How does a FI car control idle speed?

[Benbay001]

I keep trying to work this one out, but never seem to be able to come to any conclusions.
Does a fuel injected car have some sort of control of the throttle? Does it run lean usually, then adds more fuel if it needs to up the idle?

Thanks.

[eliot]

Search google for "idle air valve" - as the name suggests, its an electric valve controlled by the ECU to allow air into the engine which goes around or parallel to the throttle plate.

[Benbay001]

Cheers

[DVandrews]

There is also a degree (no pun intended) of idle speed control using variable ignition advance.

Dave

[shoehorn]

A lot of newer stuff have no dedicated ICV anymore,electronically controlled throttles seem to have taken over that job.
I would imagine though,that idle speed refinement would be the very last thing they would be concerned about,the engines always seems to run very fast or are constantly altering rpm even in neutral.

[Sensibleboy]

Do F1 cars use conventional throttle butterflies?

[Megaflow]

FI = Fuel Injection. Not F1...

[anonymous-user]

Pretty much every modern car, since around 2003 is run with a "Torque based" engine management system. These use engine torque as their primary control parameter, and are calibrated with both a "Forwards" and an "Inverse" torque, model, so the actual flywheel torque can both be estimated and controlled many times a second. For a gasoline engine, primary torque control is effected via ignition angle control (the fast path) and an electronically controlled throttle plate (the slow air path). Once you know the engine torque for any given operating condition, controlling things such as idle speed, or cruise control speed, or engine speed during gear shifting, and even traction control become very much easier (if still complex)

For a diesel engine, injection mass and angle are the fast path control, and inlet manifold air density (boost pressure) the slow path in effect. Often, these days, even diesels are throttled in order to build a high enough pressure ratio across the combustion chamber to pump sufficient EGR mass for emissions / economy reasons.

[Mr2Mike]

Max_Torque said:

For a diesel engine, injection mass and angle are the fast path control, and inlet manifold air density (boost pressure) the slow path in effect. Often, these days, even diesels are throttled in order to build a high enough pressure ratio across the combustion chamber to pump sufficient EGR mass for emissions / economy reasons.

I thought the primary goal for throttling on diesels was reduced NOx, or is that a secondary effect caused by increased EGR?

[Steve H]

Mr2Mike said:

I thought the primary goal for throttling on diesels was reduced NOx, or is that a secondary effect caused by increased EGR?

Yep, egr is about reducing combustion temperatures (resulting in less NOx) and throttling the inlet increases the egr effect.