1978 article from le Double Chevron 52 about the integrated electronic ignition fitted to the CitroŽn Visa
The integrated Electronic Ignition . used in the Citroen VISA Special and Club models is a technological break-through in the ﬁeld of ignition.
Designed by Thomson CSF in close liaison with the Research and Development Management of Citroen, it is here used for the first time in a mass-produced car.
It is the most advanced automobile ignition system presently available.
Electronics is the science of the motion of electric charges (electrons) through semiconductors.
It has already modiﬁed motor-car technology (rev counters, automatic gearboxes, fuel injection, etc. ).
It is, justifiably, considered that this pathway can only broaden with time.
It is from this science that the motor car may now expect its most important advances.
One of these, concerning ignition, is already an accomplished fact.
The purpose of ignition is, of course, to produce the energy required to ﬁre the air-fuel mixture, at the desired moment in the engine's functioning cycle,and to distribute this energy, in the right order, to the various cylinders.
Since the mixture volume catches ﬁre in successive "slices" it is necessary, according to the piston’s travel, that ignition should always take place with a certain advance, which increases with the engine’s
speed of rotation.
Dependent on satisfactory ignition and spare advance, at all times geared to engine speed and load, is the engine's efficiency, or in other words its low consumption and correspondingly reduced pollution, both these factors having assumed major importance of recent years.
From incandescent-tube ignition at the end of the XIXth century, the motor car went on to magneto ignition (which produces a low tension in a magnetic ﬁeld, and transforms it to HT before distributing it to
the plugs), then distributor and coil ignition, first generation of modern ignition systems: the battery-stored low tension current (6 to 24 volts) runs through the primary of a coil; interruptions in this
current produce voltage variations generating high tension (15,000 to 20,000 volts) in the coil’s secondary windings.
This current, distributed to the plugs, produces the spark.
It is the distributor that provokes periodical breaks in the LT current, breaking the contact between the "points", it is driven by cams connected to the engine timing shaft.
Centrifugal masses and depression capsules modify the way the cams operate the make-and-break in such a way that spark advance remains adapted to engine speed and load.
For each cycle of the engine, there will be as many breaks in the current — and therefore as many ignition sparks — as there are cylinders in the engine concerned.
1 engine cycle = 2 engine revolutions = 2 sparks for a twin, 4 sparks for a 4-cylinder engine, etc.
A 4-cylinder engine running at 6,000 rpm will have 12,000 make-and-break operations per minute, i.e. 200 per second, or 20 every tenth of a second!
These values, today considered normal, are already very high for a purely mechanical device.
High engine revs will provoke make-and-break ﬂutter, the system being unable to keep up with the pace.
This results in a voltage drop in the secondary.
For this reason, transistorized, or second-generation, ignition has been called upon.
Surviving components are the make-and-break (in certain cases), and the classic advance corrector and distributor; but to them is added a transistorized module which regulates the coil's charging-up time so that a high primary current is secured, resulting in increased voltage in the secondary, the voltage remaining constant whatever the engine speed.
This makes for easier cold starting and improves engine efficiency, thus reducing consumption.
A yet more advanced system, used for instance in the
CitroŽn CX 2400 GTI, has a magnetic sensor transmitting its signals to the module, instead of the classic make and break.
But these systems retain all the mechanical advance correctors, with their proneness to wear and breakdown, which may degrade the trueness of the advance curve.
This is why 100% electronic ignition has been envisaged: here now is the third-generation ignition.
This system, using an electronic advance calculator and energy regulation, functions without being mechanically connected to the engine.
The make and break is done away with, while the transistorized module of second -generation systems is replaced by an electronic calculator of the logic analogic type, which receives and processes data as
would a computer.
Two proximity sensors (with integrated electronic circuits: oscillator, amplifying filter) input the engine speed into the computer.
A depression sensor inputs the engine's state of load (inlet manifold pressure drop).
From these data, the computer instantaneously decides sparking time, simultaneously correcting the advance curve and sending to the coil the primary current necessary to produce constant, high energy in the secondary, irrespective of engine speed.
The advantages of Integrated Electronic Ignition are many:
|© 1978 le Double Chevron/2013 CitroŽnŽt
- thanks to JL