Abstract:
An apparatus is provided for locating a vehicle electronic key including a fob for receiving a low frequency signal, measuring the low frequency signal strength, and providing a radio frequency response signal, a portion of the response signal including the signal strength determination. A low frequency antenna is located within the vehicle cabin for providing the low signal. A controller receives the response signal and compares the signal strength against a predetermined threshold. A vehicle engine immobilizer is responsive to the controller where the controller controls the immobilizer in response to the comparison.

Description:
TECHNICAL FIELD 
     The present invention relates to vehicle electronic key systems and is particularly directed to an apparatus for locating a vehicle electronic key and determining whether the electronic key is inside or outside of the vehicle&#39;s cabin. 
     BACKGROUND 
     Vehicle entry and ignition systems that use a unique, physical key to enter and start the vehicle engine are well known in the art. Also, electrical fobs that wirelessly transmit an electrical signal such as a radio frequency (“RF”) signal for controlling locking and unlocking functions of the vehicle doors are known. Recently, passive keyless systems have been developed for vehicles that include a fob carried by a vehicle operator that control door lock/unlock functions and engine immobilization automatically in response to the presence of the fob. As the operator approaches the vehicle and touches a portion of the vehicle, such as the door handle, the vehicle lock/unlocking system automatically sends an interrogation signal to the fob and monitors for a fob response signal. Once identification and authentication occurs between the vehicle system and fob, and if authentication is accomplished, the door is unlocked. Once inside the vehicle, if the fob carried by the operator is the correct fob associated with that vehicle, the vehicle can be started with a simple pushing of a start button located on the vehicle dash, i.e., no form of physical key is needed to start the vehicle. Such systems have become known as “keyless-go” ignition systems. 
     As part of the authentication process between the vehicle system and the fob, identification (“ID”) codes are sent and compared. For example, the fob may send a coded ID signal via RF to an on-board vehicle system. The on-board vehicle system determines if the received ID code is a valid ID from a fob associated with that vehicle. If the ID code is a valid code, as determined via a comparison against a prestored code, the vehicle will be able to start when the start button is pushed. If the received ID code is not valid, i.e., the received code does not match the prestored code, the vehicle engine is immobilized. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an apparatus is provided for locating an electronic key in a vehicle system and determining if the electronic key is inside the vehicle cabin or outside of the vehicle cabin. 
     In accordance with one example embodiment of the present invention, an apparatus is provided for locating a vehicle electronic key including a fob for receiving a low frequency signal, measuring the low frequency signal strength, and providing a radio frequency response signal, a portion of the response signal including the signal strength determination. A low frequency antenna is located within the vehicle cabin for providing the low signal. A controller receives the response signal and compares the signal strength against a predetermined threshold. A vehicle engine immobilizer is responsive to the controller where the controller controls the immobilizer in response to the comparison. 
     In accordance with another example embodiment of the present invention, an apparatus is provided for locating a vehicle electronic key comprising a fob having a low frequency antenna in three coordinates for receiving a low frequency signal and providing three measured low frequency signal strength values. The fob further includes means for determining a single value signal strength of the monitored low frequency field and provides a radio frequency signal that includes the low frequency signal strength signal information. A low frequency transmitter is located within the vehicle cabin for providing a low frequency signal though out a cabin of a vehicle. A controller for storing a premeasured low frequency signal strength map of the vehicle cabin is provided and compares the measured signal strength signal against the stored premeasured low frequency signal strength map of the vehicle cabin to determine if the fob is inside of the vehicle cabin. A vehicle engine immobilizer is responsive to the controller. The controller controls the immobilizer in response to the comparison. 
     In accordance with another example embodiment of the present invention, an apparatus is provided for locating a vehicle electronic key comprising a low frequency transmitter for transmitting a low frequency energy signal in the vehicle of a cabin and an electron vehicle key for receiving the low frequency energy signal, measuring the low frequency energy signal strength, and transmitting a radio frequency signal having a unique identification code and a field strength code. A controller connects to the vehicle ignition system for monitoring the radio frequency signal and enabling the vehicle ignition system only if the identification code matches a prestored code and the field strength code indicates, via a threshold comparison, that the electronic key is inside of the vehicle cabin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which: 
         FIG. 1  is a top plan view of a vehicle having an apparatus for locating a vehicle electronic key in accordance with one example embodiment of the present invention; 
         FIG. 2  is a top plan view similar to  FIG. 1  showing the approximate extent of the LF fields provided by the LF antennas of  FIG. 1 ; and 
         FIG. 3  is a side view partially in section of the fob shown in  FIG. 1  and made in accordance with one example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a vehicle  10  includes an electronic key system  12  for locating a vehicle electronic key in accordance with one example embodiment of the present invention. The electronic key system  12  provides passive entry unlocking and locking of the vehicle entry points and also permits passive starting of the vehicle ignition system by simply pushing a start button on the vehicle dashboard as described below. 
     The electronic key system  12  includes a fob  14  carried by the vehicle operator and a vehicle system  16  mounted in the vehicle  10 . The vehicle system  16  includes a plurality of low frequency (“LF”) transmission antennas arranged to provide the interior cabin  18  of the vehicle  10  with a LF interrogation signal. Specifically, a central LF antenna  20  is located near a console of the vehicle. A first B-pillar LF antenna  22  is located in the driver&#39;s b-pillar of the vehicle  10 . A second B-pillar LF antenna  24  is located in the passenger&#39;s B-pillar of the vehicle  10 . A trunk LF antenna  26  is located in the trunk of the vehicle  10 . The distance traveled by the LF signals by each of antennas is relatively short. The strength of the LF field transmitted by any of the LF antennas  20 ,  22 ,  24 , and  26  decreases as the inverse cube of the distance. 
     Referring to  FIG. 2 , a field pattern  30  can be seen generated by the LF antenna  20  from the console location. The outer field  32  can be seen generated by the LF antenna  22  from the B-pillar on the driver&#39;s side of the vehicle. The outer field  34  can be seen generated by the LF antenna  24  from the B-pillar on the passenger&#39;s side of the vehicle. The field by the trunk LF antenna  26  is, for the most part, confined to the interior of the vehicle (as long as the trunk lit remains closed) and into the cabin  18  covering the rear package shelf. 
     Referring again to  FIG. 1 , the LF antennas  20 ,  22 ,  24 , and  26 , are connected to an electronic control unit (“ECU”)  40  for controlling the energization of the LF antennas. The ECU  40  is also connected to a sensor  42  in the driver&#39;s door handle and a sensor  44  in the passenger&#39;s door handle. Whenever the door handles  42  or  44  have been touched, the ECU  40  will activate the associated LF antenna  22  or  24  to provide a LF interrogation signal so as to determine if a fob  14  is in proximity to the outside of the vehicle. The ECU also includes a radio frequency (“RF”) receiver for receiving a response signal from the fob  14 . After an interrogation signal is received by a fob associated with the vehicle, it provides a RF response signal having the appropriate ID code that is then received by the ECU RF receiver. If the code matches a prestored code, the ECU  40  will send an unlock signal to the door unlocking devices to unlock the vehicle door locks. 
     Referring to  FIG. 3 , the fob  14  includes electronic circuitry  50  mounted on a printed circuit board (“PCB”)  51  including a microcontroller  52  for controlling the fob&#39;s several functions. Those skilled in the art will appreciate that the control functions of the fob  14  could also be accomplished using discrete circuitry or an application specific integrated circuit (“ASIC”). The fob  14  includes several buttons  54 ,  56 , and  58  that a vehicle operator could use could to control vehicle convenience functions controlled by the fob  14  such as door locking/unlocking, etc. 
     The fob  14  includes three LF antennas oriented to detect LF energy relative to a self defined X, Y, Z coordinate system. In particular, LF antenna  60  detects LF-X, antenna  62  detects LF-Y, and antenna  64  detects LF-Z. To establish a LF intensity value, the controller  52  takes each of the values measured by LF-X, LF-Y, and LF-Z, squares them and then sums the squares. This will be referred to herein as the LF sum of the squares. 
     The fob  14  further includes an RF transmitter  70 . When the fob  14  receives an LF interrogation signal from one of the associated vehicle B-pillar antennas  22  or  24 , it responds by transmitting a (“RF”) response signal that is received by the ECU  40 . All of the electronic circuitry of the fob  14  is powered by an internal battery  72 . 
     Referring again to  FIG. 1 , as part of the keyless-go system of the vehicle, a push button ignition module  80  is connected to the ECU  40 . The ECU  40  is connected to an engine immobilizer/starting circuitry  82  that is, in turn, operatively coupled to the vehicle engine  84 . If an associated E-key, i.e., fob  14  is located within the cabin  18  and has been verified by the ECU  40 , the ECU  40  will disable the immobilizer  82  so that pushing of the start button on the ignition module  80  will allow the engine  84  to start. 
     In accordance with one example embodiment of the present invention, once the ECU  40  unlocks the vehicle doors (using LF signals generated by the B-pillar LF antennas  22  or  24 ), and upon activation of the start button  80 , only the console LF antenna  20  is energized to provide an LF interrogation signal  30  predominately on the inside of the vehicle cabin  18 . The controller  52  uses the LF-X antenna  60 , the LF-Y antenna  62 , and the LF-Z antenna  64  to measure the LF field strength by squaring each of the intensity signals and summing the squares. In effect, the controller  52 , via an RSSI circuit technique determines signal strength of the LF field. 
     For each vehicle platform for which the present invention is to be used, a LF field is generated by the console antenna  20 . At a plurality of X, Y, and Z points within and exterior to the vehicle cabin  18 , the LF field strength is measured and mapped. This measured field strength map is then stored in the ECU  40  with the intention to define an inside the vehicle determination for immobilization deactivation, that only extends beyond the side door glass by less than 20 cm. The RSSI field strength measured and transmitted by the fob  14  via RF to the ECU  40  is then compared against the prestored LF field strength map in the ECU  40  so that the ECU can make a determination as to whether the fob  14  is inside of the cabin  18  or outside of the cabin  18 . For example, it may be determined that at a minimum, all LF field strength readings inside of the cabin  18  from the predetermined measurements always are greater than 3 and greater than 20 cm outside of the cabin are less than 3. If the fob sends a RF field strength reading of 4, the ECU “knows” that the fob is inside of the cabin  18  and will disable the immobilizer  82 . If the fob sends a RF field strength reading of 1, the ECU “knows” that the fob is greater than 20 cm outside of the cabin  18  and will not disable the immobilizer  82 . Again, the prestored mapping of the field strength of the cabin  18  is platform dependent and is performed empirically. 
     If the console antenna  20  does not provide sufficient coverage within the cabin  18 , it is possible to use a trunk antenna  26 . Such antenna would not be energized at the same time as the console antenna but alternatively with the console antenna. The trunk antenna field has been found to not generate a field much beyond the rear area of the trunk as long as the trunk lid is down. 
     Alternatively, the two side pillar antennas could also be used in a sequential energization by using a field strength mapping and triangulation technique to locate the position of the fob within or outside of the cabin  18 , and utilizing a multiple antenna map. 
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.