Electromechanical Power Steering: Notes

With the E92, an electromechanical power steering (EPS: Electronic Power Steering) is introduced in the BMW 3-Series. The EPS will be introduced with diesel engine M57TU2 in 09/2006. Gradually, the EPS will be introduced as a CO2 reducing measure on all other models.

The electromechanical power steering (EPS) differs from conventional hydraulic steering in that it has steering servo. The EPS supports the driver with an electrical servomotor instead of a hydraulic drive. The servomotor is only active when the steering is used. This means that the servomotor consumes no power during straight-ahead driving.

Electromechanical power steering offers the following advantages:

lower steering forces on parking
integrated, driving-speed-dependent power steering assistance (Servotronic)
lower bumpiness when cornering as well as lower steering wheel vibrations
active steering wheel return
saves up to 0.2 l of fuel per 100 km, thus reducing CO2 emissions
no hydraulic fluid necessary

On the E92, the drive for the EPS is arranged parallel to the axle. The arrangement parallel to the axle has advantages compared to arrangements on the pinion or steering column. The arrangement parallel to the axle has advantages with regard to the steering track rod forces that can be achieved, the vibrational properties as well as the acoustic pattern.

Fig 1: Identifying EPS Control Unit Components

Courtesy of BMW OF NORTH AMERICA, INC.

Item	Explanation
1	EPS control unit
2	Servomotor
3	Steering box
4	Steering-torque sensor