The AntiLagSystem (ALS) is a mode, where you try to make the turbo spin when switching gears (or at the starting line). This should be activated with a switch except for racecars.
ALS can be achieved by retarding the spark very heavily, eg. 10..30crankdegrees after TDC (the distributor might not allow too late, but we usually distributorless anyway).
At the same time the idle strategy is different than for normal nonALS streetdriving:
- For streetdriving all injection and spark is cut above ~1500 RPM, so the RPM drops fast.
- With ALS mode switched on we allow the RPM (controlled by the Idle Valve) to decay slowly.
The point in this is to push through much air through the engine to spin the turbo without spinning up the engine to skyrocket RPM at shifting. This does no good for efficiency or the clutch, or the valves / exhaust system.
See MembersPage/GaborRacz/NewAlsLaunchAndOthers for the current bleeding-edge ALS implementation.
Here is the latest and greatest on ALS - Frank Katzenberger
There is a method to the madness of fast power... assuming the ALS inhibet switch is off. When the driver lets off on the throttle and TPS-WAS > X setpoint and MAP-WAS > Y setpoint, you engage the ALS and retard the timing by 10 degrees from TDC and dump extra fuel (MAP-WAS vs PW modifier - tablelookup). This extra fuel (aka pig rich) doesnt burn off completely during the exhaust cycle and either continues to burn or re-ignites off of the hot manifold creating pressure to spool the turbo. You will need to keep the Idle at around 10% to keep flow.
This keeps positive pressure before the throttle body and keeps lag (power avalability) way down.
People complain about trashing your exhaust valves or manifold or turbo, but with a programmable system with a tablelookup, you can set strength of ALS. I would also incorporate a failsafe by looking at coolant temp and if it is too high, then keep it from engaging.
Additional ALS info can be found here:
http://www.rallycars.com/Cars/bangbang.html
Fast ALS cooldown - Jörgen.
In those cases where a constant large throttle opening is used (instead of a throttle bump solenoid or bypass valve.) the idle is very high. By using a soft touch rev limiter that cut fuel instead of spark you can have a very decent idle and cool down the valves, exhaust manifold and turbo VERY quickly. Sequential injection is needed for this to work ritght.
See IdleControl for more info
Info on ALS
Most racing implementations have user selectable anti-lag settings depending on the terrain, usually three settings can be selected by the driver going from mild to very aggressive.
Note that some regional or national European events prohibit the use of ALS systems while more and more WRC events regulate the noise levels allowed by competition cars effectively disabling ALS.
Starting in 2002 new anti-lag techniques, such as Exhaust Gas Recirculation (EGR), are slowly overtaking the method described above as they are kinder on the engine's mechanical parts.
ALS ideas:
I've checked the working of the ALS in a group-A rally car, powered by motec. I think we could use theese methods. Several thing works already in our firmware, but it could be usefull to check my list.
- ALS is switched on by a switch.
- Extra air is needed for working of ALS.It could be done by slightly opened throttle plate, extra air valve, or using the IAC stepper/pwm valve for it.I think the last solution is the best for street applications.
- There is a selectable EGT or working time limit, to protect the engine. I think the time limit is more usable because of any possible EGT errors. They use 10 sec for time limit. When the ALS working time reaches that given time limit, than the ALS turns off, until the TPS reaches about 60-70% again, or it's turned Off and On again.
- Fuel enrichment % is needed too.
- We need to define a TPS %. Below this % the ALS mode'll be active. The IGN retard, the fuel enrichment, and the extra air will be activate.
- We need to define the IGN retard degrees.
- If the TPS<IAC_tps_treshold than we need to limit the RPM, because of the extra air, the RPM should raise very high. We need it to do it by IGN cutting(ALS RPM limit).
I think it could be a good working ALS method. But we have to think about the start RPM limiter too.We need to do it by IGN cut.ALS and startRPM limiter are offten used together when starting.After start, the RPM limiter is turned off, but the ALS stays working. So another switch input is needed for RPM limiter. When we turn on the ALS and the RPM limiter too, than we sould be able to build up the boost with fully opened throttle plate. So i think, we need to use use the start RPM limit instead of the ALS RPM limit, and we need ALS working too in that situation. And i think we need to use IGN cutting rev limiter with ALS mode, for max RPM limiter too.
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We have tested the current ALS functionality (v13rc5 firmware) for launchcontrol with success, micke's audi produced 1.2 bar boost off the line, at 6200 rpm, with a setting of 70% fuel enrichment and retard to 0 degrees (entered 40deg in the menu)
- Great, but ALS is not only for start, it's great during gearchange.SO we should think about that. The TPS is almost 0 during gearchange, but we need the boost during that. Another question. Could it be ratard after TDC(negative degrees)? For example 30deg in the spark table, and 40 deg retard means 10 deg ATDC?
- The CVS committed implementation has some limitations, spark can not delayed after TDC. Someone need to commit the [patch] which allow 20 degrees ATDC. Beware! there is an even newer than this! See GenBoard/UnderDevelopment/FirmWare/PowerRelated
Cutting spark instead of the current fuelcut method probably builds more boost, but is more dangerous to the engine, we cant se any rising EGT with these things enabled.. - I see.
Another idea i have is that we should have a separate ALS sparktable, as most tables are retarding ignition more with a raised boost, and the other way around is probably better for antilag. - Many programmable systems use ALS spark table.
I like the EGT limiter, but its important to always keep the ALS revlimiter active with the switch activated, we dont want any blown engines here. The option would be "Fuel cut above EGT:"
also "Fuelcut only above KPA:"
- I think we need ALS_RPM_limit it's a relative low RPM(for example 1500RPM). It's used when ALS switch is turned on and start RPM limiter switch is turned OFF. This way ALS boost can help during gearchange, and the RPM stays low if we doesn't push the throttle. During start, we hold down the start RPM limiter switch and the ALS switch is turned ON too.Now the Start_RPM_Limit is the max RPM(for example 6000), and the IGN retard and fuel enricment works too, with full opened TPS.After the car started, than the RPM limiter switch is released. This way, we have boost when starting, and we have boost during gearchange too.:))
See GenBoard/UnderDevelopment/FirmWare/PowerRelated for recent stuff
See also
- MembersPage/GaborRacz/NewAlsLaunchAndOthers Gabor's great ALS stuff