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Hybrid-Powered Vehicles 2nd Edition, March 16, 2011
Description / Abstract:
Executive Summary
Gasoline and diesel internal-combustion engines have two huge advantages over competitors. First, liquid fuels have extremely high-energy density, allowing long driving ranges with small storage tanks. Second, they enjoy an established infrastructure that would cost hundreds of billions of dollars to recreate for any new fuel. These have proven to be daunting barriers to alternative fuel and propulsion technologies.
Even more important, the internal-combustion engine keeps raising the bar every time it is challenged. For example, 15 years ago, it was "common knowledge" that the internal-combustion engine was inherently dirty and must be replaced to achieve air-quality goals. Engineers responded by developing emissions control technology that reduced criteria-pollutant emissions so much that little additional improvement is available from any alternative.
The remaining drivers to switch to a new propulsion technology or fuel are global warming and energy security. Again, recent developments in computer simulation and computer-aided design are facilitating the design of a host of new technologies to improve the efficiency of conventional vehicles and engines. These improvements make it harder to justify spending hundreds of billions of dollars to create a new infrastructure because they reduce the incremental efficiency advantages of alternative technologies. Thus, internal-combustion engines running on liquid fuels will likely remain the dominant technology for light-duty vehicles until the supply of relatively cheap oil starts to run out.
The increasing concerns with global warming and energy security also are spurring interest in hybrid vehicles. Hybrid vehicles use the existing infrastructure and offer a way to significantly reduce fuel use, with corresponding reductions in global warming gases, fuel cost to consumers, and upstream air pollutants from fuel refining, distribution, and refueling evaporative emissions.
A hybrid vehicle combines two different types of propulsion systems. Most hybrid vehicles combine an electric motor and an internal-combustion engine, although other types of hybrid systems are possible. In light-duty vehicles, parallel hybrid systems generally are used, where the internal-combustion engine, the electric motor, or both can drive the vehicle. This design offers improvements in efficiency by turning off the engine at idle, using the motor as a generator to recapture energy usually lost to the brakes, improving alternator efficiency, reducing accessory loads, and using the electric motor to improve the efficiency of the engine. For example, the engine can be downsized as a result of the motor assist on acceleration, the engine can be operated at higher efficiency speed and load points by carefully integrating engine operation with operation of the electric motor and transmission, and the electric motor and battery pack can be used to supply propulsion energy at low speeds and loads, allowing the engine to be shut off under inefficient conditions.
Honda's hybrids bolt the electric motor to the engine, which is an example of a single-clutch parallel system. Either the engine or the motor or both can directly provide power to the drivetrain. Toyota chose to develop a more sophisticated input power-split system for its hybrids, starting with the Prius, using a planetary gear system and two motors. Ford independently developed a similar system. The input power-split excels at optimizing engine and motor operation during city driving and it replaces the conventional transmission. However, it has some efficiency losses during highway driving and it is more complicated and expensive than the simple parallel hybrid system.
Gasoline and diesel internal-combustion engines have two huge advantages over competitors. First, liquid fuels have extremely high-energy density, allowing long driving ranges with small storage tanks. Second, they enjoy an established infrastructure that would cost hundreds of billions of dollars to recreate for any new fuel. These have proven to be daunting barriers to alternative fuel and propulsion technologies.
Even more important, the internal-combustion engine keeps raising the bar every time it is challenged. For example, 15 years ago, it was "common knowledge" that the internal-combustion engine was inherently dirty and must be replaced to achieve air-quality goals. Engineers responded by developing emissions control technology that reduced criteria-pollutant emissions so much that little additional improvement is available from any alternative.
The remaining drivers to switch to a new propulsion technology or fuel are global warming and energy security. Again, recent developments in computer simulation and computer-aided design are facilitating the design of a host of new technologies to improve the efficiency of conventional vehicles and engines. These improvements make it harder to justify spending hundreds of billions of dollars to create a new infrastructure because they reduce the incremental efficiency advantages of alternative technologies. Thus, internal-combustion engines running on liquid fuels will likely remain the dominant technology for light-duty vehicles until the supply of relatively cheap oil starts to run out.
The increasing concerns with global warming and energy security also are spurring interest in hybrid vehicles. Hybrid vehicles use the existing infrastructure and offer a way to significantly reduce fuel use, with corresponding reductions in global warming gases, fuel cost to consumers, and upstream air pollutants from fuel refining, distribution, and refueling evaporative emissions.
A hybrid vehicle combines two different types of propulsion systems. Most hybrid vehicles combine an electric motor and an internal-combustion engine, although other types of hybrid systems are possible. In light-duty vehicles, parallel hybrid systems generally are used, where the internal-combustion engine, the electric motor, or both can drive the vehicle. This design offers improvements in efficiency by turning off the engine at idle, using the motor as a generator to recapture energy usually lost to the brakes, improving alternator efficiency, reducing accessory loads, and using the electric motor to improve the efficiency of the engine. For example, the engine can be downsized as a result of the motor assist on acceleration, the engine can be operated at higher efficiency speed and load points by carefully integrating engine operation with operation of the electric motor and transmission, and the electric motor and battery pack can be used to supply propulsion energy at low speeds and loads, allowing the engine to be shut off under inefficient conditions.
Honda's hybrids bolt the electric motor to the engine, which is an example of a single-clutch parallel system. Either the engine or the motor or both can directly provide power to the drivetrain. Toyota chose to develop a more sophisticated input power-split system for its hybrids, starting with the Prius, using a planetary gear system and two motors. Ford independently developed a similar system. The input power-split excels at optimizing engine and motor operation during city driving and it replaces the conventional transmission. However, it has some efficiency losses during highway driving and it is more complicated and expensive than the simple parallel hybrid system.
Hybrid-Powered Vehicles 2nd Edition, March 16, 2011