GB2171862A - Vehicle dim-dip lighting device - Google Patents

Abstract

The device comprises an AND-gate 11 having inputs 12, 13 from the vehicle's ignition circuit and side/parking lighting circuit so as to sense when both the latter said circuits are energised and thereupon enable an oscillator 14 which when enabled provides a power output which fluctuates between a full or substantially full power condition and a zero or substantially zero power condition and which via semiconductor switch 15 makes the dipped beam filaments of the vehicle's headlamps emit light at a desired intensity. A delayed turn-off timer (23), (Figs. 3,4,6), may be provided to turn the dipped beam filaments on at full power for a predetermined time in response to the side/parking lights being turned off. Preferably the timer (23) is only enabled if the ignition switch has also been turned off. <IMAGE>

Description

SPECIFICATION Vehicle dim-dip lighting device This invention concerns vehicle dim-dip lighting devices, that is to say a device for connection to the headlamps of a motor vehicle for the purpose of reducing the normal intensity of a dipped beam of light emitted by each said headlamp.

A motor vehicle headlamp normally comprises a housing (usually recessed into the body of the vehicle) containing a paraboloid reflector, a twin-filament lamp mounted in a socket at the bottom of the paraboloid reflector and a light-diffusing glass cover. A low intensity parking light bulb can also be mounted on the reflector below the lamp.

With a reflector which is a paraboloid, all the rays of light emitted from one of the filaments of the lamp located at the focus of the paraboloid are reflected in a direction parallel with the axis of the reflector. This filament is the high or full beam filament of the headlamp.

The other one of the two filaments is the low or dipped beam filament of the headlamp. The low or dipped beam filament is a small distance in front of the focus and is shielded from underneath so that the light emitted by this filament is directed to the top of the reflector and is reflected as a downward directed spreading beam.

Vehicle headlamps if used on dipped beam are still bright enough even on well lit roads to cause dazzle to other road users, both travelling in front of the vehicle and on-coming.

Of course, it is quite obvious that dazzle can lead to accidents between vehicles.

In the United Kingdom an attempt has been made to remedy this situation by statute.

With certain exceptions, any motor vehicle which is manufactured on or after the 1st October 1986, and is first used on or after the 1st Apri! 1987, must either be fitted with a dim-dip lighting device or be provided with an additional (i.e. to the normal headlamps) pair of front lamps. The dim-dip lighting device must automatically operate whenever the obligatory parking or side lights (i.e. lights used to indicate the presence and width of a vehicle) are switched on and either (i) the engine of the vehicle is running or (ii) the key or devices which control the starting or stopping of the engine are in the normal position for driving the vehice.This is so that the dippedbeam filament of each obligatory head lamp can be energised such that the light output is approximately 10% of normal intensity in the case of a halogen-filament lamp and approximately 15% of normal intensity for any other type of filament lamp. This requirement could be met by using a dropper resistor in the lamp circuit. However, the power dissapation would be large and thus the surface temperature high, unless the resistor is of substantial size. In this case, the dropper resistor would be expensive. The high surface temperature of the resistor could cause injury to personnel working in its vicinity and would also be a potential fire risk. Furthermore, the value of the resistor would need to be selected for each different voltage and wattage of lamp and combination of lamps.

With respect to the statute being complied with by providing the vehicle with an additional large pair of front lamps, this form of compliance puts stringent demands and limitations on lamp size, position and maximum and minimum light intensities. The general consensus of opinion is that this method of compliance with the statute would be uneconomic.

An object of the present invention is to provide a dim-dip lighting device which complies with the statute as aforesaid, is also easy and inexpensive to manufacture and to install into new and existing motor vehicles, and is economic to operate, not least in terms of its power consumption.

With this object in view, the present invention provides a vehicle dim-dip lighting device comprising inputs from the vehicle's lighting circuit and ignition circuit and at least one output to dipped-beam filaments of the vehicle's headlamps, the device also comprising energisation means, associated with said inputs and the or each said output, for the dipped-beam filaments so that when both the lighting circuit and the ignition circuit are energised the or each said output fluctuates between full or substantially full power condition and zero or substantially zero power condition to achieve light emmision of a desired intensity from each of said filaments.

The fluctuation of power at said output is sufficiently rapid so that the light intensity of the filaments is substantially constant. In actuality, the dipped-beam filaments are switched on and off by the energisation means so rapidly that when on the filaments appear to be only partially on or dim. One advantage of this is that the reduction of energising power to the filaments can be determined by a pre-set ratio. This pre-set or on/off ratio determines the percentage power and thus the light intensity of the filaments. Thus the reduction of said light intensity is independent of lamp voltage and wattage. Hence, the device can be used for a variety of different types of headlamps e.g. 6 volt or 12 volt single headlamps, 12 volt pairs for cars and 24 volt headlamps for heavy goods vehicles and public service vehicles.

Another advantageous aspect of the device of the invention is that its power dissipation is low both in the high and low energisation state of the filaments. Thus its average power loss is low (it is energy efficient) and the termperature rise is moderate bearing in mind that the device is small and compact.

In the simplest form of the device of the present invention, the inputs are advantageously provided by a logic circuit having an AND-gate and the energisation means is advantageously an oscillator enabled by the output of the AND-gate. The or each output of the device to the dipped-beam filaments may be provided directly by the or each output of the oscillator or preferably by the or each output of a semi-conductor switch connected between the oscillator and the filaments and to which the or each output of the oscillator is first fed.

The energisation means can, in place of the oscillator, be a multi-vibrator if so desired.

Connection of the inputs is preferably to the side lights or the parking lights of the lighting dircuit and the oil pressure warning light or oil pressure switch of the ignition circuit.

The dim-dip lighting device of the invention meets statutory requirements for such devices, as aforesaid, in that the AND-gate of the logic circuit senses when lighting circuit is energised e.g. the side lights or the parking lights of the vehicle are on, and when the ignition circuit is energised e.g. when the oil pressure warning light goes out. Both of these latter two situations can only occur if the engine of the vehicle is switched on or at the very least when the ignition key is in the normal position for driving the vehicle. In fact sensing when the oil pressure warning light is de-energised is more favourable as this would prevent the device operating when starting the engine and thus eliminate undue drain on the vehicle battery when starting the vehicle with the parking lights on.The logic circuit of the device does not rely on power being drawn from the ignition or parking light circuits. Thus existing vehicle fuses and wiring does not need to be upgraded when fitting the device, making said device easy to fit even to older vehicles and vehicles with unmodified lighting circuits.

Connection of the device to existing vehicle electrical circuitry draws negligible current as they are just sensing lines for the logic circuit.

Power for the device can be obtained by adding a wire from the device to a permanent voltage feed. An inline fuse directly onto the vehicle battery can be used if a suitably fused permanent feed is not readily available or accessible.

The invention will be described further, by way of example, with reference to the accompanying drawings in which: Figure 1 is a block circuit diagram of a basic preferred embodiment of the vehicle dim-dip lighting device of the invention; Figure 2 is a schematic circuit diagram of an oscillator which forms part of the circuit of the device shown in Fig. 1; Figure 3 is a schematic circuit diagram of a delayed turn-off timer which can form part of the circuit of the basic preferred embodiment of Fig. 1; Figure 4 is a block circuit diagram of the embodiment of Fig. 1 connected to the delayed turn-off timer of Fig. 3; Figure 5 is a schematic circuit diagram of an ignition energisation and lighting energisation circuit which can be substituted for the ANDgate of the basic preferred embodiment of the circuit shown in Fig. 1;; Figure 6 is a schematic circuit diagram of an alternative preferred embodiment of the vehicle dim-dip lighting device of the invention; and Figure 7 is a schematic circuit diagram illustrating the way in which the preferred embodiments of the device of the invention can be fitted into the conventional vehicle lighting circuit.

Referring firstly to Fig. 1, the basic preferred embodiment of the vehicle dim-dip lighting device 10 comprises inputs in the form of a logic circuit provided by an AND-gate 11 having one input connection 12 to the obligatory vehicie's lighting circuit (e.g. side lights/parking lights) and another input connection 13 to the vehicle's ignition circuit (e.g. oil pressure warning light). The device 10 also comprises energisation means, for the dipped-beam filaments of the vehicle's headlamps, in the form of an oscillator 14 connected to and enabled by the AND-gate 11, the oscillator 14 in turn being connected to a semi-conductor switch 15 which has a direct connection 16 from the vehicle's battery and a direct connection 17 to the dipped-beam filament of each of the vehicie's headlamps.As the input connections 12, 13 to the AND-gate 11 carry very low level currents, the connection of the device 10 to the ignition circuit can be made to any point of said circuit that is only energised when the vehicle's ignition switch (not shown) is in its on position. For example, the connection could be made to the oil pressure warning light as aforesaid leading to the advantages already described.

When both the input connections 12, 13 of the AND-gate 11 are energised, the AND-gate 11 sends an enable signal to the oscillator 14.

When, enabled the oscillator 14 serves as an output of the device and supplies, via the semi-conductor switch 15, an alternating or fluctuating power output to the dipped-beam filaments of the headlamps for rapid substantially on/off energisation thereof. Said power output fluctuates between full or substantially full power condition and zero or substantially zero power condition. In effect this provides for rapid on/off switching of said filaments by the oscillator so that the filaments appear to be only partially on or dim. The on/off time or mark space ratio can be predetermined to give the required light intensity of the dimmed beams.

Referring now to Fig. 2, oscillator 14 consists of a logic gate known as a NAND Schmidt trigger 18. Said trigger 18 has a capacitor 19 which alternately charges and discharges between the upper and lower trip points of the trigger 18. To achieve the required mark space ratio, the charging and discharging paths of the capacitor 19 are made intentionally different in resistance value i.e.

charging through resistor 20 and discharging through resistor 20 and diode 21/resistor 22.

It is advantageous to provide the basic embodiment of the device 10 with a built in safety feature in the form of a delayed turn-off timer 23 shown in detail in Fig. 3. As the parking lights of the vehicle are turned off, the headlamps are turned on at full brightness and remain on for a set period of time. Thus when the driver of the vehicle get out of the vehicle, iilumination is automatically provided (to assist the driver and any other occupant to get safely to e.g. the garage or front door of the house). The headlamps are then extinguished automatically. In the preferred device 10 this feature only comes into operation if the ignition switch has been returned to its off position. In practice this feature also makes it less likely that the side/parking lights would be left on inadvertently.The delayed turn-off timer 23 utilises spare gates of NAND Schmidt trigger 24. Enabled input 25 to said latter gate 24 comes via an inverter 26 connected to the lighting circuit (line 13) e.g. side lights, so that the timer 23 is disabled until the side lights are turned off. The delay is achieved by a resistor 27 and a capacitor 28 on the other input 29 of the gate 24.

The input 13 can come direct from the sidelight circuit along line 30 (Figs. 3 and 4). The headlights would then come on for the set time period, if the side-lights were switched on and then off. However, if the input 13 is taken to the output of the AND-gate 11 the headlights would only come on if the ignition had been on in the meantime.

Both the preferred circuits of the oscillator 14 and the delayed turn-off timer 23 have inherently inverted outputs. Whilst Fig. 4 illustrates that the outputs of the oscillator 14 and the timer 23 are fed to an OR-gate 31, a practical circuit can utilize a NAND-gate immediately following those two inverted signals to reaiise an OR function (i.e. a NAND gate with inverted inputs in equivalent to an OR gate).

The output is thus activated by the oscillator 14 or the timer 23. The inverter can also be realised by using a NAND-gate with its two inputs connected together.

A suitable ignition energisation (i.e. sidelights energisation) detection circuit is readily provided. Such a circuit is shown in Fig. 5 and comprises a resistor 32 and a diode 33.

It should be noted that the output can only be energised if both the ignition and the side-light circuits are energised. That is, the circuit has the AND characteristic so the AND-gate (11-Fig. 1) can be replaced by the resistor and diode. Also provided is means for inhibiting the oscillator when full beam is on. This feature is preferred since the dim-dip beam is superfluous when the main beam is on, and would otherwise be wasteful. This means is provided by returning the supply current for the device to the full beam circuit instead of a direct return to the battery common (e.g.

chassis). When the full beam filaments are at the battery potential (on) no current will flow in the device.

Within a typical Schmidt trigger integrated circuit package (such as CMOS 400 SERIES, TYPE 4093) there are four gates. The description of the basic preferred device has referred to two NAND Schmidt trigger gates.

Shown in Fig. 6 is the circuit of an alternative preferred embodiment of the device of the invention. This embodiment of the device is indicated generally by the reference numeral 34. It will readily be seen that the device 34 comprises the ignition energisation detection circuit (diode 32 and resistor 33), the oscillator 14 and the delayed turn-off timer 23. The latter two components 14, 23 each have one NAND Schmidt trigger gates. The device 34 has two further NAND Schmidt trigger gates.

One of these gates 35 is equivalent to the inverter 26 of Fig. 3 in that it serves as an inverter for the delayed turn off timer 23. The other gate 36 receives inputs from the output of the timer 23 and from the output of the oscillator 14 and serves as a NAND gate. The output of the timer 23 is taken, via a diode 37 and a resistor 38, back to the ignition energisation detection circuit. This ensures that the timer 23 cannot operate whilst the vehicle is being driven (i.e. whilst ignition is on).

Fig. 6 also shows the circuit of the semiconductor switch 15 in detail. The switching is solid state and is performed by an N.P.N.

power transistor 39 (e.g. type BUV26) driven by a P.N.P. transistor 40 (e.g. type ZTX 752) in turn connected to a N.P.N. transistor 41 which itself receives the inverted output of NAND gate 36 via a resistor 42. One side of the transistor 41 is connected via a resistor 43 to line 44 to the main beam filaments of the headlamp.

Fig. 7 shows how the device (10 or 34) of the invention can be easily inserted into the typical existing lighting circuit wiring system of vehicles. In Fig. 7 component 45 indicates the vehicle's lighting switch, the inputs to the side lights are indicated by the letter A, the inputs to the main beam filaments by B, the inputs to the dipped beam filaments by C. The line to the device (10 or 34) from the ignition circuit (e.g. oil pressure warning switch is indicated by the reference numeral 13 and from the battery by reference numeral 16.

It will be appreciated that the device (10 or 34) can either be connected to the lighting switch 45 or direct to either one of the headlamps indicated by reference numerals 48, connection to one of the headlamps 48 effectively being connection to both headlamps because of their associated electrical wiring.

The integrated circuit forming the embodiment of the device 34 of Fig. 6 includes a safety device comprising a zenor diode 46 in line with a resistor 47 which limits the voltage supplied to the integrated circuit.

Claims (16)

1. A vehicle dim-dip lighting device comprising inputs from the vehicle's lighting circuit and ignition circuit and at least one output to dipped-beam filaments of the vehicle's headlamps, the device also comprising energisation means, associated with said inputs and the or each said output, for the dipped-beam filaments so that when both the lighting circuit and the ignition circuit are energised the or each said output fluctuates between full or substantially full power condition and zero or substantially zero power condition to achieve light emmision of a desired intensity from each of said filaments.

2. A device as claimed in claim 1 wherein the inputs are provided by a logic circuit having an AND-gate.

3. A device as claimed in claim 1 or 2 wherein the energisation means is an oscillator.

4. A device as claimed in claim 1 or 2 wherein the energisation means is a multi-vibrator.

5. A device as claimed in claims 1, 2 and 3, or in claims 1, 2 and 4, wherein the output of the energisation means is direct to the dipped beam filaments.

6. A device as claimed in claims 1, 2 and 3, or in claims 1, 2 and 4 wherein the output of the energisation means is to a semi-conductor switch connected between the energisation means and the dipped beam filaments.

7. A device as claimed in claim 3 wherein the oscillator consists of a logic gate known as a NAND Schmidt trigger, said trigger having a capacitor which alternately charges and discharges between the upper and lower trip points of the trigger.

8. A device as claimed in claim 7 wherein to achieve the required mark space ratio the charging and discharging paths of the capacitor are made intentionally different in resistance value, the charging path being through a resistor and the discharging path through a resistor and a diode/resistor combination.

9. A device as claimed in any preceding claim wherein it is further provided with a delayed turn off timer consisting of a NAND Schmidt trigger one input of which comes via an inverter connected to the lighting circuit and the other input of which comes from the AND gate via a resistor and a capacitor.

10. A device as claimed in any preceding claim wherein the outputs of the energisation means and the timer are fed to an OR-gate, or a NAND gate which can realise an OR function, prior to being fed to the semi-conductor switch.

11. A device as claimed in claim 1 wherein the inputs are provided by an ignition energisation detection circuit comprising a resistor and a diode.

12. A device as claimed in claim 9 wherein the inverter for the timer is provided by a NAND Schmidt trigger.

13. A device as claimed in claim 12 wherein the output of the NAND Schmidt trigger is taken via a diode and a resistor back to the ignition energisation detection circuit.

14. A device as claimed in claim 10 wherein the OR-gate or NAND gate is provided by a NAND Schmidt trigger.

15. A device as claimed in claim 6 wherein the semi-conductor switch comprises solid state switching performed by an N.P.N. power transistor driven by a P.N.P. transistor.

16. A vehicle dim-dip lighting device substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 4 and 7, or in Figs. 5, 6 and 7 of the accompanying drawings.