JP4934560B2 - Smart key system - Google Patents

Description

  The present invention relates to a smart key system.

  Nowadays, it is becoming popular to equip automobiles with so-called smart key systems. In the smart key system, when a user or driver approaches the vehicle from outside the vehicle, signals are automatically transmitted and received between the user's portable device (smart key, electronic key) and the communication device mounted on the vehicle. To check whether the portable device is a portable device for the vehicle. If the result of the verification is affirmative, the sensor detects when the user touches the vehicle door and automatically unlocks (unlocks). There is a smart entry system that locks.

  There is also a system called a smart start system, which is a system in which the engine can be started by pressing a switch for starting the engine if the result is affirmed by checking between the portable device and the communication device in the passenger compartment. . In general, a smart key system is a system in which such a plurality of functions are combined.

  Various technologies have been proposed for such smart key systems. For example, Patent Document 1 below discloses a technique for reducing power consumption in a portable device or an in-vehicle communication device. Specifically, when there is a smart key in the passenger compartment, the response signal from the smart key is stopped when the electric field strength of the electromagnetic wave transmitted from the smart key to each antenna is the same as the previous transmission.

JP 2007-146501 A

  In the in-vehicle communication device in the smart key system, the wiring having the configuration shown in FIG. 6 is generally used as the conventional configuration of the wireless transmission portion. Here, the terminals A and B are terminals connected to an output terminal from which a voltage waveform including a digital signal in the verification ECU is output. The terminals A and B and the transmitting antenna 30 are connected by the first analog circuit unit 107, the second analog circuit unit 108, and the wire harness 50. As shown in FIG. 6, the first analog circuit unit 107 and the second analog circuit unit 108 incorporate a resistor 71 and a capacitance 72. In addition, an inductance 70 is incorporated in the transmitting antenna 30.

  In a conventional smart key system using an in-vehicle communication device having such a configuration, when a portable device is arranged in the vicinity of the wire harness 50, there is a case where collation is obtained. Usually, in a smart key system, antennas are arranged at a plurality of positions of a vehicle, and a range to be covered by each is determined. For example, there are an antenna that covers the outside of the vehicle, an antenna that covers the inside of the vehicle, and an antenna that covers the inside of the trunk.

  For example, it is indispensable for a smart key system to identify whether a person who has a portable device is outside a vehicle or inside a vehicle. Therefore, it is a serious obstacle to the basic function of the smart key system that the collation can be taken in the vicinity of the wire harness regardless of the position where the antenna is arranged.

  FIG. 4 shows the cause of the phenomenon that the collation can be taken in the vicinity of the wire harness 50. The sinusoidal waveforms i1 and i2 shown in FIG. 4 are current waveforms of one conductor part and the other conductor part in the wire harness 50 in the wiring of FIG. FIG. 2 shows the definitions of i1 and i2. Normally, both are considered to match, but as shown in FIG. Therefore, since they do not cancel each other, it is equivalent to a difference current flowing through the wire harness 50, and electromagnetic waves are transmitted from the wire harness 50. The fact that the current values of i1 and i2 do not become the same value in this way indicates that the circuit of FIG. 6 needs to be handled as a distributed form rather than a simple lumped parameter system. Further, if the first analog circuit unit 107 and the second analog circuit unit 108 in the wiring are balanced as shown in FIG. 1 described later, the output voltage becomes the same, and the noise level can be reduced. Therefore, the arrangement of impedance in the wiring of FIG. 6 must be considered.

  Furthermore, the electromagnetic wave transmitted from the wire harness as described above also has a side surface as noise. The presence of electromagnetic noise may adversely affect the functions of various electronic devices, and it is necessary to suppress electromagnetic waves from the wire harness not only from the problem of matching but also from the problem of noise.

  Thus, it is important for a smart key system to eliminate the difference between the current values of i1 and i2 so that an electromagnetic wave is not transmitted from the wire harness. However, in the prior art including the technique of Patent Document 1, such a problem of electromagnetic wave transmission from the wire harness portion has not been considered.

  Therefore, in view of the above problems, the problem to be solved by the present invention is to avoid collation of portable devices in the vicinity of the wire harness by suppressing leakage of electromagnetic waves from the wire harness, and to prevent wireless noise from the wire harness. The purpose is to provide a smart key system with a reduced size.

Means for Solving the Problems and Effects of the Invention

  In order to achieve the above object, a smart key system according to the present invention includes a portable device having a wireless communication function and a communication device mounted on a vehicle, and wireless communication between the portable device and the communication device. A smart key system for collating portable devices, wherein the communication device switches between a transmission antenna for transmitting radio waves to the portable device and a binary voltage value including digital information to be transmitted to the transmission antenna. A switching circuit that outputs a voltage waveform from a pair of output terminals; and an analog circuit configured by a resistor element, a capacitor element, or an inductive element, and a first analog circuit unit connected to one of the pair of output terminals; A second analog circuit unit connected to the other of the pair of output terminals, the analog circuit including a resistor element, a capacitor element, or an inductive element; A first wire portion connected between the analog circuit portion and one terminal of the transmitting antenna; a second wire portion connected between the second analog circuit portion and the other terminal of the transmitting antenna; And an impedance value in the first analog circuit section is the same as that in the second analog circuit section.

  As a result, in the smart key system of the present invention, the impedance values in the first analog circuit unit and the second analog circuit unit arranged between the switching circuit and the wire harness are the same, so the wiring connecting the switching circuit and the transmitting antenna Since the impedance in the forward path and the return path is symmetrical, the current values in the forward path and the return path coincide with each other, so that leakage of electromagnetic waves from the wire harness can be suppressed. Therefore, there is no collation of the portable device near the wire harness, and a smart key system having accurate collation performance can be configured by performing proper collation using the antenna. Further, since wireless noise emitted from the wire harness is also suppressed, it is a smart key system in which wireless noise is suppressed.

  In addition, a resistor element and a capacitor element may be incorporated in the first analog circuit unit and the second analog circuit unit, and an induction element may be incorporated in the transmission antenna.

  By using a configuration whose effect has been proved by verification by such an experiment, leakage of electromagnetic waves from the wire harness can be reduced, so that collation of the portable device is suppressed in the vicinity of the wire harness, and wireless signals emitted from the wire harness A smart key system with reduced noise can be realized. Further, since the resistive element and the capacitive element are not incorporated in the transmitting antenna portion that may be disposed outside the vehicle, it is possible to avoid deterioration of the element in the external environment. Therefore, the system can maintain the performance in the long term.

  The twisted twist pitch in the wire harness may be less than 45 millimeters.

  By using the twist pitch of the wire harness that has been proved by such experiments, the leakage of electromagnetic waves from the wire harness can be reduced. A smart key system that suppresses wireless noise generated from the camera can be realized.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a main configuration diagram of the entire smart key system 1 according to the present invention.

  In the smart key system 1, the portable device is collated by wireless communication between the collation ECU 10, which is a collation ECU (electronic control unit) mounted on the vehicle, and the portable device 40. The verification ECU 10 includes an RF antenna 20 that is a reception antenna and an LF antenna 30 that is a transmission antenna for the wireless communication. Various wirings are made, and signals are transmitted by the wire harness (W / H) 50 between the LF antenna 30 and the verification ECU.

  The verification ECU 10 includes, as its main structure, a CPU 11 that performs calculation and signal processing, a RAM 12 in its work area, a ROM 13 that is a storage means, a reception circuit 14, and a transmission circuit 15, which are connected by a bus to exchange signals. . The receiving circuit 14 is connected to the RF antenna 20, receives a signal transmitted from the portable device 40, and sends the signal to the CPU 11, the RAM 12, and the like. The transmission circuit 15 is connected to the LF antenna 30 via the W / H 50, and transmits a signal for collation work to the portable device 40 using an electromagnetic wave in the LF (long wave) band.

  The structure of the transmission circuit 15 is shown in FIG. First, the baseband signal generation unit 101 generates a baseband signal that is a signal carrying information to be transmitted to the portable device 40 in accordance with a command from the CPU 11. Then, the carrier wave signal generation unit 102 generates a carrier wave signal that is modulated by the baseband signal and transmitted with information.

  Examples of baseband signals and carrier signals are shown in FIG. In the figure, binary values of digital information are indicated by H and L. As shown in the figure, the baseband signal is a square wave in which binary values of H and L are switched, and the carrier wave signal is a square wave having a shorter cycle than the switching of H and L in the baseband signal. Then, a logical product of the baseband signal and the carrier wave signal is obtained by a logical product circuit (AND circuit) 103, and so-called on / off modulation is performed. Hereinafter, the output of the AND circuit 103 is referred to as a modulated wave signal. An example of a modulated wave signal corresponding to the baseband signal and the carrier wave signal of FIG. 7 is shown in FIG.

  Next, the modulated wave signal is input to the drive circuit 104. The drive circuit 104 is a circuit for driving the H bridge circuit 106. As shown in FIG. 1, the H bridge circuit 106 is a circuit having four FETs (field effect transistors) 110, 111, 112, and 113, and includes the LF antenna 30 by using the FETs 110, 111, 112, and 113 as switches. It is a circuit that determines the voltage input to the part. The drive circuit 104 is connected to the gate portions of the FETs 110, 111, 112, and 113 of the H-bridge circuit, and the gate voltage of the FETs 110, 111, 112, and 113 is determined by the drive circuit 104.

  Although the specific circuit configuration of the drive circuit 104 is omitted, the gate voltage of the FETs 110 and 113 is driven by the drive circuit 104 when the value of the modulation wave signal is H. State), and the gate voltages of the FETs 111 and 112 are set to zero. When the value of the modulation wave signal is L, the gate voltage of the FETs 111 and 112 is set to a voltage value at which the FETs 111 and 112 are driven, and the gate voltage of the FETs 110 and 113 is set to zero.

  The power supply circuit 105 is a circuit that sets a voltage supplied to the LF antenna 30. Hereinafter, the voltage value determined by the power supply circuit 105 is assumed to be Vcc. When the value of the modulation wave signal is H due to the function of the drive circuit described above, the voltage VAB (the value obtained by subtracting the potential at point B from the potential at point A) shown in FIG. , + Vcc, and when the value of the modulation wave signal is L, the voltage VAB is −Vcc. The behavior of the FETs 110, 111, 112, 113 and VAB according to the above description is shown in FIG.

  The point A serves as a terminal of the input unit to the first analog circuit unit 107. Point B is a terminal of the input unit to the second analog circuit unit 108. By determining the voltage VAB between the points A and B, the electrical behavior of the first analog circuit unit 107, the second analog circuit unit 108, the W / H 50, and the LF antenna 30 is determined.

  As already described, the first analog circuit unit 107, the second analog circuit unit 108, the W / H 50, and the LF antenna 30 are the main components of the present invention. In the present invention, the first analog circuit unit 107 and the second analog circuit unit 108 are circuits including the resistor 60 and the capacitance 61 (capacitance element) shown in FIG. In the conventional example, the first analog circuit unit 107, the second analog circuit unit 108, the W / H 50, and the LF antenna 30 have the circuit configuration shown in FIG.

  The antenna voltage and current waveforms are generated from the square-wave VAB by such a circuit configuration in which the resistance, inductance (inductive element), and capacitance are connected. As shown in FIG. 7, in the time interval in which VAB oscillates between + Vcc and −Vcc to form a square wave waveform, the current waveform in the LF antenna 30 is (transient state has passed) due to this square wave. Sine wave).

  The amplitude and period of the sine wave are determined by the first analog circuit unit 107, the second analog circuit unit 108, the W / H 50, and the resistance, inductance, and capacitance arranged in the LF antenna 30. In the time interval in which VAB is −Vcc, the current waveform in the LF antenna 30 is also zero due to the presence of capacitance (after passing the transient state).

  The first analog circuit unit 107, the second analog circuit unit 108, and the LF antenna 30 are connected by a W / H 50. The twist pitch of W / H50 of the present invention shown in FIG. 1 is a value less than 45 mm, which is conventionally used, and is particularly 25 mm. The twist pitch is a twist pitch in W / H50, and is the length of P in FIG.

  An inductance 70 is incorporated in the LF antenna 30. A radio signal related to verification is transmitted from the LF antenna 30 to the portable device 40, and the radio wave returned from the portable device 40 is received by the RF antenna 20. Verification is performed by transmitting and receiving signals between the portable device 40 and the LF antenna 30 and the RF antenna 20.

  An example of the analog circuit unit 107, the W / H 50, and the LF antenna 30 that are conventionally used is shown in FIG. In the example of FIG. 6, the resistor 71 is arranged on the terminal A side and the capacitance 72 is arranged on the terminal B side.

  Table 1 shows the experimental results showing the effects of the first analog circuit unit 107, the second analog circuit unit 108, the W / H 50, and the LF antenna 30 of the present invention shown in FIG. In order from the top in Table 1, when the twist pitch is 45 mm, when the twist pitch is 45 mm, when the twist pitch is 45 mm, when the twist pitch is 45 mm, when the twist pitch is 25 mm, in the layout of FIG. When the twist pitch is 45 mm, when it is 25 mm, when the twist pitch in the arrangement of FIG. 5B is 45 mm, and when it is 25 mm, the radio noise peak value and the collable distance are shown.

  A method for measuring the collable distance is shown in FIG. As shown in FIG. 3, the W / H 50 is disposed on the floor 90, and the portable device 40 is disposed vertically upward therefrom, and the distance L that can be verified is measured. In FIG. 3, illustration of devices connected to the W / H 50 is omitted. As shown in FIG. 3, X, Y, and Z shown in Table 1 indicate the posture of the portable device 40. X is a posture in the horizontal orientation, Y is a posture in the vertical orientation, and lay down. The posture is Z. For radio noise, the peak value of radio noise at 100 kHz to 1710 kHz from W / H50 was measured.

  5 (a) and 5 (b) are modified examples of the present invention, and the wiring example of FIG. 5 (a) is a case where a resistor 71 and a capacitance 72 are arranged in the LF antenna 30, and FIG. In this case, the capacitance 72 is arranged in the LF antenna 30, the resistance is divided into two, and the resistors 73 and 73 are arranged in the first analog circuit unit 107 and the second analog circuit unit 108, respectively.

  1, 6, and 7, the resistance values of the resistors 71 are all the same. The resistors 60 and 73 all have the same resistance value, and are half of the resistance value of the resistor 71. The capacitances 61 and 72 are all assumed to have the same capacitance value. It is assumed that all the inductances 70 have the same induction value.

  As shown in Table 1, according to the wiring of FIG. 1, the radio noise is reduced and the collation possible distance is smaller than that of FIG. 6 (conventional). Further, in the wiring of FIG. 1, when the twist pitch is 25 mm, both the radio noise and the collation possible distance are reduced as compared with the case of 45 mm.

  From Table 1, the modified examples of FIGS. 5A and 5B show characteristics that are superior in both radio noise and collable distance compared to the wiring of FIG. 1, particularly when the twist pitch is 25 mm. However, in the wirings shown in FIGS. 5A and 5B, the resistance and the capacitance are arranged in the LF antenna. However, the LF antenna may be arranged to be exposed outside the vehicle. In this case, the characteristics of the element are external. There are cases where people don't like to deteriorate under the environment.

  Therefore, if the wiring of FIG. 5 is used, it is preferable when only radio noise and collation possible distance are regarded as important. On the other hand, if the wiring of FIG. The effect that the characteristics are not easily deteriorated can be obtained.

1 is a schematic diagram of a smart key system in an embodiment of the present invention. The figure which shows a wire harness. The block diagram of the experiment for verification of the effect of this invention. The figure which shows the current waveform of the outward path | route in the conventional wire harness, and a return path | route. The figure which shows the 1st analog circuit part in the modification of this invention, the 2nd analog circuit part, a wire harness, and the antenna for transmission. The figure which shows the 1st analog circuit part in a prior art example, the 2nd analog circuit part, a wire harness, and the antenna for transmission. The figure which shows the example of the time waveform of a baseband signal, a carrier wave signal, a modulated wave signal, the behavior of FET, VAB, and LF antenna current.

Explanation of symbols

1 Smart Key System 10 Verification ECU (Communication Device)
20 RF antenna 30 LF antenna (transmitting antenna)
40 Mobile device (smart key)
50 Wire harness (W / H)
70 Inductance (inductive element)
60, 71, 73 Resistance (resistance element)
61, 72 Capacitance (capacitive element)
106 H-bridge circuit (switching circuit)
107 1st analog circuit part 108 2nd analog circuit part

Claims (3)

A smart key system comprising a portable device having a wireless communication function and a communication device mounted on a vehicle, and performing collation of the portable device by wireless communication between the portable device and the communication device,
The communication device
A transmitting antenna for transmitting radio waves to the portable device;
A switching circuit that outputs a voltage waveform obtained by switching binary voltage values including digital information to be transmitted to the transmitting antenna from a pair of output terminals;
A first analog circuit unit connected to one of the pair of output terminals, an analog circuit composed of a resistive element, a capacitive element, or an inductive element;
A second analog circuit unit connected to the other of the pair of output terminals, an analog circuit composed of a resistive element, a capacitive element, or an inductive element;
A first wire portion connecting between the first analog circuit portion and one terminal of the transmitting antenna, and a second connecting between the second analog circuit portion and the other terminal of the transmitting antenna. A wire harness formed by twisting the wire part;
The smart key system, wherein an impedance value in the first analog circuit unit and an impedance value in the second analog circuit unit are the same. In the first analog circuit portion and the second analog circuit portion, a resistive element and a capacitive element are incorporated,
The smart key system according to claim 1, wherein an inductive element is incorporated in the transmitting antenna.   The smart key system according to claim 1 or 2, wherein a pitch of twisted twists in the wire harness is less than 45 millimeters.

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