A system apparatus, structure and method for controlling a plurality of
variable reflectance mirrors (or mirror segments), including a rearview
mirror and side view mirrors, which change their reflectance level in
response to a plurality of drive voltages applied thereto, for an
automotive vehicle. The system includes a light sensing device and a
control circuit formed as a single VLSI CMOS circuit. The light sensing
device comprises a
photosensor array having a field of view encompassing
a rear window area and at least a portion of at least one side window
area of the vehicle. The logic and control circuit determines a
background light signal from photosensor element signals generated by
the photosensor elements in the photosensor array indicative of light
levels incident on the photosensor elements. The circuit also determines
a peak light signal in three different zones or sub-arrays of the
photosensor array. The zones or sub-arrays may correspond to three
mirrors or mirror segments. The peak light signals in each of the zones
and a common background light signal are used to determine independent
and separate control signals, which are then output to separate mirror
drive circuits for independently controlling the reflectance level of
the rearview mirror and the left and right side view mirrors, or
alternatively the segments of a mirror.
Description
This application is a divisional of application Ser. No. 08/023,918 filed Feb. 26, 1993, now U.S. Pat. No. 5,550,677.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an automatic rearview mirror system for
automotive vehicles which automatically changes reflectance level in
response to glare causing light, and more particularly relates to an
improved automatic rearview mirror system using only a rearwardly facing
sensor.
2. Description of Related Art
Automatic rearview mirrors and mirror systems have been devised for
varying the reflectance level of a variable reflectance rearview mirror
by reducing the reflectance automatically in response to annoying glare
light, as seen rearwardly of the rearview mirror or mirrors by a driver
of the vehicle, and by increasing automatically the reflectance to a
normal or maximum reflectance level when the annoying glare light
subsides. These automatic mirrors have been changed over the years in an
effort to improve their performance characteristics and associated
level of glare protection.
Early automatic rearview mirrors used a rearwardly facing sensor and
control circuit to change mirror reflectance. One example of such a
"single-sensor" type mirror is described in U.S. Pat. No. 4,266,856. In
these prior art single-sensor type mirrors, the rear glare light was
incident on a rearwardly facing sensor or photocell, such as a
photodiode, photoresistor or phototransistor. These mirrors suffered
from various problems, however, including the problem that these mirrors
would become increasingly sensitive and even "lock-up" in their minimum
reflectance level or state as the driver encountered significantly
higher light levels in town or city driving. This required the driver to
repeatedly adjust the mirror's sensitivity control to prevent such
problems.
To overcome the problems of single-sensor type mirrors, a non-rearwardly
facing photocell for sensing "ambient" light was added. It was believed
that the desired reflectance necessary to relieve the driver from glare
depended not only on glare light but also on ambient light.
Accordingly, these "two-sensor" type mirrors used two separate
photocells, one generally facing rearwardly and one generally facing
forwardly (or other non-rearwardly facing direction) of the mirror or
vehicle. The signals from these two photocells were then compared in
some fashion, and when, for example, the glare light from the rear was
comparatively high with respect to the "ambient" light, a control
circuit would apply a control signal to reduce mirror reflectance. Some
examples are described in German Laid-Open Patent No. 3,041,692;
Japanese Laid-Open Patent No. 58-19941; and U.S. Pat. Nos. 3,601,614;
3,612,666; 3,680,951; 3,746,430; 4,443,057; 4,580,875; 4,690,508; and
4,917,477. In many of these prior art automatic rearview mirrors, light
generally forward of the mirror or vehicle was incident on the second
photocell.
These arrangements, however, also had problems. In some of these mirrors
the forwardly facing or "ambient" light sensor was inaccurate because
it did not correctly measure ambient light levels since it did not
include light generally rearward of the mirror or vehicle. Some examples
include the devices described in U.S. Pat. Nos. 4,443,057 and
4,917,477. Other prior art devices overcame these deficiencies by
providing a control circuit which correctly measured ambient light as a
combination of both the forward and rear light levels. Examples of this
significantly different approach are described in U.S. Pat. Nos.
4,793,690 and 4,886,960.
The prior art two-sensor type systems generally provided improved
performance over prior art single-sensor type systems but were also more
complex and costly. In part, this was because using separate forwardly
and rearwardly facing photocells required that the performance
characteristics of the two separate photocells, such as photoresistors,
be matched appropriately to ensure consistent performance under various
operating conditions. Matching photocells such as photoresistors,
however, generally involves complex, expensive and time consuming
operations and procedures.
Both the prior art single-sensor and two-sensor type mirrors presented
additional problems when they were also used to control the exterior
side view mirrors. This is because such prior art systems used a common
control or drive signal to change the reflectance level of both the
interior rearview mirror and the exterior left and/or right side view
mirrors by substantially the same amount. In U.S. Pat. No. 4,669,826,
for example, a single-sensor type mirror system used two rearwardly
facing photodiodes to control both an interior rearview mirror and the
left and/or right side view mirrors based on the direction of incident
light from the rear. Another example includes the two-sensor type system
described in U.S. Pat. No. 4,917,477.
In rearview mirror systems, however, each of the interior rearview and
exterior side view mirrors may reflect different source light levels.
More specifically, the inside rearview mirror, left side view mirror and
right side view mirror each enable the driver to view a different
portion or zone of the total rearward area. Of course, there may be some
overlap of the image information contained in each of the three zones.
The situation is further complicated with multi-lane traffic because
each of the mirrors reflects different light levels caused by the
headlights of the vehicles which are following, passing or being passed.
As a result, in the prior art systems, when the reflectance level of
the interior rearview mirror was reduced to decrease the glare of
headlights reflected therein, the reflectance level of the exterior left
and right side view mirrors was also reduced by substantially the same
amount, even though, for example, the side view mirrors might not be
reflecting the same level of glare light, if any. Accordingly, rear
vision in the exterior left and right side view mirrors could be
improperly reduced.
Other prior art two-sensor type systems used a common ambient light
sensor and several rearwardly facing sensors, one for each of the
mirrors. An example is the alternate system also described in U.S. Pat.
No. 4,917,477. This approach is not satisfactory, however, because it
reduces system reliability and increases complexity and cost.
Finally, some prior anti-glare mirrors used several sensors to control
the segments of a variable reflectance mirror. One example is disclosed
in U.S. Pat. No. 4,632,509, which discloses a single-sensor type mirror
using three rearwardly facing photocells to control three mirror
segments depending on the direction of incident light from the rear. See
also U.S. Pat. No. 4,697,883. These prior mirror systems generally have
the same problems as the other single-sensor type mirrors. Some other
anti-glare mirrors are generally disclosed in U.S. Pat. Nos. 3,986,022;
4,614,415; and 4,672,457.
Consequently, there is a need for an automatic rearview mirror system
for an automotive vehicle having improved reliability and low cost,
which accurately determines or otherwise discriminates light levels that
the driver will experience as glare without the need for a separate
forwardly facing photocell. In addition, as noted above, there is also a
need for an automatic rearview mirror system of high reliability and
low cost, which accurately determines light levels that the driver will
experience as glare, and which can control independently the reflectance
of a plurality of mirrors according to the light levels actually
reflected by each of the rearview and exterior side view mirrors without
the need for additional and separate rearwardly facing photocells.
There is also a need for an automatic rearview mirror system that can
independently control the segments of a variable reflectance mirror
while accurately determining light levels that the driver will
experience as glare in each segment of the mirror without the need for
additional and separate forwardly and rearwardly facing photocells.
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