Knock Sensor: Description and Operation

Ignition System

General information

The functional principle of the ignition system for the DFI flat-six engines essentially corresponds to that of the Cayenne V8 DFI engines. The ignition system map in the DME control unit has been designed to meet DFI-specific requirements.

Knock sensors

One knock sensor each is bolted to the left and right crankcase sides. These sensors detect knocking combustion in the corresponding cylinders. To prevent knocking, the cylinder-selective knock control system monitors the electronic ignition-timing control system. Based on the signals from the knock sensors, the DME control unit adjusts the ignition timing angle for the knocking cylinder until the knocking stops. If a knock sensor fails, the ignition timing angles of all cylinders are retarded under load. In other words, a safety timing angle in the "retarded" direction is set. This considerably reduces the engine power and increases fuel consumption.

Ignition coils







The DFI flat-six engines feature static high-voltage ignition distribution with active individual ignition coils directly on the spark plugs. The new individual ignition coils feature an integrated output driver (active ignition module) that is activated individually for each cylinder in the firing order 1-6-2-4-3-5 by the DME control unit. Furthermore, the diagnostic function is also integrated into the ignition module. If an ignition coil fails, fuel injection for the affected cylinder is deactivated.

This system offers the following advantages:
- High level of ignition reliability
- Minimum electromagnetic interference with other electronic components
- No requirement for ignition cables and ignition distributor

Ignition coil with integral driver

All parts in this newly developed component are installed as a complete unit in a special rod ignition module housing. This is connected electrically and mechanically to the spark plug in the spark-plug recess via the short high-voltage plug. The component is also secured mechanically using bolts. The ignition coil is sealed at the four-pin plug and in the spark-plug recess to protect it from spray water. Compared to the illustrated Cayenne V8 ignition coil, the output stage of the new sports car rod ignition module is located directly on the printed circuit board. There is no longer a separate heat sink (2). The cooling concept has been integrated into the printed circuit board.







NOTE: The ignition coil must not be tilted when it is removed, because the body of the coil reaches into the spark-plug recess.

Surface-gap spark plugs

The four ground electrodes are arranged around the ceramic insulator in the surface-gap spark plugs. The sparks (1) cross the surface of the insulator (4) and arc across a small gas gap to the ground electrode (2), which improves the ignition properties. The main advantage of the surface-gap spark plugs is the self-cleaning effect of the insulator foot tip, since any shunts that occur between the center electrode and the ground electrode through the surface gaps, in particular during a cold start, are eliminated.







NOTE: Refer to the market-specific maintenance schedule for the change interval of the surface-gap spark plugs.