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F30 / F31 / F32 / F33 (2012 - current)
The sixth generation 3 series, chassis code F30. 2013 model year 328i and 335i sedans now in production. Read the F30 frequently asked question thread for all your basic question and dive into all the details in the ultimate F30 information thread.

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  #76  
Old 11-19-2011, 07:39 AM
LS2 MN6 LS2 MN6 is offline
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Quote:
Originally Posted by Nedmundo View Post
Part of the problem is the weak return to center, which you just explained. My Acura is better in this respect than my dad's Ford Fusion, but it still bugs me. The new Ford Focus is better still, which perhaps reflects the evolution of EPS. I wonder whether the need for EPS to "drive" the wheel back to center is exactly what eliminates so much road feel. The "wiggles" mentioned before -- one hallmark of good steering feedback -- are simply filtered out because the road surface imperfections don't prompt the EPS to "drive" back and forth. I assume EPS could be tuned for this, and hopefully the system in the new 3 Series has been.
A lot of those wiggles are eliminated before you even get a chance to tune.

The biggest reason is that if you manually move the gear back you have to back drive a huge electric motor as well as the rack and pinion. When you get a hydraulic system in manual mode it's difficult to move, however not as difficult as an EPS system, since the hydraulic only back drives the rack and pinion, no motor.

That I think is the biggest cause of road feel removal. The only way to get it back is to have a motor artificially create it.
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  #77  
Old 11-19-2011, 09:17 AM
Nedmundo Nedmundo is offline
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Originally Posted by LS2 MN6 View Post
A lot of those wiggles are eliminated before you even get a chance to tune.

The biggest reason is that if you manually move the gear back you have to back drive a huge electric motor as well as the rack and pinion. When you get a hydraulic system in manual mode it's difficult to move, however not as difficult as an EPS system, since the hydraulic only back drives the rack and pinion, no motor.

That I think is the biggest cause of road feel removal. The only way to get it back is to have a motor artificially create it.
I figured it was something like that. I know electric motors have lots of torque, so if that torque is applied in one direction, it must be very difficult to oppose. Thanks for the explanation.

One question: Could the EPS create the road feel through quick, progressive disengagement of the motor from the rack? In other words, when the system senses force opposite to the assist, it could disengage to an extent, transmitting more road feel, then re-engage for application of assist if needed. Given your explanation above, it seems reduction of assist wouldn't change road feel, so you'd need to either create it artificially with the motor, or de-couple the motor from the rack in some way.
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  #78  
Old 11-19-2011, 10:22 AM
LS2 MN6 LS2 MN6 is offline
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Quote:
Originally Posted by Nedmundo View Post
I figured it was something like that. I know electric motors have lots of torque, so if that torque is applied in one direction, it must be very difficult to oppose. Thanks for the explanation.

One question: Could the EPS create the road feel through quick, progressive disengagement of the motor from the rack? In other words, when the system senses force opposite to the assist, it could disengage to an extent, transmitting more road feel, then re-engage for application of assist if needed. Given your explanation above, it seems reduction of assist wouldn't change road feel, so you'd need to either create it artificially with the motor, or de-couple the motor from the rack in some way.
Uncoupling would be difficult. What the EPS companies try to do is lower the friction in the system. That way it makes it easier to back drive a motor.

For example the Belt Driven systems have a Recirculating Ball Nut Gear that spins in place as the rack back and forth. By lowering the friction in that unit the ability to move the rack without the motor "holding you up" is increased. In a Dual Pinion system they try to do the same by lowering the friction in the worm wheel to worm gear. However you still have to drive the second pinion. This is why inherently Belt Driven EPS are smoother than Dual Pinion ones and can transmit more feedback.

The problem is you can only remove friction so much as you need the motor to drive the system forward with minimal loss. They attempt to make the belts and gears in the system work better one way than the other (for example slanted teeth) so you get more bite when the motor drives the system and less friction when the system tries to back drive the motor.

I think in the future such things will get better and better.
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  #79  
Old 11-19-2011, 10:53 AM
Nedmundo Nedmundo is offline
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Very cool. I've searched the 'net for a good explanation of why EPS deadens road feel, and it's finally here. It seems the the systems can and will probably improve. I just hope our collective experience with relatively feel-free steering won't lower the standards for what constitutes good steering feel. Some of this "dumbing down" might be inevitable, because mainstream buyers often prefer isolation, but I hope the engineers at BMW, Porsche, etc. don't lose sight of the target for enthusiasts.
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