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Electrical System

Spark Plug Development and Testing

HOW INVOLVED IS BOSCH IN THE DEVELOPMENT AND MANUFACTURING OF SPARK PLUGS?

The history of the spark plug, one of Bosch's most traditional products, goes back 100 years. In 1902 Robert Bosch presented for the first time an ignition system with spark plugs, the so-called high-voltage magneto ignition. Since then, Bosch spark plugs have been continuously developed into environmentally friendly system components. Today spark plugs make a significant contribution to protecting the engine and catalytic converter and increasing economy in fuel combustion.

With years of know-how and intensive further development of spark plugs in close working cooperation with practically every vehicle manufacturer in the world, Bosch has gained a competitive advantage in development and secured its position as a market leader. With more than 1,400 versions of spark plugs, Bosch covers the entire market.

Whether air, land or sea - Bosch spark plugs are in use everywhere. The spark plug product range covers approximately 98% of all passenger car engines on a worldwide scale. The Bosch spark plug product range comprises the most varied spark plug techniques and concepts, mirroring the multiplicity of spark plug applications.

Every day a million spark plugs leave the Bamberg, Germany plant, Bosch's sole production facility in Europe for spark plugs. For targeted supply of local markets and original equipment manufacturers, spark plugs are also produced in India, Brazil, china and Russia according to Bosch's worldwide standards of high quality.

WHAT TESTING IS CONDUCTED BY BOSCH TO DETERMINE THE PROPER SPARK PLUG FOR A VEHICLE?

Bosch uses high sophisticated methods for spark plug testing. The first step is to determine the hottest cylinder in the engine. To do this, Bosch uses a special spark plug called a thermo-couple plug (temperature measuring spark plug). It looks similar to a conventional spark plug, except the center electrode has been modified to accept a small thermo-couple. The thermo-couple spark plug is installed in the cylinder, and the vehicle is then driven on a chassis dynamometer. The vehicle is driven at full load (accelerator pedal to the floor) and the vehicle speed is controlled by the dynamometer. The dynamometer absorbs the maximum horsepower (hp) produced by the engine at each set RPM point. Absorbing this hp allows the engine to reach peak cylinder temperatures at each set point. The temperature measurement is then repeated with the same temperature measuring spark plug in all cylinders in turn (i.e. a 6-cylinder engine requires six separate measurements.)

Next, it is necessary to match the thermal behavior of the spark plug to the engine type. The temperature of the insulator nose must be high enough to ensure that soot deposits are either avoided or burnt-off. On the other hand, the spark plug must not become so hot in the critical operating ranges that the air-fuel mixture is ignited by the hot surfaces (thermal ignition) of the spark plug. Therefore, a temperature measurement alone is insufficient for determining the required heat range.

After testing each cylinder, a comparison of cylinder temperatures at each set point is made. From that information the hottest cylinder is determined. Now the ionic current measurement method can be used to determine the correct spark plug for the engine. In simple terms, ionic current measurement is a procedure developed by Bosch, which uses the spark plug as a sensor. The gap between the center electrode and ground electrode is used to measure the ionization of the gases. As the cylinder temperature increases, the spark plug may become thermally overloaded (too hot) and will cause the air-fuel mixture to ignite before the standard ignition point (pre-ignition) or after the standard ignition point (post-ignition) resulting in ionic current flow, which can be monitored with an oscilloscope.

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