Anti Lag System - I need help on implementation

Competition engines and ancillaries - general discussion
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NickRP
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Anti Lag System - I need help on implementation

Post by NickRP »

Hello everyone,

EDIT: I added some ALS background, to clarify what and how is achieved by applying such a strategy.
===============================================
As many of us know, the problem with the turbocharged engines is that it takes certain time ('lag') for the turbocharger to 'spool' to certain stabile rotating speed (imposed mainly by moment of inertia of the rotating assembly (this affects shaft acceleration only), available exhaust gasses energy, friction and pumping work compressor is doing). Furthermore, to put it simple, compressor speed has lot to do with the available pressure - there is high level of correlation between the two.

The goal on racing cars is to keep the turbocharger rotating assembly rotating as fast as possible, as long as possible, so that the effect of the 'lag' is minimized. This is accomplished by mechanical design of components and suitable control strategy.

I will go in detail into control strategy optimization. We have the following parts of equation:
moment of inertia of rotating assembly - can not be affected by electronic management system
friction - can not be affected by EMS
energy of exhaust gasses - CAN be affected by EMS
pumping work of the compressor - CAN be affected by the EMS

To explain the typical situation, after a straight section of the track, where full boost is reached, car is approaching a curve, that requires car speed to be reduced. This is done by braking. Driver releases the throttle (more or less) and applies brakes. The moment he lifts his foot from the throttle, energy of exhaust gasses goes down and pumping work of the compressor increases (it has to work against higher resistance in the inlet tract). This imposes reduction of turbocharger speed, until an equilibrium is reached again. Once the driver needs more power, it will take time for the turbocharger to accelerate to the level it can generate full boost. Depending on turbocharger, it can be anything from a few tenths of second to a few seconds.

Anti lag control strategy is counteracting this. I like to speak of ALS as another method of torque control. Instead of throttling intake flow (with the effects as above), we let it flow a lot (big bypass valve opens, or throttle kicker solenoid activates), but we retard ignition significantly. So, there is much less throttling in the intake tract and there is lot of exhaust gasses energy to keep the compressor spinning fast (due to good cylinder filling through unthrottled intake and low combustion energy utilization due to retarded ignition).

However, apart from maintaining the charger spinning), this is putting lot of stress on turbocharger and exhaust system. And it is creating familiar 'pops' out of exhaust.

===============================================

I am programming ALS functionality into my control units for turbocharged applications. I read much about this subject, spoke to some people that used it, did some field tests etc.

So, I will explain briefly how it works at the moment in my system:

Parameters:
Max. ignition retard (self-explanatory)
Min. throttle to activate ALS - the throttle position has to be below this preset level to consider activating ALS
Ignition retard slope - once throttle is lower than the min. ALS threshold (parameter above), ignition retard is introduced with this slope (the more the user releases the throttle, the bigger the retard is, up to the max. ignition retard)
ALS min RPM - ALS will be active only if RPM is higher than this value
ALS timeout - once the ALS is activated, it can stay on not more than tis time
ALS fuel correction - when ALS is activated fueling will be altered by percentage given by this parameter


Functional description:
User activates ALS switch - this is a signal for the control unit to activate ALS when conditions are reached. Once the RPM is high enough and throttle is closed enough (on deceleration for example), primary and where available secondary idle valve opens fully, ignition is retarded and fueling is corrected. ALS timer starts ticking. ALS mode is over if any of the following conditions is met:
1) Throttle position higher than minimum for ALS
2) RPM to low for ALS
3) ALS timeout elapsed

End of ALS activity is abrupt, so suddenly idle valve(s) are closed, ignition and fueling restored to normal.

I would be interested to hear if anyone has some more (hands-on) expirience with ALS (either as user or as developer), its parameters, ideas etc. I am not so interested to hear what magazines write about that, as:
1) I've read many of them already
2) It is not always correct (more often the subject is significantly simplified and made sound logical to typical reader, ignoring "second order of effects")
3) I got no impression that the journalist have actually tried to calibrate the thing themselves, they were more reproducing what the manufacturers were saying.

Many thanks,
Nikola Radenkovic
P.S. Please excuse my English writing skills, hopefully it is understandable enough.
Last edited by NickRP on February 22nd, 2007, 10:16 am, edited 1 time in total.
NickRP
Posts: 126
Joined: September 28th, 2006, 3:26 pm
Location: Nis, Serbia, Europe (A)
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Post by NickRP »

I've tried it already - it works. However, what concerns me is the 'kick' that the test car was getting once the ALS timer elapsed.

So, the situation was like this:
Throttle was at 20‚°, ALS active, ignition 40‚° retarded, fuel enrichment 15%. Test driver was doing circles with Dedra integrale (4WD), and when the ALS timer expired (ignition and fuel restored to normal, idle valves closed) the car got a heavy torque kick that resulted in very sudden and unpleasent sliding.

To counteract this, I either have to disable the ALS timer, or to set it to a value that is longer than any deceleration area on the track, or to set back the limit for throttle opening for ALS activity to a value that would not create the kick.

Best regards,
Nikola
G&G Motorsport

Post by G&G Motorsport »

Hello.
There are a number of issues that surround ALS.
1 of which can cause un told damage. Exhaust Gas temps go Sky High due to the torque the engine produces being limited via a massive ignition retard( although there is some compensation with fuel trims). This kills turbos very very quiclkly.

Have you thought of runninmg a duel charge system?

Phill
Acki

Post by Acki »

A bi turbo isn't a solution.
With ALS you have pressure when when the car stands on the start at sthe quarter or you shift the gear.
Because of the damage of the turbo you can't use it in dailyuse, you know?

The WRC teams (rallye) have no problem with damaged turbos. When the turbo is damaged the install a new.

Another nice idea is the use of NOS.
Not like in films, you give the engine a small shot at low revs and this make a lot of exhaust gas which spin up the turbo!
You don't use the NOS to have ore power, only to have no lag anymore.
It's like driving a super charged engine but with all advantages of a turbo.
NickRP
Posts: 126
Joined: September 28th, 2006, 3:26 pm
Location: Nis, Serbia, Europe (A)
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Post by NickRP »

Hello everyone,

after many ALS tests performed, I am quite confident a set of parameters for mild ALS can be developed, so that there are no bad effects on turbo and exhaust system (providing that they are in good condition) and still much of the turbo lag is gone.

So, if one's satisfied with 1 bar absolute pressure in the intake manifold on deceleration or gear shift, I have a set of parameters ready for that. There is plenty of exhaust gasses airflow and the turbo is already spinning fast. Once the throttle is opened, the pressure in the intake manifold goes up instantly (there is already pressure built-up in intercooler and piping).

Problems start if more ALS effect is required. But for purpose of hobby driving, this is really not neccessary.

For some reason, people jugde ALS strategy without really having hands-on expirience with it. It's like everyone knows that this kills turbos instantly, melts exhaust valves etc, but this is simply NOT happening if the parameters are tuned carefully.

Best regards,
Nikola Radenkovic
G&G Motorsport

Post by G&G Motorsport »

Re Duel charge,

I didn't mean bi Turbo set ups, I mean a super charger and a turbo. This totaly stops any lag at all.
Well done Nick, 1 bar Absolute off the throttle will make up for some lag.
Once you get in to possitive charge the cars tend to becomes quite nasty to drive, The last set up I did had 1.2 bar of static boost on launch. horrable thing!!! All or nothing.
How does the car feel to drive? Is the engine braking not being as strong a issue? Have you managed to get enough air on closed throttle with out having to fit a throttle kicker?

I would be interested to see what perameters you have ended up with.

Thanks

Phill
NickRP
Posts: 126
Joined: September 28th, 2006, 3:26 pm
Location: Nis, Serbia, Europe (A)
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Post by NickRP »

Hi Phill,

I optimized parameterers for one car myself. I can PM you the values I ended up with. A tuner in the UK that uses my ALS software on Cossies has ended up with different parameters... the ones I supplied were optimal for Integrale 8v, but he found out that Cossie YB engine was reacting better to different setup. Many things play role here, size of the turbocharger, throttle plate, air flow on ALS, physical layout of engine etc.

Two idle valves, with one of them being ported were supplying enough air for moderately agressive ALS action. So I am quite satisfied with that. On Cossie they often use so called ALS idle valve, but I didn't have good expiriences with it. It is practically useless for idle speed control strategies, as it basically only operates as ON/OFF valve :(.

Best regards,
Nikola
Acki

Post by Acki »

Do you changes something on the motor managment when you used your valve?!
NickRP
Posts: 126
Joined: September 28th, 2006, 3:26 pm
Location: Nis, Serbia, Europe (A)
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Post by NickRP »

Acki, if you follow my posts in this thread, you will note that I was developping anti lag system for my own EMS, so changes needed for secondary idle valve support were not a problem.

Best regards,
Nikola
Acki

Post by Acki »

Ups sorry, didn't noticed the changes in the topic. Sorry. With a aftermarket okay... I thought you use the standard ecu.
NickRP
Posts: 126
Joined: September 28th, 2006, 3:26 pm
Location: Nis, Serbia, Europe (A)
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Post by NickRP »

It is standard IAW series 4 ECU base, but with my software and modifications that make it programmable and suport many extra features... one of which is the above mentioned ALS.

Best regards,
Nikola
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