Rack and Pinion location, ...behind or in front of the front wheel centerline Options

[meb58]

Are there any pure performance benefits to locating the rack and pinion gear ahead of the front wheel center line? Feel for example? I know from experience that alignment relationships between camber and tow are more natural; more neg camber adds more toe out...perhaps this is natural to only me.

I imagine in today's world we worry about crashing and the cost of repairs when the rack is ahead of the front wheel centerline...and perhaps packaging.

[Greg Locock]

Are there any pure performance benefits to locating the rack and pinion gear ahead of the front wheel center line? Feel for example?

It is mostly driven by packaging. With FWD it is very hard to get the IS past the engine for a front mounted rack. Mounting racks in B cars and smaller is very tricky.

With a proper engine a front rack is doable, it allows you to drop the sump to the ground clearance line. In theory you can then mount the rack stiffly and soften off the lateral arm bushes to give some compliance understeer. In practice drivers hate that.

If we ever go to steer by wire with no column at all then I think front rack will become almost universal, just because of packaging.

[meb58]

Steer by wire ? I never saw that coming...aren't there some concerns about electronic failure?

[gruntguru]

Steer by wire ? I never saw that coming...aren't there some concerns about electronic failure?

I doubt Toyota will be first out of the blocks.

[johnny yuma]

I doubt Toyota will be first out of the blocks.

It impresses me that most cars have had power steering and auto trans for 20 plus years,but because fuel injection and engine management systems are so good,people never seem to experience the almost impossibly heavy steering you get if your motor cuts out.If steer by wire arrives it would need to be,somehow,foolproof.

[Greg Locock]

If steer by wire arrives it would need to be,somehow,foolproof.

Because politicians and lawyers and the meeja are involved, yes. Of course in theory one would merely need to do a cost benefit analysis showing that on average society benefits from the elimination of the mechanical linkage. In less emotive industries that is precisely how safety/cost tradeoffs are done. However given that every single "tree jumped out at me" incident will be blamed on the steer by wire I am fairly sure that it'll be a while yet.

[cheapracer]

if a rack and control arms are solidly mounted then it only matters where the rack is relative to whatever travel radiuses are happening - comes down to planning. If however bushes are used then I would prefer a rear mounted rack as you are more likely to get toe in with deflection when hitting a bump mid corner.

[gordmac]

How would you get any feel in a steer by wire system?

[meb58]

I agree, feel was one of my first concerns after system failure. But, assuming steer by wire were fool proof, we are but a small leap from cars that drive us to and fro sans our involvement...for better or worse.

[kikiturbo2]

I agree, feel was one of my first concerns after system failure. But, assuming steer by wire were fool proof, we are but a small leap from cars that drive us to and fro sans our involvement...for better or worse.

exactly, I also wanted to point out that most modern steering systems with electric power steering are very poor on the steering feel front..

[Tony Matthews]

exactly, I also wanted to point out that most modern steering systems with electric power steering are very poor on the steering feel front..

The Child Bride's Honda Civic has electric power steering, which seemed OK for the first short trundle or two. Now I've had the chance to fully assess it - I loath it. Very little feel, and despite it being a small, light car, tiring, as the constant small corrections you have to make in a straight line make my forearms ache after half an hour.

[saudoso]

How would you get any feel in a steer by wire system?

Logitech has that figured out.

About reliability, much like hydraulic braking assistance. 2/3 of drivers wouldn't be able to stop a car if it failed. I happened to me once, and it was close. It just does not fail that usually.

But then again, why would someone fix what is working so well. Don't see it coming until cars handle themselves.

This post has been edited by saudoso: Nov 7 2009, 11:22

[DaveW]

Steer by wire ? I never saw that coming...aren't there some concerns about electronic failure?

My not infallible memory suggests that Daimler Benz has used steer-by-wire for PSV's.

[McGuire]

Because politicians and lawyers and the meeja are involved, yes. Of course in theory one would merely need to do a cost benefit analysis showing that on average society benefits from the elimination of the mechanical linkage. In less emotive industries that is precisely how safety/cost tradeoffs are done. However given that every single "tree jumped out at me" incident will be blamed on the steer by wire I am fairly sure that it'll be a while yet.

The auto industry is not competent enough to do fly-by-wire steering.

[gruntguru]

Because politicians and lawyers and the meeja are involved, yes. Of course in theory one would merely need to do a cost benefit analysis showing that on average society benefits from the elimination of the mechanical linkage. In less emotive industries that is precisely how safety/cost tradeoffs are done. However given that every single "tree jumped out at me" incident will be blamed on the steer by wire I am fairly sure that it'll be a while yet.

The auto industry is not competent enough to do fly-by-wire steering.

The cost:benefit and risk:benefit ratios must be very big numbers at present and not dropping too fast either.

[Greg Locock]

The auto industry is not competent enough to do fly-by-wire steering.

The cost:benefit and risk:benefit ratios must be very big numbers at present and not dropping too fast either.

Sort of agree, so far as maturity goes we can thank our friends in Germany who have at least twice in recent history have bamboozled the world while introducing active safety features - ESC on the A class was overkill, and their rigged demo of active braking wasn't very helpful either.

But imagine the benefit of no steering column on crash. And if we go to robot steering frankly why bother with a column? Maybe the aero would improve if you don't have to mount the engine so far 'above' the ground line? There are lots of possibilities.

[DaveW]

My not infallible memory suggests that Daimler Benz has used steer-by-wire for PSV's.

A quick search suggested my memory is fallible (perhaps fortunately). However, DB has worked on steer-by-wire, possibly starting in the 1980s, that resulted in several patents, see for example US6394218. Why PSV? I guess because of the compromises inherent in connecting a steering wheel located some way forward of the steered axle.

BTW, Lotus did build a programmable steer-by-wire research vehicle in 1985-ish complete with artificial feel. It incorporated manual reversion, however. In my experience, it was demonstrated most frequently with a steering gain of -1. Most drivers could adapt to gain reversal, except when they had to react instinctively.... Happened in a car park once, fortunately with damage only to the driver's pride.

[carlt]

The Child Bride's Honda Civic has electric power steering, which seemed OK for the first short trundle or two. Now I've had the chance to fully assess it - I loath it. Very little feel, and despite it being a small, light car, tiring, as the constant small corrections you have to make in a straight line make my forearms ache after half an hour.

by inference -

Child bride causes muscle decay in the forearms

[Tony Matthews]

by inference -

Child bride causes muscle decay in the forearms

Actually the reverse - if I drive it much longer I'll end up with arms like Popeye. I much prefer my Volkswagon Transporter.

[cheapracer]

Actually the reverse - if I drive it much longer I'll end up with arms like Popeye. I much prefer my Volkswagon Transporter.

[Tony Matthews]

If only... Although my son wants one more than I do.

[Greg Locock]

BTW, Lotus did build a programmable steer-by-wire research vehicle in 1985-ish complete with artificial feel. It incorporated manual reversion, however. In my experience, it was demonstrated most frequently with a steering gain of -1. Most drivers could adapt to gain reversal, except when they had to react instinctively.... Happened in a car park once, fortunately with damage only to the driver's pride.

Trilby? I happened to reread my notes on that a while back. The most reassuring noise was the clunk as the real steering column re-engaged.

[meb58]

One of my chief complaints about Honda products...and I've put over 600,000 miles on some of those cars. 1" total toe in keeps more or less on track

I am a little confused about compliance understeer Greg...do mean this be toe in in bump as cheapracer wrote? However, one seem like pure bushing complinace where the other is geometrically defined?

The Child Bride's Honda Civic has electric power steering, which seemed OK for the first short trundle or two. Now I've had the chance to fully assess it - I loath it. Very little feel, and despite it being a small, light car, tiring, as the constant small corrections you have to make in a straight line make my forearms ache after half an hour.

This post has been edited by meb58: Nov 9 2009, 13:22

[Greg Locock]

I am a little confused about compliance understeer Greg...do mean this be toe in in bump as cheapracer wrote? However, one seem like pure bushing complinace where the other is geometrically defined?

compliance steer is the way that the wheels steer (in degrees) per kN of lateral force. Due to pneumatic trail this force is actually applied a little behind the wheel centre, so the easiest thing is to apply the force below the wheel centre, to give deg/kN, and also measure the torsional stiffness about the vertical axis, deg/kNm. Then when you know your trail you can add these together appropriately to get an estimate of the compliance steer.

[Tony Matthews]

1" total toe in keeps more or less on track

Car or wife?

[meb58]

I have to work on an answer...my wife is in line...it's the girl friend I have to worry about...

Car or wife?

[Tony Matthews]

I have to work on an answer...my wife is in line...it's the girl friend I have to worry about...

Steer carefully or you'll be on the rack, pinioned too, probably.

[meb58]

I am always careful...but being racked and pinioned may be, from a particular syntax perspective, a good thing...

Steer carefully or you'll be on the rack, pinioned too, probably.

[Tony Matthews]

One man's rack and pinion is another man's recirculating ball...

[meb58]

...well, the girl friend can do more with the recirculating ball for sure...but of course, as the steering changes so does the caster angle...

One man's rack and pinion is another man's recirculating ball...