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View Full Version : Last chance for my AVCR to shine



Legnum Boy
18-01-2005, 05:00 AM
As you may be aware, from day one I have not been totally convinced of the Apexi AVCR performance in my car. I still believe the tiptronic box to be part of the issue, and I have also read somewhere that the design for all boost controllers is a flawed one. (signal from pressure to vacuum technical stuff and nonsense)
On my travels, I found a rather indepth explaination for some of the functions AVCR utilises. I will be trying to follow the method in the madness to see if it cures any current problems.



A turbo works by reacting to load demand, you should always set the boost profile up where the turbo is under the full load it will see, which is in the higher gears of 4th/5th on the car. Once the boost profile is setup you then have a problem in that the turbo wont spool as quickly in the lower gears because the load on the engine isnt as high. To get around this you need to alter the waste gate solonoids duty settings to alter its profile to compensate for this lack of load.

With the AVCR you have trim settings for each gear which enables you to run more solonoid duty in that gear. You also have a setting for feedback speed that the AVCR uses to work out the profile of this trim.

You need to run a larger % increase in the 1st than 2nd, and more in 2nd than 3rd, 4th and 5th dont need any trimming as the engine is fully loaded in those two gears.

It’s probably worth expanding a bit on what the various functions of the AVCR are there for.

The learning functionality isn’t really there to give you the correct boost setting when you are setting this up for the first time; it’s just a by-product of that functionality that you can use it to help with the initial setup. The learning function is there to allow you to have a control system in place that can auto tune the boost profile to take into account variations in turbo dynamics due to temperature and atmospheric changes.

The way the boost is controlled is by altering the duty cycle on the waste gate actuator solenoid, that’s all that controls what boost the turbo produces as far as electronics is concerned.

Now with the AVC-R you have two main settings that are used to achieve the turbo boost level required, the first is the target boost level you are aiming for, the second is the waste gate duty value, both of these are set at the various rpm points you set with your NE point programming. The NE points you choose have an effect on how well you control boost, they can have a major impact on how the initial spool of the turbo is controlled. I’ll come back to that.

When in learning mode the AVCR reads the waste gate duty you set initially in your target setting and outputs the waste gate duty to the solenoid at that value, it then reads the value of the MAP sensor and compares that value to the target boost level you have set. If there is a difference between your target boost level and the real level being achieved it then alters the value in the preset waste gate duty to a different value that it thinks will generate the desired boost next time through that rpm point. It will only do this when you go 80% throttle and above and only in the gear where learning is enabled. It will do this for ever in that gear, slowly honing in on the correct value for waste gate duty that will achieve your target boost level until it no longer needs to alter this value. It will then make small changes should atmospheric conditions change in the future. It needs to be in the right ball park in order to do some fine tuning though, if the waste gate duty is too far away from the correct value, it will never be able to start the auto tune process.

When you are setting the AVC-R up for the first time, the best way to go about this is to switch learning off completely and manually tune the waste gate duty to achieve the boost you want to achieve. This means ideally you need two people, one to drive and one to note the boost being achieved and to alter the waste gate duty to a value that achieves that. Once you have the waste gate duty values correct to provide you with the boost you want, only then should you switch learning on to ensure if conditions change your boost will stabilise around your target values.

In order to stop the AVC-R constantly fighting itself, you should choose just one gear to control the self learn fine tuning, and that gear should be the one that is used the most where the engine is under full load, this is usually 4th gear. The problem with choosing a lower gear for self learn is that the engine isn’t fully loaded, especially in the low-mid range, so with self learning on there you are going to have too much waste gate duty when you give the engine full load in 4th/5th because it will have upped the duty to compensate for a lack of load on the turbo.

Choosing the rpm range you start to control the waste gate solenoid via the AVC-R is critical for a couple of reasons. Firstly the max duty the AVCR can output is 90%, but for initial spool you want the duty to be 100%, so to generate maximum spool you don’t want the AVCR doing anything until the point at which the turbo needs to be controlled externally. This means a larger turbo should have the first NE point higher up the rpm range than a small turbo, so the turbo can spool as quickly as possible without any interference from the AVCR running at its 90% maximum. The second reason is you only have a few rpm points to use and you need to spread these to enable you to have control of the waste gate duty in the most critical areas where the dynamics of the turbo are changing the most. If you are wasting a couple of rpm points early on running these at max to try and generate some spool you are taking these away from the most important area in the mid range where you need fine control of the waste gate solenoid to give you stable boost.

Once you have all these areas setup, you can then move on to looking at how the turbo is performing where the engine isn’t fully loaded in the lower gears. Because the engine revs up faster in 1st and doesn’t have the load on it due to the lower gearing, the turbo will not produce the same boost as it is doing when in a high gear such as 4th. What this means is your engine is producing less power in 1st than it is in 4th. This can be a good thing if you have problems with traction, but if you have good traction or prefer to balance traction on the throttle rather than by limiting power, you can force the turbo to work harder by increasing the waste gate duty on the solenoid. As you go up through the gears you find the amount you have to increase the base duty cycle by decreases because engine load is going up, by the time you are in 4th gear you are in a stable condition so don’t need any increase in base duty for 4th/5th.

Another thing to bear in mind with the in gear % adjust is how you will be driving the car. If you want this setup for road driving where you will be going through the gears normally, covering the whole rpm range you are going to be seeing high engine load around the 4000rpm area. The turbo will respond to this well and will pull good boost without much increase needed in the 2nd/3rd gear adjustments. However, if you are doing a drag type run where you take the engine to the red line, then up shift, you will never see this midrange high load area. What that means is the turbo won’t be able to pull the same boost because the load isn’t as high, so you need to run a higher % increase for 2nd/3rd. Because of this I have 2 sets of values for the % adjust, one set for the road and one set for the drag strip or if I want to nail it from the lights. *cough*

I am not 100% sure how feedback speed is working, but I have found running with it set to 3 in the higher gears and 1 or 2 in the lower 3 gears gives the most stable response with the least oscillation of the boost.

Hopefully this helps explain a bit about how the AVC-R works and helps get your setup in the right ballpark. It’s quite a complicated piece of kit but when you break it down into its component parts its quite simple. It really does help if you have someone experienced to help you set this up though, I am sure there are plenty of AVC-R’s out there that could be optimised to provide much better spool in particular. :rolleyes5 :rolleyes5

Some of it, I do not agree with, i.e. the part about the pre NE1 point being 100% duty. I think it is more like 0% duty, but other parts are quite rational and make logical sense.

ileonc
20-01-2005, 10:41 AM
How did it go?

Would be very interested to find out what happened!

enigma
20-01-2005, 11:03 AM
Some of it, I do not agree with, i.e. the part about the pre NE1 point being 100% duty. I think it is more like 0% duty, but other parts are quite rational and make logical sense.


If NE1 is at 100% this means the Turbo can boost to its hearts content! Thus faster spool up. Setting it to 0% would mean the solenoid is always closed so the wastegate will start to open.

The rest of the article is just the instructions rewritten! :lipsrseal

Legnum Boy
20-01-2005, 03:22 PM
If NE1 is at 100% this means the Turbo can boost to its hearts content! Thus faster spool up. Setting it to 0% would mean the solenoid is always closed so the wastegate will start to open.

The rest of the article is just the instructions rewritten! :lipsrseal

Sorry, mis-typed what I meant to say.

What I meant was, the boost level of any revs prior to the duty setting of NE1 are going to be controlled by the duty cycle setting 'OF' NE1, where as the chap that wrote the article seemed to be under the impression that boost prior to NE1 was not controlled at all - effectively 100% duty, which is clearly not the case.

As for the rest being the instructions re-written, you must have a differing set of instructions with your AVCR, as there is no way mine explains anything in anywhere near as much detail and plain english.... ;)

After resetting my AVCR and setting up from scratch, following the 're-written' instructions, I am now getting way more controllable boost, and the learning function is getting a lot smarter with its re-plumbing of the duty cycle.

Still get the occasional spike at gearchange, and still haven't sussed out a way to stop the over-boost of the pre-spooled turbo's, short of being vigilant with the right foot :sad3:
On the plus side, I no longer get fuel cut, as the spikes are a bit smaller than before and I recorded my best 0-62 time yesterday, so not all bad. Will have to give it a little longer before deciding its fate.... :p