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Study of eco-driving in hybrids finds need for systems that facilitate energy-efficient behaviors

30 January 2016

A study of eco-driving behavior in hybrid electric vehicles (HEVs) by a team from Technische Universität Chemnitz (Germany) and the University of Southampton (UK) has found that simply providing drivers with a technology that has the potential for high energy savings—i.e., a hybrid—is not sufficient to result in high energy savings; systems must be developed in a way that facilitates energy efficient behaviors.

Put another way, they found that eco-driving motivation does not guarantee ecodriving success. Their study showed that even among drivers who were highly motivated for eco-driving, the individual differences in applied ecodriving strategies were still substantial. Building on the results, the team presented a number of suggestions for the design of systems that facilitate ecodriving. A paper on their study is published in the journal Applied Ergonomics.

Franke
The conceptual framework of adaptive control of ecodriving strategy selection in HEV driving. The depiction shows processes at the trip-level. Long-term relationships between variables are omitted for clarity. Franke et al. Click to enlarge.

HEVs are key for sustainable road transport as they can reduce fuel consumption without necessitating complex changes in energy-supply infrastructure (in contrast to plug-in or fuel cell electric vehicles). Yet, ultimately, sustainability strongly depends on the actual energy efficiency that users achieve in everyday usage. User behaviour is, therefore, a critical factor with regard to the ultimate effect that such systems have on making the road transport system more sustainable.

Ecodriving has emerged as a term that encompasses all the influences users have on the real-world energy efficiency of a road vehicle. As well as strategic and tactical ecodriving measures (e.g., optimize tyre pressure, route choice), specific driving behaviours (i.e., operational ecodriving strategies) are a core element of ecodriving. Electric drivetrains have been discussed as particularly challenging due to the novelty of their energy dynamics (e.g., consumption dynamics of electric propulsion, bidirectional energy flow resulting from regenerative braking). HEVs represent the most complex drivetrain in this respect because of the extremely dynamic interplay between the different drivetrain components, and the central role of bidirectional energy flow. Hence, maximising HEV fuel-efficiency can be considered particularly challenging, not only requiring ecodriving motivation, but also a sufficient level of technical system knowledge. From the perspective of green ergonomics a key challenge, therefore, is to advance understanding of user-energy interaction and support drivers’ ecodriving efforts.

—Franke et al.

For the study, the team used 39 HEV drivers—Toyota Prius Gen 2 and Gen 3 and Prius c—with above-average fuel efficiencies and collected interview data, questionnaire responses, and long-term fuel efficiency recordings.

The team probed for motivation and knowledge; eco-driving strategy selection; conceptualizations (i.e., how do HEV drivers conceptualise HEV energy efficiency); and false beliefs.

They found large individual differences in strategy selection. They also found that the drivers expressed a large number of different conceptualizations of HEV energy efficiency, as well as various false beliefs that could affect fuel economy.

They also found certain decision biases in user-energy interaction. As an example, some of the results suggested that there might be something like an “energy conversion fallacy”—many drivers were not aware of the considerable losses incurred when converting energy, and often reported over-utilization of electric propulsion and regenerative braking, overvaluing their energy efficiency.

The drivers also provided suggestions for advanced ecodriving support systems in HEVs, which the research team consolidated and presented as general design guidelines, including:

  • Comprehensive feedback. Four key types of user-interface information appear crucial: (1) predictive information (for supporting adaptation to upcoming road events); (2) concurrent tracking feedback (to support the targeting of optimally efficient drivetrain states); (3) real-time performance feedback (i.e., indicators of momentary energy efficiency); and (4) aggregated performance feedback (i.e., aggregated indicators of energy efficiency).

  • Ease of perception. System design should maximize ease of perception and minimize distraction. For instance, drivers suggested haptic presentation for concurrent tracking feedback, enabling peripheral monitoring of momentary performance feedback, and generally shifting ecodriving information to the central gaze direction.

  • Strategy acquisition support. Ecodriving support systems should support efficient strategy acquisition. The data suggested two opportunities in particular: (a) a tutor system that provides explicit advice on correct strategies, and the reasons for strategy effectiveness; or (b) a system that communicates this advice implicitly via the interface information described above, thereby supporting trial-and-error learning.

  • Automated functions. Ecodriving is always a balance of different driver motives and current situation characteristics, and some drivers expressed their dissatisfaction with the design of current simple automated system interventions. Shared control may be a fruitful approach—e.g., an adaptive eco cruise control (eco-ACC) for efficient longitudinal control that allows drivers to influence key parameters (e.g., the intensity of energy efficiency optimization, system flexibility to change speed) so that automated vehicle control matches drivers’ momentary preferences.

  • System transparency display. A display that shows drivetrain dynamics (e.g., energy flows) can be beneficial for ecodriving. Some drivers argued that a precise understanding of the drivetrain functionality would be helpful in preventing false strategies, and several drivers requested more information on system states.

  • Configurability. Drivers of different levels of system understanding (or technical knowledge or ecodriving skill) will have different information needs. Further, differences in strategy preferences can also lead to different information needs. For an optimal ecodriving support system, some level of adaptability (e.g., the option to switch between basic vs. advanced eco-driving support) is necessary.

It could be argued that facilitating efficient user-energy interaction (i.e., sustainability-by-design, increasing usability of the user-energy interaction) is a particularly powerful approach for the support of sustainable behaviours, as it would enable all those with basic motivation to utilize energy resource efficiently (i.e., this might partly bypass the need to establish strong positive attitudes towards environmentally friendly behaviours). This underlines the potential of green ergonomics. The ultimate goal of green ergonomics is to develop a general theory of user behaviour in low-resource systems (i.e., resource efficient systems); the present study is one step in this long-term agenda.

—Franke et al.

Resources

  • Thomas Franke, Matthias Georg Arend, Rich C. McIlroy, Neville A. Stanton (2016) “Ecodriving in hybrid electric vehicles – Exploring challenges for user-energy interaction,” Applied Ergonomics, Volume 55, Pages 33-45 doi: 10.1016/j.apergo.2016.01.007

January 30, 2016 in Behavior, Fuel Efficiency, Hybrids | Permalink | Comments (4)

Comments

Almost every new automobile or new engine development does not promote eco-driving. It is almost always about faster acceleration, more horsepower (kilowatts), and higher speeds. The relative failure of the TATA-NANO is a demonstration of the ideals promoted by most automobile manufactures of Bigger and Faster and more expensive entertainments. It is well known in the automotive industry that fast acceleration and fast braking and fast driving expends fuel, but there is no substantial move by governments to limit speeds on motorways. With many computers each in many automobiles speeding could be easily eliminated by program changes as could fast accelerations. Safety regulations such as those that require large car seats for children have forced the use of larger heavier vehicles. Why are there few if any vehicles which accommodate three persons in the front seat instead of massive electronics.

Electric automobiles and electric hybrids with large batteries are themselves now obsolete when it comes to fuel savings because it has been demonstrated that hydraulic hybrids with digital hydraulic motor and pump valve control can do far better braking energy recovery and far better engine efficiency control.

The INNAS NOAX crankshaft-free hydraulic pump with higher efficiency and more reliability due to fewer parts can further reduce the fuel consumption because it operates on a stroke by stroke basis only as needed. It is one of the few engines that can be modified to use compression ignition on high octane low cetane fuels such as methane. It can obviously be modified to use Homogenious Charge Compression Ignition Cycles without damage to reduce particulates and nitrogen oxides and increase efficiency.

Two such pistons might be desired for vibration reduction, but only one is needed to operate a vehicle if one fails for super reliability combined with two or more wheel motors which each can be designed to operate at lower power with one or more failures of its multiple pistons. There are no issues of clutch or gear failures and standard brakes can last for a long time as most braking, even to a complete stop can be done with the hydraulic motors which can also hold the vehicle at a certain stopped position. No expensive high power motor drive electronics are needed or used.

When Bosch held the use rights on one similar system invented and prototyped and proved by Artemis Intelligent power, it seems, not one company was induced to use it even in a test automobile even when it doubled the fuel efficiency for most driving.

After governments failed to require the high efficiency Artemis type automotive improvements, Artemis was paid by a government agency to develop a wind turbine low failure rate high performance efficient transmission. Artemis demonstrated the system and MHI bought the whole company and has now built one small and two super large prototype wind turbines. Such machines need no high-power generator electronics because the hydraulics allows one or more standard generators to operate at mains frequency. Even very inexpensive simple induction motors can be used as generators if driven at slightly higher than mains frequency as they are in small hydroelectric systems. Such a system can produce far more power than rated for a few seconds without damage if required to stabilize the mains. ABB can build their cable wound motors to any medium voltage less than about 30 KV so that even transformers are not required to connect to such mains.

Digital displacement hydraulic technology or at least the mechanical efficient hydraulic from INNAS should be required to be built into every Lorry(truck)when the new or replacement engine is installed and this will save far more energy at lower costs than all the wind-turbines can generate and do it more reliably. Freight vehicles use far more fuel and will save far more by conversion as demonstrated by Ian Wright of WrightSpeed.

Every automobile producing company should be required to introduce this technology into at least one vehicle that they sell by every nation where they sell vehicles. Even at the far lower costs of hydraulics relative to electrics, converting most existing automobiles will not be economic because of the low yearly fuel consumption of most vehicles and their short life. A major repair of the transmission might be an incentive to convert.. ..HG..

One of the irritating features of my Fusion Energi's information systems is that its "battery gauge" reads, not in kWh, but in "miles".  It appears to re-estimate energy consumption per mile after every leg and re-calculate remaining range based on that.

All this tells you is how far you might go if you drive the exact same speed and conditions as the last leg.  It does not give you any tools to estimate how far you'll go if you drive differently, or how differently you'll have to drive to make your next stop on the remaining battery power.  THAT is something you can only guesstimate from experience.

What the car really needs is a kWh meter and a set of remaining ranges based on speed/energy consumption rate.  It also needs a history function to go back several legs and show consumption and efficiency; right now, that information is erased after each new start.

When Toyota provided its Prius owners with an instant MPG gauge it created an ongoing competition among some of those drivers called "hypermiling."

Some of these “hypermilers” consistently break 70 mpg - in a car the EPA says should only get 50. And we know how overly optimistic the EPA ratings are, don't we?

Seeing what every little adjustment to your driving style actually does to your MPGs makes all the difference.

This sounds like if the car does not get the mileage we say, it is your fault.

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