812 Electronic Power Steering

http://www.caranddriver.com/features/electric-vs-hydraulic-steering-a-comprehensive-comparison-test-feature

T

 

Thanks for that !

Cheers

 

Firstly, it's called electric, not electronic. It's basically an electric motor assisting the rack and pinion. The mechanical connection remains. An electronic system would imply drive-by-wire and so far only Infinity tangles with that, without much success it must be said.

Secondly, EPAS (Electrically Power Assisted Steeering) has some advantages and some disadvantages. Many of the things you listed as advantages are in fact exactly the opposite.

1) There are indeed no parasitic losses on the engine in an EPAS. There is another system that addresses that too, the electro-hydraulic power steering. In that application (used in the LaFerrari), an electric motor provides the power needed to the hydraulic pump and there are many reasons that make a hydraulic system preferable, listed below.

2) The function of the power assistance depending on the operation of the engine is not that important. A blocked electric motor though can immobilise the steering completely, whereas a failed hydraulic system means that you have no assistance, but you can still turn the wheel.

3) The electric system is indeed simpler and lighter. It used to be more expensive, but not any more.

4) It 's actually the other way round. EPAS failures are not uncommon and in some cars (in FIATs for example) it was a very frequent failure and you had to change the whole motor. Hydraulic systems are more reliable and durable.

5) All systems can be adjusted, especially in newer cars. The steering weight on the 458 for example can be altered by the factory; a mate of mine did that at Maranello. I believe that dealers can do it too, but I am not certain. They just plug a computer into the car's ECU and change the resistance level by altering the pressure of the system.

6) I would love to meet those so called journos. It is common knowledge that the hydraulic power steering offers much greater feeling. Feel is one of the constant sources of grievance regarding EPAS. A comparison between a 997 and a 991 makes it crystal clear!

Another advantage of EPAS that you haven't mentioned is the ability to actively provide torque to the steering. That is helpful when the car is trying to make a suggestion in the form of a steering input (i.e. help counter steer). It is also helpful in the cause of autonomous driving. In a hydraulic system you would have to add a specialised motor to achieve the same result.

 

The rear is truly a drive-by-wire system but the front remains mechanical with an electric assistance.

I am really anxious to read the first 812 review regarding the EPAS. The journos crucified Porsche in the first iteration of their system...

 

I also have to disagree on all counts. I've been a range rover fan for many years, My latest 2 14 & 17 have the electro-mechanical steering. IT SUCKS! I can't stand it at all!

Near zero road feedback, You can't tell when the front tires are about to lose their grip. I've had 2 racks go bad on the 14, and the car was towed to a dealer because it couldn't be driven . At least with the hydraulic systems you can still drive the vehicle with additional force to steer, when the electro-mechanical there is NO connection between the steering wheel and the rack & pinion system.

I've had to re-train my driving to not feel in the wheel what the vehicle is doing , now I have to pay attention to my lower body and listen more to the tires and road noise. I get more engine power, mpgs, etc ... but it takes out a lot of sense of feel , driving out of the vehicle.

I drove my Jag to a factory show in Boston, HUGE difference in feel between my current Jag and the new electro-mechanical systems. I even told the Jag factory reps " you've ruined the car with that steering system. Get rid of the mechanical hydraulic pump, and put a electrical one in, leave the rest of it alone! "

 

Gents, the journalist do not have anywhere near the in-depth knowledge the likes of you and others find/bring to the forum/world/etc.....I take the reviews of the gents on this forum more serious than what 90% of magazines and TV shows have to say.....anyways, like most of us, I'm always going to be F-car biased

 

I was surprised it was close, indeed even in favor of EAS over HAS. My Porsche is a 997.2 S, and this article has made me curious to test drive a 991.1 to see if there is a noticeable difference in steering "feel", especially as one of the things I love about my Porsche is the steering. Thanks for starting this thread! Very interesting…T

 

I would assume since it's built in the UK, they'd prob use Bosch or ZF , most likely ZF since the tranny and transfer cases are from ZF.

As I said, 2 failed systems where they replaced the entire steering assembly , 2nd time they replaced the steering column. There is are stepper motors in the steering column to attempt to give you feedback and reverse the steering wheel while it's self parking even though there isn't a connection between the steering wheel and the electro-mechanical system connected to the wheels.

 

14 was the 1st gen of the electro-mechanical steering, after they replaced it twice , and the steering column with the stepper motors and sensors it was fine. The current 17 has a bit more feedback with gen 2 system but you can tell it's not physically connected to the wheels. 17 is now 16 weeks old has 9100 miles on it only thing it's had done was a oil change at 7500 miles . I have a major issue with LR/Jag wanting to go 20K on oil, so I do it every 7500 miles.

 

I'm not sure I agree with the thought that just because EPAS is not 'steer by wire' it therefore still has a direct connection to the road. This is about steering feel, so with a hydraulic system the road surface and resistance detail is fed back through the column to the wheelrim via a non-thinking hydraulic PAS. It has no ability to interpret what the road is doing, it simply relays it. Like English to English.

An EPAS system is English to say, French. It is the electric motor and its software that is listening to the road surface and providing what it thinks is the same level of resistance/assistance to the wheelrim. In that sense there is not a direct connection to the road in terms of steering feel because it is the steering ECU that is providing the feel. Which is why a system going bad renders the car inoperable - the wheel cannot be moved, save for what the ECU allows.

Just like in languages, when you first learn a language, you can communicate. But not with the nuanced phrasing and intonation or word-selection that comes from that particular language being your mother tongue. Eventually you get more and more fluent, to such a degree that it is almost imperceptible that the language is, in fact, a learned one.

The 991.1 EPAS was widely criticised, not at first - "considering this is an EPAS it is the best we've driven, but I still prefer the HPAS", but when the next version came out, the 991.1 GT3 - "this update to the EPAS is brilliant and rights many of the issues with the 991.1 Carrera". The point is, like the language, it is something that can be learned, but perhaps never quite made as technically good as a 'mother tongue' HPAS.

We may find other benefits in time though. I enjoy listening to French people talking brilliant English. It's interesting and lends a character all of its own to my mother tongue. Perhaps the same will apply to EPAS in time. The pleasure of hearing Shakespeare in it's native English will always be there though. Just as I suspect there will always be that something about a hydraulic, or better still, an unassisted system in terms of road feel.

 

In all steering systems, bar the brake-by-wire, the steering wheel is physically connected to the wheels, via the rack and pinion. I think you are bit confused.

 

I get what you are saying, but the fact remains that there is still a connection between the steering wheel and the wheels. The electric motor provides the assistance, not the connection. It does corrupt the experience though as it piggybacks on the rack and pinion. By the way, an unassisted system would be awful nowadays (case in point the Elise and the 4C, in vastly lighter cars too), as it would either be nearly immovable, or have a lot of turns making it slow.

 

Interesting discussion since our Acura TL is at the dealer with an electric power steering failure. 2012, with less than 40k miles. Car worked fine, then when re-started, it had the dash warning light of EPS failure. Both the ECU for the steering and another module called gauge control module failed.

With the failure, there was no steering, not even muscling it a little. Luckily, we were not on the highway at speed (yes, we have a highway in Alaska). Car is AWD and was stuck in a parking garage. Getting the one tow truck in town that fit in the parking garage and could get all four wheels off the ground is another whole story.

Dealer said they have seen it before. Sometimes intermittent, sometimes complete failure. Over $3000 to fix (and tow, and rental car, etc.).

Hope Ferrari's is more reliable or has a limp mode to get it off the road or out of the garage.

 

My Corvette C7 had it and it was one of the reasons I got rid of it.

I hope they learn from Chevy's mistake. The car worked like a video game. I swear some programmer genius thought he could create something better than mother nature.

The problem was at very low speeds the wheel was feather light. At higher speeds, the wheel became heavy.

This is the exact opposite of what it's supposed to be doing.

In addition, you could "program" your own feeling which made it seem completely artificial.

Chevy said the system was lighter, which it probably is. But its also less organic and more digital, and that's a bad thing.

Electric power steering reminds me of these systems that make an artificial engine sound through the speakers. It's like using CGI in a movie where before someone would actually blow something up on film.

 

That is the right way of doing it and manufacturers have been doing the same with hydraulic power steering for decades. The reason is that at low speeds you want ease of use, while at higher speeds you need more resistance in order not to make unwanted direction changes. The implementaion though can be bad (for example way too light or heavy), but the principle is correct.

 

HOLY CARP! That had to be as scary as heck. Can't believe there isn't some fail safe if the EPS fails.
That could be catastrophic on a crowded highway.

Dumb question - what happens if the hydraulic power steering fails?

T

 

Typically you just lose the assistance (which makes the steering very heavy because an assisted steering is more direct that a non assisted one) and you still can steer.
I am not sure why an EPS could not behave the same since the steering is still based on a mechanical rack and pinion.