US2598420A

US2598420A - Light responsive system

Info

Publication number: US2598420A
Application number: US171363A
Authority: US
Inventors: Jr George W Onksen
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1948-07-10
Filing date: 1950-06-30
Publication date: 1952-05-27
Anticipated expiration: 1969-05-27

Description

y 1952 G. w. ONKSEN, JR

LIGHT RESFONSIVE SYSTEM Original Filed July 10, 1948 2 SHEETS-SHEET l Ihwentor @aga @2%W/m/z May 27, 1952 G. W. ONKSEN, JR

LIGHT RESFONSIVE SYSTEM Original Filed July 10, 1948 2 SHEETSSHEET 2 Patented May 27, 1952 2,598,420 LIGnr ltnsr'onsivn SYSTEM George Qnksenrjn, Anderson, Indl, assignor to General MotorsCorporation, Detroit, Micli., a ccrpofation of Delaware Giigin'al application July 1 I948, Serial No; 37,984: Divided and this application June 30, 1950, Serial No; 171,363

55 Claims.

No. i198}; filed July 16, N48,; in the. names of George W. Onkserr, Jr., and- Charles W. Miller,

entitled-f1 flight Responsive System!" Inc illumination systems of automotive ve-.

hiclesare generally provided with dual filament headlamps with eachfilament in separate l y energiza-bleelectrical circuits controlled for alternate energization by the operator. i The filament are positioned with respect to the headlamp reflector to project a high andv low beam of light declining to thelongi-tudinal axis of the vehicle at different angles so that illumination patterns are cast at di-iferentdistances inits path ahead. The high beam is generally preferred for nightdriving on rural highways which are not illuminated fromother sources, whereas thelow beam is generally used for city driving conditionswhere additional illumination is provided: i

To eliminate theha zard-s of passing due to the glare and dazzling q effect of the high beam; the operator is required to manually; operate a switch which selectively energizes the low beam circuit. This operationma-y distract the operators attentionfrom; the path ahead and when the operator tailsto depress the beam, extremelyhazardous conditions prevail for the passing of oncoming era rs It is therefore an object of the present invention to minimize the driving hazards prevalent under conditions of night driving by providing a light-sensitive electrical circuit for automatically controlling the illumination system of vehicl'es in response to the intensity of illumination of a similar approaching system.

This and other objects are obtained in accordance with the present invention by providing a selective light-sensitive electrical circuit for con; trolling vehicle headlighting' systems which is responsive to a predetermined light intensity to dim the systemyet may be subjected to'a wide variation of light intensity without affecting a d-enrgization of the dim circuit once it has been energized. A headlight system embodying the present invention comprises the conventional dual filament headlamps with independent electrical circuits for energizing one or the other a light-sensitive electrical circuit including aphotoelectriccell, a first and second stage of amplificationya relay" for selectively energizing the inde- 2 pendent filament circuits and a common source of electrical energy. The responsiveness to a predetermined light-intensity while remaining un affectd by Wid variations of light intensities once the system has been dimmed is obtained by including in the second stage of amplification,

tow amplifier tubes of difiring characteristics electrically connected in parallel.

Further objects and advantages of my invention will become apparent as the renewing description proceeds and the features of novelty which characterize my invention will be pointed outwith particularity in the claims annexed to and forming part of this specification.

For better understanding of my" invention reference may be had to the accompanying drawings in which Figure 1 is a schematic diagram of the circuit utilizing the present invention for controlling a vehicle. headlightin'g system; Figure 2 is a schematic diagram illustrating one form of modif cation and Figure 3 is a schematic diagram illustrating still another modification.

Referring now to Figure l of the drawings, there is illustrated a vehicle headlighting system embodying the present invention in which apair of conventional headlamps, not shown,

including high and low beam filaments 2' and 4 respectively,- form part of electrical circuits energizable to provide either a manual or' automatic control of the system.

In the system,- a conventional automotive vehicle storage battery 6 of the 6-volt type is provided as a source of electrical power. In this connection it will be understood that the battery 6 is a source of power for the ignition system of the vehicle as well as the lighting system. The negative terminal of battery} is connectedto ground and the positiveterminal is connected through conductor 8 to the movable arm ID of asingle pole,-. sing-1e throw master switch l2." The stationary contact [4 of Switch; E2 is connected through conductcr l6, current limiting fuse l8 and conductor 20 toa terminal junction 22'. A branch conductor 24; connects terminal 22 with the movable arm 28 of a single pole, double throw electromagnetic relay switch 28 provided with oppositely disposed. stationary contact terminals 30" and 32. Themovable arm 26' of switch 28 is normally held in yieldingengag e rnent with stationary contact terminal 32 which in turn is connected through conductor 34 to the low beam filaments Qof theheadlan psl The other sids (if the headlamp filaments 4 are grounded uirdugn" a-condu'ctor 36. The circuit comprising contact 32, conductor 34, filaments 4 and conductor 36 form one branch of the headlamp circuit. The other branch comprises a conductor 38 which connects the high beam filaments 2 of the headlamps to contact 38 of the switch 28 and conductor 48 which connects the other sides of the filaments 2 to ground.

To provide for the independent manual energization and deenergization of the headlamp circuits, the solenoid coil 42 of switch 28 forms part of a circuit which includes in series relationship a single pole, double throw, selector switch 44 and a single pole, double throw foot selector switch 46. Terminal 22 is connected to the movable arm 48 of switch 44 through conductor 58. The movable arm 48 is shown in a position to bridge two stationary contacts 52 and 54, both of which are connected in circuits to the automatic control and indicating means and will be described in detail hereinafter. An oppositely disposed contact 56 of switch 44 is connected through conductor 58, terminal 68, conductor 62, terminal 64 and conductor 66 to a stationary contact 68 of the foot selector switch 46. The movable arm I8 of switch 46 is adapted to engage contact 68 and complete a circuit through conductor I2, solenoid coil 42 of switch 28 and conductor I4 to ground.

For automatic control of the headlamp filaments a circuit is provided from the source 6 to the solenoid coil 42 which includes a lightresponsive, single pole, single throw electromagnetic relay switch I6 capable of energization and deenergization at substantially different current values. In this circuit the stationary contact 52 of selector switch 44 is connected by a conductor I8 to a terminal junction 88 which in turn is connected to the movable arm 82 of relay switch I6 through conductor 84, terminal junction 86 and conductor 88. The movable arm 82 cooperates with stationary contact 98 of relay switch I6 and is normally in yielding open circuit relationship. Contact 98 is connected through conductor 92, terminal junction 94 and conductor 96 to the remaining oppositely disposed stationary contact 98 of foot selector switch 46.,

To reduce the destructive efiect of arcing between the movable arm 82 and the stationary contact 98 of relay switch I6, a shunt circuit including a 100 ohm resistor 100 and a .1 mfd. capacitor I82 isconnected in series between the terminals 86 and 94.

In the headlighting system of the present invention the voltages suitable to the most eificient operation of the light responsive apparatus are provided by a conversion device I84 for changing the low voltage direct current of the vehicle electrical system to'a high voltage direct current suitable for the operation of the electronic elements in the circuit. Conversion devices such'as the device employed in the system of the present invention are well-known and are employed extensively to provide suitable voltages for the operation of vehicle radios. In this connection the positive input terminal I86 of the converter is connected through conductor I88. terminal junction H8 and conductor II2 to the terminal 88. The negative terminal I I4 is connected to ground by conductor III. The high voltage output terminal H6 is connected by a conductor II8, terminal junction I28, conductor I22, terminal junction I24 and conductor I26 to the solenoid coil I28 of the light responsive relay switch I6. The

negative output terminal of the converter is connected within the converter to ground through terminal H4. The light responsive relay I6 has the other end of its solenoid coil I28 connected through conductor I38, terminal junction I32, conductor I34, terminal junction I36, a 25,000 ohm resistor I38 and conductor I48 to the stationary contact I42 of a single pole, single throw, manual switch I44. The movable arm I45 of switch I44 is in yielding open circuit relation with contact I42 and is connected to ground by conductor I46. A shunt circuit is provided for the solenoid coil I28 of relay switch I6 which includes an 8 mid. capacitor I43 connected between the ends of the solenoid coil.

To provide the different voltages necessary to the operation of the various electronic elements in the light responsive apparatus a voltage divider network I4'I comprising 4 sections of series-connected resistances I48, I58, I52 and I54 of 5888 ohms, 880 ohms and 15,000 ohms respectively, is connected between the high voltage terminal I24 and ground. The respective resistances are connected together in the order enumerated by terminals I56, I58 and I68.

A filter I62 or 16 mfd. capacitance is connected across the output terminals II 6 and II 4 by means of conductor II8, terminal I28, conductor I68 and conductors I I8 and I I I, to minimize the A. C. ripple voltage that is present in the output circuit of the converter I 84.

As the voltage at the output terminals of the converter varies between about 260 and 420 volts due to the variation of the vehicle system voltage between about 5.5 and 7 volts, voltage regulator means I64 and I66 are connected in parallel with sections of the voltage divider network M1 to obtain stable voltage levels of 150 and volts respectively. The voltage regulator means I64 and I66 comprise a VRl50 glow discharge tube which is connected by conductors I12 and H4 between terminal I56 and ground, and a VR75 glow discharge tube which is connected by conductors I 16 and H8 between terminal I68 and ground.

The electronic elements that comprise the light responsive apparatus and provide for the energization and deenergization of relay switch I6 include a photocell II9 which controls a power amplifying tube I98 hereinafter referred to as a first stage or primary amplifier and a pair of power amplifying tubes I98 and 286 which are controlled by the output of the primary amplifier and have their plates connected in parallel to the solenoid coil I28 of the relay switch I6. The pair of amplifying tubes I98 and 286 will be referred to hereinafter as the second stage or secondary amplifier. The photocell I19 is connected to the voltage divider M1 by a conductor I88 which connects its anode terminal to terminal I58 at the junction of the voltage divider resistance sections I58 and I52. By connecting the photocell anode to the voltage divider at this point, a voltage of about to volts is provided for the operation of the cell at the most efficient portion of its response curve. The cathode of the photocell is connected by conductor I8I to a terminal junction I82 which in turn is connected through a 500 megohm resistor I84 to ground and to the positive terminal of a one and one-fourth volt biasingbattery I86 which has its negative terminal connected by a conductor I88 to the control grid of the multiple grid power amplifying tube I88 comprising the first stage or primary amplifier. The output or plate of tube I98 is connected by conductor I 92, terminal junction I94 and conductor I96 to the-control grid-of themuh tiplegrid power amplifying tube" I 66 comprising partof the second stage or secondary amplifier and through terminal I94, resistor I96, terminal junction I91, conductor 200, resistor 202'- andconductor 204 tothe control grid of the multiple grid power amplifying tube 266 comprising the other part of the-second-stageorsecondary amplifier. The resistors I65 and 202 have respectiveresistance values of 2 and 100 megohms. The plate of tube I95) is also-connected-by terminal- I91 to terminal 5-58 of the voltage divider through an 8 megohm resistor 208, conductor 2 I 0, terminal junction 2I2 and conductor 2I-4. A- 70,0'00 ohm potentiometer 2I3 is connected between termi-nal 2I-2 and ground and carries a sliding contact 2I 5'which is connected by a con-- ductor 216 to the screen grid of first stage amplifying tube I00. Current for heating the filament of tube- I66 is supplied by connecting the filaments of tubes I90 and I98 are connected to ground. To obtain a stable voltage input of 156 Current is also supplied volts to the screen grids of tubes I98 and 206 of for the cathodes of tubes I68 and 266 are-supplied fromthe' voltage divider I41; the cathode and suppressor'grid of tube I98'being connectedby' conductor 232m terminal 2I2' and the cathode and i suppressorgrid of tube 266' being connected by conductor234 to the sliding contact 236 on thep'otentiometer section I54. The cathode of tube 206 is heatedby an independent filament which has one side connected: by conductor 235' to the 6-volt' battery source at the junction of conductor" 88 and movable arm 82 of switch 16 and the other side" connected to ground. The plates of the tubes I98'an'd 206' are connected in parallel to the solenoid coil I28 ofrelay switch 16", the plate of tube 206* being connected to terminal I32 through a j-000 ohm' resistor I33 and the plate oftu-be I96 being" connected to terminal I36 by conductor'23B.

Indicating means for the'li'ght responsive and manual control circuits are included in the switchingcircuit': These means comprise indicat'or lamps 250' and 242. Lamp 240 has on'e'si'de of its filament connected to" terminal 60 byconductor 24-4 and the other side of the filament connected' to the contact 54 of switch 44 by conductor 246, junction terminal 248 and conductor 260. The filament of lamp 242 has one side connected to ground and the other side connected through aconductor 252 to'the stationary contact 254= ofan electromagnetic relay switch 256. The movable arm 255 of the relay switch 256 is in" yielding closed' circuit relationship withcontact 254" and is connected by'conductor' 251;.te'rminaljunction 259 and conductor 26I' to the'terminal 2481 The coil 263 of the relay 256 is energized through a circuit which co'mie'cts one: end of the coil through a conductor 265 to terminal B4'andthe other end of coil to. terminal 256.

In the circuit modification of the light responsive apparatus illustrated in Figure 2, the air connection with the circuitofl igure I.

. 206 by conductor 26-1.

rangement of a the circuit and electronic elements"- is substantially the-same as that of Figure 1:exce'ptthat a duc diode tube 256" is cormected between' the'multi pl'e grid tube I90 or theprimary amplifier and: the multiple grid tube 206- oi the secondary amplifier.-

In this circuit the plate of: the primary am pl ifier tube I90 is ccnnecte'd to terminal I94 by conductor" I92 withbranch circuits connecting: terminal I94 with thecontrol grid of tube I98 one ofthe cathodesof tube 256 and the volt terminal or the voltage divider In.- The circuit connecting the grid oftube I98 and'thc plate oftube is the same as hereinabove described in: Tliecir cult to the 75 volt" terminal of the voltage divider includesa lo megohm' resistor 260 connected lieftween terminals H14 and 2l2 byconductors zia and 262.- -A conductor 255 connects terminal 94 with the cathode of tube 256: The voltage of the control and oftube 206 controlled 'by" the output plates crtube fisx These plates are cohf nected in parallel circuits to" aterminal' junction 265: which is connected tothe-contrcl-g' rid of tube oneplate or the diode-is connected to terminal 265- through a 1 volt biasing battery 268 which has its positive terminal connected to theplate'of'tube2-56' by con-- ductor'2-69 and its negative-terminal-connected to terminal 265' by conductor 266. Theotherplate ofitube2'56' is connectedto' terminal' 265 by -co'nduct'or' 264. The heater fil'ame'nts' of tube 256' are'connected in series between ground and the conductor-235 by conductor- 21I-.- The r'emaining cathode oftube 256' is connected through a 2 megohm' resistor 213- to the cathode of tube 206.

In the circuit modification of the light responsive apparatus illustrated in Figure 3- there is in cluded apair'ofmultiple grid tubes 210 and 212'- comprising a first stage or primary amplifier which have'their outputs controlled by the photo-- cell and which in turncontrolthe outputs of another pair of multiple grid tubes 214- and 216' comprising a second stag'eor secondary amplifier;-

In this circuit arrangement the control-grid oftube 212 is connectedtothe' cathode of the-photo cell I19 through conductor 218, terminal unction 280 and a 1% volt biasing battery 282' which is arranged with its negativeterminal connected-to th'e control grid and the-positive terminal connected to the terminal 280. A- meg'ohm resistor' .284: in series witha 500 megohm -resistor 286' are connected between terminal 280 and ground. A conductor 288- connects the junctionof resistors 284 and 286'to the control grid of tube 210. The plates of tubes 210 and 212 are con-- nected' respectively by conductors 290 and 29-2- to the control grids of tubes 214 and 216. Current is-sup'plied to-the filaments of tubes 2-10, 212' and 216 from the 6-volt battery circuitthrough tar-- minal IIII, choke coil 2I8 andballast r'esistor'220 and-the branch circuits'c'omprising the condu'c tors 294- and 296-. The filaments of tubes 210 and 212 are connected in series circuit relationship between conductor 294 and ground by conductors 298 and 300 while the filament of tube 216- hasone side connected to groundby conductor 302 and the-other side connected to-the conductor: 296. Voltage is supplied to the screen grid oftube 212 by a circuit which connects one end-of a 70,000ohm potentiometer 304- to the 75 volt terminal I60 of the voltage divider I41 and theother endof the resistor to ground. Resistor-304 is connected to terminal I60 by a circuit which includes conductor 2T4, junction terminal 308, conducto'r'flll; junction terminal 3I'2, conductor 3I4, junction terminal 3 I6 and conductor 3I8. A slidable contact 320 associated with the potentiometer 304 is connected by a conductor 322 to the screen grid of tube 212. Voltage is supplied to the screen grid of tube 210 by connecting the grid through conductor 324 to a slidable contact 236 which is associated with the potentiometer section I54 of the voltage divider I41. The cathodes and suppressor grids of tubes 214 and 216 are connected respectively to terminals 308 and 3I6 by conductors 328 and 330; the suppressor grid of tube 214 being connected to the cathode externally by conductor 321. A 250,000 ohm resistor 332 and a 500,000 ohm resistor 334 are connected respectively between the plate of tube 210 and terminal 3I2 and the plate of tube 212 and terminal 3 I 6. Current is supplied to the filament of tube 214 by conductor 235 which is connected between the movable arm 82 of relay switch 16 and one side of the filament.

The other side of the filament of tube 214 is connected to ground by conductor 338. The plates of tubes 214 and 216 are connected respectively to terminals I32 and I36 in the coil circuit of relay switch 16 through a 100,000 ohm resistor 340 and conductor 342.

For the hereinabove described light responsive circuits to operate in response to predetermined light intensities to control the energization and deenergization of the headlamp filaments 2 and 4 through relay switch 16 it is first desirable to adjust the circuit to respond with predetermined current flow at the plate output of the tubes of the secondary amplifier. In this connection, switches I2 and 44 are closed to energize the current converter I04. The electronic elements which are connected to the high potential side of the converter are allowed to heat for a period of time'so that they will operate efliciently. The sliding contacts of the three circuits are then adjusted to provide current flow through coil I28 which will vary in accordance with the intensity of light of an approaching vehicle headlight system to cause deenergization of the coil when the approaching vehicle is at a predetermined distance ahead and energization of the coil when the approaching vehicle passes by.

To provide for the automatic control of the headlighting system, switch I is closed to energize the low beam filaments 4 through current flow from the battery 6 through conductors 8, I6, I8, and 24, movable arm 26 and conductor 34. The movable arm 48 of switch 44 is then closed on contact 52 to energize the converter I04 through the circuit including conductors 18, H2 and I08.

Referring now to the circuit diagram of Figure 1 with the electronic elements sufficiently heated and no light on the photocell I19, sunicient current flows in the circuit from terminal II6 of the converter through conductors II8, I22, I26, coil I28, conductors I and I34 to the plates of tubes I98 and 206 to cause energization of the relay coil I28 and movement of arm 82 of relay switch 16 into engagement with contact 90. With the movable arm 10 of the foot switch 46 engaging contact 98 a circuit iscompleted to coil 42 from the battery through conductors 8, I6, 20, 18, 84, 86, 62, 96 and 12. With coil 42 energized the movable arm 26 of relay switch 28 moves into engagement with contact 30 causing energization of the high beam filaments 2.

With the approach of a similar lighting system, light of gradually increasing intensity falls on the photocell I19 causing an increasing current flow from terminal I58 of the voltage divider through conductor I80, photocell I19, conductor I8I and resistor I84 to ground. With the gradually increasing current flow in this circuit the voltage at terminal I82 changes and gradually overcomes the negative grid bias on the control grid of tube I caused by the biasing battery I86. As the bias on the control grid gradually changes from negative toward positive the flow of current from terminal I60 of the voltage divider through conductors 2 I4, 2 I0, resistors 208 and I and conductor I92 to the plate of tube I90 increases and a voltage drop occurs at terminals I91 and I94 due to the IR. drop across resistors I95 and 208. These voltage changes are carried to the control grids of tubes 206 and I98 respectively through circuits including conductor 200, resistor 202 and conductor 204 and conductor I96 respectively. This causes a change of grid bias on the control tubes I98 and 206 causing both tubes to become sequentially non-conducting; the tube I98 being the first to out off, but relay I28 will not drop out until tube 206 is cut down in conductance to a low value after tube I98 is nonconducting. With very little or no current flowing to the plates of tubes 206 and I98 the coil I28 of relay 16 is deenergized moving arm 82 out of engagement with contact 90 and the circuit through coil 42 of relay 28 is broken causing the movable arm 26 to move into engagement with contact 32 for the energization of low beam filaments 4 and the deenergization of high beam filaments 2.

If the source of illumination to which the photocell is exposed then begins to decrease in intensity, a current of decreasing value flows from the terminal I58 of the voltage divider through the circuit including the photocell to ground as hereinabove mentioned. Accordingly, the voltage at terminal I82 decreases until the voltage of the biasing battery is imposed on the control grid of tube I90. The flow of current through tube I90 decreases and consequently the voltages at terminals I91 and I94 increase altering the grid bias in tubes 206 and I88. As these biasing voltages change the flow of current in tube 206 gradually increases to normal value, and tube I98 begins to approach the conducting point. However, While tube I98 remains non-conductive there is insufficient current flow in the coil circuit of relay 16 to cause it to move the arm 82 into engagement with contact 90. When it does become conductive sufficient current flows in the relay circuit to cause relay 16 to move the arm 82 into engagement with contact 90 and filaments 2 and 4 of the headlamp circuit respectively are energized and deenergized. There is thus a definite difference in the illumination level at relay drop-out to that at relay return. With this arrrangement it will be obvious that substantial changes in intensity of illumination are required before the relay 16 will be energized or deenergized from its existing state thereby preventing flickering or repeated alternate energization of the filaments due to extraneous lighting conditions.

If the operator of the vehicle should desire to reenergize the high beam elements 2 while the low beam elements are energized and under the control of the light-responsive apparatus. the independent resetting manual foot switch I44 is provided to close a circuit through the coil I28 of relay 16 from the terminal I I6 of the converter I04 to ground. This circuit comprises conductors II8, I22, I26, relay coil I28, conductors I30, I34,

resistor I38, conductor I40, switch 144 and conheadlight system. .In this connection the movable arm 48 of selector switch 44 is moved into engagement with contact .56 thereby completing a circuit from battery .6 through conductors 8, I6.,.20, 58,58, .62 and 66 to the stationary contact 68 ofrthefoot switch '46. Whenthe movable arm 18 moves into engagement'with contact 618, the circuit is completed from the battery 6 to the coil of relay ,28.through the switch 46 and conductor 12. Movable arm 26 of relay switch 28 moves into engagement with contact 38 and the high beam filaments 2 are energized. Manually breaking the circuit at switch 46 causes a deenergization of relay coil 42 and an energization of the circuit to the low beam filaments 4.

Lamps 240 and 242 indicate the controlling condition of the light responsive apparatus and the respective energization of the headlamp filaments. With the movable arm 48 of switch 44 in engagement with contacts 52 and 54 for energization of the light responsive apparatus are hereinabove described, a circuit is completed from terminal 248 through conductor 246, lamp 246 and conductor 244 to terminal 68. An additional circuit is completed from terminal 248 through conductor 26I, coil 263 of relay switch 256 and conductor 265 to terminal 64. This circuit also includes a branch circuit from conductor 26I to the movable arm 255 through conductor 251. With the coil of relay switch 256 deenergized, this circuit is completed through contact 254, conductor 252 and lamp 242 to ground. When the arm 18 of switch 46 is in engagement with contact 98 for control of the filaments 2 and 4 by the light responsive apparatus, lamp 242 is energized, indicating that the light responsive apparatus is controlling. When the movable arm I8 of switch 46 moves into engagement with contact 68, coil 263 of relay 256 is energized moving arm 255 out of engagement with contact 254 whereby the lamp 242 is deenergized. At the same time, lamp 240 becomes energized. With switch arm 48 moved out of engagement with contact 54 both indicating lamps become deenergized. With such an arrangement of indicating lamps there is visual means for indicating which of the headlamp filaments is energized when they are controlled manually and whether the filaments are under the control of the light responsive apparatus.

The operation of the light responsive circuit of Figure 2 is substantially the same as that of Figure 1. In this circuit, the intensity of light on the photocell determines the current flow in tube I96 and through resistor 266 which in turn controls the current flow in tubes I98 and 286 by changing the voltage on the control grids of these tubes. With no light on the photocell, both tubes I98 and 266 conduct sufficient current to cause the energization of coil I28 of relay 16 at a substantially high current value. As the photocell becomes exposed to increasing intensities of light, the voltage bias on the control grids of tubes I98 and 286 causes the tube I85 to become non-conductive and reduces the current fiow of tube 286 to a sufficiently low current flow to cause relay coil I28 to become deenergized. Current value at which the relay coil becomes deenergized is substantially less than that at which it becomes;

energized. In this circuit the purpose of the diode tube 256 is to replace resistor 262 of the circuit arein turnicontrolled by the photocell.

of .Figurel and 'preventthe control grid of tube 286 from becoming positive with respect to the cathode.

Inthe lightresponsive circuit of Figure .3 the operation is substantially the same as that of light responsive circuits of Figures 1 -and'2 except that'the flow of current through tubes 214 and 216 is directly and separately controlled by tubes .216 and 212 respectively of the primary amplifier. Thesetubes of the primary amplifier As in the .light responsive circuits of Figures 1 and 2 Whenthe photocell is not exposed to light tubes 214 and 21.6 :both conduct current of substantially high valueto energize relay coil I28. As the'intensity of light on the photocell increases the photocell conducts increasingly more current in the circuit from the voltage divider to ground through the photocell, conductor 218 and resistors 284 and 286. With increasing current in this circuit voltage changes occur across resistors 284 and 286 to cause the voltage bias on the control grids of tubes 210 and 212 to change, thus changing the current output of the tubes 214 and 216 and the voltage bias on the control grids of tubes 214 and 216. With sufficient light intensity on the photocell, tube 216 no longer conducts current and tube 214 conducts current of less value than that required to retain relay coil I28 energized. While specific circuit constants have been used in connection with the description of the circuits of the present invention and their operation it will be understood by those skilled in the art that they are illustrative and that the circuits are capable of operation at other values than those recited.

With the light responsive circuits such as described above wherein the light responsive relay controlling the headlamp filament circuit is in turn controlled by an amplifier comprising two amplifier tubes in parallel, the energizing and deenergizing of the headlamp filaments is accomplished at substantially different intensities of illumination. This important feature makes the operation of an automatic dimmer device for vehicle headlighting systems feasible because of the lack of response of the device to other sources of light causing flickering due to the repeated energization and deenergization of the high and low beam headlamp filaments.

What I claim as new and desire to obtain by Letters Patent of the United States is:

1. In an automatic vehicle headlight control system, the combination of power supply, a phototube connected thereto, a dark actuated amplifier circuit connected between the phototube and the power supply, a relay in the output circuit of the amplifier, and an electronic means to pull on the relay armature in the absence of light on the phototube, wherein, said relay armature operating as a means to automatically switch lights from high beam to low beam upon the application of light and returning them to high beam when the light is removed.

2. In a control for automatically dimming multiple filament headlamps, a light sensitive pick-up device, a source of electrical power, voltage amplifier means connected to the source of power and to the pickup device, current amplifying means connected to the output of the voltage amplifying means, a relay connected to the output of the current amplifying means, said relay being normally energized in the absence of light on the pickup device and deenergized upon the application of light thereto, and a switch operated by the relay to change the power source from the headlight high beam to the headlight low beam filament when the relay is deenergized by light falling on the pickup device and upon removal of the light to change the power source back to high beam filament.

3. 'In a control system for automatically dimming multiple filament headlamps, a light sensitive pickup device, a source of electrical power, a multi-element voltage amplifier tube connected to said source of power and having a control grid and plate, said control grid being connected to the pickup device, a current amplifier tube having a control grid and plate, said control grid being connected to the plate of the voltage amplifier tube and relay means connected in the plate circuit of the current amplifying means normally energized in the absence of light on said pickup device and deenergized upon the application of light to the pickup device, and switching means operated by the relay to change the power source from the headlight high beam filament to the low beam filament when it is deenergized by light falling on the pickup device and return it to the high beam filament when the light is removed.

GEORGE W. ONKSEN, JR.

No references cited.