You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a filler cap assembly, and in particular, to a filler cap assembly for fuel tanks of automobiles, which automatically opens with a fuel tank door when an opening lever is manipulated. 
     (b) Description of the Related Art 
     Cap assemblies for fuel tanks are well known. Typically, a fuel tank has an opening in a side thereof, a substantially cylindrical tube with a threaded end is inserted into the opening and fixed to the tank, and a filler cap is screwed on to the threaded end. 
     FIG. 3 shows a prior art cap assembly. As shown in FIG. 3, a fuel inlet of a tube  18  which is connected to a fuel tank is secured in a recess formed on an exterior panel  10  of a vehicle and is sealed by a filler cap  16 . The filler cap  16  is protected by a fuel tank door  14  which is pivotally connected to the panel  10  and biased in its opening direction by a torsion spring  12 . The fuel tank door  14  is held closed by a locking device  6  that hooks on a protrusion formed on an inner surface of the fuel tank door  14 . The locking device  6  is connected to an opening lever  2  arranged in a driver&#39;s compartment by a cable  4  such that the locking device  6  unlocks if a driver pulls the opening lever  2  to open the fuel tank door. 
     In this case, the fuel tank is opened by the driver&#39;s manipulation from within the vehicle, but the filler cap  16  is manually opened and closed by a service station attendant when refilling the fuel tank, so the driver cannot ensure that the inlet opening is completely sealed. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to solve the above problems of the prior art. 
     It is an object of the present invention to provide a filler cap assembly which is automatically opened with and at the same time as a fuel tank door by a driver&#39;s manipulation of an opening lever. 
     To achieve the above object, the filler cap assembly comprises a first sensor mounted to one end portion of a cable that connects an opening lever to a fuel tank door locking device, the first sensor detecting if the opening lever is operated to open the fuel tank door, an actuator mounted near a fuel inlet for selectively generating rotational force and being electrically connected to a battery when the first sensor detects that the opening lever is operated to open the fuel tank door; a filler cap fitted into a fuel inlet and connected to the actuator by means of a gear mechanism such that the filler cap screws into or out of the inlet according to a direction of the rotational force generated by the actuator, and a second sensor mounted inside the fuel inlet for detecting if the filler cap is fitted into the fuel inlet, the second sensor electrically connecting the actuator to the battery if the filler cap is fitted into the fuel inlet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and together with the description, serve to explain the principles of the invention: 
     FIG. 1 is a front cross-sectional view showing a filler cap assembly in an open state according to a preferred embodiment of the present invention; 
     FIG. 2 is a front cross-sectional view showing a filler cap assembly of FIG. 1 in a closed state; 
     FIG. 3 is a front cross sectional view showing a prior art filler cap assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will be described hereinafter with reference to the accompanying drawings. 
     FIG.  1  and FIG. 2 show a filler cap assembly respectively as opened and closed according to a preferred embodiment of the present invention. 
     As shown in FIG. 1, the filler cap assembly  22  comprises a first sensor  24 , an actuator  26 , a filler cap  28 , and a second sensor  30 . 
     The first sensor  24  is mounted to one end portion of a connection cable  58  near an opening lever  34  provided in a driver&#39;s compartment. The sensor  24  includes a first conductor  38  fixed to the cable  58  and slidably housed in a cylindrical housing  40 , and two first sensor terminals  46  mounted around an opening lever portion of the housing  40  such that an electric connection is established therebetween when the first conductor  38  adjoins the two first sensor terminals  46 . One first sensor terminal  46  is electrically connected to a battery  42  and another is connected to a first relay  44 . The first conductor  38  is biased by a coil spring  48  that is installed in the housing  40 . 
     The actuator  26  is provided with a motor  52  that is electrically connected to the two first sensor terminals  46  of the first sensor  24  via the first relay  44  and a first transistor  50 , and a long driving gear  56  is fixed to a rotational shaft of the motor  52  such that the driving gear  56  rotates when an electric connection is established between the first sensor  24  and the motor  52 . 
     The filler cap  28  is formed with a body  62  that is threaded on its lower portion so as to be screwed into a fuel inlet  67 , a head  60  formed at an upper end of the body  62 , a second conductor  66  fixed to the lower end of the body  62 , and a driven gear  64  mounted around an upper portion of the body  62  so as to be engaged with the driving gear  56  of the actuator  26  such that the filler cap is actuated if the motor  52  of the actuator  26  generates a rotational force. 
     The second sensor  30  is provided with two second sensor terminals  70  mounted inside the fuel inlet and electrically connected to the battery  42  and second relay  68  respectively, such that an electric connection is established when is the second conductor  66  is located between the two second sensor terminals  70  when the filler cap  28  is placed in the fuel inlet. 
     The operation of the filler cap assembly according to the present invention will be described hereinafter. 
     FIG. 2 shows the filler cap assembly as closed. In this state, if the opening lever  34  is pulled, a locking device  76  that is pivotally connected to an end of the cable  58  and hooked on a hook  78  formed on an inner surface of the fuel tank door  32  is released such that the fuel tank door  32  is opened by an elastic force of a torsion spring arranged with a hinge mechanism which pivotally connects the fuel tank door  32  to the vehicle body. At the same time, the first conductor  38  which is fixed on the cable  58  moves in the opening lever direction against the coil spring  48  and connects the two first sensor terminals such that electrical continuity is established between the battery  42  and the motor  52  of the actuator via the first relay  44  and the first transistor  50 . Electric current from the battery  42  is amplified by the first transistor  50  and then supplied to the motor  52  of the actuator  26  such that the motor  52  generates rotational force to rotate the driving gear  56 . Accordingly, the filler cap  28  is screwed out of the inlet pipe by the driven gear  64  engagement with the rotating driving gear  56 . 
     The filler cap  28  is designed in such way that when it is screwed out it remains in place on the inlet opening so that a service station attendant can remove it and refill the fuel tank. After filling the fuel tank, the attendant simply need place the filler cap  26  on the fuel inlet  30  and close the fuel tank door  32 . 
     If the filler cap  26  is placed on the fuel inlet  30 , the second conductor  66  is located between the two second sensor terminals  70  of the second sensor  30  such that the battery  42  and the motor  52  of the actuator  26  are electrically connected to each other via a second relay  68  and a second transistor  72 . 
     Electric current from the battery  42  is amplified by the second transistor  72  and then supplied to the motor  52  of the actuator  26  such that the motor  52  generates rotational force to rotate the driving gear  56  in a direction opposite to the first rotational direction thereof. Accordingly, the filler cap  28  is screwed into the inlet pipe by the driven gear  64  engagement with the rotating driving gear  56  such that the inlet pipe becomes sealed. 
     When the fuel tank door  32  is closed, the hook  78  of the fuel tank door  32  pushes the arc-shaped upper surface of the free end of the locking device  76  such that the locking device  76  rotates around a pin  80  that is fixed to the vehicle body, and once it is clear of the hook  78 , spring pressure from the spring  48  pulls the locking device  76  into a locked position with respect to the hook  78 . Accordingly, the opening lever  34  returns to its initial position. 
     As described above, in the filler cap assembly according to the preferred embodiment of the present invention, since the filler cap and the fuel tank door are opened at the same time by the driver&#39;s manipulation, and the filler cap is opened and closed at a predetermined speed and rotational force, sealing the fuel inlet is promptly and precisely fulfilled, and furthermore the driver can check if the inlet opening is completely sealed by monitoring the position of the opening lever. 
     While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Summary:
A filler cap assembly includes a filler cap for opening and closing a fuel inlet, a first detecting arrangement for detecting if a fuel tank door is opened or not, a second detecting arrangement for detecting if the filler cap is placed in the fuel inlet, and an actuating arrangement for opening and closing the filler cap according to signals from the first and second sensors.