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      09-26-2013, 10:03 AM   #8
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Drives: BMW M2
Join Date: Aug 2012
Location: Bedford UK

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Originally Posted by solstice View Post
Anyone who want to take a stab at analyzing how this unboosted return to center system works? Is it always in effect or only when the wheel is not turned etc. Here's a piece from car and driver comparing the E90 and F30 that highlights just how important and how much potential this feature has for steering feel.

10] The slip angles producing cornering forces at the tire patches create what’s known as aligning torque—essentially, the tire trying to return to straight-ahead running. This aligning torque is fed back through the rack-and-pinion steering gear to the steering wheel. It’s part of the information the driver uses to learn what’s going on where the rubber meets the road. The K&C machine reported that aligning torque is 64 percent lower in the 328i than in the 335i. While the switch to electric power steering may improve mileage, it’s a bummer for Bimmer driving satisfaction.

EPS commonly use ball screw mechanisms to drive the rack. Ball screws can be reverse driven. So at a guess it is a case of dropping control voltage to the EPS motor when torque is removed from the steering wheel, allowing it to be back driven by the wheels centring action, rather than trying to drive it to the steering wheel position.

The problem is, bumps mid corner can 'simulate' the driver removing torque, which if simplistically done would cause a whole new problem. How does the system differentiate a bump from driver input?