US2917664A - Automatic headlight dimmer with antioscillation circuit - Google Patents

Description

Dec. 15, 1959 J. RABINOW 2,917,664

AUTOMATIC HEADLIGHT 01mm wrm ANTI-OSCILLATION cmcurr Filed on. 14, 195::

Sensitivity INVENTOR JACOB RA B/NOW MZZ ATTORNEY United States Patent AUTOMATIC HEADLIGHT DIMMER WITH ANTI- OSCILLATION CIRCUIT Jacob Rabinow, Takoma Park, Md.

Application October 14, 1953, Serial No. 385,942

14 Claims. (Cl. 315-'83) This invention relates to-an improved automa'tic'headlight dimmer of the type utilizing a photosensitive element for detection of the: light conditions in advance of a vehicle and the dimming of Vehicle headlights in ac cordance with such detection.-

A primary object of the inventionis the'provision of means for minimizing the annoyance of headlight oscillationcaused by light from'the' controlled vehicle being reflected back by roadside objects. This condition arises when the automatic dimmer on a vehicle is energized by reflected lights from the vehicle headlights striking agoo'dreflecting surface such as a bright road sign, direction'al warning reflector, etc. The reflected light causes dimming of the headlights, and very frequently the dimmed lights no longer strike the reflecting" surface with suflicient intensity to cause the automatic dimmer to remain actuated, and, as a result, the dimmer again raises the headlights. Therefore the bright lights go' mechanical scanner, and the present invention provides a compact mechanical drumfor this purpose which requires a minimum of space and is characterized by rugg'edness, simplicity and inexpensive c'onstructionl Still another object is the provision" of a compact automatic dimmer control unit of exceedingly. compact design and inexpensive construction, which isre'ad'ily' accessible for repair or tube replacement;

The specific nature of the invention as well'a's other objects and advantages will clearly; appear from a description of a preferred e'r'nbodiment'as shown in the ac-' companying drawing in which:

Fig. 1' is a circuit diagram of the invention;

Fig. 2 is a' sectional-view'taken on line 22of Fig. 3 of a c'ornpactas'sembly e'rnbodyingtlie invention but using a scanning drum instead of adisk; p

Fig. 3 is a sectional view"taken"online3 3"of'Fig. 2;

Fig. 4 is a similar sectional view of a modifiedconstruction wherein the 1on8 iS replaced" a reflector; and

Fig; 5 is a raph showing the change in sensitivity due to ordinary dilflriiilfg and fo reflective dimming. v

Referring to Fig. 1, the li htfroth the field'ofview to the left of lens 2, representinggeherally the same field as is" illuminated by the brightbeams of the headlights, passes through'the lens and is focussed in the plane'of' a spirally perforated Nip'kow' disk 4continua'lly drivenb'y a small motor 6 from a suitable supply source, which may be the standard automobile battery and generator system. AS ther'not'or 2 does no other work thallio 10' tifo the scanningdisk 4} it fiiay li'o" Small; Motors 2,917,664 Patented Dec. 15, 1959 no greater than an inch in their largest dimension are available for this purpose, and may be either the usual D.-C. motors or A.-C. motors of the type used to drive electric clocks, in which latter case the motor may be driven by the standard vibrating power supply used with automotive electronic equipment such as automobile radios, and which is also the type of power supply that would normally be used with the electronic circuit'shown in Fig. 1. Since the power supply is-conventional, and its design for any specific circuit is a matter within-the skill of any electronics circuit designer, it is not shown.

It will be seen that an image of the field of-view is formed on the surface of the scanning element 4, and'the' light from a portion of this image will be admitted through that perforation 8 which happens to be crossing the image at that point, as described in.my prior patent, No. 2,632,040. Light which passes through the perforation will, if it is of sufficient intensity, actuate the photw cell 10, producing an output signalon lead 11, which is amplified by amplifier 12 which will now be described.

The signal on lead 11' is fed to the grid of tube 13 which is operated as a cathode follower to produce an amplified power output at its cathode 13a. This is fedto apeak-to-pe'ak rectifier arrangement comprising diodes 17 and 14, and capacitors 19 and 15. The constants of the peak detector are so selected that the variations in light intensity of the normal background field of view when there is no headlight or other brightsource of illumination'present will not produce sufficient output at the grid'21 of amplifier tube 1.8 to deenergize the relay 20. The amplifier described has been found very satisfactory, but it will. be understood that any suitable amplifier' circuit may be used to provide a signal of suflicient intensity to the detector, and likewise, any suitable known signal detecting circuit may be used in place of that shown.

The light of the oncoming headlight is so much moreintense than the general background that when such a great amount of light passes through a scanning aperture of disc 4, a very high peaksignal results, of suflicient intensity to release relay 20'.

Release of the relay 20 moves both of its switches over from the position shown to the opposite position. Switch. 22 in' the position shown closes contact 24 to complete a circuit from battery 26, through footswitch 28 which is shown in the beam-up or Bright position through switch 22 and contact 24 to the bright circuit of the headlight. Uponrelea'se of relay 20 by a light in the field of. View, switch 22 engages contact 30' which disconnects the bright circuit and closes the dim circuit of the headlights, thus dimming them as required. At the same time, switch 32 of the relay changes from its Bright position to its Dim position. In the Bright position (shown in Fig. 1), switch 32 completed a circuit from potential divider 34through switch 32, through resistance 36 to ground This established a certain biasing potential, on the grid 21 of tube 18 which determined. the sensitivity of the system at a predetermined level. In the Dim position of switch 32, the circuit from potentiometer device 34 is opened, and the included partof 34 acts then only as a resistor between the grid'21- and the divider 40, so that the full potential from divider- 40 is now'impressed on the grid 21, increasing the sensi tivity of the system by a suflicient factor so that evenif the oncoming carimmediately dims its lights, the reduced intensity of its beam is compensated by the increasedsensitivity and the relay 20 remains released.

If the signal which initiated the above describedaction came not from another headlight, but was a reflection of the cars' own headlights, upon the occurrence of' dimming as described above, the reflection may greatly diminish'and the lights would, inmy prior system and" in other headlight systems, rapidly oscillate between the bright and dim positions, producing an objectionable blinking. I therefore provide a condenser 42 across re sistance 36. It will be noted that in the Dim position switch 32 has not only disconnected potential divider 3d from ground, but has also connected resistance 36 and condenser 42 through contact 44 and resistance 46 to the B-}- supply, thus putting the B-}- across condenser 42 (swltch 48 being open as shown). Now, when the relay circuit is reenergized and resumes the initial bright position as shown in Fig. l, the positive charge on the condenser opposes the potential drop which would otherwise occur through divider 34 and resistor 36, and until the condenser is discharged through resistor 36 and the grid 21 circuit, the relay remains energized and the beam remains Bright even though the photocell is being energized by a light. This continues until the condenser is sufliciently discharged so that normal operation is resumed. If the time constant of the R-C combination 36, 42 is made sufliciently great, a delay in the order of 1 /2 seconds can easily be provided, which I have found to be satisfactory for the purpose.

The operation accomplished by the above described circuit elements is as follows: When the lights are dimmed by a reflection, they go down promptly and as the reflected light is no longer seen by the photocell, relay 20 is reenergized promptly and the lights return quickly to bright. Now, for approximately 1 /2 seconds depending on the time constant of 36, 42 the lights stay bright even though the reflected light again causes a signal output to be produced by the amplifier, then there is another brief down flick and the same operation is repeated. Thus, even if the vehicle is not moving and its lights shine directly into a reflector, there is only a brief down flick for, say, of a second then the lights stay up for 1 /2 seconds, then another down flick for /5 second and up for 1 /2 seconds, etc. The road ahead remains illumin ated for approximately 90% of the time, which is deslrable, and the down flicks are so brief in duration as to be quite unobjectionable to most people. If the car is in motion as is normally the case, by the time one or two flicks have occurred, the reflector has been passed. If another car comes in sight of the photo-multiplier cell at this time and is sufliciently far away, the sensitivity of the system may be sufficiently reduced for a fraction of a second so that dimming would be delayed, but since the system need be set so as to be less sensitive only to the relatively weak reflected signal to accomplish the above anti-reflection action, a bright headlight, such as is due to a car rounding a curve or topping a hill nearby, V

will overcome the slight inhibiting potential due to condenser 42 and cause immediate dimming in any case. Furthermore, as the decay of the condenser is logarithmetic, its initial decay is quite rapid, so that the maximum loss of sensitivity is only for a fraction of a second, durlng which time a distant vehicle is relatively little annoyed by the bright headlights. In practice, this system can be readily adjusted so that a very satisfactory compromise between the reduced sensitivity to oncoming cars and good antireflection action is achieved.

One objection to the above described system is that if the dimming is due not to a reflection, but to an oncoming vehicle, as soon as that vehicle is passed there is a short period of low sensitivity, due to the above described action of condenser 42. This I eliminate by providing additional means whereby condenser 42 is effective only if the down flick is of short duration, as happens when it is caused by a reflection, but not when the down beam remains down for a substantial period, as is normally the case when the relay 2!) has been actuated by the lights of an oncoming vehicle. For this purpose 1 provide a second relay 50 which is actuated by the dimming switch 22 when it engages contact 30 to dim the headlight. Relay 50 is shunted by a condenser '52,, and a series resistor 54 is added to provide a delay action.

After a predetermined delay (approximately /5 second), relay 50 closes switch 48 to short the condenser 42 through a low resistance 56, which is provided to prevent arcing of the contacts of switch 48. It will be seen that relay 50 has no effect on the action of condenser 42 if the headlights are dimmed by reflection, because in that event, as soon as the lights dim, there is no longer a reflection and relay 20 is immediately reenergized so that there is only a brief down flick which does not give the second relay 50 time to close its contacts, due to the time delay of the R-C combination 52, 54. Thus, the R-C combination 36, 42 is effective to produce the antireflection action previously described. On the other hand, if the dimming is due to an oncoming headlight, the dim beam is practically always maintained for at least a sec end, which gives relay 50 time to close switch 48 and inhibit the delay action of R-C combination 36, 42. Thus, as soon as the oncoming vehicle is passed, the system is immediately at full sensitivity and ready to operate normally if another vehicle should at this moment appear. The action is shown by the graph of Fig. 5, where the ordinates represent sensitivity and the abscissae represent time. The initial condition (stage A) is shown in Fig. 1, with the beam bright and the sensitivity therefore low, as previously explained. In stage B, an oncoming headlight is detected and the beam dims, while the sensi tivity is increased. In stage C, the oncoming headlight is passed and the beam again brightens. In stage D, a reflection is seen and the beam dims, then immediately comes up again as the reflection is lost; however, at this time the sensitivity does not go back to its initial level C as before, but due to the action of 36, 42 goes down to a lower level than originally, and gradually resumes its original sensitivity as condenser 42 discharges. During the first part of stage E, it will therefore require a stronger signal than normal to cause dimming. This can be provided by an oncoming headlight at a reduced dis tance, but not by the relatively weak reflection. The times when reflection causes dimming are normally quite infrequent as normal reflectors on the side of the road can be avoided by the directivity of lens 2, and it is only when the road curves to the left, or at a dead-end sign, or some similar condition, that reflection will occur at all; and since the times when an oncoming headlight will appear in the field of view immediately after a stage E type of action are still less frequent, it will be evident that this represents a relatively rare condition, and even then, if the oncoming headlight is close, when immediate dimming is important, such immediate dimming will occur due to the strong signal received from the nearby headlight.

In practice, the above action has been found to produce a very satisfactory solution to the problem.

Instead of the R-C type delay shown at 52, 54, any known type of slow acting relay could, of course, be employed, such as a relay provided with a copper slug, or a dashpot or other mechanical type delay could be used.

While I have shown the above anti-reflection circuit in connection with a scanning-type dimmer such as is discussed in my prior patent, it will be evident that it is by no means restricted to this type of automatic dimmer, but will be equally effective in conjunction with any conventional type of automatic dimmer using a photosensitive element to actuate a relay through an amplifier, as the R-C delay caused by 36, 42 could be applied to the grid of a suitable stage of the amplifier to cause the above described action no matter what type of automatic dimming circuit is used. It will also be apparent that instead of an R-C delay an R-L delay, thermal delay or mechanical delay could be used in carrying out the principle which is illustrated by the above circuit, which is shown by way of example only.

It often occurs that the driver of the oncoming vehicle if he does not have an automatic headlight dimmer but relies upon. old-fashioned foot dimming will fail to re:

spend; to; the automatic dimming by also dimming his lights. In that. case, it is customary'to call his attention to. his neglect by blinking ones own lights. I provide for this situation and alsofor overriding the automatic control by means of switch 61 which is the usual foot switch actuated by a fioorboard'button 60 so that each time-button 60 is depressed, switch 28 changes from its current position; to'the opposite one, as is well known. Thus, if the beam is bright, as shown in Fig. l, and the floor switch is pressed, the beam will be depressed to dim position and stay down regardless of the automatic system, ascurrent will flow directly from battery 26 through switch 28 to the dimming circuit. When it is desired to resume automatic operation, the foot switch is again depressed.

1;. provide a spring-opened switch 62 over and out of contact. with foot switch 60. If headlights have been automatically dimmed, and switch 62 is lightly touched with the foot, the'plate of tube 18is grounded through resistance 64-, and switch 62, directly through the metal button 60 to cause relay to be energized and the lights to return to bright as'long as switch 62 is grounded. Thus, by lightly tapping switch 62 a few times, the lights will be made to blink to'remindthe'oncoming driver to dim his lights. However, if the foot button is heavily pressed, switch 28- will be actuated to dim position regardless of the automatic system-as above explained. It will thus be seen that the operator has full control and can at will put the automatic system into operation, overrideitto fixed dim position which he may be required. todo by law in city driving or in some tunnels or cause the beam to temporarily be bright regardless of conditions ahead.

Instead of contacting the button 60, it will be apparent that switch 61 could be grounded on any convenient spring-mounted ground contact, and instead of being directly over: button 60, it need only be sufficiently close to the button sothat the operators foot covers both switch 62 and button 60, so that a light foot pressure will first ground switch 62 and continued foot pressure will then operate button 60. However, by placing switch 62 over the'button', there is" no chance of missing one and hitting the other'when feeling for these switches with the foot. Since switch62 isat a fairly high voltage, it should, of course, be well insulated.

Referring now to Figs. 2 and 3, the entire assembly of componentsshown'in Fig; 1' can be compactly housed in" a smallcasing 70. The physical elements which must be housedin'the' casing comprise a single photo-multiplier cell 10 and a scanning drum 74 which surrounds the light-sensitive end of the tube and is provided with scanning apertures 76 so spaced in a helical-band around the drum 74 that as the drum is rotated at least a single aperture is at all times crossing the window of the photo multiplier cell, and as all the successive apertures 76 traverse the window on each revolution of the drum, the entire area of the window is scanned for each revolution of the drum. Motor 6 drives the drum by means of a belt 78 which fits an annular grooved portion 80 on the drum. The drum is provided with a rigid shaft 82 coaxial therewith which is supported for rotation by any suitable bearing 84, such .as an Oilite bearing, or small ball bearings may be used. The apertures 76 may be circular as shown, or may be square or even in some cases in the form of narrow slits, the essential thing being that a small area of the image is observed through the aperture at any one time.

Lens 2 is mounted in the front of the casing 70. A light shield 86 may be provided if desired to define the desired field of view. The interior of the casing and all components should be coated with dark non-refiecting paint to prevent optical interference with the desired light signals. Due to the curvature of the drum, its surface will not coincide exactly with the focal plane of the lens, but with suitably chosen dimensions this effect is negligible for practical purposes, asathe circumferential.

extent of the image is in the order of A- inch and the a-p proximation to a straight line of thisfshort circumferential distance is adequate for practical purposes.-

The remaining space in the casing is used to house the other circuit components of Fig. 1, except, of course, fon the battery, power supply, and floor switch.

Tubes 13 and 18 may be housed in a'single envelopeas a dual tube, and similarly the two diodes may be a dual tube as shown, or may be single diodes. The remaining circuit elements should be selected for reasonably small dimensions and can easily be housed in a very small space.

Fig. 4 shows a casing similar to Figs. 2 and 3'exceptthat the lens is replaced by a reflecting surfac'e 90 so shaped as to cause the light beam presenting, the field-of. view to focus at the same area on the surface of-drum 74' as: before in the case of drum 74. A glasswindow 92 may be provided to exclude dirt andmoisture, or the aperture may be mounted against the windshield of acar in a corner where it does not interfere with the driver s' vision but is cleaned by the windshield wiper. The powersupply (not shown) is preferably. housed in a separate unit for convenient placement in any suitable location and is connected by leads to the dimmer circuit.

One particular advantage ofthe drum shown in Figs. 2, 3 and 4 is that it may be made of magnetically permeable material and thus. serve as a magnetic shield. for the photo-multiplier cell. Such cells are highly susceptible to'the disturbing influence of magnetic fields and the proximity of the motor may introduce such a field,- which might otherwise require carefulrnagnetic shielding, but the drum may be madetoserve this function very efficiently due to its construction as a light shield.

While the main relay 20' has been shown as normally energized, being deenergized by the effect of a light signal, it will be obvious that this relay could be normally deenergized instead in which case a light signal would cause the relay to become energized; in this case the circuit including the peak detector would, of course, be reversed or inverted from the arrangement shown, but as the necessary changes are Within the skill of any circuit designer, itis not considered necessary to specifically show them;

It will be apparent that the embodimentsshown are only exemplary and that various modifications can be made in construction and arrangement within the scope of my invention as defined in the appended claims.

I claim:

1. In a headlight dimmer, sensing means to detect light in a selected field of view, said sensing means cooperatively arranged with headlight dimming means to dim the headlights of a vehicle when said light exceeds a predetermined first value, means to brighten the lights when said light decreases below a second predetermined value, and desensitizing means to reduce the sensitivity of said dimming means for a short period of time immediately following the brightening of the lights whereby the dimmer is made responsive only to light of a higher intensity than a third predetermined value higher than the said first value for the said short period.

2. An automatic headlight dimmer comprising headlights having a bright and a dim condition, a light sensitive element, means associated therewith for producing an electrical output related to the intensity of a light signal affecting said element, a headlight dimming circuit actuated by said output to produce said dim condition of the headlights when said light signal exceeds a predetermined first value, means for restoring said headlights to the bright condition when said light signal decreases below a second predetermined value, and a desensitizing means operative to reduce the sensitivity of the dimming circuit for a short period of time imme diately following the resumption of bright condition of the headlights, whereby the dimmer is made responsive during said short period only to alight signal of a level higher than a third predetermined value, said third value being higher than said first value.

3. The invention according to claim 2, and further means arranged to render ineffective said desensitizing means when the time interval between the dimming action and the subsequent brightening action is greater than a predetermined duration.

4. The invention according to claim 3 and further means arranged to render inoperative said desensitizing means after the duration of said short period of time.

5. An automobile headlight dimmer comprising a light sensitive element, circuit means associated therewith for producing an electric output related to the intensity of a light signal affecting said element, a headlight dimming circuit electrically biased to a normal level of sensitivity and actuated by said output to cause headlight dimming when said intensity is greater than a definite value and to discontinue said dimming when the intensity of the light signal is reduced below a definite level, means for increasing the sensitivity of the system during dimming and desensitizing means actuated for a definite short time period immediately after discontinuance of said dimming to change the electrical bias of said dimming circuit to reduce the senstivity of said system to a light signal.

6. The invention according to claim 5, said last means comprising time delay means effective for said definite short period, said dimming circuit comprising a dimmer relay having a first position corresponding to bright headlight condition and a second position corresponding to dim headlight condition, means connecting said time delay means into said dimming circuit in said first position of the relay, and bias changing means under control of said time delay means to reduce the sensitivity of said system to a light signal while said time delay means is efiective.

7. The invention according to claim 6, said time delay means comprising a condenser-resistor circuit having a time constant corresponding to the definite short period, means for charging said condenser-resistor circuit in the second position of said relay, and means for connecting said charged condenser to said dimming circuit to produce said bias change in the first position of said relay.

8. The invention according to claim 7, and means for rendering ineffective said desensitizing means at a definite short time period subsequent to dimming, whereby said desensitizing action occurs only when said dimming is of brief duration.

9. The invention according to claim 8, said last means comprising means for discharging said condenser in the second position of said relay, and further time delay means for delaying the operation of said discharging means for a definite short period after the relay changes from the first to the second position.

10. An automatic headlight dimmer comprising a lightconcentrating device arranged in concentrate light from a field of view in advance of a vehicle, a photo-sensitive electric cell having a photo-sensitive surface near the focus of said light-concentrating device so that light from said field of view is concentrated upon said surface, said photocell having a cylindrical exterior configuration, a cylindrical scanning drum mounted coaxially with said photocell for rotation thereabout, and having scanning apertures arranged to successively traverse contiguous portions of said surface as said drum is rotated; means for rotating said drum; and automatic headlight dimming means actuated by the response of said photo-sensitive cell to light from said field of view which passes through said apertures.

11. The invention according to claim 10 and a housin enclosing said photo-sensitive cell, drum and driving means, said light-condensing device being a lens mountcd in said housing.

12. The invention according to claim 10, said lightconcentrating device being formed by a reflecting surface of said housing.

13. The invention according to claim 10, and a peak detector responsive to the output of said photo-sensitive device, said automatic headlight dimmer being controlled by the output of said peak detector.

14. The invention according to claim 13, and a cathode follower between said photo-sensitive device and said peak detector.

References Cited in the file of this patent UNITED STATES PATENTS 2,558,969 LeCroy July 3, 1951 2,560,748 Silva July 17, 1951 2,573,627 Vanderlip Oct. 30, 1951 2,598,420 Onksen May 27, 1952 2,614,227 Bordewieck Oct. 14, 1952 2,615,079 Pardue et al. Oct. 21, 1952 2,632,040 Rabinow Mar. 17, 1953 2,687,337 Alford Aug. 24, 1954 2,707,524- Montgomery May 3, 1955 2,730,654 Rabinow Jan. 10, 1956

Images