Distributor

The distributor is an assembly of the ignition system of a multi-cylinder gasoline engine that performs several functions:

• The triggering of the spark through the Breaker ( Ignition, Ignition on contact ) or Hall effect sensor ( contactless ignition)
• Distributing the high voltage generated in the ignition coil to the spark plugs
• Chance also the speed limit of the motor.

The name of the module is based on the single recognizable from the outside of the high voltage distribution function and the other functions are invisible from the outside in the interior of the assembly take place.

Modern engines do not have a distributor yet breaker contact / Hall sender. You have full electronic ignition systems, which have no moving parts. The calculation of the ignition timing is performed by a control unit, the spark is of one-spark or double spark coil (s) is generated ( an ignition coil for two cylinders, the so-called wasted spark ).

Construction

The assembly is housed in the control in a case: the head portion consists of a distributor cap, to the ignition sequence of the engine in which the ignition cable leading to the spark plugs, as well as the high voltage cable of the ignition coil are mounted outside coming. On the inside of the cap are contact surfaces. Under the distributor cap on the distributor shaft inserted the distributor rotor rotates (also called " Distributor Rotor " ), headed by a contact surface is attached. At the time of ignition, the contact area is at the distributor rotor directly at the contact surface of the corresponding cylinder in the distributor cap. However, there is no direct contact; the narrow gap between the contacts will be skipped from the high voltage. Although there is no mechanical wear occurs on the contact surfaces, caused by the burning of the Hochspannungsfunkens wear on the contact surfaces of the rotor and cover.

The distributor rotor a suppression is often integrated to reduce radio frequency interference. Various engines (up to about the mid-1980s ) with contact or transistor ignition have distributor rotor with a working by spring force centrifugal rev: above a specified rpm, the high voltage generated is dissipated to ground and thus forwarded no more ignition voltage to the spark plugs.

Under the distributor rotor are mostly covered by a plastic cap, the Breaker, the ignition capacitor (often attached to the outside ) and the facilities for speed-dependent adjustment of the ignition ( by vacuum or by centrifugal force ). In today's conventional contactless ignition systems Breaker by an electromagnetic sensor ( Hall sensor ) is replaced, who need not necessarily be arranged in the distributor, but can also be located at the crankshaft or flywheel.

In the lower part of the housing, the transfer shaft is supported. At the top it has a receptacle for the distributor rotor to which this is attached torsion. Among them, the distributor shaft with a contact-controlled ignition system, a number of cylinders of the engine corresponding number of Zündnocken. In a four- cylinder engine, the cross section of the distributor shaft in the area of ​​Zündnocken is a square with very rounded corners. The Zündnocken operate the breaker contact. In the contactless ignition of a rotating bezel is installed which controls a Hall sensor. At the lower end of the distributor shaft, a coupling piece through which it is driven.

Since four-stroke engines the distribution shaft rotates with the camshaft rotational speed ( = half the crankshaft speed ), it is often driven directly by the camshaft, wherein the distributor is arranged at one end of the camshaft. At Volkswagen boxer engines such as the shaft of the distributor, and the oil pump of the helical gears of the camshaft is driven. This was widely used in motors with lower camshaft.

In various modern ignition systems such as the Motronic has the distributor exclusively the function of the high voltage distribution. Ignition timing and rev limit is determined directly by the engine control unit.

Function

During the rotation of the distributor shaft of the ignition contact of each Zündnocken (whose number is equal to the number of cylinders of the engine ), opened and closed. Upon opening of the contacts of the circuit of the ignition coil primary coil is interrupted. Then breaks in it along the magnetic field and induced in the secondary winding of the ignition coil a high voltage from the ignition coil (standard name: terminal 4) is sent to the central terminal 4 in the cap of the distributor. The distributor rotor located on the upper portion of the distributor shaft passes the high voltage to the connections leading to the spark plug wire. The distributor shaft rotates with the camshaft (with four-stroke engines ) or crankshaft speed ( for two-stroke engines).

Ignition timing

The ignition timing is the instant at which the ignition contact interrupts the primary circuit of the ignition coil and by the collapsing magnetic field of the primary winding into the secondary winding of the high voltage is induced. These springs in the form of a spark at the spark plug and ignited on the fuel- air mixture.

The timing of the lifting of the contacts, and thus the ignition timing is changed by rotation of the distributor housing.

Since it takes a short time to the combustion peak pressure is reached after ignition by the spark, the spark timing is always close to the top dead center of the piston in the working cycle, so that the maximum compressive at the right moment acting on the piston. A change of the ignition timing thus has an effect on the performance and life of the motor. Therefore, the name of the manufacturer must be observed.

Ignition timing

In order for the engine in all speed ranges achieved optimal performance and emission values ​​, the ignition timing must be adjusted depending on the operating condition.

• Vacuum advance

The adjustment affects especially when accelerating in the lower speed range. It is made of a diaphragm box ( vacuum box ) on the ignition distributor, which is driven by the negative pressure close to the throttle valve in the intake tract. About one connected to the diaphragm pull rod, the contact plate of the switch is turned in the direction of pre-ignition. Some distributors is for the operating state idle / coasting a second "late can" present, again "late" shifts the ignition timing to the exhaust improvement in direction, but the spark advance adjustment is subordinate with negative pressure or centrifugal force.

• Centrifugal advance

She comes first in the upper rev range effect. On the distributor shaft is a corotating with axle plate is attached to the return springs flyweights, which are pressed with increasing speed to the outside. Here the Zündnocken is twisted on the distributor shaft in the direction of "ignition " on other mechanics. By the shape and mass of the flyweights, and the spring characteristic of the return springs is formed, a motor adapted Zündverstell characteristic.

• Speed ​​limitation

To prevent too high a speed of the engine, a centrifugal speed limiter is additionally incorporated in some designs. This causes a special distributor rotor, that the high voltage spark above the shutdown is no longer distributed to the cylinders. The motor starts then lack of ignition " stutter ", and the speed is reduced again. For vehicles without this device, the speed limit on the electronic engine control is realized that allocates no more fuel from a maximum speed of the engine. To avoid damage to the catalytic converter comes with Kat vehicles, only the latter variant in question, otherwise unburned fuel enters the catalytic converter and damage it.

Functional test

The correct function of the high voltage part of an ignition system can be detected with pulling of a plug and a separate, held to ground the spark plug (Caution high voltage ). In this case, a stable compound is very important. Is this, however briefly interrupted, electronic components can be damaged by the then resulting voltage peaks. In older contact-controlled ignition systems with purely mechanical interrupter this danger does not exist.

The ignition timing can be checked in the state with a simple test light. With the engine running, he is determined with a timing light or a testing computer. The diagnosis with an engine analyzer and the determination of an oscilloscope image of the ignition system is preferable, however, to get an accurate picture of the entire ignition system.

Dysfunction

The contact gap of the circuit breaker is usually 0.4 mm. Due to wear on the bearing of moving parts and by age-related changes in force of the return springs ( centrifugal weights ) leads to differences in the timing curve. Already 0.1 mm clearance has a major influence on the engine performance and the concentricity of the engine. Therefore Distributor have been developed for older or historic vehicles in which the ignition contact was replaced by a sensor. The flyweights were replaced by electronics. The displacement curves are preprogrammed for different motors and for different usage purposes and can be selected via a switch. Some of these Distributor recognize a sensor smallest angular error in the rotational movement and correct this by moving the ignition timing.