Patent Publication Number: US-2007120642-A1

Title: Vehicle with passive key fob having presence detection arrangement with key fob

Description:
RELATED APPLICATIONS  
      The application claims priority to U.S. Provisional Application No. 60/740,069 which was filed on Nov. 28, 2005. 
    
    
     BACKGROUND OF THE INVENTION  
      Modern vehicles are being provided with key fobs that allow electronic access to the vehicle. One type of key fob is a so-called passive key fob, wherein the key fob is solely an electronic item. The key fob is inserted into a reader. The reader looks for an identifying code on the key fob, and if an appropriate code is found, it allows actuation of the vehicle such as through an ignition switch.  
      In the prior art, insertion of some device other than a key fob into a key fob reader will wake the circuit, and cause the circuit to query the device in the reader. A mechanical switch and contact mechanism has been utilized. These mechanical switches and contact mechanisms have been subject to failure after repeated wear. Further, tolerance stack-ups of all the various mechanical components have to be considered, and closely controlled to ensure switch contact as a key fob is inserted into the reader.  
      The required mechanical switches have been tailored for each individual system, which is undesirably expensive. Moreover, the required mechanical switches are relatively large in size, and require space that puts constraints on the possible locations for the reader.  
     SUMMARY OF THE INVENTION  
      In a disclosed embodiment of this invention, the presence of a key fob in a key fob reader will be determined electronically. In this manner, the mechanical switches required in the prior art are eliminated. Further, the false readings when an item other than a key fob has been inserted will also be eliminated. In a disclosed embodiment of this invention, the key fob is provided with a magnetic member. The magnetic member is sensed by a sensor such as a reed or Hall-effect sensor within the key fob reader. This sensor may be relatively small, and the elimination of the mechanical contact results in the sensor having a relatively long life compared to the prior art. Further, there is little or no deterioration of the sensor, and the detection and accuracy over the life of the product.  
      These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic view of a first embodiment.  
       FIG. 2  is a schematic view of a second embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      A first embodiment  20  is illustrated in  FIG. 1 , having a key fob reader  22  which receives a key fob  24 . As known, a printed circuit board  26  includes the electronics to query the key fob  24  and actuate a transmitter  27  which transits a code to be read by the printed circuit board  26 . If this code is as expected by the printed circuit board  26  and the associated control, then the key fob is authorized. At that point, an ignition switch  32  may be actuated to start the ignition of the car.  
      The present invention improves upon the prior art by including a magnet  30  on a key fob  24 . The presence of the magnet  30  is sensed by a sensor  28 . Sensor  28  may be a reed switch or Hall-effect switch which can sense the presence of the magnet  30 . In the prior art, a magnetic contact was made when the key fob  24  was inserted. The present invention allows a sensing range as shown by dotted line in  FIG. 1 , which will allow a reduction in the required space for the key fob reader  22 . Moreover, the elimination of the mechanical switches provides benefits as mentioned above.  
      The size of the key fob reader  22  and the key fob  24  are shown greatly exaggerated relative to the size of the vehicle. However, this is done for simplicity of understanding the illustration.  
       FIG. 2  shows a second embodiment  120 . In the second embodiment  120 , the key fob  124  is received in a reader  122  having a printed circuit board  126  as in the first embodiment. However, the sensor  128  is located remotely, and can sense the presence of an appropriate key fob  124  when the key fob first enters the vehicle.  
      Although preferred embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.