Abstract:
A method and apparatus for remotely activating vehicle control functions using a controller mounted in a vehicle and a remote keyless entry device having transmitter, a power source and at least one activatable input member corresponding to a vehicle control function. In response activation of an input member, a remote keyless entry control transmits a vehicle control function signal to the controller at a first transmitter power level. The control determines the distance between the controller and the remote keyless entry device and adjusts the transmitter power level to the minimum power level required to support communication between the controller and the remote keyless entry device. In one aspect, the control, in response to the absence of the return signal from the controller of predetermined signal strength, increases the transmitter power magnitude to a second power magnitude and retransmits the control signal. In an other aspect, the control generates the first control signal at a first high power level and decreases the power level in proportion to the magnitude of the return signal received from the controller.

Description:
BACKGROUND 
       [0001]    The present invention relates, in general, to remote keyless entry (RKE) system fobs. Wireless key fobs are widely used for vehicle access and to remotely control vehicle functions, such as locking or unlocking the door, remote engine starting, flashing of emergency horns and lights, as well as to control, locate and provide information feedback. The use of such wireless key fobs is being extended to longer range, bi-directional date transmission, and information displays on the fob. From  111   a , just copy over its entire background. 
         [0002]    With these added capabilities comes much greater power consumption and requirements for a new battery and power management strategies. Rechargeable batteries and various forms of recharging methods will add cost and weight to the fob as well as the need for periodic recharging. 
       SUMMARY 
       [0003]    A method and apparatus for remotely controlling a vehicle control functions from a remote entry device and a remote keyless entry device mountable in a vehicle. 
         [0004]    The method includes the steps of transmitting a vehicle function control signal from a remote entry device to the controller at a first transmitter power level; determining the distance between the controller and the remote entry device; and in response to the determined distance, adjusting the transmitter power level to the minimum power level required to support communication between the remote entry device and the controller. 
         [0005]    The step of adjusting the transmitter power level further comprises the step of in the absence of a return signal from a controller to the remote entry device of a predetermined signal strength, changing magnitude of the transmitter power level by a determined amount to a different power level. 
         [0006]    The step of adjusting the transmitter power level also comprises the steps of: generating a first control signal to a first high transmitter power level and decreasing the transmitter power level in proportion to discrete preset successively decreasing levels to the magnitude of a return signal from the controller. 
         [0007]    The method also includes the step of activating predetermined vehicle control functions dependant upon a distance determined by the controller between the controller and the remote entry device. 
         [0008]    The vehicle remote keyless entry apparatus includes a remote keyless entry control adapted to be mounted in a vehicle to convert wireless signals from a remote entry device to actuation of vehicle control function; a transmitter and receiver coupled to the control; a remote keyless entry device having a transmitter and a receiver; at least one input member carried on the remote entry device for causing the remote keyless entry device to generate a control signal corresponding to a vehicle control function corresponding to at least one input member; a power source carried in the remote keyless entry device for providing power to the transmitter to transmit signals to the controller, the power source providing selectable transmitter power magnitudes; a control in the remote keyless entry device selecting a first power magnitude from the power source for the remote keyless entry device control upon activation of at least one input member; and the remote keyless entry device control operating to adjust the transmitter power level to the minimum power level required to support communication between the remote keyless entry device and the controller. 
         [0009]    The remote keyless entry device control responsive to a signal strength of a return signal from the remote keyless entry control. 
         [0010]    The control of the supply of power to the transmitter for re-transmitting the control signal corresponding to activation of at least one input member at the second different power magnitude level. 
         [0011]    The apparatus also includes means for controlling the supply of power to the transmitter in response to activation of at least one input member at a first high power level and decreasing the power level in proportion for discrete preset successive decreasing levels to the magnitude of the return signal received by the remote keyless entry device control from the remote keyless entry control. 
         [0012]    The control may activate vehicle control function dependent upon the distance determined by the control between the control and the remote keyless entry device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0013]    The various features, advantages, and other uses of the present invention will become more apparent by referring to the following detailed description and drawing in which: 
           [0014]      FIG. 1  is a pictorial representation of a vehicle remote keyless entry receiver and a remote fob; 
           [0015]      FIG. 2  is a block diagram of the control circuitry of the fob; 
           [0016]      FIG. 3  is a block diagram of the control circuitry for the vehicle RKE; 
           [0017]      FIG. 4  is a graph depicting the sequence of fob signal transmission power levels relative to the distance between the fob and the vehicle RKE; and 
           [0018]      FIG. 5  is a graph depicting another aspect of the fob signal transmitter power level sequence relative to the distance between the fob and the vehicle RKE. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Referring now to the drawing, and to  FIGS. 1 ,  2  and  3  in particular, there is depicted a vehicle  10  having a remote keyless entry or RKE apparatus  12  mounted therein. A wireless key fob and transmitter  14  is associated with the RKE  12  and is identifiable by a unique frequency match to enable only the fob  14  to transmit signals to the RKE  12  which are recognized by the RKE  12  as being valid for vehicle control functions. 
         [0020]    As shown in detail in  FIG. 2 , the fob  14  includes a control  20 , which may be a processor based control executing a control program stored in a memory. One or more input members or buttons  22  are mounted on the housing  24  of the fob  14 . The input members or buttons  22  are associated with a particular vehicle function, such as locking or unlocking the vehicle doors and/or trunk or hatch, lowering the vehicle windows, remotely starting the vehicle engine, flashing the vehicle horns and/or lights, etc. A display  26  may also be mounted in the fob housing  24  to display vehicle status or button  20  selection information. 
         [0021]    It will be understood that the shape of the fob housing  24 , the number and functions designated by the buttons  22 , the addition or non-provision of the display  26  can have any configuration. 
         [0022]    A power supply, such as a battery  30 , is contained in the housing  24  for powering the components of the fob  14  as shown in  FIG. 2 . A transmitter or a transmitter/receiver, transceiver or transponder  32  is mounted in the housing  24  for transmitting a data signal generated by the control  20  in response to depression or activation of one of the buttons  22 . The transmitter  32  has a frequency of operation between 300 MHz to 450 MHz, for example only. 
         [0023]    The user depresses or activates one of the buttons  22  associated with the desired vehicle function that the user wishes to initiate. The input signal from the button  22  wakes up or activates the processor in the control  20  which outputs a data stream to the transmitter  32 . The data stream may include a data preamble, the actual vehicle function command, i.e., unlock vehicle doors, etc., an optional rolling code for vehicle to vehicle security, and possibly one or more check bits. This signal is sent by the transmitter  32  through an antenna  34  to the RKE  12  where it is received by a receiver  40  through an antenna  42 . The signal is demodulated by a vehicle access controller  44  which may also a microprocessor based controller  44 . The controller  44  outputs a signal to a vehicle function control device or to a vehicle body computer which implements the desired vehicle function. 
         [0024]    As is easily apparent, a long life for the battery  30  in the fob  14  is important. At the same time, the fob  14  must remain lightweight and small in size for easy portability and storage in a user&#39;s pocket, or purse, or on the user&#39;s key ring. To minimize power requirements for each signal transmitted by the transmitter  32  of the fob  14  and to meet FCC wireless signal interference requirements, the power level or magnitude of the signal sent by the fob transmitter  32  has a prescribed maximum. This creates a distance between the fob  14  and the vehicle RKE  12  within which the signal from the fob  14  will be received by the vehicle RKE  12 ; but beyond which the strength of the signal transmitted by the fob  14  will be too low to be received or recognized as a valid signal by the receiver  12 . This distance can be from 1 to 10 meters. The distance can be increased to 10 to 20 meters, or more for example, by increasing the signal strength or power magnitude of the signal sent by the fob transmitter  32 , but excessive battery power consumption must then be considered. 
         [0025]    As shown in  FIG. 1 , the fob  14  utilizes an adapted transmission power scheme to enhance battery life in unidirectional or bidirectional fob systems. The adaptive transmission power scheme is based on the premise that only enough power is utilized to cover the distance between the vehicle RKE  12  and the fob  14  as necessary and any higher power level which wastes battery power is unnecessary. 
         [0026]    As shown in  FIG. 1 , four ranges or zones labeled range  1 , range  2 , range  3  and range  4  are established in a radial direction from the vehicle RKE  12  which is used as a center point. The radial distance of each range may vary depending upon the fob battery  30  power level and application requirements, but by way of example only to understand the adaptive transmission power scheme, range  1  is 1 to 30 meters, range  2  is 30 to 100 meters, range  3  is 100 to 500 meters and range  4  is any distance greater than 500 meters from the vehicle RKE  12 . 
         [0027]    Also for purposes of this discussion, the maximum power of the signal transmitted by the transmitter  32  of the fob  14  will be insufficient to constitute a valid signal which can be received and recognized by the vehicle RKE  12  when the distance between the RKE  12  and the fob  14  is greater than 800 meters. 
         [0028]    In one aspect, a power level adjustment means is provided in control  30  to regulate the magnitude of power supplied by the battery  30  to the fob RKE transmitter  32 . Three reset power levels  50 ,  52  and  54 , i.e., low, medium and high, respectively, are shown by way of example only in  FIG. 4 . 
         [0029]    Two to four or more preset power levels may be provided. Alternatively, the power level adjustment means may increment the power level in incremental steps starting with the low power level. 
         [0030]    According to one aspect of the adaptive transmission power scheme, when the user presses one of the buttons  22  on the fob  14  to communicate with the vehicle RKE  12 , an initial low power level  50  is selected by the control  20  and supplied to the transmitter  32  for transmitting a RF signal containing data pertaining to the button  22  which was pressed, authentication data, check bits, etc. The receiver or transceiver in the fob  14  waits briefly for an acknowledgement or return signal to be sent by the vehicle access controller  44  in the RKE  12  through the RKE transmitter  40 . If this return signal, which is an indication that the vehicle RKE received and was able to decode the signal from the fob transmitter  32 , is not received within a predetermined time, such as two seconds, the fob control  20  increases the power of the signal transmission to the next preset or medium power level  52  and retransmits the same signal containing data corresponding to the button  22  which was pressed by the user. It should be noted that the user does not have to take any additional action to repress the same button  22 . The control  20  again awaits for a predetermined time, i.e., two seconds, for example, for the return signal from the RKE  12 . 
         [0031]    If the return signal is not received with the predetermined time, the control  20  increases the power level to the next or third high power level  54  and again retransmits the signal through the transmitter  32  to the vehicle RKE. If a return signal  56  is received within a predetermined time by the fob control  20 , the high power level  54  is maintained for any subsequent signal transmissions by the fob  14  within a predetermined time defining a signal activation sequence or series of events. 
         [0032]    It will be understood that if the distance between the fob  14  and the RKE  12  is within range  2 , a return signal from the vehicle RKE would have been received after the fob  14  transmitted a signal at the medium power level  52 . Likewise, if the fob  14  is located within range  1  to the RKE  12 , a low power level signal  50  would have enabled a valid return signal to be received by the fob control  20 . 
         [0033]    The sequence of actions of the successive power level variations can be presented by the control  20  on the fob display  26 , either in a form of text messages, such as “transmitting at low power level”, “transmitting at medium power level”, “transmitting at high power level”, etc. In addition, a no signal message could be presented when the fob  14  is located beyond range  4  from the RKE  12  which would be an indication to the user that he or she would have to move closer to the vehicle to implement the desired remote access functions through the fob  14 . 
         [0034]    Referring now to  FIG. 5 , another aspect of the adaptive transmission power scheme is disclosed. In this aspect, upon an initial depression of one of the fob buttons  22 , an initial high power level burst  60  is applied by the control  20  for transmission to the transmitter  32  to the RKE  12 . The control  20  then awaits for a return signal from the RKE  12 . If the vehicle RKE  12  responded within the time period, the signal strength of the return signal from the vehicle RKE which is proportional to the distance between the RKE  12  and the fob  14 , is determined by the control  20  and subsequent transmissions from the fob  14  will take place at a power level proportional to the lowest power level which was determined from the measured signal strength of the return signal from the vehicle RKE  12 . The power levels associated with incremental return signal strengths can be provided in a lookup table in the memory accessed by the control  20  or by a simple voltage proportioning circuit in which the ratio of the signal strength of the return signal to the maximum power level  60  of the initial signal transmitted by the fob transmitter  32  would be determined and the fob transmitter  32  power level reduced proportionately. 
         [0035]    This adaptive transmission power scheme takes into account the various ranges  1 - 3  in that the initial high power level burst  62  will always generate a return signal from the RKE when the fob  14  is within ranges  1 ,  2  or  3  from the vehicle RKE  12 . However, any subsequent signal transmissions from the fob  14  will be at the minimum power level required to successfully transmit the signal from the fob  14  to the vehicle RKE  12  thereby using only the lowest possible fob  14  battery power. 
         [0036]    In conclusion, the fob transmitter power is matched by the adaptive transmission power scheme described above to the estimated effective range for each fob signal transmission. This ensures that wireless signals are successfully transmitted between the fob  14  and the RKE  12  within the various effective ranges of signal communications established for the particular fob  14  and RKE  12  at the lowest possible fob power level. This conserves battery power and extends the life of the battery. 
         [0037]    It will be understood that the example of both aspects of the adaptive transmission power scheme described above which utilizes by way of example only the ranges  1 ,  2 ,  3  and  4  was described for an RKE system wherein any of the possible vehicle functions assessable by the fob buttons  22  can be selected and activated when a signal corresponding to a button  22  depression is successfully transmitted by the fob transmitter  32  to the vehicle RKE  12 . It is also possible, for example, to enable any single or group of vehicle control functions, such as a remote engine start signal, to be successfully completed only when the user is within a particular range or ranges. Similarly, the RKE  12  can be programmed to recognize and process signals from the fob  14  at a power level consistent with ranges  2  or  3  to unlock vehicle doors, lower vehicle windows, etc. Similarly, the maximum range  3  would allow successful signal completion between the fob  14  and the RKE  12  only for emergency activation of the vehicle horns or lights or to assist the user in locating the vehicle. 
         [0038]    Thus, the control  20  could operate according to the first aspect of the adaptive transmission power scheme for any button  22  or vehicle control function which may be selected by the user. The second aspect could still be implemented with an initial high power level signal  60 , but the subsequent reduction and signal power strength based on the return signal strength will be divided into ranges  1 ,  2  and  3  depending upon which button or control function is selected by the user. For example, if the user is within range  3  from the RKE  12 , and depresses the door unlock button, even though the signal strength of the return signal from the RKE would cause the fob control  20  to implement the subsequent signal transmissions to a certain power level, such reduced power level signals will not be successfully received by the RKE until the fob  14  is located within the prescribed range  1 ,  2  or  3  from the RKE  12  for the selected functions.