Tesla Motors famously started with a two-speed transmission but then ditched that strategy and today most electric cars use a single gear to transfer power from the motor to the wheels, and have no problems with drivability thanks to a relatively flat torque curve. This is great: smooth, comfortable driving, no costly transmission maintenance, no waiting for power while shifting, no added weight from the bulky gearbox. Plus, it's not ludicrous to think that including the unnecessary transmission with multiple gears would be less efficient due to mechanical losses. But Schaeffler is re-thinking the status quo.
Most electric cars use a single gear to transfer power from the motor to the wheels, but Schaeffler is re-thinking the status quo.
In the E-Car Rally, the goal is not to complete the course in the least amount of time, but rather using the least amount of energy, and the alpine driving event allowed Schaeffler to put the Step2 to the test. The rally, as well as other driving tests and simulations, has shown that by using the two-speed transmission with a low and high ratio, the car is actually more efficient. The group reports the gearbox-equipped Step2 reduces energy consumption by about six percent.
With greater efficiency, obviously, the car also can drive farther on a single charge. Shaeffler's vice president of automotive research and development, Uwe Wagner, says, "With a two-speed gearshift system, a low ratio for high tractive force and a high ratio for good overall efficiency also at high driving speeds, we offer higher dynamics and at the same time we achieve a longer range of electric operation."
The Step2 sounds like a fairly simple conversion from a standard internal combustion car. Beyond replacing the powertrain, fuel tank and exhaust system with an electric motor, battery and the two-speed transmission, little else was changed. Schaeffler modified the front axle, but left the steering and brakes alone. No regenerative braking to boost the efficiency numbers here. In terms of power, its output peaks at 70 kilowatts (about 94 horsepower), with 50 kilowatts (67 horsepower) offered in continuous operation. Learn more about Schaeffler's Step2 in the press release, below.
Transmissions increase range of electric mobility
Schaeffler was also represented by an electric vehicle in the E-Car Rally in Montafon (Austria), which was held for the fifth time from July 3 to July 5, 2014. After a prototype with an electric axle (2012) and the Fiesta E-Wheel Drive with an electric wheel hub drive (2013), the team lead by Uwe Wagner, Vice President R&D Automotive at Schaeffler, was competing this time with the Schaeffler STEP2. This is an all-electric vehicle with a drive from the Schaeffler subsidiary IDAM and a two-speed powershift transmission.
The E-Car Rally, which was established by the magazine „auto, motor und sport" and is held on the dream roads of Montafon and Vorarlberg, was not decided by the highest speed but the highest level of efficiency. Efficiency is also the driving force for combining an electric drive with a transmission. „With a two-speed gearshift system, a low ratio for high tractive force and a high ratio for good overall efficiency also at high driving speeds, we offer higher dynamics and at the same time we achieve a longer range of electric operation", concludes Mr. Wagner.
In simulations and test drives, the STEP2 concept vehicle has already achieved a significant reduction in consumption (as energy withdrawn from the battery) of around six percent compared to a comparable vehicle with only one gear. STEP2 is based on a volume-produced compact car. Schaeffler engineers removed the internal combustion engine, the manual six-speed transmission and the fuel tank. The front axle was also modified but the wheels, brake system and steering system were left in original condition. The electric motor was supplied by the Schaeffler subsidiary IDAM (INA – Drives & Mechatronics GmbH & Co. KG), the specialist for direct drive technology. As an electric vehicle, the Schaeffler STEP2 is now driven by an electric motor, which can be coupled with two ratios via a transmission. The transmission comprises a planetary gear set, wet multi-disk clutch, band brake and a lightweight differential. The first and second gear ratios are produced in the transmission by alternately closing the brake and clutch. The vehicle`s battery is located in place of the fuel tank and exhaust gas system below the passenger cell. The Schaeffler STEP2 has a system output of up to 70kW (peak) and 50kW in continuous operation.
Schaeffler`s engineers from the electric mobility sector gained further findings under actual alpine driving conditions during the three alpine stages and demonstrated in the field of mainly standard electric cars that the use of a transmission leads to even greater efficiency savings in terms of kilowatts, volts and amperes. The electric mobility sector at Schaeffler is involved in the development of solutions for all future mobility concepts and with its research and development work for and in collaboration with customers makes a valuable contribution to the mobility of the future.