Starter transformer for discharge lamp

Abstract: In a discharge lamp apparatus for a vehicle, it is determined that a grounded condition is present when a lamp voltage (VL) is less than a predetermined voltage and a lamp current (IL) is less than a predetermined current. Electric power supply to the lamp (2) is stopped temporarily in response to the determination of the grounded condition, and then the lighting operation is restarted again. If the grounded condition is determined again, the above operation is repeated. If this repetition continues for a predetermined period, the lighting operation is disabled continuously. In controlling the lamp (2), a voltage of a battery (1) is boosted by a transformer (41), which is turned on and off by a MOS transistor (42) so that electric power supplied to the lamp (2) is duty-controlled. An upper limit is set to the duty ratio, and the upper limit is increased as the lamp current decreases, so that the lighting characteristics of the lamp (2) is improved. A starter transformer (71) has a closed magnetic circuit core (701a), and is encased within a ballast casing (710), which is disposed under the lamp (2).

Description: The present invention relates to a discharge lamp apparatus, which drives a high voltage discharge lamp and is preferably used as a vehicle front light. Various discharge lamp apparatuses are proposed (e.g., JP-A-9-180888 (USP 5,751,121) and JP-A-8-321389), which use a high voltage discharge lamp (lamp) as a vehicle front light, drives the lamp by alternating current (a.c.) voltage after boosting a voltage of a vehicle-mounted battery by a transformer and switching the polarity of the high voltage by an inverter circuit. This lamp is mounted inside of a reflector provided at a vehicle front part. When an electric wiring part of the lamp is grounded accidentally, an excessive current flows and melts a fusible link or damage circuit devices in the discharge lamp apparatus. Further, a switching device is provided at a primary side of a voltage boosting transformer to control a primary current, and controls electric power supplied to the lamp by pulse width modulation (PWM) control based on a lamp voltage and a lamp current. In this PWM control, when the duty ratio is increased to increase the electric power of the lamp, the secondary side output of the transformer decreases oppositely. Therefore, a maximum duty ratio is set to limit the duty ratio to be less than a maximum. However, if the maximum duty ratio is set as above, the lamp can not be supplied with sufficient electric power when the lamp does not continue to light because of decrease in the lamp current at the time of starting lighting the lamp. Still further, in the above discharge lamp apparatus, an electronic unit for the lamp is encased within a ballast housing, and the ballast housing is mounted outside of the lamp. Thus, extra space is required at the outside of the lamp. EP-0735799 A2 discloses a lamp assembly for use with a rapid start metal halide bulb (11), including a lamp head housing (1) and a power supply source (51). The lamp head housing includes a circuit board (13) with power supply contact surfaces (23, 24, 25), a high voltage resistant socker (12) a reflector (15), and an on-off switch, (30). The circuit board provides an ignition voltage, an ignition voltage spike, and a supply voltage to the rapid start metal halide bulb. The power supply contact surfaces (46, 47, 48) connect power to the circuit board. The high voltage resistant socket holds the rapid start metal halide bulb and is electrically coupled with the circuit board. The reflector is arranged relative to the high voltage resistant socket, and reflects light emitted from the rapid start metal halide bulb. The on-off switch is electrically coupled with the circuit board. The power supply source provides an AC or DC power supply and is adapted to be either mechanically coupled with the lamp head housing such that its contacts contact the power supply contact surfaces of the lamp head housing or wire connected to the lamp head housing. It is primary object of the present invention to improve operation characteristics of a discharge lamp apparatus. According to the present invention, an discharge lamp apparatus with the features of claim 1 is provided, wherein a ballast casing encasing a starter transformer is mounted in a lamp. A cross sectional area S of a closed magnetic circuit core of the starter transformer and an inside height H of the ballast casing are determined to satisfy a relation of H ≦ -0.0015 S 2 + 0.54 · S - 11.49. A gap of the core is located at the central part side in the ballast casing. Other objects, features and advantages of the present invention will be understood more fully from the following detailed description made with reference to the drawings. Fig. 1 is a schematic side view showing a mounting position of a ballast casing according to a third embodiment of the present invention; Figs. 2A and 2B are sectional views showing a starter transformer encased within the ballast casing; Figs. 3A and 3B are explanatory views for evaluating a leakage flux at a gap portion of a closed magnetic circuit core; Figs. 4A and 4B are explanatory views showing a relation between a core cross sectional area and a ballast casing inside height; Figs. 5A and 5B are partial cross sectional views showing the starter transformer in the ballast casing shown in Fig. 1; Fig. 6 is a partial cross sectional view showing an example in which a gap of a closed magnetic circuit core is provided at an end side in the ballast casing; Fig. 7 is a partial cross sectional view showing another example in which the gap of the closed magnetic circuit core is provided at the end side in the ballast casing; Fig. 8 is a partial cross sectional view showing a further example in which the gap of the closed magnetic circuit core is provided at a central side in the ballast casing; Fig. 9 is a cross sectional view showing a cross section taken along line XXV-XXV in Fig. 6; and Fig. 10 is a graph showing a relation of a clearance relative to a ratio between the core cross sectional area and the gap size. The present invention will be described in detail with reference to a embodiment and modification. The embodiment is directed to an installation of the electronic unit and the lamp 2 used, for instance, in the embodiment. As shown in Fig. 1, it is preferred to encase the electronic unit in a ballast casing 710 and dispose the ballast casing 710 within a housing 711 of a vehicle front light. In this instance, the ballast casing 710 is positioned underneath a reflector 714, and therefore need be sized thin to adapt in a limited space between the reflector 714 and the housing 711. However, if the ballast casing 710 is sized thin, there arises a disadvantage that the performance of the starter transformer 71 encased in the ballast casing 710 is lessened. That is, the leakage magnetic flux increases with the result of lessening of performance, if the ballast casing 710 is sized thin, because the starter transformer 71 is a closed magnetic circuit type and the ballast casing 710 is made of a conductive material such as aluminum to shield electromagnetic wave. If the starter transformer 71 is an open magnetic circuit type in which the primary coil 71a and the secondary coil 71b (not shown) is wound around a core 701a as shown in Fig. 2A, electric current flows though the coil 71a in a direction indicated by a solid arrow. At this moment, the magnetic flux is formed in arrow directions shown in Fig. 2B by the primary coil 71a. Thus, 1 = 2 + 3 holds, in which 1 indicates the effective magnetic flux in the coil portion, 2 indicates the magnetic flux in the ballast casing 710, and 3 indicates the magnetic flux leaking to the outside of the ballast casing 710. In this case, the total magnetic flux in the ballast casing 710 is 1 - 2 (= 3). An eddy current flows through the ballast casing 710, which is a conductive body, in a direction to cancel 1 - 2 (arrow direction indicated by a dotted line in Fig. 2A). Therefore, the effective magnetic flux in the starter transformer 71 is about (1 - 3), and the performance is lessened in accordance with the amount of magnetic flux leaking to the outside of the ballast casing 710. In this instance, it becomes necessary to add a primary voltage boosting circuit, increase a capacitance of a charging capacitor, resulting in increased cost for ensuring the performance. The lessening of performance may be overcome by the use of the starter transformer 71, which is a closed magnetic circuit type, because the ratio of the above magnetic flux 3 can be decreased. Even the closed magnetic circuit type, however, has the gap in the closed magnetic circuit core to restrict magnetic saturation. Thus, it is still likely that the performance is lessened by the leakage magnetic flux at the gap portion. As a method for calculating the magnetic circuit at the gap portion, Roters permeance equation which is restricted to a simple geometric shape. The magnetic circuit at the gap portion is considered to be divided into five locations as shown in Figs. 3A and 3B, which show perspectively and cross sectionally, respectively. Each permeance P1 to P5 of the magnetic circuits is expressed by the following equation 1 to equation 5. Here, P1 is a permeance of the magnetic circuit of a semi-cylindrical part, P2 is a permeance of a the magnetic circuit of a semi-hollow cylindrical part, P3 is a permeance of the magnetic circuit of one quarter sphere, P4 is a permeance of the magnetic circuit of a shell of the one quarter sphere, and P5 is a permeance of the magnetic circuit at opposing parts. [Equation 1] P1 = 2 · 0.26 · µ 0 · (A + B) [Equation 2] P2 = 2 · µ 0 · (A + B) / π · ln(l + 2 · X / G) [Equation 3] P3 = 4 · 0.077 · µ 0 · G [Equation 4] P4 = µ 0 · X [Equation 5] P5 = µ 0 · A · B / G The ratios of the magnetic flux passing through the magnetic circuits are proportional to the ratios of the permeance, as long as the magnetic circuits are in series. In case that the ballast casing 710 is sized thin, the parts P2 and P4, which are located as the outermost shells, pass though the outside of the ballast casing 710. Thus, the lessening of performance can be estimated by the ratio of magnetic flux. In this instance, although the estimation of the lessening of performance is influenced by X, X is set to a maximum, 20mm, with which the influence of leakage magnetic flux arises. Further, as the magnitude G of the gap increases, the magnetic flux at the P1 part and the P3 part become the leakage magnetic flux, resulting in further lessening of performance. By setting G >> A, B, the lessening of performance saturates and the lessening of performance in the open magnetic circuit can be estimated. Based on the evaluation of the leakage magnetic flux at the gap portion, the lessening of performance relation between the cross sectional area S (mm 2 ) of the core and the inside height H (mm) of the ballast casing 710 is analyzed. Here, the core sectional area S and the ballast casing inside height H is shown in Fig. 4A. In case that the core sectional area S is held unchanged, the performance lessens more as the ballast casing inside height H decreases. Oppositely, in case that the ballast casing inside height H is held unchanged, the performance lessens more as the core sectional area S increases. The boundary between the core sectional area S and the ballast casing inside height H which causes 10% performance decrease by the leakage magnetic flux is shown in Fig. 4B, with respect to a case in which G is sufficiently large, that is, the magnetic circuit is in substantially the open type. This boundary is expressed as H = -0.015 · S 2 + 0.54 · S - 11.49. The open magnetic circuit type has a large lessening of performance at the lower part in the boundary. That is, the performance can not be ensured, unless the closed magnetic circuit type is used. Therefore, specifically, the embodiment using the closed magnetic circuit core is constructed as shown in Figs. 5A and 5B. In the embodiment, the ballast casing 710 made of aluminum is disposed within the housing 711 of the front light as shown in Fig. 1. Various electrical component parts for lighting the lamp 2 is encased within the ballast casing 710, although only the starter transformer 71 is shown. The starter transformer 71 1 is constructed by the closed magnetic circuit core 701a and the primary coil 71a and the secondary 71b. Although shown in Fig. 5B but not in Fig. 5A, the primary coil 71a of the starter transformer 71 is wound around the secondary coil 71b. The closed magnetic circuit core 701a is provided with a gap 701c. The closed magnetic circuit core 701a has a cross sectional area S of about 120mm 2 , and the ballast casing 710 has an inside height H of about 17mm. In this instance, as the core cross sectional area S and the ballast casing inside height H satisfy the relation, that is, H ≦ -0.0015 · S 2 + 0.54 - S - 11.49, the starter transformer 71 should be the closed magnetic circuit type to provide a sufficient performance. Further, as the starter transformer 71 constitutes a high voltage part, it is disposed at a dislocated position which is a longitudinal end part in the ballast casing 710, that is, one side in the ballast casing 710 which is in a rectangular parallelopiped shape in a longitudinal direction (that is, at the side of a side wall 701a of both side walls 710a and 710b opposing each other in the ballast casing 710). Here, the gap 701c is provided at a location, which is the other side (that is, at the side of the other side wall 710b) in the ballast casing 710 in the longitudinal direction. Thus, crossing of the leakage magnetic flux at the gap 1c with the ballast casing 710 can be restricted to reduce the lessening of performance. In positioning the starter transformer 71 at the end part in the ballast casing 710, it is considered that the gap 701c of the closed magnetic circuit core 701a is provided at the end part side in the ballast casing 710 as shown in Figs. 6 and 7. In this case, however, as the leakage flux at the gap 1c crosses the ballast casing 710, the performance lessens. As opposed to this, in case that the gap 701c of the closed magnetic circuit core 701a is provided at the side of the central part in the ballast casing 710 as shown in Figs. 5A and 5B, the gap 701c is positioned away from the side walls 710a and 710b. The crossing of the leakage magnetic flux at the gap 701c crosses less with the ballast casing 710, thereby reducing lessening of performance. It is to be noted that the gap 701c of the closed magnetic circuit core 701a may be provided at two positions at the central part in the ballast casing 710 as shown in Fig. 8. If the gap 701c is provided at the other side in the ballast casing 710 in the longitudinal direction, that is, at the side of the side wall 710b, the leakage magnetic flux can be restricted from crossing the ballast casing 710 while utilizing a wide space in the ballast casing 710. If the starter transformer 71 is disposed at the position dislocated toward one of the opposing side walls 710c and 710d in the ballast casing 710, the gap may be provided at the other one of the side walls 710c and 710d. Further, there may be a case in which the gap 701c must be provided at the end part side in the ballast casing 710, that is, at the side of the side wall 710b, as shown in Fig. 6 from the constraint in the magnetic circuit construction or in the production. In this instance also, the lessening of performance can be restricted in consideration of the following points. If there exists the gap on the side of the ballast casing 710 as shown in Fig. 6, the lessening of performance increases particularly in the regions P2 and P4, which is at the side of the wall in Fig. 9 showing a cross section along line XXV-XXV. The lessening of performance calculated using the equation 1 to equation 5 with respect to various core cross sectional area S and the gap size G results in the characteristics shown in Fig. 10. In Fig. 10, the abscissa indicates S (mm 2 ) / G (mm) and the ordinate indicates the clearance L (mm) between the inside wall of the ballast casing 710 and the gap 701c. The required clearance L is dependent on S/G. This means that the ratio of the leakage magnetic flux increases and hence the clearance against the ballast casing 710 is required, as the magnetic resistance (= S/µg : P5 region with no leakage magnetic flux considered) of the gap 701c. As understood from Fig. 10, the lessening of performance can be restricted to less than 10% as long as the relation of L ≧ 28.2 · e -0.075(S/G) is satisfied. The present invention described above should not be limited to the disclosed embodiments and modifications, but may be implemented in other ways without departing from the spirit of the invention.

Claims: A discharge lamp apparatus comprising: a ballast casing (710); and a starter transformer (71) encased in the ballast casing (710), characterized in that the starter transformer (71) has a closed magnetic circuit core (701a), and an inside height H (mm) of the ballast casing and a cross sectional area S (mm 2 ) of the closed magnetic circuit core satisfies H ≤ -0.0015 • S 2 + 0.54 • S - 11.49. A discharge lamp apparatus comprising: a ballast casing (710); and a starter transformer (71) encased in the ballast casing (710), characterized in that the starter transformer (71) has a closed magnetic circuit core (701a), and a clearance L (mm) between an inside wall of the ballast casing (710) and a gap (701c) of the closed magnetic circuit core (701a) satisfies L ≥ 28.2 • e -0.075(S/G) , with S (mm 2 ) being a cross sectional area of the closed magnetic circuit core (701a) and G (mm) being a size of the gap (701c) of the closed magnetic circuit core (701a). A discharge lamp apparatus according to claim 1 or 2, wherein the starter transformer (71) has a closed magnetic circuit core (701a), the starter transformer (71) is located closer to one of two opposing side walls (710a, 710b), characterized in that a gap (701c) of the closed magnetic circuit core (701a) is located closer to the other of the two opposing side walls (710a, 710b), and a primary coil (71a) of the starter transformer (71) is wound around a secondary coil (71b) of the starter transformer (71). A discharge lamp apparatus according to claim 3, wherein the the ballast casing (710) is in a rectangular parallelopiped shape and the starter transformer (71) is located in the ballast casing (710) in a longitudinal direction of the ballast casing (710) near one of the two opposing side walls (710a, 710b).

Inventors: FUNAYAMA TOMOYUKI, NOYORI YASUSHI, ODA GOICHI, OKUCHI HIROAKI, YAMAMOTO NOBURU, FUNAYAMA, TOMOYUKI, NOYORI, YASUSHI, ODA, GOICHI, OKUCHI, HIROAKI, YAMAMOTO, NOBURU, Noyori, Yasushi, Koito Manufacturing Co., Ltd., Oda, Goichi, Koito Manufacturing Co., Ltd., Okuchi, Hiroaki, Denso Corporation, Yamamoto, Noburu, Denso Corporation
Applicants: DENSO CORP, KOITO MFG CO LTD, DENSO CORPORATION, KOITO MANUFACTURING CO., LTD
Application year: 1999
Main classification: H05B41
IPC codes: H05B41