Quote:
Originally Posted by ptt127
There's a chart in the data section showing effort vs lateral g that says it all. Hydraulic has the stronger ramp-up in effort before it goes light right before the limit, while electric is just a straight line with a very mild slope. The only weird thing was that C&D seemed to praise this linear behavior as better, but I disagree. That buildup in effort with increasing cornering forces and wheel going light right at the limit *IS* steering feel. It's how the steering communicates to the driver how hard the front tires are working and when they are about to let go.
I certainly hope it is getting better because our 2013 F30 with DHP/VSS is frickin awful. In terms of effort it's the automotive equivalent of a weak handshake or dancing with a partner who doesn't push against you to make a frame. Driving 2 E90s back to back with it was an absolute revelation.
I agree that Sam's article has what we need to know written between the lines. That commitment to friction free and very low effort around town is the sad part. If we keep apologizing for it and heaping faint praise at it, then the terrorists have won.
|
The up-side is that you should be able to completely alter that input torque curve through software. The EPS programming we've seen so far focuses on "solving" the "problems" with hydraulic systems. The thing is, for enthusiasts, these aren't problems, they're desirable traits.
There's nothing inherent about an EPS system that requires it behave this way. With a hydraulic system, the effort is controlled by a spring operated valve. This spring is tuned to provide feedback based on the application. A weakly sprung valve will provide more assist. A stiffly sprung valve will provide less. Now, I'm simplifying greatly here, but I'm hoping this gets the idea across. The input effort in a hydraulic system naturally tracks the feedback from the front tires, because there's a spring directly between you and the front wheels that is providing the feedback loop.
EPS systems use a torque sensor instead of a spring. The input effort is fed to the steering assist computer, along with a TON of other data, such as steering input angle, speed, yaw, etc. We don't really know exactly what the input criteria are, but I've read somewhere that the computer factors in over 60 criteria. The result is this perfectly linear steering load-up. Numbness is engineered in to the product!
On the flip side, if you shift priorities, and you want to
preserve steering feel, EPS has an advantage that hydraulic systems don't: switch off the power to the assist motor and you've got a manual rack. You'll have some additional drag from the electric motor that spins as you rotate the steering wheel, but that's no where near as much load as operating a hydraulic rack that has lost pressure.
What the engineers need to do is dial back the smoothing algorithms. Let the feedback from the wheels travel backward up the column. I believe they can do this, and the greater degree of variability allowed by the electronics will ultimately result in a superior driving experience.