问题 问答题 简答题

分析齿轮齿条式转向器的特点和适用范围?

答案

参考答案:

齿轮齿条式转向器与转向轴做成一体的转向齿轮和常与转向横拉杆做成一体的齿条组。

最主要优点是:结构紧凑、简单、质量比较小、传动效率高达90%、自动消除齿间间隙、体积小、制造成本低。

主要缺点:逆效率高,驾驶员紧张,会造成打手,对驾驶员造成伤害。

广泛应用于微型、普通级、中级和中高级轿车上,甚至在高级轿车上也有采用。装载量不大、前轮采用独立悬架的货车和客车有些也有齿轮齿条式转向器。

单项选择题
单项选择题

Scattered through the seas of the world are billions of tons of small plants and animals called plankton (浮游生物). Most of these plants and animals are too small for the human eye to see. They drift about lazily with the currents, providing a basic food for many larger animals. Plankton has been described as the equivalent of grasses that grow on the dry land continents, and the comparison is an appropriate one. In the potential food value, however, plankton far outweighs that of the land grasses. One scientist has estimated that while grasses of the world produce about 49 billion tons of valuable carbohydrates (碳水化合物) each year, the sea’s plankton generates more than twice as much.

Despite its enormous food potential, little effort was made until recently to farm plankton as we farm grasses on land. Now, marine scientists have at least begun to study this possibility, especially as the sea’s resources appear even more important as a means of feeding an expanding world population.

No one yet has seriously suggested the "planktonburger" may soon become as popular as hamburger around the world. As a possible farmed supplementary food source, however, plankton is gaining considerable interest among marine scientists.

One type of plankton that seems to have great harvest possibility is a tiny shrimp-like creature called krill (磷虾). Growing to two or three inches long, krill provide the major food for the giant blue whale, the largest animal on Earth. Realizing that this whale may grow to 100 feet and weigh 150 tons at maturity, it is not surprising that each one consumes more than one ton of krill daily. Krill swim about just below the surface in huge schools sometimes miles wide, mainly in the cold Antarctic. Because of their pink color, they often appear as a solid reddish mass when viewed from a ship or from air. Krill are very high in food value. A pound of them contains about 460 calories-about the same as shrimp or lobster, to which they are related.

If the krill can feed such huge creatures as whales, many scientists reason, they must certainly be candidates as a new food source for humans.

Why does the author mention "planktonburgers" in paragraph 3()

A. To describe the appearance of one type of plankton.

B. To illustrate how much plankton a whale consumes.

C. To suggest plankton as a possible food source.

D. To compare food values of beef and plankton.