Hur övervarvningsskyddet fungerar

Ett forum för allt möjligt tekniksnack kring VTX 1300 och VTX 1800.

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Inlägg: 761
Blev medlem: 28 aug 2005, 13:36
VTX-modell, årsmodell: VTX 1800, 2002
Namn: Håkan K
Ort: Stockholm, VTX 1800

Hur övervarvningsskyddet fungerar

Inlägg av snake » 30 aug 2009, 22:12

Med anledning av diskussionen om hur mycket VTXen kan varva så kastar jag in ett gammalt inlägg jag skrev på VTXOA.COM. Den förklarar hur det hela fungerar. Dock på engelska. Är det något ni inte förstår så kan jag översätta.


The ECU reads the engine rev using the IPS (Ignition pulse sensor) and CPG (Cam pulse generator). The cam pulse generator generates a 3 pulses per cam revolution, whereas the IPS generates 11 pulses per crank revolution. This is how the ECU estimates the RPM.

The rev limiter does not affect the ignition. It only stops the injector pulses.

In the next picture you can see how the ECU stops the injector pulse when revs. exceed 5750 RPM. The time between the last two injector pulses is 20.8 ms, which corresponds to 5769 RPM. The pulses are back online at 5556 RPM.


In the next picture you can see that the ignition pulses continue to be generated. Thus, a valid spark is produced even when the rev. limiter kicks in.


The ignition system and the coils seem to have much more juice left. It is far from being saturated and the coil charging current is still good even at 5750 RPM. In fact, the coil could easily handle three times the load (rev) and still have time to rest between charges.



So, extending the revs should just be a matter of forcing a continuation of the injector pulses. An in-line pulse generator that just interpolates a regenerated signal when the ECU signal stops should be enough. Cheap hardware could do that.

Then of course it is a question about the ignition advance at those revs. I do not know if the VTX 3D ignition map will continue to advance the map when it is operating outside of specs. My measurments indicate that the ignition starts to be retarded at 5500 RPM, but I have only ran a few tests so it might be a fluke in my data...
Honda VTX 1800C -02
Excelsior Henderson Super-X -00

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