Electronic valve/spark timing

[garfayliu]

Hello

I am building a 4-stroke engine and I am looking to use electronically (software) controlled valves, spark ignition and piston. Basically replace the camshaft and crackshaft with electronics/actuators. My current system has no feedback in terms of O2 sensor and so is not very intelligent at the moment.

Does anyone have any experience or know where I could find info relating to programming such a system?

A very basic approach that I am starting with is to simply actuate my valves at certain degrees in the cycle, i.e.

Open inlet @ 20-30deg before TDC,
Close inlet @ 50-60deg after BDC,
Open outlet @ 50-60deg before BDC,
Close outlet @ 20-30deg before TDC.

I look forward to hearring your comments, thanks in advance.

Garfay, Cranfield University, UK.

 

[Warpspeed]

No crank ?? How do you extract power, and how do the induction, compression, and expansion strokes work without stored rotating inertia to drive the piston ?

 

[crysta1c1ear]

The commonsense approach is to emulate the valve operation of the base engine as much as possible until you have the engine running at least as well as the original.

Then once you have it running you can start to think about variable valve timing and lift. I believe BMW have engines that do what they call intake valve throttling. Rather than use a throttle to control the amount of air taken in to the cylinders, the intake valve can be closed when there is an appropriate amount of air.

You have said
Open inlet @ 20-30deg before TDC,
Close outlet @ 20-30deg before TDC.

From that it is not clear to me whether you plan to have any valve overlap. One of the points of electronically controlling the valves is that it allows you have different set ups at different RPM. In the joke about the mechanic and the heart surgeon talking about pay differences the surgeon says "yes, but you don't have to change the engine while the car is running". With electronic valves, you can effectively change cams - virtually I mean - while the engine is running.

So at low RPM, the valve overlap creates a problem - blowback from the exhaust to the inlet.
At high RPM, a larger valve overlap might allow the engine to breath better.

Electronic valves allow you to get these sort of improvements, as well as operating faster so that you can more of a square shape to their operation: open quicker and close quicker.

Another commonsense approach to getting started is think about how you are going to do a soft landing for the valves. You'll find they mention that on the Camcontec website; effectively they cushion the landing by applying an opening force as the valves are nearly closed.

When it's all running fine just as a normal engine, then you can start thinking about running the engine backwards (so that no reverse is required with belt and pulley type CVTs), or running as a two stoke when power surges are required eg for overtaking.

 

[garfayliu]

Warpspeed: I don't have a classic rotating crank shaft, rather I have an actuator/sensor, where the sensor phase can be used to extract power.

 

[garfayliu]

crysta1c1ear: Thanks for your post, mis-type correction should have been 'Close outlet @ 20-30deg after TDC' not before. There will be some overlap to allow scanvenging, I think thats what it is called.

I've not considered soft landing for my values, as it stands I'm having difficulting getting a good seal (even after lapping) and I've used hard contact in the form of a valve spring to pull the 'poppet valve' shut.

You mentioned BMW use some valve throttling, I'm not sure if I understand correctly. My current system will employ several flow regulating mechanisms. Firstly the flow rate is controlled with mass flow controllers, then I will have a pressure regulator, and lastly the inlet valve will act as an on off valve. The system I intend to use should enable a constant flow and pressure whether or not the inlet valve is open or closed.