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Home >> BMW >> 2013 >> M3 2D Convertible, Standard Trans >> Repair and Diagnosis (Single Page) >> General Information >> OEM General Information >> Functional Description -- M3 Convertible >> Steering System - Functional Description >> Electromechanical Power Steering >> Reduction gearset
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Reduction gearset

The reduction gear transfers the power output of the servomotor to the rack. The revolution ratio between the servomotor and steering wheel is approx. 21:1.

The reduction gear consists of a belt drive and a ball screw. The ball screw has a rise of 7 mm per revolution. The servomotor drives the toothed belt. The belt drive has a reduction ratio of 2.85:1. The toothed belt drives the ball screw. The ball screw has an internal ball return (5 rotations). The ball screw is noise-optimized.

Fig 1: Identifying Servomotor Components
G09841732Courtesy of BMW OF NORTH AMERICA, INC.
Item Explanation
1 Drive shaft of servomotor
2 Toothed belt
3 Rack
4 Bead chain