Electric lamp and discharge devices – Fluent material supply or flow directing means – Lightning or surge arrester
Reexamination Certificate
1999-02-17
2001-02-27
Font, Frank G. (Department: 2879)
Electric lamp and discharge devices
Fluent material supply or flow directing means
Lightning or surge arrester
C361S120000
Reexamination Certificate
active
06194820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a discharge tube, or more in particular, to a discharge tube comprising at least a pair of electrodes with the discharge surfaces thereof arranged in opposition to each other in a space filled with a sealing gas.
2. Description of the Related Art
The lighting circuit of a gas discharge lamp such as a metal halide lamp or a xenon lamp used as a high-voltage lamp includes a discharge tube as shown in
FIG. 5
or
6
(a switching spark gap, hereinafter sometimes referred to as “SSG”) for supplying the operating voltage to the lamp to be turned on.
The SSG
10
shown in
FIG. 5
includes a cylindrical member
12
made of an insulating material such as a ceramic, and a pair of electrodes
14
a
,
14
b
arranged with discharge surfaces
16
,
16
thereof inserted in a space portion
22
by way of the openings at the two ends of the cylindrical member
12
. The discharge surfaces
16
,
16
are arranged in opposition relation to each other through a sealing gas filled in the space portion
22
. The flat portions of the discharge surfaces
16
,
16
are coated with insulating layers
18
,
18
, respectively, of an insulating material.
The SSG
10
shown in
FIG. 6
has a substantially similar structure to the SSG shown in
FIG. 5
, except that recesses
20
,
20
are formed in the discharge surfaces of a pair of the electrodes
14
a
,
14
b
. The surfaces of the recesses
20
,
20
are coated with an insulating material thereby to form insulating layers
18
,
18
, respectively. The area of the discharge surface can be enlarged and the service life of the discharge tube can be lengthened by forming the recesses
20
,
20
in the discharge surfaces in this way.
In the case where the SSG
10
shown in
FIGS. 5 and 6
is to be discharged continually, it is necessary to supply a specific operating voltage at a frequency of several ms to several tens of ms in stable fashion to the lamp, etc. For this purpose, JP-A-9-22769 proposes a SSG in which a pair of the insulating layers
18
,
18
formed on the discharge surfaces
16
,
16
of a pair of the electrodes
14
a
,
14
b
are formed of an insulating material mixed with at least an alkali metal salt selected from potassium bromide, potassium fluoride and sodium fluoride.
When the SSG proposed in the aforementioned patent publication is discharged continually at intervals of 200 Hz (5.0 ms) in frequency, as shown in
FIG. 7
, a predetermined operating voltage can be supplied in a stable fashion. The SSG exhibiting the discharge characteristic of
FIG. 7
is the SSG
10
shown in
FIG. 5
having the insulating layers
18
mixed with potassium bromide. The potassium bromide thus added represents 15% by weight of the water glass solution forming the insulating layers
18
. This potassium bromide is dissolved in the water glass contained in the insulating material and coated on the discharge surfaces
16
,
16
of the electrode pair
14
a
,
14
b.
In
FIG. 7
, point A represents a discharge start voltage, which is set to 1000 V in this case.
In recent years, gas discharge lamps such as metal halide lamps or xenon lamps have been employed for home-use projectors or TVs or for headlights of automobiles. The SSG is used for the lighting circuit of such lamps. For automotive applications, the SSG is often installed in the engine compartment.
For this reason, demand is high for a SSG which can discharge in stable fashion even when discharged continually at intervals of 400 Hz (2.5 ms) in a high-temperature (150° C.) environment.
In the case where the SSG
10
formed with an insulating layer
18
made of potassium bromide, representing 15% by weight of a water glass solution, is discharged continually at intervals of 2.5 ms at room temperature, however, the discharge is often suspended midway as shown in FIG.
8
.
Also in the case where the SSG
10
is continually discharged at intervals of 200 Hz (5.0 ms), it has been found that when the ambient temperature of the SSG
10
is increased to 150° C., the discharge start voltage is liable to become unstable as shown in FIG.
9
.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide a SSG which can be continually discharged in a stable fashion at intervals of 2.5 ms in a high-temperature (150° C.) environment.
The present inventor, after studying this problem, has attained this invention by finding that a stable continuous discharge at intervals of 2.5 ms is possible when the insulating layers
18
,
18
formed on the discharge surfaces
16
,
16
of a pair of the electrodes
14
a
,
14
b
making up the SSG
10
are mixed with potassium bromide and nickel bromide.
Specifically, according to this invention, there is provided a discharge tube comprising at least a pair of electrodes with the discharge surfaces thereof arranged in opposition to each other in a space portion filled with a sealing gas, wherein an insulating material composed of a mixture of potassium bromide and nickel bromide is coated on the discharge surfaces of the electrode pair thereby to form insulating layers.
The discharge tube (SSG) according to this invention can discharge continually in stable fashion at intervals of 2.5 ms. This is possible even in a high-temperature (150° C.) environment.
The discharge tube (SSG) according to this invention, which can discharge stably even when mounted in the engine compartment of an automotive vehicle where the ambient temperature becomes high, is suitably applicable as a SSG for vehicles.
REFERENCES:
patent: 4665337 (1987-05-01), Watzke et al.
patent: 4924347 (1990-05-01), Cantargel
patent: 5892648 (1999-04-01), Bobert et al.
patent: 0 769 832 (1997-04-01), None
patent: 8-506449 (1996-07-01), None
Font Frank G.
Lauchman Layla G.
Pennie & Edmonds LLP
Shinko Electric Industries Co. Ltd.
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