|The second-generation eDCT is targeting A/B class cars. Click to enlarge.|
Transmission specialist Oerlikon Graziano SpA presented more detail on its prototype eDCT dual-clutch-type transmission for electric vehicles (earlier post) at the first CTI Symposium China, in Shanghai. The clutch-less and synchronizer-less eDCT uses the principles of dual clutch transmissions (DCTs) to provide seamless shifting and up to a 15% improvement in vehicle efficiency.
The four-speed transmission uses two input shafts, each driven by its own electric motor—i.e., the concept is similar to that of a DCT but uses two motors in place of the twin clutches. One motor drives a shaft that carries first and third gears, the other drives a shaft carrying second and fourth. This allows pre-selection of the next gear before the previous one has been disengaged, using the two motors to synchronize shaft speeds so that no synchronizers are needed.
|Combined area of high efficiency for the 7 operating states. Click to enlarge.|
Following gear selection, the drive torque transfers seamlessly between the motors to complete the shift. Different strategies prioritize economy or performance and the transitions between the two. The transmission has seven operating states: 1st; 1st and 2nd; 2nd; 2nd and 3rd; 3rd; 3rd and 4th; and 4th.
The first generation of design for the eDCT was targeted at a high-performance GT car application. The second generation is aimed for A/B class vehicles. The modular design allows either an opposing motor design (which is the same as used in the first generation) or a parallel motor design with a high degree of commonality of the parts. All designs have two stages with helical gears, an open differential, electro-mechanical actuation, and splash lubrication.
|Opposing motor design (left) and parallel motor design (right). Click to enlarge.|
The shift control system was developed by UK controls specialists, Vocis Driveline Controls, itself part-owned by Oerlikon Graziano. Having considerable prior expertise with DCT applications, Vocis used a range of existing algorithms from their proven software to cover Driver Strategy, Shift Sequencing, Gear Actuation and safety functions complying with OBDII requirements.
The software for the eDCT is simpler than that for a DCT application. The engine interface is replaced by a motor interface while the clutch and synchronizer control algorithms are unnecessary and are deleted entirely. The prototype uses a Vocis TMS-20 controller that, in addition to direct inputs and outputs, allows robust CAN communication with other controllers on the vehicle to ensure seamless shifting and intuitive control.
Vehicle manufacturers need innovative solutions to improve the cost, range and performance of electric drivetrains. Our multi-speed transmission can improve acceleration, topspeed and hill-climbing ability for a given motor size. Alternatively EV makers can specify smaller motors to give the same performance with less battery drain, providing greater range. The prototype is a four speed system but the technology is scalable to suit a wide range of different vehicle types.—Claudio Torrelli, Oerlikon Graziano’s Head of Product Development
Torrelli and Vocis technical specialist, Marco Fracchia, co-authored a technical paper on the eDCT presented at the CTI Symposium.
Beside the e-DCT technology, the company exhibit single- and dual-speed transaxles, providing solutions for a wide range of electric vehicle applications.
For high performance electric GT car applications, the company exhibited a rear-drive transaxle assembly with twin 125 kW electric motors. For hybrids and passenger or light commercial vehicles, a similar arrangement using twin 35 kW or 25 kW motors was on display.