In conventional automatic transmissions
Perhaps you tell me what happens during the shift?
The gear system uses planetary gear sets
not seperate gears.
Shifts use wet friction clutches and brake bands to connect or brake components in the geartrain.
The 'components' change the torque path from input to output.
Often the path is changed through the 'same'
planetary set using the 'same'
gears with a different input to output torque path.
The shift overlap is achieved by the slip in the wet friction components.
Modulation is mainly from the torque converter fluid 'slip' range, these days at high torque low gear shifts.
At higher ratios the converter is usualy locked by an internal clutch.
Dual clutch layshaft stepped gearboxes use this 'concept' but use 'dry' clutches (usualy for cost reasons and to allow one at least to be used for direct engagement). However these units do use seperate gears.
Because they use dry clutches and there is no fluid 'damper' in the form of an unlocked torque converter, the shifts have to be modulated and controlled on input torque otherwise the shifts would be sledge hammer like.
The same problem for a so called 'seamless' shift mechanisms in a single layshaft stepped gearbox.
The dual clutch boxes are faster for less judder than the single layshaft systems, however they suffer from higher windage and torque loss and a larger size and weight. Manufacturers choose them because they are cheaper than a 'proper' automatic gearbox.
The shift paddles, push buttons and any other space age gear shift gimmicks can be fitted to any of these gearboxes.
The result is the same, slower changes than from a dog ring manual gearbox less efficiency with torque transfer but with a smoother shift AND WITH THE RIGHT TORQUE TRANSFER CONTROL AND MODULATION
less wear and potential damage.
Edited by 24gerrard, 14 March 2012 - 11:08.