The electrification of the drivetrain is evolving, becoming ever more sophisticated. Drivers want electric power but delivered at the right time and in the right way to optimise the performance of their vehicles.
GKN’s Multimode eTransmission helps combine the best of electric and combustion engine power, enabling the vehicle to move seamlessly between three different drive modes from two power sources, depending on road conditions and the type of driving required.
Pure electric for those short city trips, a series hybrid mode for when that little bit of extra power is required for overtaking or a hill climb and parallel hybrid for when the combustion engine needs to take over for those longer, higher speed journeys.
Compact packaging requirements
Developed for compact packaging and high torque capacity with superior Noise, Vibration and Harshness (NVH) and efficiency, the Multimode eTransmission is setting a new level of sophistication in electrified drivetrains. The technology has launched on the Mitsubishi Outlander PHEV, which has become one of the most popular global SUVs.
The GKN Multimode eTransmission used as front transaxle offers optimum performance in three different driving modes, with two different power sources:
- Pure EV mode: the vehicle’s front and rear axle are driven by the electric motors, the front motor being attached to the Multimode eTransmission. Energy is sourced from the battery
- Series Hybrid mode: the combustion engine drives a generator to charge the traction battery on-the-go, whilst the car is still only driven by its front and rear electric motors
- Parallel Hybrid mode: the combustion engine’s torque feeds through to the Multimode via a hydraulic clutch, which remains disengaged in both other modes. Front and rear motors then supplement the petrol engine. Battery charging still occurs too.
The Outlander is powered by two 60kW electric motors, one in the front and the other one in the rear. They are fed by a large capacity lithium-ion battery, whilst a petrol engine and generator are also fitted.
Developed by GKN’s engineering team in Japan, the Multimode eTransmission consists of two distinguished gear trains, one for the electric motor and one for the internal combustion engine. Both gear trains have a fixed ratio and jointly drive the differential. The eMotor gear train is permanently engaged with the differential, whilst the combustion engine gear train uses a hydraulically actuated wet-clutch to connect to the differential when required by the drive mode.
Such a set-up required radical thinking by GKN engineers. While standard transmissions need only to consider torque flow from a single source, such as the combustion motor in contemporary systems or the electric motor in eDrive set-ups, the Multi-Mode Transmission has to manage two inputs, the ICE and the eMotor, and 2 outputs, the Generator and the output to the wheels.
The result is a compact system optimised for weight and efficiency, able to deliver 2,000Nm of torque.