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Argonne Study Shows Aggressive Driving Can Significantly Reduce Rated All Electric Range in PHEV, Suggests Engine Control Strategy to Address That
17 April 2008
Engineers at Argonne National Laboratory evaluated the impact of different drive cycles on the performance and component sizing of plug-in hybrid electric vehicles (PHEVs) and suggested an engine control strategy that can alleviate some of the range-diminishing effects of more aggressive driving.
In a paper presented at the SAE 2008 World Congress, they concluded that vehicles designed to satisfy just the EPA Urban Dynamometer Driving Schedule (UDDS), as used by CARB in its calculations for zero emission range credit, may fail to achieve their All Electric Range (AER) rating when driven more aggressively in the real world.
Using PSAT, the researchers modeled a pre-transmission parallel hybrid (similar to the configuration of the PHEV Sprinter), in which the motor is located between the clutch and the multi-gear transmission, and configured it for AERs of 10, 20 and 40 miles following the UDDS cycle. They used an charge-depleting State of Charge range from 90% to 30%, and oversized the battery by 20% to maintain similar performance between beginning and end of life.
For the study, they used six additional test cycles: Japan1015; Highway EPA Cycle (HWFET); New European Drive Cycle (NEDC); SC03; LA92; and US06. Japan 1015 is the least agressive while US06 is the most aggressive. Both LA92 and US06 represent harder accelerations, higher speeds, longer driving distances and harder decelerations.
The researchers examined two control strategies:
Engine Minimum Assistance, in which the vehicle operates all-electrically until the driving demand exceeds the power capability of the electric machine. At that point, the engine turns on and only provides the difference between the power required at the gearbox and the maximum motor power.
Engine Assistance at Best Efficiency, in which the engine is also turned on when the electric motor power reaches its peak, but operates close to its best efficiency curve, with the surplus power from the engine being used to charge the battery.
Under a control strategy of minimum engine assistance, they found that the vehicles maintained their design target AER under the Japan1015, NEDC, HWFET and UDDS, but that the all electric range values dropped under SC03, LA92 and US06, with the sharpest drop occuring in the 40AER vehicle on the US06 cycle.
That vehicle showed a decrease in electric range for 40 miles to approximately 30 on the SC03 and LA92 cycles, and down to just above 25 miles on the US06 cycle.
They found that in addition to higher power, the aggressive drive cycles also require larger electrical consumptions. While for UDDS, the Wh/mile consumption for the 10AER model was 241.5 Wh/mi, that climbed to 484.2 Wh/mi under the US06 scenario, with the engine having to provide a component of that.
Under a control strategy of best engine efficiency, while AER still decreased under the more aggressive drive cycles, the drop was not as sharp. Performance on US06 showed the greatest improvement, with the 40-mile range decreasing only to about 30 miles.
Overall, the fuel consumption of the system is improved from 484.2 Wh/mi to 453.2 Wh/mi for 10AER [under the best engine efficiency strategy]. Even though the engine consumes the same amount of input energy per unit mile, the output energy produced by the engine (output energy of the electric machine) is significantly improved because [of] the higher engine efficiency. The average engine efficiency with the engine assistance at best efficiency strategy over US06 is improved up to approximately 32%.
In considering the impact of designing the AER based on the more aggressive cycles, the researchers concluded that a PHEV sized for the US06 would need to increase the size of its motor from 44.2 kW to 58.2 kW, leading to larger and costlier electric drive requirements.
Overall, this study demonstrated that the PHEV designed to satisfy UDDS may fail to achieve all electric range for real-world driving. The alternative to overcome this failure could be employing charge depleting vehicle strategy with engine operating at best efficiency which would deliver effective utilization of the engine energy during CD operation and could have a relatively small fuel efficiency opportunity loss for longer driving distances.
Resources
Impact of Drive Cycles and Powertrain Configurations on PHEV Component Requirements (SAE 2008-01-1337)
April 17, 2008 in Plug-ins | Permalink | Comments (27) | TrackBack (0)
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Comments
We need to see the same study applied to Toyota's HSD.
Posted by: richard schumacher | Apr 17, 2008 7:02:39 AM
Why not also teach people (kids) how to drive in a way that sips fuel? The same High MPG/AMP driving skills can also be a safer way to drive.
What kid would not jump at the chance to sit in a driving simulator and learn these skills early on. A few million people getting a few more MPG per day adds up to some hefty Oil/Electric savings and if trained properly, possibly faster freeways and fewer accidents.
Posted by: Lee | Apr 17, 2008 7:29:01 AM
all cars should be fitted with this here in Italy where
aggressive driving is a national pastime !
Posted by: ANDRICHROSE | Apr 17, 2008 7:34:10 AM
I read a car magazine review of the Honda Civic hybrid done a few years ago. The difference between aggressive and mild modes was only a few mpg, but they said that the dash indicators did remind them of a more fuel efficient way to drive.
In the real world, you need to drive the way conditions warrant. It is good to drive efficiently, but traffic safety has to take first priority. That being said, this may be one way that people can learn the difference and drive more fuel efficiently.
Posted by: sjc | Apr 17, 2008 7:37:30 AM
A huge impact here comes also from the type of battery used, which is not mentioned in the article.
If you draw lots of current from lead-acid or NiMH batteries (ie driving hard), they will lose a lot of energy to internal resistance. Up to 30-40% of their charge can be lost this way before it even gets to the wheels if high current is asked for.
If you use lithium-ion, the problem is greatly reduced (losing only ~5-10% stored charge by using them at high power rates).
Finally, some motors are much more efficient over a wider power output range than others. Choice of motor plays a big role in efficiency at high vs low power outputs.
Posted by: clett | Apr 17, 2008 8:01:08 AM
The whole point of a PHEV is to commute on grid electricity alone. Show me one commuter who *can* drive aggressively on America's congested roads during rush hour!
If you want to drive with a lead foot, buy a conventional sports car and be prepared to pay for the fuel.
Posted by: Rafael Seidl | Apr 17, 2008 8:17:13 AM
"If you want to drive with a lead foot, buy a conventional sports car"
That makes a lot of sense. However, I can't count the number of times a Prius has blown by me doing 85+ MPH on the highway. Some people seem to think that having a environmentally friendly car gives them special dispensation to misbehave. These are perhaps the same folks complaining about only getting 40 MPG.
Truth is, ANYONE, in ANY CAR, can get better mileage via good driving and maintenance habits.
Posted by: hybrid fan | Apr 17, 2008 8:43:39 AM
"The whole point of a PHEV is to commute on grid electricity alone."
Exactly.
My commute is short but is mostly highway, 60 mph limit.
Other places I've been the speed limit is 75 with a minimum of 45. On the east coast the speed limits are lower and the on ramps are shorter and so are the merge areas but you still need to be up to traffic speed by the end of the on ramp.
A PEHV that tops out at 45 mph electric only is not going to do me much good.
I've looked at taking a train, but it would cost more than driving and I'd have to walk 4 mi... I'm only 5 mi from work. It is illegal to walk or bike on the interstates I take to work and the alternatives do not have sidewalks or shoulders.
Lets say I had an all electric or PEHV that could get me to work on battery power alone.
Lets assume it uses 370 watts per mile, same as the rav4 EV and Electricity is 15 cents per kwh.
If I have a car that gets 30 mpg and gas is 3.35 / regular.
I'd save $140 per year.
What's that a replacement batter for the rav4 is $26,000
Humm even if it lasts 100,000 miles that is still 26 cents per mile ... which is more than I am paying for gas.
It's diminishing returns.
On the 85 mph prius drivers, its like the people who get the supersized big mac and fries with a diet coke.
Posted by: rj | Apr 17, 2008 9:59:08 AM
Yes, people SHOULD drive less aggressively, but many don't. My wife accelerates pretty fast in our hilly neighborhood, even though she drives slow. Try talking to her about it and you get get a combination of confusion, annoyance and apathy. She's not a mechanical mind and doesn't want to think about it. So to best achieve the highest reductions in energy use you need engines that are efficient when "normal" people drive them.
Adding efficient driving techniques to the drivers education curriculum is a brilliant and inexpensive idea.
Posted by: Justin VP | Apr 17, 2008 10:46:57 AM
Phev's will likely get a bad rep in this way off the bat - if you want more power - you get more power, but it comes from the engine - and the myth of 100 MPG will escape you.
The economy reporting should be understood as more of a cumulative - say crossing 100 MPG at x distance. In most cases - and in mine in particular - that's 40 miles and it seems to work well enough regardless of road speed - 10 mph up to about 65 mph. My driving strategy has definately needed to evolve - but it's not life depriving once you get used to it.
Drive below the threshold that the engine turns on and the range will likely drop - but when you cross the x distance mark - you generally cross through the same fuel economy point after the system has been depleted.
Drive 80 MPH - and know that your energy economy is dropping roughly at the square of your speed. This seems to really get noticeable when you exceed 65-70 mph, you are driving your prius in a crosswind or temperatures below 36F.
A production system that works as an integrated part of the car - with engine/hybrid system - will be sweet but with the same amount of energy in the batt - you can only do so much.
Posted by: jeremy | Apr 17, 2008 11:22:03 AM
hybrid fan: "However, I can't count the number of times a Prius has blown by me doing 85+ MPH on the highway. Some people seem to think that having a environmentally friendly car gives them special dispensation to misbehave. These are perhaps the same folks complaining about only getting 40 MPG."
Try this version:
"However, I can't count the number of times a SUV has blown by me doing 85+ MPH on the highway. Some people seem to think that having a big, heavy with poor aerodynamics car gives them special dispensation to misbehave. These are perhaps the same folks complaining about only getting 10 MPG."
Seems to work both ways - I don't get the point of your rant - Lots of people complain about poor mileage in cars. You just happen to pay special attention to the Prius drivers because you also drive one.
Never mind the fact that those Prius drivers doing 85mph on the freeway and getting 40mpg are still burning about half the fuel of 98% of the rest of the vehicles on the road at the same speed. Or the fact that slowing down to 70mpg improves fuel economy about 20% and while that sounds like a big number, in terms of gallons saved it will still be half the amount saved when compared to your typical car reducing speed from 85mpg to 70mpg.
Anyway, the solution seems straight forward:
1. Warn consumers that aggressive driving can significantly reduce fuel economy. If they want to drive aggressively, they will pay at the "pump" regardless of what type of car they drive. They will still reduce oil consumption with some sort of hybrid vehicle.
2. A "economy" guage could be built in to the vehicle which lets the driver know how efficient his driving style is. For example, efficiency typically drops off quickly once you exceed a specific load point. A simple gauge that goes from green to red based on how much extra energy you are wasting would help inform and train drivers.
3. Reduce weight - less weight means less power required to achieve the same acceleration and deceleration.
4. If all else fails, design the drivetrain to handler higher loads more efficiently. This will be done anyway for commercial hauling applications, but the challenge will be making it light and inexpensive enough for your typical car.
Posted by: Dave | Apr 17, 2008 11:25:06 AM
You'd think folks would WANT to save a buck with efficient driving, what with gas at $4 (and soon to be $5). Cursing the darkness is a lot more fun for some people than lighting a candle.
Watching aggressive drivers is like watching some kid cutting donuts with the family car and thinking, "Now there is someone who doesn't have to buy his own tires (gas)." Or maybe these are rich people* who quite literally have money to burn.
*not really. All of the well-to-do that I personally know are pretty tight with a buck. In my experience, it's the "in debt up to their ears" folks that spend like there's no tomorrow.
Posted by: Hybrid fan | Apr 17, 2008 11:35:24 AM
As long as im in control and can put petal to metal when needed its ok. Otherwise ill blow your bleeping ass off if you mess with my car and dont change the horrid merge conditions on us freeways.
My lifw dwpwndwd on leadfooting it every day back where we used to live I litteraly could NOT have survived those years without it.
Posted by: wintermane | Apr 17, 2008 1:13:10 PM
Acquired behavior is not easy to change. As long as Automobile Ads glorify rubber burning accellerations and stops, many of our young drivers will try to imitate what they see on TV.
Why coundn't responsible car makers produce Ads showing our young and not so young drivers how to drive more safely while getting more mpg.
Why not go one step further and give free or almost free better driving lessons and/or make it compulsory for all drivers who had an accident where speed or bad driving habits were involved.
Posted by: Harvey D | Apr 17, 2008 2:40:37 PM
"the researchers concluded that a PHEV sized for the US06 would need to increase the size of its motor from 44.2 kW to 58.2 kW,"
Excuse me but since when are cars limited to one or the other?
If guzzlers can offer 6 or 8 cylinder engines as options, then an electric car mfg should be able to offer various motor sizes with equal or greater ease.
Posted by: John Taylor | Apr 17, 2008 2:48:40 PM
On my car's website, I've gotten(not earned)the reputation as the MPG guy. Not a U.S. hypermiler, only saying I feather foot & use a couple techniques for better MPG, marks me as one above (or below) the normal driver. Drivers who care to save gas by careful driving are fairly rare, even in this day of pricey gas.
Posted by: litesong | Apr 17, 2008 5:59:27 PM
In America it is not manly to be responsible, it is manly to be reckless and wasteful. That might explain the choice for president. Witness the jacked up pickups of pseudo macho men. Those monsters get horrible mileage, but the drivers barrel on with conspicuous consumption saying "look at me, I am a real man...I don't care".
Posted by: sjc | Apr 17, 2008 9:58:08 PM
Personal responsibility. Now THERE'S a concept! There are certain things each of us can do TODAY, without waiting for, let's see, oil companies, auto makers, government, etc.
How many rail against one or all of the above for doing nothing to help, while they themselves fail to do what they can TODAY. For FREE. It's far more fun to point fingers than to act. ACT, don't just whine.
Posted by: Hybrid fan | Apr 18, 2008 4:16:03 AM
If they make a car without performance then it's not going to sell.
It can't sell on cost, because the batteries cost too much. It can't sell on convenience, at least so far, because it's less convenient on long trips if nowhere else.
The Volt will have performance, convenience, and break almost even for cost. If you take the performance out, people won't buy it.
This is a case of perfect fighting good. We can have 100,000 people saving 80% gas, or 10,000 saving 90%. Somewhere logic has to overtake idealism.
Posted by: greg woulf | Apr 18, 2008 5:46:04 AM
@ Greg
So what's wrong with having options? Two motor sizes can quite easily be offered.
"We can have 100,000 people saving 80% gas, or 10,000 saving 90%."
Near as easily we can have 90,000 people saving 80% gas, with a 58.2 kW motor, AND 10,000 saving 90% using a 44.2 kW motor and some good driving techniques. (I expect to see the smaller motor selling better than at 10% though).
Having a "sport" package option is something most all gas cars offer.
Posted by: John Taylor | Apr 18, 2008 7:59:45 AM
So to best achieve the highest reductions in energy use you need engines that are efficient when "normal" people drive them.Or a mandatory "fuelishness" buzzer that goes off when a driver is being wasteful, like a seat-belt chime or upshift light.
Or a mandatory "chill out" feature in the powertrain controls which responds to sustained aggressive driving by reducing performance.
All it would take is one act of Congress.
Posted by: Reality Czech | Apr 18, 2008 8:15:00 AM
One thing I have noticed with the cruise control on my '95 Chrysler is that it accelerates more aggressively than I do without it. What were they thinking?
Posted by: tom deplume | Apr 18, 2008 11:20:33 AM
Aggressive driving reduces range? Wow. Does the Nobel committee know about this study?
Posted by: Peter | Apr 18, 2008 1:26:02 PM
Though sometimes it can be fun to go out and drive aggressively.
If I can go out and drive aggressively in a Tesla, its going to cost me a lot less than doing so in a Porsche. So will I be tempted to do it more often?
Is reducing the marginal cost of aggressive driving going to encourage aggressive driving?
Posted by: Alex, Tunbridge Wells | Apr 21, 2008 9:19:15 AM
This is a really dumb study, and a waste of our time.
You get nothing by going to a smaller motor, the study doesn't compare the efficiency of a 58.2 kw motor to a 44.2, or even the cost, just saying that the cost of a 58.2 is "higher." Mass produced motors are cheap, $10 isn't going to break the bank when we're paying $10k for a battery.
If you drive a car with a 58.2 kw motor at the same speeds as a 44.2 kw motor the 58.2 kw motor is more efficient. Look it up if you don't believe me. The larger the electric motor the more efficient it is. It's not the motor that's ever a problem, it's the driver.
If we're driving on our pure electric, like the Volt, then if we drive aggressively for 30 miles and plug in we're still using zero gasoline. The argument is about a percentage of a percentage, all to sacrifice performance. If the performance drops, less people will buy it offsetting any gains you get.
Now, on to the driver being a problem. They're comparing the efficiency in the aggressive cycle, but people don't maintain the aggressive cycle for the whole trip. So we're talking a higher percentage for a short little bit surrounded by no change according to their own study.
Then on to the whole logic of the argument that we should force smaller motors in. That's stupid first because it's not going to save a lot of money, gas or lives. It's even stupider when you consider electronically controlling a larger motor with the computer is cheaper and has almost no drawbacks to mass production.
The entire argument is false, and fostering it is foolish and will hurt the green movement. I could go on at length, both about the testing, which includes gearing that won't be on the Volt, and about the concept of freedom to drive the way we want.
We'll only convert the masses to EV's when we can show them there's no downside. Why create a downside, when so little stands to be gained.
Posted by: greg woulf | Apr 21, 2008 12:03:45 PM
Everybody knows (or should know) that Weight + accelleration + high speed + drag = more energy will be used. That is true of all ground vehicles.
If the energy used is very clean (electricity?) and nobody gets killed or hurt or disturbed or sick and you can afford it, the larger motor version may be the choice of many.
However, clean energy is not available everywhere, extreme accelleration + high speed kills and/or hurts many people, burnt rubber is bad for our health, noisy quick starts are annoying to many etc.
It would make sense if efficient driving techniques were part of all drivers training.
Posted by: Harvey D | Apr 21, 2008 6:27:59 PM
Try driving slow in the Big D its suicide especially in a small car. EVERYONE drives 85mph even in bumper to bumper traffic, cops too. I have a pic on my phone of my speedo at 90 mph and a cop in the next lane crusing with the flow of traffic. IF everyone slowed down then maybe just maybe it would save some fuel but the economy is strong here people make great money and fuel is a small part of disposable income. Dallas was the #1 growing metroarea in the US for a reason JOBS and high pay with low cost of living aka housing is cheap.
Posted by: JD | Apr 24, 2008 12:44:41 PM
