Abstract:
A control device includes a transmitter for outputting a request signal to an electronic key in response to the ON operation of a predetermined switch (start switch) among a plurality of switches (winker switch, horn switch, etc.) arranged in the vicinity of a user who has sat on the driver seat of the vehicle (request signal) generator, a transmission circuit, and a transmission antenna, a detector for detecting a response signal from the electronic key (a reception circuit and response signal matching device), and monitor for outputting a lock release instruction to an actuator when the response signal shows that the request is from a regular or proper user.

Description:
TECHNICAL FIELD 
   The present invention relates to an electronic key system for carrying out wireless communication between a transceiver or transmitter (electronic key) carried by a user and a controller mounted on the vehicle, and, when an ID is compared and there is a request from the normal user, starting the engine etc., the invention being suitable for use as, for example, an electronic key system for a vehicle such as a motorcycle. 
   BACKGROUND ART 
   Japanese Laid-Open Patent Publication No. 2001-349110 and Japanese Laid-Open Patent Publication No. 2001-349117 exist as disclosing known electronic key systems for a vehicle. The electronic key systems for a vehicle disclosed in these documents have activation means (switches) arranged in a door handle and trunk lid of the vehicle. If a user operates (activates) these activation means, communication with the electronic key commences, and a comparison is carried out between an ID transmitted from the electronic key and an ID registered in the controller. When the comparison shows that the respective ID&#39;s are matched, the door lock is released. 
   An electronic key system that has a transmission antenna provided for each door of a four-wheeled vehicle, which can release only the door that a portable device is closest to independently of the other doors of the vehicle, has also been proposed as related art (see, for example, Japanese Laid-Open Patent Publication No. 10-317754). 
   When applying this type of electronic key system to a motorcycle, it is necessary to provide some type of activation means equivalent to the activation means (switches) arranged in the door handle of the four-wheeled vehicle. In addition, when activation operations and the deposit and removal of a helmet from the motorcycle storage container by the user are taken into consideration, it is preferable to provide the activation means at positions that are within the natural reach of the user during these operations, such as on the handlebar or the seat. 
   The present invention has been conceived in view of this type of problem, and an object of the invention is to provide an electronic key system for a vehicle that can smoothly activate a controller during a series of operations by the user when boarding the vehicle, and which can improve operability of activation using the electronic key. 
   Another object of the present invention is to provide an electronic key system for a vehicle that can obtain the advantages of being small in size, lightweight and low in cost, without the need to provide a new activation means. 
   SUMMARY OF THE INVENTION 
   An electronic key system of the present invention has a controller mounted in the vehicle itself, and a portable transceiver carried by a user of the vehicle, the vehicle containing a locking unit for causing the vehicle to be locked so that the vehicle cannot be used until a lock release command is received. The controller comprises a a transmitter that outputs a request signal to the portable transceiver in response to ON operation of predetermined switches. The predetermined switches being previously identified from among a plurality of switches positioned in the vicinity of the user when the user boards the vehicle. The controller also comprises a receiver unit which receives an acknowledgement signal, in response to the request signal, from the portable transceiver, and a drive unit which outputs a lock release command to the locking unit when the acknowledgement signal is compared and judged to be a request from the user. 
   In this way, when the user boards the vehicle, communication to the portable transceiver is started by operation of any of the plurality of switches positioned close to the user. Accordingly, in a series of operations performed by the user when boarding the vehicle, operation of any of the plurality of switches can easily be performed by the user, and it is possible to smoothly carry out activation of the controller. 
   Further, since activation is performed by a user operating a predetermined switch (hereinafter referred to as the activation switch) from among the plurality of switches, it is not possible to easily discover the activation switch, even if another user (someone who is not the normal user) attempts to carry out the operation, and thus the invention also is effective for preventing theft. 
   An electronic key system for a vehicle of the present invention also has a controller mounted in the vehicle itself and a portable transmitter carried by a user of the vehicle. The vehicle contains a locking unit which causes the vehicle to be locked so that the vehicle cannot be used until a lock release command is received. The portable transmitter contains a transmitter unit that outputs a request signal to the controller in response to an operation input by the user. The controller comprises a receiver which receives a request signal from the portable transmitter in response to ON operation of predetermined switches, among a plurality of switches positioned in the vicinity of the user when the user boards the vehicle. The controller also includes a drive unit which outputs a lock release command to the locking unit when the acknowledgement signal is compared and judged to be a request from the user. 
   In this case also, it is possible to smoothly activate the controller during a series of operations performed by the user when boarding the vehicle, and it is possible to improve operability of activation using the electronic key, wherein the invention is also effective in preventing theft. 
   In the invention described above, if the vehicle is not started for a specified period of time, it is also possible to include an interrupting circuit which permits interruption of the supply of power to at least those circuits, inside the controller, that perform communication. An interrupting circuit controller is provided which permits supply of power to the circuits in response to ON operation of a predetermined switch (activation switch) among the plurality of switches positioned in the vicinity of the user when the user boards the vehicle. 
   In this way, when the vehicle has not been started for a specified period of time, thereafter, it is possible to significantly reduce power consumption during standby by stopping supply of electrical power to circuits relating to communication until the activation switch is operated. 
   Also, since as long as the specified activation switch is not operated, external communication (communication with the portable transceiver or receipt of a request signal from the portable transmitter) is not carried out, and moreover since it is not easy to discover the activation switch, the invention is effective for theft prevention. 
   If the vehicle is not started for a specific period of time, it is also possible for the invention described above to include a switching circuit which intermittently supplies power to at least those circuits, inside the controller, that perform communication. A switching circuit controller is provided which permits return from a mode in which power is supplied intermittently to a mode in which a normal supply of power is provided to the circuits. This return occurs in response to an ON operation of a predetermined switch, which has been previously selected from among a plurality of switches positioned in the vicinity of the user when the user boards the vehicle. 
   In this way, when the vehicle has not been started for a specified period of time, thereafter, it is possible to significantly reduce power consumption during standby by supply of electrical power intermittently to circuits relating to communication until the activation switch is operated. 
   It is also possible for the plurality of switches of the invention described above to be operational switches used for starting the vehicle engine, providing safety during travel, and stopping the vehicle. In this case, since it is not necessary to provide a new activation switch, it is possible to obtain the advantages of small size, lightness of weight, and reduction in cost. 
   It is also possible to include a switch for detecting that the user has boarded the vehicle (boarding detection switch) as one of the plurality of switches. When such a boarding detection switch has been switched on, a request signal is automatically output from a controller at the point in time that the user boards the vehicle, or alternatively, receipt of a request signal from a portable transmitter is started, whereby it is possible to significantly improve operability. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a structural drawing showing an electronic key system according to a first embodiment; 
       FIG. 2  is a block drawing showing the structure of an electronic key in the electronic key system of the first embodiment; 
       FIG. 3  is a block diagram showing the structure of a controller in the electronic key system of the first embodiment; 
       FIG. 4  is an explanatory drawing showing an example of operational switches (switches which are candidates for being the activation switch) disposed in the vicinity of handlebars of a motorcycle type vehicle; 
       FIG. 5  is an explanatory drawing showing an example of operational switches (switches which are candidates for being the activation switch) disposed in the vicinity of handlebars of a scooter type vehicle; 
       FIG. 6  is an explanatory drawing showing an example wherein the activation switch is arranged on a front section of a seat, in a scooter type vehicle; 
       FIG. 7A  is a side elevation showing one example of a setting position for a transmission antenna on the vehicle, and  FIG. 7B  is plan view of the same; 
       FIGS. 8A to 8E  are timing charts showing an example of processing operations in the electronic key system of the first embodiment; 
       FIG. 9  is a block drawing showing the structure of an electronic key in an electronic key system according to a second embodiment; 
       FIG. 10  is a block diagram showing the structure of a controller in the electronic key system of the second embodiment; and 
       FIG. 11  is a block diagram showing the structure of a controller in an electronic key system according to a third embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the electronic key system of the present invention applied to, for example, a motorcycle system, will now be described with reference to  FIGS. 1 through 11 . 
   As shown in  FIG. 1 , an electronic key system  10 A according to a first embodiment includes a portable transceiver  12  carried by a user, and a controller  14  mounted on the vehicle. The portable transceiver  12  either takes on the external appearance of a key with an IC chip built inside, or takes on the external appearance of a card with an IC chip built inside, but in the case where a keyless system is adopted, a card type is mainly used. With this embodiment, a description will be given assuming a portable transceiver  12  shaped like a card. Also, since the portable transceiver  12  is generally called an electronic key, the portable transceiver will also be referred to as an electronic key  12  in the following description. 
   The electronic key  12  is a card type, as described above, and as shown in  FIG. 2 , internally comprises a battery  20 , a power supply circuit  22 , a CPU  24 , a receiving circuit  26  and a transmission circuit  28 . 
   The power supply circuit  22  provides electrical power from the battery  20  to the receiving circuit  26 , transmission circuit  28  and CPU  24 . The receiving circuit  26  has a receiving antenna, not shown, and receives a request signal Sr or the like transmitted through the receiving antenna from the controller  14 , and further extracts and demodulates the signal from a carrier wave. The demodulated signal is supplied to the CPU  24 . The carrier wave frequency of the request signal Sr is 100 kHz to 300 kHz. 
   The CPU  24  executes at least the following two programs: (Request signal comparison means  30  and acknowledgement signal generating means  32 ). The request signal comparison means  30  compares whether or not a signal supplied from the receiving circuit  26  is the request signal Sr, and if it is the request signal Sr, transfers control to the acknowledgement signal generating means  32 . The acknowledgement signal generating means  32  reads out ID data stored in a ROM, not shown, in response to a request from the request signal comparison means  30 , adds an attribute representing acknowledgment to the ID data, and outputs this as transmission data Dt to the transmission circuit  28 . The transmission circuit  28  has a transmission antenna, not shown, and performs modulation of a carrier wave based on transmission data Dt supplied from the CPU  24 , and further transmits this as an acknowledgement signal Sa through the transmission antenna. The carrier frequency for the acknowledgement signal Sa is 200 MHz to 500 MHz. 
   On the other hand, as shown in  FIG. 3 , the controller  14  mounted in the vehicle is constituted by a system LSI, for example, and comprises a power supply circuit  40 , a CPU  42 , a receiving circuit  44 , a transmission circuit  46 , an input circuit  48 , a first drive circuit  52  (for actuator drive), and a second drive circuit  54  (for main relay drive). Peripheral to this controller  14 , there are provided at least a battery  60 , a main switch  62 , a handlebar actuator  64 , a main relay  66 , an activation switch  70  and a transmission antenna  72 . 
   The main switch  62  has two fixed connection points  62   a  and  62   b , and one movable connection point  62   c , with one fixed connection point  62   a  being connected to the battery  60 , and the other fixed connection point  62   b  being connected to the main relay  66 . 
   The activation switch  70  is connected to the input circuit  48 , and the ON/OFF state of the activation switch  70  is supplied through the input circuit  48  to the CPU  42 . 
   As the activation switch  70 , it is possible to set any operation switch used for, for example, starting the vehicle engine, providing safety during travel, and stopping the vehicle. Specifically, as shown in  FIG. 4 , in the case where the vehicle is a motorcycle type vehicle  100 A, it is possible to set any of a lighting dimmer switch  104 , a clutch switch  106 , an indicator switch  108 , a horn switch  110 , a front brake switch  112 , a hazard switch  114  or a starter switch  116 , all of which are provided in the vicinity of the handlebar  102 , as the activation switch  70 . 
   Also, if the vehicle is a scooter type vehicle  100 B, as shown in  FIG. 5 , it is possible to set any of a lighting dimmer switch  122 , a rear brake switch  124 , an indicator switch  126 , a horn switch  128 , a front brake switch  130 , a hazard switch  132  or a starter switch  134 , all of which are provided in the vicinity of the handlebar  120 , as the activation switch  70 . 
   Setting of the activation switch  70  is determined in advance by means of, for example, an agreement between the user and the dealer at the time the user purchases the motorcycle  100 A or scooter  100 B, and can be wired in at the factory based on the decided items. For example, wiring to connect the switch determined to be the activation switch  70  to the input circuit  48  of the controller  14  is carried out at the factory. 
   While it is possible to have any of the various switches provided in the vicinity of the handlebars  102  and  120  as described above, serve as the activation switch  70 , it is also possible, with the scooter  100 B, for example, to provide the activation switch  70  particularly close to the seat  140 , as shown in  FIG. 6 . 
   The scooter  100 B has a space in which it is possible to stow a helmet, not shown, below the seat  140 , and normally, when the scooter is not mounted, the helmet would be stowed in this space. Therefore, when the scooter  100 B is mounted, since an operation to open and close the seat  140  to remove the helmet must be performed, it is possible to easily carry out an operation of the activation switch  70  together with taking out the helmet, by providing the activation switch  70  at a front part of the seat  140 , as shown in  FIG. 6 . 
   On the other hand, the power supply circuit  40  for the controller  14  supplies electrical power from the battery  60  to the CPU  42 , the receiving circuit  44 , and the transmission circuit  46 , etc. 
   The receiving circuit  44  has a receiving antenna, not shown, and an acknowledgement signal Sa is received from the electronic key through the receiving antenna, and further is extracted and demodulated from a carrier wave. The demodulated signal is supplied to the CPU  42 . 
   The CPU  42  executes at least three programs (request signal generating means  80 , acknowledgement signal comparison means  82  and monitoring means  84 ). 
   The request signal generating means  80  reads out request data Dr (data constituting the source of the request signal Sr) from a ROM, not shown, in response to the ON operation of the activation switch  70 , and outputs the data to the transmission circuit  46 . 
   The transmission circuit  46  modulates a carrier wave based on the request data Dr supplied from the CPU  42 , for transmission via the transmission antenna  72  as the request signal Sr. 
   As shown in  FIG. 7A  and  FIG. 7B , the transmittable range of the request signal Sr, assuming the vehicle is a scooter  100 B, is a spherical range (the range shown by circle A in  FIG. 7A  and  FIG. 7B ) of a diameter of 1 to 1.5 m, with the transmission antenna fitted to the scooter  100 B at the center, and is a narrow range compared to the transmittable range of the acknowledgement signal Sa (a range of a few m radius with the electronic key  12  as the center). 
   Thus, in order for reliable contact with the electronic key  12  carried by the user, when carrying out operations such as opening the seat  140  during boarding of the vehicle, as shown in  FIG. 7A  and  FIG. 7B , it is preferable to arrange the transmission antenna  72  in the vicinity of the center of the scooter  100 B. 
   Here, when considering a line  146  between the center  142   a  of the front wheel  142  and the center  144   a  of the rear wheel  144 , the vicinity of the center of the scooter  100 B is a range from a point P 1 , which is ¼ of the line  146 , to a point P 2 , which is ¾ of the line  146 , with the center  142   a  of the front wheel  142  serving as a reference, for example. These dimensions are the same for the motorcycle  100 A. With this embodiment, the transmission antenna  72  is arranged close to the front of the seat  140 . 
   The acknowledgement signal comparison means  82  compares whether or not a signal supplied from the receiving circuit  44  is an acknowledgement signal Sa, and if it is the acknowledgement signal Sa, the acknowledgement signal comparison means  82  compares whether or not ID data contained in the acknowledgement signal Sa matches ID data stored in a memory (not shown). 
   The monitoring means  84  monitors presence or absence of arrival of an acknowledgement signal Sa (whether not an ID match is detected by the acknowledgement signal comparison means  82 ) based on output of the request signal Sr. The request signal generating means  80  awaits input of the acknowledgement signal Sa from a point in time when the request data Dr is output, and if an acknowledgement signal Sa arrives within a specified time, a lock release signal is output to the first drive circuit  52 , and an ON signal is output to the second drive circuit  54 . 
   The first drive circuit  52  drives an actuator  64  for the handlebar in response to input of the lock release signal from the CPU  42 , and releases a locked state of the handlebars  102  and  120 . 
   The second drive circuit  54  is put into an ON state based on input of an ON signal from the CPU  42 , and thereafter, starts the engine and enters a state in which travel is enabled, in a step where the main relay  66  is turned on by an ON operation of the main switch  62 . 
   If the main switch  62  is turned OFF, the main relay  66  becomes OFF, and the engine is also stopped at the same time. If a locking operation is then carried out, for example, by putting the handlebar  102  in a locked state, the comparison operation for the acknowledgement signal Sa in the controller  14  is stopped, and the second drive circuit  54  is turned OFF. 
   Next, representative processing operations of the electronic key system  10 A of the first embodiment will be described with reference to the timing charts shown in  FIGS. 8A to 8E . A request signal Sr is a signal having a pulse string based on request data Dr, and the acknowledgement signal Sa is a signal having a pulse string based on data contained in the ID data, but in  FIGS. 8A to 8E , the signals have each been shown as single pulse signals to simplify description. 
   First of all, at time t 1  in  FIG. 8A , in a state where a user is in possession of the electronic key  12 , if the activation switch  70  is turned ON, the request signal Sr is transmitted from the controller  14  (refer to time t 2 ), as shown in  FIG. 8C , and communication with the electronic key  12  commences. 
   When the user is in possession of the electronic key  12 , the request signal Sr is received by means of the receiving circuit  26  of the electronic key  12  (refer to  FIG. 2 ). As shown in  FIG. 8D , the electronic key  12  transmits an acknowledgement signal Sa in response to receipt of the request signal Sr (refer to time t 3 ). The acknowledgement signal Sa is supplied through the receiving circuit  44  of the controller  14  to the CPU  42  (refer to  FIG. 3 ), and ID data included in the acknowledgement signal Sa is compared. When it is judged that the ID data matches, the locked state of the handlebar  102  is released by means of the controller  14  and the first drive circuit  52 , as shown in  FIG. 8E  (refer to time t 4 ). At this time, the second drive circuit  54  is turned ON. 
   Continuing, if the main switch  62  is turned ON at time t 5  in  FIG. 8B , the engine is started and a state in which travel is enabled is entered. 
   In this way, in the electronic key system  10 A according to the first embodiment, since among the various switches arranged in the vicinity of the handlebars  102  and  120 , the user sets a predetermined switch as the activation switch  70 , when the user boards the vehicle, the activation switch  70  is positioned close to the user. As a result, during a series of operations performed by the user when boarding the vehicle, operation of the activation switch  70  can be carried out simply by the user, and it is possible to smoothly activate the controller  14 . 
   Also, since the activation switch  70  is a predetermined switch from among the various switches that are arranged in the vicinity of the handlebars  102  and  120 , which is set by the user at the time of making an agreement with a dealer, for example, it is not easy for another user (who is not the normal user) to easily locate the activation switch  70 , and thus the invention is effective in preventing theft. 
   In particular, in the case that one of the operational switches used in starting the vehicle engine, providing safety during travel, or stopping the vehicle, is set as the activation switch  70 , since it is not necessary to provide a new activation switch  70 , it is possible to obtain the advantages of miniaturization, lightness of weight, and low cost. 
   Also, if the activation switch  70  is attached to a front section of the seat  140 , it is possible to operate the activation switch  70  at the same time as taking out a helmet, and it is therefore possible to significantly improve operability. 
   Among the switches arranged on the vehicle, at least the switch that is set as the activation switch  70  can be a mechanical contact type switch, but as for the other switches, it is possible to use electrostatic touch switches, switches that use the principles of piezoelectric elements, or switches that take advantage of hall elements, etc. 
   Next, an electronic key system  10 B according to a second embodiment will be described with reference to  FIGS. 9 and 10 . Members and means corresponding to those in  FIGS. 2 and 3  have the same reference numerals attached thereto, and repeated description of those sections will be omitted. 
   As shown in  FIG. 9 , the electronic key  12  of the electronic key system  10 B according to the second embodiment has almost the same structure as the electronic key  12  of the first embodiment (refer to  FIG. 2 ), but is different in that it has an operation switch  150 . 
   Further, the CPU  24  executes at least one program (request signal generating means  152 ). The request signal generating means  152  is activated by an ON operation of the operation switch  150 , and reads out ID data stored in a ROM, not shown, and further adds an attribute representing acknowledgment to the ID data for output to the transmission circuit  28  as transmission data Dt. The transmission circuit  28  has a transmission antenna, not shown, and modulates a carrier wave based on the transmission data Dt supplied from the CPU  24 , to transmit the data as a request signal Sq by means of the transmission antenna. The carrier frequency of the request signal Sq is 200 MHz to 500 MHz. 
   On the other hand, as shown in  FIG. 10 , the controller  14  mounted on the vehicle has almost the same structure as the controller  14  of the first embodiment described above (refer to  FIG. 3 ), but is different in that there is no transmission circuit  46  or transmission antenna  72 . The controller  14  includes a switching circuit  160  for selectively stopping supply of electrical power to the receiving circuit  44 , and further includes a switching control circuit  154  for ON/OFF control of the switching circuit  160 , by outputting an ON signal So and an intermittent pulse signal Sk to the switching circuit  160 . 
   The receiving circuit  44  has a receiving antenna, not shown, and receives a request signal Sq that has been transmitted from the electronic key  12  by means of the receiving antenna, and further extracts and demodulates the signal from a carrier wave. The demodulated signal is supplied to the CPU  42 . 
   The CPU  42  executes at least the following three programs: (Request signal comparison means  156 , monitoring means  84 , and timer means  158 ). 
   The request signal comparison means  156  compares whether or not the signal supplied from the receiving circuit  44  is a request signal Sq, and, if it is a request signal Sq, compares whether or not ID data contained in the request signal Sq matches ID data stored in a memory, not shown. 
   The monitoring means  84  monitors presence or absence of the request signal Sq arriving (whether or not an ID match is detected by the request signal comparison means  156 ), and in the event that a request signal Sq from the electronic key  12  carried by the normal user is detected, the monitoring means  84  outputs a lock release signal to the first drive circuit  52 , releasing the locked state of the handlebars  102 ,  120 , and puts the second drive circuit  54  in an ON state. After that, the engine is started and a state in which travel is possible is enabled, at a stage of turning the main relay  660 N by operating the main switch  62 . 
   If the main switch  62  is turned OFF, the main relay  66  is turned OFF and at the same time the engine is stopped. At this time, the second drive circuit  54  is turned OFF. 
   The timer means  158  outputs a continuation instruction signal Sc to the switching control circuit  154  at the time that the activation switch  70  is turned ON and during a period when the main switch  62  is ON, as well as during a period from when the main switch  62  is turned OFF until a specified value is counted by the timer means  158 . 
   Also, the timer means  158  counts reference counts from a clock generator, not shown, from a point in time when the main switch  62  is turned OFF. When counting to a specified value has been completed (for example, after two days or a week have elapsed), the timer means  158  outputs an intermittent command signal Sp to the switching control circuit  154 . 
   The switching control circuit  154  outputs an ON signal So to the switching circuit  160  during the period when the continuation instruction signal Sc is being supplied from the timer means  158 . The switching circuit  160  turns the switch  1620 N in response to the supplied ON signal So, and in this way supply of electrical power to the receiving circuit  44  continues normally. 
   At a point in time when the intermittent instruction signal Sp is supplied from the timer means  158 , the switching control circuit  154  generates an intermittent pulse signal Sk for intermittently switching an attribute ON and OFF and outputs it to the switching circuit  160 . The switching circuit  160  intermittently repeats the ON operation and OFF operation based on the supplied intermittent pulse signal Sk. Electrical power supply to the receiving circuit  44  becomes intermittent, and the controller  14  is transferred to a power saving operating mode. 
   Then, if the activation switch  70  is turned on while in the power save operation mode, the continuation instruction signal Sc is output from the timer means  158  to the switching control circuit  154 , and in this way electrical power supply to the receiving circuit  44  continues normally. 
   In the electronic key system according to the second embodiment, if the vehicle has not been started for a specified time period, since electrical power is supplied to the receiving circuit  44  intermittently thereafter and until the activation switch  70  is turned ON, it is possible to reduce power consumption when in standby. 
   Next, an electronic key system  10 C according to a third embodiment will now be described with reference to  FIG. 11 . Members and means corresponding to those in  FIG. 10  have the same reference numerals attached thereto, and repeated description of those sections will be omitted. 
   The electronic key  12  used in the electronic key system  10 C of the third embodiment is the same as the electronic key  12  of the second embodiment described above (refer to  FIG. 9 ). 
   The controller  14  has almost the same structure as the controller  14  of the second embodiment described above (refer to  FIG. 10 ), but is different in that an ON signal So and an OFF signal Sf are output from the switching control circuit  154 . 
   Specifically, the timer means  158  outputs a continuation instruction signal Sc to the switching control circuit  154  during a period when the activation switch  70  is turned ON and the main switch  62  is ON, and during a period from when the main switch  62  is turned OFF until a specified value is counted by the timer means  158 . 
   Also, the timer means  158  counts reference counts from a clock generator, not shown, from a point in time when the main switch  62  is turned OFF. When counting to a specified value has been completed, the timer means  158  outputs a stop instruction signal Ss to the switching control circuit  154 . 
   The switching control circuit  154  outputs an ON signal So to the switching circuit  160  during the period when the continuation instruction signal Sc is being supplied from the timer means  158 , and in this way supply of electrical power to the receiving circuit  44  continues normally. 
   At a point in time when the stop signal Ss is supplied from the timer means  158 , the switching control circuit  154  outputs the OFF signal Sf. The switching circuit  160  turns OFF the switch  162  in response to the supplied OFF signal Sf, and in this way supply of electrical power to the receiving circuit  44  is stopped completely. 
   If the activation switch  70  is turned ON while electrical power to the receiving circuit  44  is stopped, a continuation instruction signal Sc is output from the timer means  158  to the switching control circuit  154 , and in this way, supply of electrical power to the receiving circuit  44  continues normally. 
   In the electronic key system  10 C according to the third embodiment, if the vehicle has not been started for a specified period of time, thereafter, supply of electrical power to the receiving circuit  44  is stopped completely until the activation switch  70  is turned ON, which makes it possible to significantly reduce power consumption when in standby. 
   Moreover, since communication is not carried out to external components (communication with the electronic key  12 ) while the specified activation switch  70  is not turned ON, and since it is not easy to locate the activation switch  70 , the system is effective for theft prevention. 
   The electronic key system of the present invention is not limited to the embodiments described above, and various structures can be introduced without departing from the spirit and scope of the invention.