Patent Publication Number: US-8525641-B2

Title: Vehicular electronic key system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2010-234872, filed Oct. 19, 2010. The contents of this application are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicular electronic key system. 
     2. Discussion of the Background 
     There is a known method that allows the owner of a vehicle to set, in an electronic key (so-called “smart key”), a mode in which specific functions of the vehicle are limited, these functions being permitted with use of the electronic key (so-called “valet mode”) and provide a person other than the vehicle&#39;s owner with the electronic key when this person drives the vehicle. 
     There is a system improves such system (e.g., see Japanese Unexamined Patent Application Publication No. 2006-225976). According to this system, for example, an electronic key includes a portable unit (key body), a mechanical key and a tongue, and transmits a state signal indicative of the attachment/detachment state of the tongue to/from the key body to a vehicle, and an on-vehicle control unit sets a valet mode when the state signal received from the electronic key indicates detachment of the tongue. 
     Since the owner of the vehicle entrusts another person with the key body having only the tongue removed from the electronic key and the mechanical key in the system according to the related art, this person can unlock doors and start the engine with the mechanical key even when the battery of the key body is dead. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a vehicular electronic key system includes a vehicle having a key cylinder and a portable device. The portable devise includes a key body and a mechanical key. The key body is communicatable with the vehicle. The mechanical key is attachable to and detachable from the key body and mechanically rotates the key cylinder whereby the communication between the vehicle and the portable device allows the vehicle to execute predetermined functions. The key body includes a key detector configured to detect an attachment state and a detachment state of the mechanical key to and from the key body so that the key body transitions to a valet mode to limit some of the predetermined functions executable by the vehicle in accordance with the communication between the vehicle and the portable device while the key detector detects the detachment state of the mechanical key from the key body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
         FIG. 1  is a diagram showing a key body and a mechanical key of an vehicular electronic key system according to an exemplary embodiment of the invention. 
         FIG. 2  is a structural diagram of the vehicular electronic key system according to the embodiment of the invention. 
         FIGS. 3A to 3C  are diagrams showing an example of a displaceable member of the vehicular electronic key system according to the embodiment of the invention. 
         FIG. 4  is a diagram showing an example of a sensor of the vehicular electronic key system according to the embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings. 
     As shown in  FIGS. 1 and 2 , for example, the vehicular electronic key system  10  according to the embodiment includes a vehicle  11  having a key cylinder  11   a , and a portable unit  12  that can communicate with the vehicle  11 . The vehicular electronic key system  10  is configured in such a way that in accordance with the communication with the portable unit  12 , the vehicle  11  executes predetermined functions. 
     The vehicle  11  includes, for example, a radio communication unit  21 , a transponder communication unit  22 , a battery  23  which is a power supply for various on-vehicle devices, a vehicle controller  24 , an internal combustion engine (hereinafter simply called “engine”)  25 , a door lock unit  26 , and a trunk lock unit  27 . 
     The radio communication unit  21  of the vehicle  11  receives an RF (Radio Frequency) signal transmitted from, for example, the portable unit  12 , and transmits an LF (Low Frequency) signal to the portable unit  12  from an LF antenna (not shown) under the control of the vehicle controller  24 . 
     Examples of the LF signals transmitted from the vehicle  11  include a request signal which is intermittently transmitted to the portable unit  12 , a signal representing a reception result when the radio communication unit  21  receives a command signal transmitted from the portable unit  12  (e.g., the reception result being the intensity or the like of a received command signal), and a signal representing whether operations of on-vehicle devices (e.g., driving of the door lock unit  26  and the trunk lock unit  27 ) instructed by the command signal transmitted from the portable unit  12  are to be executed. 
     The transponder communication unit  22  supplies power to a transponder  51  of a mechanical key  32  of the portable unit  12  through electromagnetic induction to communicate with the transponder  51 . When an identification code included in a unique signal received from the mechanical key  32  through the communication matches an identification code stored in advance, the transponder communication unit  22  outputs a signal permitting activation of the engine  25  to the vehicle controller  24 . 
     The vehicle controller  24  includes a CPU (Central Processing Unit) which controls the vehicle  11  and various on-vehicle devices mounted therein. 
     The vehicle controller  24  instructs the radio communication unit  21  to intermittently transmit a request signal carried by the LF signal to the portable unit  12 . When the radio communication unit  21  receives a response signal to the request signal from the portable unit  12 , the vehicle controller  24  compares the identification code included in the response signal with an identification code stored in advance. When the received identification code matches the stored identification code, the vehicle controller  24  permits execution of operations of various on-vehicle devices whose execution is instructed by a command signal or a limited-function command signal transmitted from the portable unit  12 . 
     In accordance with the command signal or limited-function command signal carried by the RF signal received by the radio communication unit  21  from the portable unit  12  through communication between the vehicle  11  and the portable unit  12 , the vehicle controller  24  controls execution of the operations of various on-vehicle devices whose execution is instructed by the command signal or the limited-function command signal. 
     Examples of the operations of on-vehicle devices which are instructed by the command signal carried by the RF signal transmitted from the portable unit  12  include the activation or deactivation of the engine  25 , and unlocking or locking of vehicle&#39;s doors (not shown) achieved by driving the door lock unit  26 . 
     Examples of the operations of on-vehicle devices which are instructed by the limited-function command signal carried by the RF signal transmitted from the portable unit  12  include the unlocking of a trunk (not shown) achieved by driving the trunk lock unit  27 . 
     When the signal carried by the RF signal received by the radio communication unit  21  from the portable unit  12  through communication between the vehicle  11  and the portable unit  12  indicates that a control mode is the valet mode, the vehicle controller  24  limits some of predetermined functions of the vehicle  11  (i.e., the operations of the on-vehicle devices that are instructed by the limited-function command signal) to control execution of the predetermined functions of the vehicle  11 . 
     When the signal carried by the RF signal received by the radio communication unit  21  from the portable unit  12  through communication between the vehicle  11  and the portable unit  12  indicates inhibition of transition to the valet mode, the vehicle controller  24  inhibits the transition to the valet mode, and permits execution of some of predetermined functions of the vehicle  11  (i.e., the operations of the on-vehicle devices that are instructed by the limited-function command signal). 
     In addition, the vehicle controller  24  controls activation of the engine  25  according to a signal output from the transponder communication unit  22  (i.e., signal which permits activation of the engine  25 ) through communication between the vehicle  11  and the transponder  51  of the mechanical key  32  of the portable unit  12 . 
     The door lock unit  26  includes a sensor (not shown) which detects direct contact of an operator carrying the key body  31  of the portable unit  12  with the handle (not shown) of a vehicle&#39;s door or the like. A signal showing the detection result output from the sensor is input to the vehicle controller  24 . 
     The trunk lock unit  27  likewise includes a sensor (not shown) which detects direct contact of an operator carrying the key body  31  of the portable unit  12  with the handle (not shown) of the trunk or the like. A signal showing the detection result output from this sensor is input to the vehicle controller  24 . 
     Upon reception of the signal representing direct contact of the operator carrying the key body  31  of the portable unit  12  from the door lock unit  26  or the trunk lock unit  27 , the vehicle controller  24  instructs the radio communication unit  21  to transmit this signal to the portable unit  12  together with the request signal which is intermittently transmitted to the portable unit  12 . 
     When the radio communication unit  21  receives a normal response signal to the request signal from the portable unit  12 , the vehicle controller  24  permits a predetermined function of the vehicle  11  associated with the direct contact of the operator, i.e., permits the vehicle&#39;s doors to be unlocked or locked by driving of the door lock unit  26 , or the trunk to be unlocked or locked by driving of the trunk lock unit  27 . When the radio communication unit  21  does not receive the normal response signal to the request signal from the portable unit  12 , on the other hand (i.e., when the portable unit  12  has not transmitted the response signal), the vehicle controller  24  limits a predetermined function of the vehicle  11  associated with the direct contact of the operator, i.e., the function of the vehicle  11  which is limited in the valet mode. Specifically, the vehicle controller  24  limits (e.g., inhibits) unlocking of the trunk which is achieved by driving of the trunk lock unit  27 . 
     The door lock unit  26  and the trunk lock unit  27  both include switches (not shown) for instructing control of unlocking and locking of the vehicle&#39;s doors and the trunk, respectively. Signals output from the sensors are input to the vehicle controller  24 . 
     Upon receiving a signal instructing control of unlocking and locking of the vehicle&#39;s doors or the trunk from the door lock unit  26  or the trunk lock unit  27 , the vehicle controller  24  instructs the radio communication unit  21  to transmit this signal to the portable unit  12  together with the request signal to be intermittently transmitted toward the portable unit  12 . 
     Upon receiving a signal representing the fact that the control mode has been changed from the normal mode to the valet mode from the portable unit  12  together with a normal response signal to the request signal, the vehicle controller  24  limits (e.g., inhibits) some of predetermined functions of the vehicle  11 , namely, unlocking of the trunk achieved by driving of the trunk lock unit  27 , and permits unlocking of the vehicle&#39;s doors achieved by the door lock unit  26 . 
     The portable unit  12  includes the key body  31  and the mechanical key  32  which is attachable to and detachable from the key body  31  and mechanically rotates the key cylinder  11   a  of the vehicle  11 . 
     The key body  31  includes, for example, a radio communication unit  41 , a transponder communication unit  42 , a battery  43  which is a power supply for the key body  31 , a portable-unit controller  44 , an operation switch  45 , a limited-function operation switch  46 , and a key detector  47 . 
     The radio communication unit  41  of the portable unit  12  receives, for example, an LF signal transmitted from the vehicle  11  via an LF antenna (not shown), and transmits an RF signal to the vehicle  11  via an RF antenna (not shown) under the control of the portable-unit controller  44  according to a predetermined operation or the like performed on the portable unit  12 . 
     The LF antenna of the portable unit  12  includes, three LF antennae which are disposed in parallel to three axes orthogonal to one another and have directivity. 
     Examples of the RF signal transmitted from the portable unit  12  include a response signal to a request signal transmitted from the vehicle  11 , a command signal or limited-function command signal indicating execution of operations of various on-vehicle devices of the vehicle  11 , a signal indicating that the control mode is either the normal mode or the valet mode, and a signal indicating that transition of the control mode from the normal mode to the valet mode is inhibited. 
     Predetermined operations performed on the portable unit  12  include, for example, a normal operation performed on the operation switch  45  or the limited-function operation switch  46 , and an operation in a predetermined operation pattern different from the normal operation performed on the operation switch  45  or the limited-function operation switch  46 . 
     The transponder communication unit  42  supplies power to the transponder  51  of the mechanical key  32  attached to the key body  31  by electromagnetic induction to communicate with the transponder  51 , and outputs a signal representing the communication result (e.g., result of reception of a unique signal from the mechanical key) to the key detector  47 . 
     The portable-unit controller  44  is configured to include a CPU which controls the key body  31 . 
     When the radio communication unit  41  receives a request signal carried by the LF signal transmitted from the vehicle  11 , the portable-unit controller  44  determines whether this request signal is a normal request signal. Upon determining that the request signal is a normal request signal, the portable-unit controller  44  instructs the radio communication unit  41  to transmit a response signal carried by the RF signal that has a unique identification code with respect to the request signal to the vehicle  11  if the control mode is the normal mode. 
     When the control mode is the valet mode, the portable-unit controller  44  determines whether the request signal includes a signal associated with some of predetermined functions of the vehicle  11  which are limited in the valet mode, e.g., a signal representing direct contact of the operator carrying the key body  31  of the portable unit  12  with the handle of the trunk. When the result of the determination is “YES”, the portable-unit controller  44  instructs the radio communication unit  41  to inhibit transmission of the response signal to the vehicle  11 . When the result of the determination is “NO”, on the other hand, the portable-unit controller  44  instructs the radio communication unit  41  to transmit the response signal to the vehicle  11 . 
     Then, in accordance with the operator&#39;s operation performed on the operation switch  45  or the limited-function operation switch  46 , a signal output from the key detector  47 , etc., the portable-unit controller  44  controls the radio communication unit  41  to transmit a command signal or a limited-function command signal instructing execution of the operations of various on-vehicle devices of the vehicle  11 . 
     The operation switch  45  is configured to include an unlock button  45   a  for instructing unlocking of the vehicle&#39;s doors achieved by driving of the door lock unit  26 , and a lock button  45   b  for instructing locking of the vehicle&#39;s doors achieved by driving of the door lock unit  26 . 
     The limited-function operation switch  46  is configured to include a trunk unlock button  46   a  for instructing unlocking of the trunk achieved by driving of the trunk lock unit  27 . 
     In accordance with the operator&#39;s operation of the operation switch  45  or the limited-function operation switch  46 , for example, the portable-unit controller  44  instructs the radio communication unit  41  to transmit a command signal or a limited-function command signal instructing execution of predetermined functions of the vehicle  11  to the vehicle  11  as the operations of various on-vehicle devices of the vehicle  11 . 
     Examples of the predetermined functions of the vehicle  11  as the operations of various on-vehicle devices of the vehicle  11  include activation or deactivation of the engine  25 , unlocking or locking of the vehicle&#39;s doors (not shown) achieved by the door lock unit  26 , and unlocking or locking of the trunk (not shown) achieved by the trunk lock unit  27 . 
     While detachment of the mechanical key  32  from the key body  31  is detected by the key detector  47  to be discussed later, the portable-unit controller  44  changes the control mode to the valet mode to limit some of predetermined functions of the vehicle  11  according to the command signal or the limited-function command signal (i.e., functions according to the limited-function command signal). 
     When a response signal to a request signal carried by the LF signal intermittently transmitted from the vehicle  11  is transmitted to the vehicle  11  from the portable unit  12 , the portable-unit controller  44  instructs the radio communication unit  41  to transmit the signal indicating that the control mode has been changed to valet mode from the normal mode to the vehicle  11 . 
     In the valet mode, the portable-unit controller  44  permits transmission of a command signal corresponding to the operator&#39;s normal operation of the operation switch  45  to the vehicle  11 , and inhibits transmission of a limited-function command signal corresponding to the operator&#39;s normal operation of the limited-function operation switch  46  to the vehicle  11 . 
     That is, some of the predetermined functions of the vehicle  11  which are limited in the valet mode include unlocking of the trunk achieved by driving of the trunk lock unit  27 . 
     When an operation in a predetermined operation pattern different from the normal operation on the operation switch  45  or the limited-function operation switch  46  is performed while attachment of the mechanical key  32  to the key body  31  is detected by the key detector  47  to be discussed later, for example, the portable-unit controller  44  inhibits transition to the valet mode thereafter. 
     When a response signal to the request signal carried by the LF signal intermittently transmitted from the vehicle  11  is transmitted to the vehicle  11  from the portable unit  12 , the portable-unit controller  44  instructs the radio communication unit  41  to transmit a signal indicating inhibition of the transition to the valet mode to the vehicle  11 . 
     When the radio communication unit  41  receives a signal transmitted from the vehicle  11  according to the command signal or limited-function command signal transmitted from the portable unit  12  (e.g., signal instructing execution of operations of on-vehicle devices which are instructed by the command signal or limited-function command signal), for example, the portable-unit controller  44  informs the operator of the reception through an answer-back operation of driving a portable-unit indicator (not shown) constituted by, for example, a light emitter, or a speaker (not shown). 
     In addition, in response to a signal output from a displaceable member  61  to be discussed later by the displacement of the displaceable member  61 , or a signal representing the result of detection from a sensor  62  which detects an electromagnetic change to be discussed later, or a signal output from a release button  63  to be discussed later, the portable-unit controller  44  drives the transponder communication unit  42  to supply electromagnetically induced power to the transponder  51  of the mechanical key  32  from the transponder communication unit  42  to execute communication with the transponder  51 . 
     The key detector  47  detects the attachment state and the detachment state of the mechanical key  32  to and from the key body  31 . 
     The key detector  47  detects the attachment state or the detachment state of the mechanical key  32  to and from the key body  31  based on, for example, the result of communication with the transponder  51  of the mechanical key  32  output from the transponder communication unit  42 . 
     The displaceable member  61  is displaced when it has physical contact with the mechanical key  32  according to the attachment or detachment of the mechanical key  32  to or from the key body  31 , and includes a signal output section  61   a , such as a switch, which outputs a signal according to predetermined displacement. 
     The displaceable member  61  exemplarily shown in  FIG. 3A , for example, includes a U-shaped ring  71  as shown in  FIG. 1 . The ring  71  is accommodated inside the key body  31  in such a way as to be pushed by the mechanical key  32  in the attachment state of the mechanical key  32  into the key body  31  of the mechanical key  32 , and is urged to project outside from the key body  31  by an urging member (not shown), such as a spring, provided in the key body  31  in the detachment state of the mechanical key  32  from the key body  31  of the mechanical key  32 . 
     When the mechanical key  32  is attached to the key body  31 , a movable part  61   b  including the ring  71  of the displaceable member  61  contacts the mechanical key  32  to be displaced and accommodated inside the key body  31 . As a result, the switch is turned ON to output a signal. 
     The displaceable member  61  exemplarily shown in  FIG. 3B , for example, is a switch or the like provided in an insertion part  31   a  in which a key plate  32   a  of the mechanical key  32  is inserted inside the key body  31 . 
     When the mechanical key  32  is attached to the key body  31 , the movable part  61   b  contacts the key plate  32   a  of the mechanical key  32  to be displaced. As a result, the switch is turned ON to output a signal. 
     The displaceable member  61  exemplarily shown in  FIG. 3C , for example, is a switch or the like provided at a position where the key body  31  and the mechanical key  32  contact each other with the mechanical key  32  attached to the key body  31  of the mechanical key  32 . 
     When the mechanical key  32  is attached to the key body  31 , the movable part  61   b  contacts a predetermined position of the mechanical key  32  (e.g., a projection  32   c  or the like provided on a key head  32   b  shown in  FIG. 3C ) to be displaced, so that the switch is turned ON to output a signal. 
     The sensor  62  exemplarily shown in  FIG. 4 , for example, detects an electromagnetic change according to the attachment or detachment of the mechanical key  32  to or from the key body  31  of the mechanical key  32 . For example, the sensor  62  detects the impedance of an LF antenna  41   a  having directivity in the direction of extension of the key plate  32   a  in the attachment state of the mechanical key  32  to the key body  31  of the mechanical key  32 , and outputs a signal representing the detection result. 
     This sensor  62  is designed based on the phenomenon that as the key plate  32   a  approaches the LF antenna  41   a , the inductance changes, and the impedance changes according to the change in inductance. Specifically, the value of the current flowing through the LF antenna  41   a  is detected when a voltage is applied to the LF antenna  41   a , a change in the current value is converted to a voltage, and a change in impedance is detected from the converted voltage and a change in the voltage applied to the LF antenna  41   a.    
     The timing at which a voltage is applied to the LF antenna  41   a  in the sensor  62  can be set to be, for example, normally-on, or every predetermined period, or a point of time at which the RF signal is transmitted to the vehicle  11  under the control of the portable-unit controller  44  according to a predetermined operation performed on the portable unit  12 , and is adequately set according to the power consumed by application of a voltage to the LF antenna  41   a . Note that this power consumption becomes smaller in the order of the timings named above. 
     The release button  63  is operated to disengage an engagement part  32   d  of the mechanical key  32  engaged with the key body  31  when the mechanical key  32  is attached to the key body  31 . The release button  63  outputs a signal at each of the timing at which the engagement of the engagement part  32   d  is released by, for example, the depressing operation of the operator, and the timing at which the mechanical key  32  is attached to the key body  31  to set the engagement state of the engagement part  32   d.    
     Next, an operational example of the vehicular electronic key system  10  according to the embodiment which has the foregoing structure will be described. 
     First, when the mechanical key  32  is detached from the key body  31 , the key detector  47  detects the detachment state of the mechanical key  32  from the key body  31 . Then, the portable-unit controller  44  changes the control mode to the valet mode. 
     When the operator operates the trunk unlock button  46   a  of the limited-function operation switch  46  in this situation, for example, transmission of a limited-function command signal to the vehicle  11  from the radio communication unit  41  of the key body  31  is inhibited. 
     When the operator carrying the key body  31  touches the handle to release the trunk of the vehicle  11  with the control mode changed to the valet mode, for example, a request signal including a signal indicating the direct contact of the operator with the handle of the trunk is transmitted to the portable unit  12  from the vehicle  11 . 
     Then, transmission of a response signal to the vehicle  11  from the portable unit  12  in response to the request signal is inhibited. Then, a predetermined function of the vehicle  11  associated with the direct contact of the operator, i.e., unlocking of the trunk achieved by driving of the trunk lock unit  27  or a part of predetermined functions of the vehicle  11  which is inhibited by the valet mode, is inhibited on the vehicle  11  which cannot receive the response signal to the request signal. 
     When the operator operates the switch which instructs control of unlocking of the vehicle&#39;s doors and trunk of the vehicle  11  with the control mode changed to the valet mode, a request signal including a signal instructing control of unlocking of the vehicle&#39;s doors and trunk is transmitted toward the portable unit  12  from the vehicle  11 . 
     Then, a signal indicating transmission of the control mode from the normal mode to the valet mode is transmitted, together with the response signal, to the vehicle  11  from the portable unit  12  in response to the request signal. Then, only some of predetermined functions of the vehicle  11  which has received those signals, i.e., unlocking of the trunk achieved by driving of the trunk lock unit  27  is inhibited, and unlocking of the vehicle&#39;s doors achieved by driving of the door lock unit  26  is permitted. 
     As described above, the vehicular electronic key system  10  according to the embodiment of the invention can permit the control mode to be changed to the valet mode only through a part of the operation that is normally needed for the transition of the mode of the vehicular electronic key system  10  to the valet mode, i.e., only an operation of detaching the mechanical key  32  from the key body  31 , and can permit the owner to carry the mechanical key  32  around. This can improve the convenience without impairing the operability and increasing the number of components. 
     Further, while the mechanical key  32  is detached from the key body  31 , transmission of a limited-function command signal which is triggered by the operation of the limited-function operation switch  46  for instructing execution of releasing of the limitation of the functions limited in the valet mode is inhibited, thus preventing the limited-function command signal from being transmitted to the vehicle  11  unnecessarily and preventing power consumption of the portable unit  12  from being wasted. 
     Further, inhibition and permission of the transition to the valet mode can be switched only in the attachment state where the mechanical key  32  is attached to the key body  31 , so that inhibition of the transition to the valet mode in the detachment state where the mechanical key  32  is detached from the key body  31  can be arbitrarily set while securing desired safety, thus further improving the convenience. 
     Moreover, as the attachment state and the detachment state of the mechanical key  32  to and from the key body  31  are detected through communication of the key body  31  with the transponder  51  normally provided in the mechanical key  32  in case of emergency, such as the battery of the portable unit  12  being dead, the valet mode is prevented from being released by attachment of an object other than the normal mechanical key  32 . This makes it possible to secure desired safety while sharing components. 
     Furthermore, power needed for communication with the transponder  51  of the mechanical key  32  is supplied to the transponder  51  from the key body  31  according to the timing at which the attachment or detachment of the mechanical key  32  to or from the key body  31  is detected, thus preventing power consumption of the portable unit  12  from being wasted. 
     According to the embodiment, the limited-function operation switch  46  of the key body  31  may be omitted. In this case, as described above, some of predetermined functions of the vehicle  11  (e.g., unlocking the trunk achieved by driving of the trunk lock unit  27 ) according to the operator&#39;s operation performed on the member provided on the vehicle  11  and corresponding to the limited-function operation switch  46  (e.g., the handle for releasing the trunk of the vehicle  11 ) should be limited in the valet mode. 
     Although one of predetermined functions which are limited in the valet mode is set to be unlocking of the trunk achieved by driving of the trunk lock unit  27  in the foregoing embodiment, the invention is not limited to this particular case, and another function may be added. For example, some of predetermined functions may include unlocking of the glove compartment of the vehicle  11  which is achieved by driving of a glove-compartment lock unit that switches between unlocking and locking of the glove compartment. In this case, a glove-compartment unlock button to instruct unlocking of the glove compartment by driving the glove-compartment lock unit may be provided as the limited-function operation switch  46  of the key body  31 . 
     According to the embodiment of the invention, a vehicular electronic key system includes a vehicle (e.g., vehicle  11  according to an exemplary embodiment) having a key cylinder (e.g., key cylinder  11   a  according to the exemplary embodiment), and a portable unit (e.g., portable unit  12  according to the exemplary embodiment) having a key body (e.g., key body  31  according to the exemplary embodiment) communicatable with the vehicle, and a mechanical key (e.g., mechanical key  32  according to the exemplary embodiment) attachable to and detachable from the key body and mechanically rotating the key cylinder whereby the communication between the vehicle and the portable unit allows the vehicle to execute predetermined functions, the key body including a key detection unit (e.g., key detector  47  according to the exemplary embodiment) which detects an attachment state and a detachment state of the mechanical key to and from the key body so that the key body transitions to a valet mode to limit some of the predetermined functions executable by the vehicle in accordance with the communication between the vehicle and the portable unit while the key detection unit detects the detachment state of the mechanical key from the key body. 
     According to the vehicular electronic key system of the above mentioned embodiment of the invention, transition to the valet mode is enabled by only part of an operation which is normally needed to change the vehicular electronic key system to the valet mode, i.e., only an operation of separating the mechanical key from the key body, and the owner can carry the mechanical key, so that the convenience is improved without impairing the operability and increasing the number of the components of the electronic key. 
     According to the embodiment of the invention, the portable unit may include a limited-function operation member (e.g., limited-function operation switch  46  according to an exemplary embodiment) which is operated to transmit a limited-function command signal instructing execution of a function limited by the valet mode to the vehicle, and may inhibit transmission of the limited-function command signal triggered by operation of the limited-function operation member while the key detection unit detects the detachment state of the mechanical key from the key body. 
     The vehicular electronic key system of the above mentioned embodiment of the invention prevents the limited-function command signal from being unnecessarily transmitted to the vehicle, preventing power consumption of the portable unit from being wasted. 
     According to the embodiment of the invention, the portable unit may include an operation member (e.g., operation switch  45  according to an exemplary embodiment) which is operated to transmit a command signal instructing execution of one of the predetermined functions to the vehicle, whereby when the operation member is operated in a predetermined operation pattern different from the operation to transmit the command signal to the vehicle while the attachment state of the mechanical key from the key body is detected by the key detection unit, the portable unit inhibits transition to the valet mode thereafter. 
     The vehicular electronic key system of the above mentioned embodiment of the invention can switch between inhibition and permission of transition to the valet mode only in the attachment state where the mechanical key is attached to the key body. It is therefore possible to arbitrarily set inhibition of transition to the valet mode in the detachment state where the mechanical key is separated from the key body while securing desirable safety, further improving the convenience. 
     According to the embodiment of the invention, the mechanical key may include a transponder (e.g., transponder  51  according to an exemplary embodiment) which is supplied with power from the vehicle to send a unique signal, the vehicle may include a vehicle-side transponder communication unit (e.g., transponder communication unit  22  according to the exemplary embodiment) which supplies power to the transponder of the mechanical key to carry out communication therewith, and an engine start unit (e.g., vehicle controller  24  according to the exemplary embodiment) capable of starting an engine of the vehicle through the communication of the vehicle-side transponder communication unit with the transponder, and the key body may include a key-side transponder communication unit (e.g., transponder communication unit  42  according to the exemplary embodiment) which communicates with the transponder and outputs a communication result with the mechanical key attached to the key body, whereby the key detection unit detects the attachment state and the detachment state of the mechanical key to and from the key body based on the communication result output from the key-side transponder communication unit. 
     The vehicular electronic key system of the above mentioned embodiment of the invention can prevent the valet mode from being released by attachment of an object other than the normal mechanical key by detecting the attachment state and the detachment state of the mechanical key to and from the key body through communication between the transponder generally provided in the mechanical key for emergency use, such as the battery of the portable unit being dead, and the key body. This makes it possible to secure desirable safety while sharing components. 
     According to the embodiment of the invention, the key body may include a displaceable member (e.g., displaceable member  61  according to an exemplary embodiment) which is displaced when in contact with the mechanical key in accordance with the attachment or detachment of the mechanical key to or from the key body, and the key-side transponder communication unit may communicate with the transponder in accordance with displacement of the displaceable member. 
     According to the vehicular electronic key system of the above mentioned embodiment of the invention, power needed for communication of the transponder is supplied to the key-side transponder communication unit from the key body only at the timing at which attachment or detachment of the mechanical key to or from the key body is detected, thus preventing power consumption of the portable unit from being wasted. 
     According to the embodiment of the invention, the key body may include a detection unit (e.g., sensor  62  according to an exemplary embodiment) which detects an electromagnetic change corresponding to attachment or detachment of the mechanical key to or from the key body, and the key-side transponder communication unit may communicate with the transponder when the detection unit detects the electromagnetic change. 
     According to the vehicular electronic key system of the above mentioned embodiment of the invention, power needed for communication of the transponder is supplied to the key-side transponder communication unit from the key body only at the timing at which attachment or detachment of the mechanical key to or from the key body is detected, thus preventing power consumption of the portable unit from being wasted. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.