Power steering feedback
Power steering feedback
(OP)
Todays power steering systems seem to cater to the two finger driving style by overboosting the steering assist. I personally find this discomforting at lower speeds, and flat out dangerous at highway and track speeds. A simple unintentional twitch makes a newer PS car change lanes. It is my intention to decrease the power assist of a '04 subaru imprezza.
I can only think of a few options. One is to source a new pump with lower flow, and machine a new bracket to mate with the current mounting. The second would be to install a pressure relief valve between the pump outlet and return. The latter sounds like the easier job, but I am worried about overheating the fluid. Does anyone have any suggestions? Does anyone else out there feel that manufacturers are producing cars with uncomfortable/dangerous amounts of steering assist? (or am I the only one?!)
Thanks!
-Brian
I can only think of a few options. One is to source a new pump with lower flow, and machine a new bracket to mate with the current mounting. The second would be to install a pressure relief valve between the pump outlet and return. The latter sounds like the easier job, but I am worried about overheating the fluid. Does anyone have any suggestions? Does anyone else out there feel that manufacturers are producing cars with uncomfortable/dangerous amounts of steering assist? (or am I the only one?!)
Thanks!
-Brian





RE: Power steering feedback
Fooling with pump and line pressures can impact on how the steering responds at different engine speeds, and might not give a desirable effect.
If you have the resources to make a stiffer spool valve (if that's what it's called) it will make the car non conforming to the safety laws in many countries, but I expect that route will give the performance you seek.
The valve I refer to, as I understand it, is connected to the steering input shaft. It twists according to load. If the twist is sufficient, it opens a port that allows the boost to assist. As the boost allows the output shaft to catch up, the port closes and you have more effort required again. The torsional strength and the degree of twist required to open the port, together with line pressure, controls steering feel.
Regards
pat
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RE: Power steering feedback
A castor adjustment would be nice, but I would like to reduce steering assist by 50-75%. I would simply disconnect the pump, but parking lots become a problem, and that is the least elegant solution.
I also know several other people with the same problem (finding their vehicle too squirrley on the highway due to ultra-sensitive PS), and I was hoping to find something that could be modified and used on other vehicles.
I cannot believe that anyone finds modern car steering systems enjoyable, espically on sporty(er) cars. I have driven older Porsches, VW's, and BMW's, and the steering response is the heart of the driving experience. Are customers today actually requesting less steering feedback, or complaining about steering effort? Being able to put a car into a high speed skid with 1 finger on the wheel seems dangerous, irregardless of what customers demand.
RE: Power steering feedback
You should still be able to get good feel with relatively light weight with extra castor. Heavy is not the real objective, feel is.
It does not cost much to try it.
Is it possible to change the length of the arm of the upright. Maybe the factory race model is different with regards to a relativly easy to replace part like an arm.
Regards
pat
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RE: Power steering feedback
Heavy is an issue too, though. Consider a situation where you are driving on a highway, and something suprises you. Your first instinct will be to flinch. If a steering system is too light, the car will swerve violently, and one may loose control or hit a car in a neighboring lane. A system with less assist (or damping) would absorb that low energy jerk. Right now I even have trouble staying in my lane when I hit a bump, shuffle in my seat, or change a radio station. Steering effort, self centering force, and pulling all tell you important things about the road surface and your tires avaliable grip that just get lost in these systems. I guess I have too many miles and laps with manual racks.
RE: Power steering feedback
Also heavy but very quick steering can be as unstable in such a situation as light but slow.
Regards
pat
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RE: Power steering feedback
RE: Power steering feedback
I don't think you can afford to drop the volumetric flow rate - otherwise you'll run into problems with catch-up. I don't think it is safe to mess too much with the torsion bar - it is critical to the straight line performance of the steering system. Having said that we do have tuning sets of them, and can't really see why one with a higher rate wouldn't do what you want.
So I guess I'm saying that there doesn't seem to be a simple method of getting what you want - and having seen many of the variable assistance schemes on the market I'd say nobody has really cracked this one, even at the OEM level, although BMW's system looks like a good stab (if rather complex), and the EPASs are good for small cars.
Cheers
Greg Locock
RE: Power steering feedback
RE: Power steering feedback
However, it's not an economical solution to a one off. It involves quite a trick process to make the steering racks, which have the variable ratio teeth on them which mesh with a normal involute pinion.
There are other ways also to achieve some on centre stiffness, and that's with various detent mechanism available. Some of the steering gear manufacturers offer solutions like this, some good, some not so. Sadly, good steering feel is hard to come by in modern cars full stop.
RE: Power steering feedback
Also, back in the late 70's I saw proof that a large touring car could lap faster with correctly set up power steering than with manual steering. This was with an LT1 Camero at Mount Panorama near Sydney, Australia.
Regards
pat
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RE: Power steering feedback
I run a 1984 Audi Ur quattro (turbo) which was the first of the road going 4 wheel drive "supercars" and is very similar to a modern Scooby.
The car should have a real bias to driving in a straight line even with your hands off the steering, it is 4 wheel drive and if the geometry is set up correctly it should take noticeable effort to turn. Even new cars from the dealers are sometimes not set up correctly.
Firstly I would advise visiting a specialist (4 wheel drive) wheel alignment depot to get it set up, then see how it feels. (You must tell them if you want factory spec'n or otherwise.)
Secondly I would look to fit "Asimmetric tread" pattern tires. Many friends of mine and I have found these increase the high speed stability on a highway.
Thirdly, running 1 or 2 p.s.i. below spec'n in the tires helps "feel" and lateral grip in the wet particularly. This is assuming you are not too worried about a 20% decrease in tire life !
Keep it sideways !
John.
RE: Power steering feedback
I can't really see that an understeering pig is much help in defining a good steering feel.
The mods you suggest may help, but modding castor is a better approach.
If I were to characterise JonesBoy's issue it is subjectively: "On-centre feel at high speed is too light" and objectively the likely cause is "At high speed steering wheel torque vs yaw rate is too low"
So we need to increase the feedback between the lateral forces in the tyre and the steering wheel, so increasing the trail sounds like a good move, hence the castor suggestion.
Milliken's tuning charts aren't much help for this as it is really a subjective steering issue.
Cheers
Greg Locock
RE: Power steering feedback
Also, lower tyre pressure will make it heavy but less accurate. I think this guy is chasing accuracy.
To set tyre pressure for maximum grip, you need to know a lot about the compound, track, weather, wheel loads and suspension geometry. On a road car, with road tyres, I would be setting the tyre pressure at manufacturers spec or higher, on a race car with race tyres, I would be adjusting pressure to optimise tyre temps, and steering settings to optimise feel.
Regards
pat
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RE: Power steering feedback
Greg, "understeering pig" is a bit strong me thinks
The modern (road going) Scoobies & Evo's have understeer as a characteristic to allow "front wheel drive drivers" to easily get used to the car.
Cheers,
Keep on keeping it sideways !
John.
RE: Power steering feedback
1) Steering effort is too low; small, unintended muscle movements get transformed into unintentional steering inputs. This is more noticeable at high speeds (80-140 mph). Torque vs yaw is too low is spot on.
2) Steering does not provide enough feedback; traction limits are hard to judge.
For instance, I was traveling down a snow covered road with a hardpack center crown and soft, unpacked sides. On my manual rack car (86 VW Jetta, understeering pig king, prior to major suspension mods), when I got close to the edge of the right hard pack, I could feel the self-centering disappear. As the right side tires entered the softpack, the car would pull with increasing torque proportional to the depth of the snow. This is from wheel slip (hardpack side) and the difficulty of the tire plowing the snow aside (soft side). This is your sign to move left. If you do not do not countersteer and gas it, the right side will be pulled hard enough to put you in an uncontrollable, violent skid. With the power steering, the only indication of danger is the power loss, which the viscous diffs mask a bit, making it feel like deep snow all around. Other situations, such as hydroplaning and ice, (espically on single side cases)can be felt as steering pulls, increased/decreased steering effort, and loss of self-centering on manual racks. Even on a dry pave sweeper, when steering effort begins to drop, you know you are approaching your traction limit and should lift/countersteer.
Adding castor would definately help problem #1 with minimal side affects (Thanks for all the input, Pat!). Rallye tires with harder sidewalls will help too, but the car needs a little prep work before I begin the dirt road drivers-ed beatings.
On a side note, I think the understeer to oversteer transition is smooth, predictable, and easy to control through a turn. Heck, I made three confident and smooth (and low speed) drift turns on my snowy test drive before the dealer freaked out and made me turn around. :)
John: Sideways, airborne... as long as the shiny side is up!
-Brian
RE: Power steering feedback
Regards
pat pprimmer@acay.com.au
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RE: Power steering feedback
I noticed some of the effects that Brian is complaining about. They were due to a pair of tires I installed, which had very different behaviour than the stock type tires.
When the lower wider tires were on the front, it was twitchy in a straight line. Strong turn-in, nice feel in a corner. On the rear (skinnier tires in front) it was back to docile straight-line machine.
Yes, it is possiblle there were other problems. It was just a car, and I put a bunch of miles on it!
regards
Jay
Jay Maechtlen