Navigant Research Blog

Improving the Performance of Hybrids

— April 23, 2014

The fundamental goal of a hybrid powertrain is to improve fuel efficiency by recovering kinetic energy from the vehicle as it slows down and storing it to reuse later.  Traditional vehicles convert that energy to heat in the brakes and then let it disperse into the atmosphere.  Hybrid electric vehicles (HEVs) generate electricity via an electric motor and store it in batteries or ultracapacitors.  The resistance of the motor slows the vehicle.

An understanding of how the hybrid powertrain works is helpful for drivers who wish to maximize their efficiency on the road.  Being careful not to accelerate too hard and slowing down steadily without using the foundation brakes are techniques that have been used since HEVs first went into production in the late 1990s.  As they became more popular, some original equipment manufacturers had to deal with complaints from drivers who didn’t achieve the promised fuel economy.  Some of the deficit was due to driving technique – if you hit the brakes hard when driving, then the regeneration cannot take place, and energy will not be saved for reuse.

Hills Ahead

The basic hybrid system will deliver more fuel economy benefits to drivers who understand how to get the most out of it.  But there are limits.  Once the battery is fully charged, no more energy can be stored, and the vehicle is then no more efficient than its conventional counterpart.  It’s very difficult for a driver to work out how to get around this limitation.

However, Mercedes-Benz has done just that with its latest Intelligent HYBRID operating system, which was introduced in the S-Class in summer 2013, and is now available in the new 2014 C-Class.  These cars use data from their navigation systems to look ahead for hills.  When the vehicle detects a downhill stretch coming up, it knows that the hill presents a good opportunity to capture energy, so it activates the electric motor to start draining the traction battery.  Taking more of the power from the electric drive means that the engine uses less liquid fuel, improving fuel economy.

This advanced technology is a first for the consumer market.  Another application that uses the latest digital map data is Audi’s adaptive headlight system, which can anticipate upcoming curves to better illuminate the road ahead without dazzling oncoming vehicles.  Continental’s eHorizon system optimizes gear shifting to best handle the upcoming terrain.  Mercedes is the first to offer map-based efficiency technology in consumer vehicles.

These innovations will undoubtedly benefit vehicle owners by delivering improved fuel economy in real-world usage.  However, the standardized tests used by government agencies to help consumers compare vehicles are unlikely to register an improvement because they do not include going up and down hills, and are typically conducted on a chassis dynamometer, or “rolling road.”  Another reason to reevaluate how comparison testing is done.

 

Flywheels Offer Hybrids a Mechanical Advantage

— April 4, 2014

It is often assumed that all hybrid vehicles must use a battery for energy storage.  But the essence of a hybrid powertrain is not necessarily engine-off operation, but to provide more efficient transportation over a stop/start journey drive cycle.  The key factor in this mode is to be able to recapture large amounts of energy very quickly and then reuse it, which requires high power density.  While batteries typically have a high energy density, they often do not respond well to high charge rates and may not be able to capture all the available energy from regenerative braking.  Larger vehicles, in particular, have a lot of kinetic energy to store when slowing down.

So the focus for hybrid vehicles is often high power density rather than high energy density.  It is this factor (as well as the lower cost) that has led some manufacturers, particularly Toyota, to continue installing nickel-metal hydride batteries when the rest of the industry has shifted to the higher energy density of the lithium ion battery.  But there are other options for higher power density, if total energy capacity is not an issue.  Ultracapacitors are one alternative and Navigant Research has produced a report on another option: Hydraulic Hybrid Vehicles.  However, a new alternative technology based on the flywheel is now in testing.

Powerful and Economical

Volvo Car Group has recently been conducting testing in the United Kingdom of a flywheel developed by Flybrid Automotive (now part of Torotrak) to determine the potential for fuel savings.  Initial results show a performance boost of 80 hp while improving fuel economy by up to 25%.  The testing uses real-world driving data from public roads and test tracks in both Sweden and the United Kingdom.  Volvo has installed the flywheel system on the rear axle of a front-wheel drive passenger car.  Under braking, the vehicle kinetic energy is used to spin a 6 kg carbon fiber flywheel at up to 60,000 rpm.  When the driver wants to accelerate again, the energy from the spinning flywheel drives the rear wheels directly via a specially designed transmission.

The benefits for the driver are that the engine can be switched off during some braking and accelerating maneuvers, plus there is extra power available when needed to supplement the internal combustion engine.  The Volvo test vehicle is about 1.5 seconds quicker than the standard vehicle going from 0 to 60 mph.

Mechanics of Storage

The Flybrid system uses the mechanical motion directly to power the transmission, so there are no energy losses transferring from one format to another.  Another type of flywheel system, developed for motor racing by Williams Hybrid Power (and since April 1, part of GKN), uses a flywheel driven by an electric motor.  Instead of storing energy chemically as in a battery, the energy is stored mechanically in the spinning flywheel and then converted back to electricity to be used by the electric drive motor.

Both systems use the same mechanical energy storage format and have to address the same issues.  Safety and reliability are important, as is longevity.  Cost is also important, and at present, the flywheel is a lot cheaper than a battery.  It’s good to see some alternative solutions being adopted by larger companies, and this topic will be covered in much more detail in our upcoming report on vehicle efficiency.

 

Autonomous Vehicles Drive Themselves toward Reality

— March 19, 2014

Australian startup Zoox made a splash at the LA Auto Show in December by hosting a stand at the Connected Car Expo to promote its ideas about autonomous vehicles.  Zoox’s view is that the best way to introduce fully autonomous driving is to start with a clean sheet of paper and develop a new type of transport from scratch, rather than incrementally changing existing vehicles.  The initial concept currently under development is a taxicab that uses a chassis made of four identical quadrants.  Each quadrant will have a wheel with its own electric motor, and all four wheels can steer.

The passenger compartment will have no steering wheel or pedal controls and will utilize a carriage layout, with passengers facing each other.  The design is being optimized for rapid prototype manufacturing techniques rather than mass production.  Zoox is targeting taxi fleets as its first customers, because the business model shows that the biggest savings come from eliminating the drivers’ wages.  The vehicles will be designed for low-speed travel on city streets.

Experience Not Required

At the Autonomous Driving conference in Berlin hosted by we.CONECT, the Zoox team actively sought feedback from the other participants.  They are in the first year of a 7-year product development plan, so there is no vehicle to sit in at present, but the overall concept is well thought out and some detail work has begun.  I am sure that the Zoox developers will be tracking progress of the Navia, a robotic driverless shuttle, and Tesla has shown what can be accomplished in the automotive industry without decades of experience.

One recurring theme in Berlin was how to develop an automated driving system that can return control to the driver safely when necessary, particularly when road conditions change beyond what the developers anticipated.  While driver assistance functions are steadily getting more sophisticated, there are huge advances to be made before people can safely be removed completely from the driving process.  Today’s incremental improvement process involves automating the control systems that have been developed over the last century for humans to use.  This seems to be the fundamental challenge that Zoox has identified, and it wants to approach the solution from the other direction.

Maps from the Cloud

In addition to the intriguing Zoox concept, the presentations at the Berlin conference were of high quality and networking opportunities were abundant.  Here are some of the highlights that I noted that gave me some fresh perspectives on the current state of autonomous driving technology:

  • Professor Emilio Frazzoli of the Massachusetts Institute of Technology pointed out that the biggest potential benefit from autonomous driving will be carsharing, far exceeding improved road safety.  His detailed analysis of traffic in Singapore indicated that 800,000 personal cars could be replaced by only 300,000 shared autonomous vehicles.
  • Dietmar Rabel, from digital map company HERE (formerly known as NAVTEQ and Nokia Location & Commerce), promoted the Internet cloud for continuous map updates and introduced the concept of crowdsourcing for accurate map data.  Rather than relying on map suppliers to continuously update the information, sensor data from connected vehicles could be shared through the cloud, thus providing near real-time updated map and road condition information locally.
  • Geoff Ballew of NVIDIA explained how his company has grown from a supplier of graphics boards for PCs into a high-performance computing specialist.  Rapid data processing will be a key requirement for self-driving vehicles to become a reality.

While the automotive industry makes slow but steady progress toward the goal of a self-driving vehicle, it’s also good to hear about new companies approaching the topic from a different perspective.  I shall continue to watch with interest as I work on an update to Navigant Research’s 2013  Autonomous Vehicles report.

 

Self-Driving Cars and Real-World Roadways

— February 16, 2014

On a recent weekend road trip, I took the opportunity to consider the practicality of an autonomous vehicle doing the driving. The 300-mile journey involved single-lane twisty country roads, dual carriageways (in U.S. terms, a four-lane divided highway), and motorways (freeways). The first part of my journey took place on a narrow country road with speed limits that ranged from 30 mph through small villages to 60 mph on the open stretches. On this route, there were very few opportunities for passing, so the driving process was relatively straightforward. A combination of the latest advanced driver assistance systems (ADAS) should be able to cope with such a drive with minimal driver input.

The next part of the journey took place on a dual carriageway, and again the driving process was quite simple, requiring that my vehicle stayed within well-marked lanes, kept to the speed limits, and avoided running into the back of slower vehicles.  All these functions could be handled by adaptive cruise control, lane keeping, and traffic sign recognition.  The one activity that would need a new system is lane changing to move to the inside lane when not overtaking. Blind spot detection would be a partial solution to this, but it would also need some highly sophisticated decision-making software.

Smoothing the Flow

The bulk of the driving took place on the U.K. motorway system, and the satnav in my car proved that it could handle giving directions to navigate the quickest route. Driving on motorways is where the benefits of autonomous vehicles would be more widespread. For some of the journey, traffic moved along briskly at the speed limit, but as vehicle volumes increased, there were periods where all lanes of traffic slowed down. If all the vehicles in the outside lane used adaptive cruise control, the traffic flow would be much smoother, and some traffic jams would be eliminated.

So the three main parts of my journey could have been handled effectively by technology that is available today. Intersections, however, represent more of a challenge. Simple traffic lights at a crossroads are not too difficult, but some roundabouts are a different matter, and will require considerable development of decision-making software. While the mechanics of driving can be replicated today, the role of the driver cannot. There are many considerations involved in driving, such as estimating closing speeds of vehicles in front and behind to decide whether it is appropriate and safe to change lanes. Anticipating what other drivers will do is another useful driving skill. It may be that an artificial intelligence system that can learn from experience will be a key component of the self-driving vehicle of the future.

10 Years Out

Some of the more advanced autonomous driving features that I outlined above will be coming to market in the next few years. As long as they are treated as driver assistance features, I believe they will be very attractive to customers and will contribute to safer and more efficient road travel. Full details about all the systems are described in Navigant Research’s recent report, Autonomous Vehicles. However, the jump to fully autonomous driving that can handle any situation remains at least a decade away. We can forget about catching up with emails or sleep while the car does the driving for many years, but the number of crashes due to driver error will surely be reduced, and soon.

One consideration for governments at present is how to encourage the development and implementation of this advanced driving technology. On one section of the trip, there was an alternative toll road to the standard highway. It appears that the majority of drivers prefer to travel on the free roads even when road work causes lane narrowing and speed limit reductions. It would improve revenue if more people used the toll road, so perhaps an incentive for drivers who use ADAS would make sense. A toll road that offered higher speed limits for vehicles with self-driving capability would both generate demand for the technology and increase road revenue.

I am looking forward to discussing these and other autonomous vehicle issues with industry colleagues at the upcoming Autonomous Driving 2014 conference in Berlin, Germany, February 27-28, 2014. I hope to share Navigant Research’s perspectives on the topic and learn more about other aspects of this rapidly evolving technology. Let me know if you will be there.

 

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