U.S. patent application number 10/413264 was filed with the patent office on 2003-10-30 for digital electrochromic mirror system.
This patent application is currently assigned to Donnelly Corporation. Invention is credited to Schierbeek, Kenneth L..
Application Number | 20030202249 10/413264 |
Document ID | / |
Family ID | 25261482 |
Filed Date | 2003-10-30 |
United States Patent
Application |
20030202249 |
Kind Code |
A1 |
Schierbeek, Kenneth L. |
October 30, 2003 |
Digital electrochromic mirror system
Abstract
An electrochromic rearview mirror system for a vehicle includes
an electrochromic reflective element having an electrochromic cell,
wherein the reflective element colors to a partial reflectance
level in response to a drive signal applied to the cell. The
rearview mirror assembly additionally includes a drive circuit
which applies a pulsed drive signal to the electrochromic cell in
order to establish the partial reflectance level of the reflective
element. The drive circuit controls the partial reflectance level
as a function of the duty cycle of the pulsed drive signal, which
has a pulse repetition rate of at least approximately 10 cycles per
second and preferably at least approximately 20 cycles per second.
The drive circuit additionally adjusts the amplitude of the pulses
as a function of the voltage developed across the electrochromic
cell.
Inventors: |
Schierbeek, Kenneth L.;
(Zeeland, MI) |
Correspondence
Address: |
VAN DYKE, GARDNER, LINN AND BURKHART, LLP
2851 CHARLEVOIX DRIVE, S.E.
P.O. BOX 888695
GRAND RAPIDS
MI
49588-8695
US
|
Assignee: |
Donnelly Corporation
Holland
MI
|
Family ID: |
25261482 |
Appl. No.: |
10/413264 |
Filed: |
April 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10413264 |
Apr 14, 2003 |
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09952693 |
Sep 12, 2001 |
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6547404 |
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09952693 |
Sep 12, 2001 |
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09533260 |
Mar 20, 2000 |
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6305807 |
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09533260 |
Mar 20, 2000 |
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08832380 |
Apr 2, 1997 |
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6089721 |
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Current U.S.
Class: |
359/603 ;
359/601; 359/604; 359/838; 359/871 |
Current CPC
Class: |
B60R 1/088 20130101 |
Class at
Publication: |
359/603 ;
359/601; 359/604; 359/838; 359/871 |
International
Class: |
G02B 027/00; G02B
005/08; G02B 017/00; G02B 007/182 |
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. An electrochromic rearview mirror assembly for a vehicle
comprising: an electrochromic reflective element having an
electrochromic cell wherein said reflective element colors to a
partial reflectance level in response to a drive signal applied to
said electrochromic cell; and a drive circuit which applies a
pulsed drive signal to said electrochromic cell in order to
establish said partial reflectance level of said reflective element
said drive circuit controlling said partial reflectance level at
least as a function of the duty cycle of said pulsed drive
signal.
2. The electrochromic rearview mirror assembly in claim 1 wherein
said drive circuit applies a direct current signal to said
electrochromic cell during one portion of each duty cycle and sinks
a direct current signal from said electrochromic cell during
another portion of each duty cycle.
3. The electrochromic rearview mirror assembly in claim 2 wherein
said drive circuit controls the amplitude of said pulsed drive
signal.
4. The electrochromic rearview mirror assembly in claim 3 wherein
said drive circuit monitors the voltage across said electrochromic
cell and adjusts at least one of the direct current signal applied
during subsequent pulses and the duty cycle of the pulsed drive
signal as a function of the voltage across the electrochromic
cell.
5. The electrochromic rearview mirror assembly in claim 4 wherein
said drive circuit monitors the voltage across said electrochromic
cell sampling the voltage near the end of said one portion.
6. The electrochromic rearview mirror assembly in claim 2 wherein
said drive circuit monitors the voltage across said electrochromic
cell between said portions of each duty cycle when said drive
circuit is neither applying a direct current signal to said cell
nor sinking a direct current signal from said cell in order to
control at least one of the amplitude and the duty cycle of said
pulsed drive signal.
7. The electrochromic rearview mirror assembly in claim 1 wherein
said drive circuit monitors the voltage across said electrochromic
cell and adjusts at least one of the amplitude of said drive signal
during subsequent pulses and the duty cycle of the pulsed drive
signal as a function of the voltage across the electrochromic
cell.
8. The electrochromic rearview mirror assembly in claim 1 wherein
said pulsed drive signal has a repetition rate of at least
approximately 10 cycles per second.
9. The electrochromic rearview mirror assembly in claim 8 wherein
said pulsed drive signal has a repetition rate of at least
approximately 20 cycles per second.
10. The electrochromic rearview mirror assembly in claim 1 wherein
said drive circuit comprises a microcomputer.
11. The electrochromic rearview mirror assembly in claim 10 further
including a display and at least one of a compass and an outdoor
temperature sensor, wherein said display displays vehicle heading,
outdoor temperature, or both vehicle heading and outdoor
temperature.
12. The electrochromic rearview mirror assembly in claim 11 wherein
said microcomputer controls the intensity of said display.
13. The electrochromic rearview mirror assembly in claim 12
including a light sensor which senses light level around the
vehicle, wherein said microcomputer adjusts the intensity of said
display in response to said light sensor as a function of the light
level around the vehicle.
14. The electrochromic rearview mirror assembly in claim 13 wherein
said display is positioned behind said electrochromic cell, wherein
said display is viewed through said electrochromic cell and wherein
said microcomputer adjusts the intensity of said display as a
function of the reflectance level of said reflective element.
15. The electrochromic rearview mirror system of claim 14 wherein
said drive circuit monitors the voltage across said electrochromic
cell when said cell is open-circuited in order to determine the
reflectance level of said reflective element.
16. The electrochromic rearview mirror assembly in claim 13 further
including at least one indicator, wherein said microcomputer
adjusts the intensity of said at least one indicator in response to
said light sensor as a function of the light level around the
vehicle.
17. The electrochromic rearview mirror assembly in claim 12 wherein
said display is positioned behind said electrochromic cell, wherein
said display is viewed through said electrochromic cell and wherein
said microcomputer adjusts the intensity of said display as a
function of the reflectance level of said reflective element.
18. The electrochromic rearview mirror assembly in claim 17 wherein
said drive circuit monitors the voltage across said electrochromic
cell when said cell is open-circuited in order to determine the
reflectance level of said reflective element.
19. An electrochromic rearview mirror assembly for a vehicle,
comprising: an electrochromic reflective element having an
electrochromic cell, wherein said reflective element colors to a
partial reflectance level in response to a drive signal applied to
said electrochromic cell; and a drive circuit which applies a drive
signal to said electrochromic cell in order to establish the
partial reflectance level of said reflective element, said drive
circuit including a source, a digital controller, a switching
device responsive to an output of said controller for applying said
source to said electrochromic cell and an input of said controller
responsive to the voltage developed across said electrochromic cell
by said source, wherein said digital controller monitors the
voltage developed across said electrochromic cell, adjusts said
source, and closes and opens said switching device according to a
particular duty cycle in order to control said partial reflectance
level.
20. The electrochromic rearview mirror assembly in claim 19 wherein
said controller adjusts said source in order to cause said voltage
developed across said electrochromic cell to extend beyond said
predetermined range during transitions between substantially
different reflectance levels of said reflective element.
21. The electrochromic rearview mirror assembly in claim 19 wherein
said source is a voltage divider and wherein said controller
adjusts said source by connecting at least one resistor in said
voltage divider.
22. The electrochromic rearview mirror assembly in claim 21 wherein
said at least one resistor includes at least two resistors of
substantially different values and wherein said controller adjusts
said source by connecting one or the other or both of said at least
two resistors in said voltage divider.
23. The electrochromic rearview mirror assembly in claim 22 wherein
said controller includes outputs operable between at least three
different states, wherein said controller additionally adjusts said
source by selecting a particular state for connecting one or the
other or both of said at least two resistors in said voltage
divider.
24. The electrochromic rearview mirror assembly in claim 19
including another switching device responsive to an output of said
controller for draining charge from said electrochromic cell,
wherein said controller alternatingly closes said switching devices
according to said particular duty cycle.
25. The electrochromic rearview mirror assembly in claim 24 wherein
said controller keeps both said switching devices open during a
portion of said duty cycle in order to sample residual voltage
across said electrochromic cell and thereby determine the
reflectance level of said reflective element.
26. The electrochromic rearview mirror assembly in claim 19 wherein
said controller samples said input when said binary switching
device is closed in order to monitor the voltage developed across
said electrochromic cell by said source.
27. The electrochromic rearview mirror assembly in claim 26 wherein
said controller samples said input immediately prior to opening
said switching device.
28. The electrochromic rearview mirror assembly in claim 19 wherein
said digital controller closes and opens said switching device at a
repetition rate of at least approximately 10 cycles per second.
29. The electrochromic rearview mirror assembly in claim 28 wherein
said digital controller closes and opens said switching device a
repetition rate of at least approximately 20 cycles per second.
30. The electrochromic rearview mirror assembly in claim 19 wherein
said digital controller comprises a microcomputer.
31. The electrochromic rearview mirror assembly in claim 30 further
including a display and at least one of a compass and an outdoor
temperature sensor, wherein said display displays vehicle heading,
outdoor temperature, or both vehicle heading and outdoor
temperature.
32. The electrochromic rearview mirror assembly in claim 31 wherein
said microcomputer controls the intensity of said display.
33. The electrochromic rearview mirror assembly in claim 32
including a light sensor which senses light level around the
vehicle wherein said microcomputer adjusts the intensity of said
display in response to said light sensor as a function of light
level around the vehicle.
34. The electrochromic rearview mirror assembly in claim 33 wherein
said display is positioned behind said electrochromic cell, wherein
said display is viewed through said electrochromic cell and wherein
said microcomputer adjusts the intensity of said display as a
function the reflectance level of said reflective element.
35. The electrochromic rearview mirror assembly in claim 34 wherein
said drive circuit monitors the voltage across said electrochromic
cell when said cell is open-circuited in order to determine the
reflectance level of said reflective element.
36. The electrochromic rearview mirror assembly in claim 33 further
including at least one indicator, wherein said microcomputer
adjusts the intensity of said at least one indicator in response to
said light sensor as a function of light level around the
vehicle.
37. The electrochromic rearview mirror assembly in claim 32 wherein
said display is positioned behind said electrochromic cell, wherein
said display is viewed through said electrochromic cell and wherein
said microcomputer adjusts the intensity of said display as a
function the reflectance level of said reflective element.
38. The electrochromic rearview mirror assembly in claim 37 wherein
said drive circuit monitors the voltage across said electrochromic
cell when said cell is open-circuited in order to determine the
reflectance level of said reflective element.
39. An electrochromic rearview mirror assembly for a vehicle,
comprising: an electrochromic reflective element having an
electrochromic cell, wherein said reflective element colors to a
partial reflectance level in response to a drive signal applied to
said electrochromic cell; and a drive circuit which applies a drive
signal to said electrochromic cell in order to establish the
partial reflectance level of said reflective element, said drive
circuit including a digital controller, a first switching device
responsive to an output of said controller for applying a source to
said electrochromic cell and a second switching device responsive
to an output of said controller for draining charge from said
electrochromic cell, wherein said controller alternatingly closes
said switching devices according to a particular duty cycle in
order to control said partial reflectance level at least as a
function of said duty cycle, wherein said digital controller closes
and opens said switching devices at a repetition rate of at least
approximately 10 cycles per second.
40. The electrochromic rearview mirror assembly in claim 39 wherein
said digital controller closes and opens said switching devices at
a repetition rate of at least approximately 20 cycles per
second.
41. The electrochromic rearview mirror assembly in claim 39 wherein
said digital controller comprises a microcomputer.
42. The electrochromic rearview mirror assembly in claim 41 further
including a display and at least one of a compass and an outdoor
temperature sensor, wherein said display displays vehicle heading,
outdoor temperature, or both vehicle heading and outdoor
temperature.
43. The electrochromic rearview mirror assembly in claim 42 wherein
said microcomputer controls the intensity of said display.
44. The electrochromic rearview mirror assembly in claim 43
including a light sensor which senses light level around the
vehicle wherein said microcomputer adjusts the intensity of said
display in response to said light sensor as a function of light
level around the vehicle.
45. The electrochromic rearview mirror assembly in claim 44 wherein
said display is positioned behind said electrochromic cell, wherein
said display is viewed through said electrochromic cell and wherein
said microcomputer adjusts the intensity of said display as a
function the reflectance level of said reflective element.
46. The electrochromic rearview mirror assembly in claim 45 wherein
said drive circuit monitors the voltage across said electrochromic
cell when said cell is open-circuited in order to determine the
reflectance level of said reflective element.
47. The electrochromic rearview mirror assembly in claim 44 further
including at least one indicator, wherein said microcomputer
adjusts the intensity of said at least one indicator in response to
said light sensor as a function of light level around the
vehicle.
48. The electrochromic rearview mirror assembly in claim 43 wherein
said display is positioned behind said electrochromic cell, wherein
said display is viewed through said electrochromic cell and wherein
said microcomputer adjusts the intensity of said display as a
function the reflectance level of said reflective element.
49. The electrochromic rearview mirror assembly in claim 48 wherein
said drive circuit monitors the voltage across said electrochromic
cell when said cell is open-circuited in order to determine the
reflectance level of said reflective element.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to vehicle rearview mirror
systems and, more particularly, to electro-optic mirror assemblies,
such as electrochromic rearview mirror assemblies for a
vehicle.
[0002] Electrochromic rearview mirror assemblies include an
electrochromic reflective element made up of a reflecting surface
and an electrochromic cell positioned between the driver and the
reflecting surface. The electrochromic cell responds to a direct
current (DC) voltage applied across a pair of terminals by varying
the light transmittance through the cell. In this manner, the
reflectance level of the reflective element can be varied by
varying the DC voltage applied to the electrochromic cell. The
electrochromic cell has characteristics which make control of the
reflectance level of the reflective element difficult. The
electrochromic cell operates at a relatively low voltage, typically
which may not exceed approximately 3 volts DC, more typically not
more than about 1.5 volts DC, for more than a brief period of time
or else useful life of the reflective element is compromised.
Furthermore, the amount of drive current necessary to color or
bleach the cell varies both with the temperature of the cell and
the amount of change in light transmittance undertaken. Therefore,
optimum control of the electrochromic cell requires more than
merely applying a DC voltage corresponding to the desired
reflectance level.
[0003] One approach to controlling the reflectance level of an
electrochromic cell is disclosed in commonly assigned U.S. patent
application Ser. No. 08/768,193 filed Dec. 17, 1996, by the present
inventor and Niall R. Lynam, entitled AUTOMATIC REARVIEW MIRROR
SYSTEM WITH AUTOMATIC HEADLIGHT ACTIVATION. In this co-pending
application, the electrochromic cell is driven by an analog
feedback system which translates a desired reflectance level,
produced by an analog circuit, to a signal applied to the
electrochromic cell which drives the cell to the desired
reflectance level. While such drive system is effective, it
requires the use of analog components. Such analog components would
be redundant in a digital electrochromic mirror system and,
therefore, would unnecessarily add to the cost of the system.
However, substitution of digital components for the previously used
analog components is not a straightforward matter. Digital
components typically operate between discrete output states which
may include binary devices, such as transistors, switches, and the
like, which exhibit a low and a high state, and tristate devices,
such as types of microprocessors which exhibit a neutral. a low,
and a high state. Such components are useful in processing data but
are not readily adapted to controlling the reflectance level of an
electrochromic rearview mirror. In particular, a typical
electrochromic mirror utilized as an interior mirror of a vehicle
may have a surface area in the range of 90 cm.sup.2 to 150 cm.sup.2
and typically in the range of 110 cm.sup.2 to 130 cm.sup.2. A
steady state current draw, after color transitions have settled, is
typically in the range of between approximately 60 milliamperes and
180 milliamperes with a range of 80 milliamperes to 150
milliamperes being typical. Exterior rearview mirrors can be even
larger with a surface area of approximately 350 cm.sup.2, and
greater, and a commensurate increase in current density.
SUMMARY OF THE INVENTION
[0004] The present invention provides a digital electrochromic
mirror system which utilizes primarily digital components to drive
an electrochromic cell of an electrochromic mirror system to a
desired reflectance level which not only meets, but desirably
exceeds the performance of prior analog systems.
[0005] According to an aspect of the invention, an electrochromic
rearview mirror system for a vehicle includes an electrochromic
reflective element having an electrochromic cell wherein the
reflective element colors to a partial reflectance level in
response to a drive signal applied to the electrochromic cell. The
rearview mirror assembly additionally includes a drive circuit
which applies a pulsed drive signal to the electrochromic cell in
order to establish the partial reflectance level of the reflective
element. The drive circuit controls the partial reflectance level
at least as a function of the duty cycle of the pulsed drive
signal.
[0006] According to another aspect of the invention, an
electrochromic rearview mirror assembly for a vehicle includes such
an electrochromic reflective element and a drive circuit which
applies a drive signal to the electrochromic cell in order to
establish the partial reflectance level of the reflective element.
The drive circuit includes a digital controller, a binary switching
device responsive to an output of the controller for applying a
source to the electrochromic cell, and an input of the controller.
The input of the controller is preferably responsive to the voltage
developed across the electrochromic cell by the source. The digital
controller closes and opens the binary switching device according
to a particular duty cycle in order to control the partial
reflectance level at least as a function of the duty cycle. The
digital controller additionally adjusts the source as a function of
the voltage developed across the electrochromic cell.
[0007] According to yet an additional aspect of the invention, an
electrochromic rearview mirror assembly for a vehicle includes such
an electrochromic reflective element and drive circuit which
applies a drive signal to the electrochromic cell in order to
establish the partial reflectance level of the reflective element.
The drive circuit includes a digital controller, a first binary
switching device responsive to an output of the controller for
applying a source to the electrochromic cell, and a second binary
switching device which is responsive to an output of the controller
for draining charge from the electrochromic cell. The controller
alternatingly closes the switching devices according to a
particular duty cycle in order to control the partial reflectance
level as a function of the duty cycle. The digital controller
closes and opens the binary switching device at a repetition rate
of at least approximately 10 cycles per second, more preferably at
least approximately 20 cycles per second, and most preferably at
least approximately 25 cycles per second.
[0008] An electrochromic rearview mirror assembly, according to the
various aspects of the invention, may additionally include other
functions of the rearview mirror including a display which displays
the vehicle heading, determined by a compass, the outdoor
temperature, determined by an outdoor temperature sensor, or both
the vehicle heading and outdoor temperature. The digital
controller, which is preferably a microcomputer, may additionally
control the intensity of the display. The intensity of the display
may be controlled as a function of light levels around the vehicle.
Additionally, in particular embodiments, the display may be
positioned behind the electrochromic cell wherein the display is
viewed through the electrochromic cell. In such embodiments, the
microcomputer may additionally adjust the intensity of the display
as a function of the reflectance level of the reflective element.
In this manner, the display, as perceived by the driver, does not
vary in intensity as the reflectance level of the reflective
element changes. However, the intensity of the display may be
adjusted to accommodate the physiological response of the driver's
eyes.
[0009] These and other objects, advantages and features of this
invention will become apparent upon review of the following
specification in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a side elevation of a vehicle having an
electrochromic rearview mirror assembly, according to the
invention;
[0011] FIG. 2 is a side elevation of an electrochromic rearview
mirror assembly, according to the invention, represented
schematically to illustrate components of the electronic control
thereof;
[0012] FIG. 3 is a block diagram of the electronic control in FIG.
2;
[0013] FIG. 4 is a schematic diagram of the electronic control in
FIG. 3;
[0014] FIG. 5 is a diagram of a pulsed drive signal;
[0015] FIG. 6 is the same view as FIG. 5 of an alternative
embodiment thereof;
[0016] FIG. 7 is a software flowchart of a control algorithm for an
electrochromic rearview mirror assembly;
[0017] FIG. 8 is a table of source adjustment steps; and
[0018] FIG. 9 is a schematic diagram of an alternative electronic
control.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] Referring now specifically to the drawings. and the
illustrative embodiments depicted therein, a vehicle 9 is
illustrated as having an electrochromic rearview mirror assembly 11
(FIGS. 1-3). Although the invention is illustrated in an interior
rearview mirror assembly, the invention could be equally applied to
exterior rearview mirror assemblies as well as to an entire
electrochromic rearview mirror system. Electrochromic rearview
mirror 11 includes an electronic control 12 and a variable
reflectance electrochromic reflective element 18 having an
electrochromic cell 15 and a reflective surface 17. Electrochromic
element 18 may be of any known type, such as disclosed in U.S. Pat.
No. 4,902,108 issued to Byker; commonly assigned U.S. Pat. No.
5,140,455 issued to Varaprasad et al; commonly assigned U.S. patent
application Ser. No. ______ filed Mar. 27, 1997, by Varaprasad et
al. entitled ELECTROCHROMIC POLYMERIC SOLID FILMS, MANUFACTURING
ELECTROCHROMIC DEVICES USING SUCH SOLID FILMS, AND PROCESSES FOR
MAKING SUCH SOLID FILMS AND DEVICES (continuation-in-part of
application Ser. No. 08/406,663) (Attorney Docket No. 690.3 CIP C1
CIP), and commonly assigned U.S. patent application Ser. No.
08/429,643 filed Apr. 27, 1995, by Varaprasad et al., entitled
ELECTROCHROMIC MIRRORS AND DEVICES, the disclosures of which are
hereby incorporated herein by reference. Electrochromic element 18
dims to a partial reflectance level in response to a drive signal
applied thereby.
[0020] Electronic control 12 includes a drive circuit 13 which
receives inputs from a substantially rearwardly directed light
sensor 20 and from a substantially forwardly directed light sensor
22 and provides outputs to control the reflectance level of
electrochromic partial reflective element 18. Light sensors 20, 22
make up a light sensor combination 28 which provides input to a
microcomputer U2 (FIGS. 3 and 4). A digital controller, such as
microcomputer U2, is a low current source, typically in microamps
to less than about 25 milliamperes, which provides logic level
outputs to a high current source 40 which applies direct current
pulses derived from vehicle ignition voltage, typically between 8
VDC and 18 VDC with 12 VDC nominal, to the electrochromic cell
source 40 which has a current capability of at least about 50
milliamperes, preferably of at least about 100 milliamperes, and
most preferably of at least about 200 milliamperes. As will be
described in more detail below, the duty cycle of these pulses
establishes the partial reflectance level of reflective element 18.
As schematically illustrated in FIG. 3, a blanking logic signal,
which is typically pulse-width modulated, is output at 26b from
microcomputer U2 based on the condition of highway glare light and
ambient light conditions around the vehicle as detected by the
light sensor combination 28. Such light sensor combinations are
conventional and are described in U.S. Pat. No 4,917,477 issued to
Bechtel et al., U.S. Pat. No. 4,793,690 issued to Graham et al.,
and U.S. Pat. No. 3,601,614 issued to Platzer, Jr., the disclosures
of which are hereby incorporated herein by reference. The logic
signal output at 26 is input to high current source 40. The
amplitude of the output signal from high current source 40 is
variable within a narrow range established close to, and preferably
constrained from significantly exceeding, the maximum voltage
tolerable for a sustained period by electrochromic cell 15.
[0021] The amplitude of the pulsed output signal from source 40 can
be adjusted by microcomputer U2 over outputs 26c and 26d as a
function of the voltage developed across electrochromic cell 15.
The developed voltage is sensed over a line 48 extending from a
terminal 44 of the cell to an input of microcomputer U2. Such
electrochromic cells typically develop a voltage, which is a back
Electromotive Field (EMF) upon application of an external voltage
thereto, and temporarily retain that back voltage, or back EMF,
even when the external voltage potential is removed and the cell is
open-circuited. Also, for solution-phase single compartment,
self-erasing electrochromic mirror elements commonly used
commercially today, the maximum voltage tolerable for a sustained
period is in the 1.0 V to 2.0 V range, typically less than 1.5 V
and most typically about 1.4 V. For solid-film electrochromic
devices that utilize a layer, such as a tungsten oxide thin film
layer, the maximum voltage tolerable for a sustained period is in
the 1.0 V to the 3.0 V range, typically in the 1.3 V to 1.5 V
range. Usually, application of a voltage much in excess of such
maximum tolerable voltage to the electrochromic cell for a
sustained period, typically at least several seconds, may cause
change to the electrochromic medium in the electrochromic medium in
the electrochromic cell.
[0022] In the illustrated embodiment, microcomputer U2 is marketed
by Toshiba Corporation of Japan under Model No. TMP87C4008, but
could be implemented by microcomputers marketed by other
manufacturers. Microcomputer U2 includes a plurality of inputs 24
and a plurality of outputs 26. Outputs 26 are tri-state outputs
which are capable of assuming a low state in which the output is
pulled to ground, a neutral high impedance state in which the
output is effectively open-circuited, and a high state in which the
output is driven to a positive, or negative, DC voltage. Inputs 24a
and 24b are connected with light sensor combination 28 made up of
rearward-directed light sensor 20 and forward-directed light sensor
22 electrically connected in series with each other and with a
resistor RA7. This series circuit is connected between a positive
source of voltage (5V) and ground. Input line 24a is connected with
a junction, or node, 30 between light sensors 20 and 22. Input 24b
is connected with a junction, or node, 32 between rearward light
sensor 20 and resistor RA7. As disclosed in detail in commonly
assigned co-pending application Ser. No. 08/768,193, filed Dec. 17,
1996, by Schierbeek et al., for an AUTOMATIC REARVIEW MIRROR SYSTEM
WITH AUTOMATIC HEADLIGHT ACTIVATION, the disclosure of which is
hereby incorporated herein by reference, the voltage at node 30 is
used to establish a reflectance level of electrochromic reflective
element 18. The voltage at junction 32 is representative of the
overall light level surrounding vehicle 9 and is used in a manner
which will be described below.
[0023] In the illustrative embodiment, electronic control 12
includes a display 34 which is driven by a display driver U3. In
the illustrated embodiment, display 34 is marketed by National
Electric Corporation under Model No. FIP2QMBS and driver U3 is
marketed by Allegro under Model No. UNC5812EPF, although other
commercially available components may also be used. Display 34 may
be positioned behind electrochromic cell 15 of reflective element
18 and viewed by the driver through the electrochromic cell, as
disclosed in U.S. Pat. No. 5,285,060, issued to Larson et al., for
a DISPLAY FOR AUTOMATIC REARVIEW MIRROR, the disclosure of which is
incorporated herein by reference. Alternatively, display 34 may be
positioned on a lip portion of housing 14 below reflective element
18 or on any other portion of the housing visible to the driver as
illustrated in commonly assigned patent application Ser. No.______
filed Feb. 12, 1997, by Schofield et al., for a VEHICLE BLIND SPOT
DETECTION DISPLAY SYSTEM (Attorney Docket No. DON01 P-651), the
disclosure of which is hereby incorporated herein by reference.
Alternatively, display 34 could be in the form of a heads-up
display projected from housing 14 on the vehicle windshield 16.
[0024] Electronic control 12 may additionally include a heading
sensor, or compass, 36 which produces outputs 38 indicative of the
heading of the vehicle. Such heading sensor may be of the
magneto-resistive type, such as disclosed in commonly., assigned
U.S. Pat. No. 5,255,442, issued to Schierbeek et al., for a VEHICLE
COMPASS WITH ELECTRONIC SENSOR, or may be of the magneto-inductive
type, such as disclosed in commonly assigned provisional patent
application Serial No. 60/027,996, filed Oct. 9, 1996, by Domanski
for an ELECTRONIC COMPASS, the disclosures of which are hereby
incorporated herein by reference, or may be of the flux-gate type,
or may be of the magneto-capacitive type. The heading of the
vehicle detected by heading sensor 36 is encoded on outputs 38,
decoded by driver U3 and displayed by display 34.
[0025] Microcomputer U2 includes an output 26a, which controls the
intensity of display 34. In the embodiment illustrated in FIG. 4,
microcomputer U2 provides a signal on line 26a which adjusts the
intensity of display 34 according to the light level around the
vehicle as provided on input 24b. As disclosed in the Larson et al.
'060 patent, microcomputer U2 reduces the intensity of display 34
during low light levels in order to avoid dazzling the driver.
During high light levels, microcomputer U2 increases the intensity
of display 34 in order to make the display more discernable to the
driver. If display 34 is positioned behind cell 15, wherein the
output of the display is viewed through cell 15, microcomputer U2
additionally adjusts the intensity of display 34 as a function of
the light transmission level of cell 15 in order to compensate for
attenuation of light transmission by the cell. This is accomplished
by increasing the intensity of display 34 for lower reflectance
levels of electrochromic reflective element 18 resulting from
coloration of cell 15 to a lower light transmission level as
disclosed in the Larson et al. '060 patent.
[0026] Electronic control 12 includes a source 40 for supplying
direct current energy to color cell 15 to a partial light
transmission level. Source 40 is made up of a voltage divider
composed of resistors R4 and R7 connected in series between a
.sup.+5 volt source and ground. A node 42 of the voltage divider is
supplied to a Darlington transistor pair Q1 and Q2 which apply a DC
voltage to a first terminal 44 of cell 15. Another terminal 46 of
cell 15 is connected with ground. As is known in the art, the
voltage applied to the base of transistor Q1 is decreased by two
forward base-emitter drops and applied to terminal 44. In the
illustrated embodiment, resistors R4 and R7 are selected to apply a
nominal voltage of approximately 1.35 to 1.4 volts to cell 15. This
range may vary depending upon the particular type of electrochromic
cell. A transistor Q3 is connected directed across terminals 44 and
46. When a voltage is applied to the base of transistor Q3
sufficient to drive Q3 into saturation, an essentially short
circuit is applied across cell 15 which rapidly removes at least a
portion of the charge applied to the cell. Microcomputer U2
controls tile states of transistors Q1-Q3 in a binary fashion,
wherein each transistor is either conducting or open-circuited, and
adjusts the output level of source 40, by controlling outputs 26b,
26c, 26d and 26e in a manner which will be described below.
[0027] Output 26b, when in a neutral high impedance state does, not
substantially affect the voltage at node 42 whereby the voltage at
node 42 is established solely by resistors R4 and R7. This voltage
drives transistors Q1 and Q2 into conduction and applies a voltage
level, dependent on the voltage of source 40 to cell 15. When
output 26b is driven to a low state, the voltage at node 42 is
decreased to a level at which transistors Q1 and Q2 become
open-circuited and no current is supplied to cell 15. In the
illustrated embodiment, output 26b is not driven to a high state,
although, in other embodiments, the high-output state may be useful
if appropriate adjustments are made to the circuit.
[0028] Outputs 26c and 26d serve as "fine" and "coarse"
adjustments, respectively, to the voltage level at node 42. When
output 26d, which is the "coarse" adjustment, is in a neutral high
impedance state, the output has no effect on the voltage at node
42. When output 26d is driven to a low state, a resistor R6 is
placed in parallel with resistor R7, which decreases the voltage at
node 42. When output 26d is driven to a high state, resistor R6 is
essentially in parallel with resistor R4 which increases the
voltage at node 42. Likewise, when "fine" adjustment output 26c is
neutral, it has no effect on the voltage at node 42. When output
26c is driven low, a resistor R5 is placed in parallel with
resistor R7 which decreases the voltage at node 42, and when output
26c is driven high, resistor R5 is placed in parallel with resistor
R4, which increases the voltage level at node 42. Because resistor
R6 has a low resistance value than resistor R5, the effect of
output 26d is greater than that caused by output 26c.
[0029] Output 26e controls the conductive state of transistor Q3.
When output 26e is in a neutral high impedance state, there is no
base driven to transistor Q3 and Q3 is open-circuited. When output
26e is driven high, transistor Q3 is driven to a conductance state,
which, as previously set forth, places a substantially short
circuit across cell 15 which, as is known in the art, removes at
least a portion of the charge on cell 15.
[0030] Terminal 44 of cell 15 is interconnected through a line 48
and a resistor R19 to an input 24c of microcomputer U2. This
provides an input to microcomputer U2, which represents the voltage
across cell 15. This voltage is buffered by resistor R19 in order
to avoid damage to microcomputer U2 by spurious voltages on the
cell. A capacitor C19 maintains the voltage level at input 24c
against fluctuation during each analog-to-digital conversion
carried out internally by microcomputer U2. As is known in the art,
the voltage level across cell 15 is generally, but not necessarily
precisely, related to the degree of coloration of light
transmission level of cell 15. In this manner, microcomputer U2 is
provided with information concerning the general reflectance level
of reflective element 18. This information is collected and used in
a manner which will be set forth below.
[0031] Electronic control 12 additionally includes a switch S2
which is driver-operable in order to switch the rearview mirror
between an "automatically controlled" state in which the
reflectance level of reflective element 18 is controlled and an
"off" state in which the reflectance level of reflective element 18
is not controlled. One wiper of switch S2 is connected with an 8.0
volt source and is selectively connectable with a line 50 which
supplies voltage to transistors Q1 and Q2. Therefore, when in the
position illustrated in FIG. 3, no voltage is supplied to the
transistors, and the cell remains in a high reflectance state.
Additionally, switch S2 includes a wiper which is connected through
a line 52 connected with terminal 44. When in the position
illustrated in FIG. 3, terminal 44 is directly connected with
ground which rapidly bleaches the cell to a high reflectance
condition. Alternatively, polarity to the cell could be reversed to
provide a power bleach. Electronic control 12 additionally includes
a reverse-inhibit input 24d which causes microcomputer U2 to force
output 26b to a low state and output 26e to a high state and
thereby bleaches cell 15 when the vehicle is in reverse gear.
Electronic control 12 additionally includes an indicator D2, which,
when actuated, indicates to the driver that the control is actively
controlling the reflectance level of reflective element 18.
[0032] Electronic control 12 may additionally, optionally, include
a series of resistors R20-R23 which are connected as illustrated as
voltage dividers in order to supply inputs 24e and 24f to
microcomputer U2. Inputs 24e and 24f establish the sensitivity of
microcomputer U2 to signals received from light sensor combination
28 and may be changed in value for different vehicle configurations
in which rearview mirror 11 is provided. Sensitivity settings may
additionally be stored in Erasable Electrically Programmable
Read-Only Memories (EE-PROM) and thereby electrically selectable
for the vehicle type in which rearview mirror 11 is positioned.
Additionally, such EE-PROM (not shown) may be used to provide
characterization data of light sensors 20 and 22 in order to allow
different light sensors to be utilized and to make compensation for
the different characteristics of each light sensor for use by
microcomputer U2. In known electrochromic drive circuits, it is
necessary to adjust the values of resistors RA7 and RA15 in order
to compensate for variations in light sensors 20, 22. This is
typically accomplished either by providing a variable potentiometer
to make production-line calibration adjustments or by
characterizing each light sensor and matching up suitable values of
resistors RA7 and RA15. Both procedures are cumbersome . With the
use of an EE-PROM, the characterization data of the light sensors
can be stored in the EE-PROM and used to compensate for variations
in light sensor characteristics. For example, variations which
previously would have been compensated for by selecting the value
of resistor RA7, can be compensated for by internal set point
variations in the algorithm used by microcomputer U2. Variations
which previously would have been compensated for by selecting the
value of resistor RA15 can be compensated for by providing a
resistor between a part of microcomputer U2 and a terminal of
resistor RA15, with the microcomputer selecting, a high output
state for that part to lower the resistance value of resistor RA15,
or a neutral state to not affect the resistance of resistor RA15.
Microcomputer U2 may additionally be provided with linearization
data, whereby the voltage level at node 30, which varies
non-linearly for various light levels sensed by sensors 20 and 22,
may be interpreted linearly for the purpose of producing a drive
signal to drive cell 15 to a particular reflectance level.
[0033] In operation, microcomputer U2 switches output 26b between a
neutral high impedance state and a low state in order to pulse
transistors Q1 and Q2 together and thereby apply a pulsed direct
current to cell 15. In contrast to conventional electrochromic
element drive circuits which supply a steady DC voltage level in
order to control the reflectance level of reflective element 18,
microcomputer U2 controls the reflectance level of the reflective
element by varying the duty cycle of the pulsed signal applied to
cell 15. Such a pulsed signal P is illustrated in FIG. 5 and is
shown as having an approximately 50 percent duty cycle. As the duty
cycle decreases in percent on-time verses off-time for transistors
Q1 and Q2, the current supply to cell 15 decreases and thereby the
reflective element assumes a high reflectance condition. In
contrast, as the duty cycle of signal P increases, by switching
transistors Q1 and Q2 on for a greater percentage of time as
compared to the off period of these transistors, a greater amount
of charge is supplied to cell 15 and thereby the cell colors
electrochromic reflective element 18 assumes a lower reflectance
level.
[0034] Microcomputer U2 is capable of providing a pulsed DC supply
to cell 15 according to a variable duty cycle, and thereby is
capable of establishing a particular reflectance level for
reflective element 18, by relying upon the natural tendency of cell
15 to discharge itself during periods when current is not being
supplied by transistors Q1 and Q2. In the illustrated embodiment,
discharge of cell 15, when not being charged through transistors Q1
and Q2, is enhanced by transistor Q3 which actively discharges cell
15 between pulses of DC supplied by transistors Q1 and Q2. Thus, by
reference to FIG. 4, during period A, transistors Q1 and Q2 are
driven in order supply a DC level, which is illustrated as being
positive but could also be negative, to the cell. During period B,
after microcomputer U2 has turned off transistors Q1 and Q2,
transistor Q3 is driven to a conductive state in order to rapidly
discharge cell 15. This provides superior control over the response
of cell 15 to the variable duty cycle pulse train supplied from
source 40 under the control of microcomputer U2 than would be
achieved by control of only the application of the source to the
cell. Microcomputer U2 can vary the duty cycle of drive signal P
from zero percent (0%) to one hundred percent (100%).
[0035] Other factors besides the duty cycle of the drive signal P
influence the coloration of cell 15. For example, if the amplitude
of each pulse is too high, the expected useful life of reflective
element 18 may decrease. If the amplitude of each pulse is too low,
the cell will not color to the desired level and thereby the
reflectance level of reflective element 18 will be too high.
However, the ability to control the amplitude of each pulse in
drive signal P is made difficult by the electrical characteristics
of cell 15 which vary both with temperature and the degree of
charge on the cell as well as tolerances in all of the electrical
components. By way of example, if cell 15 is completely discharged,
the cell will provide a greater electrical load and will tend to
lower the amplitude of any pulse applied to the cell. However, if
the charge on cell 15, which is represented by the voltage across
the cell, is high relative to the amplitude of the pulse being
applied, the cell will present a relatively small load on the pulse
and the amplitude of the pulse will not be lowered. In order to
provide control over the amplitude of the DC pulses applied to cell
15, electronic control 12 includes a feedback loop through
microcomputer U2 utilizing input 24c to monitor the voltage across
cell 15 through line 48 which connects with terminal 44 of the
cell. This input monitors the voltage across the cell produced by
each pulse. If the voltage is too low, the amount of drive applied
to the next pulse is increased. If the voltage produced across the
cell is too high, thereby potentially reducing the lifetime of the
cell, microcomputer U2 lowers the amplitude of the next pulse. If
the voltage across cell 15, as sampled by input 24c is within a
desirable range, then microcomputer U2 keeps the same amplitude for
the next pulse.
[0036] As can be seen by reference to FIG. 5, microcomputer U2
monitors the voltage across cell 15 by sampling the voltage on the
cell at point S which is selected to be at the end of the applied
pulse. At point S, the voltage produced across cell 15 by that
pulse will have presumably stabilized so that the measured voltage
is assume to be an accurate representation of the voltage across
the cell. Of course, it may be possible to monitor the voltage
across the cell at other points on the pulse or to measure the
amplitude at several points and average the results. By reference
to FIG. 5, the pulse sampled at S1 is determined by microcomputer
U2 to produce a voltage across cell 15 which is below the range R
established for the particular cell. Therefore, microcomputer U2
increases the amplitude of source 40 for producing the next pulse,
the effect on cell 15 of which is sampled at S2. Because in the
illustration, microcomputer U2 determines that the sampled voltage
across cell 15 at S2 is within range R, no adjustment is made to
the amplitude of source 40 for the next pulse. When a sample S3 is
made of the voltage across cell 15 during the next pulse, the
sampled voltage is greater than range R which causes microcomputer
U2 to lower the amplitude of source 40 for producing the next pulse
which is sampled at S4.
[0037] As set forth above, microcomputer U2 is capable of adjusting
the amplitude of source 40 at node 42 and thereby the amplitude of
the pulse applied to the cell by controlling the states of outputs
26c and 26d. This is accomplished digitally utilizing the port
settings illustrated in FIG. 8. By reference to FIG. 8, eight steps
of voltage adjustment are available to the microcomputer by
selecting a Most Significant Bit (MSB) as the "coarse" output 26d
and a Least Significant Bit (LSB) as "fine" output 26c. By
reference to FIG. 8, if no change is required in the voltage level
of source 40, a step number 4 is selected which provides a neutral
high impedance state on outputs 26c and 26d. In order to decrease
the voltage level of source 40, a lower step number is selected.
The greatest reduction of voltage is achieved by step number 0 in
which ports 26c and 26d are both driven to low states which are
represented by a 0. Conversely, if microcomputer U2 wishes to raise
the voltage of source 40, a step higher than 4 is selected, with
step 8 being the greatest increase.
[0038] Electronic control 12 operates as follows. Periodically
microcomputer U2 monitors the voltage at node 30 utilizing input
24a which includes an internal Analog-to-Digital (A/D) converter.
Microcomputer U2 computes the Pulse With Modulation percentage
(PWM%) corresponding to the sensed light level according to formula
1:
PWM%=G(C.sub.S-V.sub.A/D) (1)
[0039] where:
[0040] G=Gain (a constant);
[0041] C.sub.s=Voltage at the start of color of the cell; and
[0042] V.sub.A/D=A/D voltage at input 24a.
[0043] Ideally, PWM% will equal to 0 when the A/D voltage is equal
to the voltage at which it is desired to begin coloration of the
cell 15. As the voltage on node 30 decreases, the PWM% increases
until the PWM% equals 100 percent. If formula 1 yields a negative
value, microcomputer U2 sets the PWM% to 0. Any values greater than
100 PWM% are kept at 100 PWM%.
[0044] Once microcomputer U2 determines the PWM% utilizing formula
1, a control algorithm 55 is carried out (FIG. 7). The voltage
across cell 15 is measured at 60 at point S and it is determined at
62 whether the sample voltage is below the value of ECMIN, which,
in the illustrated embodiment is set to 1.35 volts. If the voltage
is less than ECMIN, it is determined at 64 whether the voltage
adjustment has been set to the maximum value. If not, the port
settings are incremented at 66 and the new port settings are
applied to source 40 at 68 in order to adjust the amplitude of the
next pulse supplied to cell 15. If it is determined at 64 that the
port setting is at a maximum value, then no additional adjustment
is possible.
[0045] If it is determined at 62 that the sample voltage across the
cell is not less than the minimum, it is determined at 70 if the
sample voltage is greater than ECMAX. In the illustrated
embodiment, ECMAX is approximately 1.40 volts. If it is determined
at 70 that the sample cell voltage is greater than ECMAX, then a
similar adjustment is made to the amplitude of source 40 for the
next pulse, except in the opposite direction, as follows. At 72, it
is determined whether the minimum voltage adjustment has been
achieved. If not, the setting is decremented at 74 and the new port
settings are outputted at 76 in order to adjust downwardly the
amplitude of source 40. If it is determined at 72 that the voltage
adjustment value is at a minimum, then a parameter MAXDC is
decreased by a value, such as 10 percent at 78. MAXDC is a maximum
duty cycle that microcomputer U2 will apply to cell 15 and is used
in order to prevent prolonged over-stimulation of the cell. By
decreasing the value of MAXDC, temporary over-voltage pulses are
applied to the cell according to a lower duty cycle and thereby
reducing the effect of the over-voltage condition on the cell.
[0046] If it is determined at 70 that the sampled voltage across
the cell is not greater than ECMAX, then the sample voltage is
within the desired range R. It is then determined at 80 whether the
value of MAXDC is less than 100 percent. If it is determined at 80
that the value of MAXDC is less than 100 percent, the value of
MAXDC is increased at 82 by 10 percent. This allows microcomputer
U2 to drive the cell at a higher duty cycle, closer to, or equal
to, 100 percent, provided that the voltage produced on the cell is
within range R.
[0047] Alternatively, a drive signal P', having a variable duty
cycle, may be utilized to drive cell 15 to the desired reflectance
level of reflective element 18 (FIG. 6). Drive signal P' includes
three distinct periods. During period A1, transistors Q1 and Q2 are
in conduction which applies a current from source 40 to charge cell
15. In period B microcomputer U2 opens transistors Q1 and Q2 and
closes transistor Q3 in order to drain the charge on cell 15.
During a period A2, between periods A1 and B, all transistors Q1-Q3
are open-circuited. At the end of period A1, microcomputer U2
samples the voltage across cell 15 at a point represented by
S.sub.ON. During period A2, when cell 15 is being neither
stimulated nor drained, a second sample S.sub.OFF is made by
microcomputer U2 of the voltage across cell 15. This sample made
during S.sub.OFF can be utilized by microcomputer U2 in order to
obtain an approximation of the level of coloration of cell 15. This
information may then be used by microcomputer U2 in order to
determine, for example, if the reflectance level desired of cell 15
is significantly greater than the present approximate reflectance
level of cell 15. This information can be used in many ways. For
example, if the sample taken at S.sub.OFF indicates that cell 15 is
in a high light transmission condition, whereby reflective element
18 is at a high reflectance level, and it is determined that the
reflectance level of the reflective element must be significantly
decreased, then microcomputer U2 may temporarily, intentionally,
apply a voltage which is greater than ECMAX and/or a duty cycle
which is greater than that which corresponds to the selected
reflectance level, in order to increase the rate of coloration of
cell 15 utilizing the principles disclosed in commonly owned U.S.
Pat. No. 5,220,317, issued to Lynam et al., for an ELECTROCHROMIC
DEVICE CAPABLE OF PROLONGED COLORATION, the disclosure of which is
hereby incorporated herein by reference. Likewise, if it is
determined at S.sub.OFF that the transmission level of cell 15 is
very low, whereby the reflectance level of reflective element 18 is
low, and it is desired to rapidly increase the reflectance level of
the element, microcomputer U2 may intentionally apply a voltage
and/or duty cycle which is temporarily below target to more quickly
achieve the desired reflectance level.
[0048] An alternative electronic control 12' is illustrated in FIG.
9, which includes an outdoor temperature sensor 86 utilized to
supply an input to a microcomputer U4 for display on a display 34'.
Additionally, electronic control 12' provides control over
indicators D4 by microcomputer U4. Indicators D4, which are red and
green in color, may provide an indication to the driver that the
electrochromic control function is operating according to high
sensitivity (green), operating according to a low sensitivity
(red), or is completely off. In this embodiment, sensitivity of the
drive circuit is user selectable utilizing soft-touch switches S1
and S2 mounted on housing 14. Electronic control 12' controls the
intensity of display 34' according to light levels surrounding the
vehicle as determined by the voltage at the light sensor (not shown
in FIG. 9). Additionally, microcomputer U4 controls the intensity
of indicators D4 according to light levels surrounding the vehicle.
In this manner, the light levels of the indicators, as well as that
of the display, are controlled according to the physiological
condition of the driver responding to light levels surrounding the
vehicle.
[0049] It has been determined that the repetition rate of the
pulses in drive signals P and P' (FIGS. 5 and 6) should be above
approximately 10 cycles per second (Hz) to avoid any significant
perception of flickering of the reflectance level of the reflective
element. While any repetition rate greater than 10 Hz is desirable,
a repetition rate above approximately 20 Hz is preferred and a
repetition rate above 25 Hz is most preferred. For example, for
electrochromic mirrors which color from 65% to 20% reflectivity in
a time period of less than about 4 seconds, it has been found that
a repetition rate of 20 Hz produced no perceivable flicker to a
human observer.
[0050] Thus, it is seen that the present invention utilizes digital
logic control, which is incorporated into vehicle functions, such
as vehicle heading display and temperature sensing and display, in
order to perform functions which require handling of a significant
amount of current while maintaining a high degree of control over
applied voltage to the electrochromic cell. By controlling the
reflectivity level of the mirror, or mirrors, utilizing the duty
cycle of a Pulse-Width Modulated (PWM), or a blanking, signal, the
information processing capabilities of digital logic may be applied
to the unique problem of controlling an electrochromic rearview
mirror element. Although the invention is illustrated as
implemented with a microcomputer, other digital logic circuits,
such as programmable arrays and the like, may be utilized.
[0051] The present invention can be used with interior rearview
mirror assemblies equipped with a variety of features, such as a
high/low (or daylight running beam/low) headlamp controller, a
hands-free phone attachment, a video camera for internal cabin
surveillance and/or video telephone function, seat occupancy
detection, a cellular phone microphone, map-reading lights,
compass/temperature display, fuel level and other vehicle status
display, a trip computer, an intrusion detector, contacting rain
sensors, non-contacting rain sensors, and the like. Such features
can share components and circuitry with the electrochromic mirror
circuitry and assembly so that provision of these extra features is
economical.
[0052] The digital electrochromic mirror system of this invention
can be utilized in a vehicle that utilizes a car area network, such
as is described in Irish Patent Application No. 970014 entitled A
VEHICLE REARVIEW MIRROR AND A VEHICLE CONTROL SYSTEM INCORPORATING
SUCH MIRROR, filed Jan. 9, 1997, the disclosure of which is hereby
incorporated by reference herein and can be a node of that car area
network, or, when multiplexing is used, such as is disclosed in
U.S. patent application Ser. No. 08/679,631 entitled VEHICLE MIRROR
DIGITAL NETWORK AND DYNAMICALLY INTERACTIVE MIRROR SYSTEM, by
O'Farrell et al., filed Jul. 11, 1996, the disclosure of which is
hereby incorporated by reference herein. Also, given that an
interior electrochromic mirror can optionally be equipped with a
myriad of features (such as map lights, reverse inhibit line,
headlamp activation, external temperature display, remote keyless
entry control, and the like), it is useful to equip such assemblies
with a standard connector (for example, a 10-pin parallel
connector) so that a common standard wiring harness can be provided
across an automaker's entire product range. Naturally, multiplexing
within the vehicle can help alleviate the need for more pins on
such a connector or allow a given pin or set of pins control more
than one function.
[0053] Using the concepts of the present invention, a drive voltage
at, or close to, the maximum voltage tolerable by the
electrochromic mirror element (ECMAX) can be selected (for example,
1.4 V) and, using this voltage ECMAX as a modulated, or a blanking,
signal, the reflectivity of the electrochromic reflective element
can be controlled to any partial reflectance level within its range
of reflectance levels from its maximum (bleached) reflectivity to
its minimum (fully dimmed) reflectivity by, for example, varying
the duty cycle of the modulated signal. The continuously variable
control of mirror reflectivity, also referred to as "gray-scale
control," is achieved by varying the duty cycle of the blanking
signal, preferably by pulse-width modulation.
[0054] Although illustrated as applied to control of an
electrochromic mirror element, the principles of the invention can
be applied to other devices including windows, glazings, contrast
enhancement filters, sunroofs, and the like.
[0055] Changes and modifications in the specifically described
embodiments can be carried out without departing from the
principles of the invention which is intended to be limited only by
the scope of the appended claims, as interpreted according to the
principles of patent law including the doctrine of equivalents
* * * * *