US2921232A - Automatic headlight system - Google Patents

Description

F. T. MACHALEK AUTOMATIC HEADLIGHT SYSTEM Filed April 18, 1957 Jan. 12, 1960 INVENTOR- FE/zD/NAND 7. MACHALEK A TTORNEY United States Patent 2,921,232 AUTOMATIC HEADLIGHT SYSTEM Ferdinand T. Machalek, Fort Wayne, Ind., assignor to International Telephone and Telegraph Corporation Application April 18, 1957, Serial No. 653,630

3 Claims. (Cl. 315-83) In operating an automotive vehicle at night, high beam or bright lighting may be needed to illuminate the roadway a substantial distance ahead of the vehicle. When operating with the headlights in high beam condition, it is often necessary to revert to low beam or dim lighting when passing an approaching vehicle or when approaching a vehicle from the rear. For this purpose, there is conventionally provided a foot-operated beam control switch, commonly called a dimmer switch, which in one position energizes the high beam circuit and in the other position the low beam circuit.

Failure to dim the headlights upon approaching a vehicle coming from the opposite direction often blinds the operator of the other vehicle to such an extent that he is unable to see the road and to properly steer the vehicle. Such blinding conditions have often been the cause of serious accidents, the blinded operator steering out of his lane either into the path of the oncoming car or off the road to the opposite side.

For promoting safer driving, automatic headlight dimming apparatuses have been proposed and in some instances have been used; however, such apparatuses have not received universal acceptance for many diiierent reasons, among which are the relatively high expense, complexity of the apparatus, erratic operation, and the like. Thus, in order for headlight-dimming apparatus to be universally acceptable, it must be inexpensive,

eflicient, reliable in operation, and the ultimate in sim- It is another object of this invention to provide a photosensitive switching circuit which is automatically compensating for changes in ambient temperature and supply voltage.

It is still another object of this invention to provide a photosensitive switchingcircuit which normally maintains the headlights in dimmed position inthe event the circuit is'not functioning properly.

In accordance with this invention there is provided an automatic headlight system which comprises photosensitive voltage-dividing means having opposite ends, an amplifier operatively coupled to said voltage-dividing means intermediate the ends, circuit means for applying a source of power to said voltage-dividing means and said amplifier, illuminating means coupled to said circuit means and disposed to irradiate only one portion of said voltage-dividing means, optical means for directing radiation from an external source onto another portion of said voltage-dividing means, and utilization means operatively coupled to said amplifier.

The above-mentioned and other features and objects might occur in the battery 9.

Patented Jan. 12, 1960- P we I of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following descrip-- tion of two embodiments of the invention taken in conjunction with the accompanying drawing, wherein:

The drawing is a schematic diagram illustrating. two difierent embodiments of this invention.

. Referring to the drawing, an amplifier or vacuum tube 1 is provided with an anode 2, a control grid 3, a space charge grid 4, a cathode 5 and a filament 6. A relay 7 isconnected between the anode 2 and space charge grid 4, a lead 8 extending from the space charge grid 4 to the positive terminal of a battery 9. The battery 9 in one embodiment of this invention is the usual l2-volt storage battery in an automobile, the negative terminal being grounded to the chassis as shown.

Two series-connected photocells 10 and 11 are connected across the battery 9, providing a voltage-dividing network. The juncture 12 between these two photocells is connected as shown to the control grid 3.

The cathode 5 is grounded through a suitable variable cathode resistor 13, and the filament 6 is connected across the battery as shown. A suitable switch 14" leading from the battery 9 to the amplifier circuitry controls the application of power thereto.

The relay 7 is provided with an armature or switch 15 which is spring biased upwardly into engagement with a contact 16 which leads to the low or dim headlight beam 17. A second contact 18 spaced from the contact 16 is engaged by the switch arm 15 when the latter is moved downwardly and is connected to the high or bright light circuit 19 of the headlights. In the illustrated position of the switch arm 15, the relay 7 is de-energized. Upon energization of the relay, the switch arm 15 is pulled or moved downwardly into engagement with the high beam contact 18.

The tube 1 in the illustrated embodiment is a 12K5 type, requiring only approximately twelve volts anode voltage for operation. Such a tube is especially useful in this invention because it may be operated directly from the automobile battery, and therefore does not require the use of a high voltage power supply of the type conventionally used in automobile radios. When energized, the filament 6 of this particular tube produces a relatively bright light, and this illumination is utilized in compensating for any voltage changes which In accomplishing this compensatory action, the photocell 10, which will hereafter he termed the compensating cell, is disposed adjacent the tube 1 so that the illumination from the filament 6 will fall thereon.

The two cells 10 and 11 may be identical in construction and composition, one embodiment of the invention using photoconductive cells composed of cad-1 mium selenid'e. The resistances of these two cells are so selected that in normal operation of the circuit with no illumination falling on the cell 11, a voltage will be provided at the juncture 12, henceon the control grid; 3, which renders the tube 1 conductive tosu'ch an extent that the relay 7 is energized, closing the switch arm 15 against the contact 18. In this condition of operation, the high beam circuit 19 is energized.

Assuming that the circuitry of the drawing is carried by a vehicle moving along a road and the photocell 11 is positioned on the vehicle to receive illumination from the headlights of an approaching vehicle, such illumination will lower the resistance of the cell 11, thereby reducing the potential on the grid 3. This reduction in grid potential renders the tube 1 nonconductive, thereby de-energizing the relay 7, which in turn releases the switch arm 15 under the force of the spring 20. The

switch arm 15 thus changing position between the contacts 18 and 16 thereby de-energizes the high beam and energizes the low beam 17. When the approaching vehicle has passed, the absence of illumination on the photocell 11 causes .an abrupt increase.inpotentialJon the. grid 3, thereby rendering: the tube: 11 conductive. The relay 7 is once again-energized, moving theswitch' arm. from the low beam to the high beamcircuit. Thus, the illumination from approaching vehiclesfalling on the 1 photocell llserves automatically to dim the headlig ts.

Since the two photocells-10 and 11 are series-connected and in a preferred embodiment of the invention :areof the same composition and electrical characteristics, any changes in ambient temperature which cause a change. in resistance thereof will not affect the potential at juncture 12, sinceeach cell changes in resistance a corresponding amount. Thus, the circuit is insensitve to changes in ambient temperature which normally aifect theresistances of the photocells.-

Since every vehicle is equipped with a battery-charging generator and voltage-controlling devices, the voltage delivered by the battery 9 or the associated generator to the illustrated amplifier shifts from approximately 10 volts to 16 volts. Because of this shift in voltage, the operating characteristics of the tube 1 will correspondingly change, causing the operation to be erratic and'unreliable. By situating the compensating cell. lfladjacent the tube 1, the illumination from the filamentr6'v falling thereon will serve to compensate.automaticallyfor:these voltage changes. This compensation thereby stabilizes cir-. cuit operation, rendering reliable performance.

This automatic compensation for voltage changes. oc-' curs in the following manner. Assuming that the circuit is operating, current flowing through the cathode and resistor 13 provides a bias on the grid 3. An increase in battery voltage serves to increase this current and the bias on the grid 3; however, this same increase in voltage causes the filament 6 to glow more brightly, which raises, the illumination on the compensating cell It This increased illumination reduces the resistance of the cell 10, thereby increasingthe voltage at the juncture'12 which serves to restore the operating bias on the grid 3 to its normal value. If the battery voltage 9 should drop, the circuit automatically reduces the bias on the grid 3,- but since the filament 6 will glow less brightly the cell will increase in resistance, thereby automatically raising the bias to its normal value. Thus, the circuit is insensitive to voltage changes in the battery supply.

Instead of using the filament 6 of the tube 1 as the means for controlling the resistance of the compensating cell 10, an ordinary lamp 21 connected across thepower supply as shown may be used. Any variation involtage of the power supply will thereupon cause a corresponding change in the brightness of the lamp 21 which in turn alters theresistance of the compensating cell 10.

Of importance is the fact that the present invention will not permit the headlights to be energized in the bright or high beam position unless the circuitry is operating properly. As has already been explained, the relay 7 must be energized before the bright lights may be energized, and in order forthis condition to prevail, it is necessary that the tube-1 be operating properly. Proper operation of the tube 1 is dependent upon division of voltage over the two photocells 10 and 11, and further that the photocell 11 is not illuminated. If for some reason the circuit is not operating properly, such as the filament 6 is burned out or the circuit is defective in some respect which will not permit the energization of relay 7, the headlights will be maintained on the low beam position.

Also, when the circuit is initially switched on," the low beam circuit will be energized until the circuit has warmed up, at which time the relay 7 is energized closing the high beam circuit. This is of course true only in the absence of any actuable illumination falling on the photocell 11.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

What is claimed is:

1. An automatic dimming system for avehicle having high and low beamheadlights, respectively, comprising a two-terminal source of voltage, an amplifier having a control grid,. an anode and a cathode, a pair of photosensitive devices connected in series across the terminals of said source and having their juncture connected to said control grid, anelectromagnetic relay having its winding serially connected between said anode and a first terminal of.said source, said relay having front and back fixed contacts with a cooperating movable contact, said high beam headlights serially connected intermediate the second terminal of said source and said front contact, ,said low beam headlights serially connected intermediate the second terminal of saidsource and said back contact, said movable contact connected to said first terminal, variable resistormeans intermediate said cathode and said second terminal for setting the operating level of said amplifier, illuminatingmeans connected across the terminals of said source and adapted to excite a first one of said photosensitive devices only and in proportion to the voltage value of said source, said second photosensitive device positioned to be excited from the headlights of an oncoming vehicle, whereby a change in said source volt-v age will correspondingly alter the amount of bias applied to said grid thereby compensating for the change in voltage of said source.

2. An automatic dimming system as claimed in claim 1, wherein said illuminating means comprises a filament for heating said cathode, said filament connected across the terminals of said source.

3. An automatic dimming system as claimed in claim 1, wherein said illuminating means comprises a lamp connected across the terminals of said source.

References Cited in the file of this patent UNITED STATES PATENTS 2,240,843 Gillespie May 6, 1941 2,423,278 Willis July 1, 1947 2,807,752 McIlvaine Sept. 24, 1957 FOREIGN PATENTS 760,773 France Mar. 2, 1934

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