GB2267564A - Automatic vehicle headlamp dipswitch - Google Patents

Abstract

The automatic vehicle head lamp dipswitch uses a simple 'fish eye' lens system 1 to form a small real image of the road ahead on the surface of a set of closely-spaced silicon photodiodes 3. If the image of an oncoming vehicle's headlights is formed on one of the photodiodes, its output will be greater than the others. The signal from each photodiode is compared electronically with a reference signal derived from the averaged output of all the photodiodes. If any is greater than this reference signal, then the vehicle's headlights are automatically dipped if they have not been dipped already by the driver. Provision is also made to prevent malfunction due to the light from oncoming vehicles being interrupted for short time intervals by obstacles, and also by excessive light levels falling on the photodiodes. <IMAGE>

Description

Automatic Vehicle Headlamp Dipswitch.

This invention is an automatic vehicle headlamp dipswitch, suitavle for any vehicle, which will dip the headlights of the vehicle to which it is fitted when the Unit detects the presence of oncomig. vehicle headlights.

Most vehicles are equippe with a manually operated dip switch; some with a foot operated dip switch.

Both present difficulties to the night hriver. The driver may be cornering, turning, changing gear, or some other operation when the headlights need to be dipped because of the presence of an oncoming wehicle.

Solutions to this problem usually involve the detection of light from the oncoming vehicle using a simple light sensor such as a photodiode, light dependent resistor, phototransistor or photocell. These usually do not work well because the illumination from a distant car headlamp can be as little as 1 or 2 Lux.

The human eye is able to detect the presence of the oncoming vehicle because the eye lens forms a real image of the vehicle headlight on the retina, and the brain recognises the high contrast between the headlight image and the surrounding areas.

It should be possible to re-create this electronically using a video camera, image digitiser, and a dedicated microprocessor programed to look for saturation spots in the image due to headlights. This would be a complex and expensive solution.

This invention uses a simple lens system, usually a 'fisheye' or wide angle lens system, to give a real image of the view from the front of the vehicle onto a set of closely spaced photodiodes. The contrast between headlight images and surrounding areas is exploited.

The image of the oncoming vehicle's headlights will be focused onto on or more of the photodiodes. The output of each photodiode is amplified and compared with a reference signal, a weighted average derived from the output of all the photodiodes. If the output of one or more of the photodiodes exceeds the reference level, then the Unit dips the headlights of the vehicle to which it is fitted if the driver has not done this already.

Provision is also made in the unit to prevent malfunction due to the temporary interruption of the light source due to moving windscren wipers, crash barrier uprights, trees, etc.

The Unit is designed to be positiond behind the vehicle windscreen so that it receives as clear a view of the road ahead as the driver.

A specific embodiment of the invention will now be described as an example, with reference to the accompanying drawings: Figure 1. Lens system and Photodiode Housing.

Figure 2. Photodiode Amplification.

Figure 3. Summation and Divide by Four Op.-Amp.

Figure 4. Reference signal or 'Weighted Average' Amplifier.

This is a variable gain amplifier with an output limiter.

Figure 5. Comparators and Logic Circuit.

Figure 6. Short Term Memory and Final Relay Drive Circuit.

Figure 7. Power Supply Circuit.

Figure 8. Connection to the Vehicle.

Figure 1. shows a suitable lens arrangement, together with a Quadrant Silicon Photodiode, in their opaque plastic housing. The lens arrangement consists of a standard 'fisheye' door viewer 1 together with a simple doublet lens 2 of focal length 13 mm. Together these give a real image, 3 mm. in diameter, of the 'fisheye' or hemispherical view of the road.

ahead as seen from a point behind the windscreen. This image is formed on the surface of four separate but closely spaced sensing photodiodes, arranged one per quadrant, housed in a 705 package. 3.

All the components push fit into the plastic tube 4.

The output voitage of each quadrant is available separately, and each is amplified using an FET input Op.-Amp.

as shown in Figure 2.

Increasing light levels cause the output potential of the op.-amp. to fall from U̇s towads OV.

A further op.-amp. is used to add the outputs of these four op.-amps together and divide by four. See Figure 3.

The resulting output is an average of the outputs of the four op.-amps in Figure 2. It is also inverted; increasing light levels cause its 'averaged' output to rise from U̇s towards Vs.

This output is fed to a sixth op.-amp. with gain variable from one to four. See Figure 4. This stage provides the 'Reference Level' with which the photodiode signals obtained from the four op.-amps in Figure 2 will be compared. The variable gain in this stage ensures that the sensitivity of the Unit is adjustable, being least sensitive when the gain is set at four, and most sensitive when the gain is set at one.

This stage also inverts the signal once more so that its output is in phase with that of the op.-amps in Figure 2.

A zener diode is used in this stage to ensure that the output of this stage, falling as light levels rise, never reaches OV.

Figure 5 shows the four comparators which compare each of the outputs of the op.-amps in Figure 2 with the 'Reference Level' obtained from the output of the op.-amp in Figure 4.

If one of the photodiodes has more light falling on it than the rest then the output from its op.-amp will be lower than the reference level. This causes the output of the comparator to which it is connected to go HIGH.

The output of each comparator is fed to a four input OR gate. Its output will be HIGH if one or more of the comparator outputs is HIGH, that is, if one or more of the photodiodes is more illuminated than the others.

Figure 6 shows the final output stage with its short term memory. If the output of the OR gate in Figure 5 goes HIGH, then the capacitor charges up, and the Darlington Pair is made to conduct, operating the output relay.

If the light signcl to the photodiodes is interrupted by working windscreen wipers, crash barrier uprights, trees, etc. for a short interval of time, the discharging capacitor continues to make the Darlington Pair conduct and the relay pull in.

If excessive amounts of light reach the photodiodes, then the outputs of their respective op.-amps in Figure 2 will fall to OV. The Zener Diode in Figure 4 ensures that the 'Reference Level' never reaches OV. Under these circumstances the comparators in Figure 5 will have a HIGH output, causing the final relay in Figure 7 to be energised, keeping the headlights dipped under these conditions.

Figure 7 shows a suitable power supply. Two stages for filtering out ignition noise are provided, one optimised for the removal of radio frequencies, the second for the removal of audio frequencies.

A bridge rectifier ensures that the unit will work with both Regative earth and Positive earth systems without modification.

An op.-amp. used as a buffer divider provides the split rail U̇s supply necessary for the other op.-amps. Decoupling capacitors are provided around each integrated circuit package.

Figure 8 shows one passible way of connecting the Unit to the existing vehicle wiring.

The cable to the 'main beam' filament is disconnected from the Dip Switch.

The 'main beam' Dip Switch contact is connected to the POLE of the Unit relay.

The 'main beam' filament cable is connected to the @ORMALLY CLOSED contact of the Unit relay.

The 'dipped beam' contact on the Dip Switch is connected to the @ORMALLY OPE@ contact of the Unit relay.

Power for the Unit can be from two sources: either (a) from the 'pole' contact on the vehicle's Dip Switch. If this is done, the Unit is energised whenever the vehicle's headlights are switched on.

or (b) from the POLE contact on the Unit relay. If this is done the unit is only energised when 'main beam' is selected on the vehicle's Dip Switch.

The Unit is earthed in the usual way to the vehicle's chassis.

Claims (4)

Claims.

1. An automatic vehicle headlamp dipswitch, using a simple 'fisheye' or wide angle lens system, to give a real image of the road ahead, formed on the surface of a set of closely spaced silicon photodiodes. The contrast between headlight images and the surrounding areas is exploited to operate the dipswitch.

2. An automatic vehicle headlamp dipswitch as claimed in Claim 1 above, in which the output of each photodiode is compared electronically with a 'reference signal' derived from the full set of photodiodes.

3. An automatic vehicle headlamp dipswitch as claimed in Claims 1 and 2 above, in which a short term memory is used to prevent malfunction due to temporary or short term interruption of the light source due to working windscreen wipers, crash barrier uprights, trees etc.

4. An automatic vehicle headlamp dipswitch as claimed in claims 1, 2 and 3 above, in which provision is made to ensure that the headlights are dipped when the vehicle is subjected to high light intensities.