APPARATUS FOR CONTROLLING THE INTENSITY OF VEHICLE HEADLAMPS
First Claim
1. Apparatus for controlling vehicle lamps in dependence upon the intensity of electrical street lighting supplied from an alternating current source, comprising conversion means including light-sensitive means, the conversion means being adapted to provide an output signal dependent on the amplitude of intensity variations at twice the frequency of the alternating current source in light incident on the vehicle from sources remote from the vehicle but independent of any substantially constant intensity component in said incident light, and control means for controlling a vehicle lamp in dependence upon a characteristic of the said output signal of the conversion means.
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Abstract
Apparatus for controlling the intensity of light from the dip filaments of vehicle headlights in accordance with the intensity of street lighting is described. Signals from a light sensor on the vehicle are processed to remove any constant intensity component due to daylight for example so that the resultant signal depends only on a cyclically variable component due to the cyclic variation in the intensity of street lighting supplied from an a.c. supply. When a vehicle passes between street lamps the amplitude of the said variable component varies, and for this reason means are provided to control the electrical supply to the dip filaments so that the intensity of light from these filaments is inversely proportional to minima in the amplitude of the variable component. In the embodiments specifically described the supply is disconnected from the filaments for fixed periods, the repetition frequency of the periods being varied to satisfy the above mentioned condition.
18 Citations
12 Claims
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1. Apparatus for controlling vehicle lamps in dependence upon the intensity of electrical street lighting supplied from an alternating current source, comprising conversion means including light-sensitive means, the conversion means being adapted to provide an output signal dependent on the amplitude of intensity variations at twice the frequency of the alternating current source in light incident on the vehicle from sources remote from the vehicle but independent of any substantially constant intensity component in said incident light, and control means for controlling a vehicle lamp in dependence upon a characteristic of the said output signal of the conversion means.
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2. Apparatus according to claim 1 wherein the control means is adapted to control the intensity of light from a lamp.
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3. Apparatus according to claim 1 wherein the light sensitive means provides a unidirectional signal dependent upon the intensity of light inCident on the vehicle, and the conversion means includes an alternating current amplifier, coupled to receive the unidirectional signal, for providing the said output signal of the conversion means in the form of an alternating current signal, the amplitude of which is proportional to the amplitude of the said intensity variations.
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4. Apparatus according to claim 3 wherein the said characteristic is the magnitude of amplitude minima in the alternating current signal, and the magnitude of amplitude maxima in the alternating current signal do not substantially affect the control of the vehicle lamp, and the control means includes means for providing a control signal dependent on the magnitude of the said minima but not substantially on that of said maxima, and means for varying the intensity of light from the lamp inversely in proportion to the magnitudes of the said minima.
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5. Apparatus according to claim 4 wherein the control means includes a d.c. restoration circuit coupled to the output of the alternating current amplifier, the d.c. restoration circuit being coupled by way of a peak-detector circuit to a low-level detector circuit for detecting minima in the output signal from the peak-detector circuit.
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6. Apparatus according to claim 3 wherein the alternating current amplifier has a high gain at the frequency of the said intensity variations compared with its gain at other frequencies.
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7. Apparatus according to claim 3 wherein the said characteristic is the magnitude of amplitude minima in the alternating current signal and the control means includes detector means for providing a square-wave signal, the mark/space ratio of which depends on the amplitude of the alternating current signal, the detector means being connected to charge and discharge a capacitor alternately, the durations of charge and discharge intervals being dependent on the said mark/space ratio, and peak detector means for detecting peaks in the voltage across the capacitor, the apparatus being such that the magnitudes of the said peaks are proportional to minima in the said intensity variations.
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8. Apparatus according to claim 3 wherein the control means controls the intensity of light from the dip filaments of the headlights of a vehicle.
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9. Apparatus for controlling vehicle lamps in dependence upon the intensity of electrical street lighting supplied from an alternating current source, comprising conversion means including light-sensitive means, the conversion means being constructed to provide an output signal dependent on the amplitude of intensity variations at twice the frequency of the alternating current source in light incident on the vehicle from sources remote from the vehicle but independent of any substantially constant intensity component in said incident light, and control means for controlling a vehicle lamp in dependence upon a characteristic of the said output signal of the conversion means, wherein the light sensitive means provides a unidirectional signal dependent upon the intensity of light incident on the vehicle, and the conversion means includes an alternating current amplifier, coupled to receive the unidirectional signal, for providing the said output signal of the conversion means in the form of an alternating current signal, the amplitude of which is proportional to the amplitude of the said intensity variations, wherein the said characteristic is the magnitude of amplitude minima in the alternating current signal and the control means includes means for providing a control signal dependent on the magnitude of the said minima, and means for varying the intensity of light from the lamp inversely in proportion to the magnitudes of the said minima, wherein the control means includes a d.c. restoration circuit coupled to the output of the alternating current amplifier, the d.c. restoration circuit being coupled by way of a peak-detector circuit to a low-level detector circuit for detecting minima in the output signal from thE peak-detector, and wherein the low-level detector circuit comprises a series resistor and a shunt capacitor connected between a pair of input and a pair of output terminals with the capacitor adjacent the output terminals, a differential amplifier having input terminals connected to the input and output terminals, respectively, and switch means connected across the output terminals, the amplifier being connected to discharge the capacitor when the voltage across the input terminals falls below that across the output terminals.
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10. Apparatus according to claim 9 wherein the control means includes means for generating constant duration pulses, a counter for counting the pulses, a comparator for comparing the number reached by the counter with the output of an inverter coupled to the low-level detector circuit, and logic means coupled to the comparator for resetting the counter and switching off a lamp controlled by the apparatus for a fixed interval, every time the number reached by the counter has a predetermined relationship with the output from the low-level detector circuit.
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11. Apparatus for controlling vehicle lamps in dependence upon the intensity of electrical street lighting supplied from an alternating current source, comprising conversion means including light-sensitive means, the conversion means being constructed to provide an output signal dependent on the amplitude of intensity variations at twice the frequency of the alternating current source in light incident on the vehicle from sources remote from the vehicle but independent of any substantially constant intensity component in said incident light, and control means for controlling a vehicle lamp in dependence upon a characteristic of the said output signal of the conversion means, wherein the light sensitive means provides a unidirectional signal dependent upon the intensity of light incident on the vehicle, and the conversion means includes an alternating current amplifier, coupled to receive the unidirectional signal, for providing the said output signal of the conversion means in the form of an alternating current signal, the amplitude of which is proportional to the amplitude of the said intensity variations, wherein the said characteristic is the magnitude of amplitude minima in the alternating current signal and the control means includes detector means for providing a square-wave signal, the mark/space ratio of which depends on the amplitude of the alternating current signal, the detector means being connected to charge and discharge a capacitor alternately, the durations of charge and discharge intervals being dependent on the said mark/space ratio, and peak detector means for detecting peaks in the voltage across the capacitor, the apparatus being such that the magnitudes of the said peaks are proportional to minima in the said intensity variations, and wherein the control means includes voltage-comparison means for comparing a rising voltage with the output voltage from the peak detector circuit, and a monostable circuit coupled to the voltagecomparison means to enter its quasi-stable state each time the rising voltage equals the said output voltage, the monostable circuit being coupled to switch off the said lamp when in the quasi-stable state, and the rising voltage commencing to rise from a predetermined value each time the monostable circuit enters its stable state.
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12. Apparatus for controlling the intensity of vehicle lamps in dependence upon the intensity of electrical street lighting supplied from an alternating current source, comprising conversion means including light sensitive means, the conversion means providing an electrical output signal dependent on the amplitude of intensity variations at twice the frequency of the alternating current source in light incident on the vehicle from said alternating current source in light incident on the vehicle from said alternating current supplied lighting remote from the vehicle, said output signal from said conversion means being independent of any constant intensity component in the said incident light, and control means for controlling a lamp, including means for providing a control signal inversely dependent upon the magnitude of minima in the amplitude of the said alternating current output signal from the conversion means but substantially independent of the magnitude of amplitude maxima in the said alternating current output signal and means for rendering the intensity of the vehicle lamp proportional to the said control signal.
Specification