The VeeCU

[WesRagle]

Hi Robert,

Thanks for the encouragement. And I've been watching your engine installation. Exciting stuff!! I wish I could weld :-)

Me, I can't wait to hook up to an actual engine. It's going to be a lot of fun.

Wes

[WesRagle]

Hi Guys,

I'm getting close to the finish line of implementing the software of the VeeCU. I'd like to bounce some ideas off you guys.

A little background. Listening to Jeff's pod cast on SDS EFI is what sent me off on this adventure.
Ref.: http://www.sonexflight.com/58/index.html

I wanted to implement an EFI system with the AeroInjector as a backup. I started studying the available solutions and,
since I knew nothing about fuel injection, I was somewhat intimidated. So I started studying EFI and envisioning what I wanted. What kept popping into my head was simple. I want it to be safe and simple.

Here is what I came up with: As currently designed the cockpit interface to the VeeCU consists of four miniature momentary SPDT toggle switches for cylinder fuel trim. A store push button to transfer user settings and fault codes to non-volatile memory. A potentiometer to adjust mixture setting. And finally a status LED to indicate operating status. That's it.

User settings consist of:

Fuel Flow Trim (%) used to make fine adjustments to the simulated Red Cube output.

Four cylinder trim (%) [-15.0 to 15.0] used to balance fuel flow between cylinders.

Prime Strength [0-5] is a multiplier for the first injection pulse during engine start to prime the engine.

Accelerator pump sensitivity (mBar). Wanting to keep the number of sensors to a minimum, I don't want to add a Throttle Position Sensor. Instead, manifold pressure change is used to sense increased load and the need for a little extra fuel. The Accelerator pump sensitivity is a threshold below which a MAP change will not trigger any extra fuel.

Accelerator pump gain [0-5]. A scaler for How much fuel to add during an accelerator pump event.

A set of fault codes. Any fault code, even if it clears, that occurred during the last flight is retained and displayed again at engine shutdown. Since all that is available is a LED to flash codes, a press of the store button saves the codes in non volatile memory so the pilot can shut down and go find the list of codes to see what happened. All user data is retrieved when the unit is powered again. The codes are then stepped through/cleared by toggling one of the trim switches with the engine shut down. Another press of the store button will permanently clear the codes. A bit of a pain but it eliminates the cost and complexity of a display. BTW, No changes are made permanent without a press of the store button.

So what do you guys think? Am I crazy? Do you have to have a display to have fuel injection? There isn't one in my pickup :-)

And here's a decision that I've been postponing. One of the aux outputs is intended to drive a fuel pump relay. The intent is to disable the fuel pump in the event of a mishap. Exactly what logic should be used to disable the pump. One thought is to enable the relay at power up and disable it after RPM has been above maybe 2400 and then returns to zero. I'm open to suggestions.

Edit: BTW, here is what Ross from SDS has to say about it in his EM5 manual.

Optional Fuel Pump Relay
SDS units can be equipped with an optional output to control a relay to switch the fuel pump off when the engine
is not turning over. This feature is designed to prevent the pump from emptying the tank in a serious accident.
The pump relay is energized for 2.8 seconds when power is turned on to pressurize the fuel rail until the EM-5
detects crank rotation. If the engine stalls the EM-5 will shut off the relay in 2.8 seconds. There is nothing
programmable for the fuel pump relay.

More on the "Tune" later.

Thanks,

Wes

[BRS]

Wes,

Your progress is exciting and I'm looking forward to the completion. What an improvement this would make to these VW engines.

As an SDS advocate (used on 3 different aircraft) I'll give me 2 cents. I don't think a display is needed at all. On one of my aircraft after the intial setup I completely removed the SDS programmer/display head. Setup is always, even with the SDS display, something that takes patience and plenty of reference to documentation. If it's done via toggle switches and indicator light, that's fine as long as documentation is clear. From your description above it was hard to envision what you were doing. Look forward to seeing it in a video.

On the fuel pump relay. I used this feature on one of the three installations I've flown. It was nice that I could turn the key to 'on' and the pump(s) would pressurize then cut off. This greatly reduced the battery draw before I would start the engine in case there was a delay in getting going. With the sonex airframe the fuel shutoff is something that most pilots are very used to using since the AeroInjector (and others) can siphon. So for an engine failure of some sort where the pilot has time to prepare for a forced landing the relay is not needed. On the otherhand if there were a botched landing or takeoff excursion then this feature would be helpful. My only hesitation with this relay is that it introduces another potential failure point. In the case of SDS it is an option the builder can use or not. Seems like a good policy to me.

Are you proposing two fuel pumps and would they both go through the relay or each have their own relay or only one wired through the relay?

[WesRagle]

Hi Brock,

Thanks a lot for the reply.

From your description above it was hard to envision what you were doing. Look forward to seeing it in a video.

I've never made a video before but I will give it a shot once I have an engine up and running. I've already borrowed a camera from my daughter and will learn how to use it. It is hard to describe how things work without pictures, but here goes.

The evaluation board that is standing in for the VeeCU has a spare LED so I've been able to program that to act as the panel LED.

For the moment assume that the tune has already been done and you are sitting in the cockpit getting ready to fly. When you power up the ECU this is what you will see: The LED will illuminate steady (assuming that all sensors are in expected range). The LED will initially act as a simple pilot light indicating power on status. Once the engine has started, the LED will flash a specific sequence a couple of times to indicate that the ECU is locking on the the alternator pulses so they can serve as a backup to the secondary ignition pulses in the event of a secondary ignition module failure. Once the phase of the alternator pulses are determined, the LED will flash at a 50% duty cycle, once per second, until the engine completes warm up (presently set at 60 Deg. C CHT). At that point, the LED extinguishes and will remain off (again assuming no faults are present) until the engine exits the "Running" state/stops.

Once the engine is running, the toggle switches can be used to trim the individual cylinder fueling. The panel LED flashes on for 1/10 of a second each time a trim switch is activated to acknowledge the action. Presently the switch adds or subtracts 0.5 % fuel for each activation. If the switch is held on for one second the switch will begin to repeat every 300 mSec. If the trim is driven to the +/- 15.0% limit, the LED will flash on for a full second each switch activation to let you know you are at the end of the range. If you are happy with the trim, a press of the store button will make the change permanent.

The only problem I see with this is getting too far off center and hitting the trim stops. With no display you can't tell how close you are to the stops. I'm hoping that can be handled by using a specific trim procedure. That is, trimming two cylinders up and two cylinders down to achieve balance. Anyway, I know, a video :-)

As for the fuel pump relay, I've never checked whether or not the Walbro fuel pump leak back through the pump while the pump is off. If not, the method Ross uses is perfect. Left to my own devices I would have already done it the way that I mentioned earlier except I suspect a violent upset might cause a momentary power interruption causing the pumps to reactivate.

So, do the Walbros have a check valve or otherwise not allow backward fuel flow?

Are you proposing two fuel pumps and would they both go through the relay or each have their own relay or only one wired through the relay?

I'll start with one pump. Take off and landings will be done using the AeroInjector. As far as wiring for two pumps, I would use two relays. One of the last minute changes to the schematic was to use a larger FET (with integral fly back diode) for fuel pump relay. Driving two relays should be no problem. Of course if one of the relay coils fails shorted, both relays would be lost unless fuses were used for the activation coils. That would add another possible failure mode :-(

I feel the same way as you about the relays. I wonder if the risk of the added failure mode is worse than the risk of a takeoff or landing mishap. But, I don't like the thought of being trapped in the cockpit and fuel being pumped out in the engine compartment so I intend to use a relay. If someone doesn't want to use it that's fine too.

Wes