GB2190516A - Day/night mirror - Google Patents

Abstract

A day/night rearview mirror comprises an optical medium which is electrically driven between transmissive and opaque states. The mirror comprises a housing containing a circuit board overlaid by a mirrored surface. The mirrored surface is in turn overlaid by an optical transmission plate containing the optical medium. Electrical conductivity from the circuit board to the transmission plate is provided by helical coiled spring conductors which are supported in sleeves integrally formed with a retaining frame for the mirrored reflecting surface of the mirror. The circuit board contains a circuit for controlling the optical transmission plate and controls which are accessible to the user to adjust operational characteristics of the mirror assembly, and a pair of sensors which sense ambient lighting and incident light from the field of view, respectively.The sensors are coupled in via electronic input circuits (104, 106) to a logic gate (108), which controls the optical transmission plate. The transmission plate is forced to an opaque condition only when both a night-time ambient condition is sensed and there are also bright lights from the field of view.The circuits impose certain timing requirements on changes in sensed conditions so that the mirror does not change state in response to momentary departures from generally prevailing conditions. <IMAGE>

Description

SPECIFICATION Day/night mirror Backgroundandsummary the invention The present invention relates to a day/night rear-view mirror. More specifically it relates to a day/night mirror in which an optical medium is electrically driven between transmissive and opaque states to impart the day/night characteristic to the mirror.

Day/night rearview mirrors are often used in automotive vehicles, particularlyforthe benefit of the driver so that at night heorshe is not blinded by bright headlightsfrom a trailing vehicle.

Known types of day/night rearview mirrors comprise mechanical operators for selectively positioning the mirrored surface depending upon prevailing conditions. Most of these are manually set bythe driverto either one position for daytime use or another position for night use. For example, one way is byflipping a lever. It is also known to perform the repositioning automatically, for example by an electromechanical device.

Another class of day/night rearview mirrors comprises an optical transmission plate disposed in front of the mirrored reflecting surface. The optical transmission plate comprises a medium whose optical properties are controlled bythe application of voltageto the medium. One particulartype oftransmission plate com- prises afluid medium disposed as a thin film between glass plates. When the medium is in its transmissive or non-opaque state, it does not attenuate light passing through itto any appreciable extent. This is the state which should be present for daytime operation so that maximum brightness ofthe reflected daylight scene is presented to the observer.

When the medium is operated to a less transmissive, or opaque state, it significantly attenuates light passing through it. Therefore, the brightness ofthe scene which is reflected to the observer is considerably less than for daytime operation; however, this nighttime mode of operation is to protect the observerfrom being blinded by headlights from a trailing vehicle.

Different types of media can be used, dichroics and nematics being examples of known fluid media. An individual medium has its own particular properties correlating the degree of opaqueness with the magnitude of applied voltage. For some media, this is a direct characteristic while for others it is an inverse char acteristic. In otherwords in a direct characteristic, the medium has full lighttransmission atzero inputvol- tage, and the opaqueness increases with increasing voltage up to a maximum opaqueness at and above a particular voltage. An inverse characteristic is just the opposite.

Mirrors embodying an optical transmission plate containing a medium which is electrically controlled to control brightness are desirable because mechanical actuators and mechanisms are not employed. Mechanical and electromechanical types of actuators and mechanisms have been deemed unacceptableto the orig- inal equipment automotive industry for various reasons, and one significant reason is that they have been unableto meetthe rigorous demands which automobile manufacturers requirefor quality functional prod- ucts.

The general idea of using an electrically controlled optical transmission plate in association with a rearview mirror is known.

The following patents are known. U.S. 3,280,701; 3,337,286; 4,299,444; 4,201,451; 3,862,798; 4,200,361; U.K. 2,029,343; and Fed. Rep. of Germany 2,808,260.

It is recognized in certain of these patents that a photocell sensing light from the rear can be used to automatically control the operation of the day/night mirror. Certain patents also show ambient sensors which attempt to distinguish between day and night conditions.

The present invention, in one respect, relates to a new and improved day/night mirror of the type in which the day/night operation is controlled by control of the voltage applied to a medium whose optical properties are related to voltage.

In orderto achieve acceptable modes of operation in a day/night mirror, it is important to adequately distinguish true day from true night conditions so that when daytime prevails the mirror remains in thefull brightness condition, yet at nighttime itwill be opaquewhen headlights from a trailing vehicle are incident upon it.

The present invention includes a new and unique control which comprises one photodetectorforsensing light incident upon the mirror from the rear, i.e. headlights from the rear, and a second photodetectorwhich takes into account ambient conditions, the circuit being organized and arranged in a new and unique manner to achieve anew and unique form of control for this type of rearview mirror.

Afurther aspect of the present invention relates to a new and unique organization of various component parts intheirassembled relationship in the mirror assembly. This is ofparticularadvantageforseveral reasons, one of which is that a mirror can be fabricated with convenient, cost-effective fabrication procedures while also resulting in afinal construction which is functional,yet sturdy and durable and in which certain operational characteristics can be easily set by the observer.

One specific aspect of the invention involves the organization and arrangement of certain parts for making electrical connection between the transmission plate and a circuit board containing the control circuit.

Afurther specific aspect of the invention comprises the arrangement of user-operable controls ofthe mirrorfor convenient accessibility bythe observer.

While the invention is illustrated as connected to an external power supply, it can also be adapted to a self-contained battery operation and wherein a dead battery can be readily replaced.

The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.

Briefdescription ofthe drawings Figure 1 is an exploded perspective view of a mirror assembly embodying principles ofthe present invention.

Figure2 is a view of a portion of the assembled mirror taken generally in the direction of arrows 2-2 in Figure 1 but with certain portions broken away.

Figure 3 is a fragmentary cross sectional view taken substantially in the direction of arrows 3-3 in Figure 2 illustrating details of the assembled relationship.

Figure4is an enlarged view in circle 4 of Figure 3, with certain portions being broken away.

Figure5is an electrical schematic diagram illustrating a presently preferred embodiment of control circuit according to the present invention.

Figures 6and 7are graph plots useful in explaining principles of operation of the control circuit.

Description ofthepreferred embodiment Figure 1 illustrates in an exploded form a mirror assembly 10 according to principles of the present invention. The mirror assembly comprises a housing 12, a circuit board assembly 14, a reflecting mirror 16, a mirror retainer frame 18, an optical transmission plate 20 and a bezel 22. The components 12 through 20 assemble into housing 12 and are retained by means of bezel 22 being assembled onto and in an interlocking relationship with housing 12. Details of how this is accomplished will be subsequently explained and seen with referenceto the various drawing figures.

The electronics ofthe circuit shown in Figure are contained on circuit board assembly 14. The circuit board comprises the various circuit components disposed against its near face. The circuit connections of the various components are on the reverse, or far, face where they cannot be seen in Figure 1. Circuit board assembly 14 has a generally rectangular shape fitting into the interior of housing 12.

Housing 12 comprises an end wall 24 bounded peripherally by a side wall 26. Circuit board assembly 14is accurately located within housing 12 on end wall 24. For this purpose end wall 24 comprises a plurality of integral posts 28 which project away from it. Figures 2 and 3 illustrate such posts 28. Certain posts 28 include locatortips 30 on their distal ends which projectthrough corresponding holes in the circuit board. The circuit board is thereby accurately located in assembly. The circuit board may be held against the posts bythe overlying parts 16, 18,20, and 22 when the latter are assembled onto the housing, or attachment means can be provided. For example, as shown,the free ends of the tips can be deformed into heads 32 to secure the circuit board in place.

The housing is preferably constructed from a suitable plastic material with tips 30 being shaped to provide for corresponding holes in the printed circuit board to pass onto them so that the board bears againstthe ends ofthe posts. The free ends of any tips which project beyond the near face of the circuit board can be deformed by any suitable means to form the heads 32 which retain the circuit board on the housing in a secure manner. Of course other attachment means may be used if desired.

Asset of suitable apertures34 is provided centrally in end wall 24to provide for the attachment of a mount (notshown) for mounting the mirror assembly for example to the windshield in the case of interior usage. A further aperture 36 is also provided to receive a connector plug 38 on thefarface of circuit board 14so that a mating plug on awiring assembly (not shown) which conducts electrical power to the mirror assembly can be connected. The housing also comprises an integral structural framework 39 for rigidity.

The bottom portion ofthe housing's peripheral wall 26 comprises an elongated slot 40 to one side, and two circular holes 42 and 44 on the other. Two electrical control devices 46 and 48 are provided on the near face of circuit board assembly 14 adjacent the bottom edge thereof. These devices have respective operators 50 and 52which,whenthe circuit board is assembled to the housing, pass through slot 40 and hole 42 respectively.

A photodetector 54 is also provided on the circuit board assembly and is disposed with its sensing zone directly above hole 44. The relative dimensions of circuit board assembly 14 in relation to housing 12 are such thatthe circuit board can be passed through the opening bounded by wall 26 and positioned to dispose operators 50 and 52 passing downwardlythrough slot 40 and hole 42 respectively.

From this much of the description it can therefore be appreciated that the circuit board assembly is securely assembled and accurately located with respect to housing 12.

The circuit board is further provided with a pair ofterminals 56 and 58 respectively adjacent the midpoints ofthe side edges thereof. Terminals 56 and 58 provide the control voltage for transmission plate 20 in a mannerto be described in more detail hereinafter. Terminals 56,58 may take any suitable form, for example U-shaped clips fitted onto the side edges of the circuit board, to establish connection with particular circuits on the far face of the circuit board. Contact to the transmission plate can be made via the near face as seen in Figure 1.

Mirror 16 is shaped to fit over and essentially conceal circuit board assembly 14. The mirror's periphery is also shaped to fit snugly within a groove 59 which extends around the perimeter of retainer frame 18 and which faces end wall 24of housing 12. Retainer frame 18 also comprises a pair of small integral sleeves 60 substantially as the midpoint of each of its two shorter sides. These sleeves 60 extend toward circuit board assembly 14 and form respective holders for respective spring connectors 62 which serve to make electrical connection between terminals 56,58 respectively and terminals 64,66 respectively on transmission plate 20.

Transmission plate 20 fits over and againstthe nearface of retainerframe 18. Bezel 22, when assembledto housing 12, serves two hold the transmission plate 20, retainerframe 18, and mirror 16 in assembly relationship on housing 12. In the assembled mirror, connectors 62, which are in the form of helical coiled springs, are disposed within sleeves 60 with one end of each connector bearing against the corresponding terminal 56,58 of circuit board assembly 14 and the opposite end against the corresponding terminal 64,66 oftransmission plate 20. Figures 3 and 4 show aetails.

It can be seen in Figure 2thata further posts 69 extend from the end wall ofthe housing, and it is against these further posts that mirror 16 abuts in the assembled mirror. Thus, in effect, bezel 22 serves to sandwich transmission plate 22, retainer 18, and mirror 16 in a secure manneragainstthe housing end wall.

The length of each sleeve 60 is made less than the length of its connector 62, and each connector 62 is made of such a length that in the assembled mirror, they are compressed axially between the terminals on the transmission plate and those on the circuit board assembly such that a satisfactory electrical connection is established between the circuit board and the transmission plate. Sleeves 60 serveto hold and correctly locate the spring contacts 62. The construction is advantageous not only functionally but also from a manufacturing standpoint. All that need be done is to place the springs in the sleeves during assembly, and to assemblethe components together in the manner of sandwiching as described above.

It can be seen in Figure 2 that bezel 22 comprises a lip 70 around its inner peripherywhich bears againstthe periphery of transmission plate 20. The outer periphery of the bezel comprises a lip 72 which locks with a catch 74 extending around the outside of the free edge of housing side wall 26 when the bezel is assembled to the housing. With this arrangement no separate attaching parts are required and the bezel serves to retain the components within housing 26 in a secure and what is intended to be a permanent manner. Bezel 22 and retainerframe 18, like housing 12, can be molded plastic parts.

Transmission plate 20 is illustrated as comprising a pair of glass plates 76,78 respectively with an optical medium 80 captured between them as a very thin film. Conductors deposited as extremely thin films on the confronting surface portions of the two glass plates are selectively energized from circuit board via the two connectors 62 to control the optical character of optical medium 80 and thereby endow the mirror assembly with day/night capability. As can be seen in Figures 1 and 3, terminal 64 fits onto the edge of the near glass plate 78, and is in electrical contact with the conductive film on that plate. Terminal 64 is shown as a U-shaped clip.The side edges of the two plates are not congruent so that in the case of the left-hand side as viewed in Figure 1, plate 76 is clear of terminal 64, and in the case of the right-hand side, plate 78 allows terminal 66, a U-shaped clip also, to fit onto the edge of plate 76 to make contact with the conductive film on that plate. Thus, the two spring connectors make contact between terminals 56 and 64 on the left and between terminals 58 and 66 on the right.

Thefaruppercorneroftransmission plate 20 is left clear of medium 80 so that the two glass plates arefully transparent in this region 82. In the assembled mirror, region 82 registers with a non-silvered, transparent region 68 of mirror 16 and a second photodetector 84 on printed circuit board assembly 14. This second photodetector is so arranged that its sensing element senses light incident upon the mirrorfrom the rear, i.e., it senses light passing through regions 82 and 68.

The sides of the sleeves 60 comprise longitudinal slots extending partially along their lengths. Both sleeves and slots may have a slight ta per (i.e. draft) which is imparted in the manufacture of part 18 which is preferably an injection molded plastic.

The fabrication of transmission plate 20 may be accomplished with known fabrication procedures. The films of conductors on the two plates are ultra-thinfilms, such as gold, which can be deposited to provide suitable conductivity for purposes of controlling the optical medium but without any significant attenuation of light transmission.

With this much of a description having been given, it is now appropriate to consider details of the electronic control circuit contained on printed circuit board assembly 14.

Figures schematically portrays a presently preferred embodiment of control circuitforthe transmission plate. Like components in the several drawing figures are identified by like reference numerals and therefore the electrical schematic diagram illustrates the devices 46 and 48 and their respective operators 50 and 52, along with the two photodetectors 54 and 84.

The control circuit is designated by the general reference numeral 100 and powerforthe circuit is delivered via connector plug 38 which connects to a mating plug (not shown) ofthe vehicle's wiring harness two supply vehicle battery power (i.e. +12 volts relative to ground)to circuit board assembly 14.

Because various electronic circuit components require a well-regulated DC supply, a simple regulator circuit 102 receives the battery voltage and develops a regulated supply voltage +E volts relative to ground.

This is supplied to the various circuits as indicated in the schematic.

Photodetector 54 is disposed within the mirror assembly with its sensing zone facing downwardly to sense light passing through hole 44. As such it senses the general prevailing ambient light level and hence for convenience will hereinafter sometimes be referred to as the ambient light sensor. It is to be observed that this sensor does not face toward the field of view and therefore is not directly subjectto incident lightfrom the rear. It is however sensitive to the prevailing ambient light level which in daytime will be a general daytime brightness and at night a general darkness but with the expectation that at night the sensor can be subjectto reflected or direct artificial light sources. These sources could be the vehicle's own interior lights, ortheycould be external lights such as street lights, parking lot lights, lights of othervehicles.

Sensor 54 is intended to face directly toward the vehicle's dashboard, which will typically be a low reflectivity, or light scattering, surface. However depending upon the exact positioning of the sensor and the size of hole 44 and the nature of the specific vehicle construction, the sensor may have a certain sensitivityto otherthan the light from the dashboard.

Photodetector 84 was previously described as facing toward the rearfield of view so that its sensing zone is responsive to incident light from the rear. For convenience photodetector 84will sometimes hereinafter be referred to as mirror sensor 84.

Ambient sensor 54 is connected in one input circuit 104while mirror sensor 84 is connected in another input circuit 106. The two input circuits 104, 106 have respective outputs which are supplied as inputsto respective input terminals of a logic gate 108. Briefly the output of logic gate 108 controls transmission plate 20, and the illustrated logic gate 108 is an OR logic gate constructed from diodes. The general operational logic is such that the mirror is forced to its bright state when either daytime is sensed by ambient sensor54, or when there are no bright lights from the rear sensed by mirror sensor 84. Stated differently, the mirror is forced to its dark state only if nighttime and bright lights from the rear are both sensed.

For convenience of description circuit 104 may be considered to comprise a first stage 110 coupled via a timing circuit 1 12to a second stage 114. The outputofthesecond stage 1 14forms an inputto acorresponding input of logic gate 108.

Ambient sensor 54 is operatively coupled in the input circuit of stage 110. Stage 110 comprises an oper- ational amplifier 116 which comprises an inverting inputterminal 11 6a, a non-inverting input terminal 11 6b, and an outputterminal 116c.

Ambient sensor 54 connects in series with a resistor 118 and this series combination is connected across the +E supply. The junction of ambient sensor 54 and resistor 118 is connected to the inverting input terminal 116a of amplifier 116.

A pair of resistors 120 and 122 connect in series across the +E power supply and their junction is connected to the non-inverting input terminal 11 6b of amplifier 116. A resistor 124 is connected between outputterminal ll6candtheinputterminal 116b.

The signal which is provided to the non-inverting input 11 6b defines a threshold. The signal supplied to the inverting input 11 6a is measured againstthethreshold.

The ambient light level sensed by sensor 54causes a corresponding signal to be supplied to input 11 6a. As the ambient light level varies so does the signal to input 11 6a. The arrangement is such in the disclosed preferred embodiment that operational amplifier 116 operates in what may be generally designated as a switching mode. This in effect means thatthe output signal which appears at terminal 11 6c may assume eithera"high"ora"low"state.

Because of the provision of resistor 124, the threshold level at input 11 6b becomes a function of the state of the output signal at 116caws coupled by resistor 124 back to the common junction of the three resistors 120, 122,124.

In orderto aid in explaining the operation of stage 110 reference is also made to Figure 6 which shows a graph plot 126 illustrative of the operation. Graph plot 126 comprises four segments identified by the refer- encenumerals 128,130, 132, and 134.

If it is assumed that stage 110 is in a state indicative of nighttime, segment 128 applies. So long asthe anbient light sensor level indicates a light intensity below the threshold designated TAl, the stage 110 does not change state. However, ifthethreshold TAl is exceeded, then the state ofthe stage changes to establish an output indicative of daytime. The transition, which is in the form of a step, may be considered as occurring along segment 130 so that the new state corresponding to daytime conditions is represented by segment 132.

When the output of the amplifier stage changes, the effect is fed back via resistor 124 to changethe threshold from TAl to TA2, a lowerthreshold level. Forthe stage to switch backto a state represented bythe segment 128,the level sensed by sensor 54 must fall below that corresponding to the new lowerthreshold TA2. The transition back to segment 128 will occur along the segment 134.

From consideration of Figure 6 it can thus be appreciated that the construction embodies a hysteresis characteristic in the operation of the stage. Importantly, the difference between the thresholds represented by segments 134 and 130 corresponds to a difference of to 1 in respective sensed intensities. This 2 to 1 ratio corresponds approximately to the minimum difference which can be sensed by the typical human eye. In other words, in orderforthe stage to revertto daytime from nighttime indication the ambient light level must change noticeably from that which caused the change to nighttime, and vice versa. Because of this attribute, the circuit responds only to changes in light intensity which would have an effect on the typical observer and it avoids response to changes which would not be perceptible to the average observer.

Based upon this description of operation of stage 110 it can be appreciated that the stage provides a step input to timing circuit 112 whenever there is a transition between day and night. It can be further appreciated that the direction of the step will be one way for a transition from night to day while it will be in the opposite direction for an opposite transition.

Circuit 112 comprises a resistor 138 and a capacitor 140 which forms a time delay circuit characterized by a particulartime constant. In response to a step input to circuit 112 from the output of circuit 110, the voltage at the junction of resistor 138 and capacitor 140 executes an exponential transient, and the direction ofthis transient will be one way for a night-to-day transition and opposite forthe oppositetransition.

The junction of resistor 138 and capacitor 140 is connected to an input to stage 114. Stage 114 comprises an operational am plifier 142 having inverting and non-inverting input terminals 142a, 142b respectively and an output terminal 142c. The output from timing circuit 112forms an input to the inverting input terminal 142a.

A pair of resistors 144, 146 are connected in series acrossthe +E supply and their junction is connected as an input to the non-inverting input terminal 142b. Afurther resistor 148 connects output 142cto input 1 42b.

Stage 114 may be considered to operate in a switching mode such that the output signal at output l42cwill be either high or low. The state is determined by the relationship of the signals to the two inputs 1 42a, 1 42b.

The signal supplied to input 142forms a threshold, and the level ofthis threshold depends upon the state of the output signal at 142c. Hence this stage may be considered to have a hysteresis characteristic similarto that illustrated in Figure 6, but the hysteresis characteristic of stage 114 is for a very different purpose.

Stage 114 operates to change state a certain pre-calculated time after a step input is supplied to timing circuit 112 regardless of the direction of the step. This may be understood by considering that when the step inputto circuit 112 is in one direction, the exponential transient will be in a corresponding direction, saya rising direction. For stage 114to always switch at the same pre-calculated time after a step regardless ofthe direction of the step, the transient is always allowed to execute one time constant (i.e. the product of resistor 138 and capacitor 140).Arising exponential transient will attain approximately 63% of its finial value in one time constant and a falling transientwill attain approximately 37% of its final value in onetime constant. The provision of resistor 148 in association with resistors 144 and 146 serves to establish these two respective levels, 63% in the case of a rising signal and 37% in the case offalling signal.

Timing circuit 112 serves two impose a delay in the switching of stage 1 14which otherwisewouldoccur essentially instantaneously in response to a step in the output of stage 110. The purpose of providing the delay in circuit 104 is to avoid a false response of the circuit to temporary conditions which may not be representative of the true longer term general ambient condition.For example, when the circuit has properly assumed a nighttime indicating state, temporary bursts of ambient light, such as might occurwhen passing beneath spaced apart street lights or by the lighting of a cigarette iighter, and which are of momentary duration butwhich may create intensities on the ambient sensor exceeding the prevailing threshold at input 11 6b are prevented from having an ultimate effect on the output of circuit 104.

In the case of circuit 1 12 it can be seen thatthistiming requirement is bi-directional; in other words delay is imposed not only for a day-to-nighttransition but also for a night-to-day one.

By imposing delay in the expectation that many such temporary conditions will last less than onetime constant of the timing circuit even though they exceed the prevailing threshold, many spurious changes are avoided. It is to be recognized that an exponential transient which is initiated in response to a change in the output of stage 110 will decay exponentially back to its initial value once the output of stage 110 reverts back to its previous state. However, where a change past the prevailing threshold lasts for longer than onetiming circuit time constant, that is deemed representative oftrue change, or an apparently true change.An example of an apparentlytrue changeto daytime would be the nighttime presence of the automobile in awell-lighted parking lotforan amountoftime longerthan the onetime constant, and in that environment it maybe desirable a daytime indication to be given so that the mirror will assume its bright state.

The selection of parameters may be such that stage 110 will change state at the appropriate sensed levels without the need for any separate calibration; however if desired, a calibration feature could be included. For example this might involve an adjustable resistance in association with the input circuit containing the ambient sensor.

Circuit 106 is in many respects very similar to circuit 104 and therefore certain features will be described in detail since their organization and arrangement and mode of operation will be recognized from the preceeding detailed description of circuit 104.

Circuit 106 comprises a first stage 150, a timing circuit 152 and a second stage 154 with the output of stage 150 being operatively coupled with the input of stage 154through timing circuit 152.

Stage 150 comprises an operational amplifier 156 having inverting and non-inverting and inputterminals 156a, 156b respectively and an output terminal 156c. Athreshold signal is supplied to the non-inverting input 156a. The level of the threshold signal is established at the common junction of two resistors 158 and 160 connected serially across the power supply as modified by the further resistor 162 in accordance with the condition ofthe output signal of stage 150. Hence this stage isvery similarto stage 110, and its operation is characterized by a similar graph plot 164 in Figure 7. Depending upon the state of stage 150 the threshold is either at a level TM2 or at a level TMl.

Mirror sensor 84 is operatively coupled in an input circuit to the inverting input terminal 156a. This circuit comprises a resistor 165 and a selectable portion of a potentiometer 166 as selected by a wiper 168. The potentiometer 166 is the device 46 while the wiper 168 is underthe control of operator48.

Figure 7 illustrates the operational characteristic of stage 150for a given setting of potentiometerwiper 168. The characteristic is similarto that of the ambient sensor's circuit in that the two threshold levels TMl and TM2 differ by the intensity difference of approximately a 2 to 1 ratio. The adjustment provided by the wiper 168 of potentiometer 166 is effective to shiftthe characteristic curve of Figure 7 horizontally. In otherwords although the actual threshold voltages at which the stage switches do not change, either a greater or lower intensity of light is required for the input to the non-inverting input terminal to pass through the prevailing threshold.

Thus from the description and consideration of Figure 7 it can be appreciated that when the mirror sensor is sensing the presence of bright lights from the rear, stage 150 provides a brightness indication and when the mirrorsensorfailsto detect bright lights stage 150 provides a dim indication.

Timing circuit 152 is similartotiming circuit 112 in that it comprises atime delay circuit comprising a resistor 170 and a capacitor 172, but it also includes a diode 174 poled as shown. The purpose of diode 174 is to renderthe operation of the circuit uni-directional; in other words a timing requirement is imposed onlyon a rising transientwhen the step inputto the timing circuit is from lowto high, but not on afalling step. Inthe illustrated circuit a rising transient occurs in response to the disappearance of bright lights from the rear, and therefore an already darkened mirror will not immediately brighten.This is desirable because the disappearance of bright incident light from the rear may be only a momentary phenomenon, for example when the automobile has just passed over a hill or around a curve and a trailing vehicle with its headlights on has not yet negotiated either.

However when the mirror sensor is indicating a dim field of view, and then suddenly senses a bright one, the change in the output of stage 150 is immediate. The purpose is to provide as instantaneous a response as possible to the sudden appearance of bright lights from the rear.

The optical transmission plate may inherently possess a certain delay in switching from one state to the other. While this may be desirable in the case where the transition is from a bright to a dim field of view, it may not be deemed long enough and therefore the uni-directionai character of the timing circuit can augment an inherent delay in responseto the optical transmission plateforthattype oftransition. In the case of the opposite transition, the circuit insures that essentially the only delay in darkening the mirrorwill be that which is inherent in the characteristics of the optical medium itself.

Stage 154 has a configuration exactly identical to that of stage 114. It comprises an operational amplifier 176 and three resistors 178, 180, 182 connected as illustrated. These resistors establish the threshold for a rising exponential transient, and although the threshold is diminished for a falling transient, the diminished threshold is of no significant consequence because diode 174 essentially shorts out resistor 172 so that the fall is essentially instantaneous.

Diode logic gate 108 comprises plural diodes having cathodes connected in common. The anode of one diode connects to the output of circuit 104 and the anode of another diode 186 connects to the output of circuit 106. When the output of either circuit 104 or 106 is high,the OR logic gate 108 provides a corresponding high output signal at the common cathodes. This output signal is used to control the optical transmission plate when device 48, which is a selector switch, is in what is called the automatic position.This position is indicated in Figures where the operator 52 has setthe switch to establish continuity from the output of the OR logic gate 108 to an oscillator circuit 190which can develop an oscillating voltagefor delivery totransmis- sion plate 20.

When the output of OR gate 108 is high and switch 48 is in the automatic position, oscillator 190 is en energized to cause full voltage to be applied across the transmission plate. With the medium being a material which has an inverse characteristic, the application of full voltage causes the medium to be transparent so thatthe mirror is bright. When the voltage is removed, the medium goes opaque so that the mirror darkens.

Only underthe condition where outputs from both circuits 104 and 106 are low will the oscillator circuit not be energized, and under this condition the optical transmission plate will be opaque. This corresponds to circuit 104 indicating the presence of bright headlights from the rear.

Under other conditions the mirror is allowed to assume full brightness. These other conditions are: 1) when circuit 104 indicates daytime regardless of what circuit 106 indicates; and 2) when circuit 104 indicates nighttime and circuit 106 senses the absence of bright lights from the rear. Underthese conditions itis acceptable and indeed even desirable forthe mirror to be at full brightness.

It is possible to override the automatic control and provide either a continuously darkened or a continuously bright mirror by operation of switch 48 to appropriate positions. These are designated in thedrawins figure as "night" and "day". In the night position the oscillator is not energized while in the day position it is.

The illustrated circuit 100 also includes a third input circuit 200 and a third diode 202 in the OR logic gate.

The third input circuit connects to the vehicle's back-up lamp circuit. The backup circuit is energized when the vehicle's transmission is placed in reverse, and thus causes a high signal to be appliedto the anode ofthe third diode 202 of gate 108. With switch 48 in automatic this causes oscillator 190to be energized regardless ofthe conditions of the othertwo input circuits 104,106 to the diode logic gate. In other words when the vehicle is placed in reverse gear, the mirror is caused to assume full brightness even if the ambient sensor and the mirror sensor were otherwise calling for the mirror to be darkened. It will be appreciated thatthe back-up lamp input circuit introduces no delay so that the only delay which occurs when the transmission is put in reversewill be that which is inherent in the optical transmission plate's characteristic. Rather than the backup lamp circuit being directly connected to the input of the diode gate, appropriate isolating provisions are made to prevent transients which may be present in the vehicle wiring from intruding into the mirror control circuit and likewise provision is made for preventing feedbacks from the mirror control circuit both to the back-up lamp circuit and also to the vehicle battery.

Oscillator 190 for driving optical transmission plate 20 is shown to comprise a conventional push-pull configuration and with power being coupled through a transformer 204 whose secondary is connected ac ross the transmission plate.

In the case of an optical material which has a direct characteristic and not an inverse characteristic, appropriate provision can be made to ensure correct operation, for example by placing an inverter in the line from switch 48 to oscillator 190. It is also to be recognized that different configurationsforthe logic and for the coupling of the logicwith the optical transmission plate can be employed otherthan that shown.

Based upon the foregoing description the readerwill appreciatethat a new and unique arrangementfora day/night mirror has been disclosed. In any given implementation of principles of the invention, particular constructional differences may exist from the disclosed embodiment. The illustrated embodiment is one which is well-suited to mass production application for automotive rearview mirror usage. It is cost-effective and can meetthe demands of automobile manufacturers. Thefouroperational amplifiers are implemented in a single integrated circuit chip. The mirror can be fabricated with conventional procedures and iswell-suited to automated assembly. Power levels required for operation of the optical medium are low.While the illustra ted embodiment showsthe mirrorto be energized fromthevehicle battery, it is possibleto implementthe design such that a separate replaceable battery is used. Such a battery can be removably inserted by a removable cover provided in the mirror housing, and this would render the mirror suitable for aftermarket usage where awiring harness may not be convenient to desired location forthe mirror.

The following identifies the components ofthe circu it with reference to specific values and identifications.

This list is considered to be representative of the preferred embodiment, and it will be appreciated that principles of the invention are applicable to other embodiments. For example, the mirrored surface could be incorporated into the transmission plate.

Resistors 120,122,144, 146,158,160,178,180 100K Resistors 124,162 390K Resistors 138,152 1M Potentiometer 166 100K Resistor 118 15K Resistor 165 1K Resistors 148,182 150K Sensors 54, 84 Vactec VT82L (LDR's) Capacitors 140,172 1 off Diodes of OR gate 108 and Diode 174 1 N4148 OpAmps 116,142,156,176 LM324 Transformer 204 1K:20K 100mW Oscillator 190 Diodes 1 N4148 Oscillator 190 Capacitor 0.liif Oscillator 190 Resistors 10K Oscillator 190 Transistors 2N4401 Regulator 102 Diodes 1N4004 Regulator102Zener 1N4743A

Claims (19)

1. In a day/night rearview mirror assembly having a mirrored surface in association with a voltagecontrolled optical medium wherein the medium controls the brightness of the field of view reflected bythe mirrored surface in accordance with voltage applied to the medium and a control circuit for applying control voltage to the medium including a sensor for sensing incident light from the field of view to distinguish between afield of view which is bright and one which is dim and a second sensorforsensing general ambient light in the vicinity ofthe mirror assembly to distinguish between daytime conditions and nighttime conditions, the improvement which comprises said control circuit comprising means for operating said mirror assembly to two different states of brightness, one higher and the other lower, comprising a logic gate having an output and plural inputs, means operatively coupling the logic gate output with the optical medium such that the logic gate output causes control voltage to be selectively applied to said medium to thereby selectively operate the mirror assembly to the two different states of brightness in accordance with a control provided by said logic gate, plural input circuits each ofwhich has an output connected to a corresponding one of the inputs of said logic gate, one of said input circuits containing thefirst-mentioned sensorand another of said input circuits containing the second sensor, each input circuit comprising its own timing means for imposing a certain predetermined minimum time requirement on certain change sensed bythe corresponding sensor before the effect of such change is allowed to occur atthe output of thecor- responding input circuit, the timing means of said second inputcircuitimposing a minimum time require ment on both a change in sensed ambient light indicative of transition from day to night as well as a change in sensed ambient light indicative oftransition from night to day, and the timing means of said first input circuit imposing a minimum time requirement only on a change in sensed lightfrom the field of view indicative of a transition from brightto dim and not on a change indicative of a transition from dim to bright.

2. The improvement set forth in claim 1 in which said one and said another input circuits each comprises a corresponding operational amplifier stage with the corresponding sensor being operatively coupled with an input of the corresponding amplifier stage, and in which change in each of the respective sensors, between bright and dim forthefirst sensor and between night and dayforthe second sensor, is effective to changethe state ofthe corresponding operational amplifier, each operational amplifier stage including means providing a threshold signal against which a corresponding signal developed from the corresponding sensor is measured and means for selectively establishing each threshold signal in accordance with the condition of the corresponding stage's output.

3. The improvement setforth in claim 2 in which each threshold is selectively established at threshold ievels corresponding to a difference in sensed light intensity of substantially a 2 to 1 ratio.

4. The improvement setforth in claim 2 in which.each input circuit includes a second operational amplifier stage, and the corresponding timing means is connected between the first and second operational amplifier stages in each input circuit, each second amplifier stage having means providing a threshold at which it responds to change passed from the corresponding first amplifier stage by the corresponding timing means including means for selectively establishing the corresponding threshold in accordance with the condition of the output signal of the corresponding second operational amplifier stage.

5. The improvement setforth in claim 4in which thetiming means in said second input circuitcomprises means for imposing a pre-calculated delay in passing change in the first stage's output to the second stage's input regardless ofwhetherthe change is indicative of transition from day to night or of transition from night today.

6. The improvementsetforth in claim 5 in which each timing means comprises an RCtime delay circuit and in which the timing means of said first input circuit includes a diode arranged cooperatively with the RC circuit to prevent imposition of a minimum time requirement on a change indicative of a transition from brig ht to dim.

7. The improvement set forth in claim 6 in which the means providing a threshold for each second amplifier stage comprises means for establishing the threshold at a level which corresponds to the RC time con stantofthecorrespondingtiming means.

8. The improvementsetforth in claim 1 in which said logic gate comprises an OR logic gatearrangedto selectively control the mirror assembly to the two different states of brightness such that the low stateof brightness occurs only when said first input circuit is indicating a bright condition and when said second input circuit indicates a nighttime condition.

9. In a day/night rearview mirror assembly having a mirrored surface in association with a voltagecontrolled optical medium wherein the medium controls the brightness of the field of view reflected by the mirrored surface in accordance with voltage applied to the medium and a control circuit for applying control voltagetothe medium including a sensorfor sensing incident lightfrom the field of viewto distinguish between a field of view which is bright and one which is dim and a second sensor for sensing general ambient light in the vicinity of the mirror assembly to distinguish between daytime and nighttime conditions, the improvement which comprises means for operating said mirror assembly to two different states of brightness, one higher and the other lower, comprising a logic gate having an output and plural inputs, means operatively coupling the logic gate output with the optical medium such that the logic gate output causes control voltage to be selectively applied to said medium to thereby selectively operate the mirror assembly to the two different stages of brightness in accordance with the condition of inputs to the logic gate, each sensor being operatively coupled in an input circuitto a corresponding input of the logic gate, each input circuit comprising timing means imposing certain time requirements on certain changes sensed bythe sensors, said logic gate providing control such that the optical medium assumes an opaque condition to causethe mirror assembly to operate at the higher state of brightness if either the first input circuit is indicating the absence of bright Iightfrom the field of view or the second circuit is indicating a daytime condition.

10. The improvement setforth in claim 9 in which each input circuit comprises a first operational ampli fier stage and a second operational amplifier stage, each operational amplifier stage comprises its own operational amplifier and said four operational amplifiers being contained in a quad op amp integrated circuit chip.

11. In a rearview mirror assembly containing a mirrored reflecting surface overlaid by an optical medium whose opaqueness is controlled by the application of a control voltage to the medium and wherein the mirrored reflecting surface overlies an assembly from which the control voltage is delivered to the optical medium, the improvement for establishing electrical circuit continuity between the assembly and the optical medium which comprises conductors having a yieldably resilient axially compressible characteristics.

12. The improvement set forth in claim 11 in which said conductors comprise helical coil springs.

13. The improvement set forth in claim 12 in which said helical springs are disposed within sleeves in a retainerframeforthe mirrored reflecting surface.

14. The improvement set forth in claim 13 in which there are two such spring conductors each disposed within a sleeve on opposite sides of the retainerframe.

15. The improvement setforth in claim 11 in which said assembly is a circuit board containing control circuitryforthe optical medium.

16. The improvement set forth in claim 15 in which the optical medium is contained on a transmission plate assembly composed of a pair of glass plates and wherein one conductor has electrical continuity with a conductive film on one plate and the other conductor has electrical continuity with a conductive film on the other plate.

17. The improvement setforth in claim 16 in which solid metal surfaces are provided on the circuit board and the glass plates and the conductor bear forcefully against the solid metal surfaces.

18. The improvement set forth in claim 17 in which said solid metal surfaces are in the form of clips fitted onto edges of the circuit board and of the transmission plate, and said conductors are helical coil springs.

19. A rear view mirror assembly constructed and arranged to operate substantially as hereinbeforedes- cribed with reference to and as illustrated in the accompanying drawings.