Power Steering on Performance Cars

The vast majority of my sports cars have been old English ones that didn't have big enough boots on them to need assisted steering (except my Jensen CV8 which I had a fair bit of rubber on and which used an MG Magnette rack - OK on the highway but a PITA for parallel parking).

These days, tires are wider and stickier than ever before and power assist has become an issue.  I don't mean the retro fitted kits - I make mock of the guys with cars like MGBs that want power steering because they are weak armed, although I try not to apply that to the very elderly or the owners with physical impairments that require PAS.

My question is whether my impressions about modern steering systems is correct. Obviously I have driven fewer modern cars than many here, but I have found that all of the cars that use EPS lack feedback - lack feedback or steering feel, to one extent or another. 

I know it isn't just me as one of my cars, a BMW Z4MC, had a unique power steering system fitted by the factory, no doubt at some expense, rather than the EPS used in the regular Z4 models.

I have tried some EPS systems that struck me as not being too bad (a C6 - can't recall what year) but mostly I have found that they lack the same feel as hydraulic systems offer and some have widely varying assist levels between low speed parking and high speed driving.

Has anyone found a really well designed EPS with good feel throughout the range on the new cars?

You can definitely tune EPS poorly. I've driven things where there was barely any indication that the steering wheel was connected to anything. But you can also do it very well. That Z4M was from the time when EPS was new and everyone was struggling to figure it out. Lots of performance cars held on to HPS for a long time for that reason. Porsche didn't switch to EPS until the 981/991 generation (2013). I seem to be blessed with not being overly sensitive to bad steering feel, but both of my cars (fiesta st and 981 cayman) have EPS and both I find to be pretty decent. The fiesta is even a column mounted assist system, which is usually the easiest to screw up. I think both are better than my former Z3M roadster with HPS, but that thing was surprisngly numb even with grippy tires on it.

Jaguar non-power steering cars are superb in feedback feel  when they went to power steering it became over boosted. With zero feel. 
luckily it's a GM pump and a relatively simple matter to get a different sized pulley to provide a better feel.  
      Rob Beere provides a dial assist to make the boost whatever you want and with that you also get a better feed back.  

The current Porsche GT3 has the best feedback I've ever felt in a non-race car and they are equipped with EPS.

I haven't driven a wide range of moderns either so my experience is very limited, what few I have driven with EPAS were horrifically numb and  uncommunicative.

In my old 1986 Saab 900 I swapped for a 1979 900 EMS manual rack which was fun at speed but a big chore when slow or parking.

Gave a go at translating this old article back when I was deep in the throes of Swedefreekiness...

Stig med servo!
En annan nyhet på Saab-sidan är att Stig Blomqvist snart kommer med servostyrning både i rally och rallycross.Roger Johansson har ju i år provat ut servostyrning i rallycross och fått allt att fungera.Premiär för Stigs del med servostyrning blir det i Svenska Rallyt.
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The other news about Saab is that Stig Blomqvist will soon get power-steering both in rally and rallycross. Roger Johansson has tried out power-steering last year in rallycross and got it all working. The Premier for Stigs part will be in the Swedish Rally.
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Vi har länge diskuterat om det inte är dags att prova servostyrning,säger Börje Jarl,ansvarig för den tekniska utvecklingen på Saabs tävlingsavdelning.Men hittills har vi varit begränsade av att de servostyrningar som funnits inte varit tillräckligt reaktionssnabba.Det problemet är nu borta.Den nya servon till 900:an är otroligt snabb och har mycket hög precision.
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We have long discussed about it but have not had time to test power-steering, said Börje Jarl, responsible for the technical development of Saabs competition department. But until now we have been limited to power-steering which is not of sufficiently quick reaction. The problem is now gone.The new servo to 900:model is unbelievably quick and has great high precision.
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Servostyrningen för Saab innebär inte bara att bilen blir mer lättstyrd.Nu kan stallet också börja vidareutveckla chassiet.Man kan t ex använda väsenligt bredare däck.
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Power-steering for Saab does not involve just the cars becoming more easy steering, now it is stable enough to also commence developing the chassis. One can use important wider tires.
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Jag har hittills gjort en hel del prov med servo,säger Stig Blomqvist.Resultaten är förbluffande.Bara genom att lägga på bredare däck kan jag åka mer än en sekund fortare per kilometer,vilket i t ex RAC+rallyt skulle innebära drygt 10 minuter kortare körtid på sträckorna.Dessutom blir precisionen bättre än tidigare och jag blir inte trött på långsträckorna.
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I have so far done the whole trial part with servo,says Stig Blomqvist.The results are amazing.Just through putting on wider tires I can drive more than one second quicker per kilometer,which in Rac-rally would mean more than 10 minutes shorter drivetime on the stages. In addition to being of better precision than earlier, I do not get tired on long stages.
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Det Saab främst kommer att utveckla under året är just vägegenskaperna. Motor och växellåda anser man vara nog utprovade idag.Turbomotorn ger nu 270 hästkrafter och ett vridmoment på 37 kpm.
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Mainly during this year,Saab will be developing the road-handling. The motor and gearbox are considered to be improved enough today, the turbo-motor now gives 270 horsepower and the torque is at 37 kpm.

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So far off topic now that I'll go ahead whole hog and also lament another loss of the modern era --- it seems that actual paperbound factory service manuals have become a quaint thing of the past in many cases.

It was great to have such good reference material.

For me , I want EPS to park and move at slow speeds  on my  older cars , 

do some of them "time out" above a certain speed ?

Weirdly, the S2000 had EPS wayyy back, relatively, and I don't recall mags of the day having a single bad word to say about it. Honda just nail it right the first time? SW20 MR2s had it in the early 90s, and no one seemed to mind either.

Haven't had a chance to watch it, but this might be of interest.

https://www.youtube.com/watch?v=YqxwPmPW_yA

In reply to californiamilleghia :

Yes, better, in fact.  The can have a speed input and vary the boost by speed, not just turn it off.

Something to think about - it's easy to mistake weight for feel. A good EPAS system will have the latter but not necessarily the former. It's a mistake a lot of us make when driving EPAS cars for the first time. I've never been a manual steering purist, I don't equate the need to work harder with quality.

One thing EPAS allows is a fully controllable assist level, more so than you could with a simple pump unless you had extra complexity in the system. If you can dial the assistance up and down depending on a whole bunch of factors, you can get away with things like ridiculous amounts of caster without the steering characteristics that usually result from it.

I've driven ND Miatas with both EPAS and hydraulic PS and I have to say that steering feel just isn't something you notice as being radically different.

In reply to Keith Tanner :

This. I hate sport modes that just make the steering firmer (looking at you, Focus RS) rather than make it give you feedback. My '14 Mini JCW has nicely weighted steering, but no feedback that I can tell. My '07 E91 has better feel (HPS) but too much assistance. I challenge anyone who has driven a good modern car to drive an unassisted sports car and see how they truly compare. I am a manual steering purist when it's on the right car, and my Elise is definitely the right car. As long as the front wheels are rolling at any speed, the inputs are not hard at all thanks in part to having only about 400lb on each front wheel. 

fatallightning said:

Weirdly, the S2000 had EPS wayyy back, relatively, and I don't recall mags of the day having a single bad word to say about it. Honda just nail it right the first time? SW20 MR2s had it in the early 90s, and no one seemed to mind either.

I just googled "s2000 steering feel" and pretty much all the results are people complaining about it, so there's that...for whatever a bunch of people on the internet is worth (probably next to nothing).

The MR2s were still hydraulic assist, just the pump was up front and powered by an electric motor instead of a belt drive on the engine. Interestingly, porsche never did that and just ran a pair of lines the length of the car and never seemed to have any issues with it. Wonder which way was actually cheaper/easier.

In reply to cyow5 :

Certainly the biggest issue with a bigger tuning envelope is that it allows the manufacturers to tune the system to what the average idiot customer thinks a sporty car should feel like, not what it actually does feel like. It's about the only issue I have with the Civic Type R, the suspension and throttle tunes across the modes are all pretty reasonable, but the Rrrrr mode steering is clearly just heavy for the sake of being heavy. If you could pick and choose from the settings it would be a non-issue, R mode suspension and throttle, sport mode steering.

Caveat: I've been doing more thinking than researching. The following is  my current working theory, possibly enunciated via my hindquarters.

I've been trying to get my head around it, and while I don't think this is applicable to all EPAS, it seems that the form factor is often a worm drive, and what's going on is that the strain gauge in the steering column finds out what you're trying to do and tries to help you do it. The thing is, that's a system that can't really have any play in it, so the wheel more or less goes where the motor puts it, but you're telling the computer where you want the motor to put it. Beyond a certain point, you're trying to drive a worm gear with a spur gear, and that's not really going to happen nicely. So... To a great extent, while the shaft you're holding by the wheel goes all the way to the rack, you're more controlling the motor than controlling the rack, and the assist system has no way of providing feedback (e.g. another strain gauge below the motor that would allow it to, say, vary the force at the wheel based on changes at the tire). A small kick back through the rack here would basically get bound by the difficulty of back-driving a worm.

In an attempt to TL;DR, I think you can think of EPAS often as thinking to itself "driver's trying to move the wheel *this* hard, so go *this* fast to try to keep up with the request." Naturally adjusting constantly.

By contrast, a hydraulic system uses your force to turn the wheels, and only *assists* based on the effort going in; in one example, you're flexing a torsion shaft, and the flex that ensues opens a proportional valve to provide assist. So there's an assist curve, but the important summary is "the driver's trying to move the wheel *this* hard, so add *this* much force."

In the latter system, changes in perceived effort based on changes at the tires are naturally communicated; if grip falls off, centering force falls off, force on the shaft falls off, the torsion spring returns, and assist falls off.

I think you're a little off base but the concept of "assist" vs "doing it for you" is at least somewhat valid. Also the concept you described towards the end of the first paragraph is why column assist systems tend to suck the most, because the assist point is basically directly attached to the steering wheel and the further away it is from the tires the more feedback gets filtered out, regardless of how the system is tuned.

dps214 said:

I think you're a little off base

I would not be the least bit surprised. :)
Just out of curiosity, happen to be able to point out where I went most obviously off the rails?

Of course, I'm curious enough I should really go read more about how they actually work instead of pawning that off on you...

Well, you are turn the wheels yourself.  Turn off your engine and turn the wheels, they still move just fine in an EPS car (they wouldn't if you were trying to back-drive a worm gear)  Its not just the motor doing the work.  

Can you show a diagram of the worm setup you are describing?

In reply to ProDarwin :

That's exactly where we went to the talking-out-my-butt aspect; it was based on a peek at an assembled aftermarket EPS and what it appeared to be. That said, and quick search did indicate that worm drive is one of the systems used. My search-fu is crap today for finding a good overview, so one example is from a seller of associated lube... It does seem that a relatively high-angle worm drive would be back-driveable, but it would still have some of that intrinsic stiffness of doing so.

https://support.newgatesimms.com/electric-power-steering-worm-gear-lubrication/

This jibes with what I observe about my Mini's power steering; the power-off effort is way higher than I would expect it to be, but you can certainly turn it. The F56 rack has the packaging impression of a worm drive arrangement:

All that said, I'm sort of explaining how I got to what I was thinking; as I caveated (totally a word!) and was pointed out, I almost certainly don't have it all (or even mostly?) correct.

Hey, here's the site of the place that does the aftermarket system that all my assumptions are based on... Guess I know where I should start reading, huh?

https://www.dcemotorsport.com/Home/EPAS

I guess I could also refine my summary of the electric system assist: It's got a load cell indicating driver input, and it's probably more accurate to say that it's got an algorithm that chases keeping that within a window, also influenced by what the system knows about the motor's output for a given level of drive power modulation. So not so much "move the wheel this fast", but much more about driving the motor X hard based on Y driver input and Z resultant motion and ZZ other data than simply an "amplifier" of driver force.

Oof; I really should have just started an "enlighten me" thread, after doing some research, instead of derailing this one. Mea culpa.

Fun fact - if you take a full CAN log of a drive in an ND Miata and then feed it back into the system, the car will go through the motions. Speedometer works, tach works, blinkers blink...and the front wheels will turn. Not fully, but the assist requested at the time is rendered again and that's enough to get the rack moving at least partially.

You can do the same to a rack on the bench and make it twitch around.

It's got a rack mounted motor instead of a shaft mounted one so I don't know how different the mechanisms are. But it's hilarious to watch. 

I am experimenting with a hybrid electric power system that I stole from a Volvo. It is a electric pump feeding a conventional power steering rack. In this case, a Mustang rack.

Relatively easy to mount and wire in, and saves on figuring how to mount a pump to the engine accessory drive system.  The pump itself is hard wired "ON" al the time with a key-on power source to tell it to run. There are two other wires that would control pump output based on speed, but since they are not fully understood, it will be operating at full assist all the time. Love to understand more about how the feedback circuits work with the other two wires.

What is steering "feel?"  A 1968 Cadillac Coupe DeVille steered like a boat--it was designed to make you not "feel" what was going on, so in that case, feel was deleted, as it was in many of the older-era hydraulic setups.  Nobody wanted to feel the steering in a car back then.  It's hysterical that the "feel" argument (mainly of the popular car mags) against EPS has still not ended after so many years.  Electric power steering is great, amazing, and perfect.

For ammo, I have owned Honda, Toyota, and VW vehicles with electric power steering, and all worked/work flawlessly and felt dead-on sporty in contrast to old-world hydraulic setups.  I also built my own EPS setup using Unisteer parts (EPS unit and a lousy R&P setup made for the car); it worked great, managed its own levels of input with an electronic controller, and it felt great all the time.  There was no feeling of loss for fluid leaks or slop or belt squeal.  The same car (due to chassis swap) then went back to a 90s-era hydraulic system with factory R&P that still feels great, but no more or less than the EPS setup.

Here's a great differentiator:  You can smash the steering in an EPS system to the stops like a total slob, and you'll never get belt squeal or leaks.  Win.

rustomatic said:

Here's a great differentiator:  You can smash the steering in an EPS system to the stops like a total slob, and you'll never get belt squeal or leaks.  Win.

That shouldn't cause squeal or leaks in a hydraulic setup either.  You'll just hear the pump relief valve open when you hit the end of travel.  If that's causing a leak or belt squeal, either something is worn out, damaged, or a bad design. 

My old 88 Fiero GT had manual steering (front tires were 205x60-15 but also the weight was not so much on the front in a mid-engined car as it would have been in a front engine car). The steering was brilliant (pre-88s not quite so much).  My Solstice GXP has good steering feel but during the overlap in ownership, it was still like a breath of fresh air to get into the Fiero again.

californiamilleghia said:

For me , I want EPS to park and move at slow speeds  on my  older cars , 

do some of them "time out" above a certain speed ?

 

Yup. EPS is basically a manual rack with an electric motor attached to it, so the manufacturer decides how and when the motor engages. If you're really desperate for a manual rack you can just unplug the motor, but with wide tires and quick rack ratios that might not be terribly pleasant even at speed.

rustomatic said:

What is steering "feel?"  A 1968 Cadillac Coupe DeVille steered like a boat--it was designed to make you not "feel" what was going on, so in that case, feel was deleted, as it was in many of the older-era hydraulic setups.  Nobody wanted to feel the steering in a car back then.  It's hysterical that the "feel" argument (mainly of the popular car mags) against EPS has still not ended after so many years.  Electric power steering is great, amazing, and perfect.

For ammo, I have owned Honda, Toyota, and VW vehicles with electric power steering, and all worked/work flawlessly and felt dead-on sporty in contrast to old-world hydraulic setups.  I also built my own EPS setup using Unisteer parts (EPS unit and a lousy R&P setup made for the car); it worked great, managed its own levels of input with an electronic controller, and it felt great all the time.  There was no feeling of loss for fluid leaks or slop or belt squeal.  The same car (due to chassis swap) then went back to a 90s-era hydraulic system with factory R&P that still feels great, but no more or less than the EPS setup.

Here's a great differentiator:  You can smash the steering in an EPS system to the stops like a total slob, and you'll never get belt squeal or leaks.  Win.

For me, and I think others in this discussion feel is the ability to easily sense what the front tires are doing as they approach the limits of adheason.  As you pointed out a lot of old school hydraulic systems had none.  Your only clue that the front tires were sliding was the sound and the fact that the car wasn't turning.  My truck with its conventional hydraulic system has the weight without feel that Keith was complaining about. 

I think that some of the early EPS systems were just not very good and/or installed on cars that the manufacturers didn't think justified the time to tune for good feel.  I'm not convinced that there's anything inherent in either an electric or a hydraulic system that dictates feel.  I've certinally driven cars with both systems that have great feel and cars with both that have crappy feel.