U.S. patent application number 09/878022 was filed with the patent office on 2002-03-07 for individual mirror control system.
Invention is credited to Knapp, Robert C., Turnbull, Robert R., Vawter, Roy E..
Application Number | 20020027713 09/878022 |
Document ID | / |
Family ID | 24093059 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020027713 |
Kind Code |
A1 |
Turnbull, Robert R. ; et
al. |
March 7, 2002 |
Individual mirror control system
Abstract
A control system for a plurality of electrochromic elements, for
example, used in automobiles, to control the glare of the IEC
elements used as a rearview mirror (20) as well as the OEC elements
(24, 26) used as sideview mirrors (24, 26). The IEC element and
each of the OEC elements is provided with an individual drive
circuit (21, 22). The drive circuits for the OEC's elements may be
customized to account for various factors such as the type of
curvature as well as the size and shape. Since individual drive
circuitry is provided for the IEC elements and each of the OEC
elements, the reflectance of each of the electrochromic elements
(20, 24, 26) can be relatively accurately controlled by way of
glare signal from inside the automobile.
Inventors: |
Turnbull, Robert R.;
(Holland, MI) ; Knapp, Robert C.; (Coloma, MI)
; Vawter, Roy E.; (Dorr, MI) |
Correspondence
Address: |
PRICE, HENEVELD, COOPER, DEWITT, & LITTON
695 KENMOOR, S.E.
P O BOX 2567
GRAND RAPIDS
MI
49501
US
|
Family ID: |
24093059 |
Appl. No.: |
09/878022 |
Filed: |
June 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09878022 |
Jun 8, 2001 |
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09525391 |
Mar 15, 2000 |
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6247819 |
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09525391 |
Mar 15, 2000 |
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PCT/US97/16946 |
Sep 16, 1997 |
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Current U.S.
Class: |
359/604 ;
359/265; 359/272; 359/601 |
Current CPC
Class: |
B60R 1/088 20130101 |
Class at
Publication: |
359/604 ;
359/265; 359/272; 359/601 |
International
Class: |
G02F 001/15 |
Claims
The invention claimed is:
1. A method for controlling the reflected light level of an inside
electrochromic element and an outside electrochromic element of a
vehicle to maintain a relatively constant reflected light level at
a predetermined reference point where the vehicle includes a rear
window made of privacy glass, the method comprising the steps of:
varying the reflectivity of the mirrors in response to a sensed
glare level and in accordance with a reflectance curve that
establishes a relationship between sensed glare levels and desired
reflectivity levels; and providing a first reflectance curve for
the inside electrochromic element and a second reflectance curve
for the outside electrochromic element, the first reflectance curve
having at least one different characteristic than the second
reflectance curve to compensate for the privacy glass of the rear
window.
2. The method of claim 1, wherein the different reflectance curve
characteristic is the slope.
3. The method of claim 1, wherein the different reflectance curve
characteristic is the offset.
4. A system for controlling reflectance levels of an inside
rearview mirror and at least one outside rearview mirror of a
vehicle having a rear window made of privacy glass, the system
comprising: a glare sensor for sensing the level of light received
from behind the vehicle, and for generating a glare signal
representing the sensed light level; and a control subsystem
coupled to the inside and outside rearview mirrors and said glare
sensor for receiving said glare signal and for generating
electrical signals to control the reflectivity of the inside and
outside rearview mirrors, said control subsystem controls the
reflectivity of the inside rearview mirror differently than that of
the at least one outside rearview mirror to compensate for the
privacy glass of the rear window.
5. The system of claim 4, wherein said control subsystem includes a
controller and individual drive circuits for each mirror, said
individual drive circuits are coupled to said controller.
6. The system of claim 4, wherein said glare sensor is mounted
inside the vehicle such that light received from behind the vehicle
projects through the privacy glass of the rear window before
reaching said glare sensor.
7. The system of claim 6, wherein said glare sensor mounted in a
housing of the inside rearview mirror.
8. The system of claim 4, wherein said control subsystem includes a
controller coupled to the glare sensor and individual drive
circuits for each mirror, said individual drive circuits are
coupled to said controller.
9. The system of claim 8, wherein each of the mirrors includes a
housing and wherein said individual drive circuits are mounted in
the respective housings.
10. The system of claim 9, wherein said controller is mounted in
the housing of the inside rearview mirror.
11. The system of claim 4, wherein said control subsystem controls
the reflectivity of the mirrors such that the reflected light at a
predetermined reference point is relatively constant.
12. The system of claim 4, wherein said control subsystem controls
the reflectivity of each of the mirrors based upon a reflectance
curve associated with each mirror, the reflectance curve
establishes a relationship between sensed glare levels and desired
reflectivity levels, wherein the reflectance curve for the inside
rearview mirror has at least one different characteristic than the
reflectance curve of the outside rearview mirror.
13. The system of claim 12, wherein said different characteristic
is the slope.
14. The system of claim 12, wherein said different characteristic
is the offset.
15. A rear vision system for a vehicle, the vehicle having a rear
window made of privacy glass, the rear vision system comprising: an
outside rearview mirror for mounting to the outside of the vehicle,
said outside mirror having a reflectivity that varies in response
to an electrical control signal; an inside rearview mirror for
mounting to the inside of the vehicle to reflect light entering
through the privacy glass of the rear window towards the eyes of
the driver, said inside mirror having a reflectivity that varies in
response to an electrical control signal; a glare sensor for
sensing the level of light received from behind the vehicle, and
for generating a glare signal representing the sensed light level;
and a control subsystem coupled to said inside and outside rearview
mirrors and said glare sensor for receiving said glare signal and
for generating electrical signals to control the reflectivity of
said inside and outside rearview mirrors, said control subsystem
controls the reflectivity of said inside rearview mirror
differently than that of said outside rearview mirror to compensate
for the privacy glass of the rear window.
16. The rear vision system of claim 15 and further including a
second outside rearview mirror for mounting to the exterior of the
vehicle, said second outside mirror having a reflectivity that
varies in response to an electrical control signal.
17. The rear vision system of claim 15, wherein said glare sensor
is mounted inside the vehicle such that light received from behind
the vehicle projects through the privacy glass of the rear window
before reaching said glare sensor.
18. The rear vision system of claim 17, wherein said glare sensor
mounted in a housing of said inside rearview mirror.
19. The rear vision system of claim 15, wherein said control
subsystem includes a controller coupled to said glare sensor and
individual drive circuits for each mirror, said individual drive
circuits are coupled to said controller.
20. The rear vision system of claim 19, wherein each of said
mirrors includes a housing and wherein said individual drive
circuits are mounted in the respective housings.
21. The rear vision system of claim 20, wherein said controller is
mounted in the housing of said inside rearview mirror.
22. The rear vision system of claim 15, wherein said control
subsystem controls the reflectivity of said mirrors such that the
reflected light at a predetermined reference point is relatively
constant.
23. The rear vision system of claim 15, wherein said control
subsystem controls the reflectivity of each of said mirrors based
upon a reflectance curve associated with each mirror, the
reflectance curve establishes a relationship between sensed glare
levels and desired reflectivity levels, wherein the reflectance
curve for said inside rearview mirror has at least one different
characteristic than the reflectance curve of said outside rearview
mirror.
24. The rear vision system of claim 23, wherein said different
characteristic is the slope.
25. The rear vision system of claim 23, wherein said different
characteristic is the offset.
26. The rear vision system of claim 15, wherein each of said
mirrors are electrochromic mirrors.
27. An outside rearview mirror assembly for a vehicle, said outside
rearview mirror assembly comprising: a housing for mounting to the
exterior of the vehicle; a mirror element mounted in said housing
and having a reflectivity that varies in response to a variable
electrical drive signal; and a drive circuit mounted in said
housing and coupled to the mirror element, said drive circuit
generates, selectively varies, and supplies the drive signal to
said mirror element in response to a glare signal received by said
drive circuit from a glare sensor, the glare signal representing a
glare level, said drive circuit selectively varies the drive signal
as a function of the glare level based upon a reflectance curve.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 09/525,391, entitled "INDIVIDUAL MIRROR
CONTROL SYSTEM," filed on Mar. 15, 2000, by Robert R. Turnbull et
al., which is a continuation under 35 U.S.C. .sctn.120 of
International PCT Application No. PCT/US97/16946, filed on Sep. 16,
1997, the disclosures of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a control system for
electrochromic mirrors for use, for example, in automobiles and
more particularly to a control system for an inside electrochromic
(IEC) mirror and one or more outside electrochromic (OEC) mirrors,
which are controlled by a glare signal generated within the
vehicle.
[0003] Various electrochromic mirror and electrochromic window
systems (hereinafter "electrochromic elements") are generally known
in the art. Such systems normally include a plurality of
electrochromic elements. For example, in automotive applications,
electrochromic elements are known to be used for both the rearview
mirror and one or more sideview mirrors as well as in window
applications for sun load control. It is known that the reflectance
of electrochromic elements used as mirrors (or transmittance in the
case of electrochromic elements used for window applications) is a
function of the voltage applied to the electrochromic element, for
example, as generally described in commonly assigned U.S. Pat. No.
4,902,108, which is hereby incorporated by reference. Because of
this characteristic, such electrochromic elements are known to be
used in systems which automatically control glare from external
light sources in various automotive and other applications. In
automotive applications, the 12-volt vehicle battery is used as the
electrical power source for the electrochromic elements. The
electrochromic elements generally operate at a nominal voltage of
about 1.2 volts. Since the actual electrochromic element voltages
are relatively low compared to the supply voltage, it is known to
use a single drive circuit for multiple electrochromic elements. In
such applications, the electrochromic elements for the inside and
outside mirrors are known to be connected either in series,
parallel, or series parallel and driven from a single drive
circuit.
[0004] In order to prevent damage to the electrochromic elements as
well as control their reflectance, the voltage across each
electrochromic element must be rather precisely controlled.
However, it is known that the resistance of the electrochromic
elements may vary as a function of temperature. Thus, in
applications with the electrochromic elements being used both
inside and outside the vehicle, the temperature difference between
the inside and outside electrochromic elements can be relatively
significant which can make relatively precise control of the
electrochromic elements difficult.
[0005] There are other factors which make relatively precise
control of the electrochromic elements difficult. For example, in
known systems, a glare signal, typically generated within the
vehicle, is transmitted by hardwiring to the OEC elements used for
the sideview mirrors. The glare signal is used to control the
reflectance of the electrochromic elements used for the sideview
mirrors. As mentioned above, the OEC elements are normally
connected in either series, series parallel, or in parallel with
the IEC element used for the rearview mirror assemblies often
requiring the voltage to the OEC elements to be scaled or offset.
It is known that electrochromic elements typically require a low
voltage drive, typically 1.2-1.4 volts to achieve minimum
reflectance. As such, a drive voltage accuracy of 0.1 volts or
better is required to maintain adequate glare control.
Unfortunately, the ground system in an automotive environment can
have differences in ground potential exceeding 2.0 volts under some
conditions, which can drastically affect the operation of the
electrochromic elements. In order to resolve this problem in known
automotive applications OEC elements, relatively heavy gauge
conductors are typically routed to each of the OEC elements
transmission of the glare signal, which increase the cost and
weight of installing such a system in an automobile.
[0006] There are other problems associated with the relatively
accurate control of OEC elements. In particular, OEC elements can
be classified according to three major types: flat, convex, and
aspheric. The effective magnification or reflectance levels differ
for each of the different curvature types. For example, flat
mirrors are known to have the highest effective reflectance or
magnification (i.e., 1 to 1) while the aspheric and convex mirrors
provide relatively lower reflectance (i.e., 1 to 3 and 1 to 4,
respectively) depending upon the degree of curvature. The different
reflectance or magnification levels of the different OEC element
types typically require different drive voltages, thus adding to
the complexity of relatively accurate control of the OEC elements.
Moreover, OEC elements come in a relatively large array of shapes
and sizes which may require different drive voltages to compensate
for voltage drops in the various coatings, solution, chemicals, and
chemistry, for example, on the larger mirrors.
[0007] In order to provide the driver with acceptable glare levels
from the IEC mirrors as well as the OEC mirrors, for example,
during night driving, the drive voltages to each of the mirrors
must be appropriately scaled. Since the IEC and the OEC elements do
not share a common thermal environment, it has been relatively
difficult if not impossible to correct for temperature-related
performance changes in the OEC elements from the inside.
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to solve various
known problems in the prior art.
[0009] It is yet another object of the present invention to provide
a control system for OEC elements wherein the drive voltage for the
OEC elements can be relatively accurately controlled.
[0010] Briefly, the present invention relates to a control system
for a plurality of electrochromic mirrors, for example, used in
automobiles, to control the glare level of the IEC elements used as
rearview mirrors as well as the OEC elements used as sideview
mirrors. The IEC element and each of the OEC elements are provided
with an individual drive circuit. The drive circuits for the OEC
elements may be customized to account for various factors, such as
the type of curvature as well as the size and shape. Since
individual drive circuitry is provided for the IEC element and each
of the OEC elements, the reflectance of each of the elements can be
relatively accurately controlled by way of glare signal generated
inside the automobile. More particularly, the individual drive
circuits for each of the outside mirrors can be used to scale the
drive voltage for each electrochromic element to compensate for
differences in the curvature or size as well as temperature of
operation of the OEC elements. By providing individual drive
circuits for each of the OEC elements, the need for two relatively
heavy gauge conductors in order to limit the voltage drop and a
ground referenced to the inside mirror and associated drive
circuitry is eliminated, thus simplifying the manufacturing
process. In particular, in the present invention, the ground
voltage does not need to be referenced to the IEC element, thus
only one conductor and chassis ground is sufficient. In one
embodiment of the invention, the control system is adapted to
control all the electrochromic elements to provide a relatively
constant level of glare at a predetermined reference point, such as
the driver's eye level, from all of the electrochromic
elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These and other objects of the present invention will be
readily understood with reference to the specification and the
following drawings, wherein:
[0012] FIG. 1 is a block diagram of the system in accordance with
the present invention;
[0013] FIG. 2 is an alternate embodiment of the block diagram
illustrated in FIG. 1;
[0014] FIG. 3 is a graphical illustration of exemplary reflectance
curves illustrating the reflectance of exemplary inside and OEC
elements as a function of the light from the rear of the vehicle
and also illustrates the reflectance of the electrochromic elements
as a function of the reflected light at the driver's eye level;
[0015] FIG. 4 is similar to FIG. 3, but illustrates compensation of
the reflected light using slope adjustment in accordance with one
embodiment of the invention;
[0016] FIG. 5 is similar to FIG. 4 illustrating the difference in
reflected light utilizing offset adjustment in accordance with an
alternative embodiment of the invention;
[0017] FIG. 6 is an exemplary graphical illustration showing the
duty cycle for different types of OEC elements relative to an
exemplary IEC element;
[0018] FIG. 7 is an exemplary schematic diagram of a drive circuit
for an electrochrornic element for use with the present
invention;
[0019] FIG. 8 is an exemplary schematic diagram of a drive circuit
for an element heater for an electrochromic element in accordance
with the present invention; and
[0020] FIG. 9 is a graphical illustration of an exemplary slope and
offset adjustment in accordance with the present invention
illustrating the duty cycle in percent on the horizontal axis and
the averaged glare signal GLARE and element voltage EC-REQ in volts
on the vertical axis.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] The present invention relates to a control system for
electrochromic elements that is particularly useful in automotive
applications where an IEC element 20 is used as a rearview mirror
and one or more OEC elements 24, 26 are used for the driver and
passenger sideview mirrors. An important aspect of the invention
relates to the fact that the IEC element 20 and one or more OEC
elements 24, 26 are individually controlled. More particularly, in
order to solve the various problems discussed above, individual
drive circuits are provided for each of the mirrors containing
electrochromic elements as opposed to driving the OEC elements, in
series, parallel, or series parallel with the IEC element, as is
known in the art. The drive circuits for each of the mirrors may be
incorporated into the individual mirror assemblies (not shown) to
enable the mirrors to be controlled by a glare signal, for example,
a pulse width modulated (PWM) signal or digital signal, from inside
the automobile.
[0022] The glare signal may be developed by a rearward-facing
sensor 21 (FIG. 1), such as a photocell, and a forward-facing
sensor 22, which may also be a photocell, to provide a glare signal
relative to the ambient light level in order to control the
reflectance of the electrochromic elements for the IEC 20 and OEC
24, 26 elements. These sensors 21 and 22 are known to be integrated
in the inside mirror assembly.
[0023] The glare signal is used for driving OEC elements 24 and 26.
Since each of the OEC elements 24, 26 is provided with an
individual drive circuit, the glare signal may be coupled either
directly with the OEC elements 24, 26 or by way of a bus interface,
generally identified by the reference numerals 28 (FIG. 1) and 30
(FIG. 2). By providing an individual drive circuit for each of the
electrochromic elements 20, 24, 26, the system in accordance with
the present invention is adapted to compensate for differences in
the thermal environment between the IEC 20 and the OEC 24, 26
elements as well for differences in the curvatures as well as size
of the OEC elements 24, 26. In particular, the glare signal can be
scaled to compensate for differences in the curvature, size, and
the various coatings used for the OEC 24, 26 elements as well as
differences in the thermal environment relative to the IEC element
20. As such, a relatively accurately scaled element voltage may be
generated for each electrochromic element that takes into account
the size as well as the curvature and even the temperature
environment of the OEC elements 24, 26 used for sideview mirrors.
This allows automobile manufacturers to stock fewer inside mirror
types, each capable of being used with a variety of different types
of outside mirrors. Since the outside mirrors are nearly always
unique to a particular model of an automobile, the customization of
the outside element drive voltages for optimal glare control may be
accomplished without an inventory and complexity penalty to the
automobile manufacturer. Moreover, since the glare level is
transmitted digitally or via a PWM signal, any ground voltage
difference will not affect the glare signal at the OEC elements 24,
26, thus allowing the glare signal to be transmitted to the OEC
elements 24, 26 using a relatively light gauge wire using a common
chassis ground to save cost and weight.
[0024] FIGS. 1 and 2 show two exemplary embodiments of the
invention. In both embodiments, one or more glare signals is
transmitted to the outside OEC elements 24, 26, which contain
integral drive circuits which can be scaled to provide relatively
accurate control of the OEC elements 24, 26 as discussed above.
Both embodiments illustrate the use of an optional bus interface,
generally identified with the reference numerals 28 and 30. The
optional bus interfaces 28 and 30 are merely exemplary and are not
required for the practice of the invention. Such bus interfaces 28,
30 normally include a bus interface 32, 34, for example, a Motorola
type 68HC705X4 and one or more bus receivers 36, 38, and 40, for
example, a Unitrode, model No. UC 5350 bus receiver. In the
embodiment illustrated in FIG. 1, the OEC elements 24 and 26 are
driven from a common glare signal. Alternatively, in FIG. 2,
separate glare signals may be generated for the passenger and
driver side OEC elements 24, 26. The separate glare signals may be
used to provide additional compensation in applications where
convex mirrors are used on the passenger side of the vehicle, which
are known to have relatively poor reflectance levels. In such
applications, passenger OEC and driver_OEC glare signals are
developed from the rearward and frontward facing sensors 21 and 22.
The passenger glare signal passenger_OEC may be scaled to
compensate for relatively poor reflectance of the convex mirror.
Both signals are applied to the bus interface 34 and, in turn, to a
driver bus receiver 38 and passenger bus receiver 40. The driver
bus receiver 38 generates a driver_PWM signal used for driving the
driver's side OEC 24. Similarly, the passenger_bus_receiver 40
generates a passenger_PWM signal for driving passenger_OEC 26.
[0025] The individual drive circuits also enable compensation for
environmental factors, such as rear and side window tinting
("privacy glass") and/or front windshield masking. In such
applications, due to the environmental factors, the light levels
experienced at the respective mirror surfaces may be different at
the driver eye level. The curves illustrated in FIGS. 3-5 represent
an exemplary application where the transmittance of the rear window
is about 30 percent while the transmittance of the side windows is
about 70 percent. Exemplary mirrors are used for FIGS. 3-5. The
reflectance of the IEC is selected with a maximum reflectance of
about 75 percent while the maximum reflectance of the driver's side
flat outside mirror is selected to be about 55 percent. The
passenger side convex outside mirror is used with a perceived
maximum reflectance value of about 18 percent. In particular, for
flat mirrors, the measured reflectance levels are the same as the
perceived reflectance levels. However, convex mirrors result in a
lower perceived reflectance level due to the light diverging from
the surface of the mirror. This difference is related to the radius
of curvature of the mirror surface as well as the distance of an
object from the mirror. As will be discussed in more detail below,
the system in accordance with the present invention is able to
compensate for these environmental factors in order to force the
reflected light from the IEC element 20 as well as the OEC elements
24, 26 to be relatively constant at a predetermined reference
point, such as the driver's eye level.
[0026] FIG. 3 is an exemplary graphical illustration illustrating
the effects of the privacy glass on the reflected light at a
predetermined reference point, such as the driver's eye level. The
curve 40 represents the reflectance of an IEC element as a function
of the light from the rear of the vehicle. The curves 42 and 44
illustrate the reflectance of a flat OEC element and a convex OEC
element, respectively, as a function of the light from the rear of
the vehicle. As illustrated, all three electrochromic elements are
at a maximum reflectance level at relatively low light levels. As
the light from the rear of the vehicle increases, the reflectance
level of the various electrochromic elements decreases to a minimum
reflectance value as shown. The light at the driver's eye level
from each of the electrochromic elements is shown by way of the
curves 46, 48, and 50. As shown in FIG. 3, the reflectance level of
all three electrochromic elements start to decrease with relatively
equal light from the rear of the vehicle. All three electrochromic
elements also achieved a minimum reflectance at similar light
levels.
[0027] However, as shown by the curves 46, 48, and 50, the
reflected light to the driver differs significantly for each
electrochromic element. This is shown in FIG. 3 by the different
reflectance levels for the three electrochromic elements in the
region, for example, between 0.500 lux and 5.000 lux along the
curves 46, 48, and 50, which is based upon the forward sensor being
exposed to about 1.0 lux . Optimum performance is for the light
levels at the driver's eye level to be fairly constant and equal in
the range from about 0.500 lux to about 5.000 lux, which represents
the active region of the exemplary IEC element 20 and exemplary OEC
elements 24 and 26.
[0028] FIGS. 4 and 5 relate to different methods in accordance with
the present invention for compensating for differences in reflected
light at a predetermined reference point, such as the driver's eye
level due to, for example, the privacy glass. Referring to FIG. 4,
the curves 52 and 54 for the OEC elements 24, 26 are similar to the
curves 42 and 44 illustrated in FIG. 3. However, in this
embodiment, a characteristic of the reflectance curve for the
mirror curve 56 is modified. In particular, the slope 57 in the
active region of the reflectance curve for the IEC 20 is decreased.
By decreasing the slope, the reflected light to the driver's eye
level from both the IEC 20 and driver's side flat OEC elements 24,
as represented by the curves 58 and 62, are much closer in the
active region of the electrochromic elements than in FIG. 3, for
example, in the region between 0.500 lux and about 5.000 lux.
However, the slope adjustment does not affect the light at the
driver's eye level from the passenger side convex OEC element 26,
which, as illustrated in FIG. 4, does not provide light at the
driver's eye level close to the driver's side OEC and IEC
elements.
[0029] FIG. 5 illustrates an embodiment in which the reflected
light at a predetermined reference point, such as the driver's eye
level, is relatively constant for the IEC 20 as well as for both of
the exemplary OEC elements 24, 26. Referring to FIG. 5, the
reflectance of the IEC 20 as well as the outside convex OEC 26 is
represented by the curves 64 and 66, respectively, which are
similar to the curves 40 and 44, respectively. In this embodiment,
a characteristic of the reflectance curve for one of the OEC
elements is altered. In particular, the offset of the driver's side
flat OEC 24 reflectance is varied. In this embodiment, the point
generally designated with the reference numeral 76, at which the
flat outside mirror starts to decrease in reflectance, is offset as
shown. By offsetting the point at which the mirror starts to
decrease in reflectance, the reflected light levels from all three
electrochromic elements at the driver's eye level will be
approximately the same.
[0030] As should be clear in FIGS. 3-5, the privacy glass
compensation results in relatively constant light levels for the
IEC element 20 as well as the OEC elements 24, 26 at a
predetermined reference point, such as the driver's level. Although
specific examples for compensation for reflected light levels at
the driver's eye level for exemplary IEC and OEC elements are
discussed herein, the principles of the invention are not so
limited. In particular, the principles of the present invention may
be used to control virtually any combination of electrochromic
elements in applications with and without privacy glass and
virtually any reference point in automobile and non-automobile
applications.
[0031] As mentioned above, the electrochromic elements are
controlled, for example, by a PWM signal. The reflectance level of
the particular electrochromic element, aside from the slope and
offset adjustment discussed above, is varied by varying the duty
cycle of the PWM signal. Exemplary duty cycles for an IEC element
20, flat OEC element 24 and a convex OEC element 26 are illustrated
in FIG. 6. As shown, the IEC element 20 responds (dims) when the
duty cycle reaches about 30 percent of its control range and may be
fully dimmed when the duty cycle reaches approximately 80 percent.
A flat OEC element 24, due to its lower reflectance level and the
transmission rate of the driver's side window, needs to respond
(dim) when the duty cycle reaches 15 percent and be fully dimmed
when the duty cycle reaches about 60 percent. However, a convex OEC
element 26, due to its perceived reflectance level, may not need to
respond (dim) until the duty cycle reaches 45 percent and may be
fully dimmed when the duty cycle reaches 95 percent. By designing
the electrochromic elements, such that their operational response
to the duty cycle, is based on the location of the electrochromic
elements on the vehicle and the path that the light takes to reach
the electrochromic elements, the IEC element 20 and the OEC
elements 24, 26 may be controlled to maintain a relatively constant
level of reflected light at a predetermined reference point, such
as the driver's eye level.
[0032] Various electronic drive circuits are suitable for use with
the present invention. FIG. 7 is an exemplary schematic of a drive
circuit for an electrochromic element while FIG. 8 represents an
exemplary drive circuit for an optional element heater for an
electrochromic element for use with the present invention. Other
drive circuits for the electrochromic elements are considered to be
within the broad principles of the invention.
[0033] Referring first to FIG. 7, the resistors R10, R16, and the
transistor Q3 are used to simulate a pulse width modulated signal
PWM_IN, which represents the glare level control signal. These
components R10, R16, and Q3 do not form part of the electronic
drive circuit for the electrochromic element in accordance with the
present invention, generally identified with the reference numeral
80. As mentioned above, the electronic drive circuit 80 is powered
by the nominal 12-volt vehicle battery 82. A resistor R8 along with
the Zener diode D2 form a Zener regulated supply V.sub.DD as well
as provide a reference for the difference amplifiers U1 and U2. A
capacitor C5, connected between the positive terminal of the
battery 82 and ground, provides electromagnetic interference (EMI)
bypassing. A diode D2, connected with its anode to the positive
terminal of the battery and its cathode connected to the 12-volt
supply 12V_IN, provides reverse polarity protection. R3, R14, R15,
C6, U1A, R11, R17, and R18 form a comparator circuit to eliminate
ground and amplitude errors in the PWM glare signal from the inside
mirror assembly. In some cases, where a bus receiver is located
physically close to the OEC assembly, this section may not be
required.
[0034] The PWM signal PWM_IN is applied to an inverting terminal of
a difference amplifier U1A by way of resistor R14. The resistor
R14, together with a resistor R15, connected between the inverting
terminal of the difference amplifier U1A and ground, form a voltage
divider to prevent the PWM_IN signal from exceeding the common mode
range of the difference amplifier U1A. A resistor R3, coupled to
the 12-volt supply 12V IN, is used to pull up the PWM signal
PWM_IN. A capacitor C6 is connected between the inverting terminal
of the difference amplifier U1A and ground to provide a filtering
and radio frequency (RF) immunity.
[0035] A reference voltage supply is applied to the non-inverting
terminal of the difference amplifier U1A. In particular, a pair of
resistors R11 and R17 are used to form a voltage divider to create
a reference voltage U1A at the non-inverting input of the
difference amplifier U1A. A feedback resistor R18, connected
between the output and the non-inverting input of the difference
amplifier U1A, provides hysteresis in order to improve the noise
immunity of the difference amplifier U1A.
[0036] The output of the difference amplifier U1A is a glare
control signal GLARE which has two states: nominally 0 and 3.4
volts, and is proportional to the glare level sensed and
transmitted by the inside mirror assembly. A capacitor C2 is
coupled between the non-inverting input of the difference amplifier
U2 and ground to average the PWM signal to provide a DC glare
signal EC-REQ, which is proportional to the duty cycle.
[0037] The glare signal GLARE is applied to a slope and an offset
adjust circuit which includes a difference amplifier U2 and a
plurality of resistors R12, R19, R26, R27, R28, and R31 and a
filter circuit using C2. The gain or slope of the reflectance curve
of the electrochromic element is set by the ratio of the resistors
R26/R28, which is identical to the ratio of the resistors R19/R12.
The slope may be selected as discussed above such that the
reflected light at the driver's eye level is relatively the same
for the inside and outside electrochromic mirrors. With the values
shown in FIG. 7, the slope is such that the maximum element voltage
is reached at about 70 percent duty cycle of the GLARE signal as
illustrated in FIG. 9.
[0038] The resistors R27 and R31 are used to adjust the offset as
discussed above. A negative offset may optionally be added by the
resistors R27 and R31 to hold the electrochromic element voltage
EC-DRIVE at about 0 volts until a minimum duty cycle is achieved.
With the values shown in FIG. 7, the electrochromic element voltage
will remain at about 0 volts until a duty cycle of 25 percent is
reached as illustrated in FIG. 9.
[0039] The output of the difference amplifier U2 is scaled by a
pair of resistors R29 and R30, which establish the maximum element
voltage so that for a full scale output, the electrochromic element
voltage is 1.2 volts, for example. Optional temperature
compensation may be provided for the glare signal EC-REQ by way of
a pair of resistors R5 and R13 and a thermistor TH1 in order to
provide increased drive voltage at low temperatures to improve the
response time.
[0040] A pair of difference amplifiers U1B and U1C are used to
drive the drive transistors Q1 and Q2 to either drive or short the
electrochromic element R_EC depending on the difference between the
voltage EC_REQ, the DC glare signal, and the electrochromic element
voltage EC-DRIVE. If the electrochromic element voltage EC-DRIVE
exceeds the glare signal voltage EC_REQ, the difference amplifier
U1C will go high, thereby turning on the drive transistor Q2, which
shunts the electrochromic element R_EC, which, in turn, discharges
the electrochromic element causing its reflectance to increase. The
voltage at the output of the difference amplifier U1C will
stabilize at that point required to cause the drive transistor Q2
to sink just enough current to match the EC-DRIVE and the EC_REQ
signals.
[0041] A resistor R4, connected to the output of the difference
amplifier U1C, limits the base current to the drive transistor Q2.
The combination of a capacitor C1 and a resistor R4 provide high
frequency negative feedback to stabilize the U1C-Q2 feedback loop
and to reduce EMI. A resistor R9, coupled between the non-inverting
input of the difference amplifier U1C and the electrochromic
element R_EC, provides electrostatic discharge (ESD) protection for
the difference amplifiers U1B and U1C .
[0042] If the DC glare signal EC_REQ exceeds the drive signal
EC-DRIVE by more than approximately 25 millivolts, for example, the
output of the difference amplifier U1B will go high turning on the
drive transistor Q1. The voltage at the output of the difference
amplifier U1B will stabilize at the point required to cause the
drive transistor Q1 to source just enough current to match the
EC-DRIVE and EC-REQ+25 MV. The resistors R6 and R7 offset the
voltage at the inverting input of the difference amplifier U1B by
approximately 25 millivolts. Since the resistor R7 is much larger
than resistor R6, it behaves more like a current source than as a
voltage divider. This causes the largest percentage error when the
electrochromic element voltage is near OV. Since the electrochromic
element is clear until its voltage reaches about 0.4 volt, this
error is negligible once the element begins to darken. The current
supplied by the resistor R7 flows through R6 and adds approximately
25 millivolts to EC-DRIVE signal to produce the signal EC-REQ+25
MV. This offset insures that the drive transistors Q1 and Q2 will
not turn on at the same time. A pair of capacitors C7 and C4
control the loop gain of the U1B-Q1 Loop at high frequencies to
ensure stability. The resistor R2 connected to the output of the
difference amplifier U1B, limits the base current to the transistor
Q1 and in conjunction with the capacitor C4, sets a high frequency
pole. The combination of the resistor R6 and capacitor C7 sets
another high frequency pole. The resistor R6 also provides ESD
protection to the comparator U1B. A resistor R1 limits the
collector current of the drive transistor Q1.
[0043] A capacitor C3 provides a power supply bypass to ensure the
stability of the difference amplifier U1. A pair of capacitors C1
and C4, coupled to the drive transistors Q1 and Q2, provide EMI and
ESD protection to the drive circuit 80. A resistor R1, disposed in
series with the collector of the transistor Q1, reduces Q1's power
dissipation.
[0044] An optional heater control circuit is illustrated in FIG. 8.
A resistor R22 in series with a thermistor TH2 forms a voltage
divider with a temperature dependent output. As the temperature
drops, the voltage on the comparator U1D increases. A pair of
resistors, R22 and R23, connected between the power supply V.sub.DD
and the non-inverting and inverting inputs of the difference
amplifier U1D, respectively, form a voltage divider with a fixed
reference output at the inverting input of the difference amplifier
U1D.
[0045] The output of the difference amplifier U1D will go high when
the mirror temperature drops below, for example, 0.degree. C.,
turning on the transistor Q4 to activate a mirror element heater,
represented as the element R20. A resistor R25 connected between
the output and the non-inverting input of the difference amplifier
U1D provides hysteresis. A resistor R21 connected between the base
of the drive transistor Q4 and the output of the difference
amplifier U1D limits the base current into the drive transistor Q4.
A capacitor C9 provides for EMI protection for the circuit.
[0046] While the invention has been described with reference to
details of the embodiments shown in the drawings, these details are
not intended to limit the scope of the invention as described in
the appended claims.
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