|
||||||||||
|
|
Hybrids are Happening Hybrid-electric vehicles (HEVs) combine an electric motor with an internal combustion engine. The result is an extra-efficient, no-compromises powertrain that takes advantage of the efficiency benefits of electric drive as well as the performance of a gasoline engine. Model year 2002 sees two of these advanced technology vehicles offered in the market. The Honda Insight, a two-seater coupe featuring Honda's Integrated Motor Assist (IMA) hybrid system, is the greenest car now available. The Toyota Prius, introduced here last summer after three years in the Japanese market, is the greenest family sedan and uses the Toyota Hybrid System (THS). More hybrid-electric vehicles are on the near horizon. Honda just released its model year 2003 Civic Hybrid, an IMA hybrid version of the popular compact car. Other announcements include SUVs and pickups from Ford, GM, and DaimlerChrysler promised by 2003-2004. The way this technology is advancing, we might well see some additional HEV entries over the next few years. The world's first mass-produced hybrid electric vehicle is a product of many technological and design advances. But it is its powertrain, which combines an efficient gasoline engine with a smooth and quiet electric motor, that gives the Prius its biggest boost in green performance. The heart of the Prius powertrain is contained in what is in effect the car's automatic transmission. This "Toyota Hybrid System" (THS) device is no ordinary transmission. Inside is a special "planetary" gear set coupled to an electric motor and a generator, all operated under computer control. The sophisticated combination of electrical and mechanical components makes it, in effect, a super-smart transmission. But it is really more than a transmission, since it also sends power back and forth among the engine, wheels, motor, generator, and battery.
When starting from a stop, the Prius's gasoline engine need not come on at all; the battery supplies power to the electric drive motor. The engine also stops when the car is idling, coasting, or at other times when low power is needed. This "idle off" feature of the hybrid system results in a 13 percent fuel savings in city driving. The engine restarts quickly and quietly whenever more power is needed. The gasoline engine also runs as needed to keep the battery charged. Among the benefits of hybrid drive is regenerative braking, which converts wheel rotation into electricity. When the car is coasting down or when the brakes are applied, the electric motor acts as a generator, recapturing energy. The recovered energy is stored in the battery rather than lost as friction in the brakes. During the stop-and-go of city driving, this feature provides up to a 19 percent improvement in fuel efficiency. The Prius gasoline engine itself is of a special design, achieving very high efficiency for its displacement while also trimming weight. The 1.5-liter four-cylinder engine produces 70 horsepower at 4500 RPM. Limiting the engine to this relatively low-RPM redline enables the use of lighter components and reduces friction. Toyota could take this approach because they didn't have to maximize the engine's power, since the electric motor provides over 40 horsepower of additional muscle. A crankshaft offset from the cylinder centerline is another friction-cutting feature, one that is also used on Toyota's new Camry and Echo inline fours. Finally, a sophisticated emissions control system and advanced catalyst cut tailpipe pollution to Super-Ultra-Low-Emission (SULEV) levels. Thus, the Prius is both far cleaner at the tailpipe as well as much more efficient than average in fuel use. Honda Hybrids: Insight First, Civic on the Way The Honda Insight is the most fuel-efficient gasoline vehicle you can buy, even among small cars. It is also a technological showcase, featuring not only hybrid drive but also advances in every other key vehicle system. To engineer the Insight for record fuel economy, Honda focused on three broad areas of design.
First, a strong, lightweight aluminum structure and highly streamlined body reduce the overall power needed for moving the car, accounting for a 30 percent efficiency increase. The lower power requirements that go with lower weight permit a smaller and less costly powertrain for a given level of performance. Second, the Insight's 1.0-liter VTEC-E gasoline engine is highly efficient by virtue of its compact size and the use of variable valve control, lean combustion, and advanced techniques for cutting friction. The engine enhancements provide another 30 percent efficiency increase. Third, the Insight's electric drive components-motor, battery, and controls-recover braking energy and boost power, so that good performance is achieved with the smaller engine. The hybrid drivetrain also allows the engine to stop when it is idling and full power is not needed. These features provide the remaining 25 percent step up to the 85 percent total efficiency increase demonstrated by the Insight's design. The Honda Insight's lightweight structural innovations represent an important facet of the automotive future. Various combinations of materials are being investigated for cutting vehicle weight while enhancing safety and structural performance. One of the best options is optimized use of aluminum. The front and rear sections of the Insight's frame use advances, such as hexagonal sections adapted from race car frames, to absorb crash energy. These techniques exploit aluminum's special properties, enabling a controlled cushioning that protects occupants from crash forces. The inner structure has pillars and beams to form a rigid cage around the driver and passenger, resisting intrusion and deformation. As a result, even though it is a small car, the Honda Insight earns 4-star ratings for both frontal and side-impact crashworthiness. The Insight's gasoline engine-a 1.0-liter, 3-cylinder, 12-valve design-is one of the most efficient gasoline engines in production. It puts out 67 horsepower, nearly 20 percent more per liter than the average new car and light truck, all the more remarkable because it is tuned for high efficiency. In the automatic version of the Insight, a continuously variable transmission (CVT) provides for smooth, responsive, and efficient coupling of the gasoline engine and hybrid drive to drive the front wheels. The heart of the hybrid in Honda's case is called "Integrated Motor Assist" (IMA) because an electric motor is merged right onto the back of the engine, assisting it with up to 30 foot-pounds of added torque. Power assist is one of the key fuel-saving techniques of hybrid drive. Energy is saved if one uses a small engine (like the 1.0-liter Insight engine); it is also saved if an engine is operated as much as possible at low RPM. But a smaller engine has less torque, and high RPM provides high power. Thus, using the efficient electric motor to put back the torque, especially at low RPM, provides the performance that would otherwise be lost. The IMA system also recaptures braking energy and allows the engine to be turned off when the car is stopped but restart quickly as soon as power is needed. The latest hybrid to hit the streets is Honda's brand new Civic Hybrid. Based on thier popular Civic model, this early model year 2003 car is arriving in showrooms in April 2002. To develop a hybrid-electric Civic, Honda made numerous advances, building on the experience gained with the Insight. The Civic hybrid also features the first U.S. application of a lean-burn dual spark-ignition gasoline engine. Called i-DSI by Honda, it represents yet another advance in the state-of-the-art for engine efficiency. GreenerCars.com has evaluated the Civic Hybrid, and calculated preliminary Green Scores for both the automatic and manual transmission versions. For more information, read our related press release. The IMA system used on the Civic Hybrid is an improved version with even better technical efficiency than the first-generation IMA system used on the Honda Insight. A basic function of the IMA is to provide extra torque during acceleration and other times of heavy engine load. The motor assist shuts down at cruising speeds when engine load is lower.
Like all hybrid drives, the IMA provides regenerative braking, so the motor acts as a generator to convert captured energy into electricity. But an innovation on the i-DSI engine enables the valves to disengage and seal off up to three cylinders during deceleration. This cylinder-idling feature reduces the friction inside the engine that otherwise slows a car when you lift your foot off the accelerator. Since such engine braking represents lost energy, this feature allows more energy to be regenerated through electric braking. As in the Insight, the Civic's engine-IMA system also uses idle stop. The engine shuts off automatically if the vehicle comes to a complete halt and then restarts immediately when the accelerator pedal is pressed. Honda made many other refinements for the new Civic IMA system, yielding better efficiency, more compact components, and lower cost. Improvements to the internal magnetic coils of the ultra-thin DC brushless motor, which boasts the world's highest output density and overall efficiency, achieve 30 percent greater torque than the version used in the Insight. The power electronics have been redesigned, cutting their weight by 30 percent and cutting volume by 40 percent. The efficiency of the battery modules has been increased and the battery's peripheral systems have been made more compact as well. Putting it all together, the Honda Civic Hybrid uses its 1.3-liter i-DSI engine with a continuously variable transmission (CVT) and the IMA system, to yield nearly 50 MPG in both city and highway, while meeting the California ULEV standard. The Ford Motor Company is planning to introduce a hybrid-electric version of its Escape SUV in 2003. The Escape HEV will feature an electric drivetrain combined with a new version of Ford's four-cylinder "Zetec" gasoline engine tuned to run at extra-high efficiency. Combining this engine with a 87 hp electric motor will enable the Escape HEV to perform just as well as a V-6 version while achieving 35-40 MPG in city driving and up to 30 MPG on the highway. Today's comparable Ford Escape V-6 is rated at 19 MPG city and 24 MPG highway.
Ford's design strategy for the Escape uses the electric drive to supplement the power of the gasoline engine, enabling the engine to be designed for higher efficiency than it could when used without a hybrid powertrain. The Escape HEV will use a special version of Ford's Zetec inline four-cylinder engine. Existing versions of this engine are used in the 4-cylinder versions of today's Escape as well as the Ford Focus. The Zetec has a lightweight, low-friction design that can achieve significant gains in fuel economy without compromising on responsiveness and drivability. Different version of the engine are used for different purposes. For example, Ford's "Special Vehicle Team" (SVT) version of the Focus uses a suped-up 2.0-liter Zetec engine that puts out 170 hp. By comparison, the engines used in the Focus ZX3 and Escape XLS models put out just under 130 hp. An opposite tack is taken for the version of the Zetec being developed for the hybrid Escape. Because up to 87 hp of extra power can be provided by the electric motor, the engine is designed to use a special "Atkinson" cycle that is significantly more efficient than a conventional four-stroke gasoline engine cycle. This type of engine design sacrifices torque-but torque is the strong suit of an electric motor. As a result, the Escape's hybrid drive system puts back the power and responsiveness that would otherwise be sacrificed with the special engine cycle. A similar approach is used in the Toyota Prius, which also has an Atkinson cycle engine. In addition to the 87 hp (65 kW) electric drive motor, the Ford Escape's hybrid system will have a 28 kW generator, providing regenerative braking and battery charging from the engine. A special 300-volt battery, to be supplied by Sanyo, will be packaged under the rear floor of the Escape HEV, without any loss of cargo space. The hybrid system will also be able to drive the vehicle at low speeds as well as turn off the combustion engine when the vehicle is stopped while instantly restarting it as soon as motive power is needed. In terms of tailpipe pollution, the Escape HEV is being designed to qualify as a Super-Ultra-Low-Emission Vehicle (SULEV) under California standards. General Motors Hybrid Pickup and SUV GM has promised a hybrid system as an option on its Chevy Silverado and GMC Sierra pickups in 2004. The result will be a fully capable, V-8-powered pickup truck that hauls just as much as its conventional gasoline-only counterparts, offers supplemental power outlets, and gets better fuel economy. The truck will use GM's 5.3-liter "Vortec" V-8, one of the larger engines in the Silverado and Sierra 1500-series. Its hybrid design is not used to downsize or de-rate the engine for extra-high efficiency. Instead, a modest efficiency improvement is obtained from this hybrid design, which integrates the electric motor/generator between the engine and transmission. The system doubles as the starter and allows the engine to be turned off during idle; it also recaptures energy of motion when the brakes are applied. Model year 2002 Silverados with the 5.3-liter engine have a city-plus-highway average fuel economy of 15 MPG with 4-wheel drive and 16 MPG with 2-wheel drive. GM's hybrid versions will have up to 15 percent better fuel economy, suggesting averages of 17-18 MPG. That's even higher than today's version of the trucks with the smaller, 4.3-liter base engines, which average about 7 percent more fuel efficient than their 5.3-liter counterparts. The Silverado and Sierra hybrid pickups will use a 42-volt system, with the integrated starter/generator charging an advanced lead-acid battery pack. Solid-state electronics control not only the charging and engine restart functions, but also boost the current to 110 volts at up to 20 amps for the supplemental power outlets. The plugs can be used for power tools, camping equipment, or other recreational gear. GM will offer an even more sophisticated hybrid system in a new SUV slated to debut in 2004. The vehicle is being designed as one version of a mid-sized platform code-named Epsilon. This version of GM's hybrid system is called "ParadiGM" and it may eventually be used in a variety of vehicles, including SUVs, new crossover vehicles, and traditional sedans. The new SUV will use a ParadiGM configuration that couples a 3.6-liter V-6 gasoline engine with a hybrid drive package containing a pair of electric motors connected to a battery pack. The V-6 engine will put out 220 hp, with a boost of up to 32 hp more coming from the electric motors. GM projects that the new hybrid SUV will deliver about 20 percent better fuel economy than a non-hybrid version of this vehicle. The result will be roughly 30 MPG as an average of the city and highway MPG label ratings, but most of the efficiency gain will come in city driving. But the design may also push boundaries on hot performance, since GM expects an SUV powered by the ParadiGM powertrain to accelerate from 0-60 mph in just over 7 seconds. DaimlerChrysler's first announced hybrid vehicle for the U.S. market will be a HEV version of the Durango SUV. The vehicle will combine an 89 hp electric motor with a 175 hp, 3.9-liter V-6 gasoline engine. Thus, its performance will match that of a Durango equipped with DaimlerChrysler's 5.9-liter V-8, while its fuel economy will be 20 percent higher. The result will be 17 MPG in average city plus highway driving, compared to an average of 14 MPG with today's 4-wheel drive V-8 Durango. Slated for introduction in 2003, the Durango hybrid SUV will accomplish its efficiency gain by using a unique, split hybrid technology that DaimlerChrysler calls "Through-The-Road" (TTR). Instead of coupling the gasoline engine and electric motor/generator with a shaft, the engineers designed the system so that the road on which the vehicle runs acts almost like a belt connecting the two parts of the powertrain. The TTR system also provides 4-wheel drive functionality without the efficiency penalties of a conventional transfer case.
In the Durango HEV, a V-6 engine and automatic transmission connect to a conventional drive shaft that turns the rear wheels. A three-phase electric motor drives the front wheels, laying extra power on the pavement to assist the gasoline engine during acceleration. When the vehicle is decelerating, the motor regenerates braking energy from the front wheels. If the battery charge gets too low, the control system switches the motor into generator mode while the vehicle is cruising. The resulting drag on the road pulls extra power out of the gasoline engine-another aspect of the Through-The-Road coupling that gives the system its name. DaimlerChrysler has also shown European concept versions of this TTR hybrid system for two Mercedes-Benz models. The "HyPer" applies hybrid technology to a Mercedes A-Class car, and the "Hymatic" is based on a Mercedes E-Class sedan. DaimlerChrysler's other announced hybrid is the Contractor Special, to be offered as an option for Dodge Ram full-size pickup trucks starting in 2004. This hybrid design is different than the company's TTR configuration. Its electric motor is mounted between the transmission and the transfer case of a 4x4 truck. The motor will provide extra power for acceleration and double as a generator to supply electric power. In this regard, it is similar to GM's planned Silverado/Sierra hybrids. When parked, the Contractor Special's hybrid components can function as a stationary electrical generator, delivering up to 20 kW of 110/220 volt AC power for worksite, campsite, or home uses. However, the Dodge Contractor Special has a different design emphasis than GM's announced hybrid pickups. Its hybrid system will be used for boosting the performance of the gasoline engine, not just for recovering braking energy and providing auxiliary power. DaimlerChrysler plans to build these hybrid variants of the Ram to provide higher fuel efficiency and lower emissions as well as superior performance. For example, the 5.2-liter gas-electric motor hybrid will do 0-60 mph in 10.0 seconds while having a rated fuel efficiency of 18 MPG, compared to a 10.6 second 0-60 time and 16 MPG for the 5.9-liter gasoline-only models. |
 |
 |
 |
 |