Flasher
A flasher is used to switch lamps on and off rhythmically. In the best-known case, flasher units are part of the direction indicator of motor vehicles and switch the direction indicators there, whereby for this application the exact function of the flasher unit is specified in the relevant laws through detailed equipment regulations, such as for Germany in the StVZO or for Austria in the KFG .
Basics
The most common application for a flasher unit is the switching of signal lamps, for example in railway or automotive engineering . The circuit is often set up in such a way that the switching processes can be heard as a clear click or by another signal. In the motor vehicle, it reminds the driver to reset the turn signal if this does not happen automatically; in other applications it makes troubleshooting easier if a turn signal fails. The flashing frequency is between 60 and 120 cycles per minute, depending on the flasher unit. Flasher units are designed for a specific voltage and a specific current. When replacing, make sure that the power and number of lamps match the data of the flasher unit. In vehicle technology, it must be taken into account that in very old motor vehicles and some two-wheeled vehicles, lower-powered indicators of 18 or 15 watts power (normally 21 watts) or other on-board voltages (6 volts ) than are common today (12 volts, sometimes 24 volts) were installed. This must be taken into account when exchanging. However, there are also LED-compatible flasher units that can handle the lower power consumption of light-emitting diodes - retrofits ( LED lamps ).
Vehicle technology
Layout and function
Each flasher unit consists of a pulse generator and a circuit breaker. The circuit breaker can either be a relay or a transistor ( solid state relay ). The flasher unit is connected to terminal 15 , the so-called ignition plus , and is ready for operation after switching on the ignition switch . The direction switch is switched between the flasher unit and the flasher lights. This is a toggle switch that is interrupted in the middle position. In the middle position, the flasher does not work - it only becomes active when the switch is switched in one of the two directions of travel (left or right). When the hazard warning switch is actuated, the flasher unit is supplied with power regardless of the position of the ignition lock and the direction switch, and all of the vehicle's indicators are activated.
Some manufacturers deviate from this standard structure. In these flashing systems, the interconnection initially runs from the ignition plus to the travel direction switch, from its two outgoing contacts to a two-circuit flashing device and then to the respective flashing lamps. There are also flasher units that are signaled via serial digital data transmission what they should do. Combination of hazard warning lights / direction indicators generate the signals of hazard lights and the direction indicator in one device.
While bimetal flasher units get by with two connection contacts, other flasher units require three or more connection contacts. There are flasher units - especially combined flasher units with two-circuit control - that have up to eight connection contacts.
What all flashers have in common is that they can detect defective lamps. This was already done with the first bimetal and hot wire flasher devices based on the thermal time constants and the heating power, which is proportional to the square of the load current. A faster flashing sequence was the hallmark of a lamp failure. Electronic flasher units require a current measurement ( shunt ) for this function and simulate the failure signal in the same way.
Fully electronic flasher units often generate the typical blinking sound of the (no longer present) relay.
Flashing rhythms
A distinction is made between two flashing cards on motor vehicles:
- Direction indicators
- Hazard warning lights
Direction indicator flashing means the synchronous flashing of the direction indicators on one side of the vehicle; when the hazard warning lights are flashing, all of the vehicle's direction indicators light up Hazard warning lights were approved in motor vehicles from 1963. In the older vehicles equipped with bimetal and hot wire flasher units, an additional flasher unit was required, which had to be retrofitted. Both flasher units were connected to a special hazard warning flasher switch, with the hazard warning lights having priority. From the end of the 1960s, all new cars were equipped with combined directional and hazard warning flasher devices. From January 1, 1973, old cars also had to have hazard warning lights.
Dedicated hazard warning flasher units differ from flasher units partly in terms of their frequency, but generally in terms of their duty cycle . In the case of the hazard warning lights, the lamps are switched on for a shorter period of time and switched off longer in order to protect the vehicle longer with one battery charge. From the 1970s onwards, a flasher relay was mainly used by a switch to control the direction and hazard lights. In today's motor vehicles, the indicators are controlled via bus systems and the on-board power supply control unit; Here the hazard warning mode is often switched with a shorter lighting phase to protect the vehicle battery when the engine is switched off.
The lamp failure is indicated by an increased flashing frequency, see section Structure and function .
Flasher types
Various types of flasher have been designed and used over the years. These are among others:
- Thermal flasher
- Pneumatic flasher
- Electronic flasher
- Conventionally connected flasher units with electronic timer and lamp failure control
- Digital flasher units that get their signal via a serial bus connection
Bimetal flasher
The first flasher units used a bimetallic strip to delay suit and fall , which is periodically heated by a heating coil. The bimetal contact is designed as a break contact and connected in series with the heating coil. This is why these flasher units only need two connections. When the travel direction switch is switched off, the bimetal is cold and the normally closed contact is closed.
When the travel direction switch is activated, a current flows through the bimetal strip, the heating coil and the flashing lamps. The heating coil heats the bimetal strip. The normally closed contact is opened after a few seconds by the bending bimetal, whereby both the indicator lamps and the heating coil lying in series are de-energized. The open switch contact now interrupts the flow of current; the bimetal strip cools down, whereupon the switching contact closes again. This process is repeated periodically.
This type of flasher unit has two special design-related features: on the one hand, the first flashing interval lasts longer than the following (because the bimetal strip has to warm up first), and on the other hand, the failure of a flashing lamp results in a significant increase in the flashing frequency: due to the lower current flow, it heats up the bimetallic strip is less strong, does not stand out as far from the contact point and also closes the contact again quickly because it cools down quickly.
Today the bimetal flasher unit is only used in historical motor vehicles ( oldtimers ).
Hot wire flasher
Hot wire flasher units were used in vehicles until the 1990s. In the idle state, a hot wire (see also hot wire instrument ), an electromagnet and the indicator bulbs are connected in series . The resistance of the hot wire and a series resistor is so great that the current flowing is too small to make the lamps glow. In front of the magnetic coil , similar to a relay , there is an armature which is kept away from the coil by the tensioned, cold hot wire.
The wire is now heated by the current flow, expands and enables the armature to be attracted more and more by the magnetic field of the coil. At the end of this movement, the armature reaches a switching contact that short-circuits the hot wire. The current now flows through the coil directly to the light bulb. The incandescent lamp lights up because the voltage drop across the coil is only slight. While the magnetic force of the coil through which the strong lamp current flows, attracts the armature all the more, the heating wire cools down and tries to shorten itself again. After cooling down sufficiently, the hot wire contracts so much that it can pull the armature away from the coil against the magnetic force and open the contact. The lamp goes out and the process starts again.
The advantage of the principle is the support of the contact force and the release of the contact (feedback effect), so that the contact is spared and lives longer.
There are hot wire flasher units that start with the light phase and those that start with the dark phase. With the light-phase flasher unit, the current flows immediately to the turn signal lights after the steering column switch is operated, so the flasher unit begins with the light phase. For this purpose, the current flows from the connection terminal 49, via the closed flashing contact, the current relay and the connection terminal 49a to the turned-on flashing lights. At the same time, the current relay switches ground potential via terminal 31 to the series resistor and the hot wire. This heats up, expands and the hinged armature pretensioned in the direction of the voltage coil opens the flashing contact. At the same time, the current relay drops out and de-energizes the hot wire, which contracts again and closes the flashing contact. The game starts all over again. The voltage relay ensures a steady flashing rhythm. In the dark phase it receives ground potential via the currentless flashing lights (PTC thermistors) and attracts the hinged armature until the contracting hot wire can overcome this magnetic field. In the light phase the voltage relay is de-energized because it receives positive potential on both connections.
A characteristic of this type of flasher is the fact that if one of the flasher lights fails, the still functioning light is supplied with permanent light because the current relay can no longer switch on the hot wire. With the dark phase flasher unit, however, the blinking frequency increases and the flasher unit “races”.
For flasher units that begin with a dark phase, this is shortened by a property of the light bulb. Incandescent lamps are PTC thermistors and have a resistance that is around ten times smaller when switched off than when they are in operation. A much higher current flows through the bulb, which is cold when the flasher is switched on, which leads to a faster expansion of the hot wire, so that the flasher switches to the light phase in the legally prescribed time. The incandescent lamp never cools down completely during regular flashing operation, which means that its PTC behavior is less important.
The disadvantage of these flasher units is that they are very sensitive to voltage fluctuations. In the event of undervoltage, the flashing frequency of the flasher unit decreases. In addition, the principle is subject to aging: the wire must never reach the plastic range when heated, but should be allowed to get as hot as possible because of the stroke. This is why some hot wire flasher units have an adjusting screw for the heating wire. This adjusting screw is often located behind the insulating support and can be reached through a drill hole in the insulating support. In order to protect the mechanism of the flasher from moisture, the drill hole is often sealed with an adhesive strip. After setting the correct flashing frequency using the adjusting screw is not easy and should be left to a specialist.
Pneumatic flasher
In the 1960s there were also flasher units with pneumatic switching delay. With this type of flasher type, a small piston is pulled into a cylinder by a coil through which the lamp current flows, until it causes an armature to switch over and thus interrupts the lamp and coil current. A spring then pushes the piston out of the cylinder again until the power is turned on again. The armature is alternately attracted and released by the solenoid.
The armature controls the contacts for the flashing lamp current. In principle, such a flasher works like a horn . However, the frequency of the oscillating armature is much too high for the direction indicator control. For this reason, the armature movement is dampened by the housing being hermetically sealed and the air displaced by the piston having to flow through a nozzle. The term "pneumatic" is derived from this so-called air brake.
Pneumatic flasher units are largely independent of the load and can be used with different vehicle electrical system voltages (e.g. with Pneutron type AB 16: 2 to 6 × 26 W at 6 or 12 V). However, they were rarely used, mainly as hazard warning lights, and were quickly replaced by electronic flasher units.
Electronic flasher
From the end of the 1960s, flasher units with an electronic pulse generator were used. This initially consisted of discrete components . For this purpose, resistors, capacitors and transistors were connected to form a so-called astable multivibrator . Relays and occasionally also transistors were used as circuit breakers. From around the mid-1970s, the discrete components were increasingly replaced by integrated circuits (e.g. timer IC type NE555 ). Since 1981 there have been special indicator ICs which also take over the failure control based on a current measurement. Widely used indicator ICs are z. B. the U643B and the U6043B from Atmel .
If one of the bulbs fails, the current flowing through the flasher unit is reduced. The built-in control circuit recognizes this and doubles the flashing frequency - imitating the system-related behavior of the historically used bimetal flashers. Flasher units for trailer operation have an additional output (C2) to control the special trailer indicator light, which enables the vehicle driver to check the direction indicators of the trailer as required. Electronic flasher units have a very constant frequency and are insensitive to temperature and voltage. Flasher units for 12 volts also work properly at 9 volts. This means that these flasher units have a constant flashing rhythm even in the event of a breakdown when the on- board voltage has dropped significantly. From around the end of the 1990s, these separate flasher units were replaced by solutions integrated into the central vehicle electrical system.
Integrated flasher
A separate flasher unit is no longer installed in modern vehicles. The flashing (switching on and off) is generated in a central control unit , usually the so-called on- board control unit (Body Control Module, BCM; at Ford also called Generic Electronic Module, GEM). This is activated by the turn signal switch, through which only a small control current flows. The power for the indicator lamps is switched via the electronics of the control unit. With this technology, as with separate flasher units, it is possible to detect a lamp failure by internal monitoring of the lamp current in the control unit. As with the older technology, feedback to the driver then takes place via the higher flashing frequency, if necessary also via a text message in the instrument cluster (e.g. "Front right flashing light - please check!"). The acoustic control of the flashing process is mostly implemented by a small (piezo) loudspeaker behind the dashboard (mostly built into the instrument cluster), whereby in some instrument clusters even very realistic audio samples of clicking indicator relays are used. In addition to the failure of a lamp, control units also detect short circuits and switch off the affected lamp circuits without the fuse being triggered. As soon as the damage is repaired, the corresponding lamp is activated again. In some vehicles there is also a small relay built in, which is only used to generate a click in the rhythm of the flashing frequency.
Error control
As a special feature, as already mentioned, flasher units have a monitoring function for the flasher lamps. This error control can be done optically or acoustically. If a bulb fails, the flow of current in the flasher circuit is reduced. The flasher unit then works with twice the switching frequency and indicates to the driver that there is a fault in the flasher system: audible by the faster ticking and visible by the faster flashing of the green indicator light . In addition to doubling the flashing frequency, it is also possible to implement failure control by not activating the control lamp. There are basically two options for checking the function of the indicators on towing vehicles with trailers, the single-circuit control and the dual-circuit control.
With single-circuit control, both the trailer and the towing vehicle have a common control circuit. Two indicator lights are controlled via the control circuit in the rhythm of the flashing frequency. If one or more flashing lights on the towing vehicle or trailer fail, both control lights remain dark. With this system, it is not possible to assign a lamp fault to the trailer or the towing vehicle. The flashing frequency remains unchanged.
With the two-circuit control, there are separate control circuits with separate control lights for the trailer and for the towing vehicle. If a control lamp remains dark, a clear assignment of the lamp fault is possible. Depending on which indicator light does not light up, there is a lamp fault either on the towing vehicle or on the trailer. The flashing frequency remains unchanged in this system as well.
Other uses
Flasher units are also used for error messages in electronic controls and in some household appliances.
Flasher units are also used in surveillance systems, traffic lights, St. Andrew's crosses and the like. a. Signal systems.
Legal bases and other regulations
- Road Traffic Licensing Regulations (StVZO), in particular Section 54
- EC Directive 76/756 / EEC
- BS ISO 7588-1 Road vehicles - Electrical / electronic switchgear - Relays and flasher units
literature
- Jürgen Kasedorf, Richard Koch: Service primer for vehicle electrics , 14th revised edition. Vogel Buchverlag, 2001, ISBN 3-8023-1881-1
Individual evidence
- ↑ a b c d e f g h i Rudolf Hüppen, Dieter Korp: Auto electrics - all types . Motorbuchverlag, Stuttgart 1968, ISBN 3-87943-059-4
- ↑ a b c d e f g h i Erich Hoepke, Stefan Breuer (ed.): Commercial vehicle technology, fundamentals, systems, components , 6th edition. Vieweg + Teubner, Wiesbaden 2010, ISBN 978-3-8348-0995-7
- ↑ a b c Kai Borgeest: Electronics in vehicle technology . 2nd Edition. Vieweg + Teubner, Wiesbaden 2010, ISBN 978-3-8348-0548-5
- ↑ a b Repair Instructions 355, Fiat 126 . Verlag Bucheli, Zug 1977, ISBN 3-7168-1441-5
- ↑ a b c Norbert Adolph: Autoelectronics / Basics and building suggestions . Publishing company Schulfernsehen, Cologne, ISBN 3-8025-1128-X
- ↑ Bosch: Technical instruction on circuit symbols and circuit diagrams for vehicle electrics. 2nd edition, Robert Bosch GmbH, Stuttgart, 1974, VDT-UBE 001/10
- ↑ Harry Dittrich, Günther Krumm: Elektro-Werkkunde Volume 5 / Professional practice for telecommunications fitters and telecommunications mechanics . 4th edition. Winklers Verlag, Darmstadt, 1971
- ↑ MRS Electronic GmbH (Ed.): Vehicle / utility vehicle electronics . MRS catalog version 2009.07, Rottwell 2009
- ↑ Journal elektronik industrie 7-2009, p. 17
- ↑ a b www.cardone.com - manufacturer of GEM modules ( Memento from February 17, 2010 in the Internet Archive )
- ↑ Patent specification for electronic flasher unit: DE19817335C1 September 9, 1999
- ↑ a b Hella KGaA Hueck & Co (ed.): Hella Elektrik 2012-13 . Electronics catalog, Lippstadt 2012
- ^ A b c Robert Bosch GmbH (Ed.): Kraftfahrtechnisches Taschenbuch , 27th edition. Vieweg + Teubner, Wiesbaden 2011, ISBN 978-3-8348-1440-1
- ↑ Gerhard OW Fischer: Car electronics made easy . Verlagsgesellschaft Rudolf Müller, Cologne Braunsfeld 1974, ISBN 3-481-22501-6
Web links
- internal switching of an electronic flasher unit (last accessed on April 15, 2014)
- Data sheet for the U643B indicator IC from Atmel (English PDF) ( Memento from February 15, 2010 in the Internet Archive ) (accessed)