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The future of hybrid vehicles

Tuesday, January 1, 2019 - 08:00
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At the turn of the 20th century the idea that automobiles, a new technology at the time, had to be powered by gasoline wasn’t a given. Inventors of these vehicles experimented with various ways in which cars could be powered including electricity, fossil fuels, steam and/or combinations of these power sources. In 1898 Jacob Lohner, a coach builder, teamed up with Ferdinand Porsche who had recently invented the electric wheel-hub motor. The motor fit inside the wheel’s hub and was powered by lead-acid batteries. Using one of Lohner’s coaches, at the time a more common term than “car,” Porsche fitted two wheel-hub motors and a battery to create an all-electric vehicle —  the Elektromobil.

(Photo courtesy of Porsche Museum) The Lohner-Porsche "Mixte" touring car from 1903. Ferdinand Porsche is at the wheel. The wheel hub motors can be seen mounted to the front wheels

It suffered from the same problem that electric cars face today — limited range due to battery technology. Porsche added a gasoline-fueled, internal combustion engine that ran a generator to charge the battery making the Elektromobil the first vehicle to combine these power sources and thus the first hybrid. With the batteries fully charged it could reach the blistering speed of 38 miles per hour. This early hybrid was shown to the public at the 1900 Exposition Universelle, held in Paris, which showcased innovations like the Ferris wheel, diesel engines, talking films and escalators.

Within a few decades other hybrid vehicles came into existence—one traveled on land and the other underwater. Invented in the 1930s, diesel/electric locomotives used a diesel engine to drive a generator that provided power for an electric motor connected to the locomotive’s wheels. This technology led to an early from of regenerative braking, called rheostatic braking where the electric motors reversed their function and became generators driven by the weight of the train slowing down. The electricity produced was connected to on-board resistors (braking grid) that dissipated the braking energy as heat. This process is similar to regenerative braking used on modern hybrid cars to charge the battery.

Hybrid cars like the Toyota Prius offer drivers the choice of using gasoline or electricity as a power source. Future hybrid technology will offer increases in efficiency for electric motors, batteries and gas- or diesel-powered engines.

Another early hybrid vehicle was the diesel/electric submarine that came about in 1929. A diesel engine was used to propel the submarine and to charge large batteries. The sub used battery power when submerged and switched back to diesel propulsion when on the surface. Today a nuclear powered submarine can be considered a hybrid in that it uses a nuclear reactor, steam turbine, generator and electric motors to provide propulsion. Today we refer to a car or light truck that uses more than one power source as a hybrid. Typically these vehicles combine gas, or a diesel-fueled internal combustion engine, with a battery-driven electric motor.

Since 1900 a few hybrid cars were created but it wasn’t until 1997 when the Toyota Prius was introduced in Japan that the technology took off. Toyota sold the Prius in the U.S. starting in 2001 and by 2007 they had sold a million worldwide. Currently, many OEMs offer hybrid cars, SUVs, vans and even hybrid trucks. As the U.S. moves toward independence from foreign oil sources (and the climate heats up) the motivation for selling hybrid vehicles is ever increasing. OEMs are spending millions of dollars for research and development of all-electric and hybrid technologies. For at least the next decade hybrids will bridge the gap between fuel-only and all electric vehicles.

Future of hybrid powertrains

Powertrain configurations that will be used for hybrid cars of the future could take many forms. Because the reason for hybrids existing in the first place is energy efficiency it makes sense that the internal combustion engines (gasoline or diesel fueled) and electric motors used for hybrids be as efficient as possible. All internal combustion engines (ICE) are the most efficient when they are operated under a constant load. An ICE running at full power will extract the most heat energy from the fuel it consumed. Vehicles that use only an ICE cannot operate constantly at full power because the engine’s power output must be regulated for slower or faster driving conditions. This throttling of the engine causes it to be less efficient. Conversely, an electric motor is highly efficient under variable loads because maximum torque is available at all speeds. In addition, they can be used to recover lost energy through regenerative braking (see sidebar). A hybrid vehicle combines the advantages of both types of power sources — gasoline (or diesel) and electricity.

Just how much power does it take? More is needed to get a car moving than is needed to keep a car moving.

The graphs shown illustrate what amount of horse power is required for constant speed driving and acceleration. The upper graph shows how much horse power is required for acceleration of a 3050 lb. car with a frontal area of 22 square feet (Toyota Prius numbers). To go from 0-to-60 in 10 seconds requires 140 horse power. 0-to-40 mph in 10 seconds takes about 85 H.P. The faster the car is accelerated from a stop the more power is required. For example, 0-to-60 in 4 seconds takes 330 horse power (Tesla model S numbers). The lower graph shows that the same vehicle only needs a fraction of the power used for acceleration to maintain constant speeds. In this example just 12 horse power can maintain a steady speed of 60 mph.

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