Abstract:
An improved and compact key operated vehicle antitheft device and more particularly to a compact and highly efficient antitheft device that is easily mounted on a vehicle such as a motorcycle without adversely affecting its performance and in which the antenna coil is spaced from the ferromagnetic parts and attachment fasteners.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to a key operated vehicle antitheft device and more particularly to a compact and highly efficient antitheft device that is easily mounted on a vehicle such as a motorcycle without adversely affecting its performance.  
           [0002]    A very successful anti theft system and structure therefore is shown in Japanese Published Patent Application JP-A-2001-71867, published Mar. 21, 2001 and its US equivalent U.S. Pat. No. 6,525,433, Issued Feb. 25, 2003. With that system a vehicle an anti-theft immobilizer has a main switch body mounted to the vehicle body. A ring-shaped antenna coil in mounted in the vicinity of a key receiving opening of the tumbler of the main switch. The associated key has a transponder built in thee grip part of the key. A control circuit receiving via the antenna coil and identifies an ID code transmitted by the transponder. If the ID code is registered in the transponder when the key is inserted and turned ON the engine start is permitted. However, if the key is determined to be a false one, engine start is prohibited.  
           [0003]    When mounting this immobilizer to a vehicle body, it is necessary to arrange the main switch body and the immobilizer in the vehicle body in a compact. In particular and specifically for a vehicle such as a motorcycle, the available space is limited. In a motorcycle, the key cylinder is typically disposed in the vicinity of an upper bracket connecting left and right front forks.  
           [0004]    A disadvantage of this prior art construction can be best understood by reference to FIG. 1, which is a side elevational view of the assembly with a key, indicated at  11 , inserted. A main switch (not shown) is built in a main switch body, indicated at  12  and which includes a lock tumbler  13 . The key  11  is inserted into the receiving opening of the tumbler  13  of the main switch body  12 . The key  11  has a transponder  14  embedded in a hand grip part  15  of the key  11 .  
           [0005]    A ring-shaped antenna coil  16 encircles the end part of the key receiving opening (at an upper end surface in the drawing) of the tumbler  13  and is embedded in the main switch body  12 . This antenna coil  16  is formed with a substantial number of turns. When electric current is applied to the antenna coil  16  from the power voltage of a battery, magnetic flux shown by an arrow “B” flows around the antenna coil  16 . Thereby, the electromagnetic energy is generated and forwarded to the transponder  14 .  
           [0006]    In order to obtain a large electromagnetic energy, it is necessary to expand magnetic field by increasing magnetic flux “B”. Thus, it is necessary to widen the space between the flow path of the magnetic flux from the antenna coil  16  and the tumbler body  13 . That is, the antenna coil  16  needs to be spaced from the tumbler body  12  as much as possible in order to minimize influence of the ferromagnetic material while maximizing the flow path of the magnetic flux. As a result, a diameter of the antenna coil  16  is increased as is the entire main switch body  12 . However, this enlarged diameter of the antenna coil  16  may result in a problem of difficult mounting of the antenna coil  16  to the vehicle body. In addition, it compromises the layout of surrounding parts.  
           [0007]    In addition to the interference of the flux path by the tumbler body  12 , it is attached to the vehicle by fasteners that juxtaposed to the antenna coil and which are also formed from ferromagnetic material. This further interferes with the flux path and makes a greater number of windings necessary further increasing the size.  
           [0008]    Further to these problems, the construction as described is rather difficult because of its size and shape to conveniently mount on a small, compact vehicle such as a motorcycle.  
           [0009]    It is, therefore, a principle object of the invention to provide an improved, compact, high efficiency and low cost key operated vehicle antitheft device.  
           [0010]    It is a further object of the invention to provide key operated vehicle antitheft device that has a compact but highly efficient antenna coil.  
           [0011]    It is a yet further object of the invention to provide key operated vehicle antitheft device that can be easily mounted on a small vehicle such as a motorcycle.  
         SUMMARY OF INVENTION  
         [0012]    A first feature of the invention is adapted to be embodied in a key operated vehicle antitheft device for cooperation with a key having a key portion and a transponder. The antitheft device is comprised of a tumbler having a key receiving opening adapted to receive the key, an antenna coil for receiving the signal of the key transponder and a circuit including a receiver for sensing and recognizing the output of the transponder. The antenna coil is disposed in a spaced relation from any ferromagnetic portion of the key operated vehicle antitheft device in the direction from which the key is inserted into said key receiving opening.  
           [0013]    In a specific example of the invention the antenna coil is disposed in a spaced relation from the key tumbler.  
           [0014]    In another specific example of the invention the antenna coil is disposed in a spaced relation from the mounting fasteners of the device.  
           [0015]    In still another feature of the invention, the body of the key operated vehicle antitheft device is mounted to an upper bracket that joins the forks of a motorcycle. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0016]    [0016]FIG. 1 is a side elevational view of a prior art construction to illustrate the problem solved by the present invention.  
         [0017]    [0017]FIG. 2 is a partially schematic view illustrating how the invention is incorporated in a complete vehicle.  
         [0018]    [0018]FIG. 3 is a side elevational view, in part similar to FIG. 1, but shows a feature of the present invention.  
         [0019]    [0019]FIG. 4 is a side elevational view, showing the relation between the antenna coil and the associated circuit.  
         [0020]    [0020]FIG. 5 is an exploded perspective view of the device.  
         [0021]    [0021]FIG. 6 is a side elevational view, in part similar to FIG. 3, but showing more details of the actual construction.  
         [0022]    [0022]FIG. 7 is a top plan view of the device.  
         [0023]    [0023]FIG. 8 is a side elevational view taken at 90° to that of FIG. 6, but with the key removed.  
         [0024]    [0024]FIG. 9 is an exploded view showing how the device is mounted on a motorcycle.  
         [0025]    [0025]FIG. 10 is a top plan view of the mounted device.  
         [0026]    [0026]FIG. 11 is a cross sectional view of the mounted device. 
     
    
     DETAILED DESCRIPTION  
       [0027]    Referring now in detail to the drawings and initially to FIG. 2, this is an overall schematic diagram showing key operated vehicle antitheft device of the present invention. The main unit is identified generally by the reference numeral  51  and includes a main switch  52  contained within a main switch body  53 . A key receiving hole  54  is formed in the end surface of the main switch body  53 .  
         [0028]    An enlarged case portion  55  housing an antenna coil  56  is provided at the peripheral part of the end surface of the main switch body  53  around the key receiving hole  54 . The antenna coil  56  is a ring-shaped coil. When a key  57  is inserted into the key receiving hole  54  and into a tumbler thereof and turned, the main switch  52  is turned ON/OFF. A transponder  58  is embedded in a hand grip part  59  of the key  57 . An ID code is registered in the transponder  58 . The transponder  58  receives electromagnetic energy from the antenna coil  56  as shown by an arrow P and uses it as power source to transmit an ID code signal as shown by an arrow Q. The ID code signal received by the antenna coil  56  is forwarded to an ID reading circuit  61  in a control circuit unit  62  of the key operated vehicle antitheft device main unit  51 .  
         [0029]    Except as hereinafter noted, the control circuit unit  62  is formed on a sheet of printed circuit board that is not shown in this drawing. This printed circuit board (control circuit board) is integrated with the antenna coil  56  within the case  55  to form the key operated antitheft device main unit  51 . An key operated antitheft device integrally combining (shown separately in FIG. 2) the antenna coil  56  within the case  55  with the printed circuit board forming the control circuit unit  62  is further integrally combined with the main switch body  53  as will be described later in order to form an immobilizer/main switch assembly.  
         [0030]    Continuing to refer mainly to FIG. 2, the control circuit unit  62  includes the ID reading circuit  61 , a CPU  63 , a power circuit  64 , and an EEPROM  65  that cooperate to control an ignition circuit  66 . The ignition circuit  66 preferably is formed separately from the printed circuit board but is shown schematically as part of the control circuit unit in FIG. 2 for simplification.  
         [0031]    The ID reading circuit  61  reads the key ID code signal received by the antenna coil  56  and regulates electric current supplied to the antenna coil  56  for sending electromagnetic energy from the coil to the transponder  58 .  
         [0032]    The CPU  63  then compares the received ID code with an authorized ID code pre-registered in the EEPROM  65  in order to determine whether or not the key  57  is the right one. If the key is determined to be the right key, ignition of an engine  67  is permitted through the ignition circuit  66  to start the engine  67 . If the key is determined to be a false one, ignition of the engine  67  by the ignition circuit  66  is prohibited and the engine  67  is not allowed to start.  
         [0033]    The power circuit  64  receives voltage from a battery  68  through the main switch  52  and supplies predetermined voltage to each circuit within the control circuit unit  62  through the CPU  63 . This power circuit  64  includes a self-holding circuit (not shown) that allows itself to operate for a predetermined duration after the main switch  52  is turned OFF.  
         [0034]    The CPU  63  is connected to an alarm unit  69  through an interface circuit (not shown). The alarm unit  69  includes an inclination sensor  71  for detecting inclination and vibration of a vehicle and an alarm  72  such as siren and lamp. When the vehicle leans or vibrates when it is in an alarm state (when the anti-theft system is in an operable state), the inclination sensor  71  detects the motion and activates the siren  72 . However, if the control circuit unit  62  determines that the key  57  is the right one, the CPU  63  sends an alarm release signal to the alarm unit  69  to stop the siren.  
         [0035]    The CPU  63  is connected to a display  73  for displaying the operating state of the immobilizer (anti-theft system) to an operator.  
         [0036]    Before describing in more detail the actual physical construction of the key operated antitheft device main unit  51 , by reference to FIGS.  4 - 8 , its size compared to the prior art construction of FIG. 1 may be understood by reference to FIG. 3. As seen in this figure, the thickness “d” of the antenna coil  56  is smaller than a gap “G” between an end rim  74  of the grip part  59  of the key  57  and the end surface  75  around the key insertion hole of a tumbler body  76  of the main switch body  53 . Thereby, the inner diameter side of the antenna coil  56  can be as close as possible to the key  57 , allowing a reduction in the outer diameter of the main switch body  53  as compared with the prior art construction in FIG. 1.  
         [0037]    The detailed construction of the key operated antitheft device main unit  51  will now be described by reference to FIGS.  4 - 8 . Referring first to FIG. 4 and as already described, it includes a printed circuit board  77 , as previously stated but not previously shown. On this printed circuit board  77  are forming the control circuit unit  62  and a connection for connecting the antenna coil  56 . These elements are mounted in the case  55  as a unit.  
         [0038]    The case  55  comprises a resin-molded body including a cylindrical part  55   a  and a box part  55   b  coupled with the outer periphery at the end of the cylindrical part  55   a.  The inner periphery of the box part  55   b  is opened as shown in FIG. 5, which will be described later. The ring-shaped antenna coil  56  is mounted concentrically with an axis C in the end of the cylindrical part  55   a  that is on the opposite side of the box part  55 b. The printed board  77  is disposed in parallel to the axis C within the box part  55   b.    
         [0039]    The antenna coil  56  is connected to the printed circuit board  77  through a terminal member  78  comprised of a bent metallic plate. In this embodiment, a length “a” of the terminal member  78  within the cylindrical part  55   a  to the point at which the terminal member  78  is bent (substantially corresponding to the length in the axial direction of the cylindrical part  55 a) is longer than a length “b” of the bent part of the terminal member  78  (substantially corresponding to the projecting length toward the outer periphery of the box part  55   b ). Thereby, installation of the key operated antitheft device main unit  51  to a later-described upper bracket of front forks can be carried out efficiently in terms of space without interfering with other parts within a narrow space.  
         [0040]    Bolt mounting holes  79  for coupling with other parts are formed in both sides of the side surface of a projecting part  55   c  of the main switch body  55 .  
         [0041]    Referring now primarily to the exploded view of FIG. 5, it will be seen that the antenna coil  56  is wound around a ring-shaped bobbin  81  made of molded resin. The terminal member  78  actually comprises a pair of members that are mounted on both sides of a connection piece  81   a  made of molded resin integrated with the bobbin  81 . In each terminal member  78 , one of the pin terminals  78   a  and  78   b  are provided to which the beginning and the ending of the coil  56  is connected.  
         [0042]    After the antenna coil  56  wrapped around the bobbin  81  and the terminal members  78  are connected and assembled, this assembly is set within a die for molding the main switch case portion  55  to form a molded body integrated with the main switch body  53 . After the molding is completed, the printed board  77  is fitted into the main switch body part  55   b.  When this is done, a projection  78   c  of the terminal members  78  extends through a hole formed in the printed board  77 . These top projections  78   c  are soldered so that the printed board  77  is secured within the main switch body part  55   b  and the electrical connections are completed.  
         [0043]    A cable  82  is connected to the printed board  77  through a connector  83 . A cut-away portion  84  for inserting the cable  82  is formed at the bottom of the main switch body part  55   b  of the main switch case portion  55 . The hole  54  for inserting the key  57  is formed in the central part of the top surface of the cylindrical part  55   a  of the case  55 . When the main switch case portion  55  is assembled, the key receiving hole  54  is exposed (see FIG. 7).  
         [0044]    How the main switch body  53  is affixed to the remainder of the main switch  52  as well as further details of the main unit  51  may be best understood by reference to FIGS.  6 - 8 . As previously noted, the assembled main switch body  53 , is coupled to the main switch  52 , by bolts  85  (see FIGS. 7 and 8). Each bolt  85  is screwed into the bolt mounting hole  79  of the projecting part  55   c  integrally formed in both sides of the side surface of the box part  55   b  of the case  55 , whereby the main switch  52  is coupled with the main switch body  53  to form the main unit  51 .  
         [0045]    As previously mentioned, the antenna coil  56  is housed in the case portion  55 , for example embedded in a molded resin. The case portion  55  includes the printed board  77  forming the control circuit unit  62  of the main unit  51 . The case portion  55  including the antenna coil  56  and the printed board  77  forming the control circuit unit  62  are integrated by the molded resin to form the main unit  51 .  
         [0046]    Further, the main switch  52  and main switch body are integrally coupled by the bolts  85  (FIG. 9) to form a single unit. As noted, the bolt mounting holes  79  are formed in the projecting parts  55   c  formed in both sides on the side surface of the box part  55   b.  As seen in FIG. 8, each bolt  85  extends through a through hole  86  formed in the projecting part  55   c  of the main switch body  53  and is screwed into the bolt mounting hole  79 . Since the bolt mounting holes  79  are spaced from the antenna coil  56  of the cylindrical part  55   a,  the magnetic influence of the metallic bolt  79  on the coil  56  is reduced or substantially eliminated. Also the tumbler body  76  is spaced from the coil  56  as seen in FIG. 3 so that the magnetic influence of its ferromagnetic components on the coil  56  is reduced or substantially eliminated.  
         [0047]    An anti-theft handle lock  87  is provided for preventing rotation of a steering shaft (not shown) of the handlebar when the associated motorcycle is parked. As shown in FIGS.  6  - 8 , the main switch body  53  has a bolt insertion holes  88  for securing the main unit  51  to the vehicle (for example to an upper bracket for connecting front forks of a front wheel) as will be described later by reference to FIGS.  9 - 11 .  
         [0048]    Also, the formation of one collective assembly part by integrally arranging the main switch body  53 , the antenna coil  56 , and the printed board  77  forming the control circuit unit allows easy handling and facilitates parts management.  
         [0049]    Referring now to FIGS.  9 - 11 , these figures show the frame structure of a front section of the body of the motorcycle to which the collective assembly part of the main unit  51  is mounted. The motorcycle has a head pipe  89  is secured to a main frame  91  forming the front section of the motorcycle body.  
         [0050]    A steering shaft  92  is dirigibly supported by the head pipe  89 . An upper bracket  93  and an under bracket  94  are secured on both upper and lower ends of the steering shaft  92 . Left and right front forks  95  are inserted and secured to the upper and under brackets  93  and  94 . The left and right front forks  95  are coupled to both sides of a wheel shaft of the front wheel (not shown) in a known manner. Handlebars  96  are secured to the upper bracket  93 . By operating the handlebars  96 , the upper bracket  93  integrated with the handlebars  96 , the steering shaft  92 , and the under bracket  94  are rotated relative to the head pipe  89  secured to the vehicle body. Thereby, the front forks  95  are steered with the front wheel relative to the vehicle body to change the vehicle direction.  
         [0051]    The upper bracket  93  has a mounting hole  97  for mounting the main unit  51  and specifically the main switch body  53 . This mounting arrangement is best shown in FIGS. 10 and 11. As seen there, the central part of the upper bracket  93  is formed with a hole  98  for inserting and securing the steering shaft. At both ends of the upper bracket  93 , holes  99  are formed for inserting and securing the front forks  95 .  
         [0052]    The cylindrical part  55   a  of the main switch body  53  is fitted into the mounting hole  97  of the upper bracket  93  and secured there by bolts  101 . The bolts  101  are screwed through the bolt insertion holes  88  of the main switch body  53  into a screw hole formed in a boss integrally formed with the lower side of the upper bracket  93 . Thereby, the main unit  51  is secured to the upper bracket  93 .  
         [0053]    Thus from the foregoing description it should be readily apparent that the construction allows the formation of a compact and unitary key operated vehicle antitheft device. In addition, electromagnetic influence over the antenna coil by the ferromagnetic components and mounting bolts is substantially reduced. Of course those skilled in the art will readily understand that the described construction is that of a preferred embodiment and various changes and modifications therefrom can be made without departing from the spirit and scope of the invention, as defined by the appended claims.