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In order to calculate the ratios of intermediate gears there are two formal methods that are named according to the type of layout:

Progressive layout

Geometric layout

In the geometric layout, the speed jump is constant when shifting in all gears. The resulting speed-velocity-diagram is shown in the figure.

The shifting speed nu at which a shift into the next smaller gear results in the maximum speed nperm being achieved, remains the same for all transmission ratios.

From

Eq. 3-29

Results

Eq. 3-30

The step jump αG remains the same when shifting in all gears. In a transmission with z gear levels, its size can be determined by the total step jump αGtot, which is also called the setting range or the spread of the transmission. As a result, the step jump is defined.

Starting with the ratio of the largest gear i(z), the remaining ratios can be determined by the formation of a geometric series.

Finally Eq. 3-35

While the difference Δn between the permissible maximum speed nperm and shift speed nu remains constant, the difference of maximum velocities of successive gear levels Δv gets larger with a decreasing ratio or increasing gear number.

Eq. 3-39