JP6294103B2 - Area correction device - Google Patents

Description

  The present invention relates to an area correction apparatus.

  Conventionally, an antenna device that transmits a radio signal to an electronic key is provided in a vehicle (see, for example, Patent Document 1). The electronic key receives a radio signal from the antenna device. An area where the electronic key can receive and recognize a radio signal from the antenna device is a communication area.

JP 2000-104429 A

  The size of the communication area varies from antenna device to antenna device for various reasons. For example, the antenna device includes a drive circuit, a coil, a resistor, a capacitor, and the like. For each antenna device, the resistance value of the resistor, the inductance of the coil, and the capacitance of the capacitor vary. This variation can contribute to variations in the communication area.

  Also, variations in the internal resistance value of the drive circuit in the antenna device can contribute to variations in the communication area. Furthermore, the shape of the vehicle body, the drive circuit, the resistance value of the connection line such as the coil, the resistor, and the capacitor can also contribute to the variation in the communication area.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an area correction apparatus that corrects variations in communication areas.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
An area correction apparatus that solves the above problem calculates an inductance of the coil by changing a driving frequency of a current supplied to the antenna while detecting a current flowing through the antenna having the coil, and performs communication based on the inductance. A communication area in which a target recognizes a radio signal transmitted from the antenna is corrected.

  According to this configuration, the area correction device calculates the inductance of the coil in the antenna by detecting the current flowing through the antenna and changing the drive frequency of the current supplied to the antenna. Here, the output of the antenna is proportional to a value obtained by multiplying the inductance, the square of the current supplied to the antenna, and 1/2. The output of the antenna is proportional to the communication area formed by the antenna. Therefore, the area correction device can appropriately correct the communication area by calculating the inductance. Therefore, the variation in the communication area can be corrected.

  In the area correction device, the resistance value R of the resistor connected to the coil, the drive voltage V applied to the drive circuit that supplies an alternating current to the antenna, and the antenna when transmitting the radio signal to the communication target When the communication driving frequency f, which is the driving frequency of the current supplied to the antenna, is changed, the peak current Ip at which the current flowing through the antenna becomes maximum by changing the driving frequency under a constant voltage and the peak current Ip are detected. The peak drive frequency f0 that is the drive frequency at the time of measurement is measured, and the drive frequencies f1 and f2 at which the current flowing through the antenna becomes n × Ip (where n <1) are measured, and the following formula ( It is preferable to calculate the inductance L of the coil from a) and (b).

R = V / Ip (a)
L = R × √ (1 / n ² −1) / (2πf1-2πf2) (b)
In this method, the value necessary for calculating the inductance L can be easily obtained by changing the drive frequency f while detecting the current flowing through the antenna.

  In the area correction device, the resistance value R of the resistor connected to the coil, the drive voltage V applied to the drive circuit that supplies an alternating current to the antenna, and the antenna when transmitting the radio signal to the communication target When the communication driving frequency f, which is the driving frequency of the current supplied to the antenna, is changed, the peak current Ip at which the current flowing through the antenna becomes maximum by changing the driving frequency under a constant voltage and the peak current Ip are detected. Then, the peak drive frequency f0 that is the drive frequency f when measured is measured, and the phase difference θ between the communication drive frequency f and the current flowing through the antenna is measured, and the above formula (a) and the following formula (c) ) To calculate the inductance L of the coil.

L = 2πf × R × tan θ / {(2πf) ² − (2πf0) ² } (c)
According to this configuration, the inductance L of the coil can be calculated from the equations (a) and (c). In this method, a value necessary for calculating the inductance L can be acquired through measurement of the phase difference θ between the communication driving frequency f and the current flowing through the antenna.

  In the area correction device, the driving frequencies f1 and f2 are half-width frequencies at which the current flowing through the antenna becomes Ip / √2, and the inductance L of the coil is calculated from the above formula (a) and the following formula (A). Is preferably calculated.

L = R / (2πf1-2πf2) (A)
According to this configuration, the drive frequencies f1 and f2 are half-width frequencies at which the current flowing through the antenna becomes Ip / √2. In this case, the inductance L of the coil can be calculated through simpler calculation as in the above equation (A).

  In the area correction apparatus, it is preferable that the communication area is corrected by changing an output of the antenna by changing a current flowing through the antenna when the wireless signal is transmitted to the communication target.

  According to this configuration, as described above, the output of the antenna and thus the communication area change according to the current flowing through the antenna. Therefore, the communication area can be easily corrected by changing the current flowing through the antenna.

  With respect to the area correction device, when the communication target receives the wireless signal having a signal strength equal to or higher than a threshold, the communication target recognizes the wireless signal, and the area correction device corrects the communication area by changing the threshold. It is preferable.

  According to this configuration, the communication target recognizes a radio signal when receiving a radio signal having a signal strength equal to or higher than a threshold value. The area correction device corrects the communication area by changing the threshold value. Thus, the communication area can be corrected only by changing the communication target threshold.

  According to the present invention, the area correction apparatus can correct variations in the communication area.

The block diagram which shows the structure of an electronic key system. The top view of the vehicle which shows a communication area. The flowchart which shows the process sequence which ECU performs. The graph which showed the relationship between the antenna current and the drive frequency.

(First embodiment)
A first embodiment in which the area correction apparatus is embodied as an electronic key system will be described below.

  As shown in FIG. 1, the electronic key system includes an electronic key 10 that is an example of a communication target possessed by a user and a vehicle 20. The electronic key system is a system that enables unlocking of a vehicle door and the like through wireless two-way communication between the electronic key 10 and the vehicle 20.

(Structure of electronic key)
As shown in FIG. 1, the electronic key 10 includes a microcomputer 11, an LF reception circuit 12, and a UHF transmission circuit 13. The microcomputer 11 includes a nonvolatile memory 11a. In this memory 11a, an ID code unique to the electronic key 10 is stored.

  When receiving the LF band request signal wirelessly transmitted from the vehicle 20, the LF reception circuit 12 demodulates the received request signal and outputs the demodulated request signal to the microcomputer 11. When the microcomputer 11 recognizes the request signal, the microcomputer 11 generates a response signal including the ID code stored in the memory 11 a and outputs the generated response signal to the UHF transmission circuit 13. The UHF transmission circuit 13 modulates the response signal and wirelessly transmits the modulated response signal as a radio signal in the UHF (Ultra High Frequency) band.

(Vehicle configuration)
As shown in FIG. 1, the vehicle 20 includes an LF transmission circuit 23, a UHF reception circuit 24, and an ECU (Electronic Control Unit) 21. The ECU 21, which is an example of the area correction device, includes a nonvolatile memory 21a, and the same ID code as that of the electronic key 10 is stored in the memory 21a. In addition, a door lock switch 35 and a door lock device 38 are electrically connected to the ECU 21.

  As shown in FIG. 2, the door lock switch 35 is provided on the outside door handle 28 so as to be pushed. When the door lock switch 35 is pushed, an operation signal to that effect is output to the ECU 21.

  As shown in FIG. 1, the ECU 21 periodically generates a request signal and outputs the generated request signal to the LF transmission circuit 23. A transmission antenna 25 is electrically connected to the LF transmission circuit 23. As shown in FIG. 2, the transmission antennas 25 are built into the plurality of outside door handles 28 one by one.

  As shown in FIG. 1, each transmission antenna 25 includes a coil 40L and a capacitor 40C. Each LF transmission circuit 23 includes a current detection sensor 27, a drive circuit 26, and a resistor 40R.

  The current detection sensor 27 detects the antenna current Ia flowing through the transmission antenna 25 and outputs the detection result to the ECU 21. A resistor 40R, a coil 40L, and a capacitor 40C are connected to the drive circuit 26 in series.

  The drive circuit 26 is composed of, for example, an H bridge circuit having a plurality of switch elements SW. The ECU 21 converts the direct current from the battery Vt into an alternating current request signal by switching the switch element SW between the on and off states, and supplies the converted request signal to the transmission antenna 25. Each transmitting antenna 25 transmits the request signal (alternating current) as a radio signal in the LF band (Low Frequency).

  The UHF receiving circuit 24 demodulates the received response signal and outputs it to the ECU 21. When the ECU 21 recognizes the response signal, the ECU 21 compares the ID code included in the response signal with the ID code stored in the memory 21a. When the ECU 21 recognizes that the door lock switch 35 has been pushed in the state where the ID verification is established, the ECU 21 switches the lock / unlock state of the vehicle door through the door lock device 38.

(Communication area correction method)
As described above in “Problems to be Solved by the Invention”, the size of the communication area 50 varies. Processing for correcting this variation is executed by the ECU 21.

  This correction process will be described with reference to FIGS. This correction process is executed, for example, when the transmission antenna 25 is attached to the vehicle 20 having the ECU 21 and the LF transmission circuit 23.

  First, the ECU 21 measures the peak current Ip and the peak drive frequency f0 by varying the drive frequency of the alternating current supplied to the transmission antenna 25 through the drive circuit 26 (more precisely, the change of the switching cycle of the switch element SW). (S101). The peak current Ip is the maximum current that flows through the transmitting antenna 25 obtained by changing the drive frequency under a constant voltage. The peak drive frequency f0 is a drive frequency when the peak current Ip is detected.

  Then, the ECU 21 measures the drive frequencies f1 and f2 when the antenna current Ia detected by the current detection sensor 27 becomes Ip / √2. That is, in the present embodiment, the drive frequencies f1 and f2 are half-width frequencies.

  Then, the resistance value R of the resistor 40R, the inductance L of the coil 40L, and the capacitance C of the capacitor 40C are calculated using the following equations (1) to (3). In the following expression, the driving voltage in the driving circuit 26 applied from the battery Vt is V, and is the driving frequency of the current supplied to the transmission antenna 25 when a request signal is transmitted to the electronic key 10. It is assumed that the communication driving frequency is f.

R = V / Ip (1)
L = R / (2πf1-2πf2) (2)
C = 1 / {(2πf0) ² × L} (3)
The above formula (2) is calculated from the Q value = 2πf0 / (2πf1-2πf2) = 2π · f0 · L / R. Further, the above formula (3) is calculated from f0 = 1 / {2π√ (LC))}.

Further, the output of the transmission antenna 25 is calculated from the following equation (4).
Output ^{= L · Ia 2/2 ...} (4)
In this equation (4), the inductance L is calculated from the above equation (2). Therefore, the ECU 21 changes the current Ia flowing through the transmission antenna 25 through the change of the drive voltage V. Thereby, the ECU 21 sets the output of the transmission antenna 25 to the target value. At this time, since the inductance L is calculated, an appropriate current Ia can be set quickly. The ECU 21 thereafter supplies the current Ia set to the transmission antenna 25 so that the output of the transmission antenna 25 becomes the target value. Thereby, the communication area 50 can be set to a desired range, and variations in the communication area 50 can be suppressed.

  For example, as shown in FIG. 2, it is assumed that a communication area 50b smaller than the communication area 50a can be formed due to variations with respect to the appropriate communication area 50a. In this case, the ECU 21 sets the output of the transmission antenna 25 to a target value by increasing the current Ia supplied to the antenna. Thereby, an appropriate communication area 50a is set.

As described above, according to the embodiment described above, the following effects can be obtained.
(1) The ECU 21 calculates the inductance L of the coil 40L in the transmission antenna 25 by changing the drive frequency of the current supplied to the transmission antenna 25 while detecting the current Ia flowing through the transmission antenna 25. Here, the output of the transmission antenna 25 is a value obtained by multiplying the inductance L, the square of the current Ia supplied to the transmission antenna 25, and 1/2. The output of the transmission antenna 25 is proportional to the size of the communication area 50 formed by the transmission antenna 25. Therefore, the ECU 21 can adjust the current Ia supplied to the transmission antenna 25 to a value that makes the communication area 50 appropriate by calculating the inductance L. Therefore, the variation in the communication area 50 can be corrected.

(2) Since the inductance L is calculated, it is possible to set the current Ia that makes the communication area 50 appropriate more quickly than when the inductance L is not calculated.
(3) The inductance L of the coil 40L can be calculated from the above equations (1) and (2). In this method, the value necessary for calculating the inductance L can be easily obtained by changing the drive frequency while detecting the current Ia flowing through the transmission antenna 25.

  (4) When the ECU 21 detects that the transmission antenna 25 is attached to the vehicle 20, the ECU 21 executes a correction process for the communication area 50 shown in FIG. For this reason, the communication area 50 can be automatically corrected by simply mounting the transmission antenna 25 on the vehicle 20.

  (5) The ECU 21 corrects the output of the antenna, and thus the communication area 50, according to the current Ia flowing through the antenna. The correction of the communication area 50 can be performed only by the vehicle 20.

(Second Embodiment)
Hereinafter, the second embodiment will be described. This embodiment is different from the first embodiment in the method of calculating the inductance L and the capacitance C. Hereinafter, a description will be given focusing on differences from the first embodiment.

  In the present embodiment, the resistance value R, the inductance L, and the capacitance C are calculated using the following equations (5) and (6) in addition to the above equation (1). Note that the phase difference between the drive voltage V at the communication drive frequency f and the current Ia of the transmission antenna 25 is θ.

L = 2πf × R × tan θ / {(2πf) ² − (2πf0) ² } (5)
C = 1 / {(2πf0) ² × L} (6)
The above equation (5) is calculated from the equation of tan θ = {2πfL−1 / (2πfC)} / R and the equation of 2πf0 = 1 / √ (LC). Further, the above equation (6) is calculated from f0 = 1 / {2π√ (LC))}. Other points are the same as those in the first embodiment.

As described above, according to the embodiment described above, the following effects can be achieved in addition to the effects (1) to (5) of the first embodiment.
(6) The inductance L can be calculated from the equations (1) and (5). In this method, a value necessary for calculating the inductance L can be obtained through measurement of the phase difference θ between the drive voltage V at the communication drive frequency f and the current flowing through the transmission antenna 25.

In addition, both the said embodiment can be implemented with the following forms which changed this suitably.
In each embodiment described above, the ECU 21 corrects the communication area 50 by changing the current Ia supplied to the transmission antenna 25. However, the communication area 50 may be corrected by changing the threshold value of the received signal strength of the electronic key 10.

  For example, the ECU 21 wirelessly transmits information related to the output calculated using the above formula (4) via the LF transmission circuit 23 and the transmission antenna 25. When the microcomputer 11 of the electronic key 10 receives the information via the LF receiving circuit 12, the microcomputer 11 changes the threshold according to the information. Specifically, the threshold is increased when the output related to the information is larger than the target value, and the threshold is decreased when the output is smaller than the target value. When the signal strength of the request signal received through the LF receiving circuit 12 is equal to or greater than the threshold value, the microcomputer 11 recognizes the request signal and wirelessly transmits a response signal. Therefore, the communication area 50 becomes smaller as the threshold value becomes larger. With this configuration, it is not necessary to change the current Ia supplied to the antenna when the communication area 50 is changed. Also in this configuration, the same effects as those in the above embodiments can be obtained.

  In the above embodiment, the resistor 40R is built in the LF transmission circuit 23, but the resistor 40R may be provided on the transmission antenna 25 side. Conversely, the capacitor 40 </ b> C may be built in the LF transmission circuit 23.

In each of the above embodiments, the capacitance C of the capacitor 40C is calculated through the equations (3) and (6), but this may be omitted.
In each of the above embodiments, the transmission antenna 25 is used outside the vehicle, but may be a transmission antenna inside the vehicle.

In each of the above embodiments, the electronic key system is for a vehicle, but may be a residential electronic key system.
In addition, although the electronic key 10 is employed as a communication target, the electronic key 10 is not limited to the electronic key 10 as long as it can receive a radio signal from the transmission antenna 25.

  In each of the above embodiments, when the ECU 21 detects that the transmission antenna 25 is attached to the vehicle 20, the ECU 21 executes the correction process for the communication area 50 shown in FIG. Not limited to this, it may be executed in accordance with a user operation, or may be executed periodically.

  In the above embodiment, the drive frequencies f1 and f2 are half-width frequencies when the antenna current Ia becomes Ip / √2. However, the drive frequencies f1 and f2 do not have to be half-width frequencies. Specifically, the drive frequencies f1 and f2 at which the antenna current Ia is n × Ip (where n <1) are measured, and the inductance of the coil 40L may be calculated using the following equation (b).

L = R × √ (1 / n ² −1) / (2πf1-2πf2) (b)
This formula (b) is derived as follows, for example.
From Z = R / n = √ (R ² + (ωL−1 / (ωC)) ² ), ωL−1 / (ωC) = ± R × √ (1 / n ² −1)
ω = (± R × √ (1 / n ² −1) ± √ (R ² × (1 / n ² −1) + 4L / C)) / 2L
From ω1> 0, ω1 = 2πf1 = (R × √ (1 / n ² −1) + √ (R ² × (1 / n ² −1) + 4L / C)) / 2L
From ω2> 0, ω2 = 2πf2 = (− R × √ (1 / n ² −1) + √ (R ² × (1 / n ² −1) +4 L / C)) / 2L
2πf1-2πf2 = R × √ (1 / n ² −1) / L
L = R × √ (1 / n ² −1)) / (2πf1-2πf2)
Next, the technical idea that can be grasped from the embodiment will be described together with the effects.

(A) Area correction device that performs correction of the communication area when the antenna is connected to the drive circuit According to this configuration, the area correction device can be used for the communication area when the antenna is connected to the drive circuit. Perform correction. Therefore, when the antenna is attached to the vehicle, the communication area is automatically corrected.

  θ: phase difference, C: capacitance, f: driving frequency during communication, L: inductance, R: resistance value, V: driving voltage, f0: peak driving frequency, Ia: antenna current, Ip: peak current, 10 ... Electronic key, 11 ... microcomputer, 12 ... LF reception circuit, 13 ... UHF transmission circuit, 20 ... vehicle, 21 ... ECU, 23 ... LF transmission circuit, 24 ... UHF reception circuit, 25 ... transmission antenna, 26 ... drive circuit, 27 ... Current detection sensor, 28 ... Outside door handle, 40C ... Capacitor, 40L ... Coil, 40R ... Resistance, 50 ... Communication area.

Claims (6)

The inductance of the coil is calculated by changing the drive frequency of the current supplied to the antenna while detecting the current flowing through the antenna having the coil, and the output of the antenna is obtained based on the current and the inductance. output, the area correction unit for correcting a communication area by communication target is set to the output of the target value becomes an appropriate communication area as the communication area recognizing a radio signal transmitted from the antenna. The area correction apparatus according to claim 1,
A resistance value R of a resistor connected in series to the coil;
A driving voltage V applied to a driving circuit for supplying an alternating current to the antenna;
When defining a communication driving frequency f that is a driving frequency of a current supplied to the antenna when transmitting the wireless signal to the communication target,
The peak current Ip that maximizes the current flowing through the antenna by changing the drive frequency when the drive voltage V is a constant voltage, and the peak drive frequency f0 that is the drive frequency when the peak current Ip is detected. Further, driving frequencies f1 and f2 at which the current flowing through the antenna is n × Ip (where n <1) are measured,
An area correction device for calculating the inductance L of the coil from the following equations (a) and (b).
R = V / Ip (a)
L = R × √ (1 / n ² −1) / (2πf1-2πf2) (b) The area correction apparatus according to claim 1,
A resistance value R of a resistor connected in series to the coil;
A driving voltage V applied to a driving circuit for supplying an alternating current to the antenna;
When defining a communication driving frequency f that is a driving frequency of a current supplied to the antenna when transmitting the wireless signal to the communication target,
The peak drive frequency which is a driving frequency when the current flowing through the antenna by the driving voltage V varies the original said driving frequency of the constant voltage is detected peak current Ip and the peak current Ip becomes maximum Measure f0, and further measure the phase difference θ between the drive voltage V at the communication drive frequency f and the current flowing through the antenna,
An area correction apparatus for calculating an inductance L of the coil from the equation (a) and the following equation (c).
L = 2πf × R × tan θ / {(2πf) ² − (2πf0) ² } (c) The area correction apparatus according to claim 2,
The driving frequencies f1 and f2 are half-width frequencies at which the current flowing through the antenna becomes Ip / √2.
An area correction apparatus for calculating an inductance L of the coil from the equation (a) and the following equation (A).
L = R / (2πf1-2πf2) (A) In the area correction apparatus according to any one of claims 1 to 4,
An area correction apparatus that corrects the communication area by changing an output of the antenna by changing a current flowing through the antenna when the wireless signal is transmitted to the communication target. In the area correction apparatus as described in any one of Claims 1-4 ,
The communication object recognizes the radio signal when the radio signal having a signal strength equal to or higher than a threshold value is received,
The area correction apparatus corrects the communication area by changing the threshold value.