Hybrid Automobiles

In technology, as in biology, a hybrid is the result of ‘‘cross-fertilization,’’ in this case referring to the application of technologies to produce a similar yet slightly different entity. Recent research in the history of automotive technology shows that hybridization has been much more common than previously thought. Thus, the automobile itself can be viewed as a hybrid with a century-long history of crossover phenomena from electrical engineering to mechanical engineering that resulted in an ‘‘electrified gasoline car.’’

The term hybrid, however, is generally reserved for combinations of propulsion systems in automobiles. Most common in the history of the automobile is the thermoelectric hybrid, mainly a combination of the internal combustion engine (gasoline or diesel) and an electric propulsion system (electric motor, battery set). Thermomechanical hybrids are possible when a combustion engine is combined with a flywheel system in which part of the kinetic energy during braking can be stored and released the moment this energy is needed, for instance for acceleration from standstill. Similarly, thermohydraulic hybrids combine combustion engines with a hydraulic energy storage system (a pump and a hydraulic accumulator).

Electroelectric hybrids are also known; in these cases the actual propulsion is done by one electric motor, but the energy supply is a combination of battery storage and a supply from overhead trolley wires. Combinations of trolley systems and mechanical flywheel storage systems have also been built. Viewed from this perspective, the automobile as we know it at the end of the twentieth century is but one case among many possibilities. Thermoelectric hybrids are nearly as old as automotive technology. Before 1900, the Belgian automobile producer Henri Pieper developed a car that was equipped with an electromagetically controlled carburetor. His patents were later bought by car manufacturers like Siemens– Schuckert (Germany), Daimler (Coventry, U.K.) and the French Socie´te´ Ge´ne´ rale d’Automobiles e´lectro-Me´caniques (GEM). In 1908 the latter company proposed a Pieper-like hybrid called ‘‘Automobile Synthesis.’’ At about the same time, German battery producer AFA (now Varta AG) bought a Pieper to develop a special battery for hybrid car applications. Another famous hybrid vehicle builder was the French electrical engineer Louis Krie´ ger. He started hybrid development in 1902 and produced a car he drove during the rallye from Paris to Florence a year later. In 1904 his hybrid was the sensation of the Paris automobile show. In 1906 he conceived a drive train based on an electric propulsion system and a gas turbine, and in the same year he developed a hybrid taxicab, 100 of which were intended to be built.

In Austria, Lohner built 52 hybrids between 1898 and 1910, designed by electrical engineer Ferdinand Porsche. These cars were later sold by Daimler, Germany, which founded a separate company for this purpose, Socie´te´ Mercedes Mixte. In Germany several local fire companies built thermoelectric fire engines, some of these a combination of an electric motor with batteries and a steam engine. In this configuration, the electric drive system was meant for quick starting and for use during the first few kilometers of the trip. After ten minutes, when kettle pressure had built up, the steam engine took over to propel the truck to the fire location. All in all however, no more than a hundred or so hybrids were sold in Europe before World War I. In the U.S., there was even less hybrid construction activity during this period, the most famous being the Woods Dual Power, which was produced during the war. Hybrids were supposed to combine the advantages of two systems while avoiding their disadvantages. For instance, because the thermal element in the hybrid system was often used (in combination with the electric motor, which for this purpose had to be repolarized to become an electricity generator) to supply a part of the stored electricity, the battery set in a hybrid tended to be smaller. It was lighter than that in a full-blown electric motor where all the energy for a trip had to be stored in the batteries before the start of the trip. In most cases the combination of systems led to a more complex and expensive construction, jeopardizing state-of-the-art reliability standards, and complicated control problems, which would only be overcome with the emergence of postwar automotive electronics. Also, despite the lighter battery, the total drive train became heavier. For this reason hybrid alternatives were especially popular among producers of heavy vehicles such as buses and trucks in which the relative importance of the drive train weight is less. Well-known examples in this respect are the brands Fisher (U.S.), Thornicroft (U.K.) and Faun (Germany). The popularity of hybrid propulsion systems among engineers was not only, and according to some analysts not primarily, the result of technical considerations. During the first quarter century of automotive history, when the struggle between proponents of steam, electric, and gasoline engine propulsion was not yet over, hybridization often functioned as a strategic and social compromise as well. This was very clear in the case of the German fire engine community before World War I. A fierce controversy raged over the apparent unreliability of the gas combustion engine, but the proponents of electric drive trains, who boasted that electric drive trains guaranteed quick starting, high acceleration, high reliability, and no danger of fuel explosions in the neighborhood of fires, were not strong enough to monopolize the field. Several fire officials then opted for a hybrid drive, combining the advantages of electric with the advantages of the combustion engine (primarily a greater driving range), but they encountered heavy resistance from a combination of both other fire officials and the established automobile industry. Nevertheless, in 1910 the German fire engine fleet included about 15 heavy hybrids.

As with the electric alternative, hybrid automobiles experienced a revival during the last quarter of the twentieth century. This resulted in at least one commercially available hybrid automobile, the Toyota Prius. During this period, the issue of energy consumption played a role as well. Heavily subsidized by local, regional, and federal governments in Europe, Japan, and the U.S., hybrid projects used new light materials such as magnesium, plastics, and carbon fibers; and sophisticated electronic control systems (borrowed from related industries such as aerospace and information and communication technology) to enable very energy efficient solutions, initially to the surprise of many engineers. For example, a Dutch–Italian hybrid bus project resulted in exhaust emissions that were barely measurable and demonstrated very low energy consumption rates. Similar results in other experimental areas have been possible because of sophisticated combinations of small engines, flywheel systems with continuously variable transmissions, and even engine concepts that were considered obsolete, such as Sterling engines, micro gas turbines, and two-stroke engines. By now, the field of possible alternatives is so vast that several classification schemes have been proposed. The most common classification is that which distinguishes between ‘‘series hybrids,’’ where the electric element is positioned between the thermal element and the drive wheels, and ‘‘parallel hybrids,’’ where both the thermal and the electric element can be used separately to propel the vehicle. At the beginning of the twenty-first century, the ‘‘mild hybrid’’ was the latest development, in which the electric system is so small that it resembles the electric starter motor. If this development materializes, automotive history will have come full circle, producing a true compromise of an electrified gasoline car.