Pictures of the Future    Spring 2006

Fine Tuning the Hybrid

Inspired by Toyota’s success, automakers around the world are working on hybrid vehicles that offer high potential fuel savings—and a green image. Siemens is developing solutions that will help automobile manufacturers fine tune this complex technology.

Over the past few years, hardly any technology has been as underestimated as the hybrid drive, which consists of an internal combustion engine complemented by an electric drive. Back in the mid-1990s, the Volkswagen Group found it almost impossible to sell its hybrid Audi 80 Duo because of its high price. After that setback, it wasn’t entirely surprising that no automaker reacted in earnest when Toyota introduced the Prius in 1997, its first mass-produced hybrid. The ascent of the hybrid finally began with the introduction of the second Prius generation in 2003. Today, the word "hybrid" is on everybody’s lips—although unit sales remain very modest.

The hybrid boasts several advantages. Fuel consumption is significantly lower than that of a vehicle powered exclusively by an internal combustion engine, especially in city traffic. Carbon dioxide emissions are also much lower. When braking, the electric machine functions as a generator and recovers energy, which is stored. The electric motor can also deliver additional torque during acceleration.

All major auto manufacturers are currently focusing on this topic and showing their cars at international exhibitions in versions ranging from micro to full hybrid (see box). Suppliers are also being challenged. "Without a doubt, this is a very interesting market," says Norbert Bieler of Business Development for Hybrid Vehicles at Siemens VDO (SV).

Experts predict that 1.5 million hybrid vehicles will be sold worldwide in 2012. Compared to other vehicles, that’s not much. In 2005, for instance, DaimlerChrysler alone sold more than four million automobiles, an increase of nearly 4 %. But hybrid sales are growing much faster. Toyota sold 230,000 hybrid vehicles in 2005, around two-thirds more than in 2004. Consultants at PricewaterhouseCoopers anticipate a tripling of the model types to 74 by 2010. Nine of every ten hybrid cars are currently sold in the U.S., where a tax break of up to $3,000 is on offer until the end of 2006. Ten models, ranging from small cars to pickup trucks, are now available in the U.S.

Compared to economy cars with internal combustion engines, the hybrids score with their green image. In slow traffic, they can switch to 100 % electric power, and thus emit less exhaust and make less noise. In Europe, however, manufacturers’ enthusiasm for hybrids is limited. The reason is simple: In terms of fuel economy values, diesels are roughly comparable to hybrids. An electric motor makes the car heavier and requires a high-performance, long life battery. As a result, European automakers prefer to view hybrids as a supplement and are focusing on existing technology. "Internal combustion engines have a lot of development potential, even with gasoline, " says Bieler. Direct gasoline injection with piezo technology cuts fuel consumption by up to 20 % compared to the common intake injection method. In 2005, Siemens and Bosch won the German Future Prize for the further development of piezo injection technology.

In Europe, the market share of diesel vehicles is 50 %; in France, it is 70 %. So it’s no wonder that the second-largest European automobile manufacturer has taken a different path. "We’re focusing on diesel hybrids," says Robert Peugeot, board member responsible for innovation and quality at PSA Peugeot Citroën in Paris (see interview). "We don’t see any market for gasoline hybrids in Europe." The company therefore combines a diesel engine with an electric drive, thus drastically reducing carbon dioxide emissions. A prototype consumes 3.4 l per 100 km. PSA’s goal is to reduce costs to such an extent that by 2010 a mass-produced diesel hybrid vehicle will cost no more than a comparable diesel, or about 2,000 € more than its gasoline equivalent today. "A great deal of research will be required to achieve that goal," says Peugeot.

"The deeper we delve into this topic, the more we discover that hybridization goes far beyond the electric drive system," says Bieler. According to Bieler, it is obviously important to ensure perfect interplay between a hybrid’s internal combustion engine and its electric drive. However, just as important is the interplay with the transmission, the valve timing, the auxiliary units and the battery, as well as a host of electrical devices. For a hybrid vehicle to function optimally, important decisions must be made in milliseconds. For example, should the electric motor be switched on and, if so, for how long? Or: Can the electric motor handle braking on its own or should the disc brakes be engaged?

One challenge associated with hybrid systems is how to deal with voltages and currents, which are higher than those found in today’s electric components. "Electric motors and power semiconductors have been optimized for a wide range of applications, but not for automotive ones," says Prof. Eckhard Wolfgang, Director of the Center for Power Electronics at Siemens Corporate Technology (CT) in Erlangen, Germany.

The Toyota Prius, for example, works in the power train with voltages up to 500 V, says Dr. Martin März, head of the Power Electronics Department at the Fraunhofer Institute for Integrated Systems and Component Technology in Nuremberg. The currents reach peak values of several hundred amperes. "To ensure system reliability, the Prius has its own cooling water circuit for the electronics," says März. Then too, the environment in an automobile is anything but electronics-friendly. Sensitive components must endure icy cold and intense heat as well as powerful vibrations. And in the future, many components will have to get a lot smaller. "Today, a 100-kW industrial frequency converter sits in a large switchgear cabinet," says März. "In an automobile, it has to fit into a shoebox." Toyota solved the space problem with a new vehicle design, which is oriented toward the hybrid. For the future, März is working on converters that can be installed directly in the electric motor (see box in the Trends article). "We want to make the technology ripe for implementation within two generations of hybrid vehicles—in other words, by 2012 to 2015."

For several years, Wolfgang and his team have been striving to make electronic components tough enough to withstand higher temperatures. In the EU’s HIMRATE and HOTCAR projects, which have now been completed, researchers modified silicon power semiconductor modules and parts of the control electronics so that they could withstand up to 150 °C—some 25 degrees more than was previously possible. Siemens is playing the leading role in the EU’s HOPE project, which started this year. Here, 13 partners from industry and research are investigating the possibility of using silicon carbide (SiC) in fuel cells and hybrid drives. SiC components can withstand much higher temperatures and have lower losses than silicon components. "The advantage would be a more compact, simpler and lighter construction," says Wolfgang.

Another important building block for a future hybrid vehicle would be an innovative, fully electric transmission that could replace the mechanical transmission. "We are currently investigating the feasibility of such a power train," says Markus Wilke of Corporate Technology in Erlangen. It would have to be better than the automatic transmissions and drive systems used in full hybrids—both of which are very complex. In the Toyota Prius, for example, two electric devices are linked to the internal combustion engine via a planetary gear. This configuration, however, reduces efficiency because the gasoline engine’s torque has to be converted several times before it reaches the gearbox.

Much earlier, perhaps even by the end of 2006, SV plans to have a full hybrid demo car available for customers. "We are building a sports coupe with a 2.3-l supercharged engine. This will be augmented by a 75-kW electric motor, an automatic transmission and a high-performance battery, which will enable electric driving," says Bieler, who believes that hybrid technology can enrich the vehicle spectrum. For small cars, the main attraction will be economy; for larger and heavier vehicles, it will be the additional torque and functions such as electric all-wheel drive. "We want to demonstrate that in addition to reducing fuel consumption, hybrids are also a lot of fun to drive," says Bieler.
                                                                                                Norbert Aschenbrenner