1. Field of the Invention
The present invention relates generally to discharge tubes, and more particularly to a discharge tube that causes discharge to repeatedly occur between the discharge surface of an upper discharge electrode end and the discharge surface of a lower discharge electrode end, the discharge surfaces opposing each other at the center inside an airtight tube.
2. Description of the Related Art
For instance, Japanese Laid-Open Patent Application No. 10-335042 discloses a switching discharge tube (hereinafter, simply referred to as “discharge tube”) used in lighting circuits for an HID (High Intensity Discharge) lamp for vehicles, projector lamp, and a back lamp for rear-projection TVs.
Referring to
Disk-like lid bodies 26 and 28 are formed integrally with the upper discharge electrode 22 and the lower discharge electrode 24, respectively. A metallized surface 40 is formed at each of the upper-end opening and the lower-end opening of the airtight tube 10D. Accordingly, the upper discharge electrode 22 and the lower discharge electrode 24 are joined to the airtight tube 10D by brazing the lid bodies 26 and 28 integrated with the upper and lower discharge electrodes 22 and 24, respectively, to the metallized surfaces 40 formed at the upper-end and lower-end openings of the airtight tube 10D. Referring to
The upper discharge electrode 22 projects from the lid body 26 toward the center position of the airtight tube 10D. The end portion of the upper discharge electrode 22 is shaped like a cylinder of a small diameter. A discharge surface 23 is formed on the small-diameter cylindrical end portion of the upper discharge electrode 22 (hereinafter referred to as “upper discharge surface 23”). The upper discharge surface 23 includes a recess 27 for causing discharge to occur in a stabilized manner.
The lower discharge electrode 24 is structured in the same manner. The end portion of the lower discharge electrode 24 is shaped like a cylinder of a small diameter. A discharge surface 25 is formed on the small-diameter cylindrical end portion of the lower discharge electrode 24 (hereinafter referred to as “lower discharge surface 25”). The lower discharge surface 25 also includes the recess 27 for causing discharge to occur in a stabilized manner. In the discharge tube 100A, discharges occur in the space between the upper discharge surface 23 and the lower discharge surface 25. This space is hereinafter referred to as a “discharge gap 29.”
Referring to
According to the second conventional discharge tube 100B, two sub discharge trigger wires 20 as well as the eight main discharge trigger wires 30 are formed on the inner sidewall of an airtight tube 10E. Each sub discharge trigger wire 20 is formed at a center position of the eight main discharge trigger wires 30. That is, four of the main trigger wires 30 are provided in each of the two spaces between the paired sub discharge trigger wires 20.
Like the main discharge trigger wires 30, the sub discharge trigger wires 20 are formed along the axial directions of the airtight tube 10E (or the Y1 and Y2 directions of
Conventionally, the sub discharge trigger wires 20 and the main discharge trigger wires 30 are also formed along the axial directions of the airtight tube 10E (or the Y1 and Y2 directions of
In this test, the initial discharge starting voltage FVs and the mean discharge voltage Vs MEAN at the time of causing the discharge tube 100A to perform discharging after the discharge tube 100A was left in a completely dark place at −40° C. for a predetermined period of time were studied at each predetermined point. Specific test conditions are as follows:
Specifically, in the case of measuring data at a specified measurement number of 20,000, the test cycle is stopped when the number of times the test cycle is repeated reaches 200, and the discharge tube 100A is left as it is for an hour. Thereafter, the discharge tube 100A is caused to operate for one test cycle, and the initial discharge starting voltage FVs and the mean discharge voltage Vs MEAN are measured and calculated. When this measurement operation is completed, the test cycle is started, and is repeated until the next specified measurement number (for instance, 40,000). This operation is repeatedly performed until a specified measurement number of 2,000,000; and
The discharge life test is conducted based on the above-described conditions. This discharge life test, which is conducted in a completely dark place in an environment of −40° C., is the severest one of the discharge life tests. This is because there is no effect of thermoelectrons in the environment of −40° C., nor is there any effect of photoelectrons in the completely dark place, thus making it difficult for discharging to occur. A brief description is given below of the effect of photoelectrons and the effect of thermoelectrons.
The effect of photoelectrons refers to the effect that the discharge characteristic of a discharge tube is made faster by photoelectrons. That is, photoelectrons are constantly emitted from the light source of, for instance, an illuminator, so that sufficient photoelectrons have also penetrated into the discharge tube in a light environment. These photoelectrons have the effect of exciting gas sealed in the discharge tube into an easily dischargeable state. Accordingly, the discharge tube placed in a light environment is in a stabilized and easily dischargeable state, thus causing a decrease in the initial discharge start voltage FVs. On the other hand, in a dark place, these photoelectrons do not exist, so that the discharge tube is unstable and it is difficult for discharging to occur, thus causing an increase in the initial discharge start voltage FVs.
The effect of thermoelectrons refers to the effect that the discharge characteristic of a discharge tube is made faster by thermoelectrons. That is, with an increase in temperature, an electron in the outermost shell of an atom becomes more likely to be emitted from the orbit of the outermost shell. Accordingly, the number of thermoelectrons generated also increases in the discharge tube as temperature increases. Therefore, the discharge tube is in a stabilized and easily dischargeable state in a high-temperature environment, thus causing a decrease in the initial discharge start voltage FVs. On the other hand, in a low-temperature environment, the number of thermoelectrons generated is reduced, so that the discharge tube is unstable and it is difficult for discharging to occur, thus causing an increase in the initial discharge start voltage FVs.
For the above-described reasons, the environment of −40° C. and complete darkness (hereinafter referred to as “dark cold environment”) is a harsh environment where it is difficult for the discharge tube 100A to cause discharging to occur. On the other hand, if a desired discharge characteristic can be obtained in this dark cold environment, a good FVs characteristic may be obtained in any environment.
Referring to
Thus, the discharge tube 100A has a problem in that the occurrence of surface corona discharge is delayed so as to reduce the response speed of the initial discharge start voltage FVs. Further, the initial discharge start voltage FVs increases with an increase in the cumulative number of discharges. In particular, the initial discharge start voltage FVs exceeds 1000 V around when the cumulative number of discharges exceeds 800,000, thus causing a problem in that the discharge life of the discharge tube 100A is reduced.
Meanwhile,
Specifically, referring to
Thus, fluctuations in the initial discharge start voltage FVs cause the operation of a ballast circuit for lighting an HID lamp using the discharge tube 100B to be unstable. However, compared with the FVs characteristic of the discharge tube 100A, the initial discharge start voltage FVs is prevented from rising excessively in the discharge tube 100B.
Accordingly, it is a general object of the present invention to provide a discharge tube in which the above-described disadvantages are eliminated.
A more specific object of the present invention is to provide a discharge tube with a longer useful service life and a capability to generate stable discharging.
The above objects of the present invention are achieved by a discharge tube, including: an airtight tube formed of an insulator, the airtight tube having first and second end surfaces each having a metallized surface formed thereon; a first discharge electrode joined to the metallized surface formed on the first end surface of the airtight tube; a second discharge electrode joined to the metallized surface formed on the second end surface of the airtight tube; and a plurality of trigger lines formed on an inner wall surface of the airtight tube so as to extend in axial directions of the airtight tube, wherein: the first and second discharge electrodes are joined to the metallized surfaces so that a discharge gap is formed between the first and second discharge electrodes and the airtight tube is hermetically sealed; the trigger lines include one or more first trigger lines connected to the metallized surfaces and a plurality of second trigger lines isolated from the metallized surfaces; and the second trigger lines are formed at equal intervals on the inner wall surface of the airtight tube and each of the one or more first trigger lines is formed between a corresponding pair of adjacent ones of the second trigger lines.
The above objects of the present invention are also achieved by a discharge tube, including: an airtight tube formed of an insulator, the airtight tube having first and second end surfaces each having a metallized surface formed thereon; a first discharge electrode joined to the metallized surface formed on the first end surface of the airtight tube; a second discharge electrode joined to the metallized surface formed on the second end surface of the airtight tube; and a plurality of trigger lines formed on an inner wall surface of the airtight tube so as to extend in axial directions of the airtight tube, wherein: the first and second discharge electrodes are joined to the metallized surfaces so that a discharge gap is formed between the first and second discharge electrodes and the airtight tube is hermetically sealed; the trigger lines include one or more first trigger lines connected to the metallized surfaces, a plurality of second trigger lines isolated from the metallized surfaces, and one or more third trigger lines isolated from the metallized surfaces; and the second trigger lines are formed at equal intervals on the inner wall surface of the airtight tube and each of the one or more third trigger lines is formed between a corresponding pair of adjacent ones of the second trigger lines.
The above objects of the present invention are also achieved by a discharge tube, including: an airtight tube having first and second end surfaces each including a metallized surface; first and second discharge electrodes joined to the metallized surfaces of the first and second end surfaces, respectively, of the airtight tube so that a discharge gap is formed between the first and second discharge electrodes and the airtight tube is hermetically sealed; and a plurality of trigger lines arranged on an inner wall surface of the airtight tube so that each trigger line extends along an axis of the airtight tube, the trigger lines being spaced at first and second intervals in first and second parts, respectively, of the inner wall surface, the first and second intervals being different from each other.
According to the present invention, in a discharge tube, trigger lines, arranged with a first part where the trigger lines are arranged at a first interval and a second part where the trigger lines are arranged at a second interval different from the first interval, are formed in the arrangement. This configuration enables the discharge tube to have a longer useful service life and to stabilize discharge potentials repeatedly generated in the discharge tube.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:
Next, a description is given, with reference to the accompanying drawings, of embodiments of the present invention.
Referring to
The airtight tube 10A is shaped like a cylinder and formed of an insulator such as a ceramic. The outside dimensions of the airtight tube 10A are defined so that the airtight tube 10A is, for instance, 8.0 mm in outside diameter, 6.0 mm in inside diameter, and 4.7 mm in length. Further, the metallized surfaces 40 are formed at the upper-end opening and the lower-end opening of the airtight tube 10A.
Each of the lid bodies 26 and 28 is formed of metal such as 42 alloy (an iron-nickel alloy), and has a substantially disk shape. The upper discharge electrode 22 is integrated with the lid body 26, and the lower discharge electrode 24 is integrated with the lid body 28. The lid bodies 26 and 28 are joined to the upper-end opening and the lower-end opening, respectively, of the airtight tube 10A. Specifically, the lid bodies 26 and 28 are joined to the airtight tube 10A by being brazed to the corresponding metallized surfaces 40.
This joining is performed so that the upper discharge electrode 22 and the lower discharge electrode 24 oppose each other in the airtight tube 10A. Further, at the time of this joining, the airtight tube 10A is filled with a gas mixture of inert gas. Accordingly, the gas mixture filling the airtight tube 10A is hermetically sealed in the airtight tube 10A by joining the lid bodies 26 and 28 to the airtight tube 10A.
With the lid member 26 being joined to the airtight tube 10A, the upper discharge electrode 22 projects from the lid member 26 toward the center position of the airtight tube 10A. Further, the upper discharge surface 23 is formed on the end portion of the upper discharge electrode 22. The upper discharge surface 23 includes the recess 27 for causing discharge to occur in a stabilized manner.
Likewise, with the lid member 28 being joined to the airtight tube 10A, the lower discharge electrode 24 projects from the lid member 28 toward the center position of the airtight tube 10A. Further, the lower discharge surface 25 is formed on the end portion of the lower discharge electrode 24. The lower discharge surface 25 includes the recess 27 for causing discharge to occur in a stabilized manner.
In the discharge tube 1A, discharges occur in the discharge gap 29, which is the space between the upper discharge surface 23 and the lower discharge surface 25.
According to this embodiment, the recess 27 formed on each of the upper discharge surface 23 and the lower discharge surface 25 includes irregularities in order to increase the area of each of the discharge surfaces 23 and 25 so that the discharge (service) life of the discharge tube 1A is prolonged. That is, since the discharge life of a discharge tube is proportional to the area of a discharge surface, the discharge life of the discharge tube 1A can be prolonged by increasing the area of each of the discharge surfaces 23 and 25 by providing irregularities thereto.
Referring to
Each main discharge trigger wire 80 is made of a conductive material such as carbon, and is defined to be approximately 0.5 mm in line width w (
Each sub discharge trigger wire 60 is made of a conductive material such as carbon, and is set to be approximately 0.5 mm in line width but shorter in length than the main discharge trigger wires 80. One of the upper end and the lower end of each sub discharge trigger wire 60 is electrically connected to the metallized surface 40 formed on the upper-end or lower-end surface of the airtight tube 10A.
Further, referring to
A description is given below, with reference to
The ten main discharge trigger wires 80 are formed at equal intervals (with the same pitch W). That is, the interval between each pair of the adjacent main discharge trigger wires 80 is the regular interval W. On the other hand, the sub discharge trigger wires 60 are formed 180° apart from each other. Accordingly, five of the main discharge trigger wires 80 are provided in each of the two spaces between the pair of the sub discharge trigger wires 60.
Referring back to
On the other hand, referring to
In particular, according to this embodiment, each sub discharge trigger wire 60 is positioned in the center between the paired main discharge trigger wires 80 (indicated by arrows MT1 and MT2). Accordingly, the interval between each sub discharge trigger wire 60 and the corresponding main discharge trigger wire 80 indicated by arrow MT1 is W/2 and the interval between each sub discharge trigger wire 60 and the corresponding main discharge trigger wire 80 indicated by arrow MT2 is also W/2.
Accordingly, equal interval parts and unequal interval parts are formed in the overall trigger wire arrangement of the sub discharge trigger wires 60 and the main discharge trigger wires 80. That is, the equal interval parts where the main discharge trigger wires 80 are equally spaced side by side at the same interval (regular intervals) W (each region indicated by arrow A in
In this test, the initial discharge starting voltage FVs and the mean discharge voltage Vs MEAN at the time of causing the discharge tube 1A to perform discharging after the discharge tube 1A was left in a completely dark place at −40° C. (dark cold environment) for a predetermined period of time were also studied at each predetermined point as in the discharge life tests described with reference to
As described above, the initial discharge starting voltage FVs is stable in the discharge tube 1A according to this embodiment. Accordingly, in the case of employing the discharge tube 1A in an HID lamp lighting circuit, a stable circuit operation can be realized. Further, there is no rise over time in the initial discharge starting voltage FVs, which enables the discharge tube 1A to have a longer useful service life.
Next, a description is given of a second embodiment of the present invention.
Compared with the discharge tube 1A according to the first embodiment, the discharge tube 1B according to this embodiment is characterized by further including interposition discharge trigger wires 90 (third trigger lines) each formed between a corresponding pair of the main discharge trigger wires 80. Like the main discharge trigger wires 80 and the sub discharge trigger wires 60, the interposition discharge trigger wires 90 are made of a conductive material such as carbon, and are formed (to extend) along the axial directions of the airtight tube 10B (or the Y1 and Y2 directions of
A description is given below of the state of disposition (arrangement) of the sub discharge trigger wires 60, the main discharge trigger wires 80, and the interposition discharge trigger wires 90 formed on the airtight tube 10B according to this embodiment.
First, the ten main discharge trigger wires 80 are also formed at regular intervals (with the same pitch W) in this embodiment. The sub discharge trigger wires 60 are formed 180° apart from each other. Accordingly, five of the main discharge trigger wires 80 are provided in each space between the pair of the sub discharge trigger wires 60. Further, each sub discharge trigger wire 60 is disposed between a corresponding pair of the main discharge trigger wires 80 (indicated by arrows MT1 and MT2 in
This embodiment is characterized in that each interposition discharge trigger wire 90 is further disposed between a corresponding pair of the main discharge trigger wires 80 (indicated by arrows MT3 and MT4) spaced at this regular interval W.
In particular, according to this embodiment, each interposition discharge trigger wire 90 is positioned in the center between the paired main discharge trigger wires 80 (indicated by arrows MT3 and MT4). Accordingly, the interval between each interposition discharge trigger wire 90 and the corresponding main discharge trigger wire 80 indicated by arrow MT3 is W/2 and the interval between each interposition discharge trigger wire 90 and the corresponding main discharge trigger wire 80 indicated by arrow MT4 is also W/2.
Accordingly, in the discharge tube 1B according to this embodiment, equal interval parts and unequal interval parts are also formed in the arrangement of the sub discharge trigger wires 60, the main discharge trigger wires 80, and the interposition discharge trigger wires 90. That is, the equal interval parts where the main discharge trigger wires 80 are equally spaced side by side at the same interval (regular intervals) W (each region indicated by arrow A in
In this test, the initial discharge starting voltage FVs and the mean discharge voltage Vs MEAN at the time of causing the discharge tube 1B to perform discharging after the discharge tube 1B was left in a completely dark place at −40° C. (dark cold environment) for a predetermined period of time were also studied at each predetermined point as in the discharge life tests described with reference to
Next, a description is given of a third embodiment of the present invention.
Like the above-described discharge tube 1B according to the second embodiment, the discharge tube 1C according to this embodiment is characterized by including the interposition discharge trigger wires 90 each formed between a corresponding pair of the main discharge trigger wires 80. The configuration of each interposition discharge trigger wire 90 is equal to that described in the second embodiment.
A description is given below of the state of disposition (arrangement) of the sub discharge trigger wires 60, the main discharge trigger wires 80, and the interposition discharge trigger wires 90 formed on the airtight tube 10C according to this embodiment.
In this embodiment, the main discharge trigger wires 80 are also formed at regular intervals (with the same pitch W). The sub discharge trigger wires 60 are formed 180° apart from each other. Accordingly, five of the main discharge trigger wires 80 are provided in each space between the pair of the sub discharge trigger wires 60. Further, each sub discharge trigger wire 60 is disposed between a corresponding pair of the main discharge trigger wires 80 (indicated by arrows MT1 and MT2 in
This embodiment is characterized in that each interposition discharge trigger wire 90 is further disposed between a corresponding pair of the main discharge trigger wires 80 positioned close to each sub discharge trigger wire 60. Specifically, referring to
Further, according to this embodiment, each interposition discharge trigger wire 90 is positioned at the center between a corresponding pair of the main discharge trigger wires 80 (MT1 and MT5 or MT2 and MT6). Accordingly, the interval between each interposition discharge trigger wire 90 and each of its adjacent main discharge trigger wires 80 (MT1 and MT5 or MT2 and MT6) is W/2.
Accordingly, in the discharge tube 1C according to this embodiment, equal interval parts and unequal interval parts are also formed in the arrangement of the sub discharge trigger wires 60, the main discharge trigger wires 80, and the interposition discharge trigger wires 90. That is, the equal interval parts where the main discharge trigger wires 80 are equally spaced side by side at the same interval (regular intervals) W (each region indicated by arrow A in
In this test, the initial discharge starting voltage FVs and the mean discharge voltage Vs MEAN at the time of causing the discharge tube 1C to perform discharging after the discharge tube 1C was left in a completely dark place at −40° C. (dark cold environment) for a predetermined period of time were also studied at each predetermined point as in the discharge life tests described with reference to
However, each of the positions at which the sub discharge trigger wires 60 and the interposition discharge trigger wires 90 are formed, respectively, is not limited to the center position between the corresponding pair of the main discharge trigger wires 80. Referring to
Further, the number of the sub discharge trigger wires 60 and the number of the interposition discharge trigger wires 90 are not limited to one, but may be more than one. In the configuration shown in
Thus, according to the present invention, in a discharge tube, trigger wires, arranged with a first part where the trigger wires are arranged at a first interval and a second part where the trigger wires are arranged at a second interval different from the first interval, are formed in the arrangement. This configuration enables the discharge tube to have a longer useful service life and to stabilize discharge potentials repeatedly generated in the discharge tube.
The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.
The present application is based on Japanese Priority Patent Application No. 2003-347031, filed on Oct. 6, 2003, the entire contents of which are hereby incorporated by reference.
Number | Date | Country | Kind |
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2003-347031 | Oct 2003 | JP | national |