BOSCH L JETRONIC / LUCAS 5CU
ORIGINS
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.
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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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