LOCKING SYSTEM FOR A VEHICLE

TECHNICAL FIELD

The present invention generally relates to a locking system for a vehicle and, more particularly, to an electric locking system suitable for an anti-theft system for a vehicle.

BACKGROUND ART

Japanese Laid-Open Patent Utility Model Application No.6-40247 discloses a locking system for a vehicle which comprises a coil provided in a key and an antenna coil provided in a key cylinder into which the key is inserted. When the key is inserted into the key cylinder, an identification (ID) signal is transmitted from the key to the key cylinder so as to check whether the ID signal transmitted from the key matches a registered ID signal. Operation of the vehicle is permitted when it is determined that the ID signal transmitted from the key matches the registered ID signal. According to this locking system, the vehicle can be locked electrically in addition to a mechanical lock system. This ensures locking of the vehicle.

In order to achieve an accurate transmission of the ID signal between the coil of the key and the antenna coil of the key cylinder, it is desired to increase an electromagnetic conversion efficiency as much as possible. Thus, in the above-mentioned conventional locking system, the antenna coil is arranged in the key cylinder so that the center axis of the antenna coil aligns with the center of the coil of the key when the key is inserted into the

key cylinder. According to this arrangement, a strong electromagnetic coupling between the coil of the key and the antenna coil of the key cylinder is provided. Thus, a change in the magnetic flux density generated by the coil of the key is efficiently transmitted to the antenna coil of the key cylinder.

In the conventional locking system, there is a gap formed between the coil of the key and the antenna coil of the key cylinder. In order to increase the electromagnetic conversion efficiency between the coil and the antenna coil, the gap between the coil and the antenna coil should be as small as possible. In this respect, the above-mentioned conventional locking system has a problem in that a width of the gap between the coil and antenna coil cannot be decreased beyond a limit due to the arrangement of the coil of the key and the antenna coil of the key cylinder.

DISCLOSURE OF THE INVENTION It is a general object of the present invention to provide an improved and useful locking a system for a vehicle in which the above-mentioned problem is eliminated.

A more specific object of the present invention is to provide a locking system for a vehicle having a high electromagnetic conversion efficiency between a coil of a key and an antenna coil of a key cylinder by reducing a width of a gap formed between the coil and the antenna coil when the key is inserted into the key cylinder. In order to achieve the above-mentioned objects, there is provided according to the present invention a locking system for a vehicle comprising a key system having a key cylinder and a key inserted into the key

cylinder, the key cylinder including an antenna coil and the key including a coil, the coil transmitting data to the antenna coil by an electromagnetic conversion method so that a locking operation of the vehicle is controlled by an electrical control unit based on the data transmitted from the key, characterized in that: one of the antenna coil and the coil is located inside the other one of the antenna coil and the coil when the key is inserted into the key cylinder.

According to the above-mentioned invention, since one of the antenna coil provided in the key cylinder and the coil provided in the key is located inside the other one of the antenna coil and the coil, magnetic flux generated by one of the antenna coil and the coil effectively passes through the other one of the antenna coil and the coil. Thus, a high electromagnetic conversion efficiency is provided between the antenna coil of the key cylinder and the coil of the key. This ensures reliable communication between the antenna coil of the key cylinder and the coil of the key.

In one embodiment of the present invention, the antenna coil is provided inside a protrusion formed on a surface of the key cylinder and the coil is provided inside an annular portion of the key so that the protrusion protrudes into a center opening of the annular portion when the key is inserted into the key cylinder.

In another embodiment, the key cylinder has an opening which receives a portion of the key, the coil provided inside the portion of the key, the antenna coil surrounding the opening.

In the locking system according to the present invention, the one of the antenna coil and the coil may

have a magnetic material core inside thereof.

Additionally, the one of the antenna coil and the coil may be surrounded by a magnetic material, the magnetic material being located inside the other one of the antenna coil and the coil when the key is inserted into the key cylinder.

Further, in the locking system according to the present invention, the data transmitted from the coil to the antenna coil may include a code signal, and the electrical control unit permits an unlocking operation of the vehicle when the code signal matches a code signal registered in the vehicle.

Additionally, the key cylinder may include at least one key slot, and the key may include at least one key blade adapted to be inserted into the key slot, and the key may include at least one handle to rotate the key. Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.l is an illustration of the entire structure of a locking system for a vehicle according to a first embodiment of the present invention;

FIG.2 is a perspective view of a key shown in FIG.l to show an interior of the key;

FIG.3 is a perspective view of an interior of an antenna coil portion shown in FIG.l; FIG.4 is a block diagram of an electric circuit provided in the locking system shown in FIG.l;

FIG.5 is a block diagram of an electric circuit comprising a coil and an IC circuit incorporated in a key

shown in FIG.l;

FIG.6 is a waveform chart of a drive signal supplied to a switch circuit shown in FIG.5; and

FIG.7 is an illustration of the entire structure of a locking system for a vehicle according to a second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE PRESENT INVENTION A description will now be given of a locking system for a vehicle according to a first embodiment of the present invention. FIG.l is an illustration of the entire structure of the locking system for a vehicle according to the first embodiment of the present invention. The locking system according to the first embodiment comprises a key 10, a key cylinder 12, an amplifier 14, an electronic control unit (ECU) 16 and an engine control computer (EFI computer) 18. The key 10 may be an ignition key to start the vehicle. The key cylinder 12 is provided on the vehicle. In the locking system according to the first embodiment of the present invention, an ID code is transmitted between the key 10 and the key cylinder 12 so that the vehicle is permitted to be operated only when a correct ID code is transmitted from the key 10 to the key cylinder 12.

As shown in FIG.l, the key 10 comprises an annular portion 10a, key blades 10b and 10c and handle portions lOd and lOe. The key blades 10b and 10c protrude from one side of the annular portion 10a. The handle portions lOd and lOe protrude from the other side of the annular portion 10a.

FIG.2 is a perspective view of the key 10 showing an interior of the key. As shown in FIG.2, a coil

lOf having m turns is embedded in the annular portion 10a of the key 10. Additionally, an IC circuit lOg is embedded in the handle portion lOd. The coil lOf is electrically connected to the IC circuit lOg. As shown in FIG.l, the key cylinder 12 has insertion slots 12a and 12b into which the corresponding key blades 10b and 10c of the key 10 are inserted. An antenna coil portion 20 is formed to protrude from a surface in which the insertion slots 12a and 12b are formed. The antenna coil portion 20 is positioned in a center between the insertion slots 20a and 20b so that the antenna coil portion 20 protrudes through the center opening of the annular portion 10a of the key 10 when the key blades 10b and 10c are inserted into the insertion slots 12a and 12b, respectively.

FIG.3 is a perspective view of an interior of the antenna coil portion 20. As shown in FIG.3, an antenna coil 20a having n turns is provided inside the antenna coil portion 20. The antenna coil 20a is wound on a ferrite core 20b. The antenna coil is electrically connected to the amplifier 14.

FIG.4 is a block diagram of an electric circuit provided in the locking system according to the first embodiment of the present invention. The electric circuit shown in FIG. comprises the antenna coil 20a, the amplifier 14, the ECU 16 and the EFI computer 18. As shown in FIG.4, the ECU 16 has a power source terminal (+B terminal) and a ground terminal (GND terminal) . The power source terminal is connected to a positive pole terminal of a battery for the vehicle, and the ground terminal is connected to a negative pole terminal of the battery. The ECU 16 has a +B terminal and a power source circuit 28 which is connected to the GND terminal of the battery.

The power source circuit 28 generates a voltage of 5 volts from a voltage provided from the battery at the +B terminal. The voltage of 5 volts generated by the power source circuit 28 is supplied to a 5-volt terminal 30 of the ECU 16.

The ECU 16 has a resistor 32 one end of which is connected to the +B terminal thereof. The other end of the resistor 32 is connected to a current supply terminal 34 of the ECU 16 and the microcomputer 36. The microcomputer 36 is connected to an EEPROM 38 which is a non-volatile memory incorporated in the ECU 16. The microcomputer 36 is also connected to the EFI 18.

The EEPROM 38 stores a 64-bit ID code previously set for the vehicle. The microcomputer 36 encodes a change in the voltage appearing on the current supply terminal 34, as described later. The microcomputer 36 then determines whether or not the encoded data matches an ID code stored in the EEPROM 38. If it is determined that the encoded ID code matches the stored ID code, the microcomputer 36 generates an instruction to enable the vehicle to be in an operative condition. That is, an ignition operation and a fuel injection operation are enabled. On the other hand, if the encoded ID code does not match the stored ID code, The microcomputer 36 does not generate the instruction to enable the vehicle to be in an operative state. Accordingly, in the system according to the present embodiment, an operation of the vehicle is enabled only when a change in the voltage appearing on the current supply terminal 34 matches the predetermined ID code.

The ECU 16 is provided with reference potential terminals 40 and 42 in addition to the above-mentioned current supply circuit 34 and 5-volt terminal 30. The

reference potential terminals 40 and 42 are connected to the GND terminal 26. The 5-volt terminal 30, the current supply terminal 34 and the reference potential terminals 40 and 42 of the ECU 16 are connected to a 5-volt terminal 50, a current supply terminal 52 and reference potential terminals 54 and 56 of the amplifier 14, respectively, via connectors 44 and 46 and a wire harness 48 provided therebetween.

The amplifier 14 has a drive circuit 58 connected to the 5-volt terminal 50 and the reference potential terminal 58. The drive circuit has two output terminals 58a and 58b. The drive circuit outputs a voltage signal between the terminals 58a and 58b. The voltage signal has a predetermined amplitude with a predetermined frequency. In the present embodiment, when a 5 volts voltage difference is generated between the 5- volt terminal 50 and the reference potential terminal 56, a voltage signal having an amplitude of 5 volts with a frequency of 125 kHz is output between the output terminals 58a and 58b.

The other output terminal 58a of the drive circuit 58 is connected to an output terminal of the amplifier 14. The output terminal 62 is connected to one end of the antenna coil 20a. The opposite end of the antenna coil 20a is connected to an output terminal 64 of the amplifier 14. The output terminal 64 is connected to the output terminal 58b of the drive circuit 58 via a capacitor 66.

As mentioned above, the antenna coil 20a and the capacitor 66 are connected in parallel to the drive circuit 58 so that the antenna coil 20 and the capacitor 66 together constitute an LC resonance circuit. The frequency of the voltage signal output by the drive

circuit 58 is set to match the resonance frequency of the LC resonance circuit. Accordingly, when an operation of the drive circuit 58 is started, an LC oscillation is generated by the antenna coil 20a and the capacitor 66. In the present embodiment, a voltage difference of about

150 volts is generated between the output terminals 62 and 64 of the amplifier 14.

The output terminal of the amplifier 14 is connected to a demodulation circuit 68. The demodulation circuit 68 is connected to the reference potential terminal 56 of the amplifier 14. The demodulation circuit 68 detects an amplitude of the voltage signal at the output terminal 64 so as to generate a high-level output when the detected amplitude is greater than a predetermined level and to generate a low level output when the detected amplitude is less than the predetermined level. In the present embodiment, the demodulation circuit 68 outputs the high-level output when the voltage signal having an amplitude of about 150 volts is detected at the output terminal 64 of the amplifier 14. On the other hand, the demodulation circuit 68 outputs the low- level output when the voltage signal detected at the output terminal 64 has an amplitude less than 150 volts, such as a voltage 20-30 mV lower than 150 volts. The voltage signal output from the demodulation circuit 68 is supplied to a base terminal of a switching element 70. The switching element 70 comprises an NPN transistor. A collector terminal of the switching element 70 is connected to the current supply terminal 52 of the amplifier 14. An emitter terminal of the switching element 70 is connected to the reference potential terminal 54 of the amplifier 14. The switching element 70 is turned to a conductive state when the voltage signal

provided to the base terminal thereof is the high-level output. On the other hand the switching element 70 is turned to a non-conductive state when the voltage signal provided to the base terminal is the low-level output. A description will now be given, with reference to FIG.5, of a construction of the electric circuit comprising the coil lOf and the IC circuit lOg incorporated in the key 10. FIG.5 is a block diagram of the electric circuit comprising the coil lOf and the IC circuit lOg. The IC circuit lOg comprises a capacitor 74, a power source circuit 76, a switch circuit 78 and two load circuits 80 and 82. One end (upper end shown in FIG.5) of the coil lOf is connected to an end of the capacitor 74, an end of the power source circuit 76 and an input terminal of the switch circuit 78. An opposite end of the coil lOf is connected to the other end of the capacitor 74, the other end of the power source circuit 76 and the load circuits 80 and 82.

When a voltage change having a predetermined frequency is generated between the opposite ends of the antenna coil 20a in a state where the key 10 is inserted into the key cylinder 12, a voltage variation having the same frequency is generated between the opposite ends of the coil lOf due to electromagnetic induction. The power source circuit 76 comprises a circuit which generates a direct current voltage by rectifying the voltage change generated between the opposite ends of the coil lOf.

The direct current voltage generated by the power source circuit 76 is supplied to a control circuit 84. A memory 86 is connected to the control circuit. The memory 86 stores an ID code which is the same as the ID code stored in the EEPROM 38 shown in FIG.4. The control circuit 84 supplies a switch signal to the switch circuit

78 in accordance with the ID code stored in the memory 86 when power is supplied from the power source circuit 76.

The load circuits 80 and 82 are provided with different loads ZI and Z2, respectively. hen the control circuit 84 supplies to the switch circuit 78 the drive signal designating the load circuit 80 to be connected, the load ZI is connected to the LC circuit comprising the coil lOf and the capacitor 74. Hereinafter, this state is referred to as a first state. On the other hand, when the control circuit 84 supplies to the switch circuit 78 the drive signal designating the load circuit 82 to be connected, the load Z2 is connected to the LC circuit comprising the coil lOf and the capacitor 74. Hereinafter, this state is referred to as a second state. There is a difference in resonance conditions when the load ZI is connected to the LC circuit and when the load Z2 is connected to the LC circuit. In the present embodiment, the inductance L of the coil 10f, the capacitance C of the capacitor 74 and the values of the load ZI and Z2 are determined so that the resonance frequency of the circuit comprising the coil 10f, the capacitor 74 and the load circuit 80 matches the frequency of the voltage signal generated by the antenna coil 20 when the load ZI is connected to the LC circuit, and also the resonance frequency of the circuit comprising the coil lOf, the capacitor 74 and the load circuit 82 differs, by a predetermined frequency difference, from the frequency of the voltage signal generated by the antenna coil 20 when the load Z2 is connected to the LC circuit. Accordingly, voltage signals having different amplitudes are generated between the opposite ends of the coil lOf depending on whether the switch circuit 78 is in the first state or the second state.

FIG.6 is a waveform chart of the drive signal supplied to the switch circuit 78. The drive signal is generated by the control circuit 84 by encoding the ID signal stored in the memory 86. In the present embodiment, the ID signal comprises 64 bits.

Additionally, communication of the ID signal is performed using CDP pulses.

That is, the control circuit 84 supplies the drive signal to the switch circuit 78 so that the bits of the ID signal stored in the memory 86 are arranged in series. At this time, the control circuit 84 controls the drive signal so that when the bit of the ID signal is "0", one of the first state and the second state is switched to the other state during a predetermined time period. Additionally, the control circuit 84 controls the drive signal so that when the bit of the ID signal is "l", one of the first state and the second state is maintained for the predetermined time period.

Prior to the supply of the drive signal corresponding to the ID signal, the control circuit 84 supplies the drive signal corresponding to a start signal to the switch circuit 78. Additionally, the control circuit 84 supplies the drive signal corresponding to a stop signal to the switch circuit 78 immediately after the completion of the supply of the ID signal. Accordingly, the following variation of the voltage amplitude appears between the opposite ends of the coil lOf, in that order, after the IC circuit is activated: 1) variation of voltage amplitude corresponding to the start signal; 2) variation of voltage amplitude corresponding to the ID signal; and 3) variation of voltage amplitude corresponding to the stop signal.

A description will now be given of an operation

of the locking system according to the present invention. As shown in FIG.l, the key blades 10b and 10c of the key 10 are inserted into the key slots 12a and 12b of the key cylinder 12, respectively. During the key insertion process, when a distance between the antenna coil portion 20 and the annular portion 10a of the key 10 becomes less than a predetermined distance, the IC circuit lOg incorporated in the key 10 is activated due to an electromagnetic wave transmitted by the antenna coil 20a. When the IC circuit lOg is activated, the voltage signal having a voltage amplitude, which varies in response to the start signal, the ID signal and the stop signal, is generated between the opposite ends of the coil lOf. In a state where the annular portion 10a of the key 10 is sufficiently close to the antenna coil portion

20, a mutual inductance M is generated between the antenna coil 20a of the key cylinder 12 and the coil lOf of the key 10. In this state, the inductance characteristic of the antenna coil 20a is influenced by a state of the coil lOf. When an electromagnetic signal is generated by the antenna coil 20a, the coil lOf of the key 10 generates a voltage signal between the opposite ends thereof. Thus, there is a difference between the voltage amplitudes generated between the opposite ends of the antenna coil 20a when the voltage signal having a large amplitude is generated between the opposite ends of the coil lOf of the key 10 and when the voltage signal having a small amplitude is generated between the opposite ends of the coil lOf. For the reason mentioned above, when the load 80 is connected to the coil lOf in the IC circuit lOg, that is, when the circuit is in the first state, a voltage signal having a large amplitude is generated at the output

terminal 64 of the amplifier 14. On the other hand, when the load 82 is connected to the coil lOf in the IC circuit lOg, that is, when the circuit is in the second state, a voltage signal having a small amplitude is generated at the output terminal 64 of the amplifier 14.

During the process for inserting the key 10, when a voltage amplitude variation of 20 to 30 mV is generated at the output terminal 64, the voltage amplitude variation can be detected by the demodulation circuit 68. In this state, the demodulation circuit 68 supplies to the switching element 70 the high-level output when the voltage amplitude is large and the low-level output when the voltage amplitude is small.

The switching element 70 is set to the non- conductive state when the low-level output is supplied to the base terminal thereof. When the switching element 70 is set to the non-conductive state, no current flows to the resistor 32 provided in the ECU 16 (refer to FIG.4). Accordingly, in this state, the power source voltage is provided to the current supply terminal 34 of the ECU 16. On the other hand, when the high-level output is provided to the base terminal of the switching element 70, the switching element 70 is set to the conductive state, and thus a current flows to the resistor 32. In this case, a voltage drop is generated when the current passes through the resistor 32, and almost the ground level voltage appears at the current supply terminal 34.

As mentioned above, one of the power source voltage and the ground level voltage appears at the current supply terminal 34 of the ECU 16 in responεe to the voltage signal supplied to the switching element 70 depending on whether it is in the high-level or the low- level, that is, whether the voltage amplitude at the

output terminal 64 is large or small. The microcomputer 36, which is connected to the current supply terminal 34, determines the magnitude of the amplitude of the voltage signal at the output terminal 64 based on the variation in the voltage at the current supply terminal 34.

Additionally, the microcomputer 36 determines that the bit value of the signal transmitted from the key 10 is equal to "1" when it is determined that the large amplitude voltage signal is generated for a predetermined time period or when it is determined that the small amplitude voltage signal is generated for the predetermined time period. The microcomputer 36 determines that the bit value transmitted from the key 10 is equal to "0" when the amplitude of the voltage signal is varied during the predetermined time period.

The microcomputer 36 determines the bit value of each bit transmitted from the key 10 so as to detect the ID signal comprising 64 bits after a series of bit signals representing the start signal is detected. Then, the microcomputer 36 determines whether or not the detected ID signal matches the ID signal stored in the EEPROM 38. The microcomputer 36 permits the EFI computer 18 to enable operation of the vehicle only when the detected ID code matches the stored ID code. As mentioned above, the microcomputer 36 decodes the ID signal transmitted from the key 10 based on the variation in the amplitude of the voltage signal generated between the opposite ends of the antenna coil 20a. Accordingly, in order to accurately and easily decode the ID signal, it is advantageous if a large variation is generated in the amplitude of the voltage signal between the first state and the second state of the IC circuit lOg.

In the locking system according to the present embodiment, the variation in the voltage amplitude generated between the opposite ends of the antenna coil 20 is increased as the electromagnetic conversion efficiency between the antenna coil 20a and the coil lOf is increased. The electromagnetic conversion efficiency is increased as the distance between the antenna coil 20a and the coil lOf is decreased. Accordingly, in order to facilitate the decoding of the ID code, it is effective to locate the antenna coil 20a and the coil lOf as close as possible to increase the electromagnetic conversion efficiency between the antenna coil 20a and the coil lOf.

As mentioned previously, in the locking system according to the present embodiment, the antenna coil portion 20 of the key cylinder 12 is adapted to protrude through the center opening of the annular portion 10a of the key 10 when the key 10 is inserted into the key cylinder 12. According to this arrangement, the coil lOf of the key 10 can be located at a short distance to the antenna coil 20a so as to sufficiently increase the electromagnetic conversion efficiency between the antenna coil 20a and the coil lOf. Accordingly, in the locking system according to the present embodiment, the ECU 16 can easily and accurately read the ID code transmitted from the key 10.

Additionally, in the present embodiment, the ferrite core 20b is provided inside the antenna coil 20a. That is, the antenna coil 20a is wound on the ferrite core 20b. Thus, the magnetic flux generated by the antenna coil 20a is concentrated in the ferrite core 20b. When the magnetic flux is concentrated in the ferrite core 20b, the magnetic flux generated by the antenna coil 20a hardly leaks outside the coil lOf when the key 10 is inserted

into the key cylinder 12. That is, the magnetic flux generated by the antenna coil 20a efficiently passes through the coil lOf.

Similarly, the magnetic flux generated by the coil lOf is concentrated in the ferrite core 20b when the key 10 is inserted into the cylinder 12. When the magnetic flux generated by the coil lOf is concentrated in the ferrite core 2Ob, the magnetic flux generated by the coil lOf hardly leaks outside the antenna coil 20a when the key 10 is inserted into the key cylinder 12. That is, the magnetic flux generated by the coil lOf efficiently passes through the antenna coil 20a.

As mentioned above, when the ferrite core 20b is provided inside the antenna coil 20a, the electromagnetic conversion efficiency is increased between the antenna coil 20a and the coil lOf when the antenna coil 20a works as an elementary coil and the coil lOf works as a secondary coil and when the coil lOf works as an elementary coil and the antenna coil 20a works as a secondary coil. Accordingly, in the locking system according to the present embodiment, an efficient communication capability is provided between the antenna coil 20a and the coil lOf by the arrangement of the coil lOf and the antenna coil 20a and the ferrite core 20b inside the antenna coil 20a.

In the present embodiment, although the magnetic material (ferrite core 20) is provided inside the antenna coil 20a, the position of the magnetic material is not limited to the inside of the antenna coil 20a. That is, an annular magnetic material which surrounds the antenna coil 20a may be provided inside the coil lOf or outside the antenna coil. This arrangement provides the same effect as the effect obtained by providing the magnetic

material inside the antenna coil 20a.

Additionally, in the present embodiment, although the magnetic material (ferrite core 20b) is provided inside the antenna coil 20a, the magnetic material is not always needed to achieve the effect of the present invention. That is, both the antenna coil 20a and the coil lOf may be annular coils without cores therein.

A description will now be given, with reference to FIG.7, of a second embodiment of the present invention. FIG.7 is an illustration of the entire structure of a locking system for a vehicle according to the second embodiment of the present invention. In FIG.7, parts that are the same as the parts shown in FIG.l are given the same reference numerals, and descriptions thereof will be omitted.

As shown in FIG.7, a key 90 comprises a handle 90a and a key blade 10b. The IC circuit lOg and a coil assembly 92 are incorporated inside the handle 90a. The coil assembly 92 comprises a coil 92a and a core 92b provided inside the coil 92a similar to the assembly of the antenna coil 20a and the ferrite core 20b of the first embodiment. The coil 92a is electrically connected to the IC circuit lOg.

In a key cylinder 94, there is provided a slot 94a into which the key blade 90b is inserted.

Additionally, a coil accommodating opening 94b into which a portion of the handle 92 is inserted is formed in the key cylinder 94. The coil assembly 92 is provided inside the portion which is inserted into the opening 94b. That is, the opening 94b of the key cylinder 94 receives the portion of the handle 90a of the key 90 in which portion the core 92b is incorporated. In the key cylinder 94, there is provided an antenna coil 96 which surrounds the

l coil accommodating portion 94b. The antenna coil 96 is electrically connected to the amplifier 14 similar to the antenna coil 20a of the first embodiment.

According to the above-mentioned construction,

5 when the key 90 is inserted into the key cylinder 94, the coil assembly 92 protrudes inside the antenna coil 96. That is, the coil 92b is located inside the antenna coil 96. In this state, similar to the firεt embodiment, the electromagnetic conversion efficiency is increased between

10 the antenna coil 96 and the coil 92a when the antenna coil 96 works as an elementary coil and the coil 92a works as a secondary coil and when the coil 92a works as an elementary coil and the antenna coil 96 works as a secondary coil. Accordingly, in the locking system

15 according to the present embodiment, an efficient communication capability is provided between the antenna coil 96 and the coil 92a by the arrangement of the coil 92a and the antenna coil 96 and the ferrite core 92b inside the coil 92a.

20 In the present embodiment, although the magnetic material (ferrite core 92b) is provided inside the coil 92, the position of the magnetic material is not limited to the inside of the coil 92. That is, an annular magnetic material which surrounds the coil 92 may be

25 provided inside the antenna coil 96 or outside the coil 92a. This arrangement provides the same effect as the effect obtained by providing the magnetic material inside the coil 92a.

Additionally, in the present embodiment,

30 although the magnetic material (ferrite core 92b) is provided inside the coil 92a, the magnetic material is not always needed to achieve the effect of the present invention. That is, both the antenna coil 96 and the coil

92b may be annular coils without cores therein. The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.

INDUSTRIAL APPLICABILITY

According to the above-mentioned invention, since one of the antenna coil provided in the key cylinder and the coil provided in the key is located inside the other one of the antenna coil and the coil, magnetic flux generated by one of the antenna coil and the coil effectively passes through the other one of the antenna coil and the coil. Thus, a high electromagnetic conversion efficiency is provided between the antenna coil of the key cylinder and the coil of the key. This ensures reliable communication between the antenna coil of the key cylinder and the coil of the key.