Illumination – Light modifier – Translucent or opaque
Utility Patent
1999-11-09
2001-01-02
Cariaso, Alan (Department: 2875)
Illumination
Light modifier
Translucent or opaque
C362S255000, C362S539000
Utility Patent
active
06168297
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vehicular headlamp provided with a discharge bulb as a light source.
BACKGROUND OF THE INVENTION
In recent years, a discharge bulb has been widely adopted as a light source for vehicular headlamps because of its high intensity light output.
The discharge bulb is generally provided with an arc tube having a discharge light-emitting portion extending in the fore-to-aft direction. In order to be used as a light source for low-beam emission, there is also known a discharge bulb wherein an outer tube tubularly surrounding the arc tube is provided and a glare protection film is formed on the outer peripheral surface of the outer tube.
In a discharge bulb of this type, as shown in
FIG. 7
, a glare protection film
128
is formed such that upper edges
128
L
a
,
128
R
a
thereof are located on left and right sides of an outer peripheral face
126
a
of an outer tube
126
. The angular range of the glare protection film
128
is set to 165°, with the center being a discharge light-emitting portion
124
a
. In many cases, the glare protection film
128
is formed as a pair of left and right black stripes
128
L,
128
R with the glare protection film being omitted in a lower area of the outer peripheral face
126
a
, as can be seen from FIG.
7
.
A discharge bulb
118
is securely supported by a reflector such that one of the upper edges of the glare protection film
128
(the upper edge
128
R
a
of the right-side black stripe
128
R in
FIG. 7
) is located at the same height as the discharge light-emitting portion
124
a
(more precisely, a line connecting both end electrodes of the discharge light-emitting portion
24
a
lies in the same horizontal plane as the upper edge
124
R
a
). As a result, there is produced a light distribution pattern P′ having a horizontal cut-off line CL
1
′ and an inclined cut-off line CL
2
′ rising from the horizontal cut-off line CL
1
′ with an angle of 15°, as is apparent from FIG.
8
.
During adjustment of the beams (aiming) at the time of low-beam emission, aiming in the up-and-down direction is performed with the location of the horizontal cut-off line adopted as a base. Therefore, the dark-light ratio of the is horizontal cut-off line needs to be enhanced sufficiently.
However, if the dark-light ratio of the horizontal cut-off line is set too high, in the case where, for example, the vehicle enters a flat road after having descended a slope, there is a possibility, depending on the running condition of the vehicle, that the visibility of the road far ahead of the vehicle deteriorates due to sudden darkening, making it difficult for the driver to properly drive the vehicle. Further, if the horizontal cut-off line is displaced slightly upward or downward owing to pitching of the vehicle or the like, there is a risk of dazzling drivers of oncoming vehicles.
In particular, in the case where a discharge bulb is used as a light source of the headlamp, since the discharge bulb has much greater power than a halogen bulb or the like, the aforementioned problem is exacerbated.
The present invention has been made in consideration of such circumstances.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a vehicular headlamp equipped with a discharge bulb which provides a light distribution pattern for low-beam emission that facilitates driving of the vehicle and minimizes the risk of dazzling drivers of oncoming vehicles.
The present invention is designed to achieve the above-stated object by the provision of an appropriate structure wherein the discharge bulb is securely supported by the reflector.
According to the present invention, there is provided a vehicular headlamp including a discharge bulb provided with an arc tube having a discharge light-emitting portion extending in the fore-to-aft direction, an outer tube tubularly surrounding the arc tube having a glare protection film formed on an outer peripheral surface thereof over a predetermined angular range such that the upper edges of the glare protection film are located on left and right sides of the outer peripheral surface, and a reflector that securely supports the discharge bulb and reflects light from the discharge light-emitting portion of the discharge bulb forward, wherein the discharge bulb is securely supported by the reflector and the upper edges of the glare protection film are located substantially at an equal height, that is, the upper edges are located in a horizontal plane.
The “predetermined angular range” mentioned above refers to the entire angular range between the upper edges of the glare protection film. If there is a section within the angular range where the glare protection film is not formed, the predetermined angular range also includes an angular range corresponding to the section.
As indicated by the aforementioned construction, a vehicular headlamp according to the present invention employs a discharge bulb having the glare protection film as a light source thereof, and the discharge bulb is securely supported by the reflector such that the upper edges of the glare protection film are located substantially at an equal height on the left and right sides of the outer peripheral surface of the outer tube. By arranging these upper edges in proper position to the optical axis of the reflector, a light distribution pattern having horizontal cut-off lines on left and right sides of a line V (i.e., the vertical line perpendicular to the lighting fixture reference axis, see
FIG. 3
) is obtained.
Light distribution of the reflector, the lens or the like can be controlled to transform the horizontal cut-off lines into left and right horizontal cut-off lines that are on different levels, and thus an appropriate light distribution pattern for low-beam emission can be obtained.
For a light distribution pattern having left and right horizontal cut-off lines that are on different levels, either the location of the left-side horizontal line or the location of the right-side horizontal line can be adopted as a base for aiming in up-and-down directions. If aiming in the up-and-down direction is performed with the high-level horizontal cut-off line as a base, there is no need to significantly enhance the dark-light ratio as to the low-level horizontal cut-off line.
Accordingly, by setting the dark-light ratio of the low-level horizontal cut-off line and the location of the low-level horizontal cut-off line properly, even in the case where, for example, the vehicle enters a flat road after having descended a slope, deterioration in visibility of the road far ahead of the vehicle resulting from sudden darkening is inhibited. Further, even if the horizontal cut-off line is slightly displaced upward or downward, owing to pitching of the vehicle or the like, the luminous intensity of light emitted upward is prevented from becoming too high. Therefore, the risk of dazzling drivers of oncoming vehicles is reduced.
Thus, the present invention provides a vehicular headlamp is using a discharge bulb as a light source, and having a light distribution pattern for low-beam emission that facilitates driving of the vehicle, and minimizes the risk of dazzling drivers of oncoming vehicles.
Further, as described above, according to the present invention, the aiming operation can be performed with the location of the high-level horizontal cut-off line adopted as a base. Wherein, the target location of the aiming operation is set so that the high-level horizontal cut-off line coincides with a line H (i.e. the horizontal line perpendicular to the lighting fixture reference axis). Therefore, even if no special equipment for aiming measurement is used, the aiming operation of the light distribution pattern can be easily performed merely by making the high-level horizontal cut-off line coincident with the road clearance of the lighting fixture reference axis.
In the present invention, in order to obtain a light distribution pattern having horizontal cut-off lines on the left and right sides of the line V, t
Cariaso Alan
DelGizzi Ronald E.
Koito Manufacturing Co. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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