Oerlikon Graziano reveals details of new multi-speed EV transmission10 January 2012
High-performance transmission specialist Oerlikon Graziano has revealed further technical details of its revolutionary multi-speed transmission for electric vehicles (EVs). The innovative transmission uses the principles of dual clutch transmissions (DCTs) to provide seamless shifting and up to 15 percent improvement in vehicle efficiency.
Most current EVs use a single-speed transmission, relying on the electric motor's torque spread to provide adequate performance. However this means the motor spends much of its time operating at only 60 to 70 percent efficiency. Oerlikon Graziano's new transmission instead uses two smaller motors to provide four speeds, running the motors closer to their peak efficiency of approximately 90 percent. The result is an overall efficiency improvement of up to 15 percent, which translates into increased range or improved performance for the vehicle.
"Vehicle manufacturers need innovative solutions to improve the cost, range and performance of electric drivetrains," says Oerlikon Graziano's head of product development, Claudio Torrelli. "Our multi-speed transmission can improve acceleration, top-speed 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 transmission's unique configuration uses two input shafts, each driven by its own electric motor. The concept is similar to a DCT but using 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 synchronise shaft speeds so that no synchronisers are needed.
Following gear selection, the drive torque transfers seamlessly between the motors to complete the shift. Different strategies prioritise economy or performance and the transitions between the two.
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.
Oerlikon Graziano SpA
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