Electric power steering · Focus Mk3, opened up

Torque path: column, torsion bar, motor, belt and ball nut while the motor is helpingTorque sensor window: the two marks part as the torsion bar twistsRack, tie rods and knuckles: inner wheel turns further than outerThe Mk3 Focus has no power-steering pump. A torsion bar at the bottom of the column twists slightly when you turn the wheel; the torque sensor reads that twist and the control module on the rack tells the motor how hard to help. The motor drives the rack through a toothed belt, most likely onto a ball nut around the rack, which is how rack-mounted belt-drive EPAS is usually built. Assist is greatest when parking and fades with speed, so the car is light in a car park and steady on the motorway. The 2012 Focus sedan has a 14.7:1 overall ratio and 2.6 turns lock to lock, so the road wheels reach about 31.8° on average; the inner wheel turns further than the outer. The assist curve and tyre loads shown are illustrative, not Ford's calibration.

Interactive figures of a Ford Focus Mk3 sedan (C346, 1.6 Ti-VCT, PowerShift automatic). Drawn with the MIT-licensed anatomy isometric kit. Not affiliated with Ford.