Control apparatus for vehicle directional lamps

Claim 1

In a direction indicating system in which either one of two lamp groups, each thereof having at least front, rear and side directional lamps connected in parallel with each other, is energized by a battery and flash periodically for indicating the turning direction of a vehicle and in which the wattage of at least the side directional lamps is different from the said front and rear lamps in the respective groups, improved control apparatus comprising: a resistor, connected in series with said battery, for developing a voltage thereacross corresponding to the electric current flowing from said battery to an energized one of said lamp groups; an amplifier, connected to be responsive to said voltage developed across said resistor, for producing an output signal having a first constant level indicative of no disconnection of said front, rear and side directional lamps of said energized group, a second constant level indicative of the disconnection of at least one of said front and rear directional lamps of said energized group, and a third level intermediate between said first and second constant levels and indicative of the disconnection of said side directional lamp of said energized group; a pulse signal generator, connected to be responsive to said output signal of said amplifier, for generating a train of pulse signals at first, second and third frequencies in response to said first, second and third levels of said output signal, respectively; and switching means, connected to be responsive to said pulse signals, for energizing said lamp group periodically, whereby the flashing frequency of said lamp group is changed in accordance with lamp disconnections, said pulse generator including: a constant current circuit for producing constant charging and discharging currents; a capacitor, connected to be charged and discharged by said respective constant charging and discharging currents, for producing a triangular signal; and a comparison circuit, connected to alternately compare the level of said triangular signal with predetermined high and low levels one of which is changed in accordance with said first, second and third levels of said output signal of said amplifier, for producing said pulse signals and allowing said constant current circuit to produce said charging and discharging currents alternately in synchronized relationship with said pulse signals.