Navigant Research Blog

Quest for Aerodynamic Vehicles Faces Headwinds

— January 8, 2015

Although recent reductions in oil prices have slightly eased demand for more efficient vehicles, national governments are still pushing the rollout of more stringent emissions standards.  Because electric vehicles remain saddled with heavy, bulky, costly batteries,  the automotive industry is now investing in other technologies that improve the fuel economy of vehicles powered by conventional internal combustion engines that run on gasoline or diesel fuel.  Navigant Research has recently released a detailed report on this topic: Automotive Fuel Efficiency Technologies.

The report concludes that there is no single solution, and future improvements will be accomplished via many small changes that will combine to deliver measurable results.  Downsizing engines, adding turbocharging, reducing losses in transmissions, lowering mass, and improving aerodynamics will all make contributions.  The features that offer the largest benefit for the lowest cost will be implemented first.  What makes sense for a luxury vehicle may not be right for an entry-level car.  One of the primary avenues for fuel economy improvements is likely to be making cars more aerodynamically efficient.

Drag Reduction

Manufacturers must balance many factors, such as the customers who want better fuel economy but will not necessarily be willing to sacrifice performance to get it.  Less dense materials are more expensive than steel, and lighter vehicles must still meet all the relevant structural standards.  Ideal shapes for the best aerodynamic performance may be impractical to manufacture and difficult for people to get in and out of.

At an investor day hosted by Fiat Chrysler Automobiles in May 2014, the company outlined its new approach to global vehicle architectures.  In the presentation, engineers outlined their analysis of the relative importance of different factors affecting the amount of energy required to propel the vehicle.  The biggest factor in city driving was the vehicle weight, followed closely by tire drag and then aerodynamic drag.  On the highway, aerodynamics was the biggest factor, followed again by tire drag.

Lose the Mirrors

So it’s likely that aerodynamic performance will be getting plenty of attention for vehicles coming to market in the coming years.  Some features being looked at include active components, such as grill shutters that only open when cooling is needed, a feature that is already available on certain Ford Focus models in Europe.  Smoother airflow over and under the body and reducing the drag coefficient of the vehicle are options under development in both computer-aided analysis software and wind tunnels.

One of the easiest ways to reduce aerodynamic drag by 3% to 6% would be to eliminate external mirrors.  Tesla has been campaigning with the National Highway Traffic Safety Administration (NHTSA) to try to get the U.S. law changed to allow an external camera with an internal video screen as an alternative to an external mirror (as featured on its Model X design) and probably has support from many other original equipment manufacturers (OEMs).  Volkswagen is also pushing for change in Europe to expand the market for its ultra efficient XL1 vehicle that also has this feature.  If governments are serious about fuel efficiency, this would be an easy change to make by modifying the wording to require a rear view rather than specifying a mirror.

 

Wrightspeed Targets E-Truck Market

— December 30, 2014

The medium and heavy duty truck industry has tried for years to join the rush to powertrain hybridization and electrification with very little success.  The incremental cost has been difficult to justify for all but specific niche uses.  New market entrant Wrightspeed recognizes this situation, and it is targeting its new integrated powertrain at a specific type of fleet that uses medium duty trucks with high annual mileage (30,000-plus miles) and a drive cycle that includes a lot of stopping and starting.  The system is also suitable for heavy duty refuse trucks.  The design is essentially a plug-in all-electric drive with a range-extending engine to recharge the battery pack.

Founder Ian Wright, a member of Elon Musk’s original team that established Tesla Motors, has focused on developing a system that addresses a well-defined niche in the truck market.  Wrightspeed uses lithium ion (Li-ion) battery cells from A123 Systems to build a battery pack and installs its own thermal management system and charge management software.  Electric motors are built by a supplier to proprietary design specifications, and the control software is also developed in-house.  The system uses onboard individual wheel motors, and the software to control them is written by the company’s engineers.  Wright believes that it is important for a powertrain supplier to develop the complete system, not just improve individual components.

Weight Loss

The most dramatically different component is the choice of engine to provide charge to the battery pack.  Wrightspeed has gone with a microturbine from Capstone Turbine Corp.  This engine weighs approximately 220 lbs, about one-tenth of the mass of a typical diesel engine that can deliver similar power.  And because it runs at very high speed, the generator attached is only about the size of a 1-liter bottle.  The turbine can run on almost any liquid or gaseous fuel, and because of its burn efficiency, it does not need any exhaust after-treatment to remove toxic waste products.

Wrightspeed’s plan is to first address the replacement powertrain market for high-mileage medium duty trucks in large fleets, rather than aim at Tier One status with truck manufacturers.  Wright believes that, once fleet managers have had experience with the unique features of his system, his company will be able to move up.  Although it’s more expensive than a conventional diesel engine and transmission, the complete Wrightspeed solution of battery pack, electric motors, power electronics, and range-extending engine weighs about the same. The company reports substantial fuel savings from a combination of high-power regenerative braking and only running the engine in its most efficient mode.  Average fuel economy figures are estimated by Wrightspeed to go from 8 mpg to 10 mpg with a conventional powertrain, to 25 mpg to 30 mpg with its replacement system.  The powerful regenerative brakes also save significant maintenance costs for fleets, a major factor in the refuse truck market.

To date, Wrightspeed has reported orders for some test systems to be installed in garbage trucks, and FedEx ordered four units in February 2014, followed by an additional order for 25 more in July.  Deliveries are scheduled for the first quarter of 2015, and this new approach to hybrid trucks will be interesting to watch.

 

Electric Turbochargers: The Next Big Thing in Fuel Efficiency

— October 23, 2014

The key to the next major advance in internal combustion engine fuel efficiency could well be the electric turbocharger.  At a recent fuel economy technology showcase at the U.S. Environmental Protection Agency (EPA) National Vehicle Emissions and Fuel Lab in Ann Arbor, Michigan, Valeo showed off the motor-driven turbo it will supply to an unannounced automaker.  The first production applications are scheduled to begin arriving in 2016, according to the company.

The aggressive expansion of fuel efficient technologies, such as electrification, multi-speed automatic transmissions, and engine downsizing, has played a major part in increasing miles per gallon.  The average fuel economy of the American new light duty vehicle fleet has improved by almost 25% over the past decade.  Meanwhile, gasoline direct injection and turbocharging have enabled engineers to cut engine displacement by 30% or more without sacrificing the performance that drivers have come to expect.  As of the 2014 model year, approximately 75% of Ford gasoline and diesel engines globally are turbocharged while 85% of Volkswagen engines are boosted.

Response Time

Part of the concept behind boosted engines is to use smaller engines with turbochargers that provide performance on-demand.  There has always been an inherent time lag, however, between the time the driver presses the accelerator and the generation of enough extra exhaust gas to spin up the turbo and provide boost.  Mechanically-driven superchargers eliminate much of the lag at the cost of substantial friction at higher speeds.

Replacing the exhaust-driven turbine side of the turbocharger with an electric motor provides a number of advantages, most notably in packaging, responsiveness, and operational flexibility.  One of the fuel economy benefits Valeo highlights is the combination of an electric turbo with the cylinder deactivation – i.e., the ability to shut off multiple cylinders under light loads in order to improve fuel efficiency.

The fuel savings achieved by shutting off unneeded cylinders can be quickly lost when driving on roads that aren’t completely flat.  Even a mild grade can cause an engine to switch back to running on all cylinders in order to produce enough torque to maintain speed.  “With an electric turbo, the engine management system can request small amounts of boost on-demand to increase torque while climbing a grade while keeping as many as half of the cylinders inactive,” Ronald Wegener, application engineering manager with Valeo, told me.  “This can yield up to a 10% improvement in efficiency.”

Valeo has developed versions of the device for both 12V and 48V electrical systems so that the turbo can also be used as part of a mild hybrid system during off-throttle conditions.  Intake air flowing through the compressor drives the motor to generate electricity, charging the battery.  Audi is using this as one of the two forms of energy recovery on its Le Mans-winning R18 e-tron race car.  Many of the current crop of Formula One cars have also adopted this approach.  Earlier this year, Audi announced that the next-generation Q7 TDI, scheduled for model year 2016, would be its first production application of the technology.

Shrinking Engines

Electric turbochargers also provide packaging benefits to engine designers.  Traditional turbos require complex plumbing to route exhaust gases to the turbine side of the turbo and feed the boosted intake charge to the other side of the engine.  Disconnecting the turbo from the exhaust allows designers to place the turbo wherever it fits best for packaging and performance.

Executives and engineers agree that while electric vehicles will gain market share in the coming years, internal combustion engines will likely remain the dominant powertrain choice in the transportation space at least through the 2020s.  With engines continuing to shrink, it seems likely that electric turbochargers will account for a growing share of the boosted engine market in the next decade.

 

DeltaWing Offers a Radical Alternative to Vehicle Architecture

— October 6, 2014

Automotive manufacturers are working hard to improve the fuel efficiency of their vehicles without sacrificing internal space, comfort, or performance.  Having concluded that the energy density of battery technology is unlikely to increase enough and prices are unlikely to fall far enough in time to enable them to meet upcoming emissions (CO2) legislation, automakers are investing heavily in technology that delivers greater fuel efficiency in conventional vehicles rather than switching the majority of their fleets to electric or hybrid drive.  Battery electric and hybrid vehicles will continue to be developed and offered, but the gasoline and diesel internal combustion engine (ICE) will remain the primary source of motive power for the foreseeable future, as described in more detail in Navigant Research’s report, Transportation Forecast: Light Duty Vehicles.

Slimmer & Sleeker

In a recent Investor Day presentation by Fiat Chrysler Automobiles (FCA), the company pointed out that CO2 emissions are highly influenced by weight in the EPA’s city drive cycle.  The biggest factor in the highway test cycle is aerodynamic resistance.  Tire drag is the other major factor in both cycles, but it’s much harder to reduce while retaining acceptable ride and handling properties.  So the manufacturers are focusing most of their efforts into weight reduction and aerodynamic improvements.  Most of the changes are incremental, in the hope that many small benefits will combine to make a significant overall improvement.

BMW concluded in the early stages of the development of its electric i3 and i8 vehicles that incremental changes would not give them enough improvement.  Rather than simply exchange the conventional powertrain for a battery and electric motor in an existing model, engineers developed an entirely new architecture for the new range of vehicles, which included new materials, such as carbon fiber, and new manufacturing processes.  Other volume manufacturers have, so far, taken a more cautious route and focused on smaller improvements to components while maintaining current vehicle architecture.

New Look

DeltaWing Technologies is a company best known for developing a radically different racing car that is currently competing in IMSA sports car road races.  It is now looking to partner with major automakers to develop vehicles that will meet and exceed the fuel efficiency targets of the future.  The DeltaWing concept is a radical change from most current road vehicles.  The engine is located at the rear, and the front wheelbase is narrow with thinner tires that reduce rolling resistance without sacrificing road holding.  The distinctive shape has improved aerodynamic properties over conventional vehicle shapes, and the overall design uses lightweight materials extensively.

According to the company, its concept vehicle offers a 35% reduction in overall mass and consumes 35% less fuel for equivalent performance in a four-passenger sedan.  The current performance targets are 0 to 60 mph in about 6 seconds, 130 mph top speed, and up to 70 mpg when using a small displacement, four-cylinder engine producing between 85 and 110 horsepower.  These specifications are clearly attractive to OEMs.  It will be interesting to see if any are prepared to commit to such a radical change.  A more detailed analysis of the options under consideration is included in our upcoming report, Automotive Fuel Efficiency.

 

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