THe answer gets a little complicated. The reason accelerating fast consumes more energy is similar to who AC units and chillers are more efficient at part load. Under normal loads, IC engines in cars are most efficient at lowers RPM's and partial throttle positions. They burn the most lean and more improtantly, make full use of their compresssion ratio. Meaning that more energy goes into moving the piston and less into waste heat. At full throttle and high RPM, the mixture is more rich, and sice throttle positon is larger, more air is pushed into the piston, so pressures and heat increase and more energy is lost to waste heat.
Originally Posted by Space Racer
However, on a electric motor and drive, the permenant magnet motors used make peka torque at 0 RPM and there's little change in efficinecy as RPM increases. However, the drive, is most efficient at full load. At part load it uses I beleive pulse width modulation and some waste heat is created switching on/off the circuits. So you want the electric motor at full load, but the IC engine at minimum RPM and throttle and more improtantly, if it's a automatic, it needs to have the torque converter locked up.
Oh... and jsut ot further comlicate matters, engine effciency and fuel economy are not nessesary the same thing. Efficiency would be fuel conmption rate per delivered HP. Fuel economy is fuel consumed per unit of distance traveled. Many engine reach peak efficiency I beileive right at the point where the torque curves begins to taper off.
OH and in reality, the instanataneous fuel consumption of a engine varies much more dramatically. Very lgiht throttle at low RPM's on a small 2.5L 4 cylinger for example is probably around 50mpg, but full throttle near redline is around 8-10mpg. AN IC engien at idle probably only makes about 5-10HP depending on throttle positon, AC and alternator loads. At a highway crusing speed of 65mph @ 2000RPM and part throttle, it's probably around 40HP and at a nice efficient 45mph, its' maybe just 20HP at 1500RPM.
That's all well and good, but:
Originally Posted by motoguy128
1. I used the example of the gas engine because it's something we are all familiar with. It's easier to talk about miles per gallon than watts per foot-pound per revolution or some such ratio. Of course gas engines are less efficient and have different power curves. But in this case, that's beside the point. I was merely illustrating a point, not carrying on a scientific discourse or comparing efficiency ratios.
2. A lead foot is a lead foot. If you are driving in a 30 mph zone and zoom up to 50 so you can pass a slowpoke and beat him to the red light and stomp on the brakes, while I drive 25 and arrive at the light a few seconds after it has turned green and barely take my foot off the gas, you have wasted more energy than I, regardless of engine type, and regardless of regenerative braking. (Yes, I am one of those guys who gets a kick out of passing lead-footers at the light. In a series of ten traffic lights, I'll pass the same idiot ten times (in light traffic). I've even had people pull into parking lots behind me to tell me my brake lights didn't work.)
IF you have regenerative braking, how hard you accelerate becomes irrelevant and in some cases you need to accelerate harder for best overall system efficiency.
But I agree, driving technique makes a big difference. However my time is worth more than saving a few cents. SO I drive 5-10mph over the limit but I do pay attention to timed lights. However occassionally some are off sequence and it drives me nuts when someone is going 5 under or right at the speed limit when I know that going 2-3mph over will allow you to "make" a light vs. sitting for 2 minutes.
Plus in residential area (when no children are around) going 30mph yields better mileage than 25mph.
True. Rate of acceleration has much less to do with energy waste in electric motors. But excessive speed is wasteful, even when some of the energy is recovered. And for those who like to drive fast, RB provides a rationalization for their bad habits. It does not justify them.
Originally Posted by motoguy128
You might beat traffic at a yellow light, but it will all catch up to you at the next light.
There was an experiment done several years ago about driving habits and time saved. Two drivers drove across the city of Chicago. One drove at or below the speed limit, seldom changed lanes, and stopped at yellow lights whenever possible. The other drove above the speed limit, changed lanes often, and ran yellow lights. I don't remember the exact result, but the fast driver beat the slow driver by about 2-3 minutes (a little over a minute per hour). What did he accomplish? How many lives did he endanger? What happened to his gas mileage? How much extra wear and tear to his car did he cause? How much stress did he endure? I don't have the answers to these questions, but I suspect they were all negative.
I have no desire to prove how many pennies you might save with good driving habits. My only point about RB is that it is most useful for those drivers who spend a lot of time slowing down. If you spend a lot of time slowing down, RB provides a way to recover some of the energy you wasted. But if you prefer to drive at a constant rate, RB provides less benefit.
The people who will benefit the most from RB are bad drivers. With RB on their cars, they will feel more encouraged to continue their bad habits. But they will accomplish little beyond endangering the lives of others and causing excessive wear to their cars.
I think this is a great idea. If they could get the top speed up to 45 mph and the range around 30 miles a lot of people would buy if gas prices keep going up. You would basically have an electric car for commuting to work that could run on gas for longer trips.
The USA has plenty of power plants to turn coal and nutrons into electrical power. They just kinda cruise at night when power is not required. We need to figure out how to push cars around with this power instead of buying oil from the crazys in the mid-east.
I think we're losing sight of some dinimshing retruns here. TO get more range and speed, you quickly need much larger motors and batteries. IF the car isn't custom built for that function, you're adding a lot of weight, taking up a LOT of space. THere's a reason the Prius, Volt, Insight are all compact cars. I think you'll be surprised at how large a battery you need with a full size IC engine and with full regenerative braking.
We also could get people to just buy smaller cars and not live 40 miles from work. I only drive 6000 miles per year or less. A guy that drives 15,000 miles per year might get almost 2X the mileage, but still consumes more fuel.
Maybe it should considered this way. Without regenerative braking, you will overall consume MORE energy with this system. You are simply deferring some of it to the grid. This is more like a hydrogen system.
I'm highly skeptical until this system replaces all 4 brake rotors and is integrated with the transmission and engine computer to optimize it as it is in current hybrid electrics.
I hate to day it, but high and sustained fuel prices are the best way to drive innovation and make consumers desire more fuel efficient vehciles . Last I checked, large SUV's, full size trucks were still selling well. One BIG sep forward is that midsized cars are now starting to match and in some cases exceed the economy of smaller compact cars... at least on the highway where they are used the most.
IF we stopped supporting these s*** hole countries with benefits and subsidies to better secure their oil supplies and instead let the open market do it's thing. I think plug in electric hybrids with a small CNG could be a viable option as well.
Also if we were really serious, we might impose lower speed limits for vehicles over 3000lbs or with fuel economies under 40mpg combined similar to trucks. Then also raise fuel taxes a little higher and specifically target those funds for subsidising the purchase of electric vehicles.