BMW's Electric-Booster Research Engine

Wednesday August 13, 2003

BMW researchers have recorded fuel savings as high as 15 % and produced 1,000 Nm of torque at low revs by using a high-power electric booster motor positioned between the combustion engine and gearbox of an experimental BMW X5.

The aim of BMW's Efficient Dynamics program is to provide greater efficiency, lower emissions and enhanced step-off torque that will benefit stop-start city driving in particular.

The research engine achieves this by removing the thirstiest part of the combustion engine's drive cycle - moving the vehicle from rest.

Combustion engines produce very little torque at low revs, but in electric motors the maximum torque is produced as soon as they start to spin. The experimental X5 combines these characteristics by boosting the combustion engine using the electric motor at step-off. This brings the engine up to optimal speed faster and once the vehicle picks up speed, the electric motor is cut back.

The electric motor draws its energy from an electrostatic high-performance reservoir with no moving parts, saving on service costs and offering a long working life.

The power reservoir also stores kinetic energy generated under braking or when the motor is not under load and also provides current to run the vehicle's on-board networks.