Page 260 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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244 Automobile mechanical and electrical systems

Figure 2.325 Inductive distributor

Figure 2.326 Distributorless ignition coil in position

2.6.3 Distributorless ignition system (DIS)

Key fact Distributorless ignition uses a special type of ignition coil, which outputs to the
Distributorless ignition outputs to spark plugs without the need for a high-tension distributor ( Fig. 2.326 ).
the spark plugs without using a
distributor. The basic principle is that of the ‘lost spark’ ( Fig. 2.327 ). The distribution of the
spark is achieved by using two double-ended coils, which are fi red alternately by
the ECU. The timing is determined from a crankshaft speed and position sensor
as well as a load (MAP) sensor and other corrections such as engine temperature.
When one of the coils is fi red a spark is delivered to two engine cylinders, either
1 and 4 or 2 and 3. The spark delivered to the cylinder on the compression stroke
will ignite the mixture as normal. The spark produced in the other cylinder will
have no effect, as this cylinder will be just completing its exhaust stroke.
Because of the low compression, and the exhaust gas in the lost spark cylinder,
the voltage used for the spark to jump the gap is only about 3 kV. The spark
produced in the compression cylinder is therefore not affected. An interesting
point here is that the spark on one of the cylinders will jump from the earth
electrode to the spark plug centre. Many years ago this would not have been
acceptable as the spark quality when jumping this way would not have been as
good as when jumping from the hotter-centre electrode. However, the energy
available from modern constant energy systems will result in a spark of high
quality regardless of its polarity.
The DIS consists of three main components: the ECU, a crankshaft position
sensor and the DIS coil. An MAP sensor is integrated in the module or mounted