ME7.1 output transistor current rating

[sambb]

As the title suggests, I'm wondering if anyone has the ECU specs. I'm looking to maybe double up the hardware running off an output. eg two throttle bodies. I've searched high and low and can't find any specs on the current rating of the output transistors. If anyone knows, please let me know!
thanks
sam

[DV52]

sambb: Hi.

Hmm..... very ambitious quest indeed!! I wish you luck finding out anything about the internal circuit specifications on ANY VAG module. These matters are almost certainly closely held commercial secrets by the deities on the VAG mother-ship and the module specs are likely ONLY divulged to the wizened troglodytes that are incarcerated in the dank dungeons at Wolfsberg!!

Yes, it's true that these modules use lots of electronic components which are from third party manufacturers - but the sourcing/sinking specifications of the electrical load at the module pin will likely be limited by the in-circuit configuration of the output transistor. So, the pin rating may, or may-not be the same as the rating on the transistor product sheet.

I attempted to do a similar thing on the BCM on a Golf mk7 many years ago. My approach was to open the module housing and recreate the circuit diagram by tracing the copper tracks on the PC board (see the module motherboard below). It was a totally futile exercise for many reason including the fact that the module motherboard was multi-layered!!

I'm not sure why, or how controlling two throttle bodies from the one ECU works - but I suggest that you design and use an external circuit to manage the power requirements for the set-up and that you perhaps isolate the control pins with opto-couplers for electrical safety.

Don

PS: You have piqued my curiosity!! How do you expect to control 2 x separate throttle bodies with an ECU that's designed to operate only ONE of these units? Even if you manage to address the power supply requirements - how will the ONE set of control/sensor pins on the ECU correctly accommodate signals from/to two separate throttle valve modules?

[sambb]

Hi mate,

I have a 1.8T 20V. I've been doing a bit of research into pre-turbo throttle bodies - their use in the first turbo F1 era, indycar, wrc etc basically anywhere where turbos were used but anti-lag wasn't allowed in the rules. Even current mercedes, Honda and maybe renault F1 motors use it. My aim was to run the standard throttle body in the standard location but basically have a second mounted post MAF but pre turbo, mimicing the movements of the main one. Being that they are stepper motors though, I'm now pretty sure they can't be run in electrical parrallel because they are a current+- signal, No? I have a new idea though. I'll use the OEM electric signal to the pneumatic diverter valve to operate a hard open/close plate. ie it will close fully when a DV would normally open and reopen thererafter. I'm thinking a normally open exhaust vacuum valve would do it. You can run a single throttle body pre-turbo but then the entire inlet tract goes into full vacuum which will suck silicon hoses shut etc. Running the usual plenum throttle body prevents that but still allows for the compressor to run in the vacuum immediately behind the pre-turbo plate thereby allowing it to actually accelerate the turbo on gearshifts.

thanks
sam

[DV52]

Sam: Yeah - the 1.8T 20V engine is ubiquitous across many car Brands albeit it's not an engine with which I'm familiar.

As for the specific questions in your post- let's start with terminology and let's give this unit its formal VAG name "Throttle Valve Module" - and let's abbreviate the name by using the wiring diagram label GX3.

I'm not really sure how the second GX3 helps make stuff better in your configuration - but I bow to your better understanding of these matters. Also. and I don't intend any offense - but are you sure about the stepper-motor bit in your explanation?

My hunch (emphasis on "hunch") is that the motor in GX3 is driven by the more usual motor control protocol - Pulse Width Modulation (PWM).. It's not clear to me why motor-control on a throttle valve module needs the precision, or the complexity of stepper motor technology - particularly when stuff like engine rev control would appear to be better suited to a continuously variable signal that is typical of PWM. Plus, as shown in my wiring diagram below, the motor on GX3 has only two wires - stepper motors have multiple stator coils, so they need typically 4 x wires for motor control.

As I said, this is my hunch, I'm not sure - so I'm more than happy to be advised otherwise! Do you have access to an oscilloscope? If so, maybe look at the waveform on a working GX3 to confirm the motor control protocol. You will find many examples of typical PWM waveforms on the electric internet. Please report your observations - for my benefit

As for your substantive questions - this is my very cut-down wiring diagram for the general VAG set-up for GX3:



I apologize if you already know this stuff (you probably do) - but GX3 is a classic example of what's known in control theory as a closed loop system. This system is also called a feedback controller because it has a feedback loop that controls the motor position to the set-point that's calculated by the ECU algorithm.

From a circuit perspective, the pins that I call "TPS" in my diagram above constitute the feedback loop. As you can see from my diagram, the feedback circuit has its-own power supply which I have labeled 5V because this is the set-up on modern VAG vehicles. Again, I'm not sure how this power supply works on a 1.8T 20V engine - maybe it's 12V?

So, with regard to your project - clearly the feedback circuit for the primary GX3 will be managed by ECU. I assume that the feedback circuit for the second GX3 will not be connected - is this correct?. If so, the second GX3 will use the feedback circumstances in the primary GX3 notwithstanding that it's actually located downstream in the engine's air-circuit! Is this a viable set-up for proper engine performance - I don't know?

If it IS kosher to operate 2 x GX3s in this manner and if my PWM guess is correct - then I suspect that all that's needed is an interfacing device that uses the PWM drive signal from the ECU to the primary GX3 as an "input" to generate a second PWM drive signal for the second GX3 motor. In essence, the "interfacing device" for the second GX3 is functionally the same as an audio amplifier albeit the frequency response is very different.

Again as a working assumption (meaning that I haven't actually research my hypothesis), I wouldn't think that my suggested "interfacing device" is anything special - it's just a normal, bog-standard, low-power, 12 Volt PWM controller. These are readily available - I'm sure that you will find lots on eBay.

Don

[sambb]

Thankyou very much Don. Yeah the idea was that the secondary pre turbo throttle would just slave its position to whatever the original one, with feedback only coming from the original. Yeah my stepper thoughts were just an assumption. If the throttle bodies are PWM then what you suggest would be possible yeah? First step probably would be to just reposition the original pre turbo and check that everything still runs aok. It could play havoc with the MAF signal, or it could cause MAP sensor errors as it'd be going into vacuum when the lowest it normally sees is atmospheric when the diverter valve opens. Once thats verified then I can look into running the pair. I have seen a pre turbo throttle on a bike engined hillclimb open wheeler. Can't hurt to try other than potentially overspeeding the turbo!!
sam