With the progressive diffusion of the electric car, the change seems to be destined to become just a distant memory. Or maybe not. On thermal cars, the transmission is essential for adjusting the torque delivery to the wheels in relation to the driving speed and the driver’s request for the pedal. Thanks to the great ductility of the electric motor, which has the maximum torque already at minimum speeds, with the possibility of controlling the intensity combined with the power by acting on voltage and current intensity, the gearbox becomes redundant since there are already other tools available for the modulation of the thrust. The non-essentiality does not, however, exclude that the transmission can still be exploited to further optimize the performance of the powertrain. It is no coincidence that the examples of multi-gear reducers on electric-propelled vehicles are mainly concentrated in the sports car segment.
The latest is the concept of Dodge Charger Daytona SRT, Stellantis’ first 100% electric muscle car that could be the starting point for a model to go into production in 2024. In its presentation last August, Dodge highlighted how the all-electric Charger features a multi-speed electromechanical transmission. Recently Micky Bly, head of global propulsion systems, explained to Society of Automotive Engineers the reasons behind the adoption of a multi-ratio gearbox on an electric powertrain, statements reported in the September monthly drafted by SAE: “The eRupt system throws the machine very violently, exploiting a great multiplication of the pair. It can then be slowed down to keep the EDM, the Electric Drive Module, in a more efficient window to achieve greater autonomy. So you get a high performance still shot and a good autonomy “.
The adoption of a high transmission ratio increases the availability of torque to the wheels, but at the same time forces the electric motor to higher rotation speeds, compromising its electromechanical efficiency and increasing the friction losses due to the rotation of the mechanical parts. also going to reduce the speed range in which, with the same voltage from the battery, the vehicle can use the maximum power. Hence, a multi-speed gearbox allows you to engage a high ratio to increase the torque for starting from a standstill, then shift to a high gear to reduce internal losses and increase the vehicle’s range. Micky Bly did not provide further information on the eRupt gearbox, in particular on the number of gears available and on its architecture, with the concrete possibility that however these curiosities will be satisfied should the entry into production in 2024 materialize.
The eRupt transmission also works in synergy with the mapping PowerShot to enhance the acceleration performance of the Dodge Charger Daytona SRT. This is a control strategy that for a few seconds extracts extra power from the battery, briefly subjecting it to unsustainable thermal and electrical loads during prolonged use. No application data has been released on the muscle car, but on the Dodge Hornet the PowerShot function guarantees 25 more horsepower for 15 seconds, with the possibility of a subsequent reactivation after cooling for another 15 seconds. The full electric Charger thus has more artifices to emphasize performance and sporty driving sensations, without resorting exclusively to batteries and oversized motors.
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