GB2174559A

GB2174559A - Road vehicle lighting system

Info

Publication number: GB2174559A
Application number: GB08511250A
Authority: GB
Inventors: Edward Graham Phillips
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1985-05-02
Filing date: 1985-05-02
Publication date: 1986-11-05
Also published as: GB8511250D0; GB2174559B

Abstract

The system includes a control circuit for energising the dipped beam bulbs of the vehicle headlamps 14 whenever the lighting switch 10 is in the "sidelights only" position and the vehicle ignition switch 17 is on. The circuit includes a relay 15 which has a change-over contact 15a which connects a dimming resistor 16 in series with the dipped beam bulbs 14 D/B whenever the relay is energised. The relay has its winding connected in series with a transistor Q1, which is on whenever the ignition is on, across the side light supply. Another transistor Q2 is connected to turn transistor Q1 off whenever the headlights are directly energised via the lighting switch 10. The lighting switch 10 and dip switch used in the circuit may be of conventional construction and the arrangement prevents rear fog lights 18 being energised via the resistor 16. The transistor Q1, Q2 may be replaced by a reed relay (20), (Figure 2). <IMAGE>

Description

SPECIFICATION Road vehicle lighting systems This invention relates to road vehicle lighting systems of the general type in which a lighting switch is used to control selection of side and tail lights or headlights and an independent dip switch is used to control selection of dipped beam or main beam operation of the headlamps.

It is considered desirable to prevent driving of a vehicle with only side and tail lights energised and it has been proposed to make it obligatory for dimmed, dipped headlights to be used during driving.

The simplest way of accomplishing this requirement automatically is to provide a relay or like circuit to connect the dipped beam filaments of the headlights to the supply through a dimming resistor whenever the lighting switch is in the side and tail light position at the same time as the ignition switch is energised.

No modification to the conventional lighting switch and dip switch is required, but this scheme, although very simple, has the disadvantagethatwhenever dimmed, dipped headlight operation is selected, any rear fog lamps controlled by the lighting switch will also be energised dimly, if the switch controlling these has been left closed. Such switch normally connects the headlamp output terminal of the lighting switch to the rear fog lamps, so that the rear fog lamps can be used only when the headlights are energised.

It is accordingly an object of the invention to provide a lighting system in which the above mentioned problem is overcome without giving rise to a need for special lighting and/or dip switches.

A lighting system in accordance with the invention incorporates a relay having a change-over contact which in a first position connects the dipped beam terminals of the headlights to the dipped beam terminal of the dip switch and in a second position connects the dipped beam terminals of the headlights to a supply point via said resistor, and a control circuit for said relay connected to the ignition switch and the lighting switch such that the changeover contact thereof is moved to said first position only when the ignition switch is closed and the side lights are energised and the headlights are not energised.

Preferably the control circuit includes a switch means in series with the relay winding, the series circuit thus formed being connected between one of two terminals comprising the ignition switch output terminal and the side light output terminal of the lighting switch and ground, said switch means being controlled by a signal from the other of said two terminals and inhibiting means connected to the headlight output terminal of the lighting switch to inhibit energisation of the relay winding when the headlights are energised.

Conveniently said inhibiting means is connected to said switch means to render same non-conductive when the headlights are energised.

The switch means is conveniently a transistor the base of which is connected to the other of said two teminals to render it conductive when the voltage at such terminal is high. In this case the inhibiting means is preferably another transistor connected across the base-emitter of the first mentioned transistor and having its base connected to the headlight output terminal of the lighting switch so as to turn on said other transistor and divert the base current of the first mentioned transistor when the headlights are energised.

In the accompanying drawings Figure lisa circuit diagram of one example of the invention and Figure2 is a partial circuit diagram of another example of the invention.

The lighting system shown in Figure 1 includes a conventional lighting switch 10 which has an input terminal 10a connected to the vehicle battery, a side light output terminal 1 Ob connected to the side and tail lights 11, 12 and a headlight output terminal 11h connected to the common terminal 13a of a dip switch 13boa main beam outputterminal 13 ofthe switch 13 is connected to the main beam terminals ofthe headlights 14 and a dip beam outputterminal 13c of the dip switch 13 is connected via a changeover contact 1 5a of a relay 15 to the dip beam terminals of the headlights. The switch 10 has the usual three positions, namely an off position, a side light position and a side light + headlight position.

The relay 13 is provided to enable dimmed dipped operation of the headlights to be obtained in certain conditions. To this end the common terminal 1 sic of contact 15a is connected to the dipped beam input terminals of the headlights, the normally closed contact 1 sod is connected to the dip beam output terminal of the dip switch 13 and the normally open contact 15e is connected via a dimming resistor 16 to the battery. Thus when the relay 15 is not energised the dip beam headlight filaments are controlled by the lighting switch and the dip switch in series as usual. When relay 15 is energised, however, the dip beam filaments are energised via the resistor 16.

The relay 15 is associated with a control circuit which causes it to be energised only when the vehicle ignition switch 17 is closed and the lighting switch is in the side and tail lights only position. This circuit includes a diode D1 having its cathode connected to one end of the relay winding and its anode connected to the side light output terminal of lighting switch 10. Switch means in the form of an npn transistor Q1 is connected in series with the relay winding the collector of this transistor being connected to the other end of the relay winding and its emitter being connected to the electrical ground of the vehicle. The base of the transistor Q1 is connected by a resistor R1 to the cathode of a diode D2, the anode of which is connected to the output terminal of the ignition switch 17.A pull-down resistor R2 is connected between the cathode of diode D2 and ground so that transistor Q1 is positively turned off when the ignition switch is off.

For inhibiting operation of the above mentioned switch means a second npn transistor Q2 is provided which has its collector connected to the base of transistor Q1 and its emitter is grounded, so that when transistor Q2 is turned on any base current flowing to transistor Q1 is diverted. The base of transistor Q2 is connected by a resistor R3 to the cathode of a diode D3 which has its anode connected to the headlight output terminal lOc of the lighting switch 10. A pull-down resistor R4 is connected between the cathode of diode D3 and ground.

A current recirculating diode D4 is connected across the relay winding and a protective zener diode is connected across the transistor Q1 for the usual reasons, i.e. to protect the transistor Q1 against any high voltage spike which may occur when current in transistor Q1 is interrupted.

In use, the relay is de-energised except when the ignition is on and the lighting switch is in the side and tail lights only position. In these circumstances transistor Q1 is turned on and current flows through the lighting switch 10 the diode D1, the relay winding and the transistor Q1 in series. Dimmed dipped operation of the headlights is therefore provided. If the lighting switch 10 is now moved to its head and side lights position, the transistor Q2 is turned on, thereby turning off the transistor Q1 and deenergising relay 15. The headlights are thereby placed under the control of the dip switch 13.

It will be noted that the relay 15 isolates the dip beam filaments from the headlight output terminal 1 Oc whenever dimmed dipped operation is selected.

Thus there is no possibility of any rearfog lamps 18 connected to this terminal 1 Oc being energised via the resistor 16.

Many changes may be made to the relay control circuit. For example, diodes D1 and D2 may be connected to the ignition switch and the lighting switch respectively instead of the reverse. Relays may be used instead of the transistors.

Figure 2 shows a second example of the invention in which a relay 20 is used instead oftransistor switches. The relay 20, which may be of the sealed reed type having a single normally open contact pair 20a, has its winding connected between the cathodes of the diodes D2 and D3,the cathode of diode D3 being connected to ground by a resistor R5.

The normally open contact 20a is connected between the anode of diode D1 and the main relay winding 15. The relay winding 20 has a relatively high resistance (e.g. several hundred ohms) and has an operating voltage significantly lower than the supply voltage (e.g. a 6V relay can be used in a 12V system). The resistor R5 thus operates in the side lights and ignition on condition to limit the current in the relay winding 20 and reduce the voltage across it. When the head lamps are energised both ends of the relay winding 20 are at the same voltage so that relay 20 drops out. The energy dissipated in resistor R5 in this condition is not excessive.

Claims

1. A road vehicle lighting system of the type specified which includes a relay having a changeover contact which in a first position connects the dipped beam terminals of the headlights to the dipped beam terminal of the dip switch and in a second position connects the dipped beam terminals of the headlights to a supply point via said resistor, and a control circuit for said relay connected to the ignition switch and the lighting switch such that said change-over contact thereof is moved to said first position only when the ignition switch is closed and the side lights are energised and the headlights are not energised.

2. A road vehicle lighting system as claimed in claim 1 which said control circuit includes a switch means in series with the relay winding, the series circuit thus formed being connected between one of two terminals comprising the ignition switch output terminal and the side light output terminal of the lighting switch and ground, said switch means being controlled by a signal from the other of said two terminals and inhibiting means connected to the headlight output terminal of the lighting switch to inhibit energisation of the relay winding when the headlights are energised.

3. A road vehicle lighting system as claimed in claim 2 in which said inhibiting means is connected to said switch means to render same non-conductive when the headlights are energised.

4. A road vehicle lighting system as claimed in claim 3 in which said switch means is a transistor, the base of which is connected to the other of said two terminals, so as to render the transistor conductive when the voltage at such terminal is high.

5. A road vehicle lighting system as claimed in claim 4 in which the inhibiting means is another transistor having its collector-emitter path connected across the base emitter of the first-mentioned transistor and having its base connected to the headlightoutputterminal of the lighting switch so as to turn on said other transistor and divert the base current of the first mentioned transistor when the headlights are energised.

6. A road vehicle lighting system substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

7. A road vehicle lighting system substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.