Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2000-12-20
2002-11-12
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S056000, C315S307000
Reexamination Certificate
active
06479950
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a high intensity discharge lamp for use in such apparatuses as general illumination apparatuses and vehicle headlamps that use the lamp mounted to a reflector, a driving apparatus for a high intensity discharge lamp, and a high intensity discharge lamp system employing the lamp and the driving apparatus.
(2) Description of the Related Art
In recent years, high intensity discharge lamps have been employed for projectors and vehicle headlamps in which the lamps are mounted to reflectors. Such discharge lamps exhibit high efficiency, low power consumption, and high intensity in comparison with halogen lamps, and therefore are expected to receive more widespread commercial acceptance.
When a conventional high intensity discharge lamp is positioned in such a manner that the line connecting the pair of electrodes becomes horizontal, and operated by applying voltage across the pair of electrodes, (the operation in this manner is hereinafter referred to as “horizontal operation” or “horizontally operated”), the arc is bent upwards. As a result, the temperature of the upper portion of the arc tube locally becomes high, which causes such problems that devitrification of the upper portion of the arc tube or deformation of the arc tube begins at a relatively early stage in lamp life and thus the lamp life reduces.
In view of the problems, much research has been carried out to develop the technique for suppressing the arc bend and thereby improving lamp life. For example, Japanese Unpublished Patent Publication Nos. 55-86062 and 9-161725 disclose a technique for suppressing the arc bend by applying a magnetic field to a metal halide lamp.
The technique disclosed in Japanese Unpublished Patent Publication No. 55-86062 is such that by providing a strong rare earth magnet above the arc tube to apply a magnetic field to the arc tube from the upper direction thereof, the arc is forced downwards by the repulsion force between the magnet and the arc so that the upward arc bend is suppressed.
Recently, as environmental concerns have increasingly been regarded as important, it has been required that mercury not be used for general high intensity discharge lamps. However, the lamps disclosed in the above publications employ mercury as a filling material to be enclosed in the arc tube. Therefore, in order to meet such requirements as described above, it is necessary that the arc bend be suppressed in the high intensity discharge lamp in which mercury is not employed to improve the lamp life.
In addition, the high intensity discharge lamp requires a dedicated operating circuit, which incurs higher cost. Unlike a halogen lamp having two filaments, it is difficult for the high intensity discharge lamp to attain both high beam and low beam with only one lamp. For this reason, in a vehicle headlamp system, normally, two high intensity discharge lamps are used for low beam lamps in which the frequency of use is high, and two halogen lamps are used for high beam lamps. Thus, this configuration also requires four sets of mechanism for adjusting the reflector and the light axis, which also incurs high manufacturing cost and limits the freedom in the vehicle designing.
In view of this problem, there is a need for a technique by which high beam and low beam can be selected with the use of only one high intensity discharge lamp. A typical example of such a technique is, for example, described in Japanese Unexamined Patent Publication No. 11-312495, in which by using an electromagnet, the arc bend amount is varied to move the position of the light source. This technique is such that, in a discharge lamp disposed in a reflector such that the axis line of the discharge electrodes is in a horizontal direction (a horizontally operated lamp), a magnetic field transverse to the axis line is applied to the arc by an electromagnet. By applying a magnetic field in such a manner, the arc can be deflected (bent) in a downward direction by the effect of Lorentz force. In addition, by controlling the electric power supplied to the electromagnet, the Lorentz force can be varied such that selecting of low beam and high beam is possible.
However, according to a technique of controlling arc deflection by an electromagnet such as described above, an additional circuit for controlling the electric power supplied to the electromagnet is necessary, which incurs complicated device configurations and the increase in manufacturing cost. It might be possible to control the arc deflection by varying a lamp current or a discharge electrode gap, rather than varying the electric power supplied to the electromagnet, but in practice, it would be very difficult to control variations in such factors.
In addition, the present inventors found in the course of various experiments to accomplish the invention that when a magnetic field is applied to a discharge lamp, variation of luminance, flickering, occurs at times. This flickering can be classified into two kinds: the flickering that occurs at the start of the light beam immediately after the start of the lamp and the flickering that occurs during the stable operation
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the foregoing and other problems in prior art. Accordingly, it is an object of the present invention to provide a mercury-free high intensity discharge lamp in which mercury is not contained inside the arc tube, and arc bend is suppressed and long lamp life can be obtained.
It is another object of the invention to provide, with a simple and low cost configuration, a high intensity discharge lamp in which at least one of an arc bend amount and an apparent arc width can be controlled.
It is further another object of the invention to provide a driving apparatus for the high intensity discharge lamp.
It is still another object of the invention to provide a high intensity discharge lamp system employing the high intensity discharge lamp and the high intensity discharge lamp system.
It is to be understood that the aspects of the present invention to be detailed hereinafter are accomplished on the basis of an identical technical idea. Nonetheless, each of the aspects is embodied by a different embodiment or an example, and accordingly, the invention is divided into two groups, Embodiment I and Embodiment II, in which more closely related aspects are grouped. Hereinafter, the details are discussed according to each embodiment.
Summary of Embodiment I
In the process of the research and development of a high intensity discharge lamp that does not use mercury, the present inventors found that the high intensity discharge lamp in which mercury is enclosed in the arc tube exhibits a larger degree of arc bend than a discharge lamp in which mercury is enclosed in the arc tube.
When the present inventors performed the experiment in which a magnetic field is applied to the high intensity discharge lamp having a large degree of arc bend to suppress the arc bend, the present inventors surprisingly found that the magnetic flux required to eliminate the arc bend is smaller in the lamp in which mercury is not enclosed than in the lamp in which mercury is enclosed, that is, the lamp in which mercury is not enclosed does not require a strong magnetic field. The present inventors considered that the principle of suppressing the arc bend in the high intensity discharge lamp in which mercury is not enclosed may differ from that in the lamp in which mercury is enclosed.
This phenomenon was discovered from the study of the degree of the arc bend in which a magnetic field is applied to each of the lamp in which mercury is not enclosed in the arc tube and the lamp in which mercury is enclosed in the course of the research and development. By the discovery of such a phenomenon, a mercury-free high intensity discharge lamp of the invention, which utilizes a low-cost and practical technique to suppress the arc bend and thereby to improve lamp life, has been accomplished.
Thus, the foregoing and other
Horiuchi Makoto
Kaneko Yuriko
Kiryu Hideaki
Minamihata Ryo
Murase Takayuki
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Vu Jimmy T.
Wong Don
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