我们常用的圆柱齿轮传动比小，体积大、结构笨重。

We have used the CYLINDRICAL gear transmission ratio of small, large, heavy structure.

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有些车的转向系角传动比是可变的，这种转向器采用齿轮齿条式，它在中间而不是外部，有不同的齿密度（每寸齿数）。

Some cars have variable-ratio steering, which uses a rack-and-pinion gear set that has a different tooth pitch (number of teeth per inch) in the center than it has on the outside.

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例如，两个齿轮的传动机构中，如果一齿轮的尺寸是另一齿轮的两倍，那么传动比就是2：1。

For instance, in a device with two gears, if one gear is twice the size of the other, the ratio would be 2:1.

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