Optical: systems and elements – Glare or unwanted light reduction – With mirror
Reexamination Certificate
1999-11-29
2001-06-05
Sikder, Mohammad (Department: 2872)
Optical: systems and elements
Glare or unwanted light reduction
With mirror
C359S601000, C359S604000, C359S265000, C359S267000
Reexamination Certificate
active
06243205
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a device for driving an EC (electrochromic) automatic dimming mirror (hereinafter simply referred to as “EC dimming mirror” or “dimming mirror”) used as an interior or exterior rear view mirror of a vehicle.
An EC dimming mirror is made by disposing an EC element film on the front surface of the reflecting surface of a mirror and achieves a dimming effect against light from headlights of a succeeding vehicle while running at night by changing the amount of coloration of the EC element and thereby controlling reflectivity of the mirror. For obtaining such dimming effect, the dimming mirror is so controlled that, upon detection of quantity of incident light from the rear, the amount of coloration increases (i.e., reflectivity decreases) when the light from the rear is strong whereas the amount of coloration decreases (the color fades, i.e., reflectivity increases) when the light from the rear is weak.
On the other hand, the glare of the light to the human eye is produced by all of the surrounding light and, therefore, the control based on the light from the rear only does not match the human sense. For this reason, a control is generally made in such a manner that not only rear light but also surrounding light is detected and color imparting and color fading controls are made in accordance with quantity of the detected rear and surrounding light. More specifically, when surrounding light is strong, the glare of the light is not so strong notwithstanding that there is rear light. In this case, the sensitivity of detection for the rear light is reduced for making it harder for the EC element to be colored. When the surrounding light is weak, the glare of the light to the rear light is strong and, in this case, sensitivity of detection for the rear light is raised for making it easier for the EC element to be colored.
In the prior art EC dimming mirror, surrounding light and rear light are detected and a value of voltage applied to the EC element is obtained by arithmetic operation in accordance with a combination of the surrounding light and the rear light and the amount of coloration, i.e., reflectivity, is controlled by this voltage. This prior art method, however, requires a structure for combining detected values of the surrounding light and the rear light and obtaining a control amount of a single object of control by arithmetic operation.
For overcoming this problem, the applicant of the present application has proposed, by U.S. Pat. No. 5,486,952 (Japanese Patent Application Laid-open Publication No. Hei 7-281212), a device for driving an EC dimming mirror which enables control of the amount of coloration by controlling the surrounding light and the rear light individually as separate objects of control and thereby realizes a simplified structure of the device.
This device includes oscillation means capable of controlling duration of an “H” level and duration of an “L” level individually and separately. The duration of one level of an oscillation signal produced by the oscillation means is variably controlled in response to surrounding light quantity and the duration of the other level of the oscillation signal is variably controlled in response to rear light quantity. Polarity of drive voltage is switched in accordance with the “H” level and “L” level of the oscillation signal from the oscillation means to pulse drive the EC element and thereby control the amount of coloration of the EC element.
As shown in
FIG. 2
, the value of drive current for driving an EC element becomes the largest at the moment the polarity of the current is switched from one polarity to the other. For this reason, according to the above described drive method utilizing the pulse voltage, each time the level of the pulse is switched between “H” and “L” (e.g., more than 100 times per minute), current of a large value flows as shown in
FIG. 3 and
, as a result, the device requires a very large power consumption.
Further, according to the drive system utilizing the pulse voltage, characteristics (sensitivity curve) of a color imparting area and a color fading area as shown in
FIG. 4
are provided in response to quantities of surrounding light and rear light. This sensitivity curve can be partly modified as shown by broken lines in
FIG. 5
by changing value of resistance in the oscillation circuit. For totally changing the sensitivity curve (i.e., parallel shifting of the curve) as shown in
FIG. 6
, however, there is no alternative but to change transmittance of a filter provided on the front surface of a light sensor. Thus, total changing of the sensitivity curve by adjustment in the circuit was not possible in the prior art device.
It is, therefore, an object of the invention to provide a device for driving an EC dimming mirror which has overcome the above described problems of the prior art device and is capable of controlling the amount of coloration by controlling duration of pulse, realizing a lower power consumption, and achieving total change of the sensitivity curve by adjustment in the circuit.
SUMMARY OF THE INVENTION
For achieving the object of the invention, a device for driving an EC dimming mirror in which reflectivity is variably controlled by an EC element comprises surrounding light quantity detection means for detecting quantity of light surrounding a vehicle, rear light quantity detection means for detecting quantity of light in the rear of the vehicle, an oscillation circuit for generating an oscillation signal of an “H” level and an oscillation signal of an “L” level repeatedly and alternately, duration of one level of the oscillation signals being variably controlled in response to quantity of light detected by the surrounding light quantity detection means and the other level of the oscillation signals being variably controlled in response to quantity of light detected by the rear light quantity detection means, a DC voltage output circuit for outputting DC voltage in accordance with duty factor of an oscillation output of the oscillation circuit, a drive power source for driving the EC element, and an EC element drive circuit for adjusting polarity and level of drive voltage supplied from the drive power source in response to the level of the output from the DC voltage output circuit, said oscillation circuit performing control, when the one level of the oscillation signals is set to drive the EC element in a color imparting direction and the other level of the oscillation signals is set to drive the EC element in a color fading direction, in such a manner that, when surrounding light quantity is larger, the duration of the one level is shorter and, when the surrounding light quantity is smaller, the duration of the one level is longer and that, when the rear light quantity is larger, the duration of the other level is shorter and, when the rear light quantity is smaller, the duration of the other level is longer, and said oscillation circuit performing control, when the one level of the oscillation signals is set to drive the EC element in a color fading direction and the other level of the oscillation signals is set to drive the EC element in a color imparting direction, in such a manner that, when the surrounding light quantity is larger, the duration of the one level is longer and, when the surrounding light quantity is smaller, the duration of the one level is shorter and that, when the rear light quantity is larger, the duration of the other level is longer and, when the rear light quantity is smaller, the duration of the other level is shorter.
According to the invention, DC voltage is produced in response to the duty factor of the pulse signal for driving the EC element and the EC element is driven in response to this DC voltage and, accordingly, the number of times of switching the polarity of the drive current can be reduced and, moreover, rush current occurring in switching of the polarity can be held at a low value.
Further, by providing a level shift circuit for shifting the level of the output voltage of t
Kobayashi Akiyoshi
Nagao Mitsuyoshi
Hedman & Costigan
Murakami Corporation
Sikder Mohammad
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