http://www.drivecult.com/blogs/culti...at-pas-debate/

This article was written by a bloke who is a test driver ( Vehicle Dynamics Technical Specialist) and seems to knows his stuff.

So basically EPAS isn't utter shite, it's just not quite there yet.

 

"EPAS is fairly new" pffft....

 

That's a bit basic.

I described a while back how the GT86 uses a column-mounted EPS unit which cleverly compares the movement of the lower steering shaft and filters out the 'desirable' feel and transmits the feel artificially to the motor. It has quite complex algorithms to stop the inevitable feedback loop...

Yes, they WILL get there, but it'll be a while yet.

HPAS systems were in reality pretty crap, really until the 1980s when FWD & ULP tyres made them urgently necessary.

 

The piece is crap.

"An EPAS drive system has lots of rotating parts" - one of the reasons EPAS is so popular (with manufacturers) is that it has fewer and cheaper components than HPAS.

 

What he meant was it has a bloody great armature with a lot of inertia. Which is the problem. Alfa has tried decopling it & putting it on a 2nd pinion on the "RHD" end of the steering rack on the Giulietta, so the column is not directly affected. Unfortunately the Giulietta is set up to mimic an Audi (by Alfa's admission) so no hack has exactly creamed their kecks over the result.

Citroen's DIRAVI system had a lot of moving parts - in a complex valve body. But that was in effect DBW with artificial feel like an aircraft!

 

I don't really buy the inertia in the armature argument; the armature is effectively the existing rack albeit with additional machining for the concentric electric motor - which is of course part of the steering rack body and not the rack per se.

My feeling is the 'issues' (such as they are....) with EPAS may well be a symptom of the hysteresis inherent with the sensors and the processing in the system.

 

It's the screw thread driving the magnetic bit, too, which adds friction.

In the same way that worm & roller (and to a lesser extent recirculating ball) systems have a 'deader' feel than the now-ubiquitous rack & pinion systems, I believe.

Again, Alfa's pinion system ought to have helped. In theory...

But yes, the ECUs are set up to ignore extraenous kickback through the systems & its that which requires better understanding.

 

I never understood why you couldn't have a simple system that helped you at low speed, then disengaged completely (i.e. by a clutch or similar) once you're moving.

Fortunately mine isn't working properly and is often too heavy. Which makes things much better.