School project - car ignition

[robert1275]

Hello,

My name is Robert and I'm doing a project for my school about car ignition systems.

I'm trying to make an electrical system that will stop the engine from firing on all cylinders.

Like if the car is a 4 cylinder - only 1, 2 & 4 will fire.

How could this be done using the 555 timer - my physics teacher said it can be done by interrupting the signal from the ECU to the ignition drivers but won't explain how.

Please help.

Thank you very much.

Robert

 

[Diver300]

A timer won't help much, as the time between sparks depends on how fast the engine is going.

How you deal with this also depends on how the ignition circuit is arranged. I've seen 4 cylinder engines with 1, 2 and 4 coils. If there is one coil, you need to stop every 4th spark. If there are two coils, you have to stop every second spark. If there are 4 coils, just disconnect one of them.

Is it vital to make sure that a particular cylinder fails to fire? If so, you can't just skip every 2nd or 4th spark, as every now and then you will miss a count and it will be a different cylinder that is missed. Therefore you'll need some way to keep it synchronised to one particular cylinder if that is important.

A lot of cars have the ignition drivers within the ECU, so you may not be able to find the connections easily. The ignition coils store the energy needed for the spark, and the spark happens when the current is turned off, so you have to turn off the signal for a variable amount of time, depending on engine speed.

On most modern cars, you can easily burn out the catalytic converter by running with not all the cylinders firing, as the unburnt fuel will burn in the exhaust system. The ECU may go into a reduced power mode and register a fault if one cylinder isn't firing.

It may be easier to disconnect an injector, as most modern petrol cars have one per cylinder.

 

[robert1275]

Thank you for pointing that out - I didn't think about that.

I think it would be easier to stop the injector from firing.

Would using a 555 timer be able to shut off injectors one by one after certain period of time?

 

[crutschow]

Shutting off the spark to a cylinder will take more gas since that cylinder will no longer be providng power but still taking in the gasoline charge, and the others have to make up the difference.

Shutting off the injector will save a small amount of gas.

How will you determine when to shut off an injector?

 

[MrDEB]

there are some engines in the automotive industry that shut off several cylinders BUT the intake valve is disabled so no intake charge is used. The valve not working will prevent compression building up and saves gasoline. Don't know if it is still used today??

 

[crutschow]

there are some engines in the automotive industry that shut off several cylinders BUT the intake valve is disabled so no intake charge is used. The valve not working will prevent compression building up and saves gasoline. Don't know if it is still used today??

I believe there are still some that do that (Honda and possibly others) but don't know exactly how it is done.

 

[MrDEB]

I recall Cadillac had an 8 cylinder that shuts off 4 of the cylinders.
The ignition is the easy part as is the fuel injection. the valve train is the hard part. I wonder if the valve train was/ is operated by pneumatic actuation. I know this method has been used in high performance racing engines with better results than mechanical push-rods.

 

[robert1275]

How will you determine when to shut off an injector?

I was hoping to have the first injector shut off by a switch then the others follow on after a period of time - like 2 minutes.

MrDEB - Thank you for that information. I'll see what I can find about it.

 

[tcmtech]

I am just curious as to what gains or reasonings you could have for wanting to turn off only parts of your engine?

Dropping out one cylinder out of four creates a power stroke imbalance that is very noticeable when driving. The few production vehicle engines that do it always drop out the cylinders in pairs to keep the power strokes balanced and they are correct on the closing the intake valves too.

If the dead cylinder is still pumping air through the engine the O2 sensors will get a massive lean burn readings and over richen the cylinders that are fireing to the point it fouls plugs and greatly diminishes the power that they are producing.

 

[robert1275]

I am just curious as to what gains or reasonings you could have for wanting to turn off only parts of your engine?

Dropping out one cylinder out of four creates a power stroke imbalance that is very noticeable when driving. The few production vehicle engines that do it always drop out the cylinders in pairs to keep the power strokes balanced and they are correct on the closing the intake valves too.

If the dead cylinder is still pumping air through the engine the O2 sensors will get a massive lean burn readings and over richen the cylinders that are fireing to the point it fouls plugs and greatly diminishes the power that they are producing.

It is for a school project looking at ways to stop vehicles without using spike strips - I originally thought about cutting the ignition process but as pointed out it looks rather difficult - the injectors were mentioned and my teacher said this is ok as long as I can explain why.

i understand a little bit about car engines, so I appreciate how this will create an inbalance, but as the project is needed to bring a vehicle to stop it's not goning to be a problem.

 

[Diver300]

You aren't going to stop a 4+ cylinder vehicle by shutting off one cylinder. With one or two cylinders running on a 4 cylinder engine, a car can still be driven.

 

[tcmtech]

Maybe he wants to add insult to injury for the car thieves by having it slowly give up on them during the high speed ~ medium speed ~ slow speed ~ embarrassing speed chase!

 

[robert1275]

Maybe he wants to add insult to injury for the car thieves by having it slowly give up on them during the high speed ~ medium speed ~ slow speed ~ embarrassing speed chase!

That's what I was planning.

I was wanting the system to shut the engine down over a period of time, so the vacuum assisted brakes still work.

 

[shortbus=]

I was wanting the system to shut the engine down over a period of time, so the vacuum assisted brakes still work.

The power brakes will still work for a couple of times, even with the motor shut down all at once.