GrantG

I hear you, but the GT2/3/RS are not priced that far from the Maclaren and the upcoming 918 and 960 will be ever pricier with aggregate volumes much higher than the Mac. Seems like a terrible place to cut corners too...

Izzone

Prescription muscle relaxers.....they work great

911SLOW

We covered this before in the technical section but for those that missed it.



Porsche said that they have deleted the servo pump in order to decrease fuel consumption.
So far so good..

But;
if you order the car with the optional PDCC (might be std in the new GT3), they put back an hydraulic pump in its place..







PS. the fact that the electromechanical steering allows them to run the PlayStation inspired and safety oriented pulse steering driver assistance function, is purely coincidental.

Nizer

Pay no attention to the man behind the curtain...

Mike in CA

The rumored price of the 991 GT3 is $140K, a Maclaren is $230K. $90K is a fair amount of wiggle room with regard to what kind of content to provide. We're seeing the first generation (for Porsche) EM steering and it's considered to be among the best of it's type, which includes Ferrari, BMW, et al. I would hope it continues to improve to the point where this discussion becomes irrelevant.

Would the same hydraulic pump be used for both PDCC and power steering, or would you need two? Also, would the demands on a pump and load on the engine be the same for both PDCC and PS? Seems possible that either way, there could still be efficiency gains from EM steering, small though they might be. But maybe I'm missing something.

GrantG

How? If it's an electric motor that is driven by the onboard electrical system (battery and alternator), how would a little more (or less) electrical efficiency matter for gasoline efficiency? I think the alternator always draws about the same amount of motive force (parasitic loss) from the engine, within reason.

911SLOW

Mike , I might be against this on principle alone, but, I do fully understand the challenges that Porsche is facing ,trying to get ready for the EPA fuel efficiency rules, which will probably change forever the cars we drive.

OTOH, I do not understand why it had to be done this way.

I mean, using the available technology to push down their fleet's MPG numbers (see 918 prototype) is inevitable.
But, where do we draw the line for one of the best sport/fun/toy cars ever made?


Why they didn't use the electric steering assistance from the Cup cars? It is cheap, simple to make (people in this forum have managed to convert 996 cars using simple electric pumps from other manufacturers) and would have removed all the parasitic losses, freeing up a few HP, while keeping consumption down a bit.
(BTW the published figure for the 991's electromechanical-steering fuel savings is 0.1L/100klm_)

And on the same page;
why do they have to sabotage the 2 major interactive inputs between the man and the machine?
why do they have to implement all these gismos that can't even be turned off?
I have no real issue with driver aids, but please, allow me to choose!



I am under the impression that I do know the answer.
They are doing it because the majority doesn't give a damn.
They have done their research. Have no doubt.

Will the new cars be more efficient? Sure

Will they be faster and safer. Hell yes

Do I care? Of course not; these are irrelevant.

GrantG

And the top 911 (GT2RS) will be more expensive than Maclaren (not to mention 918 and 960 which will be much more). Yes, it would be nice to think EM steering will be as good as hydraulic, but then again, hydraulic never became nearly as good as manual after 65 years of trying...

Mike in CA

I think we're off track a bit, Grant. I was responding to John's post about eliminating the hydraulic PS pump, then adding one back for PDCC. I questioned that if two hydraulic pumps were required for PS and PDCC then EM steering saved one pump. If one pump does both jobs, then the load on the pump and therefore the engine might be less if the PS function was eliminated by having EM steering. Either way, there could still be a gain in efficiency from reduced load on the engine by having EM steering, even if the car had PDCC.

I wasn't originally making a point about electrical efficiency and gasoline efficiency so I'm not sure what your comment about that refers to. But FWIW, the more electrical devices that are being run, the harder the alternator has to work and the more parasitic loss there is from it's load on the engine. There is no free energy lunch. My Audi A3 TDI even has a monitor which reminds the driver to shut down unused devices like ventilation fans and seat heaters to improve fuel efficiency.

John, I appreciate your perspective, and I don't necessarily disagree. It's confusing, though. I read posts from critical, intelligent people (some of whom I've met and driven with personally), with racing backgrounds, advanced engineering degrees, and plenty of seat time in all kinds of road and race cars, including owning a 991. They are very enthusiastic about the car and feel that EMS, PDDC, PTV, etc. don't dilute the driving experience. OTOH, there are others who see these features as the end of Porsche as we know it. Are the former delusional? Are the latter hyperbolic? Maybe I'm the crazy one! Like I said, it's confusing....

stevecolletti

I couldn't agree more.

I want everything to be under my control, even if I need to disable it each time.

My worry is that once we have all these unkillable 'aids' in place, and no physical connection to the control mechanisms, it will be left to the programming to decide what I can and should be allowed to do based on what (location, carbon footprint, fuel mileage, noise, etc)?

I can easily imagine flooring the throttle sensor on our pdk-equipped 'sports car', and let the computer decide what level of performance should be allowed. I hate to sound paranoid, but I spend too much money on these cars for them to have another master.

GrantG

Got it - sorry

fbirch

As far as the cost issue is concerned: Toyota used an electro-hydraulic steering system on the MR2 back in the early 90's, and BMW used electro-hydraulic steering on the fisrt generation of the new Mini Cooper. Neither of those are expensive cars, so electro-hydraulic steering units don't have to be expensive. They are also more efficient than pure hydraulic systems, but perhaps fractionally less so in comparison to electro-mechanical systems.

Mike in CA

Which brings the discussion back full circle. My original post about cost, or more specifically cost as it relates to availabilty, was that Tadge Juechter, chief engineer for the new Corvette, said that they used EM steering because no supplier now would bid on a hydraulic system. I thought that was interesting and relevant. An electro-hydraulic system may not be inherently expensive, but if a manufacturer can no longer buy component parts for a reasonable price, you can see how it might become so.

I'm not necessarily arguing for EMS, I'm just pointing out one of many realities that car makers are faced with in today's environment, and suggesting that it might have something to do with the decisions that are being made about the kind of steering system that goes in our cars.

Mike in CA

No sweat.

fbirch

Looks as if Nissan and Hitachi are making electro hydraulic power steering (EHPS) units right now:

http://www.nissan-global.com/EN/TECH...IEW/ehpss.html

Hyundai is also using EHPS (scroll down the features list):

https://www.hyundaiusa.com/about-hyu...-20120613.aspx

Didn’t spend a lot of time searching, but there are probably a few others still in production. It may not exist within the supplier network that GM uses. But if a car manufacturer really wanted EHPS, given that at least a dozen different manufacturers have used this system over the recent past in some pretty low cost models, it can’t be rocket science to work with a supplier to create this capability at a reasonable cost.

I can believe that an electro-mechanical system might ultimately be cheaper by a few dollars per vehicle because it eliminates a few low-cost parts, and that it would yield a very fractional increase in fuel economy. If .1L/100KM is really the gain relative to pure hydraulics (20MPG improves to 20.16 MPG if my quick math is correct), the improvement will be even less than 0.16MPG in comparison to EHPS, probably a lot less. Those improvements may have been the basis for Porsche to adopt electro mechanical steering, or maybe it was something else entirely, such as long-term reliability, controllability, packaging, etc.