Electric lamp and discharge devices: systems – Special application – Vehicle
Reexamination Certificate
1999-12-10
2001-08-28
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Special application
Vehicle
C315S088000, C315S307000, C307S010800, C340S475000
Reexamination Certificate
active
06281631
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vehicle headlight system, and in particular to an automobile headlight system that controls a pulsed power source to energize a set of lighting elements.
2. Related Art
Motor vehicle headlight systems generally allow a set of headlamps to be illuminated in a low beam mode or a high beam mode. Usually, each headlamp includes a low beam filament and a high beam filament, wherein the low beam filaments are energized in the low beam mode and the high beam filaments are energized in the high beam mode. Such a system usually includes two relays and four fuses. One relay is used to energize both low beam filaments at full intensity and the other relay is used to energize both high beam filaments at full intensity. Each fuse is associated with, and provides overload protection, for a particular filament.
The system described above has a number of disadvantages. First, such a system does not allow pulsed power to be applied across the headlamp filaments because pulsed voltage cannot be continuously applied across a relay. Instead, the filaments are continuously energized at a particular voltage level; usually battery voltage minus small voltage drops from the system. Continuously energizing the filaments at high intensity causes high power consumption and shortens the life of the filaments. Also, fuses are mechanical devices that must be manually replaced in the event of a short to ground. When a fuse blows, the vehicle is usually taken to a dealer to replace the fuse for a cost or under warranty. As mechanical devices, fuses can be less reliable than semiconductor devices. Additionally, fuses do not allow the system to sense whether there is an open or short circuit condition in the headlight system and to automatically switch power to an operable filament when a fault condition is present with a particular filament.
Therefore, it is desirable to provide a vehicle headlight system that allows pulsed power to be applied across selected headlight filaments. It is also desirable to provide a vehicle headlight system which includes solid state switching devices to connect the filaments to the power source, and a control element to detect the presence of a fault condition and automatically adjust the headlight system to overcome detected fault conditions.
SUMMARY OF THE INVENTION
The present invention is a headlight system that provides pulsed power to the headlamp filaments through a set of solid state switching devices controlled by a control element. The present headlight system is capable of supplying pulsed power to maintain a constant RMS value across the selected headlamp filaments.
Using solid state switching devices reduces the need to have a fuse for each filament and thus the requirement of fuse serviceability. The present headlight system also recognizes when a fault condition exists for a particular filament and automatically switches to an operable filament. The present vehicle headlight system is also configured to adjust a characteristic of the pulsed power, for example, by adjusting the duty cycle of a PWM drive signal, in order to adjust the brightness of the filaments in either headlamp. For example, it may be desirable to compensate for the loss of low beam filament in one headlamp by energizing the high beam filament and adjusting the pulsed power across the high beam filament so that the brightness of that high beam filament approximates the brightness of the low beam filaments of the unaffected headlamp.
In one embodiment, the present vehicle headlight system comprises: a first lamp comprising first and second filaments; a second lamp comprising third and fourth filaments; a power supply; first and second switches, each of the switches having an input coupled to the power supply and an output coupled to a respective one of the first and second lamps, each switch output providing one of a constant output and a pulsed output in response to a control signal; first and second sensors respectively operatively coupled to one of the first and second switches, the first and second sensors providing a fault indication when a respective one of the first, second, third and fourth filaments are inoperable; a control unit coupled to the first and second switches and adapted to provide the control signal, the control signal automatically causing one of the first and second switches to provide a first pulsed output so that the brightness of the second and fourth filaments is approximately equal to the brightness of the first and third filaments when the fault indication is present.
In another embodiment of the present invention, each of the headlamps include one filament and a control unit that controls a characteristic of the pulsed power across a particular filament to provide both low and high beam brightness levels from the filament. Here, only one filament is required to provide both levels of brightness. For example, the headlight system may be configured to provide PWM signal to the headlight filaments and the control unit may adjust the brightness of the filaments by adjusting the duty cycle of the PWM signal. In another embodiment, a range of duty cycles may be provided in order to provide a range of headlamp brightness levels rather than only low beam and high beam levels.
Further details and advantages of the invention will be apparent from the accompanying drawing and following description.
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Siemens PROFET Preliminary Data Sheet BTS550P, Aug. 31, 1998 PCT International Search Report.
Poirier James Anthony
Schaffer Thomas Scott
Philogene Haissa
Siemens Automotive Corporation
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