15-02-2010, 07:10 PM
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ABSTRACT
The number of vehicles on our roads is burgeoning day by day. This is turn forced almost all this vehicle manufactures to think about the extra safety instruments and electronic controls to attach with these products for giving the users a safety derived in all road conditions through a mass flow traffic. If asked, one should always mention that the right driving is very cumbersome due to the dazzling light problems and the frequent dipping of headlights by manual means that often causes fatigue to the driver particularly at the time of peak traffic. So naturally to get rid of this perennial problem, an automatic mechanism has to come up to dip the headlamp automatically whenever required. For keeping a motor vehicle under perfect control and reins of the driver, different types of controls and accessories are provided in an automobile around the driverâ„¢s seat, on the dashboard and at the footboard. Simply, an automatic dipper is a unit, which can automatically judge when the headlight beam needs to be lowered, and which dip the headlamp from which beam to a dipped beam. As the dipper unit is well connected to the lighting system of the vehicle, we have to look short into the type and construction of a head light before discussing the wiring diagram or the construction of Automatic dippers.
INTRODUCTION
The number of vehicles on our roads is burgeoning day by day. This is turn forced almost all this vehicle manufactures to think about the extra safety instruments and electronic controls to attach with these products for giving the users a safety derived in all road conditions through a mass flow traffic. If asked, one should always mention that the right driving is very cumbersome due to the dazzling light problems and the frequent dipping of headlights by manual means that often causes fatigue to the driver particularly at the time of peak traffic. So naturally to get rid of this perennial problem, an automatic mechanism has to come up to dip the headlamp automatically whenever required.
For keeping a motor vehicle under perfect control and reins of the driver, different types of controls and accessories are provided in an automobile around the driverâ„¢s seat, on the dashboard and at the footboard. There are controls like clutch, brake pedal, accelerator pedal, and sharing the same importance, the dimmer switch is changed with time, and its pace in the filed of automobile safety is one of the uppermost.
Simply, an automatic dipper is a unit, which can automatically judge when the headlight beam needs to be lowered, and which dip the headlamp from which beam to a dipped beam. As the dipper unit is well connected to the lighting system of the vehicle, we have to look short into the type and construction of a head light before discussing the wiring diagram or the construction of Automatic dippers.
HEADLAMPS
The modern lighting system consists of switches, lamps, wiring harness, and fuses or circuit breakers. It may be mentioned that the primary purpose of the headlight design is to produce illumination over considerable distance ahead of the vehicle and enable the driver to drive at reasonable speeds at night with safety. But the provision should also be made that the drivers of other vehicles coming from the opposite direction to not experience a glare. For this purpose a dipped or meeting beam is also provided for maintaining the reasonable speed with safety without dazzling the coming driver. To prevent dazzle to the on coming driver during particularly misty or hazy conditions the light about the horizontal should be cut off. This is called dipping of the head light beam.
In an average car, the lighting system consumes about 70 “ 75% of electrical energy when driven at night. In terms of amperage the consumption may be from 24 “ 40 A at night for al purposes including the radio, heater, and transmission controls.
Light Source
There are two kinds of light sources, namely, the one that emits light and the other that reflects light. In the case of headlamp used in automobiles, both the things are combines in A. The filament of the electric lamp is the primary source, while the reflector is referred to as the secondary source. The intensity, colour and distribution are the important characteristics of any light source.
The headlight is composed of three elements:
1. The light filament that gives off light when a current flows through it.
2. The parabolic reflector that reflect the light in front: and
3. The lens that refracts of distorts the light beam into an illuminating pattern.
Construction
The present day headlights are the outcome of a lot of research and development. Earlier a single electric bulb of the carbon filament type was employed. The bulb was placed at the focus of a parabolic silvered reflector in order to give a parallel beam of light. The following figure shows a parabolic reflector with bulb, the lines showing light rays emitted from the filament of the bulb in all directions. This type of headlight given a parallel light beam, that saves greater illumination nearer the axis. It may be mentioned that the bulb itself and the intensity of light fall off towards the outer portion of the beam block a small amount of light.
From figure it may be seen that if the bulb filament is moved from position Ëœdâ„¢, the focus of reflector, to a position Ëœaâ„¢, the light beam Ëœabcâ„¢ will no longer be a parallel one but will become divergent. On the contrary, if the filament is moved to position Ëœfâ„¢ the beam will take the course a shown by Ëœfbgâ„¢ and will meet at a point on the axis of the bulb. It may be mentioned that by a single adjustment of the bulb, the beam cane be concentrated at a ore-determined distance ahead of the vehicle in order to give a spot light effect.
Formerly the headlight was provided with certain means of adjusting the bulb holder with respect to the reflector along with the bulb axis in order to focus it. It had to be done up every time the bulb was changed. This was essential, otherwise it would cause increased dazzle to other motorists. The filament is encased in an airtight bulb in order to prevent burning up of the white-hot filament because of oxygen in the air. The reflector is generally of polished metal and it throws all the light rays into a cylindrical beam.
The lens is made up of a number of glass prisms molded together and they bend the beam of light into an oval pattern which is aimed ahead of the vehicle and somewhat in the downward direction. A part of the light is spread out in front of the vehicle for providing local illumination, whereas the rest of it is focused into a hot spot that provides distant illumination.
The first major advancement in headlight design took place with the introduction of pre-focused bulbs. It has two filaments, one for normal driving and the other for city driving or for overtaking. These days even two sets of headlights are used for the above said purposes. Generally a foot selector switch is provided, which enables the driver to select either the normal driving or the passing beam.
The parabolic reflector showing light
rays emitted from the filament of the bulb
The effect of changing the position of
filament on the nature of the light beam
Sealed-Beam Headlights
In a sealed beam headlight, the filament and the reflector along with the lens are sealed in an airtight unit. The front face of the sealed beam unit is a lens, which is fused to the reflector after the two filament units, has been inserted through the center of the reflector and sealed in position. The complete unit is then evaluated and filled with inert gas. With these units the only service required is to aim them. This type of headlight introduced in 1940 in the U.S.A.
Sealed beam headlights have the following advantages:
1. The glass unit is self-contained with accurately focused filaments.
2. Dust, moisture, etc. are prevented from entering from the back of the lens and the reflector.
3. A greater amount of light is provided in the beam because, of the absence of a filament bulb and
4. The beam of light obtained is greatly improved due to the pre-focused filament and permanently bright reflector.
It is essential to have a provision for horizontal and vertical adjustment of the beam by titling the sealed beam unit in its body housing. Two adjusting screws, as shown in the following figure, generally do it. Fig. shows an improved version of a selected beam unit with the provision of a metal mask or shield in front of the upper filament to prevent stray light rays from escaping upwards and reflecting back to the eyes of the driver. This type of headlights gives a brighter beam pattern and further reduces the repair and maintenance time. Such type of units are, however, more expensive or replace than plain or pre-focused type of units. Recently headlights of 50-60 W for the lower filament and 40-45 for the upper filament have been used, thus increasing their light output.
Control of Headlight Beam
The circular beam can be spread horizontally to any desired extent with the help of prisms, molded in the inside of the headlight cover glass, as shown in the figure. The horizontal light intensity can be controlled in any desired way by a suitable design of the headlight. The circular beam can also be controlled in the vertical direction with the help of prisms molded in front of the glass, thus redirecting the light rays in the downward direction. This way the downward reflected beam does not obstruct the vision of the other road users coming from the opposite side. With these two combinations, any required main beam illumination, combined with side illumination nearer to the vehicle can be produced.
RECENT DEVELOPMENTS
Technology improves day and day in the field of automobile headlamp construction and it left out the earlier single electric bulb of the carbon filament type and in place modern sealed beam headlights are using nowadays. The light circuits of todayâ„¢s vehicles can consist of more that 50 light bulbs and hundreds of feet of wiring. Incorporated within these circuits are circuitsâ„¢ protector, relays, switches lamps, and connectors. In addition more sophisticated lighting systems use computers and sensors. The lighting circuit consists of an array of interior and exterior lights, courtesy lights and so on. Federal laws largely regulate the lighting circuits, so the systems are similar between the various manufactures.
Halogen lamps
The halogen lamps are mostly introduced and consist of tungsten filaments in the atmosphere of some halogen element such as chlorine, bromine, or iodine. The tungsten evaporated from the filaments reacts with halogen gas to form tungsten halide, which is decomposed back into halogen and tungsten due to high temperature at the filaments, thus causing the tungsten to get redeposit on the filaments. In this way the life of the bulb is increased.
Besides, the filament can operate at still higher temperature, which increases its light intensity. However, the halogen attacks metals at cold temperatures. Thus other metals within the enclosure, viz. the metal shield and the second filament, which is not being used, are attacked by the halogen. To avoid this happening, pure halogen is replaced by dibromomethane gas, which does not cause deterioration of the cold metals. With these headlamps quartz glass is used since ordinary glass tends to crack due to higher operating temperature.
Composite headlights
Many of todayâ„¢s vehicles have a halogen head light system using a replaceable bulb. This system is called composite headlights. By using the composite headlight system, vehicle manufacturers are able to produce any style of headlight lens by desire. This improves the aerodynamics, duel economy, and styling of the vehicle. Many manufacturers vent the composite headlight housing because of the increased amount of the heat developed by these bulbs. Because the housing is vented, condensation is not harmful to the bulb and does not affect the headlight operation. When the headlights are turned on, the heat generated from the halogen bulbs will dissipate the condensation quickly. On systems using non-vented composite headlights, condensation is not considered normal. The assembly should be replaced.
HID Headlamps
High Intensity Discharge (HID) headlamps are the latest headlight development. These headlamps put out three times more light and twice spread on the road then conventional halogen headlamps. They also use about two-thirds less power to operate will last two to three times larger. HID lamps produce light in tooth ultraviolet and visible wavelengths. This advantage allows highway signs and other reflective materials to glow. This type lamp first appeared on select models from BMW in 1993, Ford in 1995, and Porche in 1996.
These lamps do not relay on growing filament for light. Rather light is provided as a high voltage bridges an air gap between two electrodes. The presence of inert gas amplifies the light given off by the arching. More than 15,000 volts are used to jump the gap between the electrodes. To provide this voltage, only about 80 volts is required to keep current flow across the gap. The great light output of these lamps allows the headlamp assembly to be smaller and lighter. These advantages allow designers more flexibility in body designs as they attempt to make their vehicles more aerodynamic and efficient.
HEADLIGHT DAZZLE
The dazzle effect is one of the major problems faced by a driver in night driving. So one has to stop the high intensity light from the eyes of the incoming driver or road users to prevent the dazzle effect. Automatic Dipper is one such mechanism, which is employed for safety night driving without the intense dazzling effects. Without much efforts from the driver which otherwise has to dim the lights every seconds by manual means may lead to fatigue to the driver especially during peak traffics. So it will be better to know Ëœwhat is meant by dazzleâ„¢ and Ëœwhat all devices are often used in preventing dazzle effectâ„¢ before mentioning the advantages and uses of an auto dipper.
The problem of headlight dazzle is linked with many factors of which, the human eyes is the most important. In fact, it is the final judge in respect of dazzle and illumination. It may be mentioned that for driving, bright illumination is essential. In short, condition of illumination, should be such that there is clear vision for all motorists. Dazzle is nothing but brightness, which causes interference with vision. The various factors, which govern it, are: brightness, contrast, and the angle subtended by the bright area on the eye. It is the contrast between the bright and dark areas, which is one of the main causes of dazzle. However, it is difficult to lay down in terms of quantity the fixed ratio of the brightness of the two areas which is likely to produce or eliminate the effect of dazzle since it is controlled by the brightness of the lighter of the two areas. The ratio between the absolute black area and a dimly lit area may be quite great but there will be no dazzle effect. Further, an intensity bright area with very dark surroundings, does not give a dazzling effect.
The dazzling effect can be prevented by,
¢ Reducing the brightness of the headlights of the vehicles.
¢ Stopping high intensity light from entering the yes of on-coming drivers or road users.
¢ Reducing the contrast between the surrounding area and the headlight of the vehicle.
DIPPING OF HEADLIGHTS
When the vehicle is driven on the highways, it is required that light beam should be of high density and should illuminate the road at a distance sufficiently ahead. However when a vehicle coming in the opposite direction approaches a vehicle fitted with such headlights, driver of that vehicle will experience a glare, which will blind him. To avoid this, a separate filament is fitted at such a position that that light beam from this filament is deflected both down and sideways so that the driver of the oncoming car is not blinded. Some of the ways in which this can be achieved are shown in the following figure.
The main filament may be placed at the focus with the dipper filament slightly above it or the main filament and the dipper filament may be placed slightly below and above the focus respectively, with the reflector tilted. Another popular method is to place the main filament at the focus and the dipper filament slightly in front of the same with a mental shield placed below the dipper filament. In this only this upper half of converging beam comes out of the reflector. Thus it prevents the other rays from setting reflected from the lower half of the reflector and emerging in the upward direction to cause glare. The beam (main or dipper) are selected by the driver y means of a foot operated or steering column mounted stick type dimmer switch but in case of automatic dippers the light from the oncoming vehicle will trigger the dipper unit. The illumination of road by main bam and the dipper beam is shown in the above figure.
Bifocal Bulb
In the earlier days, a dipping reflector was used as one of the popular anti-dazzle devices. In this case, the movement of the reflector within the headlight casing dipped the headlight beam. The solenoid, mounted at the back of the reflector, controlled the movement of the reflector.
The bifocal both is an extensively used anti-dazzle device in the U.S.A and the U.K this type of both has two filaments, one being either in front of or above the other filament. The following figure shows this type of a bulb.
It will be seen that a metal shield is provided below the forward filament. Its main purpose is to prevent the light rays from the filament striking the lower half of the reflector. Switching over from one filament to the other may provide the normal and dipped beams. The figure & shows the manner in which the headlight beam is dipped while changing over the normal to the dipped beam. The bifocal bulb is simple in installation and is also an effective method of dipping the beam of the headlight.
Two Filament Bulbs
In two filaments modern headlights there uses a two-filament bulb with a fixed reflector. In this case, one filament is meant for the dipping beam and the other main beam filament is beneath it and it is located at the focus of the reflector. The nature of the dipped beam can be controlled by the help of prisons and lenses provided at the front cover of the headlight.
Anti-dazzle Devices
Most of the modern anti dazzle devices depend upon the redirection of the light rays. This can be achieved by various ways as by lenses, by specially designed reflectors, by bulbs of special design or by dipping reflector mechanisms. Now it is common practice to control the beam from the driverâ„¢s seat, as and when required. If the initial focusing of the lamp is correct, the dazzle effect is considerably reduced and at the same time it provides sufficient illumination for the driver.
In the case, the upper and the lower levels of the reflector are displaced by an amount equal to the filament length. It results in projection of light rays parallel and downwards and not upwards. It may be noted the correct focusing of the filament with respect to the two halves of the reflector will greatly help in the elimination of these upward rays.
Methods of getting dipped beams Bifocal bulb and the manner in which the headlight beam is dipped
A double “ filament lamp
AUTOMATIC DIPPER (AUTRONIC DYE)
Autronic dipper
An autronic dipper is a unit which can automatically judge when the head light beam needs to be lowered. The auto dippers are basically switches, which dip the headlamp from high beam to a dipped beam if a certain amount of light falls on its photo sensor. This is a system, which electronically selects the proper headlamp beam for country driving. It holds the lights on upper, or high, beam until a car trigger the system so that it shifts the headlamps to the lower beam. When the other car had passed, the system electronically shifts the headlamps back to the upper beam.
Location
As the operation of the auto dipper trigger out only when the light from the on-coming vehicles falls directly on the photo sensor unit, it has to be ideally located in a place where the light beams can freely entered without any obstruction. Commonly auto dipper meters from the ground. The suggested position for passenger cars is in the place between windshield and rear position f cabin rear view mirror.
Applications
Some American manufactures have first used photoelectric cells for automatic dipping of headlights. In the ËœAutronic Eyeâ„¢, the photoelectric cell senses the intensity of light from the oncoming vehicles and dips the heedful accordingly; the driver does not have to control the headlights. This type of system is very successful on American roads. But on Indian roads with frequent curves etc., especially in case of rural areas and with non-uniform light intensities automatic dipper has got not much use. But in high way driving through level straight roads having a large number of vehicles and without having sharp turns etc., the automatic dipper helps the drivers in eliminating the fatigue of operating the dipper switch intensity level will always be there for satisfying he minimum intensity needed for the system to function even on small breathing turns which is often seen in high ways.
Possibility of Manual Override
As the automatic dipper is particularly designed and good for the high way driving, but the vehicle is meant for all type of roads, and for facing some particular situation where the driver needs more light to see by etc., manual override is also fitted with the automatic dipper unit by which the driver can operate the heedful becomes manually leaving out the auto system inoperative. The driver has a sensitivity control, which allows adjustment of the system to the surrounding light.
The override system can be used when the oncoming driver does not dim, the driver needs more light to see by and also on rural road where not much vehicles are there at night and also sharp turns are there.
WORKING OF AUTO DIPPER
Automatic headlight dipping automatically switches the headlight from high beam to beams when light from oncoming vehicle strikes the photocell or phototube (Photo amplifier) of the vehicle. Thus we can select the proper headlight during country driving and it saves the driver from the trouble of depressing the foot switch for lowering this headlight beam. It holds the lights on the upper beam until the vehicle approaches from the other direction. And also the moment the other car passes by, it shifts automatically the headlights back to upper beam. The auto dipper is a device, which is highly immune to lights from street lamps, roadside light sources and other manual sources of light.
Modern automatic dipping systems use solid-state circuiting and electromagnet relays to control the beam switching. Most systems consist of the following major components.
1. Light sensitive photocell
2. High-low beam relay
3. Sensitivity control
4. Amplifier
5. Dimmer and auxiliary foot switch
6. Wiring harness.
We can analyze the working of the system by considering the following schematic circuit diagram of the auto-dipper.
The phototube is a variable resistor that used light to change the existence. The phototube amplifier is usually mounted behind the front grill or on the one side of the dashboard or in the rear view mirror support where it will be in limn with the light from the vehicle approaching from the opposite direction. The sensitivity control sets the intensity level at which the photocell amplifier will energize. This control of set by the driver and is located next to, or is a part of, the headlight switch assembly. The sensitivity control is a potentiometer that allows the driver to adjust the sensitivity of the automatic dipper (dimmer) system to surrounding ambient light conditions. The driver is able to adjust the sensitivity level of the system by rotating the control knob. An increase in the sensitivity level will make the headlights switch to the low beams sooner (approaching vehicle is further away). A decrease in the sensitivity level will switch the headlight to low beams when the approaching vehicle is closer. If the knob is located at full counter clockwise position, the system enters manual override. The high-low rely is a single pole, double throw unit that provides the switching of the headlight beams.
When the light from the oncoming strikes the light sensitive plate provided in it, an electric current is released. When the oncoming vehicle is nearing, its strong light sets the amplifier unit into operation. A special electronic tube is contained in the amplifier unit know as thyraton, which amplifies the current entering its grid. The thyraton greatly amplifies the current provided by the phototube. It becomes strong enough to put the power relay unit into operation.
Schematic Circuit Diagram of an Autronic Eye
The windings of the power relay are connected to the thyraton. There are two sets of points provided when the upper contacts are closed, the high filament of the headlight is connected to the battery. When the lower contacts are closed, the low filaments are connected to the battery. Depending upon the strength f the current from the thyraton, the points open and close lighting the upper or lower beam.
An auxiliary foot switches also provided in addition to this arrangement which this the driver can hold the upper beam on, even though the auto-dipper has operated, this shifting the headlights to the lower beam. This switch is used when signaling to the other motorists.
The above figure shows the simplified schematic diagram of the auto-dipper (autronic eye). The switches, resistance units, and other components are not shown. The curve in the phototube indicates the light sensitive plate. The dotted line in the thyraton unit indicates the grid.
CONCLUSION
Newer and better technologies always come with time and it will help in reducing the manual labor and difficulties in the sectors where it is made use. And in our case, the auto dipper can perform a great deal in reducing the manual efforts and fatigue of drivers in dipping the headlamp frequently while driving through highways full of moving vehicles. However, vehicles employed with automatic dippers are not very often seen in our cities, and it may be due to lack of information about the system and also because of giving attention to the people saying that it is not at all practicable in our highways. Yes, of course it has got some drawbacks like that one which is most common, when we drive the vehicle fitted with automatic dippers on a road in which different types of vehicles and hence varying light intensities cause frequent flickering of the headlight. And also the operation of the system eliminated or reduced by devising newer methods and technologies. The one nowadays available is only useful in highways and straight width roads.
Truly speaking, auto dippers are devices, which will attain more and more importance in the forthcoming years. In short, it is a device with a very bright future. The number of vehicles and the condition of the roads are improving very fast and the day is near, when the driving regulation, nature of traffic etc., are growing up to the levels which is already their in countries like America who successfully using auto dippers in their highways.
REFERENCES
1 AUTOMOTIVE ELECTRICITY, ELECTRONICS AND COMPUTER CONTROLS
- Barry Hollem Beak
2 AUTOMOTIVE ELECTRICAL EQUIPMENT “ P.L. Kohli
3 AUTOMOBILE ENGINEERING “ Kirpal Singh
4 AUTOMOBILE ENGINEERING “ R.B. Gupta
