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ORNL researchers propose optimization framework for use in real-time feedback systems to improve driving styles with reduced fuel consumption

3 October 2012

Malikopoulos1
Cumulative fuel consumption of the original and optimized Japan 10-15 driving cycle. Source: Malikopoulos and Aguilar. Click to enlarge.

Studies have concluded that optimizing a driver’s driving style can reduce fuel consumption and emissions by up to 40%; exactly how to achieve that optimization across a large and diverse driving population remains an area of active investigation—and one of great opportunity.

Dr. Andreas Malikopoulos at Oak Ridge National Laboratory and colleague Juan Aguilar have developed an optimization framework based on their assessment of driving style factors that have a major impact on fuel economy. The framework can be used to develop real-time feedback systems to enable drivers to alter driving styles in response to actual driving conditions to be more fuel efficient and environmentally friendly, the two suggested in a paper presented at the 2012 15th International IEEE Conference on Intelligent Transportation Systems (ITSC 2012) in September.

This paper has two main objectives: (a) to investigate those driving factors that have a major impact on fuel economy and (b) to optimize driving styles with respect to these driving factors. In this context, we formulate an optimization framework that aims to modify driving styles with respect to key driving factors.

...Individual driving styles are different and rarely meet the driving conditions posited in testing (e.g., engine optimization with respect to steady state operating points or vehicle speed profiles for particular highway and city driving). The optimization framework adopted here facilitates better understanding of the potential benefits from employing a more conservative driving.

—Malikopoulos and Aguilar

One of the most promising approaches identified in other work to optimize driver behavior is to provide the driver with immediate information about the effect of his or her behavior on fuel consumption, they noted. In their work, Malikopoulos and Aguilar identified two factors that have a major impact on engine operation, and so on fuel economy: the stop factor and the coefficient of power demand.

  • The stop factor is defined as the amount of time during a driving cycle that the vehicle is stopped (i.e., time that the vehicle’s velocity is zero divided by the total duration of the driving cycle). This factor indicates idle engine operation over a driving cycle.

    There is a linear correlation between the stop factor and fuel consumption, the authors note; as the stop factor increases, fuel consumption also increases.

  • The coefficient of power demand provides an indication of the transient engine operation since it is proportional to power demanded by the driver. The power demanded by the driver is proportional to the product of the vehicle speed and acceleration; this product is defined as the coefficient of power demand.

    In their analysis, they also found a linear correlation between the coefficient of power demand and fuel consumption.

The stop factor represents a commuting aspect rather than a driving one—i.e., it is route-dependent, rather than dependent on driving behavior, and can be altered only by changing the route. Furthermore, hybridization of vehicles has aimed to address the stop factor by shutting off the engine when the vehicle is stopped and thus eliminating near-idle engine operation. Therefore, Malikopoulos and Aguilar focused on the problem of optimizing a driving cycle with respect to the coefficient of power demand.

To develop the optimization framework with respect to the coefficient of power demand, they used Autonomie—a Matlab/Simulink simulation package for powertrain and vehicle model development developed by Argonne National Laboratory. They built a set of polynomial metamodels to construct an explicit relation between fuel consumption and the coefficient of power demand and so to formulate the optimization problem analytically significantly to reduce computation time. The models can reflect the responses in fuel consumption produced by changes in the coefficient of power demand.

Applying the optimization framework to three driving cycles—Japan 10-15, combined FTP and HWFET, and FTP—they found that the optimized cycles:

  • Increased travel time 28% in the Japan 10-15 cycle, with a 22.3% improvement in fuel consumption;

  • Increased travel time in the combined FTP and HWFET by 9.8%, with a 15.9% improvement in fuel consumption; and

  • Increased travel time 14.1% in the FTP cycle, with a 23.2% improvement in fuel consumption.

In other words, a more conservative driving style that delays destination arrival had a significant impact on fuel consumption. One approach for using the framework to develop a real-time feedback system for a driver would be as follows, as the authors suggest in a separate paper under review for publication in IEEE Transactions on Intelligent Transportation Systems:

  • The driver first drives the desired route by employing his or her typical style. A flash drive plugged into the onboard diagnostics (OBD) of the engine records two required signals: (a) the vehicle speed profile, and (b) the fuel consumption rate.

  • After the trip, the driver downloads these two signals in an application running the optimization framework.

  • The user can select the criteria for optimizing his or her driving style in the optimization problem; for example, an optimized driving style should be no less than a certain value of speed from the original one, or the arrival time should not exceed a certain percentage of the original time.

  • Malikopoulos2
    Visual instruction area in red corresponding to the driver’s acceleration profile when operating the vehicle. Click to enlarge.

    The new optimized vehicle speed profile forms the basis of a real-time feedback system— e.g., an actual acceleration profile (red square) should be less than or just overlap the optimal acceleration profile (green square) at each instant of time. (Diagram at right.)

    The belief implicit here is that after repeating the same route by following these visual instructions, the driver will eventually learn the optimized driving style. Thus, eventually, the driver will learn the most efficient position of the accelerator pedal to achieve a certain amount of benefit in fuel economy.

...The long-term potential benefits of this driver feedback system are substantial. Drivers will be able to evaluate their driving behavior and learn how to improve their driving styles based on their own preferences. Realizing a more eco-driving style can contribute significantly to sustainable mobility.

—Malikopoulos and Aguilar (under review)

Resources

  • Andreas A. Malikopoulos and Juan P. Aguilar (2012) Optimization of Driving Styles for Fuel Economy Improvement. (ITSC 2012 MA8.2)

  • Andreas A. Malikopoulos and Juan P. Aguilar (under review) An Optimization Framework for Driver Feedback Systems

October 3, 2012 in Behavior, Fuel Efficiency, Vehicle Systems | Permalink | Comments (23) | TrackBack (0)

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Comments

(hmm, I think I got censored for using the word #$%^&*. Try again)

I think all cars should have a voice that chastises inefficient driving with some appropriate scolding of the perpetrators.

For example:

"You just accelerated and braked like complete #$%^&^&. If you do not improve your behavior, you will be forcible drafted into the US Army and sent to the frontlines as cannon-fodder in our latest immoral and illegal war over oil. This is your final warning."

Most of the 3% and about half the remaining 97% and most of our young drivers are not at all ready for that.

You could have a servo which pushes back on the gas pedal when people are driving too aggressively.  It would not force them to slow down, but they'd get feedback in a very visceral way.

@Jus7tme

What, you do not have a wife?

Some of you folks have a serious case of energy obsession. First we need to get people pay attention and stop driving with intent to kill.

This is BS.

If you want to save fuel badly enough to try something like this (I would gladly, if it worked - I think it will NOT).

If you want to drive special to save fuel:

#1. Those red and green boxes are not needed if there is no traffic - just coast down as much as you can stand to for every red light, every corner, every off ramp ...). DO NOT BRAKE.
This can get you BETTER mpg in the city than you can get on the highway, at 75mph steady state, you almost never brake and wind resistance is small.

The red and green boxes are an impediment and distraction if there IS traffic and you are trying to anticipate (coast down for) the next on ramp, corner or red light.

Just do whaterver you reasoably can to stay off the brakes. Cars today are MOST efficient at moderately high torque - except an AT stays in a lower gear (bad) and you can end up approaching a stop at 50+ mph (really bad).

Slow acceleration promotes early AT upshift and indirectly helps avoid brake use. If you have a manual Gbox, just upshift early; THAT will eliminate fast accels.

Freedom to do ALL what one wants to do regardless of the consequences to others may be possible if you live alone on a samll island or if you are part of the Lords and Kings of yesterdays.

The Constitution was written and updated for the general well being of the majority living in a complex equitable world, not to restrict protection to loners and the 3%. Nobody should have, or think they have the right to run over others because they have a larger muscle car or a deeper pocket book. The majority has to be protected against those people with appropriate traffic laws and regulations and limitations as required.

And then, the BS about:
- coefficient of power demand (naught but delivered hp)
- an optimization framework (= %$#&^%)
- The stop factor (minimize idling; a real eye opener)

The actuality here is that if a driver repeated the same route at a later time, following the visual instructions, he would stop on green lights, miss other green lights, run red lights and drive into cars ahead.

These are very valuable data. This research is very useful for future reference and very helpful for racing.

J. Harp@Truck Driving School

I don't need a computer system to tell me that I need to lay off the pedal on the highway, stop punching it off the mark, downshift instead of brake, slowly approach red lights instead of gassing up to stops.

But if a computer could tell me at the end of each tank of fuel what stupid-%$$ nonsense I had done, then it would be good feedback and in psychology, we have determined that observable functions are controllable functions.

Good data makes better drivers.

@E-P,
That thing already exists. It's called:

"Nissan ECO-Pedal"

"downshift instead of brake" ? ?

You DO need a computer to tell you.

There are already efficiency feedback mechanisms in place on most hybrids, such as the Prius (instantaneous, near term, long term), Escape (more 'leaves' for better driving), etc.

Even my 2000 Honda Insight has instantaneous, mid term (odom A), long term (odom B), and lifetime.

With over 108,000/year road fatalities, over 540,000/years serious injuries, close 3,000,000/year lighter injuries and 20,000,000/year property/vehicle damage 90% caused by human drivers mistakes, it is difficult to understand that faulty drivers are still allowed to drive.

How can you kill and/or injure over 2,000,000 people a year and get away with it? It is almost as bad as an ongoing non-stop WW-II?

Driver less small e-buses are currently being built. It could become a first application in many cities followed by driver less e-cars. Small driver less city e-buses could reduce the use of dangerous human driven gas guzzlers in down town areas. Highway driver less vehicles should be easier to do. It could eliminate about 90% of current accidents.

Feedback CAN help - but few know how to use the feedback.

Feedback only helps if you already know how to drive for high MPG.

Acceleration in high gear is fine - but it can last a long time and it is a mistake to rush it and cause a down shift.

Hard acceleration in high gear is fine – BUT not if this means you will overrun slower traffic or approach the next slowdown with more speed than you need.

Feedback shows very high mpg when braking - but braking is almost always really BAD (a collision is worse).


Feedback only helps if you already know how to drive for high MPG.

>>Feedback shows very high mpg when braking - but braking is almost always really BAD (a collision is worse).

In this case, you mean feedback in the form of an instantaneous MPG display.

Yeah, showing high MPG when coasting is accurate feedback, but showing high MPG is misl;eading if you took the foot of the gas pedal although you might be standing on the brake and expending all your hard-earned kinetic energy.

However, drivers might learn that the high MPG reading does not last long when the car slows down.

>@Jus7tme
>What, you do not have a wife?

Kit P: The good joke aside, not all women, wives or not, are efficient and sensible drivers that would chastise their mates for driving inefficiently. In fact, I see so many women driving foolishly that I think they are just as bad as men, energy-wise.

Kit P,

>Some of you folks have a serious case of energy obsession. First we >need to get people pay attention and stop driving with intent to kill.

I admit to be energy-obsessed, but in a good way. We all should be!

No need to do one OR the other. Everyone should drive efficiently and safely. No need to make a choice between the two.

Any of the feedbacks available today is much the same as calculating MPG at each filling of the tank - much faster, of course, and more frequent but not much better.

Personal feedback can actually be better, easier and simpler.

Are you pushing on the brake?

If so, you were going too fast for the situation.

That leaves a lot of complex decisions to be made on how to avoid braking beforehand, but the weird Malikopoulos system proposal is worse.

An very low cost electric fence can teach a cow 'Feedback' in less than a single day. More complex electronics could teach the average American some basic easy feedback after a few months? If not, USA is heading for major problems?

For those not-so-poor people with profligate driving habit and enjoying it, help is on the way. Afterall, what is the point in purchasing a 300-hp and don't get to floor the gas pedal every once in a while and to slam hard on the brakes?
I would like to offer a high-end PHEV as a means for highly-spirited driving while still conserving petrol, energy, and the environment!

Let's consider a 300-hp PHEV with a serial and parallel power-split architecture having a 200-hp electric power and a 100-hp ICE, with a 8-kWh battery pack. A 100 hp Atkinson-cycle or Miller-cycle engine is downsized enough to run the engine in the peak efficiency nearly all the time. The 200-hp electric component is hefty enough to allow complete braking energy regeneration for 95-99% of the time, even with lead-footed driving haabit. Likewise, the high-powered electric components with low internal resistance also allows fast accelerations with less resistive loss than in a HEV with limited electric component. A 2-speed gear change transmission can allow even more tire-smoking acceleration without stressing the electrical components. The owner can elect to plug it in every night or even twice daily to enjoy nearly petroleum-free driving and significant fuel cost savings to more than recoup the price premium of this PHEV.

If the owner is too lazy to plug it in this Super PHEV every night, still, the purpose is still served to allow very spirited driving at much lower petroleum consumption than would be possible with a comparable ICEV. The petroleum consumption can be reduced to 1/2 of that of a comparable ICEV even if the owner forgets to plug in the vehicle for most of the time.

Has anyone thought of common sense? Keep it smooth and drive like you have no brake, within reason, if you can. On my way home up the A1 most traffic was bunched into the passing lane to a degree where staying in the inside lane guaranteed smoother and even quicker progress. The result for me was getting better than the official mileage stats because I had room, whilst others in the passing lane followed too close, braking, accelerating and braking and so on.

How about a few thousand race tracks for stressed drivers with 300+ hp monsters and roads for others?

Race tracks? How about just semi-empty roads? Impromptu traffic-light drag racing is the most fun! Instant gratification in just seconds! It's not about stress relief but the fun in driving.

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