KD EFI Patent
Kokusan Denki Patent US 6,854,450 B2
This 2005 patent reveals some of the inner workings of the ECU. Even by patent standards, it's not particularly easy to read. There is a lot of redundancy and it was probably translated directly from Japanese into English. There are 13 claims.
I will offer my interpretation below. If you prefer to read the primary source, it is available in the adjacent panel.
I find it ironic that the patent's intent is to provide improved starting, when difficult starting was the number one complaint most new OSSA owners had.
Kokusan Denki ECU Patent US6854450B2.pdfPatent Highlights
The following highlights are incomplete, but better than nothing...
The ECU was developed for small-displacement engines without a battery, and thus started by human power via kicking or a recoil (pull) starter, both of which are subject to variations in cranking speed.
One objective was to improve starting by determining the injection pulse width after consideration of variations in the cranking speed (which affects the amount of air inducted and thus influences the correct amount of fuel to inject). Paraphrasing the patent: The first injection amount decision determines an injection time (the injection amount) in accordance with cranking speed. The injection time becomes shorter as the cranking speed becomes higher.
Engine temperature plays a role in the starting algorithm.
Partly, the rate of rise of the generator's output voltage is used to “speculate” cranking speed.
Injection only commences when the output of the generator reaches a value capable of opening the injector.
The first injection/ignition event is special. It follows a different algorithm than subsequent steady-state running.
Spark is inhibited until an injection has occurred (an effort not to waste precious generator power on a useless event).
Sufficient fuel evaporation time is allowed before the ignition is made operational.
It's possible that a successful injection decision for a given cranking speed is saved in non-volatile memory for future use.
Because the generator's output frequency is used to speculate crankshaft position, a ring gear sensor is not necessary to obtain minute crank-angle information. Thus, a simple pulser may be used to obtain the rotational speed information, and a cost savings may be realized.
The current embodiment of the AC generator produces 6 cycles per revolution. Thus, that waveform's phase is “reversed” (crosses zero) every 30 degrees of crankshaft rotation.
Figures 2 and 4 appear to be identical with the exception of an additional block (65 Phase Winding) in Fig. 4 block 49' (prime) contains the addition of “phase reversion number” as well. In the current embodiment, 8 phase reversals (240 degrees of crank rotation) is considered sufficient fuel evaporation time for the first ignition event.
Webmaster's note: The procedure for starting an EFI OSSA is quite different from starting a 4-stroke EFI Montesa (which uses a Keihin integrated ECU / throttle body). From experience, I know the OSSA requires a quick forceful movement of the kickstart lever, whereas the Montesa requires a slow deliberate movement of the kickstart lever.
SAE 2003-32-0067
This all reminds me of the 2003 SAE paper Drivetrain Effects on Small Engine Performance. It talked about challenges in simulating high performance single-cylinder two-stroke engines due to significant “in-cycle” fluctuations in crankshaft speed. That is to say, the instantaneous crankshaft speed is anything but constant -- it is lower during the compression phase and higher during the power phase. Several factors were identified as being pertinent:
• low firing frequency
• low number of cylinders (or groups of simultaneously firing cylinders)
• low rotational inertia
• high peak cylinder pressure