N75 Frequency

With my GTB2056VL, i receive simple electric actuator, motor and position sensor...

http://forums.tdiclub.com/showthread.php?t=249349&page=2&highlight=gtb2056vl

This is a good base for custom electronic actuator project!
I work with Microchip MCU, is not very hard to do a good control unit.




Dieseleux

Dieselux: I would be interested in a pic adapter; I have a controller that looks like the one in post 21. I've worked with both DS and 8-bit pics.

I finally got around to measuring the N75 signal.

According to my Bentley's, the N75 valve gets 12V on one of its wires and the other wire goes to the ECU. The ECU has a pull down switch to activate the circuit.

I connected the probe lead to the N75 "signal" wire (going to the ECU) and the ground to the engine block.

Here are the oscilloscope plots:

The ECU turned on, but the engine is off:


The engine at idle:


Revving the engine: (I don't know the rpm or anything about the engine at this point, I can't run VAG-COM and the scope at the same time)


The plots generally show a frequency of 300hz, with an increasing duty cycle as the engine speed increases.

Good info!
You make mesurement on MK4 ecu?



Dieseleux

That's some good info there bud!


Might be that the n75 valve is more tolerant to altering frequencies than I originally thought! (it's not a bad development either).

I do have another question, and this one's even tougher - does anyone here know how the ecu actually manages boost?

The way I understand it, without knowing your management systems too well, you have a boost map which is rpm against injected quantity, with the resulting figure being the duty cycle sent to the n75. That sounds simple, but vane position (or duty cycle) alters the behaviour of the turbo rather than the boost limit, so there has to be some code somewhere that manages spool and boost hold for a given target boost.

Just wonder if anyone knows how the ecu arranges this task. I know the questions keep coming but you've all been very informative so far

Dieselux:
You make mesurement on MK4 ecu?

Click to expand...

Good question - full disclosure would require that.

I originally needed an ECU that could control a 1Z motor from a 1996 Passat. I found this one in Germany:

VAG #028 906 021 GN
Bosch# 0 281 001 660
68 pin with tube for boost.

It was modded by Jeff @ RC to control a VNT and accept an MK4 MAF.

@ Dakta:
I can see where the frequency wouldn't matter for the standard N75 valve as long as it was close enough. It may be critical for an electrical actuator.

Since Jeff modified my ECU to work with a VNT, he may be able to shed some light on exactly how it works, if he has some spare time. He's awfully busy.

cheers we'l see!

@ Dakta:
I can see where the frequency wouldn't matter for the standard N75 valve as long as it was close enough. It may be critical for an electrical actuator.

Click to expand...

Yeah I thought so too. My big concern with using a different frequency was that 90% at a slower frequency might occasionally appear like 100% at the correct frequency (just an example) because of the longer window, which I'm not sure if the n75 would respond accurately to that. We'l see!

e*clipse said:

Dieselux: I would be interested in a pic adapter; I have a controller that looks like the one in post 21. I've worked with both DS and 8-bit pics.

I finally got around to measuring the N75 signal.

According to my Bentley's, the N75 valve gets 12V on one of its wires and the other wire goes to the ECU. The ECU has a pull down switch to activate the circuit.

I connected the probe lead to the N75 "signal" wire (going to the ECU) and the ground to the engine block.

Here are the oscilloscope plots:

The ECU turned on, but the engine is off:

The engine at idle:

Revving the engine: (I don't know the rpm or anything about the engine at this point, I can't run VAG-COM and the scope at the same time)

The plots generally show a frequency of 300khz, with an increasing duty cycle as the engine speed increases.

Click to expand...

Isn't it .300Khz, so 300Hz?

Rub87:
Isn't it .300Khz, so 300Hz?

Click to expand...

d'oH!

Yea, good catch. 300khz would be kinda fast for an air valve's response.

Rub87: Do you know the pinouts for the Hella VNT controller?

not by hard.. but as you can see on the pic I posted mine only has sensing circuit, the other pins went directly to the DC motor

the MB ones look much more interesting..

Ruben

There are some very interesting links on this topic. Thanks everyone.

This link has the pinouts for the Hella controller I have:
http://superturbodiesel.com/std/garrett-vnt-hella-actuator-t-614.html

It appears there's a 140hz PWM cycle controlling it, and it only requires ground, 12V, and the signal.

That should be relatively easy. All one would need is something to change the 300hz cycle to 140hz and pass through the duty cycle. If it's reasonably robust, it might allow a 150hz signal - it should be pretty easy to cut the frequency in half.

I wonder what type of safeties the circuits have. The vacuum actuator is nice because all problems default to open vanes. I could see problems with the electronic acutator getting "stuck" wide open.

any news here guys?

well i've built a pid controller that actuates the vacuum solenoid at 250hz.

It uses a map sensor to measure boost, and it uses another adc (potentiometer) to set boost (i.e chose the map voltage you desire).

It will need a fair bit of pid tuning to get right i expect if it works at all, testing will take me a while as i'm fairly new to electronics.

If I get it working, my next step will be to build another input to tap into the TPS with a routine to scale target boost based on throttle. Or I could place a map in the chip's eprom. We'l see

Haven't done anything for the turbos with electronic actuators. (mines vacuum + n75). I assume i'd just have to change the duty cycle voltage to meet whatever the electric actuator uses.

Best is RPM, TPS, MAP for input.
Good project!


Dieseleux

I already built one to control boost... if you need C coding for boost control I can provide for pic 16f876.

It works pretty well.

Go on then, i'l take a look

I haven't made much progress as my cars been off the road due to redundancy but i'm looking forward to testing mine.

My long term development plan is to go beyond 'boost control' and be able to work to rpm and load based maps in order to give the turbo a bit of a break at the operating points where emp is likely to be an issue.

So yeah, any info, schematics, binaries anything like that would be helpful!

Hmmmm- wonder if there's a DC servo motor (spring return) that would accept the 12-14Vdc PWM signal from the ECU? ... Crafty work.

The pm signal is 3000hz.

I know this is an old thread of mine, but for any budding developers out there - vac systems the frequency was ultimately not very important.

I've used 150hz on slower oscillators and still had very precise control of the actuator.

@TDI Bug - I didn't try your route but i did think of stepper motors, only problem is most didn't have much torque potential or the speed.

Always wondered with the idea of trying to get a CAN based electric actuator to work...I have one in my boot but suffering from a serious bout of cant be arsed :|

Personally I wouldn't put too much effort into the electronic side unless you have to. A circuit to drive an n75 by MCU is simple, and vacuum gets the job done.

Getting the vanes where you want em is quite simple. Describing a turbo's behaviour in mathematics and chosing where you want the vanes at any given moment in a dynamic environment is less so.

edit:

The information given by people in this thread was very helpful for developing a controller, it's an old vid but you can see it's being put to good use - cheers:

https://www.youtube.com/watch?v=t-PnqPviRR8

I bypassed all of that and just run and simple actuator. It's not as variable as the elctronics, but it gets the job done and is bullet proof. On mine I just run on boost all the time, but I don't really see any milage loss. I do believe that because I have no intercooler that the high temps cause the computer to retard things, but I am ordering the intercooler here soon to get put back on, then see what happens.

For a quick and easy setup, that's all you need.

In fact, if I was prepping a car just for use on track or dragstrip, that's the way i'd do it myself.

The only problem really is, doing it that way means the turbo is always oriented towards creating boost with no consideration to engine flow and backpressure, and there will undoubtedly be operating points where the engine's torque production will actually be inhibited due to the 'all or nothing' opening and closing of the vanes. For instance, where the initial emp spike is just on spool. (when graphed).

It also means, especially where the cars are likely to be quite highly tuned, the turbo is going to clock up a lot of wear, it might still take months or even years to fail but will no doubt live a generally harder life than one whose vanes is controlled by more than just if it's hitting a max boost value or not.

Don't get me wrong, it would cure a lot of headaches to just slap on an actuator. I actually did it initially back in my earlier days with a GT2256, being aware of the drawbacks I bought a soft actuator to try and persuade it to creep rather than be on-off, however it's ability to control boost was, in practice actually rather crap even for a rudimentary control device and i decided not to put too much effort into making what already appeared to be a compromise, work.

That said, the old fashioned method of putting a boost valve from the boost system to the vacuum pipe to purge the system on boost spikes is something i'm retaining as a 'safety' feature.

radion_auto said:

Hey fun story for anyone that's interested. My MG ZR runs the controller that Dakta made as a result of the information on this thread. It has had a GTB1756VK fitted for the past ~4 years without issue!

Click to expand...

you can use a standard merc electronic acruator and have the ecu control it directly if you mess with the map

Sent from my ASUS_X00ID using Tapatalk

radion_auto said:

Hey fun story for anyone that's interested. My MG ZR runs the controller that Dakta made as a result of the information on this thread. It has had a GTB1756VK fitted for the past ~4 years without issue!

Click to expand...

Hi, I'm puzzling how to connect an electronic activator from Mercedes to my EDC15vm, there are cards in the ECU firmware where you can change the frequency from 300 Hz to 140 Hz, I know that the N75 valve card works from 14% to 98%