Fuel injection and the Jaguar XJ6 4.2 Series 3 [ Main ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ]

Roger Bywater of AJ6 Engineering,
former power units engineer at Jaguar



Bosch introduced the first volume produced Electronic Fuel Injection system in the mid-1960s calling it D Jetronic. Really, it owed a lot to the innovative work carried out earlier by Bendix in the USA and the fundamental operating principle of controlling the amount of fuel admitted to each engine cylinder via solenoid operated fuel injector valves is still with us today. Instead of having a system of metering orifices like a carburetter does to control the flow of fuel, metering was achieved by varying the duration of pulses applied to the solenoid injectors. By generating one pulse for each engine cycle and controlling its duration according to signals from various sensors about the engine the fuel input could be matched closely to the requirements of that engine.
The primary sensor used by D Jetronic was a manifold pressure sensor of variable inductance to monitor engine load and further correction was added according to engine speed to take into account changes of volumetric efficiency. The analogue technology of the time employed a large number of discrete transistors, resistors and capacitors to generate the injector pulses according to laws in the form of simple curves which were best matched to the engine requirement. Further corrections were applied according to coolant temperature and air temperature sensed by suitably placed thermistors (temperature sensitive resistors). A rather complicated rotary switch attached to the throttle linkage identified the closed throttle condition, produced a sequence of acceleration enrichment pulses as the throttle opened and, in USA emission versions, activated power enrichment at the full throttle position. In European versions this latter function was incorporated into the pressure sensor instead. A variant of D Jetronic survived on the Jaguar V12 until 1980.

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