Abstract:
A vehicle-use electronic key system includes a control unit mounted on a real car, and an electronic key for sending a response signal on receiving a request signal sent from the control unit via a transmission antenna, the antenna being installed near the middle of the real car. Specifically, when a line segment (wheel base) connecting the center of a front wheel to the center of a rear wheel is assumed, the transmission antenna is installed in any location within a range from the upper part to the lower part of the real car within a range from a ¼ point to a ¾ point of the wheel base with the center of the front wheel as a reference.

Description:
TECHNICAL FIELD 
   This invention relates to an electronic key system for a vehicle wherein radio communication is performed between a transmitter/receiver (electronic key) carried by a user and a control apparatus mounted on an actual vehicle to verify an ID and, if a communication received originates from a legal user, then starting of an engine or some other action is performed. More particularly, this invention relates to an electronic key system for a vehicle suitable for use with, for example, a motorcycle. 
   BACKGROUND ART 
   An electronic key system for a vehicle is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2001-349110 and Japanese Laid-Open Patent Publication No. 2001-349117. In the electronic key system for a vehicle disclosed in Japanese Laid-Open Patent Publication No. 2001-349110 and Japanese Laid-Open Patent Publication No. 2001-349117, starting means (switches) are provided on a door handle and a trunk lid of an actual vehicle. If a user operates (starts) any of the starting means, then communication of a control apparatus with an electronic key begins. Then, the control apparatus verifies an ID transmitted thereto from the electronic key with an ID registered therein. Thus, if it is verified that the IDs are coincident with each other, then the doors are unlocked and so forth. 
   Further, in Japanese Laid-Open Patent Publication No. 2001-349110 and Japanese Laid-Open Patent Publication No. 2001-349117 described above, a starting means (switch) is provided also on an ignition switch. If the user operates the ignition switch after the user gets on the four-wheeled car, then the communication between the electronic key and the starting means is performed again to perform ID verifying for permitting starting of the engine. Then, if it is verified that the IDs are coincident with each other, the engine is started. 
   In particular, in the conventional vehicle electronic key system for a four-wheeled car, the electronic key functions both to unlock a door and to permit starting of an engine. 
   Further, as a different prior art apparatus, an electronic key system is proposed (refer to, for example, Japanese Laid-Open Patent Publication No. 10-317754) wherein transmitting antennas are provided individually for doors of a four wheeled car, and only that one of the doors which is approached by a portable device can be unlocked independently of the other doors of the vehicle. 
   In this manner, in the electronic key system described above, the range of transmitting from the control apparatus mounted on an actual vehicle in the communication between the control apparatus and the electronic key is small in comparison with that from the electronic key. Therefore, in the prior art apparatus described above, a plurality of transmitting antennas for outputting a signal from the control apparatus are provided depending upon different applications. 
   Incidentally, in order to apply such an electronic key system to a motorcycle, at least when a user gets on and activates the vehicle and when the user operates the vehicle, it is necessary for the user to communicate with certainty with the electronic key carried by the user. 
   Particularly in a motorcycle such as a scooter wherein a helmet can be accommodated or stored in a space provided under a seat, it is necessary that the control apparatus communicates with the electronic key with certainty. This applies not only when the user gets on and operates the vehicle and when the user is traveling with the vehicle, but also upon opening or closing of the seat and when the electronic key is accommodated in the helmet storage space. 
   Particularly where the vehicle is a motorcycle of a large size, in order to achieve communication of the control apparatus with the electronic key in all of the situations described above, it is necessary to install a plurality of transmitting antennas at different locations such as a front portion and a rear portion of the actual vehicle. This may increase of the cost and the weight of the electronic key system and the installation space required for the electronic key system. 
   In a motorcycle such as a scooter wherein a helmet can be accommodated in a space provided under a seat, such a method as described below is available. In particular, a locking mechanism for locking an opening/closing mechanism of a seat is provided, for example, to prevent theft. Thus, if a legal user is recognized through communication of a control apparatus with an electronic key, then the seat is unlocked. 
   In such a case as just described, it is possible that an electronic key placed in a bag or the like is accommodated in a helmet storage space. In such a manner of use as just described, if communication between the control apparatus and the electronic key is interrupted, then there is the possibility that the seat cannot be unlocked, that is, shut-in of the baggage may occur. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the issues described above, and it is an object of the present invention to provide an electronic key system for a vehicle by which communication of a control apparatus with an electronic key in all of the situations described above can be achieved without an increase in the cost and the weight, or an increase in the required installation space, and so forth, of the electronic key system. 
   Another object of the present invention to provide an electronic key system for a vehicle wherein, even if an electronic key is placed in a helmet storage space, communication of the control apparatus with the electronic key can be performed with certainty, and a so-called shut-in state of a baggage and so forth can be prevented. 
   According to the present invention, an electronic key system for a vehicle which includes a control apparatus mounted on a vehicle and an electronic key for transmitting a response signal in response to receiving of a request signal transmitted from the control apparatus through a transmitting antenna. The electronic key system is configured so that the transmitting antenna is installed in the proximity of the center of the vehicle. 
   Consequently, a request signal transmitted from the control apparatus is outputted from the location in the proximity of the vehicle. Therefore, almost the entire region of the vehicle is included in the transmitting range. As a result, communication of the control apparatus with the electronic key can be performed with certainty when the user gets on and operates the vehicle, when the user is traveling with the vehicle, upon an opening or closing operation of the seat and when the electronic key is stored in a helmet accommodating space. In this instance, since a single transmitting antenna may be installed, communication of the control apparatus with the electronic key in all of the situations described above can be achieved without increasing the cost and the weight of the device, or an increase of the required installation space and so forth. 
   Preferably, the transmitting antenna is installed at a position within a range from an upper portion to a lower portion of the vehicle, and within a range from a point at one fourth to another point at three fourths of a wheel base with reference to the center of a front wheel of the actual vehicle. 
   Particularly where the vehicle includes a seat on which a user is to be seated, preferably the transmitting antenna is installed in the proximity of a front portion of the seat. 
   According to the present invention, an electronic key system for a vehicle which includes a control apparatus mounted on a vehicle and an electronic key for transmitting a response signal in response to receiving of a request signal transmitted from the control apparatus through a transmitting antenna. The vehicle includes a seat provided for opening and closing movement and a locking apparatus for locking the seat which prevents the seat from being opened until unlocking instruction is supplied thereto. The control apparatus includes means for verifying the response signal and outputting an unlocking instruction to the locking apparatus when it is discriminated that the response signal is a request from a legal user. The transmitting antenna is installed on the seat or in the proximity of the seat. 
   Consequently, a request signal transmitted from the control apparatus is outputted from the seat or a position in the proximity of the seat. Therefore, the seat and a region around the seat are included in the transmitting range of the transmitter. As a result, even if the electronic key is shut in a helmet storage space, communication of the control apparatus with the electronic key can be performed with certainty and a so-called shut-in state of a baggage or the like can be avoided. 
   The transmitting antenna may be provided on a left side face of the seat. Normally, the user operates the seat to open or close standing on the left side of the vehicle. Therefore, by mounting the transmitting antenna on the left side face of the seat, communication of the control apparatus with the electronic key can be performed with certainty. 
   Where at least a seat handle which is used to open or close the seat by manual operation, is provided around a rear portion of the seat, the transmitting antenna may be provided on the seat handle. 
   Normally, the seat handle is mounted on a vehicle body after assembly of the vehicle. Therefore, the shape of the vehicle body or the path of wiring lines need not be changed significantly in order to provide the transmitting antenna. In other words, the transmitting antenna can be mounted with a slight design change, and also the cost can be reduced advantageously. 
   The above and other objects features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view showing an electronic key system according to a first embodiment and a second embodiment. 
       FIG. 2  is a block diagram showing a configuration of an electronic key. 
       FIG. 3  is a block diagram showing a configuration of a control apparatus. 
       FIG. 4  is a schematic view showing an example of operation switches (switches which may be listed as a candidate of a starting switch) around a handle bar on an actual vehicle of the motorcycle type. 
       FIG. 5  is a schematic view showing an example of operation switches (switches which may be listed as a candidate of a starting switch) around a handle bar on another actual vehicle of the scooter type. 
       FIG. 6  is a schematic view showing an example wherein a starting switch is installed in the proximity of a seat on an actual vehicle of the scooter type which is used by the first embodiment. 
       FIG. 7A  is a side elevational view showing an example of a location of a transmitting antenna on an actual vehicle (See  FIG. 6 ). 
       FIG. 7B  is a plan view of the same. 
       FIG. 8  is a schematic view showing an example wherein a starting switch and a transmitting antenna are provided on a seat or a seat handle on an actual vehicle of the scooter type which is used by the second embodiment. 
       FIG. 9  is an enlarged view showing a state wherein a seat is opened. 
       FIG. 10  is a side elevational view showing an example of a position at which a transmitting antenna is installed on an actual vehicle. 
       FIG. 11  is a top plan view showing the example of the position at which the transmitting antenna is installed on the actual vehicle. 
       FIGS. 12A to 12E  are timing charts illustrating processing operation of the electronic key system according to the present embodiment. 
       FIG. 13  is a schematic view showing an example wherein a transmitting unit of an electronic key system according to a third embodiment is mounted on an actual vehicle. 
       FIG. 14  is a schematic view showing an example wherein a transmitting unit of an electronic key system according to a fourth embodiment is mounted on an actual vehicle. 
       FIG. 15  is a block diagram showing a configuration of a control apparatus and the transmitting unit in the electronic key system according to the third embodiment and the fourth embodiment. 
       FIG. 16  is a schematic view showing an example wherein a transmitting/receiving unit of an electronic key system according to a fifth embodiment is mounted on an actual vehicle. 
       FIG. 17  is a schematic view showing an example wherein a transmitting/receiving unit of an electronic key system according to a sixth embodiment is mounted on an actual vehicle. 
       FIG. 18  is a block diagram showing a configuration of a control apparatus and the transmitting/receiving unit of the electronic key system according to the fifth embodiment and the sixth embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following, an embodiment wherein an electronic key system for a vehicle according to the present invention is applied, for example, to a system of a motorcycle is described with reference to  FIGS. 1 to 18 . 
   Referring to  FIG. 1 , Each of electronic key systems  10 A,  10 B according to a first and a second embodiments includes an electronic key  12  to be carried by a user and a control apparatus  14  mounted on a vehicle  100 A (refer to  FIG. 6 ) and a vehicle  100 B (refer to  FIG. 8 ). The electronic key  12  has a shape of a key as an outer shape thereof and incorporates an IC chip therein. Alternatively, electronic key  12  may have the shape of a card as an outer shape thereof and incorporates an IC chip therein. However, electronic key  12  is not limited to these shapes and other keys are available. Where the electronic key system according to the present invention is principally applied as a key-less system, a key having a shape of a card is used. In the present specification described below, it is assumed that the electronic key  12  has a shape of a card. 
   Referring to  FIG. 2 , the electronic key  12  has a shape of a card as just described and includes a battery  20 , a power supply circuit  22 , a CPU  24 , a receiving circuit  26  and a transmitting circuit  28  therein. 
   The power supply circuit  22  supplies power supplied from the battery  20  to the receiving circuit  26 , the transmitting circuit  28  and the CPU  24 . The receiving circuit  26  includes a receiving antenna not shown. Further, the receiving circuit  26  receives a request signal Sr and so forth transmitted thereto from the control apparatus  14  through the receiving antenna and extracts the signal from a carrier wave to decode the signal. The decoded signal is supplied to the CPU  24 . The frequency of the carrier wave of the request signal Sr ranges from 100 kHz to 300 kHz. 
   The CPU  24  executes at least the following two computer programs: A request signal verifying means  30  and a response signal generating means  32 . The request signal verifying means  30  verifies whether or not a signal supplied from the receiving circuit  26  is the request signal Sr. Thus, if the signal supplied is the request signal Sr, the request signal verifying means  30  passes the control to the response signal generating means  32 . The response signal generating means  32  reads out ID data recorded in a ROM not shown based on a request from the request signal verifying means  30 . Then, the response signal generating means  32  adds an attribute that indicates a response to the ID data and outputs the ID data as transmitting data Dt to the transmitting circuit  28 . The transmitting circuit  28  includes a transmitting antenna not shown. The transmitting circuit  28  modulates a carrier wave in accordance with the transmitting data Dt supplied from the CPU  24  and transmits the modulated wave as a response signal Sa through the transmitting antenna. The frequency of the carrier wave of the response signal Sa ranges from 200 MHz to 500 MHz. 
   Meanwhile, the control apparatus  14  mounted on the actual vehicles  100 A,  100 B is formed from, for example, a system LSI. Further, for example, as shown in  FIG. 3 , the control apparatus  14  includes a power supply circuit  40 , a CPU  42 , a receiving circuit  44 , a transmitting circuit  46 , an inputting circuit  48 , a first driving circuit  52  (for driving an actuator), a second driving circuit  54  (for driving a main relay) and a third driving circuit  56  (for driving an LED). At least a battery  60 , a main switch  62 , an actuator (driving source for a locking apparatus)  64 , a main relay  66 , a warning lamp  68  (LED), a starting switch  70  and a transmitting antenna  72  are installed around the control apparatus  14 . 
   The main switch  62  has two fixed contacts  62   a  and  62   b  and a movable contact  62   c . The fixed contact  62   a  is connected to the battery  60 , and the other fixed contact  62   b  is connected to the inputting circuit  48  and the main relay  66 . 
   Not only the fixed contact  62   b  of the main switch  62  but also the starting switch  70  are connected to the inputting circuit  48 . An ON/OFF state of the starting switch  70  and an ON/OFF state of the main switch  62  are supplied to the CPU  42  through the inputting circuit  48 . 
   The starting switch  70  can be set to any one of, for example, an operation switch for starting an engine of the actual vehicles  100 A,  100 B, an operation switch for security during driving and an operation switch used for stopping the engine of the actual vehicles  100 A,  100 B. In particular, where each of the actual vehicles  100 A,  100 B is of the motorcycle type as shown in  FIG. 4 , any one of a lighting dimmer switch  104 , a clutch switch  106 , a winker switch  108 , a horn switch  110 , a front brake switch  112 , a hazard switch  114  and a starter switch  116  which are installed around a handle bar  102  can be set as the starting switch  70 . 
   On the other hand, where each of the actual vehicles  100 A,  100 B is of the scooter type as shown in  FIG. 5 , any one of a lighting dimmer switch  122 , a rear brake switch  124 , a winker switch  126 , a horn switch  128 , a front brake switch  130 , a hazard switch  132  and a starter switch  134  which are installed around a handle bar  120  can be set as the starting switch  70 . 
   For the setting of the starting switch  70 , a method is available wherein, for example, when a user purchases the actual vehicles  100 A or  100 B, the user decides the setting of the starting switch  70  upon contract with a dealer, and thereafter, wiring is performed in a factory based on the decision. In particular, for example, wiring for interconnection between a switch decided as the starting switch  70  and the inputting circuit  48  of the control apparatus  14  or a like operation is performed in a factory. 
   As described above, the starting switch  70  may be set to any one of various switches installed around the handle bar  102  or  120 . For example, in a scooter, as shown in  FIG. 6 , the starting switch  70  may be provided on the seat  140  or in the proximity of the seat  140 . 
   A space  142  (helmet storage space) which can accommodate a helmet not shown is provided under the seat  140  as shown in  FIG. 9 . Normally, when the user does not ride the vehicle, a helmet is stored in the space. Further, depending upon the user, baggage may be accommodated in the space  142 . 
   Further, at least a handle  144  (hereinafter referred to as seat handle  144  for the distinction from the handle bar  120  which is operated by a driver) used to open or close the seat  140  by manual operation is provided around a rear portion of the seat  140 . 
   Accordingly, the starting switch  70  can be located on the seat handle  144 , the inside of the seat  140  or the like. When the starting switch  70  is provided on the seat handle  144 , preferably the starting switch  70  is provided at a portion of the seat handle  144  which is to be gripped with a hand when the user opens the seat  140 . On the other hand, when the starting switch  70  is provided in the inside of the seat  140 , preferably the starting switch  70  is buried at a location corresponding to a portion of the seat  140  with which the user touches when the user opens the seat  140 . 
   Consequently, if the user opens the seat  140  in order to take out the helmet, then the starting switch  70  is operated into an ON state at the same time. As a result, the operability regarding starting of the electronic key system  10  can be improved. 
   Meanwhile, the power supply circuit  40  of the control apparatus  14  supplies power from the battery  60  to the CPU  42 , receiving circuit  44 , transmitting circuit  46  and other components. 
   The receiving circuit  44  has a receiving antenna not shown. The receiving circuit  44  receives a response signal Sa and so forth transmitted thereto from the electronic key  12  through the receiving antenna, extracts the response signal Sa from the carrier wave and demodulates the response signal Sa. The demodulated signal is supplied to the CPU  42 . 
   The CPU  42  executes at least the following four programs: A request signal generating means  80 , a request signal verifying means  82 , an observing means  84  and a peripheral instruction means  86 . 
   The request signal generating means  80  reads out request data Dr (data on which a request signal Sr is to be based) from a ROM not shown in response to an ON operation of the starting switch  70  or the main switch  62  and outputs the request data Dr to the transmitting circuit  46 . Further, after the engine is started, the request signal generating means  80  reads out the request data Dr from the ROM after every fixed interval of time and outputs the request data Dr to the transmitting circuit  46 . The fixed interval of time is set to one of time periods of 10 to 100 sec taking the consumption of the battery  20  in the electronic key  12  into consideration. 
   The transmitting circuit  46  modulates the carrier wave based on the request data Dr supplied thereto from the CPU  42  and outputs a resulting signal as a request signal Sr through the transmitting antenna  72 . 
   In the actual vehicle  100 A of the first embodiment  10 A, as shown in  FIG. 6 , the transmitting antenna  72  is installed in the proximity of the center of the vehicle  100 A. As shown in  FIGS. 7A and 7B , the transmitting range of the request signal Sr is a spherical range of a radius of 1 to 1.5 m around the transmitting antenna  72  mounted on the vehicle  100 A (a range indicated by a circle A in  FIGS. 7A and 7B ). The transmitting range of the request signal Sr is smaller than the transmitting range of the response signal Sa (range of a radius of several meters around the electronic key  12 ). 
   Accordingly, where it is assumed that the vehicle  100 A is a scooter wherein a helmet storage space not shown is installed, for example, under the seat  140  as shown in  FIGS. 7A and 7B , communication of the control apparatus with the electronic key  12  carried by the user may be performed with certainty when the user gets on and operates the actual vehicle  100 A, when the user performs an operation to open the seat  140 , when the user is traveling with the vehicle  100 A, when the electronic key  12  is accommodated in the helmet storage space, and in any other case. 
   Here, a line segment (wheel base)  154  interconnecting the center  150   a  of a front wheel  150  and the center  152   a  of a rear wheel  152  is assumed. In this instance, a location in the proximity of the vehicle  100 A is, for example, a position within a range from an upper portion to a lower portion of the vehicle  100 A, and within a range from a point P 1  at one fourth the wheel base  154  to another point P 2  at three fourths the wheel base  154 , with reference to the center  150   a  of the front wheel  150 . In the vehicle  100 A, the transmitting antenna  72  is installed in the proximity of a front portion of the seat  140 . 
   Meanwhile, in the vehicle  100 B of the second embodiment  10 B, as shown in  FIG. 8 , the transmitting antenna  72  is installed on the seat  140  of the actual vehicle  100 B or in the proximity of the seat  140 . As shown in  FIGS. 10 and 11 , the transmitting range of the request signal Sr is a spherical range of a radius of 1 to 1.5 m around the transmitting antenna  72  mounted on the actual vehicle  100 B (a range indicated by a circle A in  FIGS. 10 and 11 ). The transmitting range of the request signal Sr is smaller than the transmitting range of the response signal Sa (range of a radius of several meters around the electronic key  12 ). 
   Accordingly, where it is assumed that the vehicle  100 B is a scooter wherein the helmet storage space  142  (refer to  FIG. 9 ) is installed, for example, under the seat  140  as shown in  FIGS. 10 and 11 , communication of the control apparatus  14  with the electronic key  12  can be carried by the user may be performed with certainty when the user performs an operation to open the seat  140 , when the electronic key  12  is accommodated in the helmet storage space  142 , and in some other case. 
   In  FIGS. 10 ,  11  and  8 , an example is shown wherein the transmitting antenna  72  is installed at a portion of a left side face of a rear portion of the seat  140  with which the user does not touch with its hand. 
   Alternatively, where the seat handle  144  is provided around a rear portion of the seat  140  as seen in  FIG. 9 , the transmitting antenna  72  is installed on the seat handle  144 . Also in this instance, preferably the transmitting antenna  72  is installed at a portion with which the user does not normally touch with its hand. 
   The request signal verifying means  82  verifies whether or not a signal supplied thereto from the receiving circuit  44  is a response signal Sa. Further, when the signal mentioned is a response signal Sa, the request signal verifying means  82  verifies whether or not ID data included in the response signal Sa coincides with ID data registered in a memory not shown. 
   The observing means  84  observes based on an output of a request signal Sr whether or not a response signal Sa is terminated (whether or not coincidence of the ID is detected by the request signal verifying means  82 ). The observing means  84  enters a waiting state for an input of a response signal Sa at a point of time when the request signal generating means  80  outputs request data Dr. If a response signal Sa is not terminated within a predetermined period of time (when coincidence of the ID is not detected by the request signal verifying means  82 ), then the observing means  84  increments the count value by +1 to update it. Then, at a point of time when the count value becomes higher than a predetermined value, the observing means  84  outputs a warning signal Se to the third driving circuit  56 . 
   Particularly if a response signal Sa is not terminated within the predetermined period of time after the point of time when the request data Dr is outputted in response to an ON operation of the starting switch  70  or the main switch  62 , then at this stage, the observing means  84  outputs a warning signal Se to the third driving circuit  56 . 
   The observing means  84  activates the peripheral instruction means  86  if a response signal Sa is terminated within the predetermined period of time after the point of time at which the request data Dr is outputted in response to an ON operation of the starting switch  70 . The peripheral instruction means  86  outputs an unlocking signal to the first driving circuit  52  based on a request (for unlocking) from the observing means  84 . Further, the peripheral instruction means  86  outputs an ON signal to the second driving circuit  54 . 
   The first driving circuit  52  drives the actuator  64  in response to an input of the unlocking signal from the CPU  42  to cancel the locked state of the handle bar  102  and the seat  104 . 
   The second driving circuit  54  is placed into an ON state in response to an input of the ON signal from the CPU  42 . Thereafter, when the main relay  66  is placed into an ON state in response to an ON operation of the main switch  62 , the second driving circuit  54  starts the engine to establish a state wherein the vehicle can run. 
   The third driving circuit  56  drives the warning lamp  68  in response to an input of the warning signal Se from the CPU  42  so that the warning lamp  68  emits light. For example, an LED can be used as the warning lamp  68 . 
   It is to be noted that, if the main switch  62  is turned OFF, then the main relay  66  is turned OFF and also the engine stops simultaneously. Then, if a locking operation is performed, for example, if an operation to place the seat  104  or the seat  104  into a locked state is performed, then the verifying operation of the response signal Sa by the control apparatus  14  is stopped. Further, the second driving circuit  54  is placed into an OFF state. 
   Now, processing operation of the electronic key system  10 A according to the first embodiment is described with reference to timing charts of  FIGS. 12A to 12E . It is to be noted that a request signal Sr is a signal having a pulse string based on request data Dr, and a response signal Sa is a signal having a pulse string based on data including ID data. It is to be noted, however, that, in order to simplify the description, each of the request signal Sr and the response signal Sa is represented as a signal of one pulse in  FIGS. 12A to 12E . Since processing operation of the electronic key system  10 B according to the second embodiment is almost the same as the processing operation of the first embodiment explanation of the processing operation of the second embodiment has been omitted. 
   First, in a normal state, if the starting switch  70  is operated to an ON state at time t 1  of  FIG. 12A  while the user holds the electronic key  12 , then a request signal Sr is transmitted from the control apparatus  14  as seen in  FIG. 12C  (refer to time t 2 ) and communication of the control apparatus  14  with the electronic key  12  is started. 
   When the user holds the electronic key  12 , the request signal Sr is received through the receiving circuit  26  (refer to  FIG. 2 ) of the electronic key  12 . The electronic key  12  transmits a response signal Sa as seen in  FIG. 12D  in response to the receiving of the request signal Sr (refer to time t 3 ). The response signal Sa is supplied through the receiving circuit  44  (refer to  FIG. 3 ) of the control apparatus  14  to the CPU  42 , by which ID data included in the response signal Sa is verified. If it is discriminated that the ID data exhibits coincidence, then the locked state of the handle bar  120  and the seat  140  is cancelled (unlocked) as seen in  FIG. 12E  through the control apparatus  14  and the first driving circuit  52  (refer to time t 4 ). As a result of the unlocking procedure, steering by the handle bar  120  is enabled, and the seat  140  is slightly raised. Consequently, the user can easily recognize that the locked state of the handle bar  120  and the seat  140  has been released. Further, thereupon, the second driving circuit  54  is placed into an ON state. 
   Thereafter, if the user operates the main switch  62  into an ON state at time t 5  of  FIG. 12B  while it holds the electronic key  12 , then a request signal Sr is transmitted from the control apparatus  14  as seen in  FIG. 12C  (refer to time t 6 ), and communication of the control apparatus  14  with the electronic key  12  is performed. 
   When the user holds the electronic key  12 , the electronic key  12  transmits a response signal Sa as seen in  FIG. 12D  (refer to time t 7 ) in response to the receiving of the request signal Sr in a similar manner as described hereinabove. The response signal Sa is supplied through the receiving circuit  44  of the control apparatus  14  to the CPU  42 , by which ID data included in the response signal Sa is verified. If it is discriminated that the ID data exhibits coincidence, then the processing advances to a next step, that is, to a step at which the request signal Sr is outputted after every interval τ of time. 
   After this state, for example, the user is traveling with the actual vehicle  100 A, and during the travel, the request signal Sr is outputted from the control apparatus  14  after every interval τ of time. In other words, communication of the control apparatus  14  with the electronic key  12  is performed after every interval τ of time, and the electronic key  12  outputs a response signal Sa after every substantially fixed interval τ of time. 
   The processing operation described above is a process after the user, holding the electronic key, gets on and activates the vehicle  100 A until it operates the vehicle  100 A. Now, a processing operation used when it is detected that the electronic key  12  is absent upon starting of the actual vehicle  100 A is described. 
   First, if the user operates the starting switch  70  into an ON state while it does not hold the electronic key  12 , then a request signal Sr is transmitted from the control apparatus  14 . However, the control apparatus  14  does not perceive a response signal Sa to the request signal Sr outputted therefrom. As a result, the observing means  84  outputs a warning signal Se to the third driving circuit  56 . Consequently, the warning lamp  68  is lit. Naturally, in this instance, such a process as unlocking of the handle bar  120  and the seat  140  or the like is not performed. 
   From the lighting of the warning lamp  68 , the user can recognize that he does not hold the electronic key  12 . Consequently, starting of the engine while the electronic key  12  is not held is prevented. 
   Now, a processing operation for the case when it is determined that the electronic key  12  is not present upon starting of the engine of the actual vehicle  100 A is described. 
   First, if the user turns on the starting switch  70  while holding the electronic key  12 , then a request signal Sr is transmitted from the control apparatus  14 , and communication of the control apparatus  14  with the electronic key  12  is started. Through the communication, ID data included in a response signal is verified, and if it is discriminated that the ID data does not exhibit coincidence, then the locked state of the handle bar  120  and the seat  140  is canceled. 
   Then, if the user operates the main switch  62  into an ON state without recognizing that, for example, the electronic key  12  has been dropped, then although a request signal Sr is transmitted from the control apparatus  14 , the control apparatus  14  does not receive a response signal Sa to the thus outputted request signal Sr any more. As a result, the observing means  84  outputs a warning signal Se to the third driving circuit  56 , and consequently, the warning lamp  68  is lit. 
   From the lighting of the warning lamp  68 , the user will recognize that the electronic key  12  has dropped. Consequently, otherwise possible loss of the electronic key  12  can be prevented. 
   Now, a processing operation for the case when it is determined that the electronic key  12  is not present while the vehicle  100 A is running is described briefly. 
   First, processes after an ON operation of the starting switch  70  till an ON operation of the main switch  62  are same as those at times t 1  to t 7  in  FIGS. 12A to 12E . 
   When the engine starts in response to the ON-operation of the main switch  62 , the processing advances to a step at which a request signal Sr is outputted after every interval τ of time as described hereinabove. After this stage, the user is, for example, traveling with the actual vehicle  100 A, and during the traveling, a request signal Sr is outputted from the control apparatus  14  after every interval τ of time. 
   If, for example, the electronic key  12  drops during travel of the vehicle  100 A, then a response signal Sa is no longer received by the control apparatus  14 . When a response signal Sa is not received within a predetermined interval of time after the point of time at which the request data Dr is outputted, the observing means  84  increments the count value by +1 to update it. At a point of time when the count value exceeds a predetermined value while a request signal Sr is successively outputted, the observing means  84  outputs a warning signal Se to the third driving circuit  56 . Consequently, the warning lamp  68  is lit. 
   From the lighting of the warning lamp  68 , the user will recognize that the electronic key  12  has dropped, and otherwise possible loss of the electronic key  12  can be prevented. 
   In this manner, in the electronic key system  10  according to the first embodiment, the transmitting antenna  72  of the control apparatus  14  (which transmits a request signal Sr) is installed in the proximity of the center of the actual vehicle  100 A. Therefore, the request signal Sr transmitted from the control apparatus  14  is outputted from the location in the proximity of the center of the actual vehicle  100 A. 
   Consequently, a substantially overall region of the actual vehicle  100 A is included in the transmitting range. As a result, communication of the control apparatus  14  with the electronic key  12  can be performed with certainty when the user gets on and the vehicle  100 A, when the user is operating with the vehicle  100 A, upon opening or closing operation of the seat  140  and when the electronic key  12  is accommodated in the helmet storage space. In this instance, since the single transmitting antenna  72  may be installed, communication of the control apparatus  14  with the electronic key  12  in all of the situations described above can be achieved without increasing the cost and the weight, or increasing the required installation space and so forth. 
   Further, a bag in which the electronic key  12  is placed is sometimes accommodated in the helmet storage space provided under the seat  140 . Also in this instance, however, communication between the control apparatus  14  and the electronic key  12  is performed with certainty. Consequently, a so-called shut-in state (a state wherein the seat  140  cannot be unlocked while the electronic key  12  remains accommodated in the helmet accommodating space) can be prevented. 
   In the electronic key system  10 B according to the second embodiment, the transmitting antenna  72  of the control apparatus  14  is installed on the seat  140  or the seat handle  144  of the vehicle  100 B. Therefore, the request signal Sr transmitted from the control apparatus  14  is outputted from the seat  140  or the seat handle  144 . Consequently, the seat  140  and a region around the seat  140  are included in the transmitting range. As a result, communication of the control apparatus  14  with the electronic key  12  can be performed with certainty even if the electronic key  12  is placed in the helmet storage space  142 , and a so-called shut-in state of a baggage or the like can be prevented. 
   Normally, the user opens or closes the seat  140  while standing on the left side of the actual vehicle  100 B. Therefore, by mounting the transmitting antenna  72  on the left side face of the seat  140 , communication of the control apparatus  14  with the electronic key  12  upon an operation to open or close the seat  140  can be performed with certainty. 
   Further, the seat handle  144  can normally be assembled later to the vehicle body of the actual vehicle  100 B. Therefore, where the transmitting antenna  72  or the starting switch  70  is provided on the seat handle  144 , the shape of the vehicle body or the path of wiring lines need not be changed significantly in order to provide the transmitting antenna  72  or the starting switch  70 . In other words, the transmitting antenna  72  or the starting switch  70  can be installed with a slight design change, and also the cost can be reduced advantageously. 
   Subsequently, the electronic key systems  10 C,  10 D according to a third embodiment and a fourth embodiment are described with reference to  FIGS. 13 to 15 . 
   First, the electronic key system  10 C according to the third embodiment has a configuration substantially similar to that of the electronic key system  10 A according to the first embodiment described above. However, the electronic key system  10 C is different from the electronic key system  10 A in that a transmitting unit  160  is installed in the proximity of the center of an actual vehicle  100 C as shown in  FIG. 13 . 
   The electronic key system  10 D according to the fourth embodiment has a configuration substantially similar to that of the electronic key system  10 A according to the first embodiment described above. However, the electronic key system  10 D is different from the electronic key system  10 A in that a transmitting unit  160  is installed on the seat  140  of the actual vehicle  100 D or in the proximity of the seat  140  as shown in  FIG. 14 . 
   In the transmitting unit  160 , the transmitting circuit  46  is separated from the control apparatus  14  formed from a system LSI so as to form a single electronic part  162  as shown in  FIG. 15 . The electronic part  162  is electrically connected to the transmitting antenna  72  so as to generally form a unit. 
   Subsequently, the electronic key systems  10 E,  10 F according to a fifth embodiment and a sixth embodiment are described with reference to  FIGS. 16 to 18 . 
   The electronic key system  10 E according to the fifth embodiment has a configuration substantially similar to that of the electronic key system  10 A according to the first embodiment described above. However, the electronic key system  10 E is different from the electronic key system  10 A in that a transmitting/receiving unit  170  is installed in the proximity of the center of an actual vehicle  100 E as shown in  FIG. 16 . 
   The electronic key system  10 F according to the sixth embodiment has a configuration substantially similar to that of the electronic key system  10 A according to the first embodiment described above. However, the electronic key system  10 F is different from the electronic key system  10 A in that a transmitting/receiving unit  170  is installed on the seat  140  of the actual vehicle  100 F or in the proximity of the seat  140  as shown in  FIG. 17 . 
   In the transmitting/receiving unit  170 , the receiving circuit  44  and the transmitting circuit  46  are separated from the control apparatus  14  formed from a system LSI to form a single electronic part  172 . Thus, the electronic part  172  includes the receiving circuit  44  and the transmitting circuit  46  integrated therein as seen in  FIG. 18 . The transmitting circuit  46  of the electronic part  172  and the transmitting antenna  72  are electrically connected to each other so as to generally form a unit. 
   The selection of which one of the electronic key systems  10 A to  10 F according to the first to the sixth embodiments described above should be determined by taking into consideration the size of the actual vehicles  100 A to  100 F, the paths of the wiring lines, the installation space for the transmitting antenna  72  and so. 
   It is to be noted that the electronic key system for a vehicle according to the present invention is not limited to the embodiment described above but can adopt various configurations without departing from the subject matter of the present invention.