Full trailing-spark support is implemented since 1.1.77
Useful for
- rotary (usually 2 or 3 rotor Wankel engines)
- or twin-sparkplug (usually 4-8 cylinder engines where each cyl has 2 sparkplugs) engines (eg. many alfa-romeo), low trailing spark delay is common here (often just a 0.5 degree to be softer on the harness and supply and for less electro-noise).
Important notes:
- remember to generate double RPM, eg. "10000 RPM" signal when you want 5000 RPM signal for a wankel/rotary.
- Reason: the mazda wankel has 1 sectrig pulse every 360 degree. While the signal generators assume 1 sectrig per 720 deg. (eg. VemsTune Tools / Play trigger).
- it is highly recommended to set up trailing spark with knock disabled. (bad knock settings can cause more confusion here than with a normal setup)
Below we assume 12 primary trigger pulses for 1 secondary trigger pulse, but almost any other trigger should work (including missing tooth and even subaru/fiatstilo which does not allow HALL-dirac filtering, but works with rotary).
- Adjust everything (including ign_tdcdelay) for the leading spark
- and just configure reftooth=128 for trailing spark
- which means: timed from the same tooth as the leading, just with the configured RPM-dependent delay, and using different output.
- in practice every second reftooth will be 128. The first (topmost in VemsTune) must not be 128 ... normally 0 anyway
Rotary trailing spark configlet examples - ignout and reftooth settings for trailing sparks are highlighted
2 rotor example:
(note: hexadecimal 80 = 128). ignout2 and ignout3 are leading sparks (at 0 and 6 tooth offset respectively). The trailing spark is wasted spark on ignout6.
- another_trigger_tooth=06
- h[1]=00 80 06 80 ...
- h[2]=20 60 30 60 ...
3 rotor example (ignch 2,3,4 are leading, 5,6,7 are trailing):
- another_trigger_tooth=04
- h[1]=00 80 08 80 04 80 ...
- h[2]=20 70 40 60 30 50 ...
- the delay is adjustable (0..63.75 degree) in function of RPM
- note that the definition of degree is not as self-evident as for the alternating piston engines
On the 2nd generation Mazda rotaries (1986 thru 1991), the input signals are provided by two inductive pickups in the Crank Angle Sensor (CAS). The CAS contains two reluctors, one with 24 teeth, and the other with two teeth. As I write this, I'm remembering an on-line article that provides these details better than I could:
http://www.teamfc3s.org/info/articles/demystifying.html
This covers the stock ignition system in some detail. Ideally I would like to retain the stock CAS, igniters, and coils, and drive them with a new controller.
Very good intro indeed.
So you have 2 rotors, with 4 sparkplugs: 2 leading and 2 trailing plugs. The leading plugs are fired simultaneously, the trailing plugs are fired alternating.
Translating to GenBoard usage and programming:
- feed the 24 teeth/CAS to IC3 input
- feed the 2 teeth/CAS to TACH (INT6) input
- write the phase-calculation (timing.c)
Stock Coil/Driver Configuration
This uses the factory Mazda leading and trailing coil packs, with integrated drivers.
| Coil | Firing Mechanism | Note |
| Leading Coil | 5v digital output to IgT controls firing and dwell. | Waste spark configuration; one coil fires the plugs on both rotors. |
| Trailing Coils | 5v digital output to IgT controls firing and dwell. 5v digital to Select line controls which rotor to fire. | One driver is connected to two coils. Which coil fires depends on the state of the driver's Select line. |
Dummy Coil Configuration -- Wasted Leading Spark
This configuration uses 3 coils total. One for the leading, and two for the trailing.
| Coil | Firing Mechanism | Note |
| Leading Coil | IGBT in genboard fires coil and controls dwell. | Requires a two post coil, because of wasted-spark configuration. |
| Trailing Coil (Front) | " | Connected to trailing spark plug in front rotor housing. |
| Trailing Coil (Rear) | " | Connected to trailing spark plug in rear rotor housing. |
Independent Coils -- Independent Coil Packs
This configuration uses four independent coil packs. It is the least sophisticated coil configuration, and would be the easiest to implement using existing hardware and software support.
| Coil | Firing Mechanism | Note |
| Leading (Front) | IGBT in genboard fires coil and controls dwell. | |
| Leading (Rear) | " | |
| Trailing (Front) | " | |
| Trailing (Rear) | " |
See also:
and search for rotary ...