Capacitor discharge ignition
An excerpt from the 'Motorway' Jan 11 1906, describes its use on Ford six cylinder cars: 'The efficiency of the Ford Magneto is shown by the fact that the instant it is switched in the car will pick up speed and, without changing the position of the ignition control lever, will run at least ten miles an hour faster.'
During World War Two, Bosch had fitted thyratron (tube type) CD ignitions to some piston engined fighter aircraft.
This early German system used a rotary DC converter along with fragile tube circuitry, and was not suited to life in a fighter aircraft.
In the mid-1950s, the Engineering Research Institute of the University of Michigan in cooperation with Chrysler Corporation in the United States worked to find a method to produce a viable solution.
Namely; a fast voltage rise time to fire fouled or wet spark plugs, high energy throughout the RPM range resulting in better starting, more power and economy, and lower emissions.
The unreliability of those early thyratron CD ignitions made them unsuitable for mass production despite providing short term benefits.
For the Wankel powered NSU Spider of 1964, Bosch resurrected its thyratron method for a CD ignition and used this up until at least 1966.
It was the SCR, Silicon-controlled rectifier or thyristor invented in the late 1950s that replaced the troublesome thyratron, and paved the way for a reliable solid-state CD ignition.
Unwanted trigger impulses in early attempts at using SCRs for CD ignitions were caused by electrical interference, but the main culprit proved to be 'points bounce'.
In the standard system with points, distributor, ignition coil, ignition (Kettering system) points bounce prevents the coil from saturating fully as RPM increases resulting in a weak spark, thus limiting high speed potential.
In a CD ignition, at least those early attempts, the points bounce created unwanted trigger pulses to the SCR (thyristor) that resulted in a series of weak, untimed sparks that caused extreme misfiring.
A company was formed in Ottawa in early 1963 called Hyland Electronics building CD ignitions using the Winterburn design.
Points lifespan became a factor of rubbing block (cam follower) wear and the life cycle of the spring with some lasting almost 100,000 miles.
The UK Wireless World magazine of January 1970 published a detailed Capacitor-discharge Ignition system as an electronic hobby build project by R.M.
The circuit of this system was similar to the Winterburn patent in that it used a push-pull converted switch mode oscillator for energy transfer to a store - discharge capacitor and conventional contact breakers to initiate a thyristor triggering discharge of the charged CD capacitor.
Among which: better combustion, easy starting even under subzero conditions, immunity to contactor (points) bounce and 2% - 5% fuel economy.
Subsequent letters to Wireless World ( March & May 1970), with Mr. Marston's replies, further discussed aspects of the design and build.
Most ignition systems used in cars are inductive discharge ignition (IDI) systems, which are solely relying on the electric inductance at the coil to produce high-voltage electricity to the spark plugs as the magnetic field collapses when the current to the primary coil winding is disconnected (disruptive discharge).
The amount of energy the CDI system can store for the generation of a spark is dependent on the voltage and capacitance of the capacitors used, but usually it is around 50 mJ, or more.
Actual measurements show the real world efficiency to be only 35 to 38% when coil primary winding losses are included.
This eliminates the problem of burned and worn points, and provides a hotter spark because of the faster voltage rise and collapse time in the ignition coil.
[citation needed] The fast voltage rise makes CDI systems insensitive to shunt resistance, but the limited spark duration can for some applications be too short to provide reliable ignition.
