software > fixed mechanicals.

no matter what 'kinks' there are today in EPS, they will be solved and the systems will be much superior to HPS. with software, the resistance, feedback, control, and even safety can all be programmed in. with a 'dumb' hydraulic setup, it's much harder, although of course software could control hydraulics too.

 

Typically, a variable-displacement hydraulic pump can produce 0 flow to full capacity depending on backpressure. It can be ported to deliver more boost as steering effort rises, essentially leveling out the amount of effort required to turn the wheels at all speeds.

With the engine idling, the vane-type VD pump used in these applications delivers full pressure. As engine speed increases, an eccentric on the rotor begins to center the rotor in the chamber under increasing pressure, reducing flow on demand without lowering shaft speed. At full speed, the pump is essentially "freewheeling" as all pump chambers between the vanes are of near equal size when fluid volume is not needed to turn the wheels.

Larger variable displacement pumps function much like the AC compressor on older cars that incorporated a number of axial pistons riding on a swash plate that could run in the "flat" position when refrigerant was not needed, but shift slightly to answer to the needs of the expansion valve, raising the stroke of the compressor from zero to a half-inch or more. The idea here was to allow the compressor to provide full pressure when needed, but ease off when the system was at full pressure, saving power and fuel.

Variable displacement hydraulic pumps can offer the feature of adjustability to let you set your own Power Steering boost curves for the street or track. It's a pretty slick and simple system, but even though it's all-mechanical, it's a bit more expensive than an electrically driven rack.

 

I am interested to know if the 2014 is getting EPS. Toyota said improved steering performance in PR release.

 

+1.

EPS just came out, over time it will be better then HPS in every ways. That C&D article said BMW have already made big progress on their EPS in these few years, it is already pretty close to the feedback of the HPS. Give it a few more years, no one would miss or want HPS.

 

One of the reasons I hurried up and bought my E9x 335i is because I wanted to know what GOOD power steering and steering feel felt like before they 'ruined' everything with this electronic stuff. And what a wonderful feel it is! I love it! Any change in traction with the front wheels you instantly feel through the steering wheel because resistance level changes and you can respond instantly and intuitively without even thinking. With a loss of traction it makes for safer and easier to recover car. I've had lot of the newer BMWs with EPS and have hated the complete lack of feel. You have no idea what the car is doing at the limits and the first sensation you might have of a skid is through your "butt dyno" sensors and not the steering wheel. EPS is fine for 99% of people, but for those that like to push and feel the limits and have that intimate road feel, HPS is definitely superior right now.

I'm sure that with time the EPS systems will evolve and get better and better, but I haven't been the least bit impressed with the ones I've sampled so far. Actually my old 2007 RAV4 V6 had EPS. It wasn't too bad. It actually felt better than some of the BMW systems, but still nothing like the HPS rack in my E93. Our X5d has HPS also, but the ratio is too slow and the overall feel is so light that it might as well be EPS. The X5 35i with the petrol engine has a quicker ratio with a heavier feel.

 

In the same C&D article, the testers rated the EPS vs. HPS in 10 subjective areas.

The EPS was preferred in 7 areas, tied in 2 areas and HPS was preferred in 1 area.

 

The 2nd gen IS has always had EPS. Lexus re-tweeked the steering twice at least to improve the feel. I had 2012 IS 250 AWD loaner once, and the steering felt a lot better than my 2008.

 

I meant to say. 2014 Tundra and not IS

 

I recently test drove back-to-back 2013 BMW 328i and X1 vehicles. Same engine, different suspension, dissimilar markets. The 328i's electric steering has been panned in some reviews while others believe the hydraulic unit of the X1 to have better feel. I knew this prior to the drives and believe the latter handled a bit better. Not markedly, and the difference frankly may be nothing more than expectation bias.

 

That could (?) be as much a matter of revised steering-gear-ratio as a switch to EPS.

 

FR-S/BRZ has EPS, and their system is known as one of the best.

 

There is a hybrid power steering system that tries to offer a bit of both worlds: the feedback of a hydraulic power steering system powered by an electrically-driven pump, removing the drag-inducing pump from the engine and removing the hydraulic fluid lines. Toyota offered such a system on the 1990 MR2, avoiding having to snake fluid lines over the engine (which was mounted behind the driver) and under the floor to the front steering rack.

But a hydraulic power steering (HPS) system does not allow for the discrete computer control that the electric power steering (EPS) system allows. EPS can be controlled to such an extent that it can override the driver, by providing negative torque. Computer control of the power steering allows for such functions as:

1. Lane-keeping control, turning the car back into its lane even if it drifts over the line (even if the driver inadvertantly turns the car out of lane), offering more than notifying the driver with idiot lights.
2. Hands-off parking assist, such as offered on Lexus and Ford vehicles now, where the computer steers the car back into a parking spot with the driver's hands off the steering wheel.
3. More options in stability control, other than having to rely on careful automated application of specific inside or outside, front or rear brakes to nudge the car back on course. The stability control computer can now control the steering AND the brakes to keep the car on its intended course.
4. Complete steer-by-wire steering, where the steering wheel is detached from the steering column (and steering rack), as may be offered soon in some Infiniti vehicles. Sensors determine how far and how fast the driver turns the wheel, using these signals to control the EPS; the EPS computer will also offer feedback to the steering wheel so that driver can know what is going on through the steering wheel.
5. Completely autonomous, driver-less cars that do not require an electric motor attached to the steering wheel to turn it and levers to control the accelerator and brake pedals.

As offered on aircraft fly-by-wire systems, EPS will start to offer better force-feedback systems. Force-feedback is already offered on some video game systems and will have to be used on true steer-by-wire systems.

The feel of EPS systems can also be affected by how and where it is mounted (I believe that is what Toyota/Subaru did on the FRS/BRZ).

 

I fly an Airbus A-320, the first commercially successful fly-by-wire airliner. While the aircraft handling is superb, feedback is fairly minimal and not particularly modulated to simulate the feel differences in speed and flap configurations. But it is good enough and has the ancillary benefit of flight envelope protection to prevent inadvertant airframe overstress.

I would imagine drive-by-wire steering will need robust engineering with mechanical backup. Many drivers will accept numb but effective steering while the enthusiast will crave dynamic feedback - this should be fairly easy to program?

 

The LFA steering is indeed electric. I still believe Porsche's last gen had the best steering feel out of any car I've driven (I rented a 997.2 C2 for a week back in 2011 and put a couple hundred miles on it). Certainly, it's not fair to compare MR/RR cars to FR cars since the FR cars have an engine weighing down the front axle. Either way, I'm still not looking forward to test driving the 991.


Well, I sure hope so. After all the '11 IS F had a revised steering ECU that made it so much better than the '08 IS F. In theory, we should be able to program anything into an electronic system that a hydraulic system should do. The question is whether the technology is advanced enough (and enough money is being spent) that the hardware is good enough and the software is good enough.


I believe the MP4-12C also uses such a system.

 

The engineers may have programmed in only as much feedback as they felt was necessary. And, of course, you are flying a (relatively) large commercial jetliner and not a small, single-engined Cessna general-aviation plane.

I agree.

The Nissan/Infiniti system supposedly has 3 computers for failure backup purposes and a clutch between the steering wheel and steering rack. When all electronics fail, the clutch engages, connecting the wheel and rack mechanically.