VW Direct Shift Gearbox
Most development in transmissions for EVs, at least what is shown to the public, is a futher elaboration of electronic controls developed for ICE vehicles.
Most, not all…
Take, for instance, the Modular Hybrid Transmission that Ford has in its Meta One concept vehicle. Two hydraulic clutches permit the 35 kW electric motor to operate either independently of, or in concert with, the diesel engine. This powertrain design enables start-stop functionality and regenerative braking.
Nor is Borg-Warner, the maker of the Modular Hybrid Transmission for Ford, the only manufacturer designing hydraulics into hybrid vehicles. According to GCC, the Environmental Protection Agency in partnership with Eaton Corporation are building a delivery truck for United Parcel Service that will be a full diesel-hydraulic series hybrid. Rather than the battery pack, electric generator / motor and power electronics used in electric hybrids the hybrid hydraulic system uses an accumulator (which stores energy as highly compressed nitrogen gas) and one or more hydraulic pump / motors.
And, while not yet intended for use in hybrids, there is the VW direct shift gearbox (DSG).
The DSG is essentially two gearboxes in one, combining the comfort of an automatic with the agility and economy of a manual unit. The six-speed, transversely mounted DSG has two wet clutches (offering a higher thermal load tolerance than dry clutches) with hydraulic pressure regulation. One clutch controls the odd gears plus reverse, while the other operates the even gears.
This dual approach enables the next-higher gear ratio to become engaged but on standby until it is actually selected. In other words, if the car is being driven in third gear, fourth is selected but not yet activated. As soon as the ideal shift point is reached, the clutch on the third-gear side opens, the other clutch closes and fourth gear engages under accurate electronic supervision.
Because the opening and closing actions of the two clutches overlap, a smooth gearshift results and the entire shift process is completed in 40 milliseconds.
Generally speaking, electric motors are faster; less expensive to build and maintain; and potentially more environment-friendly; whereas, hydraulic actuators are stronger and offer the advantage of continuously variable control. So, while these examples of transitional technology may lead to better drivetrains that rely solely upon an electric motor, they ultimately may have greater impact upon other areas where there is need for hydraulic-enhanced human performance augmentation, such as:
Asking the question of how useful could hydraulics be in electric drivetrains or in other areas, brought to mind another idea. Besides power assist, hydraulics now play an important role in suspensions. As with regenerative braking, what if there was a way to recover and accumulate the kinetic energy transferred to a hydraulic suspension system as it takes the bumps?
