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Gas/Electric Hybrids
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| Learn about the latest technology from Toyota and Honda |
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| Updated |
Jun 10, 2004 21:51:30 |
| Rating |
 114 ( -16 -14.03% ) | | Author | Craig Fitzgerald |
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Description:
Profile: Electric Hybrids 2001 Honda Insight
2001 Toyota Prius
How Do They Work?
Both the Insight and Prius are charge-sustaining gasoline/electric hybrids. In other words, both cars use their gasoline engines to charge their batteries, rather than having to plug them in. In both cars, the gasoline engine is the primary power source - at highway speeds, for instance, the gas engine is doing most of the work.
However, in times of peak demand, such as climbing a long hill, both the gas engine and the electric motor contribute their power simultaneously. Conversely, both the engine and the motor shut down completely when the cars stop. And the Insight and Prius both utilize "regenerative braking" systems to capture electrical energy from the spinning wheels.
Electric Start
Unlike the Insight, though, there are times while under power that the Prius electric engine will operate by itself. When starting from a dead stop, the Prius utilizes the electric engine only, until it reaches speeds somewhere between 13 and 25 miles per hour.
In general, electric motors provide outstanding torque, but they can't sustain that torque at speed without requiring massive amounts of power. But since the gas engine is exempted from having to work at speeds below 10 mph, the Prius actually gets better mileage in the city range than on the highway.
Compared to the Insight, the Prius features a larger battery pack and electric motor to facilitate its electric-only starts. These comparatively beefed-up components are also necessary to motivate the Prius' extra mass - it's a four-door sedan where the Insight is a flyweight two-seater.
Advanced Technology: Prius
The biggest difference between the Prius and the Insight is where the electric motor is mounted. The Insight utilizes a single combination electric motor/generator directly mounted between the gasoline engine and the relatively conventional five-speed manual transmission (or the optional continuously variable automatic transmission).
The Prius' electric motor configuration is significantly different and more complex, as it uses two separate motor/generators, as well as a standard continuously variable transmission. Unlike the Insight, the Prius' electric motors are connected to the wheels via a planetary gear and differential, rather than just being simply bolted between the engine and transmission.
The Prius' two electric motors take responsibility for the work done by the Insight's one motor/generator. One of them acts primarily as a motor as it provides power to the wheels and while also charging the battery from the centrifugal motion of the wheels. The other works primarily as a generator to charge the batteries, and its secondary responsibility is to start and stop the gasoline engine.
The Prius' three power sources - the battery and the two motors - are tied together by "planetary" gears. This complex gear set funnels power from the electric motor/generator only when the Prius begins to move. Once the Prius reaches 13 to 25 miles per hour, the planetary gear set then funnels power over to the generator/motor, which in turn begins to feed fuel and spark to the Prius' gas engine. The gas engine then begins to run normally.
All together, the entire system also comprises the Prius' continuously variable transmission. Interestingly, the Prius features no traditional reverse gear. When backing up, the electric motor simply runs backwards. The gasoline engine never runs while the Prius is in reverse.
Advanced Technology: Insight
While the Prius' power routing system is more complex than the Insight's, Honda's hybrid also bristles with technology. Consider the Insight's "lean burn" three-cylinder powerplant. Unlike most gasoline engines (including the Prius') that run on an air/fuel ratio of about 14.7:1, the Insight's engine operates on an amazingly lean ratio of air and fuel of as little as 22:1. This lean mixture has its own challenges, including the limitations of traditional oxygen sensors.
The Insight uses a LAF (Linear Air-Fuel) sensor, capable of measuring air-fuel ratios as lean as 23:1. Therefore, the electronic control module can maintain precise control over the mixture at normal and lean-burn conditions.
Both cars also feature technologies that reduce and recover vapors from evaporated fuel. The Insight uses a more traditional on-board vapor recovery system to capture fuel vapors when refueling. The Prius, however, uses a fuel tank with a bladder inside to separate the fuel from the air inside the tank, eliminating evaporation completely.
Daily Operation
The most surprising part about each of these hybrid's advanced technologies is how unobtrusively they work. It may spook newcomers to have their cars completely shut down at stoplights, but they both quickly start up again - the Prius wins the gold star here for its particularly seamless operation.
While both cars are hybrids, each one has a different mission. Find out more about the Insight and Prius by clicking the research links below.
Alternative Fuels
Alternatives to the internal combustion engine aren't a recent development. In fact, during the early days of the automobile in the early 20th century, there existed a battle for dominance between electric, steam-powered and internal combustion engines, much like the fight between Beta, VHS and laser disc as the dominant home entertainment medium in the 1980s.
The major problems with vehicles running solely on electric power are the same today as they were back then: energy storage and range. Batteries, even as technologically advanced as they have become in the past few years, are heavy and require a significant amount of time to recharge. Operating an electric motor at acceptable highway speeds, even in the early days, requires a massive amount of power, and therefore range is limited.
Today's electric vehicles face the same challenges. GM's EV1, available since 1998, has been a colossal failure because of the concessions required to operate it. The EV1 is currently only available in a handful of locations, most of which have sun more often that any other kind of weather. Unlike the hybrid-powered Insight and Prius, the EV1 must be plugged in for hours at a time to restore a charge to the batteries. Taking delivery of an EV1 is no easier: homes must be set up with a charging station that often requires that the home be rewired for higher voltage. Also, the EV1 is only available for lease, at a rate north of $400 per month.
As the EV1's drawbacks illustrate, perhaps the most significant reason for dearth of innovation in alternative fuels is the lack of a proper infrastructure outside of the oil industry. In the wake of the successful development of the internal combustion engine, the oil industry saw the massive potential in providing a fuel and service stations infrastructure to sustain the early automobile.
Richard G. Schallenberg's 1980 document for the Institute of Electrical and Electronics Engineers theorizes that one of the many reasons for the failure of the early electric vehicle was that the electric utilities were negligent in providing charging stations for electric vehicles. Schallenberg notes that "In a few big cities in the period 1905-1920, a few utility companies aided the electric vehicle industry by setting up garages, giving special charging rates, making available technical services, etc., but this was an uncommon phenomenon." Since we're still primarily dependent on oil to power our vehicles, the gas/electric Prius and Insight represent a first step toward bringing practical alternative power into the mainstream.
-By Craig Fitzgerald |
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