Automatic vehicle headlamp dimming control

  • US 4,727,290 A
  • Filed: 05/29/1987
  • Issued: 02/23/1988
  • Est. Priority Date: 05/29/1987
  • Status: Expired due to Fees
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First Claim
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1. A control circuit for a vehicle headlamp system having two levels of intensity comprising, in combination:

  • an electric power supply having a supply voltage;

    a first voltage divider connected across the supply voltage and having an output;

    a capacitor;

    a light sensitive resistance positioned to sense light from outside and in front of the vehicle, the light sensitive resistance being connected in electrical series with an electrically controlled variable resistance in a second voltage divider in series with the capacitor across the supply voltage, the second voltage divider having an output from the junction of the light sensitive and electrically controlled variable resistances at a control voltage;

    a fixed resistance connecting the output of the first voltage divider and the junction of the capacitor and second voltage divider;

    an energizing circuit adapted, when activated to its high beam mode, to energize the headlamp system from the power supply at the higher intensity and, when activated to its low beam mode, to activate the headlamp system at the lower intensity, the energizing circuit being responsive to the output of the second voltage divider to switch the headlamp system to its high beam mode at a control voltage varying in the direction of decreasing sensed light from a reference voltage and further being responsive to the output of the second voltage divider to switch the headlamp system to its low beam mode at control voltages varying in the direction of increasing sensed light from the reference voltage;

    first electric feedback means from the energizing circuit to the electrically controlled variable resistance for changing the electrically controlled variable resistance immediately in a step-wise manner upon switching of the headlamp system between the high and low beam modes in direction to produce hysteresis in such switching; and

    second electric feedback means from the energizing circuit to the junction of the capacitor and second voltage divider for gradually changing the voltage at the junction of the capacitor and the second voltage divider in direction to produce a gradual change in the output of the second voltage divider counter to that produced by the first electrical feedback means.

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