Passive entry system and method for a vehicle

A passive entry system and method for determining the location of a remote transmitter positioned near a vehicle. The system and method may include an irregularly shaped authorization zone. The authorization zone may be formed using as least three LF antennas. Alternatively, at least two antennas may be used to form at least one elliptically shaped authorization zone. A controller may determine the location of the fob when the fob is physically positioned within the authorization zone.

TECHNICAL FIELD

One or more embodiments of the present disclosure relate to a passive entry system that may be used to determine the location of a remote transmitter relative to a vehicle.

BACKGROUND

Exemplary passive entry systems for vehicles are described in U.S. Pat. No. 6,906,612 issued to Ghabra et al. and entitled “System and Method for Vehicle Passive Entry Having Inside/Outside Detection;” U.S. Pat. No. 7,446,648 issued to Ghabra and entitled “Passive Activation Vehicle System Alert;” U.S. Pat. No. 4,873,530 issued to Takeuchi et al. and entitled “Antenna Device In Automotive Keyless Entry System;” U.S. Pat. No. 4,942,393 issued to Waraksa et al. and entitled “Passive Keyless Entry System;” U.S. Pat. No. 5,499,022 issued to Boschini and entitled “Remote Control System For Locking And Unlocking Doors And Other Openings In A Passenger Space, In Particular In A Motor Vehicle;” U.S. Pat. No. 5,751,073 issued to Ross and entitled “Vehicle Passive Keyless Entry And Passive Engine Starting System;” U.S. Pat. No. 6,049,268 issued to Flick and entitled “Vehicle Remote Control System With Less Intrusive Audible Signals And Associated Methods;” and U.S. Pat. No. 6,236,333 issued to King and entitled “Passive Remote Keyless Entry System.”

SUMMARY OF THE INVENTION

A method and system of determining the location of a fob is disclosed. The method and system may include at least three antennas located about the vehicle. The antennas may be capable of transmitting a Low Frequency (LF) signal to a fob. The fob may receive the LF signal and determine a received signal strength indication (RSSI) of each received LF signal. The fob may transmit one or more UHF signals that include the RSSI. A controller may be configured to receive the one or more signals from the fob and compare the received signal amplitudes against a predefined authorization zone. The predefined authorization zone may include a number of inclusion and exclusion areas. At least one authorization zone may be circularly shaped with a central point radiating from each of the at least three antennas. The controller may further be configured to determine the location of the fob by determining if the fob is located within either the exclusion or inclusion areas.

An alternate method and system of determining the location of a fob is disclosed. The method and system may include at least two antennas located about the vehicle. The antennas may be capable of transmitting a Low Frequency (LF) signal to a fob. The fob may receive the LF signal and determine a received signal strength indication (RSSI) of each received LF signal. The fob may transmit one or more UHF signals that include the RSSI of the at least two received antennas. A controller may be configured to receive the signal from the fob and compare the received signal amplitudes against a predefined authorization zone. At least one of the authorization areas may be an elliptically shaped authorization area established using at least two antennas. The controller may determine the location of the fob by determining if the fob is located within the one elliptically shaped authorization area.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

With reference toFIG. 1, a vehicle10is illustrated which may include a passive entry system, denoted generally by reference numeral12, according to one non-limiting aspect of the present disclosure. The passive entry system12may include a vehicle controller14located within vehicle10. The vehicle controller14may further include one or more transceiver units having a receiver and/or transmitter unit that communicate with one or more antennas16,18,20positioned about vehicle10. The present disclosure contemplates that the transceiver units may be separate from the vehicle controller14and may be positioned about, or included in combination with antennas16,18,20. The vehicle controller14may further be configured to operate a door lock mechanism (not shown), start the ignition of the vehicle10and/or perform a variety of other functions related to the operation of the vehicle10.

The passive entry system12may further include a remote hand held transmitter, which is conventionally referred to as a fob22, which may be carried and/or operated by an operator. The fob22may be a separate unit, or may be part of an ignition key head. The fob22may include a fob controller24having a transceiver unit. The transceiver unit may include a transmitter and receiver for receiving and/or transmitting signals from the fob22. The present disclosure also contemplates that the transceiver unit may be separate from the fob controller24. The fob22may further include an antenna26configured to send and/or receive signals to and/or from antennas16,18,20.

The present disclosure contemplates that one or more signals28,30,32may be transmitted from the antennas16,18,20without an operator activating a switch or pushbutton on the fob22. The signals28,30,32may include a wakeup signal intended to activate a corresponding fob22. In turn, the fob22may receive the signals28,30, and determine the strength or intensity of the signals28,30,32.

For example,FIG. 2illustrates a graph40of the signals28,30,32respectively transmitted by antennas16,18,20that may be received by the fob22. The graph40illustrates the strength or intensity of each received signal28,30,32, more commonly referred to as the Received Signal Strength Indication (RSSI). Based upon the determined RSSI levels of each signals28,30,32, the fob controller24may determine a position report indicating the distance of the fob22relative to each antenna16,18,20. The present disclosure contemplates that the location of the fob22may also be determined using a predefined series of calibrated values that equate the determined RSSI value to a distance value.

The fob22may then transmit a response signal34that includes the position report to the antennas16,18,20. The vehicle controller14may determine the location of the fob by verifying whether the received response signal34indicates that the fob22is located within a valid authorization zone. If so, the vehicle controller14may begin an authentication/response challenge sequence between the vehicle controller14and the fob22. Upon a successful authentication/response sequence, the vehicle controller14may determine whether a particular vehicle function should be performed if the fob22is within some pre-defined distance, or location, relative to the vehicle10.

For example, if the fob22is located within a predefined authorization zone outside the vehicle10, the controller12may activate one or more door lock mechanisms (not shown) to unlock one or more of the vehicle doors. Alternatively, if the fob22is located within a predefined authorization zone within the cabin of the vehicle10, the vehicle controller14may activate the ignition of the vehicle10.

The present disclosure further contemplates that antenna26located within the fob22may be configured to transmit long-range ultra-high frequency (UHF) signals to the antennas16,18,20of the vehicle10and receive short-range Low Frequency (LF) signals from the antennas16,18, of the vehicle10. However, the present disclosure contemplates that separate antennas may be included within the fob22to transmit the UHF signal and receive the LF signal. In addition, the antennas16,18,20may be configured to transmit LF signals to the fob22and receive UHF signals from the antenna26of the fob22. However, the present disclosure contemplates that separate antennas may be included within the vehicle10to transmit LF signals to the fob22and receive the UHF signal from the fob22.

The fob22may also be configured so that the fob controller24may be capable of switching between one or more UHF channels. As such, the fob controller24may be capable of transmitting the response signal34across multiple UHF channels. By transmitting the response signal34across multiple UHF channels, the fob controller24may ensure accurate communication between the fob22and the antennas16,18,20.

FIG. 3illustrates an exemplary, flow diagram200according to one or more embodiments of the present application. However, it should be noted that the flow diagram200illustrated inFIG. 3is merely exemplary and the operation, function, or steps of the flow diagram200may be performed in a fashion other than the order described herein.

The flow diagram200may begin at operation202with an LF wakeup sequence that may include one or more wakeup signals being sent by the vehicle controller14to the fob22. Upon receiving the LF wakeup sequence, the flow diagram200may proceed to operation204.

In operation204, the fob controller24may determine the RSSI of each received LF wakeup signal. Once the fob controller24determines the RSSI of each LF wakeup signal, the flow diagram200may proceed to operation206.

In operation206, the fob controller24may transmit the fob response signal which includes the RSSI value of each antenna16,18,20as determined by the fob controller24. Once the fob response signal has been transmitted, the flow diagram proceeds to operation208.

In operation208, the vehicle controller14determines the location of the fob22using the received fob response signal. The vehicle controller14may determine the location by determining if the received fob response signal indicates that the fob22is within a predefined authorization zone.

For example, in one non-limiting embodiment of the present disclosure, the authorization zone may be established using a series of inclusion and exclusionary criteria based on the RSSI of each antenna16,18,20. The present disclosure contemplates that the authorization zone may be any irregular geometrical shape so long as the span of the shape is confined to the coverage of the LF antennas.

Using the irregular shaped authorization zone, the fob controller24may incorporate a triangulation verification procedure using the RSSI of each antenna16,18,20to determine if the fob22is located within the boundaries of the authorization zone. The fob controller24may begin the triangulation verification procedure by first determining whether the fob22is located within any specified exclusion area. If the vehicle controller14determines that the fob22is located within one of the exclusionary areas, the fob22may be denied access to the authorization zone. If the fob controller24determines that the fob22is not located within at least one of the exclusion areas, then the fob controller24may determine if the fob22is located within at least one specified inclusion areas. If the fob controller24determines that the fob22is located within at least one of the inclusion areas, then the fob22may be allowed access to the requested authorization zone.

For example,FIG. 4illustrates an exemplary irregular shaped authorization area. As illustrated, each antenna16,18,20may be configured to radiate a circular shape40,42,44. The radiation pattern may extend from a central point starting at each respective antenna16,18,20outward toward the circumference of each shape40,42,44. Furthermore, the vehicle controller14may use the shapes40-44to define one or more authorization zones having a number of exclusion and inclusion areas.

The fob controller24may determine the authorization area based upon well known Boolean principles. For example, the exclusion/inclusion area criterion may be defined using following exemplary, equation:
(a≦X≦b) AND (c≦Y≦d) AND (e≦Z≦f)  (1)
Where,X is the RSSI value of antenna16;Y is the RSSI value of antenna18;Z is the RSSI value of antenna20;a, b, c, d, e, f are a set of predefined constants.

Using Equation (1), a geometrical interpretation may be defined for the circular shapes40,42, and44. For example, if the predefined values were established as a=100, b=255, c=0, d=255, e=0 and f=255, the vehicle controller14may determine that the fob22is located within the authorization zone when the RSSI value of antenna16is greater than 100. Since each RSSI value may be converted to a distance value, there will be circle around each antenna16,18,20where the fob22may be detected.

Another non-limiting example of an inclusion/exclusion area criterion may be defined using the following exemplary, equation:
[(100≦X) AND (0≦Y) AND (0≦Z)] OR [(0≦X) AND (100≦Y) AND (0≦Z)] OR [(0≦X) AND (0≦Y) AND (100≦Z)]  (2)

As illustrated by Equation (2), the vehicle controller14may determine that the fob22is within an excluded area only if the RSSI value of each antenna16,18, and20was determined to be zero (0). Conversely, if the vehicle controller14verifies that the RSSI value of antenna16,18, or20is greater or equal to 100, then the vehicle controller14will determine that the fob22is located within one of the inclusion areas.

Using predefined Boolean criterion, any number of authorization zones by be established by the vehicle controller14. For example, with reference toFIG. 4, the vehicle controller14may define the authorization areas as the region surrounding the vehicle doors using the following exemplary, equation:
[(100≦X) AND (100≦Y)] OR (100≦Y) OR [(100≦Y) AND (100≦Z)]  (3)

Using the Boolean criteria established in Equation (3), the inclusion areas forFIG. 4may be defined as the areas48,50, and52. Conversely, the exclusion areas may be defined by areas46and54.

Using the triangulation verification procedure, the vehicle controller14may first attempt to determine whether the fob22is located within at least one of the exclusion areas46and54. If yes, the vehicle controller14may deny the fob22access to the requested authorization zone. However, if the fob22is not located within at least one of the exclusion areas, the vehicle controller14may determine whether the fob22is located within at least one of the inclusion areas48,50, and52. If yes, the vehicle controller14may unlock one or more of the vehicle doors after a successful authentication security protocol is completed.

In another non-limiting embodiment,FIG. 5illustrates that the authorization zone may be defined using only two of the antennas16,20. As illustrated, the authorization zone may be determined using a pair of spherical or circular shapes60,62whose central point radiates outward from antennas16,20, respectively. Also, each antenna16,20may be used to define the foci of an elliptical shape64. The vehicle controller14may use the elliptical shape64to define an authorization zone for the cabin area of the vehicle10.

Using the elliptical authorization zone illustrated inFIG. 5, the fob controller24may not need to determine the absolute location of the fob22using the triangulation verification procedure as described above with reference toFIG. 4. Using the characteristic shape of the ellipse, an authorization zone may be based on the signal amplitudes from each antenna16,20. Furthermore, the fob controller24may determine the location of the fob22by verifying whether the fob22is located within the boundaries of elliptically shaped authorization zone.

The present disclosure contemplates that using elliptical interpolation to define the cabin area of the vehicle10may be advantageous since only two antennas are required. Furthermore, by using elliptical interpolation, the two antennas16,20may operate to define a pair of foci76,78of the elliptical shape64, as well as, a pair of radii80,82for each circular shape60,62. Hence, the two antennas16,20may operate to form three geometrical shapes (i.e., circular shapes60,62and elliptical shape64).

The present disclosure further contemplates that antennas16,20may be positioned within the vehicle10so as to be along the major axis of the elliptical shape64. Furthermore, the antennas16,20may be positioned within the vehicle10so as to operate as a pair of foci76,78for the elliptical shape64. As such, the vehicle controller14may determine the curvature of the elliptical shape64by determining the major diameter and the distance between the pair of foci76,78. The present disclosure contemplates that the distance between the foci76,78may be determined by the vehicle controller14as the distance between antennas16,20. Because the location of the antennas16, may be predetermined, the distance between the pair of foci76,78may also be predetermined. The present disclosure further contemplates that the vehicle controller14may determine the major diameter by summing the distances from a point79along the elliptical shape64to the pair of foci76,78. The vehicle controller14may also be capable of varying the size of the elliptical shape64by modifying the major diameter.

Therefore, regardless of the point79selected along the edge of the elliptical shape64, the sum of the distances from the two foci76,78to the point79may equate to a constant value (i.e., 76+78=Constant). As such, the vehicle controller14may be able to define the authorization zone for the elliptical shape64using the following, exemplary equation:
(X+Z)≧D(4)
Where,X is the RSSI value of antenna16;Z is the RSSI value of antenna20; andD is the constant value that may characterize the ellipse along with the distance between the two foci76,78.

As illustrated by Equation (4), the fob controller24may determine that the fob22is located within the elliptical authorization area when the sum of the RSSI signals X and Z is greater than the constant that characterizes the elliptical shape64. The present disclosure also contemplates that the vehicle controller14may determine the distance from the fob22to the antennas16,20by converting the RSSI values X and Z to distance values (X′, Z′). As such, the vehicle controller14may determine whether the fob22is located within the region of the elliptical shape64if the sum of distance values (X′, Z′) is less than the major diameter of the elliptical shape64.

With reference back to the drawings,FIG. 6illustrates another non-limiting embodiment of the present disclosure. Again, three antennas16,18,20may be used to provide multiple authorization zones using both circular and elliptical shapes that cover the entire cabin area. As illustrated, a circular shape84may be defined using antenna16. In addition, an elliptical shape86may be formed using antennas16and18and another elliptical shape88may be formed using antennas16and20. Lastly, another elliptical shape90may be formed using antennas18and20.

By configuring the antennas16,18,20as shown inFIG. 6, a greater number of inclusion/exclusion areas92,94,96,98,100,102,104,106,108,110, and112may be formed.FIG. 6also illustrates that three elliptical authorization zones86,88, and90may be established. Each elliptical authorization zone86,88, and90may allow the controller to more accurately determine the location of the fob22relative to the interior or exterior of the vehicle10. Furthermore, the use of three separate elliptical authorization zones86,88, and90may allow the vehicle controller14the ability to determine the location of the fob22without having to proceed with the triangulation verification procedure.

With reference back toFIG. 3, if the vehicle controller14determines the fob22to be within the authorization zone, flow diagram200proceeds to operation210. However, if the vehicle controller14does not determine that the fob22is located within at least one of the authorization zones, flow diagram200proceeds back to operation202.

In operation210, the vehicle controller14may begin the authentication security protocol with the fob22that is determined to be located within one of the authorization zones. The authentication security protocol may include an authentication challenge signal transmitted by one or more of the antennas16,18,20. In return, the fob22may transmit a response authentication signal to the vehicle controller14. If the vehicle controller14determines the response authentication signal to be valid, the vehicle controller14may perform a particular vehicle operation (e.g., start the ignition of the vehicle or unlock one or more of the vehicle doors).

While embodiments of this disclosure may have been illustrated and described, it is not intended that those embodiments illustrate and describe the only embodiments of the disclosure. Rather, the words used in the above disclosure are words of description, rather than limitations and it should be understood that various changes may be made to the above description without departing with the spirit and scope of the disclosure. Thus, specific details disclosed are merely representative basis for teaching one skilled in the art to practice the present disclosure.