United States Patent [191
`‘Bechtel et a1.
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,917,477
`Apr. 17, 1990
`
`[54] AUTOMATIC REARVIEW MIRROR SYSTEM
`FOR AUTOMOTIVE VEHICLES
`[75] Inventors: Jon H, Bechtel; Harlan J , Byker,
`both of Holland, Mich,
`[73] Assignee: Gentex Corporation, Zeeland, Mich.
`[21] Appl, NO,: 34,913
`22 F1 _
`A 6
`[
`1
`‘ ed‘
`p" ’ 1987
`
`4,750,816 6/1988 Ito et al. ............................ .. 350/357 ‘
`Primary Examiner——Eugene R, LaRoche
`Assistant Examiner—Nathan W. McCutcheon
`Attorney, Agent, or Firm-Malcolm R. McKinnon
`[57]
`ABSTRACT
`An improved automatic rearview mirror system which
`is particularly adapted for use with automotive vehicles
`and which may be utilized as a fully integrated inside/
`
`[51] Int. GL4 . . . ' _
`_ , _ _ _ . _ _ _ _ " G021? 1/17
`[52] us. Cl. .................................. .. 350/357; 350/283;
`350/279
`[58] Field of Search ............. .. 350/357, 278, 279, 281,
`350/283
`
`[56]
`
`.
`References Clted
`U.S. PATENT DOCUMENTS
`4,443,057 4/1984 Bauer et al. ....................... .. 350/281
`
`outside rearview mirror system or as an inside or an
`outside rearview mirror system- The system includes :1
`variable re?ectance member the re?ectivity of which
`varies as a function of an electrical signal applied
`thereto, and the system also includes improved means
`operable to apply an electrical signal to the variable
`re?ectance member to vary the re?ectivity of such
`member as a function of sensed ambient light and sensed
`glare causmg llght'
`
`
`
`4,669,825 6/1987 Itoh et a1. 4,690,508 9/1987 Jacob ......................... .. 350/283 X
`
`44 Claims, 12 Drawing Sheets
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`TRW v. Magna
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`Ap1. 17,1990
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`U.S. Patent Apr;17,1990
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`
`1
`
`AUTOMATIC REARVIEW MIRROR SYSTEM FOR
`AUTOMOTIVE VEHICLES
`
`5
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`15
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`20
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`BRIEF SUMMARY OF THE INVENTION
`This invention relates to rearview mirrors for auto
`motive vehicles and, more particularly, to an improved
`automatic rearview mirror system for automotive vehi
`cles.
`Heretofore, many automatic rearview mirrors for
`automotive vehicles have been devised which automati
`cally transfer from the full re?ectance mode (day) to the
`partial reflectance mode (night) for glare protection
`purposes from light emanating from the headlights of
`vehicles approaching from the rear. Such automatic
`rearview mirrors have become increasingly sophisti
`cated over the years, and the automatic rearview mirror
`for automotive vehicles disclosed in U.S. Pat. No.
`4,443,057, issued Apr. 17, 1984, for Automatic Rear
`view Mirror for Automotive Vehicles, and assigned to
`the assignee of the present invention, is typical of such
`sophisticated automatic rearview mirrors. An improved
`electronic control system for automatic rearview mir
`rors is disclosed in U.S. Pat. No. 4,580,875, issued Apr.
`8, 1986, for Electronic Control System for Automatic
`Rearview Mirrors for Automatic Vehicles, such last
`mentioned patent also being assigned to the assignee of ‘
`the present invention. The present invention provides
`an improved automatic rearview mirror system for
`automotive vehicles, such vsystem incorporating im
`proved means for overcoming de?ciencies in prior au
`tomatic rearview mirrors of the indicated character. It
`will also be understood, however, that the present in
`vention is also applicable to other uses.
`In general, the automatic rearview mirrors disclosed
`in U.S. Pat. Nos. 4,443,057 and 4,580,875 utilize a prism
`type re?ective element which is substantially identical
`to the prism type re?ective elements utilized in manu
`ally (hand) operated day-night mirrors conventionally
`provided on modern day automobiles. The automatic
`rearview mirrors disclosed in said prior patents auto
`matically respond to annoying glare from the rear of the
`vehicle and automatically shift to the partial or low
`re?ectance mode. After the source of the annoying
`glare is removed, the automatic rearview mirrors return
`to the full or high re?ectance mode without requiring
`any action on the part of the driver of the vehicle during
`any portion of the cycle, the power required being
`drawn either from the vehicle’s electrical system or
`from a self contained battery.
`As previously mentioned, in the past, many automatic
`mirrors have been devised for the purpose of automati
`cally shifting the re?ective element incorporated
`therein between the full re?ectance and partial re?ec
`tance modes. However, proper control of an automatic
`rearview mirror is a complex task, and there has been a
`progression in the prior art. With respect to the means
`for sensing glare conditions, in early attempts to make
`automatic rearview mirrors, a single rear facing sensor
`was utilized. Such sensor sensed the glare producing
`light level impinging on the mirror from the rear, and
`such mirrors locked in the nonglare position during the
`day and required constant readjustment to prevent latch
`up or undesirably high sensitivity as the driver encoun
`tered brighter lights in city or town driving. As a ?rst
`improvement, a second sensor was added to sense the
`ambient light level and to hold the mirror in a normal
`position during the day. In most of the control circuits
`
`4,917,477
`2
`for such two sensor mirrors, the sensitivity of the mirror
`was reduced as ambient light levels approached day
`light levels until the ambient light reached a level above
`which the mirror remained in the nonglare position.
`This feature was re?ned so that the sensitivity of the
`mirror was referenced to the instantaneous ambient
`light level during nighttime driving. However, both
`ambient and glare producing light levels are quite er
`ratic since headlight beams which are momentarily
`blocked or which suddenly sweep into position cause
`erratic glare. Moreover, streetlamps, lighted roadside
`signs, and headlights of oncoming vehicles are erratic
`sources of ambient light. Thus, mirror operation of such
`prior art mirrors remained erratic in the face of these
`conditions. Moreover, the problem was compounded
`by making the glare threshold dependent on the erratic
`instantaneous light level. In an effort to overcome such
`problems, attempts were made to introduce time delays
`and to ?lter the combined ambient and glare producing
`light levels. However, none of these minor improve
`ments to the prior art mirrors resulted in a commer
`cially successful product since the added nuisance ef
`fects of the second sensor more than offset its advan
`tages with the result that the two-sensor circuits were
`often less desirable than the single-sensor circuits.
`The ?rst commercially successful automatic rearview
`mirror for automotive vehicles was disclosed in U.S.
`Pat. No. 4,443,057. The automatic mirror disclosed in
`U.S. Pat. No. 4,443,057 constituted a major advance in
`the utilization of ambient light level and the electrical
`control circuitry for such mirror included forward sen
`sor ?ltering means characterized by having a long time
`response and having a smoothing time averaged effect
`on the forward electrical signal generated by the for
`ward facing sensor means and indicative of the forward
`light level. The long, smoothed time average of the
`ambient light level, rather than the ambient light level
`itself, was then compared with the glare producing light
`level to determine the glare threshold of the mirror. Use
`of the long, smoothed time average of the ambient light
`level, instead of the instantaneous ambient light level,
`reduced and all but eliminated the effect of the erratic
`?uctuation of the ambient light level. A second impor
`tant bene?t of this long, smoothed time average is that
`it responds to ambient light level in much the same way
`as the human eye responds. In addition, in the automatic
`rearview mirror disclosed in U.S. Pat. No. 4,443,057, a
`shorter time average, which does not prevent rapid
`response of the mirror to strong glare, is optionally
`applied to the glare producing light level measurement.
`This shorter time average may be applied independently
`to the measurement of the glare producing light level or
`it may be applied to some combination of the long,
`smoothed time average of the ambient light level mea
`surement and the glare producing light level measure
`ment, the reason for this option being that the effect of
`another short time average on the long, smoothed aver
`age of the ambient light is minimal. The short time
`average applied so as to include the glare producing
`light level is not nearly as bene?cial to mirror perfor
`mance as the long, smoothed time average which is
`applied to the ambient light level. It is therefore an
`optional feature of the circuitry disclosed in U.S. Pat.
`No. 4,443,057. The main bene?t of the short time aver
`age of the signal which includes the glare producing
`light level is that it prevents some nuisance actuations of
`the mirror from outside lights and the like. The com
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`4,917,477
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`4
`mercial product which utilizes the long, smoothed aver
`that in the great majority of driving situations, including
`age of the ambient light level also has a day detect
`heavy traffic situations, the sensitivity if maintained at
`circuit which inhibits traverse of the mirror to the non
`an adequately low level and the mirror is not allowed to
`glare position whenever the instantaneous light level
`become too active. Thus, the improved electronic con
`exceeds a predetermined value. However, operation of
`trol system disclosed in U.S. Pat. No. 4,580,875 reduced
`this feature is independent of the glare producing light
`the sensitivity of the mirror when a driver encountered
`level. As previously mentioned, the use of the long,
`a situation which requires better visibility or reduced
`smoothed time average of the ambient light level re
`activity of the mirror; monitored fluctuations in, and the
`sulted in a commercially successful product, the me
`values of, the measured light levels so as to approxi
`chanical structure and the electronic circuitry of such
`mately indicate conditions where traffic is heavy or
`product being disclosed in U.S. Pat. No. 4,443,057. The
`where the mirror would normally be overly active; and
`electronic control system disclosed in U.S. Pat. No.
`reduced the sensitivity of the mirror to a value which is
`4,580,875 constituted an improvement over the cir
`lower than the sensitivity would normally be. The glare
`cuitry disclosed in U.S. Pat. No. 4,443,057.
`threshold was thus determined as a function of the am
`Automatic rearview mirrors with the long, smoothed
`bient light level, of a long, smoothed time average of the
`time average of the ambient light level measurement
`ambient light level, of a short, smoothed time average of
`adapt well to varied driving conditions and have very
`the glare producing light level, and of the recent activ
`desirable performance in most highway and small town
`ity of the mirror.
`driving situations. In light traffic situations, it is desir
`The mirrors disclosed in U.S. Pat. Nos. 4,443,057 and
`able for the mirror to transverse to the nonglare position
`4,580,875 change re?ectance by automatically indexing
`even when glare only causes mild discomfort. First,
`a two position prism mirror element between its high
`glare is most annoying and disabling when ambient light
`and its low reflectance positions. While the two position
`levels are low and when brighter lights from other
`prism mirror performs well as an inside rearview mirror
`vehicles are frequently encountered. Second, in light
`there are technical limitations which completely ex
`traf?c, it is not normally necessary for the driver to see
`clude its use as an outside mirror. The utilization of the
`as much detail in the mirror as in heavy traffic. The
`two position prism in an inside automatic mirror is also
`view provided by the mirror in either the normal posi
`subject to de?ciencies because of the noise and mechan
`tion or in the nonglare position is usually satisfactory.
`ical vibration associated with the automatic indexing
`Consequently, the mirror preferably should be in the
`mechanism. Motors, solenoids and the like used to index
`more comfortable nonglare position whenever there is
`such a mirror are normally noisy and the pivots and the
`glare. Accordingly, such a mirror performs very well in
`added weight of the indexing mechanism make it diffi
`nearly all light traffic conditions. However, in spite of
`cult to keep the mirror from vibrating. Furthermore,
`the generally excellent performance of the mirror just
`the two position prism is strictly a dual reflectance
`described, it may become too active or too sensitive in
`device which allows no option for a continuously vari
`some situations, particularly in heavy traffic situations.
`able reflectance or for intermediate re?ectance states.
`In heavy traffic situations there are a number of reasons
`Experience with mirror elements which have con
`for reducing the sensitivity of the mirror below the
`trolled intermediate re?ectance levels quickly reveals
`level normally programmed for the prevailing time
`that a dual reflectance mirror is highly inadequate.
`averaged ambient light level. First, the ambient light
`Improvements have been made with liquid crystal
`level is not highly correlated with traffic density. Bright
`type mirrors but limitations still remain. For example,
`streetlights are the source of the highest ambient light
`most liquid crystal mirrors re?ect less than half as much
`level which is normally encountered in night driving. A
`light as do the two position prism mirrors when the
`lightly traveled but brightly lighted street has a high
`mirrors are in their bright states. The dim images of
`ambient light level. A heavily traveled but dimly
`most liquid crystal mirrors are only three to ?ve times
`lighted street has a moderate ambient light level.
`dimmer than their bright images. In comparison, the
`Second, the added visibility, particularly the greatly
`dim images of two position prism mirrors are approxi
`added depth perception which normally accompanies
`mately twenty times dimmer than their bright images.
`the brighter image, is needed by the driver. Third, the
`At low temperatures, most liquid crystal mirrors do not
`driver is exposed to enough brighter lights from head
`dim properly because most freeze and cloud so as to be
`lamps and perhaps from streetlamps that glare is not so
`totally unusable until they thaw. Furthermore, circuit
`50
`annoying or disabling. Fourth, more than one set of
`or power failures cause most liquid crystal mirrors to go
`headlights are often visible in the mirror at the same
`to the dim state creating a safety hazard. With respect to
`time. The driver tends to be bothered by the brightest
`other known prior art devices, prior electrochromic
`lights while the mirror sensor measures the combined
`devices have performed relatively well but have suf
`light level of light striking the mirror from angles that
`fered from limited cycle life, from extremely slow speed
`are generally in the driver’s ?eld of view. The effect is
`in changing reflectance, and from failure of the mirror
`to increase the apparent sensitivity of the mirror when
`control circuit to properly utilize the slower speed of
`several sets of headlights contribute to the glare. Fifth,
`mirror operation.
`heavy traffic and a few other conditions such as wind
`The automatically indexed two position prism mirror
`ing or hilly roads, are usually accompanied by very
`referred to above changes from dim to bright or from
`erratic sources of glare. Automobiles change lanes and
`bright to dim in about one third of a second. Under most
`make turns, and since only strong glare is normally a
`driving conditions, the light levels sensed by the mirror
`problem, an automobile may only momentarily be close
`are quite erratic. If the transitions of the mirror were not
`enough for the glare to be a problem. The result is that
`limited in some way, there would be many driving con
`the mirror is often undesirably active in very heavy
`ditions where the mirror would change almost continu
`traffic conditions.
`ously between its dim and bright states. This constant
`U.S. Pat. No. 4,580,875 disclosed means for improv
`changing would be annoying and disorienting to the
`ing the performance of automatic rearview mirrors so
`driver thereby making the mirror almost unusable and
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`5
`6
`which allow the glare causing light threshold to be
`at the same time pose a serious safety problem. In order
`to avoid the annoying frequent transitions, the two
`increased more rapidly with increases in the ambient
`position mirror delays for about eight seconds after the
`light reference level.
`glare subsides before returning from the dim, nonglare
`Another object of the present invention is to provide
`position to the normal, bright position. Thus, any com
`an improved automatic rearview mirror system for
`plete cycle of the mirror includes a minimum of eight
`automotive vehicles incorporating an electrochromic
`seconds in the dim, nonglare position. This minimum
`mirror effective to dramatically reduce glare from fol
`lowing headlights thereby improving nighttime driving
`dwell time in the nonglare position limits the rate at
`safety and comfort.
`which the mirror can transverse between its two states,
`and this delay feature requires the incorporation of
`Another object of the present invention is to provide
`additional‘ components in the circuit. Moreover, the
`an improved automatic rearview mirror system for
`delay circuit alone does not adequately limit transitions
`automotive vehicles which eliminates mirror movement
`of the mirror and the additional stabilizing circuit of
`and vibrations and which may gradually darken in mul
`US. Pat. No. 4,580,875 is also preferably used in the
`tiple increments as opposed to a two-step process.
`control circuit for the two position prism mirror.
`Still another object of the present invention is to
`The electrochromic mirror disclosed in the copend
`provide an improved automatic rearview mirror system
`ing application of Harlan J. Byker, Ser. No. 846,354,
`for automotive vehicles wherein the amount of dim
`filed Mar. 31, 1986, for Single-Compartment, Self-Eras
`ming of the mirror depends upon the amount of glare
`ing, Solution~Phase Electrochromic Devices, Solutions
`the driver experiences.
`For Use Therein, and Uses Thereof, and assigned to the
`Yet another object of the present invention is to pro
`assignee of the present invention, overcomes many of
`vide an improved automatic rearview mirror system for
`the limitations stated above for the two position prism
`automotive vehicles wherein both the inside and the
`and liquid crystal mirrors and has an excellent cycle life
`outside rearview mirrors change re?ectance modes
`simultaneously.
`and relatively rapid response in going from the bright to
`the dim state. Accordingly, electrochromic mirrors of
`The above as well as other objects and advantages of
`25
`thetype disclosed in copending application Ser. No.
`the present invention will become apparent from the
`following description, the appended claims and the
`846,354 are incorporated in the preferred embodiments
`accompanying drawings.
`of the present invention. Such electrochromic mirrors
`dim substantially in one to three seconds and clear sub
`BRIEF DESCRIPTION OF THE DRAWINGS
`stantially in ?ve to ten seconds under the control of the
`control circuits embodying the present invention which
`FIG. 1 is a simpli?ed cross-sectional elevational view
`enable the electrochromic mirrors to be successfully
`of an electrochromic mirror, showing the same in posi
`utilized in an automotive vehicle glare control system.
`tion for viewing by the driver of an automotive vehicle;
`It will be understood, however, that many of the con
`FIG. 1a is an elevational view of a prism type electro
`trol circuit features are also applicable to the control of
`chromic mirror similar to the mirror illustrated in FIG.
`1, showing the same in position for viewing by the
`other types of mirrors.
`An object of the present invention is to overcome
`driver of an automotive vehicle;
`disadvantages in prior automatic rearview mirrors of
`FIG. 2 is a schematic electrical diagram of an auto
`matic rearview mirror system embodying the present
`the indicated character and to provide an improved
`automatic rearview mirror system for automotive vehi
`invention;
`cles, which system may be utilized as a fully integrated
`FIG. 3 is a schematic block diagram of the automatic
`rearview mirror system illustrated in FIG. 2, and show
`inside/outside rearview mirror system or as an inside or
`ing the components incorporated in various sections of
`an outside rearview mirror system and which incorpo
`rates improved means preventing the abrupt and erratic
`the system;
`changes in re?ectance levels which are associated with
`FIG. 4 is a perspective view of an automatic rearview
`most prior variable re?ectance mirrors.
`mirror system embodying the present invention, and
`Another object of the present invention is to provide
`showing an inside mirror installed on the windshield of
`an improved automatic rearview mirror system incor
`a vehicle and two outside rearview mirrors installed on
`porating improved control circuitry whereby continu
`the outside of the vehicle in a conventional manner
`ous change in the reflectivity of the mirror provides
`whereby each of the mirrors faces rearwardly of the
`continuously variable re?ectance for various embodi
`vehicle in a conventional manner;
`FIG. 5 is a chart showing the relationship of the glare
`ments of the invention.
`Another object of the present invention is to provide
`threshold in footcandles with respect to the ambient
`an improved automatic rearview mirror system for
`light reference in footcandles;
`automotive vehicles which minimizes glare that the
`FIG. 6 is a simpli?ed, generalized block diagram of
`vehicle driver sees under various driving conditions
`the system as illustrated in FIG. 10, and showing the
`while keeping the re?ectivity of the mirror sufficiently
`components incorporated in various sections of the
`high to maintain good visibility.
`system;
`Another object of the present invention is to provide
`FIG. 7 is a schematic diagram of another embodiment
`an improved automatic rearview mirror system for
`of the invention;
`automotive vehicles wherein glare is sensed after atten
`FIG. 8 is a schematic diagram of another embodiment
`uation in the mirror thereby improving the accuracy of
`of the invention;
`the re?ectance control and reducing the range of glare
`FIG. 9 is a schematic diagram of another embodiment
`causing light level signals to which the system must
`of the invention;
`FIG. 10 is a schematic electrical diagram of another
`embodiment of the invention;
`FIG. 11 is a schematic electrical diagram of still an
`other embodiment of the invention;
`
`Another object of the present invention is to provide
`an improved automatic rearview mirror system for
`automotive vehicles incorporating improved means
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`FIG. 12 is a schematic block diagram of the embodi
`electrical circuit at terminal points 8 and 9. The light
`ment of the invention illustrated in FIG. 11, and also
`ray 14 enters through the front cover glass 1, the trans
`showing the components incorporated in various sec
`parent conductive layer 2, the electrochromic layer 5,
`tions of this embodiment of the invention.
`the transparent conductive layer 3, and the mirror glass
`FIG. 13 is a family of curves showing mirror re?ec
`4 layer before being re?ected from the re?ective layer 7
`tance in percent versus glare-causing light level for six
`provided on the mirror glass layer 4. Light in the re
`different ambient (front) light levels.
`?ected ray 15 exits by the same general path trasversed
`FIG. 14 is a composite of three plots of mirror re?ec
`in the reverse direction. Both the ray 14 and the re
`tance and of the level of the re?ected light which the
`?ected ray 15 are attenuated in proportion to the degree
`driver sees.
`to which the electrochromic layer 5 is light absorbing.
`FIG. 15 is a plot similar to form in the plots of FIG.
`When the layer 5 is highly light absorbing, the intensity
`14, mirror re?ectance and the level of the re?ected light
`of the ray 15 and the ray 25 are insigni?cant and the dim
`which the driver sees being shown using the circuit of
`image remaining is from rays 16 and 17 which are re
`FIG. 11, the mirror of FIG. 1 and the through the layer
`?ected off of the front and back surfaces of the cover
`sensor con?guration of FIG. 5; and
`'
`glass 1.
`FIG. 16 is a plot similar to FIG. 15 except that the
`In operation, when the switch 18 is positioned to
`threshold point 1204A is somewhat different than the
`contact the contact 19 to connect the battery 21 to the
`corresponding threshold point 1104A of FIG. 15.
`terminals 8 and 9, as schematically illustrated in FIG. 1,
`the mirror darkens in approximately three seconds.
`When the switch 18 is positioned to contact the contact
`22 to open circuit the mirror, the mirror clears in ap
`proximately 20 seconds. Because of this property, all of
`the embodiments of the invention go to their maximum
`reflectances when power is interrupted. When the mir—
`ror is darkened and the switch 18 is positioned to
`contact the contact 20 thereby shorting the mirror, the
`mirror clears in approximately 8 seconds. Clearing and
`darkening begin almost immediately when the drive
`signal to the mirror element is changed so that signi?
`cant changes in mirror re?ectance occur in times which
`are much shorter than those stated above.
`In FIG. 1, the vehicle driver 24 views the rays 15, 16,
`17 and 25 which are re?ected from different surfaces of
`the mirror structure. When the mirror structure is thin
`and when the layers are parallel, this causes very little
`problem. However, with wider separation of the sur
`faces and with slightly nonparallel surfaces, the multiple
`imaging becomes a problem. In order to eliminate this
`multiple imaging problem, the prism structure of FIG.
`1a is optionally used, such prism structure being dis
`closed in the aforementioned copending application,
`Ser. No. 846,354. The structure of the prism mirror M-a
`of FIG. 1a is identical to that of the mirror M of FIG.
`1 except for the prism shape of the element 40. The
`angle of the prism is preferably great enough to allow
`the rays 16a, 17a and 25a to be re?ected up toward the
`roof of the automobile instead of toward the driver.
`Only the ray 15a reaches the driver 24a. The light ray
`14a makes one pass through the attenuating layer 5a
`before being re?ected by the re?ective layer 70 as a ray
`15a. The light ray 15a then makes a pass through the
`attenuating layer 50 before being viewed by the driver
`240. Since the rays 16a, 17a and 25a are directed away
`from the driver, the ray 15a is the only light viewed by
`the driver. It should be noted that the light in the ray
`15:: has made two passes through the attenuating elec
`trochromic layer 50. In operation, when the switch 18a
`is positioned to contact the contact 19a to connect the
`battery 21a to the terminals 8a and 9a, as schematically
`illustrated in FIG. 1a, the mirror darkens. When the
`switch 18a is positioned to contact the contact 22a to
`open circuit the mirror M-a, the mirror clears. When
`the mirror M-a is darkened and the switch 18a is posi
`tioned to contact the contact 200 thereby shorting the
`mirror, the mirror clears. Clearing and darkening begin
`almost immediately when the drive signal to the mirror
`element is changed. This mirror structure has a response
`
`DETAILED DESCRIPTION
`In general, in automatic rearview mirror systems
`embodying the present invention, both the inside and
`the outside rearview mirrors are comprised of a thin
`chemical layer sandwiched between two glass elements.
`As the chemical layer is electrically energized, it dark
`ens and begins to absorb light. The higher the voltage,
`the darker the mirror becomes. When the electrical
`voltage is removed, the mirror returns to its clear state.
`Automatic rearview mirror systems embodying the
`present invention also incorporate light sensing elec‘
`tronic circuitry which is effective to switch the mirrors
`to the nighttime mode when glare is detected. How
`ever, there is no glass movement, and the change is
`more subtle than the changes in conven