Abstract:
A door control system for vehicles has a transmitter and a receiver for detecting an electronic key in a first predetermined area around a vehicle. A control unit controls unlocking of a vehicle door by determining whether the detected electronic key is an authorized one. The door control system also has an object sensor for detecting an object entering into a second predetermined area covering and wider than the first predetermined area. The control unit activates the transmitter and the receiver only after the object sensor detects the object in the second predetermined area, thereby reducing power consumption.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-353472 filed on Nov. 19, 2001.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to a door control system and method for vehicles, which automatically drives locked vehicle doors to unlocked condition or to unlock standby condition through radio communication with an electronic key carried by a vehicle driver.  
         BACKGROUND OF THE INVENTION  
         [0003]    As keyless entry systems for vehicles, which automatically unlock vehicle doors without mechanical key operation, a smart entry system is proposed. In one smart entry system, a radio communication device (radio transmitter/receiver) mounted in a vehicle starts its communications with an electronic key carried by a vehicle driver only after the vehicle driver manipulates a door from the exterior side. This system drives the doors to the unlock standby condition, when the electronic key is confirmed as the authorized one. However, this system takes some time to enable the vehicle driver to open the door after he touches it.  
           [0004]    In another smart entry system, a radio device mounted in a vehicle performs data communications with an electronic key carried by a vehicle driver, when the driver approaches the vehicle. The device then unlocks the doors or drives the doors to the unlock standby condition, if the electronic key is confirmed as the authorized one. In this system, the radio device must continuously or periodically generate radio signals for communications with the electronic key while the vehicle is held parked, because it is impossible to estimate when the vehicle driver having the electronic key returns to the vehicle. Further, this device must be mounted in each door in the vehicle, so that the generated radio signal may be received by the electronic key whichever directions the vehicle driver is. This system thus consumes too much electric power of a storage battery of the vehicle.  
         SUMMARY OF THE INVENTION  
         [0005]    It is therefore an object of the present invention to provide a door control system and method for vehicles, which consumes less electric power for communications with an electronic key.  
           [0006]    According to the present invention, a door control system for vehicles has a transmitter and a receiver for detecting an electronic key in a first predetermined area around a vehicle. A control unit controls unlocking of a vehicle door by determining whether the detected electronic key is an authorized one. The door control system also has an object sensor for detecting an object entering into a second predetermined area covering and wider than the first predetermined area. The control unit activates the transmitter and the receiver only after the object sensor detects the object in the second predetermined area, thereby reducing power consumption.  
           [0007]    Preferably, the door control system has an intruder sensor for detecting an intruder, and the control unit activates the intruder sensor only after determining that the electronic key is an unauthorized one. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:  
         [0009]    [0009]FIG. 1 is a block diagram showing a smart entry system constructed as a door control system according to an embodiment of the present invention;  
         [0010]    [0010]FIG. 2 is a schematic diagram showing areas of detection of an object and an electronic key by a security ECU used in the embodiment of FIG. 1; and  
         [0011]    [0011]FIG. 3 is a flow diagram showing control processing executed by the security ECU in the embodiment of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]    Referring first to FIG. 1, a door control system for vehicles is constructed, as a smart entry system, with a door unlocking device  2  mounted on a vehicle and an electronic key  4 . The key  4  is a portable radio device carried by a vehicle driver (owner) for data communications with the device  2 . The key  4  is activated by an interrogation signal transmitted from the device  2 , and transmits in return its identification code (ID code) as a response signal. The ID code differs from key to key. The device  2  is primarily constructed with a security ECU (electronic control unit)  10 , which monitors surrounding conditions of the vehicle, when the vehicle is held parked with its all doors being locked.  
         [0013]    In the device  2 , the ECU  10  is connected to at least one radio transmitter  12  (five transmitters in FIG. 1) for transmitting the interrogation signals for the key  4 , a radio receiver  14  for receiving the response signal from the key  4 , and door ECUs  16  for controlling locking and unlocking of vehicle doors. As shown in FIG. 2, the transmitters  12  are installed in the driver-side door, the front passenger-side door, the rear passenger-side doors and the rear luggage door, respectively. The transmitters  12  transmit the interrogation signals, so that the key  4  may be activated when the vehicle driver enters predetermined first areas  4 A- 4 E of the transmitters  12 . These areas  4 A- 4 E are variable with the power levels of the interrogation signals, respectively.  
         [0014]    The key  4  responsively transmits the response signal including its specific ID code. The receiver  14  is installed in a rear view mirror above a driver&#39;s seat to receive the response signal from the key  4  and decode the ID code included in the received response signal. For radio signal communications between the device  2  and the key  4 , electromagnetic waves in the frequency band from kHz to MHz are used so that the radio signals may be transmitted and received without being interrupted by humans.  
         [0015]    The security ECU  10  determines whether the key  4  is the authorized one based on the ID code decoded by the receiver  14 , and applies an instruction signal to the door ECUs  16  for performing door unlocking operation or unlock standby operation when the key  4  is confirmed as the authorized one, that is, the key  4  has the ID code specifically assigned to the vehicle. If the driver leaves the vehicle out of the areas  4 A- 4 E, the receiver  14  does not receive the response signal. As a result, the ECU  10  applies an instruction signal to the ECUs  16  so that the ECUs  16  perform door locking operation. Although not described in detail, the door unlocking operation, unlock standby operation and locking operation vary from vehicle to vehicle. The ECUs  16  are connected to various door sensors (not shown) to receive respective door open/close detection signals for use in controlling various door locking/unlocking operations.  
         [0016]    The ECU  10  is also connected to those door sensors to receive the door open/close signals. The ECU  10  is further connected to an object sensor  22 , an intrusion sensor  24 , a sound alarm  26  and a light alarm  28 .  
         [0017]    The object sensor  22  is for detecting any objects approaching the vehicle. Specifically, the object sensor  22  generates an electromagnetic wave signal of about several GHz. If the sensor  22  receives reflection of this signal, the sensor  22  determines that an object such as a human is approaching to the vehicle. The output power of the electromagnetic wave signal is determined to be able to detect the object in a predetermined second area  22 A (FIG. 2), which covers a nearby area including the vehicle and the areas  4 A- 4 E.  
         [0018]    The intruder sensor  24  is for detecting an intruder intruding into the vehicle. Specifically, the intruder sensor  24  transmits and receives an ultrasonic wave signal in the vehicle interior. It detects an intruder, when the received signal varies from the normal one.  
         [0019]    The sound alarm  26  is for activating a siren or the like. The light alarm  28  is for activating an interior light or hazard lights. Those alarms  26  and  28  are operable with a built-in battery to provide an alarm or warning even when a normal power supply in the vehicle is shut off.  
         [0020]    In this embodiment, the security ECU  10  is programmed to execute the monitoring operation and door unlocking control as shown in FIG. 3. The ECU  10  starts this processing, when the vehicle is parked with its all doors being locked.  
         [0021]    The ECU  10  first activates the object sensor  22  at step  110  by supplying electric power, and determines at step  120  whether any object in the area  22 A is detected by the sensor  22 . If the object is detected (YES), the ECU  10  also activates the transmitters  12  and the receiver  14  at step  130 . The ECU  10  then determines at step  140  whether the authorized electronic key  4  having the right ID code in the area  4 A,  4 B,  4 C,  4 D or  4 E is detected by the receiver  14 . If no authorized key is detected (NO), the ECU  10  activates the alarms  26  and  28  at step  150 . This alarm is a notice or precaution indicating a monitored condition to such an unauthorized person, and hence should be limited to a short and/or low output level so that the buzzing and lighting will not disturb nearby persons and neighbors.  
         [0022]    The ECU  10  then activates the intruder sensor  24  at step  160 , and determines at step  170  whether an intruder is detected by the intruder sensor  24 . In addition to or in place of the intruder sensor  24 , an intruder may be detected by the door sensors and the like when a locked door is forcibly unlocked or opened. If an intruder is thus detected (YES), the ECU  10  activates the alarms  26  and  28  at step  200 . In this case the alarms  26  and  28  provides buzzing and lighting in high output levels for a long time, respectively, so that the intrusion is notified to even neighbors. These alarms  26  and  28  are kept activated until deactivated in an authorized manner.  
         [0023]    If no intruder is detected at step  170  (NO), the ECU  10  determines again at step  180  whether any object is detected by the object sensor  22 . If the object is detected (YES), the ECU  10  repeats the above key checking processing starting from step  140 . If no object is detected (NO), the ECU  10  determines that the object detected by the object sensor  22  was just a passerby. The ECU  10  therefore deactivates the transmitters  12 , receiver  14  and intruder sensor  24  at step  190 , and repeats the object detecting processing from step  120 .  
         [0024]    In case that the key  4  is determined to be an authorized one (YES) by checking its ID code at step  140 , that is, when the vehicle driver came close to the vehicle, the ECU  10  applies the instruction signal to the door ECUs  16  at step  210  so that the doors are automatically unlocked or held in the unlock standby condition. In the unlock standby condition, the ECU  16  unlocks the corresponding door only when an unlocking switch mounted on the outside of such a door is manipulated by the vehicle driver. The ECU  210  also deactivates the object sensor  22 , transmitters  12  and receiver  14  at step  210 .  
         [0025]    The ECU  10  determines at step  220  whether the door is unlocked. If it is unlocked (YES), that is, if the door is opened by the vehicle driver and hence it is not necessary to perform the monitoring operation, the ECU  10  deactivates at step  230  the object sensor  22  as well as the transmitters  12  and the receiver  14 . The intruder sensor  24  is also deactivated, if it is in operation.  
         [0026]    If the doors are not unlocked (NO) by the door ECUs  16 , the ECU  10  determines at step  240  whether any object is detected by the object sensor  22 . If the object is detected (YES), the ECU  10  repeats the unlocking detection processing from step  220 . If the object is not detected any more (NO), that is, if the driver approaching the vehicle leaves the vehicle before unlocking the door, the ECU  10  stops applying the unlock standby instruction signal to the door ECUs  16 . After step  250 , the ECU  10  repeats the object detecting operation from step  120 .  
         [0027]    According to this embodiment, the transmitters  12  and receiver  14  are activated only when the object is detected as approaching the vehicle by the object sensor  22  after the vehicle is parked, power consumption by the transmitters  12  and receiver  14  can be reduced although the object sensor  22  need be held operating. Specifically, power consumption can be reduced, because current of about milliamperes flows in the object sensor  22  while current of about tens of milliamperes flows in the transmitters  12  and receiver  14 .  
         [0028]    Further, although the intruder sensor  24  is used to detect an intruder, it is not kept activated during parking of a vehicle but activated only after the detected key (object) is determined to be an unauthorized one (person). Therefore, power consumption of the intruder sensor  24  can be reduced as well.  
         [0029]    The present invention should not be limited to the disclosed embodiment but may be implemented in many other ways without departing from the spirit of the invention.