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      10-25-2007, 10:28 AM   #67
GregW / Oregon
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Originally Posted by mkoesel View Post
Also, I am not sure I understand how the "characteristic curve" of the "MS660's Servotronic valve" relates to the weight of the steering. My limited understanding make's me guess it is the speed, not the weight, that will be effected.
By "speed" if you mean the ratio, that does not change, but is fixed at 12.5:1. What is varied by the valve, I believe, is the amount of assist offered at various speeds. The software is designed to offer more assist at low speeds, decreasing at higher speeds. The curve of this assist is varied for different steering settings.
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      10-25-2007, 10:41 AM   #68
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Quote:
Originally Posted by GregW / Oregon View Post
By "speed" if you mean the ratio, that does not change, but is fixed at 12.5:1.
Hmm, then I am confused by this quote from the text of your other post:

"The average variable overall ratio is 12.5..."

Sounds like the ratio is varying. Then again, How would that differ from Active Steering (which the car is not eqipped with)? Its surprising to me just how confusing this is (though I should not be surpised, given BMW's perchance for overly wordy "technical literature").

Quote:
What is varied by the valve, I believe, is the amount of assist offered at various speeds. The software is designed to offer more assist at low speeds, decreasing at higher speeds. The curve of this assist is varied for different steering settings.
That makes sense. One thing I am not immediately clear on is why variable assistance would be great for a performance car, while a variable ratio would not be. I wonder, does the E46 (M3 or otherwise) have variable assistance?
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      10-25-2007, 11:18 AM   #69
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Quote:
Originally Posted by mkoesel View Post
Hmm, then I am confused by this quote from the text of your other post:

"The average variable overall ratio is 12.5..."

Sounds like the ratio is varying. Then again, How would that differ from Active Steering (which the car is not eqipped with)? Its surprising to me just how confusing this is (though I should not be surpised, given BMW's perchance for overly wordy "technical literature").



That makes sense. One thing I am not immediately clear on is why variable assistance would be great for a performance car, while a variable ratio would not be. I wonder, does the E46 (M3 or otherwise) have variable assistance?
IIRC, active steering can adjust steering ratio AND even adjust within limits the direction the wheels are pointed under various circumstances, such as when DSC intervenes to prevent a spin. This is something the M3 system will not do.
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      10-25-2007, 11:49 AM   #70
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Quote:
Originally Posted by ILC32 View Post
IIRC, active steering can adjust steering ratio AND even adjust within limits the direction the wheels are pointed under various circumstances, such as when DSC intervenes to prevent a spin. This is something the M3 system will not do.
I believe you are correct.

Still, I'd like to know if there are other differences as well, with respect to whether the ratio on the M3 (and all E9X) does indeed vary, and how it varies differently from an AS equipped car.

Furthermore, I'd also like to know if the E46 cars also had variable ratios. Whatever the case, I definitely like the steering in my M3 much more than the 335i. This, despite the ratios being similar (and I realize that might be an oversimplification an pending answers to my previous questions). It could be due mostly to the amount of assistance provided. But even if so, I am also still not clear on why we need variable assitance at all (if in fact that is what we have).
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      10-25-2007, 12:02 PM   #71
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Quote:
Originally Posted by mkoesel View Post
I believe you are correct.

Still, I'd like to know if there are other differences as well, with respect to whether the ratio on the M3 (and all E9X) does indeed vary, and how it varies differently from an AS equipped car.
My understanding is that with active steering, the ratio is steplessly variable. If you are going slowly, the ratio is faster. As you speed up, the ratio slows. So at parking speeds, a slight turn of the wheel results more movement of the wheels than at higway speeds. With the M3, the ratio has different settings, but is not steplessly variable. So in the M3 once you choose a setting for the steering, the ratio stays the same until you select a different steering setting.
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      10-25-2007, 12:15 PM   #72
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Quote:
Originally Posted by ILC32 View Post
My understanding is that with active steering, the ratio is steplessly variable. If you are going slowly, the ratio is faster. As you speed up, the ratio slows. So at parking speeds, a slight turn of the wheel results more movement of the wheels than at higway speeds. With the M3, the ratio has different settings, but is not steplessly variable. So in the M3 once you choose a setting for the steering, the ratio stays the same until you select a different steering setting.
The thing is, they claim the steering is the same as the 335i in that they are both variable:

"The design of the rack-and-pinion steering system is the same as the series E92. The average variable overall ratio is 12.5 and hence sports-oriented (16 in the series E92)."

And we know the 335i does not have different steering settings. Thus the variability must be referring to something other than the settings that MDrive enables.
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      10-25-2007, 03:47 PM   #73
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Quote:
Originally Posted by mkoesel View Post
The thing is, they claim the steering is the same as the 335i in that they are both variable:

"The design of the rack-and-pinion steering system is the same as the series E92. The average variable overall ratio is 12.5 and hence sports-oriented (16 in the series E92)."

And we know the 335i does not have different steering settings. Thus the variability must be referring to something other than the settings that MDrive enables.
In both settings the M3 steering is variable.
When driving slow, i.e. parking or similar, the steering ratio and power assist changes very noticeable and makes it easy to park, you could almost believe you had 145 wide tires, not 245.
It feels weird before you get used to it, but parking the E46 has become heavy work now that I'm used to the M3... In the beginning I did not like this feature at all, but I find that I do like it now despite the artificial feeling when parking.

The biggest difference between sport and normal steering is how heavy the wheel feels, but sport is also a tad sharper in higher speeds. I think the active steering part is what confuses most journalists with lack of steering feel.
The thing is that you can really feel the ground through the wheel, although a bit muted, it is like the details are there but you have to listen for them, if you have a light grip on the wheel, all details are there, but the steering wheel will not try to wrangle itself out of your hands. This is very noticable when the car goes straight forward, it does not have the nervousnes you get from cars with tight steering and wide tires, at the same time it is like clockwork during turns because of the very same sharp steering ratio you did not feel when driving straight forward. - I think I just managed to confuse potential readers now.
Anyways: My inital impression of the steering was that it was too light and I misinterpreted this with no feel. There actually is alot of feel but it tells you what is going in a different way than I was used to from earlier models.
Just for comparsion, I really can't stand cars with too much power steering, driving in the US is like a nightmare for me. It feels like many of the cars have super charged power assist or something. The M3 is not like that.
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      10-25-2007, 04:11 PM   #74
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Quote:
Originally Posted by mkoesel View Post
Hmm, then I am confused by this quote from the text of your other post:

"The average variable overall ratio is 12.5..."

Sounds like the ratio is varying. Then again, How would that differ from Active Steering (which the car is not eqipped with)? Its surprising to me just how confusing this is (though I should not be surpised, given BMW's perchance for overly wordy "technical literature").

That makes sense. One thing I am not immediately clear on is why variable assistance would be great for a performance car, while a variable ratio would not be. I wonder, does the E46 (M3 or otherwise) have variable assistance?
Like some others, I believed the ratio does not vary, despite the wording in the previous quote. The specification sheet says the steering ratio is 12:5:1 -- there is no range given. This is what the press release says, "The optionally available MDrive configuration enables the driver to pre-select the response of the Servotronic power steering. In the process, MDrive is able to follow two control maps varying steering forces between the Normal and Sports setting as a function of road speed." Note they olnly mention the steering FORCES as being variable, not speed or ratios.

As a definitive answer, I consulted the BMW Technology Guide for "M Servotronic", and here is the description, "M Servotronic is a special form of power steering geared not to engine speed, like conventional power steering systems, but rather to the car's actual road speed. In practice this means ample power assistance when parking and manoeuvring at low speeds, followed by gradual reduction of power assistance as road speed increases to ensure greater direct contact with the road at high speeds and, as a result, an even higher standard of steering precision. Using the sports switch, the driver can also choose a second steering control curve for even sportier feedback from the steering."

I think that is clear, only assist is altered, not ratio.

http://www.bmw.com/generic/com/en/fa...ide/index.html
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      10-25-2007, 05:35 PM   #75
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For the steering ratio to be variable, this would have to be a drive/fly-by-wire system--meaning there would be no direct mechanical linkage between the steering wheel and front wheels--unless there is some kind of variable transmission built into the steering assembly. If it was a direct mechanical linkage, how else could you change the steering ratio without physically changing the gearing? A steering system without direct mechanical linkage would lack in feel. Therefore, I doubt that the steering ratio is variable. As GregW points out, variability must be associated with the amount of power assist provided under different conditions.

Having said all this, I am wondering how the "Active Steering" option in the 5-series was implemented? Is that a fly/drive-by-wire system?
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      10-25-2007, 06:21 PM   #76
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Active steering

Quote:
Originally Posted by lucid View Post
For the steering ratio to be variable, this would have to be a drive/fly-by-wire system--meaning there would be no direct mechanical linkage between the steering wheel and front wheels--unless there is some kind of variable transmission built into the steering assembly. If it was a direct mechanical linkage, how else could you change the steering ratio without physically changing the gearing? A steering system without direct mechanical linkage would lack in feel. Therefore, I doubt that the steering ratio is variable. As GregW points out, variability must be associated with the amount of power assist provided under different conditions.

Having said all this, I am wondering how the "Active Steering" option in the 5-series was implemented? Is that a fly/drive-by-wire system?
Visit the link I provided. Active steering uses a planetary gearset and a motor to provide variable ratios and variable assist.



"Active Steering gives drivers more precise handling and tracking: this ensures that their automobiles are more mobile and agile even on twisting roads. A planetary gear is integrated with the steering column; depending on the situation, the feature varies the angle of steering determined by the user at the wheel (superimposed steering).
It increases the steering angle at lower and mid-range speeds; by contrast, at higher speeds (e.g. on motorways), the steering angle is reduced. When parking, the active steering feature makes it easier to manoeuvre by amplifying the movements of the steering wheel."
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Last edited by GregW / Oregon; 10-25-2007 at 08:27 PM.
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      10-25-2007, 06:38 PM   #77
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Quote:
Originally Posted by GregW / Oregon View Post
Visit the link I provided. Active steering uses a planetary gearset and a motot to provide variable ratios and variable assist.



"Active Steering gives drivers more precise handling and tracking: this ensures that their automobiles are more mobile and agile even on twisting roads. A planetary gear is integrated with the steering column; depending on the situation, the feature varies the angle of steering determined by the user at the wheel (superimposed steering).
It increases the steering angle at lower and mid-range speeds; by contrast, at higher speeds (e.g. on motorways), the steering angle is reduced. When parking, the active steering feature makes it easier to manoeuvre by amplifying the movements of the steering wheel."
Thanks for the info. Yep, they do use variable transmission for active steering. I'm pretty sure this is not implemented in the M3. Can someone confirm this?
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      10-25-2007, 08:28 PM   #78
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Quote:
Originally Posted by lucid View Post
Thanks for the info. Yep, they do use variable transmission for active steering. I'm pretty sure this is not implemented in the M3. Can someone confirm this?
I can positively say the M Series does NOT have Active Steering. Servotronic and Active are two separate systems, and we already know the M3 has Servotronic.
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      10-25-2007, 08:29 PM   #79
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Quote:
Originally Posted by GregW / Oregon View Post
I can positively say the M Series does NOT have Active Steering.
That's what I wanted to hear. If it did, I'd want nothing to do with it!
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      10-25-2007, 09:50 PM   #80
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      10-26-2007, 10:17 AM   #81
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Quote:
Originally Posted by GregW / Oregon View Post
I think that is clear, only assist is altered, not ratio.
I wish I were as convinced, Greg.

I am quite convinced that MServotronic only varies forces (level of assist), and that MDrive changes the way in which those forces vary.

What am not convinced of is that, seperate from that technology, the ratio of the steering is not also varying.

Not that it matters at this point, because that would not be effected by MDrive one way or the other. So we are basically OT. But it has now become a big curiousity of mine.
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      10-26-2007, 10:23 AM   #82
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Quote:
Originally Posted by lucid View Post
For the steering ratio to be variable, this would have to be a drive/fly-by-wire system--meaning there would be no direct mechanical linkage between the steering wheel and front wheels--unless there is some kind of variable transmission built into the steering assembly. If it was a direct mechanical linkage, how else could you change the steering ratio without physically changing the gearing? A steering system without direct mechanical linkage would lack in feel. Therefore, I doubt that the steering ratio is variable.
lucid, check it out:

http://auto.howstuffworks.com/steering2.htm

"Some cars have variable-ratio steering, which uses a rack-and-pinion gearset that has a different tooth pitch (number of teeth per inch) in the center than it has on the outside. This makes the car respond quickly when starting a turn (the rack is near the center), and also reduces effort near the wheel's turning limits. "

It actually sounds pretty simple, yeah?

Now, I do agree that changing the *rate at which ratio changes* would be more of an engineering problem (as above with Active Steering). But we now know that that doesn't happen with MDrive steering anyway. I am still curious if any of this applies to the E9X and E46 though (in M3 form or otherwise). Like I said above tho, its OT.
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      10-26-2007, 10:28 AM   #83
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Quote:
Originally Posted by mkoesel View Post
lucid, check it out:

http://auto.howstuffworks.com/steering2.htm

"Some cars have variable-ratio steering, which uses a rack-and-pinion gearset that has a different tooth pitch (number of teeth per inch) in the center than it has on the outside. This makes the car respond quickly when starting a turn (the rack is near the center), and also reduces effort near the wheel's turning limits. "

It actually sounds pretty simple, yeah?
Well, this actually doesn't add up in my mind. I can see how the rack can have different pitch in different places, but I don't see how a pinion with uniform pitch will mesh with that rack without getting chewed up unless you let go off your tolerances and then you've got a sloppy transmission.
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      10-26-2007, 10:33 AM   #84
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Quote:
Originally Posted by ilron View Post
In both settings the M3 steering is variable.
When driving slow, i.e. parking or similar, the steering ratio and power assist changes very noticeable and makes it easy to park, you could almost believe you had 145 wide tires, not 245.
Seems it actually doesn't.

But, I can see why it would be hard to tell given that the amount of assistance is also changing. IOW, while you can tell something is going on, it would be tough to determine exacty what it is.
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      10-26-2007, 10:38 AM   #85
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Quote:
Originally Posted by lucid View Post
Well, this actually doesn't add up in my mind. I can see how the rack can have different pitch in different places, but I don't see how a pinion with uniform pitch will mesh with that rack without getting chewed up unless you let go off your tolerances and then you've got a sloppy transmission.
What if both the rack and the pinion have constant pitched teeth, but the pinion is not circular (think egg-shaped)? The steering shaft would need to be on a non-fixed-in-space mount, sure.
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      10-26-2007, 10:51 AM   #86
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Quote:
Originally Posted by mkoesel View Post
What if both the rack and the pinion have constant pitched teeth, but the pinion is not circular (think egg-shaped)? The steering shaft would need to be on a non-fixed-in-space mount, sure.
Well then you would have the varying pitch pattern repeate itself in fixed intervals and that would be really strange. The issue is that the pinion gear, generally speaking, will be small and go through several full rotations during lock-to-lock travel. Plus, I assume the gear geometries would be out of whack. If someone can shed light on the howstuffworks blurb, that would be great.
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      10-26-2007, 11:26 AM   #87
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Quote:
Originally Posted by lucid View Post
Well then you would have the varying pitch pattern repeate itself in fixed intervals and that would be really strange. The issue is that the pinion gear, generally speaking, will be small and go through several full rotations during lock-to-lock travel.
True, I guess it would only work in a non-rack-and-pinion type system, where perhaps a geared steering arm (which would naturally move <= 180 degrees) is used to control the steering linkage instead.

Quote:
If someone can shed light on the howstuffworks blurb, that would be great.
Sorry, I am CE, not ME.
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      10-26-2007, 12:01 PM   #88
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Originally Posted by mkoesel View Post
Sorry, I am CE, not ME.
I used to be ME, but haven't done any real ME in over 10 years. I doubt that I can solve a partial diff equation anymore--not that the steering issue has anything to do with it...Heck, I'd settle for integrating a complex function, but even that'd be in doubt.
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