0035] In the portable device 50, in step S21, the request signal P1 is received by the LF receiving unit 53. Next, in step S22, the proximity flag determining unit 56 determines whether the proximity flag F included in the request signal P1 is "1" or not. In this case, the proximity flag F is "0," so the determination in step S22 is NO, and the process proceeds to step S24.

[0036] In step S24, the reception strength measurement unit 55 measures reception strengths RSSI(1) and RSSI(2) for the measurement signals CW1 and CW2 included in the request signal P1. Next, in step S25, the signal generation unit 58 generates a first response signal Q1 as shown in FIG. 3(b). This response signal Q1 includes the measured values of reception strengths RSSI(1) and RSSI(2). Subsequently, in step S26, the response signal Q1 is transmitted from the UHF transmission unit 54.

[0037] In step S3 of the vehicle control device 10, the response signal Q1 is received by the UHF receiver 14. Next, in step S4, the data on the reception strengths RSSI(1) and RSSI(2) included in the response signal Q1 is acquired by the reception strength determiner 15. Then, in step S5, the reception strength determiner 15 determines whether the reception strength RSSI(1) corresponding to the measurement signal CW1 having the greater signal strength has reached the upper limit Z of the measurable range W shown in FIG. 5, which will be described later.

[0038] If the reception strength RSSI(1) has not reached the upper limit Z, the determination in step S5 is NO, and the process proceeds to step S10. In step S10, it is determined whether the difference (absolute value) between the two reception strengths RSSI(1) and RSSI(2) acquired in step S4 is within a predetermined range, i.e., X<|RSSI(1)-RSSI(2)| <Y ··· [A] Whether or not the following holds is determined by the reception intensity determination unit 15. Here, X and Y are predetermined threshold values.

[0039] If the relationship [A] above is established, the determination in step S10 is YES, and the process proceeds to step S11. On the other hand, if the relationship [A] above is not established, the determination in step S10 is NO, and the process ends without executing steps S11 and S12.

[0040] In step S11, authentication unit 18 performs authentication based on ID matching. Specifically, the ID of portable device 50 included in the response signal is matched with the ID stored in storage unit 20, and if the two match, authentication is determined to be successful; if the two do not match, authentication is determined to be unsuccessful. If authentication is successful, the determination in step S11 is YES, and the process proceeds to step S12. On the other hand, if authentication is unsuccessful, the determination in step S11 is NO, and the process ends without executing step S12.

[0041] In step S12, an unlock signal is output as a control signal from the control signal output unit 19. This unlock signal activates an unlock mechanism (not shown) of the door, thereby unlocking the door.

[0042] On the other hand, if the reception strength RSSI(1) reaches the upper limit value Z in step S5, the determination in step S5 becomes YES, and the process proceeds to step S6. In step S6, a second request signal P2 as shown in FIG. 3(c) is generated by the signal generating unit 17. This request signal P2 has the same format as the first request signal P1 in FIG. 3(a), but in step S6, the proximity flag setting unit 16 sets the proximity flag F of the request signal P2 to "1." The proximity flag F being "1" indicates that the portable device 50 is in proximity to the LF transmitting unit 13 of the vehicle control device 10. This proximity flag F set to "1" is an example of the "proximity information" in the present invention.

[0043] Next, in step S7, the second request signal P2 is transmitted from the LF transmitter 13. In this case as well, the measurement signal CW2 is transmitted after a certain time has elapsed since the measurement signal CW1 was transmitted.

[0044] In the portable device 50, in step S21, the LF receiving unit 53 receives the second request signal P2. Next, in step S22, the proximity flag determining unit 56 determines whether the proximity flag F included in the request signal P2 is "1." In this case, the proximity flag F is "1," so the determination in step S22 is YES, and the process proceeds to step S23.

[0045] In step S23, the receiving sensitivity change unit 57 reduces the receiving sensitivity for the two measurement signals CW1 and CW2 so that the measured values of the receiving strength of the measurement signals CW1 and CW2 do not reach the upper limit value Z (FIG. 5) described above. Specifically, the receiving sensitivity is reduced by changing the resistance value of the receiving circuit in the LF receiving unit 53 of the portable device 50. This will be described in detail below.

[0046] 4 shows an example of the circuit configuration of the LF receiving unit 53. The LF receiving unit 53 includes a receiving circuit 53a that receives a request signal and an A / D converter 53b that converts the analog voltage output from the receiving circuit 53a into a digital voltage. A filter circuit and the like are provided between the receiving circuit 53a and the A / D converter 53b, but are not shown here.

[0047] The receiving circuit 53a includes a coil L, a capacitor C, resistors R1 and R2, and a switch SW. The coil L, capacitor C, and resistor R1 are connected in parallel, and this parallel circuit forms a resonant circuit. The resistor R2 is connected in series with the switch SW, and this series circuit is connected in parallel with the resistor R1. The resistor R1 corresponds to the "first resistor" in this invention, and the resistor R2 corresponds to the "second resistor" in this invention.

[0048] The switch SW is turned on and off by a reception sensitivity change unit 57 of the control unit 52. In this embodiment, the switch SW is configured as a semiconductor switch, but instead, a mechanical switch having contacts may be used. The input side of the A / D converter 53b is connected to the reception circuit 53a via a filter circuit (not shown) or the like, and the output side of the A / D converter 53b is connected to the control unit 52 of FIG. 1. The A / D converter 53b may be provided inside the control unit 52.

[0049] 2, if the proximity flag F is "0" (i.e., if the portable device 50 is not in proximity to the LF transmitter 13), step S23 is not executed, and the switch SW is turned off, as shown in FIG. 4(a). Therefore, the resistor R2 is not connected in parallel with the resistor R1, and the resistance value of the receiving circuit 53a is R1.

[0050] On the other hand, if the proximity flag F is "1" in step S22 (i.e., if the portable device 50 is close to the LF transmitter 13), step S23 is executed and the switch SW is turned on as shown in Fig. 4(b). Therefore, as a result of the resistor R2 being connected in parallel to the resistor R1, the resistance value in the receiving circuit 53a becomes R1·R2 / (R1+R2), which is smaller than the resistance value R1 in the case of Fig. 4(a).

[0051] When the receiving circuit 53a sequentially receives the measurement signals CW1 and CW2, the analog voltage input to the A / D converter 53b has a value corresponding to the signal strength of each of the measurement signals CW1 and CW2. The A / D converter 53b converts this input voltage into a digital signal and outputs it to the control unit 52. This output voltage is the reception strengths RSSI(1) and RSSI(2) corresponding to the measurement signals CW1 and CW2, and these values are measured by the reception strength measurement unit 55.

[0052] 4(b), the resistance value of the receiving circuit 53a is smaller than that in FIG. 4(a), and therefore the input voltage to the A / D converter 53b is smaller than that in FIG. 4(a). As a result, the output voltage of the A / D converter 53b, i.e., the reception intensities RSSI(1) and RSSI(2) corresponding to the measurement signals CW1 and CW2, are also smaller than that in FIG. 4(a). This is because the reception sensitivity to the measurement signals CW1 and CW2 is reduced by connecting resistor R2 in parallel with resistor R1.

[0053] After reducing the receiving sensitivity in step S23, the process proceeds to step S24, where the receiving strength of the measurement signals CW1 and CW2 is measured again. The receiving strength measured in step S24 clearly differs depending on whether resistor R2 is connected in parallel with resistor R1 or not. This will be explained with reference to FIG. 5.

[0054] FIG. 5 shows an example of measured values of reception strengths RSSI(1) and RSSI(2) when the portable device 50 is close to the LF transmitter 13. When resistor R2 is not connected, the reception strength of the measurement signals CW1 and CW2 received by the portable device 50 increases, and one or both of RSSI(1) and RSSI(2) exceed the upper limit Z of the measurable range W, as shown by the open circles in FIG. 5(a). In this case, the reception strength exceeding the upper limit Z is clamped to the upper limit Z, as shown by the black circles. As a result, the difference α between RSSI(1) and RSSI(2) decreases or becomes almost zero. As a result, the relationship [A] described above does not hold, and unlocking of the door is prohibited.

[0055] In contrast, when resistor R2 is connected, the receiver sensitivity decreases, and as shown in Figure 5(b), the measured values of the receiver strengths RSSI(1) and RSSI(2) do not exceed the upper limit Z, as indicated by the white circles, but remain within the measurable range W, as indicated by the black circles. As a result, the difference β between RSSI(1) and RSSI(2) falls within the normal range, and the relationship [A] described above is established, allowing the door to be unlocked. This will be discussed later.

[0056] After the process of step S24 is completed, in step S25, the signal generator 58 generates a second response signal Q2 as shown in Fig. 3(d). This response signal Q2 has the same format as the first response signal Q1 of Fig. 3(b) and includes the reception strengths RSSI(1) and RSSI(2) measured again in step S24. Then, in step S26, this response signal Q2 is transmitted from the UHF transmitter 54.

[0057] The second transmitted response signal Q2 is received by the UHF receiver 14 of the vehicle control device 10 in step S8. In step S9, the data of the reception strengths RSSI(1) and RSSI(2) is acquired. From now on, the steps already mentioned will be S10 The process of .about.S12 is executed.

[0058] Here, even if the reception intensities RSSI(1) and RSSI(2) included in the first response signal Q1 exceed the upper limit value Z as shown in Figure 5(a), the reception intensities RSSI(1) and RSSI(2) included in the second response signal Q2 are re-measured in a state where the reception sensitivity has decreased, and therefore will be values that do not exceed the upper limit value Z as shown in Figure 5(b).

[0059] Therefore, in step S10 after the second response signal Q2 is received in step S8, β shown in FIG. 5(b), i.e., |RSSI(1)-RSSI(2)|, becomes a value greater than threshold value X and less than threshold value Y, and the relationship [A] described above is established. Therefore, the determination in step S10 becomes YES, and the door can be unlocked in steps S11 and S12.

[0060] In the case of a relay attack by a third party, as described in FIG. 9, the two reception intensities RSSI(1) and RSSI(2) relayed by the repeater 20 and received by the vehicle control device 10 will be approximately the same. Even in this case, if each reception intensity exceeds the upper limit Z, the reception sensitivity is reduced in step S23. However, since the two reception intensities are essentially the same, reducing the reception sensitivity merely reduces the reception intensities while maintaining the same relationship, and the difference between them remains small. Therefore, in step S10, |RSSI(1)-RSSI(2)|≦X, and the determination is NO. Therefore, the unlock signal (step S12) is not output, and unlocking of the doors is prohibited. This accurately identifies the occurrence of a relay attack and can prevent crimes such as theft of the vehicle or items inside the vehicle.

[0061] According to the embodiment of the present invention described above, in response to a first request signal P1 (FIG. 3(a)) transmitted from the vehicle control device 10, the portable device 50 returns a first response signal Q1 (FIG. 3(b)). If at least one of the two reception intensities RSSI(1) and RSSI(2) included in this response signal Q1 reaches the upper limit Z of the measurable range W, the vehicle control device 10 transmits a second request signal P2 (FIG. 3(c)) in which the proximity flag is set to “1.” Upon receiving this request signal P2, the portable device 50 reduces the reception sensitivity by connecting a resistor R2 (FIG. 4) so that the measured reception intensity does not reach the upper limit Z. Thereafter, the portable device 50 measures the two reception intensities RSSI(1) and RSSI(2) again and returns a second response signal Q2 (FIG. 3(d)) including the measured reception intensities to the vehicle control device 10.

[0062] By doing this, even if the portable device 50 is close to the LF transmitter 13, as described in FIG. 5(b), the reception intensities RSSI(1) and RSSI(2) measured by the portable device 50 are not clamped to the upper limit value Z, and the difference β between the two reception intensities is maintained at an appropriate value. This makes it possible to avoid erroneously determining that a relay attack has occurred when the reception intensity has reached the upper limit value Z. As a result, unlocking of the doors is not hindered, and appropriate control of the vehicle can be performed. Furthermore, if a relay attack has actually occurred, the difference between the two reception intensities becomes small as described above, and this can be used to determine that a relay attack has occurred.

[0063] In addition to the above-described embodiment, the present invention can employ various other embodiments as follows.

[0064] 3(a) and 3(c), the request signal includes a proximity flag F of "0" or "1," but the request signal may include only a proximity flag F of "1" without including a proximity flag F of "0." Furthermore, the proximity information indicating that the portable device 50 is in proximity to the LF transmitter 13 is not limited to a one-digit flag, and may be a code of any number of digits.

[0065] In the above embodiment, in step S5 of FIG. 2, it is determined whether the reception strength RSSI(1) corresponding to the measurement signal CW1 having the greater signal strength has reached the upper limit value Z. However, it may also be determined whether the reception strengths RSSI(1) and RSSI(2) corresponding to both measurement signals CW1 and CW2 have reached the upper limit value Z.

[0066] In the above embodiment, in step S10 of FIG. 2, if the difference between the two reception intensities RSSI(1) and RSSI(2) is not within a predetermined range, the processing is immediately terminated. Alternatively, if the difference is not within the predetermined range, a retry operation of retransmitting a request signal including a proximity flag F set to "1" may be repeated a predetermined number of times.

[0067] In step S10, instead of determining whether the "difference" between the reception intensities RSSI(1) and RSSI(2) is within a predetermined range, it may be determined whether the "ratio" between the reception intensities RSSI(1) and RSSI(2) is within a predetermined range.

[0068] In the above embodiment, an unlock signal is output as a control signal in step S12 of Fig. 2 when unlocking a vehicle door, but the present invention is not limited to this. For example, the present invention can also be applied to starting a vehicle engine, in which case an engine start signal is output as a control signal in step S12.

[0069] In the above embodiment, a four-wheeled motor vehicle is used as an example of a vehicle, but the present invention is not limited to this and can also be applied to motorcycles, three-wheeled motor vehicles, and the like. [Explanation of symbols]

[0070] 10 Vehicle control device 11 Control section 12 Control Unit 13 LF transmitter 14 UHF receiver 15 Reception strength determination unit 16 Proximity flag setting section 19 Control signal output section 50 Portable Devices 52 Control Unit 53 LF receiver 53a Receiving circuit 53b A / D converter 54 UHF transmitter 55 Reception strength measurement unit 56 Proximity flag determination unit 57 Receiving sensitivity change unit 100 Vehicle Control System R1 Resistor (first resistor) R2 resistance (second resistance) C capacitor L coil SW switch F Proximity Flag P1 First request signal P2 Second request signal Q1 First response signal Q2 Second response signal W Measurable range Z upper limit

Claims

1. a vehicle control device that is mounted on a vehicle and performs predetermined control on the vehicle; A vehicle control system including a portable device carried by a vehicle user and configured to wirelessly communicate with the vehicle control device, the vehicle control device transmits a first request signal including two measurement signals having different signal strengths to the portable device based on a predetermined operation being performed on the vehicle; When the portable device receives the first request signal, the portable device measures two reception intensities corresponding to the two measurement signals, and returns a first response signal including the measured two reception intensities to the vehicle control device; The vehicle control device includes: When the first response signal is received from the portable device, it is determined whether or not one or both of the two reception intensities have reached an upper limit value of a measurable range; If at least one of the two reception intensities has reached the upper limit value, a second request signal including proximity information indicating that the portable device is in proximity to a transmitter provided in the vehicle control device and the two measurement signals is transmitted to the portable device; The portable device includes: When a second request signal including the proximity information is received, the receiving sensitivity for the measurement signal is reduced so that the measured value of the reception strength of the measurement signal does not reach the upper limit value; Then, the two reception intensities corresponding to the measurement signals are measured again, and a second response signal including the two measured reception intensities is sent back to the vehicle control device. The vehicle control device includes: When the second response signal is received, the portable device determines whether the difference or ratio between the two reception intensities measured again is within a predetermined range; If the difference or ratio between the two reception intensities is within a predetermined range, a predetermined control is executed on the vehicle; A vehicle control system characterized in that, if the difference or ratio between the two reception intensities is not within a predetermined range, predetermined control of the vehicle is prohibited.

2. 2. The vehicle control system according to claim 1, The vehicle control device includes: When the predetermined control is executed, an unlock signal for unlocking the vehicle door is outputted, A vehicle control system, characterized in that when the predetermined control is prohibited, the unlock signal is not output.

3. 2. The vehicle control system according to claim 1, The portable device includes: a receiving circuit for receiving the first and second request signals; an A / D converter that converts an analog voltage output from the receiving circuit into a digital voltage; The receiving circuit a coil, a capacitor, and a first resistor connected in parallel; a series circuit of a second resistor and a switch connected in parallel with the first resistor; The portable device includes: If the second request signal does not include the proximity information, the switch is turned off so that the second resistor is not connected in parallel with the first resistor; and when the second request signal includes the proximity information, turning on the switch and connecting the second resistor in parallel with the first resistor reduces the receiving sensitivity to the measurement signal.

4. A vehicle control method in a vehicle control system including a portable device carried by a vehicle user and a vehicle control device that wirelessly communicates with the portable device, comprising: a step of transmitting, by the vehicle control device, a first request signal including two measurement signals having different signal strengths to the portable device based on a predetermined operation being performed on the vehicle; a step in which, when the portable device receives the first request signal, the portable device measures two reception intensities corresponding to the two measurement signals, and returns a first response signal including the measured two reception intensities to the vehicle control device; a step in which, when the vehicle control device receives the first response signal, the vehicle control device determines whether or not one or both of the two reception intensities have reached an upper limit value of a measurable range, and if at least one of the two reception intensities has reached the upper limit value, transmits to the portable device a second request signal including the two measurement signals and proximity information indicating that the portable device is in proximity to a transmitter provided in the vehicle control device; a step in which, when the portable device receives a second request signal including the proximity information, the portable device reduces the receiving sensitivity to the measurement signal so that the measured value of the receiving strength of the measurement signal does not reach the upper limit value, and then measures two receiving strengths corresponding to the measurement signals again, and returns a second response signal including the two measured receiving strengths to the vehicle control device; a step in which, when the vehicle control device receives the second response signal, it determines whether or not a difference or ratio between the two reception intensities measured again by the portable device is within a predetermined range; a step of the vehicle control device executing a predetermined control on the vehicle when the difference or ratio between the two reception intensities is within a predetermined range; a procedure in which, when the difference or ratio between the two reception intensities is not within a predetermined range, the vehicle control device prohibits predetermined control of the vehicle.

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