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  3. Hybrid Cars Have you pulled your car up to the gas pump lately and been shocked by the high price of gasoline? As the pump c

Hybrid Cars Have you pulled your car up to the gas pump lately and been shocked by the high price of gasoline? As the pump c

admin2013-06-02  72
问题                                        Hybrid Cars
    Have you pulled your car up to the gas pump lately and been shocked by the high price of gasoline? As the pump clicked past $20 or $30, maybe you thought about trading in your car for something that gets better mileage. Or maybe you’re worried that your car is contributing to the greenhouse effect.
    The auto industry has the technology to address these concerns. It’s the hybrid car. You’re probably aware of hybrid cars because they’ve been in the news a lot. Most automobile manufacturers have announced plans to manufacture their own versions. What makes it a "Hybrid"?
    Any vehicle is a hybrid when it combines two or more sources of power. In fact, many people have probably owned a hybrid vehicle at some point. For example, a moped (a motorized pedal bike) is a type of hybrid because it combines the power of a gasoline engine with the pedal power of its rider.
    Hybrid vehicles are all around us. Most of the locomotives we see pulling trains are diesel-electric hybrids. Cities like Seattle have diesel-electric(以柴油发动机发电的) buses—these can draw electric power from overhead wires or run on diesel when they are away from the wires. Giant mining trucks are often diesel-electric hybrids. Submarines are also hybrid vehicles — some are nuclear-electric and some are diesel-electric. The gasoline-electric hybrid car is a cross between a gasoline-powered car and an electric car.
    Hybrid Structure
    You can combine the two power sources found in a hybrid car in different ways. One way, known as a parallel hybrid, has a fuel tank, which supplies gasoline to the engine. But it also has a set of batteries that supplies power to an electric motor. Both the engine and the electric motor can turn the transmission at the same time, and the transmission then turns the wheels.
    By contrast, in a series hybrid the gasoline engine turns a generator, and the generator can either charge the batteries or power an electric motor that drives the transmission. Thus, the gasoline engine never directly powers the vehicle.
    Why Build Such a Complex Car?
    You might wonder why anyone would build such a complicated machine when most people are perfectly happy with their gasoline-powered cars. The reason is twofold: to reduce tailpipe emissions and to improve mileage. These goals are actually tightly interwoven.
    Evolution of the Hybrid
    The hybrid is a compromise. It attempts to significantly increase the mileage and reduce the emissions of a gas-powered car while overcoming the shortcomings of an electric car.
    The Problem with Gas-powered Cars
    To be useful to you or me, a car must meet certain minimum requirements. The car should be able to:
    -Drive at least 300 miles (482 km) between re-fueling
    -Be refueled quickly and easily
    -Keep up with the other traffic on the road
    A gasoline car meets these requirements but produces a relatively large amount of pollution and generally gets poor gas mileage. An electric car, on the other hand, produces almost no pollution, but it can only go 50 to 100 miles (80 to 161 km) between charges. And the problem has been that it is very slow and inconvenient to recharge.
    A driver’s desire for quick acceleration causes our cars to be much less efficient than they could be. You may have noticed that a car with a less powerful engine gets better gas mileage than an identical car with a more powerful engine. Just look at the window stickers(有图形或文字的粘贴标鉴) on new cars at a dealership for a city and highway mph comparison.
    The amazing thing is that most of what we require a car to do uses only a small percentage of its horsepower! When you are driving along the freeway at 60 mph (96.6 kph), your car engine has to provide the power to do three things:
    -Overcome the aerodynamic drag caused by pushing the car through the air;
    -Overcome all of the friction in the car’s components such as the tires, transmission, axles and brakes;
    -Provide power for accessories like air conditioning, power steering and headlights.
    For most cars, doing all this requires less than 20 horsepower! So, why do you need a car with 200 horsepower? So you can "floor it", which is the only time you use all that power. The rest of the time, you use considerably less power than you have available.
Smaller Engines are More Efficient
    Most cars require a relatively big engine to produce enough power to accelerate the car quickly. In a small engine, however, the efficiency can be improved by using smaller, lighter parts, by reducing the number of cylinders and by operating the engine closer to its maximum load.
    There are several reasons why smaller engines are more efficient than big ones:
    -The big engine is heavier than the small engine, so the car uses extra energy every time it accelerates or drives up a hill.
    -The pistons(活塞) and other internal components are heavier, requiring more energy each time they go up and down in the cylinder.
     The displacement of the cylinders is larger, so more fuel is required by each cylinder. Bigger engines usually have more cylinders, and each cylinder uses fuel every time the engine fires, even if the car isn’t moving.
    This explains why two of the same model cars with different engines can get different mileage. If both cars are driving along the freeway at the same speed, the one with the smaller engine uses less energy. Both engines have to output the same amount of power to drive the car, but the small engine uses less power to drive itself.
    Hybrid Performance
    The key to a hybrid car is that the gasoline engine can be much smaller than the one in a conventional car and therefore more efficient. But how can this smaller engine provide the power your car needs to keep up with the more powerful cars on the road?
    Let’s compare a car like the Chevy Camaro, with its big V8 engine, to our hybrid car with its small gas engine and electric motor. The engine in the Camaro has more than enough power to handle any driving situation. The engine in the hybrid car is powerful enough to move the car along on the freeway, but when it needs to get the car moving in a hurry, or go up a steep hill, it needs help. That "help" comes from the electric motor and battery this system steps in to provide the necessary extra power.
    The gas engine on a conventional car is sized for the peak power requirement (those few times when you floor the accelerator pedal). In fact, most drivers use the peak power of their engines less than one percent of the time. The hybrid car uses a much smaller engine, one that is sized closer to the average power requirement than to the peak power.
选项 A、Y
B、N
C、NG
答案B
解析 本文讲了混合动力汽车的原理及其与电动车、燃气车相比所存在的优势(advantages)，而根本没有提及其存在的不足(disadvantages)，因此题干对文章大意概括错误。
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