In the case of passenger cars, where engines produce their maximum torques at relatively larger engine speeds, a geometric transmission layout would lead to
An unacceptably high number of gears which would be detrimental to driving comfort.
An unacceptably low overall step jump, resulting in too small a starting torque or
A reduced maximum speed.
A progressive layout is common in the transmissions of today's passenger cars. The associated speed-velocity-diagram is shown in the figure above.
A characteristic for the progressive transmission layout is the speed margin Δn between maximum speed and associated shifting speed, which in this case increases with increasing gears. This takes place with equally small differences in the maximum velocity change Δvi between successive gears.
The step jump in progressive transmissions is given by:
Eq. 3-40
where: αG2 > 1; n = 0,1,2,3..., (z-2)
αG1 and αG2 are constants while the exponent n depends on the particular step.
The individual gear ratios in this case is given by:
Eq. 3-43
where x = gear number
z = number of gears
The overall step jump is given by:
