Head lamp for motor-bicycle with slant angle correction
BACKGROUND OF THE INVENTION 
     The present invention relates to a head lamp, and more particularly to a head lamp suitable for motor-bicycles wherein the body of the motor-bicycles slants or inclines while turning. 
     A conventional head lamp for motor-bicycles which slant while turning has been constructed to compensate for the body slant, as shown in FIG. 4, such that the entirety of a head lamp 22 is caused to rotate around a light illumination axis in accordance with the slant of the body 21 so that the head lamp 22 is always maintained at a given orientation relative to the ground surface. 
     The mechanism for rotating the entirety of the head lamp 22 has been found, however, not to be satisfactory due to the following problems. Namely, first the mechanism requires a large drive power sufficient for smoothly following the operation of a running motor-bicycle, thus essentially resulting in bulky size which makes it substantially difficult to mount the drive unit for the head lamp on a motor-bicycle which is to be designed as light as possible. Second, employing such a mechanism for rotating the head lamp 22 becomes more and more difficult because a motor-bicycle with a cowling has become common. Such a motor-bicycle has a rectangular head lamp integrally mounted on a cowling. In such a case, the total design of the lamp and cowling must be considered. 
     It is therefore an object of the present invention to provide a motor-bicycle head lamp which can solve the above problems. 
     SUMMARY OF THE INVENTION 
     The above object is achieved by the motor-bicycle head lamp of the present invention which comprises a reflector formed in a spheroidal shape; a convex lens disposed in front of said reflector; a shade disposed near a focal point of said convex lens substantially midway between said reflector and said convex lens; wherein said shade is adapted to be rotatable around the optical axis of said motor-bicycle head lamp in accordance with a slant angle of the body of said motor-bicycle. Therefore, the head lamp and other necessary components can be constructed small in size and pose no design problem, since it is no longer necessary to rotate the entirety of the head lamp, thus eliminating the above-described problems with the prior art. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-section illustrating a motor-bicycle head lamp according to an embodiment of this invention; 
     FIG. 2 is a schematic diagram showing the main portion of the embodiment of FIG. 1, including a perspective view of the shade; 
     FIGS. 3A to 3C are views used for explaining the operation of the motor-bicycle head lamp of the invention; and 
     FIG. 4 is a view used for explaining a conventional motor-bicycle head lamp. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     Referring to FIG. 1, a motor-bicycle head lamp of this invention is generally represented by reference numeral 1. The motor-bicycle head lamp 1 comprises a reflector 2 formed in a spheroidal shape, a light source 3 mounted at the first focal point of the reflector 2, a convex lens 4 for directing light applied from the light source and reflected from the reflector 2 in the direction of a predetermined light illumination angle, the reflector 2, light source 3 and convex lens 4 being all aligned on an optical axis AX. The motor-bicycle head lamp 1 further comprises a shade 5. The shade 5 has an aperture whose shape corresponds to a predetermined light distribution characteristic, and is mounted at substantially the same position as the focal point of the convex lens 4. With such a shape of the shade aperture, light can be radiated through the aperture toward the front side of the motor-bicycle in a similar manner to a slide projector, thus ensuring the predetermined light distribution characteristic. 
     The shade 5 is rotatably mounted on a holder 6 in operative association with the reflector 2, convex lens 4 and the like. As shown in FIG. 2, the shade 5 is arranged to rotate around the optical axis AX by means of an arc guide groove 5a, and is integrally formed with a gear 5b at the outer peripheral portion thereof. The gear 5b meshes with another gear which is fixedly connected to the shaft of a micro motor 7 or the like such that the shade 5 can be controlled to stop at a rotational desired angle. 
     For the motor-bicycle head lamp 1 constructed above, a motor control circuit MC for controlling the micro motor 7 and a distance sensor DS comprising, for example, an ultrasonic distance sensor are provided, such that the shade 5 is driven in accordance with an output from the distance sensor DS. The operation conditions are shown in FIGS. 3A to 3C. As shown in FIG. 3A, a distance D0 between the distance sensor DS and the ground surface is used as a reference distance during an ordinary running where the body 10 stands upright. If the body 10 slants to the left while turning to the left as shown in FIG. 3B, the micro motor 7 is caused to rotate, e.g., in the clockwise direction by an amount corresponding to a difference between distances D0 and D1. 
     Therefore, the shade 5 is caused to rotate until it takes the same angle relative to the ground surface as that when the body 10 stands upright. On the contrary, if the body 10 slants to the right while turning to the right as shown in FIG. 3C, the micro motor 7 is caused to rotate in the counter-clockwise direction by an amount corresponding to a difference between distances D0 and D3. Therefore, the shade 5 is caused to rotate until it takes the same angle relative to the ground surface as that when the body 10 stands upright. In the above manner, the light distribution characteristic of the head lamp 1 is maintained constant irrespective of the posture or slant of the body 10. As appreciated from the above, the motor control circuit MC for controlling and driving the micro motor 7 may use a known servo control circuit commonly employed in measuring circuits, with slight modification given thereto. 
     As seen from the foregoing description of the present invention, the shade is caused to rotate around the optical axis of the motor-bicycle head lamp in accordance with the slant angle of the motor-bicycle body. Thus, a head lamp capable of obtaining, irrespective of the posture of the body, a light distribution characteristic the same as that when the body stands upright can be realized by rotating only the very light-weight shade. Therefore, a low power micro motor can be used. Further, the drive unit can be miniaturized to facilitate mounting it on the motor-bicycle. Furthermore, a reflector, lens and other components can be fixedly mounted on the body so that, for example, a rectangular head lamp with a cowling may be used with a greater degree of design freedom.