Ignition system

As ignition is referred to the internal combustion engine, the ignition of the compressed fuel-air mixture in the combustion chamber of the cylinder. Ignition occurs in gasoline engines by a high voltage spark to the spark plug of the compressed fuel -air mixture, in the diesel engine by compression ignition of the fuel injected by an injector into highly compressed air.

The first shape of the ignition was the hot tube, in which a platinum tube was made ​​to glow in the combustion chamber of the cylinder with a small burner. This resulted in the compression of the gas mixture to ignite. However, this device was prone to failure and can not be regulated.

• 2.1 magneto ignition
• 2.2 Battery ignition
• 2.3 Transistorzündanlagen ( TSZ-h/TSZ-i/TSZ-k )
• 2.4 thyristor, high voltage capacitor ignition ( loop start )
• 2.5 Electronic Ignition System ( EZ )
• 2.6 Fully electronic ignition system ( VEZ ) 2.6.1 control

• 4.1 Reference Books
• 4.2 Brochures

Requirements for ignition

For efficient power delivery with the least possible use of fuel, the ignition timing is optimally set so that the maximum combustion pressure at all engine speeds and load cases about 10 ° to 20 ° crank angle after top dead center ( TDC) occurs. The combustion center of gravity, which is the time at which 50 % of the mass of fuel used are burned then is, at about 5 ° to 8 ° CA ​​after TDC. The fuel- air mixture must therefore be ignited before TDC.

Since the combustion time of the fuel- air mixture, however, independent of the speed is approximately 2 ms, the time of ignition with the engine speed increases has continuously be before TDC.

Selecting the wrong ignition timing

If the ignition timing is set too early, uncontrolled combustion processes with high pressure and temperature peaks can occur. Piston and cylinder head - - In this knocking combustion engine components that form the combustion chamber are very high mechanical stress, which can lead to the destruction of the engine. In addition, the exhaust gas composition is deteriorated and there are power losses. However, these correlations can not be generalized, as they still depend on other parameters. As well as the composition of the mixture (to be rich or lean mixture), the shape of the combustion chamber and the spark plug located in the combustion chamber is crucial for the susceptibility to knock of the engine.

Is the ignition timing set too late, the piston has already moved in the direction of bottom dead center before the fuel-air mixture is completely burned. The fuel used can not fully develop its energy. The combustion temperatures are still very high when the exhaust valve opens. Part of the energy conversion takes place only after the outlet from the combustion chamber. The consequences are: Poor efficiency, higher fuel consumption, overheating problems, possibly destroy the motor.

With electronic components of the ignition timing can be adjusted by an ignition performance to the optimal operation condition of the engine. This ignition map will often favor changed by so-called chip tuning for more power, which usually comes at the expense of durability, fuel consumption and environmental friendliness.

Development of systems of ignition

From the turn of the century 1900 to about 1960, the magnetic or breaker ignition was the standard variant in motor vehicles. After power electronics was available and enabled electronic, wear-free ignition systems. In vehicles without on-board ( lawn mowers, mopeds ) and in aircraft engines, the magneto ignition will still use.

Magneto ignition

In the coil generated by induced current flow is interrupted, a high voltage pulse is generated by the collapse of the magnetic field by self-induction, which is directed to the spark plug. There he produced a flashover, which ignites the previously compressed fuel mixture. The interruption of the coil current is performed by a switch contact, which is coupled with the rotary movement of the motor. The ignition coil is in contrast to cylindrical, from the battery -powered design provided with pole pieces and is - only by a narrow air gap separated - right next to the equipped with a permanent magnet flywheel. The flywheel is mounted on the crankshaft, also serves as a flywheel and is air-cooled engines with fan cooling also fitted with fan blades. Depending on the space located within the ignition coil ( outer rotor ) or outside of the pole wheel. In addition to the ignition coil, the magnet wheel induced in a coil also further the AC power for the on-board light. Only later, an accumulator was carried to use the light even when the motor is not running can. The magneto ignition does not need power supply, since a magnetic field is generated in the coil by the magnet wheel. The permanent magnetic field moves further, the magnetic field due to the closed breaker contact is maintained and only breaks along with opening the contact. Generating the high voltage ignition pulse.

In four-stroke engines, there will be an unintentional but inconsequential ignition at the end of the discharge cycle, the so-called Wasted Spark.

In the low-voltage magneto ignition, which had 1882/83 Siegfried Marcus applied for a patent, sticking a breaker mechanism in the combustion chamber of the cylinder. The coil current was there " demolished " in the rotation of the armature, hence the name break ignition. The ignition coil has only one winding, the Abreißfunke is also the spark.

1887 built Robert Bosch magneto ignition device for a low-speed stationary engines. The breakthrough for the Magneto succeeded in 1896 by the invention by Bosch employees Zähringerplatz Arnold, who finally allowed speeds over 1,000 rpm with an improved magneto. A further improved version brought the Bosch employees Gottlob Honold in 1902 as a high-voltage magneto ignition for production. This invention led to the necessary reliability of the ignition system. Here, the ignition coil has two winding parts - a low-voltage winding for connecting the interrupter contact and a high voltage winding to the spark plug terminal. Both windings are traversed by the same magnetic field, the collapse is caused by opening the interrupter contact, after the exciting permanent magnetic field has been moved.

Also magneto ignition generally have a speed-dependent adjustment for advancing the ignition timing as the speed increases by a governor. This angle adjustment is often a hand - influenced shift value switched by cable, manual adjustment of the ignition timing or to facilitate the start-up procedure. The last motorcycle from German production with this expensive -to-use adjustment, the sports bike BMW R 68 was built before 1955. Besides the normal right throttle grip was to the ignition timing and the left handle designed as a rotary handle.

Magnetos were standard on motorcycles since the early 20th century until the 1960s. Today it has become uncommon, but were made up in the 1990s in any significant quantity small motorcycles and mopeds with Magnetzündanlagen - either to waive the heavy battery to be able to, or even to spite their presence to ensure the operability of the engine when battery fails (eg Samson ). Also, some large motorcycles were operated with Magnetzündanlagen, most recently in Germany to 1969 BMW motorcycles.

Magnetos on motorcycles can usually at their cylindrical housings ( including open or the flywheel with magnets ) seen in the immediate vicinity of the cylinder or cylinders. In the early years they were often placed in front of the cylinders, but what they prone to failure made ​​by stones and dirt. In later years the arrangement behind the cylinders was common.

To date, magneto ignition in small motors, used for example in lawnmowers or chainsaws, where even with these small engines, the mechanical contact breaker is now mostly by an electronic circuit without mechanical components (and therefore without wear) replaced.

In addition, they are used in the aircraft industry. Almost all aircraft with piston engines have magneto ignition in duplicate: In aircraft spark-ignition engines for reasons of reliability, the dual ignition provision. One of the two magnetos is usually provided with a so-called snap coupling, which makes for very slow speeds (eg during the starting process by hand or with a slow starter ) for an accelerated opening of the breaker contacts and thus a strong enough spark to the spark plugs. Conventional magnetos the manufacturer Bendix or Slick do not have a centrifugal force- driven adjustment of the ignition timing, resulting, among other things, that aircraft engines can boot from the part load full load in only reluctantly. The ignition timing is for ID for the full-load power at 75 % and higher on Usually 20 ° to 25 ° spark advance set (Sources:. Lycoming Engines, Champion Aerospace Corp. )

Battery ignition

The ignition voltage is generated in the coil as in the magneto ignition with self-induction. The current for the ignition coil is in contrast to the light flywheel magneto ignition, however, from the onboard battery (more precisely: the on-board battery). For this, a current flows through the primary winding of the ignition coil which is interrupted by a mechanical interrupter contact. Due to the very rapid change in current, the magnetic field of the coil changes and there is induced a voltage pulse, which is transformed by the secondary winding to a high voltage. A starting capacitor in parallel with the contact (usually 0.22 uF ) is connected, on the one hand reduces the spark and the other part forms a resonant circuit with the primary coil, which has the same resonance frequency as the secondary coil. In this way energy transfer is enhanced by the primary to the secondary circuit.

For motors which have more cylinders than breaker contacts, a distributor ensures ( switch on the high voltage side of the ignition coil ) for a breakdown of the ignition voltage to the correct cylinder.

The setting of an ignition system requires little skill and must be done regularly: The ignition spark at the spark plug is formed when the ignition is opened ( self-induction ). When setting the ignition timing can help an attached via the contact breaker small signal lamp. First, the Zündkontaktabstand is set and then the ignition timing, as, conversely, the first set ignition timing would be adjusted by a subsequent change in the contact distance again.

Important for the function of the ignition system is the correct Zündkontaktabstand, has a direct impact on the closing angle: Too large contact distance to a weak magnetic field ( too short a time to the current build-up ) and as a result, especially at higher speeds to a weak spark. Too small contact distance leads to increased burning of breaking contact, because you can continue to flow collapsing magnetic field of the current also there through the openable in to contact ( the contact opens too slow ). Here then helps the ignition capacitor for radio suppression is limited - the contacts burn faster than usual.

The dynamic adjustment of the ignition time ( a function of the centrifugal force of the ignition timing ) is performed with a strobe, which is triggered inductively by the ignition wire of the first cylinder. So you can watch the attached to the motor shaft markings.

Transistorzündanlagen ( TSZ-h/TSZ-i/TSZ-k )

The transistor Spulenzündanlage ( TSZ ) works like the breaker ignition, the contact breaker is replaced by a transistor. The ignition signal comes mostly from a donor, either the Hall sensor ( TSZ -h) or inductive ( TSZ -i). Older Transistorzündanlagen get this information nor upon a mechanical contact breaker ( TSZ -k).

Thyristor, high voltage capacitor ignition ( loop start )

In the high-voltage capacitor ignition, also called thyristor or CDI ( from the English " capacitor discharging ignition" ), there is an ignition system, in which a capacitor is charged by a step-up converter continuously from 300 to 400 volts. The voltage may be either a battery or a further coil, which induced voltage along with magnets in the flywheel of the engine according to the principle of the generator occur. The thyristor is located together with the capacitor in the primary circuit of the ignition transformer, and has the function of a circuit breaker. It receives at the ignition timing to magnetic sensors ( Hall sensors, or inductive sensors), a control pulse, it becomes conductive and the capacitor discharges through the primary winding of the ignition transformer. The Entladestromstoß (up to 100 A) induced in the secondary coil according to the principle of a transformer, a high voltage. In contrast to the other ignition transformer is not used as an energy store ( not self-induction ); it is therefore referred to as ignition transformer. The ignition coils of battery ignitions work with 6 or 12 V battery voltage and can not be used here.

For simple circuits, the Entflammungswahrscheinlichkeit ( gas ignition ) of fuel -air mixture due to the low spark duration at the thyristor is lower than the ignition transistor. The spark duration T depends on the resistance R of the primary winding of the ignition capacitor and the capacitance C, roughly according to the formula.

This disadvantage can be eliminated by a somewhat more elaborate electronics that can be switched thyristor longer ( multi-spark ignition ) and thereby produces a much stronger and longer-lasting spark.

The advantages of the thyristor are a higher voltage reserve, insensitivity shunts ( poor insulation ) and a reliable operation over the entire speed range. The closing angle has no significance here. It is also used in racing engines, often sports cars and especially in hydrogen engines.

Electronic ignition system ( EZ )

It differs from the transistor ignition fact that a microcomputer calculates the ignition timing due to the permanently stored values ​​of an ignition characteristic. The ignition is triggered electronically by the control unit.

Fully electronic ignition system ( VEZ )

The VEZ is the most advanced ignition system. It is referred to in the variant without rotating distributor as a dormant spark distribution.

Advantages:

• Higher operational safety through a few high-voltage connections leading
• Wear due to lack of moving (rotating ) parts.
• Less radio interference as no sparks on the outside of the combustion chamber caused
• Noise reduction
• ECM (Electronic Control Module) control allows accurate signal processing

Cons:

• Standard components can not be used often engine-specific production of the components

VEZ the processed signals from the four sensors:

• Load
• Engine speed
• Motor temperature ( optional)
• Knock sensor (optional)

There are two types of ignition coils with which a VEZ can be equipped:

Single spark coils

, Each cylinder has its own ignition coil that is driven and controlled by the control unit or by the ECM (Electronic Control Module ).

Double spark coils

By a coil, two cylinders are located on the crankshaft on the same plane, provided with spark simultaneously. Here, the fuel-air mixture of the in- stroke cylinder is ignited by a spark. The ignition circuit is closed via the parallel cylinder by a so-called support spark is produced there.

Control

The ECM uses an EEPROM (Electrically Erasable Programmable Read Only Memory) or Flash memory. Until the 1990s, EPROM (Erasable Programmable Read Only Memory) were in use, which could be reprogrammed only cumbersome. With the use of flash memory and EEPROM, the ECM can be reprogrammed in the closed state. The signal processing in the ECM operates with analog to digital converters which convert the analog signals, for example from the coolant temperature sensor to digital signals, so that the microprocessor can process them. The ignition map in the microprocessor is tuned in general the following criteria:

• Consumption reduction
• Pollutant reduction
• Increase in torque at a low speed
• Power increase
• Improve the running characteristics of the engine
• Built-up parts, according to suppliers.

In all operating conditions, such as start, full load, partial load, thrust operation Zündwinkelkorrekturen can be made when external factors (for example, engine temperature, intake air temperature, battery voltage) make it necessary.

Other integrated additional functions in the ECM are for example:

• Idle speed control
• Speed ​​limit ( variably adjustable )
• Knock control
• Emergency program
• Sensor monitoring
• Self-diagnosis

The formerly independent control unit is now usually integrated into a combined ignition and fuel injection control device, thus it is with all other electronic components in the car connection.

Laser ignition

The laser firing is a firing system, in which combustion is initiated by a focused laser beam. At the focal point of the laser beam, a plasma is generated with a core temperature of about 10,000 Kelvin by ionization. The high temperature and an outgoing at supersonic speed from the plasma core pressure wave ignites the mixture.

Advantage of laser ignition is among other things the free choice of place of ignition; a wall distant ignition with their advantages in wear and combustion efficiency can be represented easily. Due to the high ignition energy laser ignition, in contrast to the spark ignition type igniting very lean mixtures.

The laser ignition was realized for example in a single-cylinder test engine, Vienna University of Technology. Some of the major hurdles for use in vehicles are size, price and power requirements of the laser ignition. In a cooperation between CTR and AVL List a laser spark plug is developed, which is suitable for mobile applications.

Overall, it must be noted that the laser ignition is still in the research stage.

Suppression

The spark generate high frequency glitches that need to be suppressed. There are the following measures:

• The spark plug or spark plugs contain a built-in suppression of about 5 k. It limits the maximum current, the rate of current rise, and thus the interference generated.
• The ignition cables are routed as close as possible to the engine block.
• The distributor receives a shielding metal cap.
• Complete shielding of ignition ( spark plug, cables, distributor )
• Firing capacitors across the interrupter contact ( necessary for the function, but also reduce the disturbances )
• Decoupling capacitors to ground in the ignition power supply circuit; they prevent the propagation of faults in the electrical system.

There are two Entstörklassen for EMI suppression: The legally prescribed for all automotive remote debugging and non-statutory Nahentstörung.

The aim of the remote debugging is the reduction of the interference field strength for the protection of radio and television reception in the vicinity of the car ( are required by law at least 5 k per ignition circuit ). 15K per ignition circuit should not be exceeded, otherwise the spark is too weak.

The Nahentstörung for vehicles with built-in radio receivers comprises not only a possibly higher suppression, but in particular blocking capacitors in the primary ignition circuit. Often the audio equipment must be protected by additional filters in the car, in order to suppress the interference of the alternator.

Literature

Reference Books

• Engineer Karl -Heinz Dietsche (FH ) Thomas Hunter, Robert Bosch GmbH: Automotive Handbook. 25th edition. Friedr. Vieweg & Sohn Verlag, Wiesbaden, 2003, ISBN 3-528-23876-3.
• Ing Jürgen Kasedorf, Richard Koch: Service Primer for the automotive electrical systems. An Introduction to the vehicle electrical system. 14th revised edition. Vogel Verlag, Würzburg 2001, ISBN 3-8023-1881-1, ( bird - book: Service Primer ).
• Rudolf Hüppen, Dipl Ing Dieter Korp: Auto Electrical. Ignition, battery, alternator, starter, instruments, appliances, lighting. 7th edition. Engine book publishing house, Stuttgart 1972, ISBN 3-87943-059-4, ( now I help myself 20).

Brochures

• Bosch Technical Instruction radio interference suppression. 1st edition, Robert Bosch GmbH, Stuttgart, 1978, VDT -U 1/2 DE
• Bosch Technical Instruction circuit symbols and circuit diagrams of the vehicle electrical system. 2nd Edition, Robert Bosch GmbH, Stuttgart, 1974, VDT - UBE 001/ 10

• Ignition (internal combustion engine )
• Fahrzeugelektrik