mmarshall

Although the famous and technologically-advanced Citroen DS-19 was the first car, in 1955, to offer power-assisted rack-and-pinon steering, it wasn't until the 1980s that we saw a sustained switch from the old recirculating-ball system (with its notorious free-play in the center) to the much more precise rack-and-pinion units....especially among American-designed cars. Though recirculating-ball systems are sometimes still found in heavier trucks because of their weight-bearing durability, the industry, for the most part, has pretty much gone over to rack-and-pinion units, even among manufacturers like Mercedes and BMW that kept them on their V8s for awhile.

Today, we are facing another revolution in steering-systems....a mass conversion among auto manufacturers from hydraulic-boost to electric-boost (except, of course, among a few very small and light vehicles like the Lotus Elise and Exige that still use unassisted systems for maximum road-feel). Eventually, the way things are going, we may end up with all-electronic steer-by-wire systems, and conventional steering wheels themselves may all be in the museum....but I don't even want to think about that.

I do, though, to some extent, agree with the changeover to electric-boost systems, even though, in some circumstances, it means less road-feel/feedback. Granted, the older hydraulic units, if not overboosted, generally gave good feel (in general, BMW and some Porsche systems were arguably the best for a classic Driver's road-feel), but there is little doubt that electric systems do have some advantages.

First, to describe the main difference between the two, in a hydraulic unit, a conventional power-steering pump circulates fluid (which is somewhat similiar to brake fluid), through hoses and return-lines, and pushes a piston in the steering rack with more fluid-pressure on one side than the other, depending on the amount of motion/input in the steering-shaft. Some systems have a constant-ratio (and amount of boost-pressure).....others, more commonly, use variable-ratio and variable boost-pressure depensing on how far off-center the steering wheel is. Most non-VW/Audi electric-boost systems, in contrast, use a sensor in the steering-shaft and an electric motor, adjacent to the steering-rack that spins a short belt and sends the motor torque to the rack-movement. VW uses a different type of motor with a hollow core that actually fits around the rack and is more-compact.

So than...what are the advantages of the electric units? As I see them, there are several, though one admitted advantage of the older hydraulic units is getting better feedback. First, electric units don't require the car's engine to drive the steering-pump, which draws less power out of the engine (that can mean up to 1 more MPG, which, with new MPG-regulations, is one reason why many manufactuers are adopting it). Second, the system uses no flammable hydraulic fluid, which means that it can't leak onto hot engine parts and catch fire (some vehicles have actually been recalled for that). Third, no fluid means no fluid changes or system-flushing, which can save money in the service department. Fourth, if the car's engine stops for any reason while the car is still moving, with a hydraulic unit, all boost goes with it, and you (may) have to be Hulk Hogan to actually steer.....the dead pump creates a lot of drag/resistance. Electric steering-assist motors can still have some reserve battery-power....unless the battery is totally dead with it. Fifth, if the electric motor does have to be replaced for any reason, it is usually a simpler, less-messy job than replacing a pump, with no fluid or hoses to contend with.....although, admittedly, replacing a pump doesn't always mean going deep into the steering system like with a motor. Sixth, an electric system is more convienient for the driver.....he or she doesn't have to periodically check the power-steering fluid level in the pump like with engine-oil, transmission-fluid, etc.....

Of course, those are simply my own views on the subject. I invite anyone who disagrees (or who has wiews/opinions of their own) to participate.

MM

Ap1_Alan

iTrader: (1)

Other advantages of the electronic system are small space and weight savings.

Some of the newer electric steering systems (like porsche) provide artificial feedback and the average person won't be able to tell the difference.

I8ABMR

I still feel like most purists, that the electric steering movement is a wrong way to go. There are many other means to extract that tiny 1 mpg improvement other than adding the numbing electric steering. Electric steering is great on an LS but I firmly believe that for a car like the new 911 to have that its just watering down the direct and more immediate steering feel we get from a car like a Porsche.

BNR34

iTrader: (1)

Car & Driver did an indepth comparison article on this subject:

http://www.caranddriver.com/features...n-test-feature

BNR34

iTrader: (1)

I don't know about the electric setup being smaller, in BMW's case, the electric setup is slightly bulkier.

Ap1_Alan

iTrader: (1)

The LS and 911 electric steering systems shouldn't be compared, they're nothing alike. I feel that the electric steering gets a bad rep because people compare it to electric systems they've driven on cruisers like the LS and stereotype based on that experience.


My old s2000 had EPS and the feedback was my only complaint, but the steering was very precise. The FRS uses EPS and it's received praise for steering feel (i believe the LFA uses EPS also?). So it can go either way, it's a relatively new technology being adopted and will only improve over time.

If you want to pull the "purist" card, go for an elise and avoid power steering all together.

LexBob2

I recenlty bought an Audi with EPS and so far I like it. It's different and after a very brief adjustment not bad at all IMO.

Ap1_Alan

iTrader: (1)

They save space where fluid lines aren't necessary, in mid/rear engine cars the space and weight savings are more significant than others since they can mount the EPS in the front and don't need to route fluid lines to the rear.

Hoovey689

iTrader: (16)

I was going to mention the weight savings like another member did

BNR34

iTrader: (1)

Good point. I was just looking at the rack itself since the huge electric motor is mounted directly to it. Where the hydraulic pump is mounted remotely on the engine. So if you count everything, I can see the electric set up is being lighter and save some space.

mmarshall

I'm not an engineer myself.....the 1 MPG figure I came up with is the average from what I've read in techincal publications. It could be more or less than that for each specific vehicle.

Some of the better electric units, like those on BMWs and Porsches, do have decent feedback. But I agree with you that it's hard to beat the traditional hydraulic BMW units for steering-feel, unless you go to a completely unasisted unit like on a Lotus.

I basically agree, but I don't see why other small sports cars like the Miata and BR-Z/FR-S don't also offer unassisted steering. The Miata, though, has kept the HPS and not (yet) gone over to EPS.

mmarshall

Some good responses here. Hoovey, you and Ap1_Alan bring up a (possible) good point about weight savings (I hadn't considered that), but some of that would depend on the weight of the average power-steering pump (and fluid) vs. the weight of a comparable electric motor and drive-belt.

BNR34

iTrader: (1)

Ap1_Alan said it best, weight savings are more significant on mid/rear engine cars because the hydraulic pump is in the back and the steering rack is on the front.

mmarshall

I agree. Good point. Having the pump in the back and rack up front means long hoses/return lines and more fluid to fill those lines. Same, of course, with the coolant-hoses for the radiator-to-engine.

BNR34

iTrader: (1)

Yeah, but then those hydraulic lines are tiny with not much fluids in them, I don't see them being that heavy, just a few pounds here and there.