DIM-DIP HEADLIGHT CIRCUIT

Abstract: Some, but not all, of a vehicle's alternator (A) phase out­ puts are summed by parallel diodes (D1, D2) to provide an accurately reduced power output for dim-dip to the dipped beam filaments (D) of the vehicle's headlights. Preferably the dim-dip power is energized by a relay switch (R1) whenever the sidelights (S) are powdered, provided that the main beam (M) is not also powered. The selection of alternator phase outputs to obtain reduced power provides greater accuracy in the dim-dip power attenuation than previously available with series resis­ tors or by chopping techniques.

Description: DIM-DIP HEADLIGHT CIRCUIT This invention relates to an electric circuit for vehicle headlights enabling a "dim-dip" mode of operation. It has been proposed that in addition to a main beam headlight, a dipped beam headlight and side-lights or parking lights, a vehicle should have a "di-dp" beam. This "dim-dip" beam would be provided by the existing dipped beam headlights, but at a reduced power of perhaps 50% or 67% of full power. Several methods of adapting the existing vehicle circuitry have been proposed to achieve this effect, by introducing series resistances or by "chopping", but suffer from unacceptably wide tolerances in the output power during "dim-dip" operation. According to the present invention, an electric circuit for supplying reduced power to a vehicle headlight comprises an alternator having multiple phase outputs, and is characterized by one or more diodes connected in the same sense in parallel between respective alternator phase outputs and a common output junction, the number of phase outputs connected to the common junction being less than the total number of phase outputs available from the alternator, a line for connecting the output junction to the headlight, and a switch in series in the connecting line. Thus the alternator is used additionally to provide, on demand, a reduced power output to the headlight, which is preferably the dipped-beam headlight. Not all the phases of the alternator are used: a suitable combination of one or more phases is used to provide to the headlight an accurate proportion of the maximum power which is provided during conventional dipped-beam or main beam operation by way of an independent circuit. The switch is preferably operated automatically to close whenever the vehicle side-lights are on. In the preferred embodiment, this is achieved by a relay switch, energized when the side-lights are powered. - It is also preferable that the dipped-beam is extinguished when the vehicle main beam is energized; the "dim-dip" power supply to the dipped-beam is therefore preferably switched off automatically when the main beam is energized. In the preferred embodiment, the relay switch is connected to be controlled by both the main beam circuit and the side-light circuit so that when both are energized the relay switch is open, but when only the side-light circuit is energized the relay switch is closed, supplying "dim-dip" power. The preferred embodiment of the invention will now be described with reference to the accompanying drawing which is a partial circuit diagram of the vehicle lighting circuit. Switch S1 controls the supply of power to sidelights S, via terminal PS, or sidelights and headlights together, via terminals PS and PH. With switch S1 at terminal PO, all lights are switched off. Switch S2 selects either a main beam filament M, via terminal PM, a dipped beam filament D, via terminal PD, to be energized when switch Sl is at terminals PS and PH. An independent circuit supplies reduced power to the dipped beam filament D from just two phases of a vehicle alternator A, by way of diodes Dl, D2 connected in parallel between respective alternator output terminals and a common junction, and a connecting line. Because just two of the three phases are summed, for the so-called "dim-dip" mode of lighting, the power is reduced to approximately 67% of the full available power. Clearly other combinations of phases are possible, by selecting and summing one or more phases of any multiple phase alternator, but not using all of the phase outputs. Where one phase only is used, diode D2 would be unnecessary. It may be found necessary to incorporate a resistor R in series in the connecting line, in order to attenuate the output to the dipped beam filament for "dim-dip" operation. The degree of attenuation provided by resistor R will still be substantially smaller than that introduced by using fewer than the maximum number of alternator phase outputs. Thus the advantage of the invention of avoiding wide tolerances in the dim-dip power is still present. A relay switch Rl controls the supply of "dim-dip" power to the dipped beam filament D. The relay switch R1 is controlled by a winding connected in both the sidelight S supply circuit and the main beam M supply circuit. When just the sidelights S are on, the relay RI sees the supply voltage at only one side, and closes thus energizing the "dim-dip" beam. When both the sidelights and the main beam are on, the relay sees the supply voltage at both sides and opens the switch, turning the "dim-dip" beam off.When the dipped beam D is turned on by switches Sl and S2, the full power is supplied to the dipped beam filament and the "dim-dip" supply does not have to be disconnected since it is effectively overridden. The relay switch thus ensures that the "dim-dip" beam is on whenever the sidelights are on without full headlights, except when the engine is off for parking. Moreover the "dim-dip" is extinguished when the main beam is on, avoiding excessive heat build-up.

Claims: CLAIMS 1. An electric circuit for supplying reduced power to a vehicle headlight (D), comprising an alternator (A) having multiple phase outputs, and characterized by one or more diodes (Dl, D2) connected in the same sense in parallel between respective alternator phase outputs and a common output junction, the number of phase outputs connected to the common junction being less than the total number of phase outputs available from the alternator, a line for connecting the output junction to the headlight, and a switch (Rl) in series in the connecting line. 2. A circuit in accordance with Claim 1, wherein the switch (Rl) is controlled automatically to close in response to the energization of the vehicle's sidelights. 3. A circuit in accordance with Claim 2, wherein the switch (Rl) is -controlled automatically to open in response to the energization of a main beam headlight (M). 4. A circuit in accordance with Claim 3, wherein the switch (Rl) is operated by a relay connected in the circuits supplying power to the sidelights (S) and to the main beam headlights (M). 5. A circuit in accordance with Claim 4, wherein the relay. (RI) is connected between the power supply (PS) to the sidelights and the power supply (PM) to the main beam headlight (M), such that the relay opens the switch in response to the main beam energization. 6. A circuit in accordance with any of Claims 1 to 5, wherein the alternator (A) has three phase outputs, only one of which is connected via a diode (Dl) to the said common junction. 7. A circuit in accordance with any of Claims 1 to 5, wherein the alternator (A) has three phase outputs, only two of which are connected via two respective similarly-poled diodes (D1, D2) to the said common junction. 8. A vehicle having a sidelight (S) and a headlight (M, D), and characterized by an electrical circuit according to -any preceding claim.

Inventors: JONES, MARTIN E.
Applicants: LEYLAND VEHICLES LIMITED
Application year: 1984
Main classification: H05B37
IPC codes: B60Q1, H05B39