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Steer by Wire


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#1 gruntguru

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Posted 04 May 2021 - 21:45

This is bound to become a very controversial topic yet this article (in revealing the technology has been adopted by Toyota for its bZ4X electric SUV) treats it in a very matter-of-fact way. https://www.designfa...rearticle&pn=04

 

 

A uniquely shaped steering wheel, which eliminates the need to change grip when steering, is part of the vehicle's steer-by-wire system. Using steer-by-wire technology does away with the mechanical connection through the steering shaft and results in a more direct response between steering operation and driving force. It also enables the vehicle to turn with less steering angle and more precision, but it could take some getting used to for some drivers.

 

Whether the steer-by-wire system makes it to the production model is not clear but it does seem the time is right. With more and more people prepared to accept hands-off driving or cars with no wheel at all, why not steer-by-wire?



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#2 Greg Locock

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Posted 04 May 2021 - 23:25

It would be a significant step forward in safety and cost. Well actually we'd probably accept the same level of safety and go for a bigger cost save. I'd have thought by now we'd have a good understanding of the failure rate of the epas/rack combination. First time I was driven in an SBW was in 1988, in the first car we built with ABS and TC and active suspension. Every single system failed within one lap, the very mechanical clunk as the steering column reconnected was reassuring.



#3 Ross Stonefeld

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Posted 05 May 2021 - 14:07

Thanks, I hate it.



#4 Canuck

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Posted 05 May 2021 - 19:06

This irritates my tinfoil hat a great deal. Of course I don't spent a lot of time thinking about the dangers of the steering column pointed at my chest, but I'd like to think* that's been largely mitigated by smart design and airbags.

 

* I'm telling myself that this is true regardless of real-world information.



#5 kikiturbo2

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Posted 05 May 2021 - 22:08

considering the lack of steering feel in conventional EPS steering, I really find nothing positive about SBW...



#6 desmo

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Posted 05 May 2021 - 22:34

Has nobody really yet done a good job of EPS? 



#7 Greg Locock

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Posted 06 May 2021 - 00:18

To be honest the aspirational target for EPAS is 'as good as HPAS' for steering feel. I like to think Ford do a good job at that, since it is part of my job, I'd be interested to hear of any reasonably modern Ford product with perceptible problems with the EPAS.

 

The fundamental issue is that the EPAS motor runs very fast, and is then heavily geared down (33:1 say) and drives the rack via a ballscrew. Backdriving that lot, which is essentially what the tie rod is trying to do to impart feel, is impossible, directly. So, electronically a balance is set up whereby the motor helps to overcome it's own inertia (N^2 relationship for inertia) and the friction in the ballscrew and so on, using feedforward and a lot of tuning. Trouble is, if you don't do enough of that compensation the system feels dead due to friction and referred inertia, and if you do too much then the system 'motors' itself, which is unnerving to say the least. Different vehicle manufacturers have different access to the tuning and strategy levels of the software. We're allowed to go deeper than most, and are learning all the time.

 

Also of course you lot insist we fit stupid low profile tires which create random inputs due to CP width that we mask. We could put a lot less masking into the system if we went back to bicycle tires. BMW used to have a 3 Hz low pass filter in their steering column. Vorsprung dur rubber.



#8 Chubby_Deuce

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Posted 06 May 2021 - 17:39

What problem would this solve? FBW makes a lot of sense for airliners with long and complex control circuits that need constant computer intervention. Cars have a very short distance from driver to steering rack and EPS already does an adequate job of adding control inputs.

 

I feel like there's just a generation of designers that really, really want to drive with a Batmobile steering wheel.



#9 404KF2

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Posted 06 May 2021 - 17:45

Yeah goodbye steering feel, although EPS even takes care of most of this on moderns.

 

A solution looking for a problem, but likely to create more.


Edited by 404KF2, 07 May 2021 - 21:50.


#10 desmo

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Posted 06 May 2021 - 23:33

From my viewpoint and admitting they're unambiguously better than old cars, modern cars are in a lot of ways crazy over engineered.



#11 Fat Boy

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Posted 06 May 2021 - 23:44

To be honest the aspirational target for EPAS is 'as good as HPAS' for steering feel. I like to think Ford do a good job at that, since it is part of my job, I'd be interested to hear of any reasonably modern Ford product with perceptible problems with the EPAS.

 

The fundamental issue is that the EPAS motor runs very fast, and is then heavily geared down (33:1 say) and drives the rack via a ballscrew. Backdriving that lot, which is essentially what the tie rod is trying to do to impart feel, is impossible, directly. So, electronically a balance is set up whereby the motor helps to overcome it's own inertia (N^2 relationship for inertia) and the friction in the ballscrew and so on, using feedforward and a lot of tuning. Trouble is, if you don't do enough of that compensation the system feels dead due to friction and referred inertia, and if you do too much then the system 'motors' itself, which is unnerving to say the least. Different vehicle manufacturers have different access to the tuning and strategy levels of the software. We're allowed to go deeper than most, and are learning all the time.

 

Also of course you lot insist we fit stupid low profile tires which create random inputs due to CP width that we mask. We could put a lot less masking into the system if we went back to bicycle tires. BMW used to have a 3 Hz low pass filter in their steering column. Vorsprung dur rubber.

I have a 2020 Ford with EPAS. I agree the steering feel is quite good, even if the ratio is a little slow. I _wish_ there were more sidewall on the tires. I would be quite happy with an extra 30mm or so of sidewall. I have absolutely zero interest in a FBW steering system, regardless of any theoretical positives.

 

Since we're talking street cars, do you ever play with the magnetic dampers? I have a stand-alone controller for mine and have been playing quite a bit with the tuning. You can do some very interesting tricks, but there are also some shortcomings, particularly larger displacement, low-frequency freeway undulations. It seems to work well in high-G situations, but the daily driving bit is more tricky to tune. I did speak to an OE tuner and he looked at the software for my controller. He said it was about 25% of the software he uses.



#12 Ross Stonefeld

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Posted 07 May 2021 - 00:47

From my viewpoint and admitting they're unambiguously better than old cars, modern cars are in a lot of ways crazy over engineered.

 

I had to ferry some people to doctor's appointments and hopped between a 1989 Saab 900 and a 2019 Subaru Outback. The latter is nice, albeit takes a few moments of "uh..is this thing done loading?" before I feel comfortable taking off. My problem is I was regularly well over the speed limit without noticing it, there's no sense of speed/weight/any physicality to the vehicle.

 

The Saab has some really clever early-version 'smart driving'. Round about 100kph/60mph the engine sags so you have to make a conscious effort to poke through the speed limit on the highway. I think there's a crack or harmonic happening somewhere but it's not unuseful and mildly amusing.



#13 Lee Nicolle

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Posted 07 May 2021 - 03:44

To be honest the aspirational target for EPAS is 'as good as HPAS' for steering feel. I like to think Ford do a good job at that, since it is part of my job, I'd be interested to hear of any reasonably modern Ford product with perceptible problems with the EPAS.

 

The fundamental issue is that the EPAS motor runs very fast, and is then heavily geared down (33:1 say) and drives the rack via a ballscrew. Backdriving that lot, which is essentially what the tie rod is trying to do to impart feel, is impossible, directly. So, electronically a balance is set up whereby the motor helps to overcome it's own inertia (N^2 relationship for inertia) and the friction in the ballscrew and so on, using feedforward and a lot of tuning. Trouble is, if you don't do enough of that compensation the system feels dead due to friction and referred inertia, and if you do too much then the system 'motors' itself, which is unnerving to say the least. Different vehicle manufacturers have different access to the tuning and strategy levels of the software. We're allowed to go deeper than most, and are learning all the time.

 

Also of course you lot insist we fit stupid low profile tires which create random inputs due to CP width that we mask. We could put a lot less masking into the system if we went back to bicycle tires. BMW used to have a 3 Hz low pass filter in their steering column. Vorsprung dur rubber.

I am never going to demand low profile tyres, ride is crap, more feed back through the steering and try to carry a load and the tyres get very hot.

60 profile 16s is the way to go.

And since I often fit tyres to these rims most are shaped every way but round



#14 Greg Locock

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Posted 07 May 2021 - 05:52

FatBoy - no Ford Australia is pretty much Ranger/Everest only. The rheo dampers are on Mustang only so far as i know in the Ford world. I'd like to use them at some point, they are very neat tech.



#15 Fat Boy

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Posted 07 May 2021 - 15:00

FatBoy - no Ford Australia is pretty much Ranger/Everest only. The rheo dampers are on Mustang only so far as i know in the Ford world. I'd like to use them at some point, they are very neat tech.

 

The ability to dynamically cross-weight the car is a powerful tool.



#16 Ross Stonefeld

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Posted 14 May 2021 - 11:24

Now in GT3 cars(racing ones)

 

https://www.motorspo...er-bmw/6506753/

 

The 'tuning out the kerb strikes' thing is...that's a benefit? Sure you don't want your arms knocked off but that sounds like less feedback? I dunno, maybe it's like F1 power steering is probably pretty good and nothing like the low-end-road-car stuff I've driven all my life.