Toyota Engine Technologies For The Future Title: Engines of Change Subtitle: Gasoline, alternative fuels, hybrid and hydrogen: what are the emerging technologies in the current automotive marketplace?
Over more than a century, the automobile has presented itself as a fascinating microcosm of technological evolution at work, with humble beginnings that embraced bicycle wheels, a tiller to steer, and a variety of rudimentary powerplants running on fuels ranging from coal gas, hydrogen and oxygen, steam, kerosene, and electricity, to the currently more common gasoline and diesel. These latter fuels power nearly all of the vehicles on our roads today.
It’s a tribute to technology and innovation that gasoline and diesel internal combustion engine vehicles continue to serve us well after more than 100 years. In response to changing consumer desires and a maturing auto market—as well as federal and state regulations—motor vehicles have evolved to become faster, more responsive, cleaner running, and safer.
This isn’t simply a result of manufacturing and design efficiencies, although these certainly contribute to the exceptional cars, trucks, and SUVs now available to us. Today, advanced technology and sophisticated electronic control have been applied to nearly all facets of an automobile’s operation, from speed-sensitive steering and anti-lock braking to multi-point electronic fuel injection, variable valve timing, and sophisticated emissions controls. This trend will surely continue to extend the role of gasoline and diesel engines well into the coming decades, even in the midst of increasingly stringent requirements for lower emissions and consumer demand for higher efficiency.
Evidence of this can be seen in the new genre of super-clean running vehicles like SULEVs (Super Ultra Low Emission Vehicles) and PZEVs (Partial Zero Emission Vehicles), gasoline internal combustion engine automobiles that operate so efficiently their tailpipe emissions have become increasingly difficult to measure.
Diesel Diesel-powered vehicles are beginning to make a comeback in the U.S. due to advancements in emissions technology and engine operation. The latest diesel vehicles benefit from such innovations as direct injection and engine control technologies that eliminate the knocking sound and reduce visible exhaust soot that have long been associated with diesel passenger-car and light-truck engines. Still, diesel engines do not meet emissions standards in five U.S. states—including California, the country’s largest motor vehicle market—which means diesels are not available to 25% of the entire US car-buying public. New stricter standards for diesel are scheduled to go into effect in 2007 and nothing on the market now will meet them. The arrival of low-sulfur diesel fuel in a few years will help, but even then additional technical improvements will be needed to allow diesel vehicles to meet these stricter emissions standards. It has yet to be determined what this will do to the cost of diesel vehicles.
Fuel Saving Strategies While advancements continue to be made in conventional areas of engine operation, other approaches are promising to add incremental efficiency improvements to the mix, bringing with them better fuel economy. Good examples are next-generation, super efficient automatic transmissions; emerging 42-volt electrical systems, which run accessories that would otherwise be powered by the engine, thereby lessening engine load and increasing fuel efficiency and technology that can disable a number of engine cylinders under certain driving conditions. This latter technology senses times of low power demand such as when highway cruising, then seamlessly disables cylinders to effectively change an 8-cylinder engine into a 4-cylinder, or a 6-cylinder into a 3- cylinder, then back again as additional power is needed.
Alternative Fuels Even as conventional engines have improved, recent years have found a growing interest in fuel alternatives that could potentially power our vehicles either more efficiently or with fewer emission byproducts. Alternative fuels are attractive because they could potentially lessen our dependence on imported oil and, in some cases, because existing vehicles can be converted to run on these fuels with minimal modification. Primary among alternative motor vehicle fuels are methanol, ethanol, natural gas, liquid petroleum gas (LPG, also known as propane), electricity, and hydrogen.
Ethanol, a wholly renewable alcohol fuel that can be made from corn, grains or biomass, has enjoyed growing favor in recent years. When blended with 15 percent gasoline to create E-85 fuel, it can power internal combustion engines with only modest upgrades in fuel system and engine management software. A variety of current vehicle models are capable of running on any combination of E- 85 or gasoline in the same tank. The downside is that ethanol is more costly than gasoline and requires significant federal subsidies to compete at the pump, plus fewer than 200 ethanol-fueling stations are found across the country, far too few to support E-85 fueled vehicles as a realistic alternative. Extremely high energy input is currently required to produce the corn that serves as the base for ethanol production. Also, most ethanol-capable vehicles are designated “flex fuel” for the purpose of tax credits or other subsidies, but rarely in fact are operated on ethanol.
The other alcohol fuel, methanol, is typically created from natural gas and thus does not offer the benefit of being a renewable fuel. It is also quite corrosive and requires special fuel lines and other fuel system components. There are very few stations carrying M-85, the motor fuel comprised of 85-percent methanol and 15- percent gasoline, which makes this an impractical fuel alternative.
Two gaseous fuels, LPG and natural gas, are also contenders. A limited number of vehicle models are made to run on these fuels, and they are primarily aimed at fleets because of the premium paid for their costly gaseous storage cylinders and other fuel system components. Plus, like all alternative fuels, fuel availability is an issue. While there are more natural gas stations available than most alternative fuels, this amount is still a relatively small number in the low thousands, compared to the 170,000 gasoline stations found across the country. Propane fueling locations are abundant compared to all other alternative fuels, but almost all are the rudimentary type used for fueling portable LPG tanks for barbecues and other consumer devices, not an attractive or familiar fueling option for drivers. Since LPG is a byproduct of natural gas production, it is in limited supply and subject to price volatility.
Hydrogen Hydrogen is one of the most exciting future fuels being examined by the auto and energy industries. Today, most major auto manufacturers, including Toyota, have hydrogen fuel cell demonstration vehicles on the road. Hydrogen-powered internal combustion engine vehicles are also being tested. When used in a fuel cell, hydrogen is the ideal motor fuel because it creates electricity without combustion to power electric drive motors, with only heat and water vapor the byproducts. What keeps this a “future” fuel are the many unanswered questions facing hydrogen today, including how it can be affordably created, safely stored, conveniently distributed, and widely used. Hydrogen and the vehicles that run on this fuel currently provide an exciting window to our driving future, but they are probably decades away from mainstream use.
Pure Electric Vehicles Battery electric vehicles have received plenty of attention over the past decade or so. These vehicles offer many advantages—such as zero localized emissions and the convenience of at-home recharging—but they also have significant challenges. Primary among these are insufficient driving range and high production costs, long recharging times (7 hours or so) largely due to the limitations of today’s battery technology. Toyota has considerable experience with electric vehicles because of its RAV4 EV demonstration program that leased vehicles to fleets during the 1990s. Ultimately, even with technologically advanced vehicles capable of running seamlessly on electric power, battery limitations have relegated full-function pure electric vehicles—at least for now—to an historical footnote.
Hybrid Vehicles The trails that battery electric vehicles blazed have helped contribute to the development of the hybrid-electric vehicles we see on American roads today. While much of the excitement surrounding hybrids is well earned, it’s important to note that not all hybrids are created equal, and important distinctions are to be made between the various hybrid systems currently on the market or soon to be released.
First, the definitions: A series hybrid is driven exclusively by one or more electric motors, with the internal combustion engine’s sole purpose that of generating electricity for powering the motors. There are currently no automobiles with a series hybrid system on the market. A parallel hybrid typically uses an internal combustion engine for most of its propulsion, relying on an electric motor for boosts of acceleration. There are variations on these two themes as well as amalgamations that result in “hybrid” hybrid powerplants, which blend a bit of both configurations into a single unit.
“Mild” hybrid systems are beginning to emerge that achieve modest fuel economy increases. These systems typically use an idle-stop feature that shuts an engine off while a vehicle is stopped, and a motor-generator that automatically starts the engine and provides initial propulsion as the vehicle starts up again. Like their full hybrid counterparts, mild hybrids use regenerative braking to capture energy as a vehicle decelerates, allowing the generator to feed some electricity back to the vehicle’s batteries. The mild hybrid’s advantage is that it is a relatively simple and affordable design. Its drawback is that it does not provide the kind of spectacular fuel economy improvements that many have come to expect from a hybrid electric vehicle.
Even the more complex hybrid systems achieving high fuel economy are not truly created equal. Some hybrid vehicles are powered by their internal combustion engines at all times, with electric assist provided only when additional acceleration or torque is needed. There is no accommodation made to run on electric power only, even when driving at slower city speeds or during times of heavy low speed urban traffic when electric drive is an efficient power option.
This is one of the reasons the original Toyota Hybrid System (THS) and second- generation hybrid system, Hybrid Synergy Drive (HSD), are firmly established at the top of the hybrid hierarchy. THS and now HSD meld the best of both series and parallel hybrid drive configurations into one cohesive system, delivering a continuously variable ratio of internal combustion engine and electric motor power to the drive wheels. HSD adds a variable voltage system that allows the electric motors to run at higher-than-battery voltage for better efficiency. Vehicles equipped with HSD can drive on electric power only at times, exclusively internal combustion engine power under other circumstances, and with both engine and motor power as necessary. Through a power split device and a sophisticated energy management system, THS, and now HSD harness both the acceleration benefits of parallel hybrid and the energy-saving efficiency of a series hybrid, offering a “hybrid” hybrid configuration that brings the best of all worlds— performance and remarkable fuel economy—to the highway.