GB2295891A

GB2295891A - Automatic anti-dazzle control of vehicle lights

Info

Publication number: GB2295891A
Application number: GB9525045A
Authority: GB
Inventors: Alexander Stewart
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-12-07
Filing date: 1995-12-07
Publication date: 1996-06-12
Also published as: GB9525045D0; GB9424702D0

Abstract

A light control system for temporarily switching off a rear fog light when a rear-facing light sensor (18) is illuminated by the headlights of a following vehicle. With increasing illumination, the resistance of the sensor (18) falls and so increases the voltage at the junction (22) between the sensor (18) and an adjustable resistor (20) to a level at which a threshold-switching amplifier (24) changes output state. After a time delay set by circuit (28), a further amplifier (46) responds to open contacts (10) and so switch off the fog light. When the sensor (18) is no longer illuminated, the contacts (10) re-close after a short time delay. A daylight sensor (60) can provide over-ride of the anti-dazzle control. The anti-dazzle control circuit can alternatively or additionally be applied to temporarily switching off a front fog light and/or dipping headlights. <IMAGE>

Description

"A Control System" This invention relates to a control system, and relates more particularly but not exclusively to an anti-dazzle light control system for controlling the light or lights of a road vehicle to avoid or mitigate dazzling of other road users by the controlled light(s).

It is known for road vehicles to utilise a form of lighting known as a "rear fog light" by which is meant a rearwardly directed spotlight emitting a bright red light when switched on. A rear fog light is considered to be useful in conditions of poor visibility, such as fog or falling snow, for the purpose of alerting the drivers of other vehicles which are behind and approaching the vehicle carrying the rear fog light.

However, once a following vehicle has approached the vehicle carrying an illuminated rear fog light, it can be assumed that the driver of the following vehicle is now aware of the vehicle in front, such that continued illumination of the rear fog light is no longer necessary. Indeed, continued illumination of the rear fog light in such circumstances is counter-productive to safety in that there is now a risk that the following driver will be dazzled. While the driver of the vehicle using the fog light could, in theory, switch off the fog light, such control requires appreciation of rearward traffic at a time when the driver is necessarily concentrating on driving through poor forward visibility.Also, it is necessary for a switched-off fog light to be switched on again in suitable conditions (eg if the following vehicle has overtaken or turned off the route), if the safety advantages of the rear fog light are not to be lost by failure to operate the light.

Analogous considerations apply to the control of a front fog light and the forwardly directed vehicle headlights, particularly in switching the headlights between "full beam" and "dipped beam".

In accordance with a first aspect of the present invention a control system for automatically controlling light emitted from a vehicle light source comprises an incident light sensor mounted on the vehicle to sense light incident on the vehicle from a direction generally corresponding to the opposite direction to the light emitted by the vehicle light source, and a control device coupled to the light sensor and to the vehicle light source, the control device controlling the light emitted by the vehicle light source in response to signals received from the sensor.

Typically, the control device may control the light emitted by the light source by controlling the power of the light emitted and/or by controlling the direction of the light emitted. Preferably, the sensor outputs a signal to the control device when the power of incident light is greater than a threshold level, and the control device reduces the power of the light emitted and/or changes the direction of the light emitted when the incident light power is above the threshold level.

Restoration of the original light power and/or direction of the light source is preferably achieved by reversal of the procedure or combination of procedures utilised to reduce the level or change of direction of light emitted by the vehicle light source in the said direction.

A reduction in the power of light produced by the light source may be brought about by reducing the level of power supplied to the light source, or by terminating the supply of power to the light source.

The direction of light emitted by the light source may be altered by re-directing a beam-forming part of the light source, or by extinguishing one lamp within the light source and thereupon lighting another lamp within the light source.

The control system preferably further comprises an ambient light sensor disposed on the vehicle to respond to ambient light, the control device being coupled to the ambient light sensor to respond to the sensing by the ambient light sensor of at least a predetermined intensity of ambient light, the response of the control device thereupon being to over-ride the response otherwise made to the incident light sensor such as to inhibit reduction of the level of light emitted by the vehicle light source in the said direction. The ambient light may be natural light.

The control system preferably further comprises timing means effective on the control device to delay responses to the incident light sensor means by a predetermined period of time, which period may be the same or different according to the direction of transition of the predetermined intensity of external light sensed by the incident light sensor.

The vehicle light source may comprise a single light source, for example a spotlight or fog light, or the vehicle light source may comprise two or more light sources arranged for conjoint operation, for example, a pair of vehicle headlights.

Preferably, the control system may control two or more vehicle light sources located on different portions of the vehicle. In this case, the system may comprise a sensor mounted on each portion, the sensors being coupled to the control device and the control device being coupled to each light source to be controlled, and the control device controlling each light source in response to signals received from the respective sensor.

One of the vehicle light sources may be a rearwardly directed fog light, and the other of the vehicle light sources may be a forwardly directed fog light or headlight system comprising one light or a plurality of lights mutually linked for conjoint operation.

In accordance with a second aspect of the present invention there is provided a vehicle comprising an externally visible vehicle light source, a power source for providing a supply of illuminating power to the light source, and a control system according to the first aspect of the present invention.

The vehicle may be a road vehicle of any nature, in particular a self-propelled vehicle for the carriage of people and/or goods.

In the case where the vehicle is a car, van, or lorry, the control system is particularly applicable to antidazzle control of the vehicle's rear fog light by switching it off when sensing the headlights of a following vehicle, and (where so applied) to antidazzle control of headlight dipping and/or anti-dazzle control of a front fog light of the vehicle when sensing the headlights of an oncoming vehicle. Where the control system comprises the ambient light sensor, this can be used to sense daylight and over-ride the anti-dazzle control to keep the fog light(s) on continuously.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings wherein: - Fig. 1 is an electric circuit diagram of a control system for providing automatic anti-dazzle control of a rear fog light; and Fig. 2 is an electric circuit diagram of a control system for providing automatic independent anti dazzle control of headlights and a rear fog light.

Referring first to Fig. 1, a rear fog light (not shown in Fig. 1) is controlled by normally-closed contacts 10 within a relay 12 (shown schematically) whose operating coil is shunted by a free-wheeling diode 14. One side of the coil of the relay 12 is connected to the positive supply +V, and the other side of the coil is connected through a transistor 16 (or any other suitable controllable current-switching device) to the supply return 0V.

When the transistor 16 is rendered conductive, the relay 12 is energised and the normally-closed contacts 10 open. This action disables the fog lamp to prevent it being illuminated. The fog lamp is otherwise under the control of the driver of the vehicle (not shown) upon which the fog lamp is mounted to shine rearwardly when in operation. Operation of the relay 12 to switch off the fog lamp under the control of the anti-dazzle circuit shown in Fig. 1 (and detailed below) relieves the driver of the need for continuous monitoring and reaction to prevent the fog light dazzling other drivers approaching the rear of the vehicle.

A light sensor 18 is mounted at a suitable location on the vehicle such that the headlights of other vehicles approaching the vehicle from the rear shine on the sensor 18. It is assumed that the more brightly do headlights shine on the rear of the vehicle and hence on the sensor 18, the closer is the approaching vehicle and the greater the need to avoid dazzling the driver of the approaching vehicle by continued operation of the fog light which is presumed then to be temporarily unnecessary by reason of the headlights directly illuminating the vehicle having the fog light such as temporarily to render the fog light redundant. (This assumption, which is inherent in the operation of the anti-dazzle circuit, automatically mimics the response of a human exercising equivalent manual control).The light sensor 18 is a two-terminal photosensitive resistor connected in series with a variable resistor 20 between the supply +V and the return 0V. The through resistance of the sensor 18 falls with increasing intensity of illumination of the sensor 18.

Consequently, the voltage at the junction 22 between the sensor 18 and the resistor 20 rises as illumination intensity increases.

The illumination-dependent voltage at the junction 22 is sensed by a threshold-switching inverting amplifier 24 which switches its output 26 "low" (close to the supply return 0V) when the voltage at the junction 22 rises above a threshold level. Conversely, the circuit output 26 goes "high" (close to the supply voltage +V) when the voltage at the junction 22 falls below the threshold level. Power connections to the amplifier 24 are omitted from Fig. 1 for clarity.

Suitable adjustment of the variable resistor 20 enables the switching point of the amplifier 24 to be set at a predetermined intensity of illumination of the sensor 18, as well as enabling compensation for manufacturing tolerances and sensitivity variations in the various components.

As depicted in Fig. 1, the amplifier 24 is formed as a two-input NOR gate having its inputs strapped together such that the NOR gate functions as an inverting amplifier. The amplifier output 26 will source current when "high" and will sink current when "low".

The output 26 from the light-switched amplifier 24 is fed through a dual time delay circuit 28 comprising a capacitor 30 and a resistor 32 connected in series between the supply +V and the return 0V. The junction 34 between the capacitor 30 and the resistor 32 is coupled to the amplifier output 26 in one direction of current flow between 26 and 34 through the series combination of a variable resistor 36 and a diode 38, and coupled in the other direction of current flow between 26 and 34 through the series combination of a variable resistor 40 and a diode 42.

When the amplifier output 26 is "high", the capacitor 30 charges up through the resistor 36 and the diode 38.

Conversely, when the amplifier output 26 is "low", the capacitor 30 discharges through the diode 42 and the resistor 40. Thus the diodes 38 and 42 steer the current to/from the timing capacitor 30 according to whether the amplifier output 26 has just gone "high" or "low", and correspondingly allow different timing periods according to whether illumination of the sensor 18 has just exceeded or fallen below the threshold intensity. These timing periods are respectively and independently set by suitable adjustment of the resistors 36 and 40 respectively.

The junction 34 serves as the output of the dual timing circuit 28, and the junction voltage is fed via a series buffer resistance 44 to a threshold-switching inverting amplifier 46 which is the same as or substantially similar to the amplifier 24 in form and function. The output 48 of the amplifier 46 is fed through a current-limiting series resistor 50 to the base of the relay-operating transistor 16.

In operation of the Fig. 1 circuit as so far described, varying levels of light on the sensor 18 result, if the illumination intensity threshold is passed in one direction or the other, in switching of the relay 12 after predetermined time delays following threshold crossing. When the circuit is suitably set up, and the fog light switched on (through the normally-closed contacts 10) by means of a separate driver-operated switch (not shown), with simultaneous concomitant energisation of the circuit of Fig. 1, the rear fog light will operate normally until such time as the headlights of a following vehicle shine on the sensor 18. Then the resistance of the light-dependent resistor forming the light-sensitive component of the sensor 18 falls and the voltage on the circuit junction 22 rises until the output 26 of the inverting amplifier 24 switches from "high" to "low".Current then sinks through the amplifier 24, the resistor 40 and the diode 42 from the circuit junction 34. After a short period of time (eg 2 seconds) set by the capacitance of the capacitor 30 and the resistance of the variable resistor 40, the output 48 of the inverting amplifier 46 switches from "low" and "high" and thereby injects current into the base/emitter junction of the transistor 26 to conduce collector/emitter current and energise the coil of the relay 12 to open the normallyclosed contacts 10.This switches off the rear fog light, thus minimising or avoiding dazzling of the driver of the following vehicle. (It is assumed that the following driver is now aware of the vehicle carrying the controlled rear fog light since it will be in the headlights of the by now close following vehicle, such that the continued illumination of the rear fog light is no longer necessary as a safety measure to enhance distant visibility and continued illumination would be counter-productive to safety by reason of dazzle). The time delay between headlight detection and fog light extinction gives the following driver adequate time to register the presence of the preceding vehicle before the rear fog light goes out.

When the sensor 18 is no longer illuminated (eg because the two vehicles diverge on difference routes, or the following vehicle stops or overtakes), the resistance in the current path through the sensor 18 rises, the voltage at the junction 22 falls, and the output 26 of the amplifier 24 switches from "low" to "high". The amplifier 24 now sources current through the resistor 36 and the diode 38 to the circuit junction 34 whose voltage rises in consequence at a rate determined partly by the capacitance of the capacitor 30 and partly by the setting of the variable resistor 36.

After a short period of time (eg 1 second), the voltage at the input to the inverting amplier 46 has risen to the level at which the amplifier output 48 switches from "high" to "low". The transistor 16 then ceases conduction, the coil of the relay 12 is de-energised, and the temporarily open contacts 10 re-close to switch the rear fog light on again.

The time delay in switching the rear fog light on again allows for momentary interruption of the light from the following vehicle, eg due to bends and/or slopes in the road, and due to pitching of the following vehicle on hitting bumps and potholes.

The "on" delay and the "off" delay together prevent flashing of the rear fog light arising from transient illumination of the sensor 18.

During daylight hours dazzling is not as big a problem as at night time, and therefore the rear fog light may be left on even when the sensor 18 is illuminated by the headlights of a following vehicle. In order to over-ride the automatic anti-dazzle control function described above, the circuit so far described with reference to Fig. 1 is provided with a daylight sensor 60 which inhibits switching of the relay 12 in the manner now to be detailed.

The daylight sensor 60 comprises a photosensitive resistor similar or identical to the sensor 18 and is connected into a similar voltage-sensing circuit (but which lacks discrete time delays). The sensor 60 is connected in series with a variable resistor 62 between the supply +V and the return 0V. The sensor 60 is mounted on the vehicle carrying the rear fog light and its control circuit in a position and attitude to sense daylight or other ambient light (eg from floodlights or high-intensity highway lighting), such that as daylight or other ambient light around the vehicle increases, the through resistance of the sensor 60 falls and voltage rises at the junction 64 of the sensor 60 with the resistor 62.

An inverting amplifier 66 (which is essentially identical to the inverting amplifier 24 and may be another gate on a quad-NOR I.C.) is coupled to the circuit junction 64 such that as illumination of the sensor 60 increases to reduce its resistance, the voltage at 64 rises and the output 68 of the amplifier 66 will eventually switch from "high" to "low". The inverting amplifier 66 is cascaded with another inverting amplifier 70 whose input is the output 68 of the amplifier 66. The output 72 of the amplifier 70 switches from "low" to "high" as the output 68 of the amplifier 66 switches from "high" to "low" and viceversa.In short, as ambient illumination of the sensor 60 increases past a threshold level (variable by selective variation of the resistance of the variable resistor 62), the output 72 will correspondingly switch from "low" to "high", and vice versa as illumination falls below the threshold.

The output 72 is fed via a signal diode 74 to the input to the amplifier 46. When the output 72 is "high", the input to the amplifier 46 is held "high" and consequently the amplifier output 48 is held "low", so preventing energisation of the relay 12, regardless of the current level of illumination of the rear light sensor 18 and by any resultant control signal. Thus a sufficient level of daylight or other ambient light (settable by adjustment of the resistor 62) prevents the anti-dazzle switch-off of the rear fog light.

On the other hand, when the level of daylight is low or non-existent (eg in fog or at night), the resistance of the sensor 60 is high and consequently the output 72 is "low". The diode 74 is then back-biassed, preventing the signal from the rear sensor 18 (via the amplifier 24 and the timing circuit 28) from being spuriously held "low". Thus in poor light or darkness, the circuit is freed to exert automatic anti-dazzle control as previously described.

As an alternative to anti-dazzle control of a rear fog light, the circuit of Fig. 1 can be adapted to the automatic anti-dazzle control of headlights having alternative "main beam" and "dipped beam" settings, by re-mounting the sensor 18 to sense the headlights of oncoming vehicles, and by re-wiring the relay 12 to switch the headlights from "main beam" (with the sensor 18 unilluminated and the relay 12 de-energised) to "dipped beam" (with the sensor 18 illuminated above a pre-set threshold, and the relay 12 energised).

Fig. 2 illustrates the circuit diagram of an adaptation of the anti-dazzle control circuit of Fig. 1 to form a control circuit for the simultaneous and independent anti-dazzle control of two separate lights or light circuits (eg a rear fog light and front headlights).

As shown in Fig. 2, the circuitry continued within the block "R" is essentially the same as the rear fog light anti-dazzle circuitry 10 - 50 of Fig. 1 (except for the omission of resistors equivalent to the resistors 32 and 44), and the circuitry contained within the block "D" is essentially the same as the daylight over-ride circuitry 60-74 of Fig. 1.

The circuitry contained within the block "F" in Fig. 2 is a duplicate of the circuitry within the block "R", and has a matching connection to the daylight over-ride circuitry in block "D".

The respective sensors in blocks "R" and "F" are directed to the rear and front of the vehicle respectively, the respective relays being connected to switch the rear fog lights off and on, and the headlights between dipped beam and main beam respectively. Although automatic anti-dazzle control of rear and front lights is effected at the same time, the rear and front lights are controlled independently of each other, in accordance with the sensing of headlights from behind or in front.

It is preferably arranged that use of the anti-dazzle control circuit does not prevent use of the conventional headlight flashing circuit by which the main beam can be momentarily switched on by manually over-riding a biassed-off switch.

When using the circuit of Fig. 2 , or using the circuit of Fig. 1 for control of front lights, it has been stated that the front lights can be headlights whose direction and intensity are controlled by switching between main beam and dipped beam; these circuits can be utilised for the automatic anti-dazzle control of additional or alternative front light(s) in the form of one or more front fog lights controlled by being switched off and on.

While certain preferred embodiments and alternatives have been described above, the invention is not restricted thereto, and other modifications and variations can be adopted without departing from the scope of the invention as defined in the appended Claims.

Claims

A control system for automatically controlling

light emitted from a vehicle light source, the control system comprising an incident light sensor mounted on the vehicle to sense light incident on the vehicle from a generally opposite direction to the direction in which light is emitted by the vehicle light source, and a control device coupled to the light sensor and to the vehicle light source, the control device altering the light emitted by the vehicle light source in response to signals received from the sensor.

A control system according to claim 1, wherein the control device alters the light emitted by the vehicle light source when the power of the incident light is above a threshold level.

A control system according to claim 1 or claim 2, wherein the control device alters the power of the light emitted by the vehicle light source.

A control system according to claim 3, wherein the power of the light emitted by the vehicle light source is reduced by the control device.

A control system according to claim 4, wherein the power is reduced by reducing the level of power supplied to the light source, or by terminating the supply of power to the light source.

A control system according to any of claims 1 to 5, wherein the control device alters the direction of the light emitted by the vehicle light source.

A control system according to claim 6, wherein the direction of light emitted by the light source is altered by re-directing a beam-forming part of the light source, or by extinguishing one lamp within the light source and thereupon lighting another lamp within the light source.

A control system according to any of the preceding claims, wherein restoration of original light power and direction is achieved by reversal of the procedure or combination of procedures utilised to alter the light emitted by the vehicle light source.

A control system according to any of the preceding claims, wherein the control system further comprises an ambient light sensor disposed on the vehicle to respond to ambient light, the control device being coupled to the ambient light sensor to respond to the sensing by the ambient light sensor of at least a predetermined intensity of ambient light, the response of the control device thereupon being to over-ride the response otherwise made to the incident light sensor such as to inhibit reduction of the level of light emitted by the vehicle light source in the said direction.

A control system according to claim 9, wherein the ambient light is natural light.

A control system according to any of the preceding claims, wherein the control system further comprises a timing device coupled to the control device to delay responses to the incident light sensor by a predetermined period of time, which period may be the same or different according to the direction of transition of the predetermined intensity of incident light sensed by the incident light sensor.

A control system according to any of the preceding claims, wherein the vehicle light source comprises a single light, for example a spotlight or fog light.

A control system according to any of claims 1 to 11, wherein the vehicle light source comprises two or more lights arranged for conjoint operation.

A control system according to any of the preceding claims, the control system further comprising a second incident light sensor mounted on the vehicle, the second incident light sensor being coupled to the control device, and the control device being coupled to a second vehicle light source, the second sensor sensing light incident on the vehicl in a direction generally opposite to the direction in which light is emitted from the second light source, and the control device altering the second vehicle light source in response to signals received from the second sensor.

A control system as claimed in claim 14, wherein one of the vehicle lights is a rearwardly directed fog light, and the other of the vehicle lights is a forwardly directed fog light or headlight system comprising one light or a plurality of lights mutually linked for conjoint operation.

A vehicle comprising an externally visible vehicle light, a power source for providing a supply of illuminating power to the light, and a control system according to any of claims 1 to 15.

An anti-dazzle light control system for controlling the light or lights of a road vehicle to avoid or mitigate dazzling of other road users by the controlled light(s), substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.

A control system substantially as hereinbefore described with reference to any of the accompanying drawings.