Patent Publication Number: US-9424698-B2

Title: Keyless entry system

Description:
CLAIM OF PRIORITY 
     This application claims benefit of Japanese Patent Application No. 2013-257178 filed on Dec. 12, 2013, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a keyless entry system that locks or unlocks a door of a vehicle by performing wireless communication between an in-vehicle device and a portable device, and more particularly, to a passive keyless entry system having a function of automatically communicating between an in-vehicle device and a portable device. 
     2. Description of the Related Art 
     In a moving vehicle such as a car, a door lock is provided in a door of the car so as to prevent the car from being robbed or to prevent the car from being invaded and devices inside the car being damaged when the car is not used. In the related art, locking or unlocking of the door lock is performed by inserting a key for engine start-up into a key hole. However, a so-called keyless entry system that performs unlocking or locking of the door lock by operating a switch of a portable device instead of inserting a key into a key hole is used from the viewpoint of convenience. Further, in recent years, a so-called passive keyless entry system that automatically performs locking or unlocking of a door lock if a predetermined portable device is carried and located in a predetermined region instead of a switch of the portable device being operated is used. Further, the passive keyless entry system is caused to have an electrical authentication function regarding start-up of an engine, and the engine is prevented from starting when authentication is not successful between a car body and the portable device for high security. 
     In an operation of the keyless entry system, when a person carrying a portable device registered in an in-vehicle device mounted in a car in advance approaches the car, a request signal that is a low frequency signal containing a start-up signal is transmitted from the in-vehicle device. Also, when the portable device receives the request signal, the portable device responsively transmits an answer signal that is a high frequency signal containing an instruction signal, and the in-vehicle device controls a controlled device according to the instruction signal contained in the answer signal when the in-vehicle device receives the answer signal. This control, for example, unlocks the door of the car or starts up the engine of the car, and thus, a car driver comes to be able to drive the car. 
     The keyless entry system in which such a series of operations are performed includes a keyless entry system having a function of contributing to start-up of an engine when a portable device is in a car&#39;s interior, and a keyless entry system having a function of contributing to locking or unlocking of a door lock when a portable device is in a car&#39;s exterior. Further, there is a keyless entry system having a function of preventing a door from being locked when the portable device is in the car&#39;s interior so as to prevent the portable device from being misplaced in the car&#39;s interior. 
     In such a keyless entry system, it is important to detect whether the portable device is in the car&#39;s interior or the car&#39;s exterior with high precision. A keyless entry system in which a plurality of antennas transmitting a request signal are arranged in the car&#39;s interior or in both the car&#39;s interior and the car&#39;s exterior is known as the keyless entry system that performs the detection or the determination. Also, according to this type of keyless entry system, since the request signal is transmitted from the in-vehicle device through the plurality of antennas, transmission and reception of a radio signal can be reliably performed between the in-vehicle device and the portable device if the portable device is in the car&#39;s interior or within a predetermined range outside the car. Accordingly, it can be accurately determined whether the portable device is in the car&#39;s interior or the car&#39;s exterior. 
     In the related art, in the portable device in these keyless entry systems, detection sensitivity of the signal is always set to high sensitivity in order for the request signal transmitted from the in-vehicle device to be necessarily detected. Therefore, there is a problem in that consumption of a battery for a power supply built in the portable device increases. In order to solve this problem, an invention of a keyless entry system in which reduction of battery lifespan is suppressed by switching the detection sensitivity is disclosed in Japanese Unexamined Patent Application Publication No. 2013-083051. A schematic configuration of a vehicle control system  900  described in Japanese Unexamined Patent Application Publication No. 2013-083051 is illustrated in  FIG. 6 . 
     The vehicle control system  900  includes a smart key  910  operated by a built-in battery and carried by a user, and a collation ECU  950  mounted on a vehicle  980 , and is configured so that wireless communication is performed between the smart key  910  and the collation ECU  950 . Also, the smart key  910  periodically switches between predetermined normal sensitivity and high sensitivity at which a detection area of a transmission signal is wider than that at the normal sensitivity as detection sensitivity for detecting a transmission signal transmitted from the collation ECU  950 . Accordingly, since it is not always necessary to detect the transmission signal with high sensitivity, current consumption of the battery can be reduced. As a result, reduction of lifespan of the battery built in the smart key  910  can be suppressed. 
     However, there are the following problems with the vehicle control system  900  described in Japanese Unexamined Patent Application Publication No. 2013-083051. A case in which it is necessary for the smart key  910  that is a portable device to detect the transmission signal transmitted from the collation ECU  950  that is an in-vehicle device includes only a case in which the smart key  910  is in the vehicle&#39;s interior or near the vehicle. Therefore, in other cases, it is not necessary to detect the transmission signal from the collation ECU  950 . However, in the vehicle control system  900 , periodic switching occurs between the normal sensitivity and the high sensitivity regardless of a position of the smart key  910 . Therefore, a period of the high sensitivity in which current consumption of the battery increases is unnecessarily long. As a result, reduction of lifespan of the battery built in the smart key  910  cannot be sufficiently suppressed. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of such a technical background, and provides a keyless entry system capable of switching detection sensitivity according to a position of a portable device and suppressing reduction of lifespan of a battery built in a portable device. 
     According to an aspect of the invention, there is provided a keyless entry system including: an in-vehicle device mounted on a vehicle, and a portable device carried by a user and operated by a built-in battery, a request signal being transmitted from the in-vehicle device to the portable device and an answer signal to the request signal being transmitted from the portable device so that wireless communication is performed between the in-vehicle device and the portable device, in which the portable device includes a control unit that is capable of setting first sensitivity that is predetermined sensitivity and second sensitivity that is higher sensitivity than the first sensitivity and at which a detection area for the request signal is wide, as detection sensitivity for detecting the request signal, determines whether the portable device is in a vehicle&#39;s interior or within a predetermined distance from the vehicle from intensity of the request signal, and switches between the first sensitivity and the second sensitivity, the control unit sets the detection sensitivity to the second sensitivity when determining that the portable device is in the vehicle&#39;s interior or within the predetermined distance from the vehicle, and the control unit sets the detection sensitivity to the first sensitivity when determining that the portable device is not in or comes to be not in the vehicle&#39;s interior or within the predetermined distance from the vehicle. 
     In the keyless entry system configured in this way, when the portable device is in the vehicle&#39;s interior or within a predetermined distance from the vehicle and it is necessary to increase the detection sensitivity for the request signal, the detection sensitivity is set to second sensitivity that is high sensitivity, and thus, the detection area is widened and the position of the portable device can be accurately determined. Further, when it is determined that the portable device is not in or comes to be not in the vehicle&#39;s interior or within a predetermined distance from the vehicle and it is not necessary to increase the detection sensitivity, the detection sensitivity is set to the first sensitivity lower than the second sensitivity, and thus, there is no increase in the current consumption of the battery in the portable device. As a result, it is possible to suppress reduction of lifespan of the battery in the portable device. 
     Further, in the above-described configuration, the in-vehicle device may transmit the request signal when an operation of opening the door of the vehicle from the vehicle&#39;s interior is performed and then an operation of locking the door of the vehicle from the outside of the vehicle is performed, and the portable device may perform authentication of the transmitted request signal, determine that the portable device is away by a predetermined distance or greater from the vehicle when the authentication is successful, and set the detection sensitivity to the first sensitivity. 
     In the keyless entry system configured in this way, when a user locks the door of the vehicle outside the vehicle at the time of getting-off, it is determined that the portable device is away a predetermined distance or greater from the vehicle when the authentication is successful, and the detection sensitivity is set to the first sensitivity lower than the second sensitivity. Thus, the battery is not unnecessarily consumed. Therefore, there is no increase in current consumption of the battery. 
     Further, in the above-described configuration, the in-vehicle device may transmit the request signal when an operation of opening the door of the vehicle from the vehicle&#39;s interior is performed, and subsequently, an operation of locking the door of the vehicle from the outside of the vehicle is performed, and the portable device may perform authentication of the transmitted request signal, and set the detection sensitivity to the first sensitivity after a predetermined time lapses when the authentication is not successful. 
     In the keyless entry system configured in this way, when the user locks the door of the vehicle outside the vehicle at the time of getting-off, it is determined that the portable device is away a predetermined distance or greater from the vehicle when the authentication is not successful, and the detection sensitivity is set to the first sensitivity lower than the second sensitivity after a predetermined time lapses. Further, even when the portable device is not away a predetermined distance or greater from the vehicle, the detection sensitivity is forcibly set to the first sensitivity lower than the second sensitivity after a predetermined time lapses in consideration of communication failure caused by jamming waves. Thus, the battery is not unnecessarily consumed, and there is no increase in current consumption of the battery. 
     Further, in the above-described configuration, the in-vehicle device may transmit the request signal when it is detected that an operation of opening the door of the vehicle from the vehicle&#39;s interior is performed and the portable device is outside the vehicle without an operation of locking the door of the vehicle being subsequently performed, and when the portable device is away a predetermined distance or greater from the vehicle, the portable device may transmit the answer signal to the in-vehicle device to cause the door of the vehicle to be locked, and set the detection sensitivity to the first sensitivity. 
     In the keyless entry system configured in this way, if the user does not lock the door of the vehicle outside the vehicle at the time of getting-off, when the portable device is away a predetermined distance or greater from the vehicle, the detection sensitivity is set to the first sensitivity lower than the second sensitivity, and thus, the battery is not unnecessarily consumed. Therefore, there is no increase in current consumption of the battery. Further, simultaneously, the door of the vehicle is caused to be locked, and thus, it is possible to prevent someone from invading the vehicle&#39;s interior and devices on the inside from being damaged or stolen even when the user forgets to lock the door. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a schematic configuration of a keyless entry system; 
         FIG. 2  is a block diagram illustrating a configuration of respective primary units of an in-vehicle device and a portable device in the keyless entry system; 
         FIG. 3  is a flowchart illustrating content of a process at the time of getting-on; 
         FIG. 4  is a flowchart illustrating content of a first process at the time of getting-off; 
         FIG. 5  is a flowchart illustrating content of a second process at the time of getting-off; and 
         FIG. 6  is a schematic diagram illustrating a configuration of a keyless entry system according to an example in the related art. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
       FIG. 1  is a diagram illustrating a schematic configuration of a keyless entry system  100 , and is a plan view when a vehicle  50  including an in-vehicle device  10  and a user  55  carrying a portable device  20  are viewed from the top. The in-vehicle device  10  is mounted on the vehicle  50 , and includes an in-vehicle device body  10   a , a vehicle-side transmission antenna  2 , and a vehicle-side reception antenna  4 . In the keyless entry system  100 , the vehicle-side transmission antenna  2  includes four antennas located in predetermined positions inside the vehicle  50 , and the one vehicle-side reception antenna  4  is arranged near the in-vehicle device body  10   a . However, an arrangement of the four vehicle-side transmission antennas  2  and the vehicle-side reception antenna  4  described herein is an example, and other arrangements may be adopted. 
     Further, generally, the number of the vehicle-side transmission antennas  2  may be at least 3 or more. The vehicle-side transmission antennas  2  or the vehicle-side reception antenna  4  described above is connected to the in-vehicle device body  10   a  through a wiring (not illustrated). Further, the portable device  20  is carried by the user  55  and operated by a built-in battery  19 . The keyless entry system  100  has a function of performing wireless communication between the in-vehicle device  10  and the portable device  20 . 
     The keyless entry system  100  has a function of automatically performing locking or unlocking of a door (so-called passive function) by performing wireless communication between the in-vehicle device  10  and the portable device  20  as described above and performing authentication using an ID code or the like. Further, when the user (driver)  55  carrying the portable device  20  enters a vehicle&#39;s interior  51 , the keyless entry system  100  permits the user to operate a main switch without inserting a key into a key cylinder. Further, such a function is well known, and thus, a description of details thereof will be omitted. 
       FIG. 2  is a block diagram illustrating a configuration of respective primary units of the in-vehicle device  10  and the portable device  20  used for the keyless entry system  100 . 
     The in-vehicle device  10  includes the vehicle-side transmission antennas  2 , the vehicle-side reception antenna  4 , and the in-vehicle device body  10   a  described above, as illustrated in  FIG. 2 . The in-vehicle device body  10   a  includes a vehicle-side transmission unit (LF-TX)  1 , a vehicle-side reception unit (RF-RX)  3 , a vehicle-side control unit (CPU)  5 , a vehicle-side oscillation unit (LF-OSC)  6 , a vehicle-side storage unit (MEM)  7 , and a driving signal transmission unit (DS-TX)  8 . In the in-vehicle device body  10   a , the vehicle-side control unit  5  is located at a center thereof, and controls the respective units connected to the vehicle-side control unit  5 . 
     In the inside of the vehicle-side transmission unit  1 , a plurality of vehicle-side transmission circuits (not illustrated) are provided, and each of the vehicle-side transmission circuits is connected to each of the plurality of the vehicle-side transmission antennas  2 , and each input terminal thereof is connected to the vehicle-side control unit  5 . The vehicle-side reception unit  3  has an input terminal connected to the vehicle-side reception antenna  4 , and an output terminal connected to the vehicle-side control unit  5 . Further, a received signal strength indication (RSSI) circuit  3   a  is built in the vehicle-side reception unit  3 . The vehicle-side oscillation unit  6  generates a low frequency signal, and an output terminal outputting this low frequency signal is connected to the vehicle-side control unit  5 . The vehicle-side storage unit  7  stores a first ID assigned to the in-vehicle device  10 , and a second ID assigned to the portable device  20  that is used together with this in-vehicle device  10 , and a control terminal thereof is connected to the vehicle-side control unit  5 . Further, the driving signal transmission unit  8  has an input terminal connected to the vehicle-side control unit  5 , and an output terminal connected to an external connection terminal  8   a.    
     The low frequency signal output from the vehicle-side oscillation unit  6  is supplied to the vehicle-side control unit  5 . When the low frequency signal is supplied, the vehicle-side control unit  5  reads a first ID from the vehicle-side storage unit  7  and adds necessary information containing the first read ID to the low frequency signal to form a request signal. Then, if a transmission timing of the request signal is set, this request signal is supplied to the vehicle-side transmission unit  1  under control of the vehicle-side control unit  5 . Each vehicle-side transmission circuit in the vehicle-side transmission unit  1  amplifies the supplied request signal up to a signal level suitable for transmission, and supplies the amplified request signal to the vehicle-side transmission antennas  2 . The request signal is wirelessly transmitted from the vehicle-side transmission antennas  2 . Further, wireless transmissions from the plurality of vehicle-side transmission antennas  2  are alternately performed one by one, and the wirelessly transmission is not simultaneously performed from the two or more vehicle-side transmission antennas  2 . 
     The vehicle-side reception unit  3  receives a high frequency signal (answer signal) containing the second ID or an instruction signal of the portable device  20  wirelessly transmitted from the portable device  20  via the vehicle-side reception antenna  4 , amplifies the received answer signal into a predetermined signal level using an amplification circuit (not illustrated), and supplies the amplified answer signal to the vehicle-side control unit  5 . Further, the RSSI circuit  3   a  in the vehicle-side reception unit  3  can receive the amplified answer signal and detect signal strength of the answer signal. The vehicle-side control unit  5  authenticates the second ID contained in the answer signal using the second ID read from the vehicle-side storage unit  7 , forms a driving signal from the instruction signal contained in the answer signal when the authentication is successful, and supplies this driving signal to the driving signal transmission unit  8 . When the driving signal is supplied, the driving signal transmission unit  8  transmits the driving signal to a controlled mechanism (not illustrated), such as a motor (not illustrated) that performs locking and unlocking of a corresponding door lock or an engine start-up circuit, and the controlled mechanism is controlled according to the driving signal. 
     Further, for example, a low frequency signal of 125 KHz is used as the above request signal, and, for example, a high frequency signal of 315 MHz is used as the answer signal. Further, a communication distance of the request signal, that is, a detection area for the request signal is about 1 m to 2 m from the vehicle-side transmission antenna  2 , and a communication distance of the answer signal, that is, a detection area for the answer signal is about 5 m to 20 m from a portable-device-side transmission antenna  12 . 
     The portable device  20  includes a portable-device-side transmission unit (RF-TX)  11 , the portable-device-side transmission antenna  12 , a portable-device-side reception unit (LF-RX)  13 , a portable-device-side reception antenna  14 , a portable-device-side control unit (CPU)  15 , a portable-device-side oscillation unit (RF-OSC)  16 , a portable-device-side storage unit (MEM)  17 , and a battery (BAT)  19  for a power supply, as illustrated in  FIG. 2 . Further, an RSSI circuit  13   a  and an amplification circuit  13   b  are built in the portable-device-side reception unit  13 . In the portable device  20 , the portable-device-side control unit  15  is located at a center thereof, and controls the respective units connected to the portable-device-side control unit  15 . 
     The portable-device-side transmission unit  11  has an input terminal connected to the portable-device-side control unit  15 , and an output terminal connected to the portable-device-side transmission antenna  12 . The portable-device-side reception unit  13  has an input terminal connected to the portable-device-side reception antenna  14 , and an output terminal connected to the portable-device-side control unit  15 . The portable-device-side oscillation unit  16  has an output terminal connected to the portable-device-side control unit  15 . The portable-device-side storage unit  17  has a control terminal connected to the portable-device-side control unit  15 . The battery  19  is connected to each unit in the portable device  20  described above, and supplies a power supply voltage to each unit. 
     The portable-device-side oscillation unit  16  oscillates a high frequency signal, and the oscillated high frequency signal is supplied to the portable-device-side control unit  15 . In this case, the portable-device-side control unit  15  adds a necessary information signal such as the second ID or the instruction signal through frequency modulation using this high frequency signal as a carrier, and forms the answer signal. This answer signal is supplied to the portable-device-side transmission antenna  12  via the portable-device-side transmission unit  11  and wirelessly transmitted. Since the first ID assigned to the in-vehicle device  10  or the second ID assigned to the own portable device  20 , and various instruction signals are stored in the portable-device-side storage unit  17 , the first ID, the second ID, or various instruction signals are appropriately read under control of the portable-device-side control unit  15 . 
     When the high frequency signal (answer signal) containing the second ID or the instruction signal is supplied from the portable-device-side control unit  15 , the portable-device-side transmission unit  11  amplifies the answer signal up to a signal level suitable for wireless transmission, and wirelessly transmits the amplified answer signal via the portable-device-side transmission antenna  12 . The portable-device-side reception unit  13  receives the request signal containing the first ID wirelessly transmitted from the in-vehicle device  10  via the portable-device-side reception antenna  14 , amplifies the received request signal up to a predetermined signal level using the amplification circuit  13   b , and supplies the amplified request signal to the portable-device-side control unit  15 . Further, the request signal amplified by the amplification circuit  13   b  can be input to the RSSI circuit  13   a , and the signal strength of the request signal can be detected. 
     In the portable-device-side control unit  15 , respective distances between the portable device  20  and the plurality of vehicle-side transmission antennas  2  can be calculated based on the signal strength of the request signal obtained by the RSSI circuit  13   a  described above. Further, the portable-device-side control unit  15  can accurately determine whether the portable device  20  is in the vehicle&#39;s interior  51  or the vehicle&#39;s exterior, or a position in the vehicle&#39;s interior  51  or the vehicle&#39;s exterior in which there is the portable device  20  through trigonometry based on the respective calculated distances. Further, the distances between the portable device  20  and the plurality of vehicle-side transmission antennas  2  calculated by the portable-device-side control unit  15 , and the position of the portable device  20  can be stored in the portable-device-side storage unit  17 . 
     As described above, the RSSI circuit  13   a  in the portable-device-side reception unit  13  can detect the signal strength of the request signal wirelessly transmitted from the in-vehicle device  10 . Also, the detection sensitivity when this signal strength is detected can be set by changing an amplification degree of the amplification circuit  13   b . Further, the amplification degree of the amplification circuit  13   b  is hereinafter referred to as an LF gain. 
     The detection sensitivity of the RSSI circuit  13   a  can be increased by causing the LF gain to be high. Therefore, when the signal strength is detected to calculate the respective distances between the portable device  20  and the plurality of vehicle-side transmission antennas  2 , the detection sensitivity of the RSSI circuit  13   a  can be second sensitivity at which the detection area is wider than that at first sensitivity by causing the LF gain to be high. Therefore, it is possible to receive the request signal from more vehicle-side transmission antennas  2 . As a result, it is possible to calculate the respective distances between the portable device  20  and the plurality of vehicle-side transmission antennas  2 , and the position of the portable device  20  more accurately. However, in the related art, when the LF gain is set to be always or periodically high, current consumption of the battery  19  supplying a power to the amplification circuit  13   b  increases. 
     Therefore, in the keyless entry system  100  of the present invention, the portable device  20  is able to set the first sensitivity that is predetermined sensitivity, and the second sensitivity that is higher sensitivity than the first sensitivity and at which a detection area of a transmission signal is wider than that at the first sensitivity, as detection sensitivity for detecting the request signal. Further, when it is determined that the portable device  20  is in the vehicle&#39;s interior  51  or within a predetermined distance from the vehicle  50 , the detection sensitivity is set to the second sensitivity that is high sensitivity, and when it is determined that the portable device  20  is not in the vehicle&#39;s interior  51  or within a predetermined distance from the vehicle  50  or comes to be not in the vehicle&#39;s interior  51  or within the predetermined distance, the detection sensitivity is set to the first sensitivity lower than the second sensitivity. In other words, the LF gain is high only when the signal strength is detected to calculate respective distances between the portable device  20  and the plurality of vehicle-side transmission antennas  2 , and the LF gain is lower in normal cases. 
     In the portable device  20 , when the request signal from the in-vehicle device  10  is transmitted, a current called a dark current periodically flows in the portable device  20  so that the request signal can be reliably received. Also, when the start-up signal in the request signal is received, the portable device  20  is started up and a current flows into, for example, the portable-device-side reception unit  13  or the portable-device-side transmission unit  11  in earnest. In this case, when the detection sensitivity is set to the second sensitivity that is high sensitivity, that is, when the LF gain is set to be high (set to High), it is necessary for the current value of the dark current to be increased. On the other hand, when the detection sensitivity is set to the first sensitivity lower than the second sensitivity, that is, when the LF gain is set to be low (set to Low), the current value of the dark current is decreased. A current value of the dark current when the LF gain is set to be low (set to Low) can be about 25% smaller than the current value of the dark current when the LF gain is set to be high (set to High). 
     The dark current itself is a very small current of several μA, but a period of time in which the portable device  20  is not used is much longer than a period of time in which the portable device  20  is used, and thus, a difference in size of a current value of this dark current is involved in current consumption of the battery  19 . 
     Thus, in the keyless entry system  100 , since the detection sensitivity is set to the second sensitivity that is high sensitivity when the portable device  20  is in the vehicle&#39;s interior  51  or within the predetermined distance from the vehicle  50  and it is necessary to increase the detection sensitivity for the request signal, the detection area is widened and the position of the portable device  20  can be accurately determined. Further, since it is determined that the portable device  20  is not in or comes to be not in the vehicle&#39;s interior  51  or within the predetermined distance from the vehicle  50  and it is not necessary to increase the detection sensitivity, the detection sensitivity is set to the first sensitivity lower than the second sensitivity, and thus, there is no increase in the current consumption of the battery  19  in the portable device  20 . As a result, reduction of lifespan of the battery  19  in the portable device  20  can be suppressed. 
     Next, an operation of the in-vehicle device  10  and the portable device  20  when the user  55  gets on the vehicle and when the user  55  gets off the vehicle will be described with reference to  FIG. 1  and  FIGS. 3 to 5 . 
       FIG. 3  is a flowchart illustrating content of a process at the time of getting-on. Further,  FIG. 4  is a flowchart illustrating processing content in a first process at the time of getting-off, and  FIG. 5  is a flowchart illustrating processing content in a second process at the time of getting-off that is different from the first process at the time of getting-off. 
     In the in-vehicle device  10 , in a process (step  60 ) at the time of getting-on, first, all doors of the vehicle  50  are locked, as illustrated in  FIG. 3  (step  61 ). The user  55  pushes a request switch installed in a door handle at the time of getting-on to unlock the door (step  62 ). Further, “pushes the request switch” to unlock the door is expressed herein, but a mechanism for unlocking the door may have a structure “contacts with the request switch” or “holds a request switch with a hand.” Then, a request signal containing a signal for (start-up+authentication) from the in-vehicle device  10  to the portable device  20  is transmitted (step  63 ). 
     In the portable device  20 , the LF gain is set to Low until the request signal is received, but the LF gain is set to High after a request signal is received and the device is started up by a signal for start-up in the request signal (step  64 ). Then, an authentication signal in the request signal is received and authentication of the authentication signal is performed (step  65 ). When the authentication of the authentication signal cannot be performed, a task of authenticating the authentication signal is repeated. If the authentication signal can be authenticated, the portable device  20  determines that the user  55  is near the vehicle  50  and maintains the LF gain at High (step  66 ). Thereafter, the LF gain is kept at High while the user  55  is in the vehicle&#39;s interior  51 . 
     On the other hand, in the in-vehicle device  10 , the user  55  starts up the engine in the vehicle&#39;s interior  51  (step  67 ). Then, the user  55  drives the vehicle  50  and locks the door by oneself or when the user  55  does not lock the door, a control signal is output from the vehicle-side control unit  5  to the driving signal transmission unit  8  and the door is locked if vehicle speed of the vehicle  50  is equal to or greater than a certain speed (step  68 ). 
     Next, content of the first process at the time of getting-off will be described. Further, the first process at the time of getting-off is a process at the time of getting-off when the user  55  locks the door at the time of getting-off by oneself. 
     In the in-vehicle device  10 , in the first process at the time of getting-off (step  70 ), first, all doors of the vehicle  50  are locked, as illustrated in  FIG. 4  (step  71 ). The user  55  unlocks the door at the time of getting-off, and exits to the outside of the vehicle (step  72 ). Also, the user  55  pushes the request switch installed in the door handle and locks the unlocked door (step  73 ). At this time, the request signal containing a signal for (start-up+authentication) is transmitted from the in-vehicle device  10  to the portable device  20  (step  74 ). 
     After the request signal is transmitted, the request signal is received in the portable device  20  and authentication of the authentication signal is performed (step  75 ). Further, at this time, the LF gain is set to High. If the authentication signal can be authenticated, the portable device  20  determines that the user  55  carrying the portable device  20  is away from the vehicle  50 , and sets the LF gain to Low (step  76 ). The user  55  carrying the portable device  20  is likely to stay near the vehicle  50 . However, when the user  55  locks the door by oneself, the user is generally away from the vehicle  50 , and thus, here, it is determined that the user  55  is away from the vehicle  50 , and the LF gain is set to Low. When the user  55  enters the vehicle&#39;s interior  51  again, the process at the time of getting-on illustrated in  FIG. 3  is performed. 
     In the authentication task (step  75 ), when the authentication signal cannot be authenticated, it is considered that the user  55  rapidly went away from the vehicle  50  after unlocking the door. Further, a possibility that communication between the in-vehicle device  10  and the portable device  20  fails due to jamming waves is also considered. In any case, the LF gain is maintained in a High state for a certain time. However, after a certain time lapses, particularly, when a situation is not changed, the LF gain is forcibly set to Low (step  77 ). 
     Next, content of the second process at the time of getting-off will be described. Further, the second process at the time of getting-off is a process at the time of getting-off when the user  55  does not lock the door by oneself at the time of getting-off. 
     In the in-vehicle device  10 , in the second process at the time of getting-off (step  80 ), first, all the doors of the vehicle  50  are locked, as illustrated in  FIG. 5  (step  81 ). The user  55  unlocks the door at the time of getting-off, exits to the outside of the vehicle, and closes the door. However, the user  55  does not lock the door (step  82 ). At this time, the portable device  20  is outside the vehicle. Then, when locking is not performed within a certain time, a request signal containing a signal for (start-up+setting of the LF gain to High) is transmitted from the in-vehicle device  10  to the portable device  20  (step  83 ). 
     On the portable device  20  side, the request signal is received and a distance between the vehicle  50  and the portable device  20  is measured based on the RSSI value obtained by the portable-device-side control unit  15 , as illustrated in  FIG. 5  (step  84 ). A result of the measurement of this distance is received, and it is determined whether the distance between the vehicle  50  and the portable device  20  is equal to or more than a predetermined distance or less than the predetermined distance (step  85 ). When it is determined that the distance is less than the predetermined distance, this determination is repeated. Also, when the distance between the vehicle  50  and the portable device  20  is equal to or more than the predetermined distance, an answer signal containing a locking signal is transmitted from the portable device  20  to the in-vehicle device  10  (step  86 ). Then, in the portable device  20 , the LF gain is set to Low (step  87 ). Further, on the in-vehicle device  10  side, the answer signal is received, and a control signal is output from the vehicle-side control unit  5  to the driving signal transmission unit  8  to lock the door (step  88 ). 
     As described above, in the keyless entry system  100 , when the user  55  locks the door of the vehicle  50  outside the vehicle at the time of getting-off, it is determined that the portable device  20  is away a predetermined distance or greater from the vehicle  50  when the authentication is successful, and sets the detection sensitivity to the first sensitivity lower than the second sensitivity. Thus, the battery  19  is not unnecessarily consumed. Therefore, there is no increase in current consumption of the battery  19 . 
     Further, when the user  55  locks the door of the vehicle  50  outside the vehicle at the time of getting-off, it is determined that the portable device  20  is away a predetermined distance or greater from the vehicle  50  when the authentication is not successful and the detection sensitivity is set to the first sensitivity lower than the second sensitivity after a predetermined time lapses. Further, even when the portable device  20  is not away a predetermined distance or greater from the vehicle  50 , the detection sensitivity is forcibly set to the first sensitivity lower than the second sensitivity after a predetermined time lapses in consideration of communication failure caused by jamming waves. Therefore, the battery  19  is not unnecessarily consumed, and there is no increase in current consumption of the battery  19 . 
     Further, if the user  55  does not lock the door of the vehicle  50  outside the vehicle at the time of getting-off, when the portable device  20  is away a predetermined distance or greater from the vehicle  50 , the detection sensitivity is set to the first sensitivity lower than the second sensitivity, and thus, the battery  19  is not unnecessarily consumed. Therefore, there is no increase in current consumption of the battery  19 . Further, simultaneously, the door of the vehicle  50  is caused to be locked, and thus, it is possible to prevent someone from invading the vehicle&#39;s interior  51  and devices in the inside from being damaged or stolen even when the user  55  forgets to lock the door. 
     As described above, in the keyless entry system of the present invention, when the portable device is in the vehicle&#39;s interior or within the predetermined distance from the vehicle and it is necessary to increase the detection sensitivity for the request signal, the detection sensitivity is set to the second sensitivity that is high sensitivity, and thus, the detection area is widened and the position of the portable device can be accurately determined. Further, when it is determined that the portable device is not in or comes to be not in the vehicle&#39;s interior or within the predetermined distance from the vehicle and it is not necessary to increase the detection sensitivity, the detection sensitivity is set to the first sensitivity lower than the second sensitivity, and thus, there is no increase in the current consumption of the battery in the portable device. As a result, it is possible to suppress reduction of lifespan of the battery in the portable device. 
     The present invention is not limited to the description of the embodiments described above, and can be appropriately implemented in an aspect in which the effects are exhibited. For example, components equivalent to the components illustrated in  FIG. 2  may be included in the keyless entry system of the present invention. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims of the equivalents thereof.