# Brake specific fuel consumption



## muffildy (Oct 11, 2011)

So,
i had an interesting thought - and i wanted to know if anyone knew if it was implemented or not.
Brake specific fuel consumption for a gas or diesel engine usually has a 'sweet spot' where the torque and rpm use the least amount of fuel. Usually auto manfucturers will make a specific gear and a specific speed meet the sweet spot eg 65 mph 4th gear = sweet spot in theory, but with changing road conditions it might not be there, so....
I was wondering if any auto manufacturers of HEV use this to advantage in the recharging of the battery pack? If the car could read the current fuel consumption and rpm, it would know the minimum torque/max torque in order to stay in the sweet spot and then use the electric motor to charge the batteries at a rate which would increase the torque to that amount. it would theoretically keep an engine in its sweet spot almost all of the time.


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## DanGT86 (Jan 1, 2011)

You bet they do. I heard just the other day that there are more lines of programming code that go into a hybrid car than a fighter jet. The algorithms that determine when to run the electric motor are always trying to make the gas motor as efficient as possible at any road speed. Between the ignition timing cam timing fuel timing and transmission shift points or cvt ratio, everything an automobile computer does is to maximize time in that "sweet spot" or make the "sweet spot" bigger. That's part of the reason that cars all went drive by wire. You use the gas pedal to tell it what you want and the car decides the best way to do it for you. 

At least that's the idea.

Just heard the other day new Buicks will have a system where a small battery will dump power into the alternator and use it at highway cruise to help the gas motor out. Like an inexpensive hybrid drive using a system that was basically already there.


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## Salty9 (Jul 13, 2009)

DanGT86 said:


> Just heard the other day new Buicks will have a system where a small battery will dump power into the alternator and use it at highway cruise to help the gas motor out. Like an inexpensive hybrid drive using a system that was basically already there.


GM (and other mfrs) have had a similar system since 2007. It's called a belt driven alternator starter (BAS). I've read that it is capable of up to 15 HP.


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## DanGT86 (Jan 1, 2011)

I think its a pretty clever idea. I would imagine the small battery pack would run out of juice eventually and you would be back to having ICE gas mileage. Its just nice to see any significant innovation towards fuel economy. There was a period of years where the major auto manufacturers were just making everything faster rather than more fuel efficient. 

They got really good at giving us 300hp family commuter sedans but we were supposed to be excited about 30mpg economy cars when we had those 30years ago?


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