Illumination – Supported by vehicle structure – Light modifier
Reexamination Certificate
2000-10-16
2002-09-03
Tso, Laura K. (Department: 2875)
Illumination
Supported by vehicle structure
Light modifier
C362S512000, C362S539000, C362S282000, C362S322000
Reexamination Certificate
active
06443606
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vehicle headlamp arranged to vary the light distribution of the headlamp by moving a movable shade.
BACKGROUND OF THE INVENTION
Vehicle headlamps are arranged to emit low or high beams by causing reflectors to reflect light from light sources forward. However, because the light distribution patterns differ between low and high beams, it is common to use a light source bulb having two light sources or two light source bulbs for the purpose of switching between the low and high beams.
Nonetheless, there is a vehicle headlamp that uses a single light source for switching beams, particularly, a two-lamp type headlamp that uses a discharge bulb as a light source bulb.
A sole light source with a movable shade may be used to switch beams. In this case, the shade is made movable between two positions by a shade driving unit. The two positions provide different degrees of screening of light from a light source that radiates to a reflector.
The shade driving unit of a solenoid type allows for a simplified construction. The solenoid shade driving unit is equipped with a solenoid and an elastic member for urging a movable iron core of the solenoid toward a non-excited position. Further, the solenoid shade driving unit operates to move the movable shade to the high-beam position by displacing the movable iron core to an excited position when power is supplied to the coil of the solenoid. It also operates to move the movable shade to the low-beam position by displacing the movable iron core to the non-excited position when the supply of power to the coil is cut off.
While the movable shade is in the low-beam position, the light distribution pattern formed by the emission of the low beam is varied when the movable shade wobbles because of vehicle vibration. If the cutoff line (the light-shade border line) of the pattern also wobbles, the forward visibility is lowered.
However, by providing a positioning member for positioning the movable shade at the low-beam position to butt against the movable shade when the movable shade is moved to the low-beam forming position, the wobble of the movable shade may be suppressed.
Switching beams from the high beam to the low beam by cutting off the power supply to the solenoid may create the following problem.
The movable shade is moved to the low-beam position as the movable iron core is displaced to the non-excited position when the supply of power to the coil of the solenoid is cut off. The movable shade is caused to butt against the positioning member with strong force because of the elastic urging force of the elastic member. The movable shade bounces off toward the high-beam position after its impact with the positioning member.
Hence, the light distribution pattern tends to be unstable when the beams are switched.
The problem of this kind arises from not only switching beams from low to high by moving such a movable shade but arises generally from switching beams by moving the movable shade.
An object of the present invention is to provide a vehicle headlamp that is designed to switch beams by moving a movable shade and that is capable of not only suppressing a knocking sound when the beam is switched but also stabilizing a light distribution pattern.
SUMMARY OF THE INVENTION
The present invention is intended to accomplish the object above by providing a novel solenoid driving circuit.
A vehicle headlamp according to an embodiment of the invention comprises a light source, a reflector for reflecting light from the light source forward, a movable shade capable of shading part of light incident on the reflector from the light source, and a shade driving unit for moving the movable shade between a first and a second position where an incident light shading quantity has different values.
The shade driving unit includes a solenoid and an elastic member for urging the movable iron core of the solenoid toward the non-excited position and for operating to move the movable shade to the first position by displacing the movable iron core to the excited position when power is supplied to the coil of the solenoid. The shade driving unit also moves the movable shade to the second position by displacing the movable iron core to the non-excited position when the supply of power to the coil is cut off. The vehicle headlamp further includes a positioning member for positioning the movable shade to the second position by butting against the movable shade when the movable shade moves to the second position. It also includes an inverted diode or capacitor connected in parallel to the coil, which is connected to a solenoid driving circuit for driving the solenoid.
The above “light source” is not limited to a specific kind but maybe any discharge light emitting bulb portion, for example, an incandescent bulb filament of such as a halogen bulb.
The above “movable shade” may be of any kind capable of shading part of light incident on the reflector from the light source bulb and not limited to a specific configuration.
The above “first and second positions” are not limited to any specific positions but may be two positions where a quantity of incident light shading has different values or may be a set of two positions for high- and low-beam or otherwise may be a set of positions for other beam emissions (e.g., a position for a fog beam, a position for an intermediate beam between the high and low beams and so forth).
The above “inverted diode” means a diode disposed in the inverted direction for supplying power to the coil of the solenoid.
The above “inverted diode” or “capacitor” may be used independently or may be connected in series with a resistor and the like.
The vehicle headlamp according to an embodiment of the invention is equipped with the shade driving unit for moving the movable shade, which is capable of shading part of light incident on the reflector from the light source, between two positions, each shading the incident light in a different degree. Although the solenoid type shade driving unit is employed, the following effect is achievable as the inverted diode or the capacitor is connected in parallel to the coil of the solenoid in the solenoid driving circuit.
When the movable shade is moved to the second position by displacing the movable iron core to the non-excited position by cutting off the supply of power to the coil of the solenoid, the movable shade is caused to butt against the positioning member generally with strong force because of the elastic urging force of the elastic member.
Since the inverted diode or capacitor in parallel with the coil of the solenoid is connected to the solenoid driving circuit in the vehicle headlamp according to an embodiment of the invention, a current can be made to flow into the coil for a while by the induced electromotive force generated across the coil when the supply of power to the coil of the solenoid is cut off. Then the movable iron core is gradually de-excited to slow the movement of the movable shade. Hence, the movable shade can be prevented from butting against the positioning member with strong force.
Consequently, a large knocking sound can be prevented from being produced by the impact force when the movable shade butts against the positioning member and also a light distribution pattern can be prevented from becoming unstable when switching beams by suppressing the tendency of the movable shade to bounce off toward the first position by the impact force.
In the vehicle headlamp arranged to switch beams by moving the movable shade according to an embodiment of the invention, not only the suppression of the knocking sound but also the stabilization of the light distribution pattern is achievable at the time of switching beams.
The above “positioning member” is not limited to a specific configuration but may be any kind that can be set in the second position by butting against the movable shade when the movable shade is moved to the second position.
If the above “positioning member” is resin-molded, the knocking sound produced when the positioni
Fish & Richardson P.C.
Koito Manufacturing Co. Ltd.
Tso Laura K.
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