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
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.
