[s-cars] active sway bar

Sun Oct 28 07:58:52 PDT 2007

no, active steering is a variable ratio steering system that varies the steering ratio depending on how fast the car is going and what the computer thinks you need.  at parking lot speeds, the ratio is increased so you can bang the wheels off the steering limiter with little more than a turn of the wheel.  at high speeds, the ratio is decreased so that it takes more steering input to change the car's direction.  dynamic roll control is the dynamic adjustment of the car's roll stiffness (front and rear) by adjusting the rate of the anti-roll bars.

i really disliked both of them when driving a 530i and 545i on the autox course.  the active steering does strange things to the steering ratio when you're driving the car hard on the autox course, with rapidly changing speeds, and i was never quite sure how much the car was going to turn for a given amount of steering input.  the car corners pretty flat, with little body roll, but the driver feedback is reduced, and i made the tail wag unexpectedly a couple of times.  i thought the car drove like a video game, and i don't mean that in a good way.

the M5 doesn't come with either active steering or dynamic roll control, and that might tell you something.

steve's proposal is to have driver-adjustable anti-roll bars.  that's not unprecedented.  some race cars have them, though i believe they're mechanical, not hydraulic.  an automatic system with less twiddling of the rate might also work well; e.g., a system that simply stiffens the roll rate and holds it there when it senses that you're flogging the car, and softens it after you've stopped driving hard.

-teddy

----- Original Message ----
From: "Pasqualoni, James E" <james.pasqualoni at gs.com>
To: sbpowers at gmail.com; tedebearp at yahoo.com
Cc: s-car-list at audifans.com
Sent: Sunday, October 28, 2007 8:06:16 AM
Subject: Re: [s-cars] active sway bar

Re: [s-cars] active sway bar

Is this a compnent of the new 'Active Steering' that is being employed by BMW?  Would certainly give the steering more "bite' in the twisties.

James Pasqualoni

Boston Global Advisors

T: 617-204-2406

----- Original Message -----

From: s-car-list-bounces at audifans.com <s-car-list-bounces at audifans.com>

To: Theodore Chen <tedebearp at yahoo.com>

Cc: S-Cars <s-car-list at audifans.com>

Sent: Sat Oct 27 11:48:10 2007

Subject: Re: [s-cars] active sway bar

your comment tells me that perhaps BMW haven't gotten it right, e.g.

the control part. I think the idea is sound but the implementation

isn't.

if it's dynamic that implies that they are pumping variable pressure

to the servo under computer control. the pressure into the servo unit

is what modifies the stiffness of the bar.

what if you replaced all that computer control crap with a hydraulic

screw pump, e.g. like what you have to adjust ride height on

motorcycle shocks. the only moving part is a "screw" into a cylinder -

pressure is increased/decreased by moving the "screw" into/out of the

cylinder.

that would allow one to set the stiffness and adjust it very easily

(within a range) if it needed changing.

Steve

On 10/26/07, Theodore Chen <tedebearp at yahoo.com> wrote:

> bmw calls it dynamic roll control.  if you like driving, run away!  it's part of what causes the recent bmws to feel more like video games.

>

>

> ----- Original Message ----

> From: Steve Powers <sbpowers at gmail.com>

> To: S-Cars <s-car-list at audifans.com>

> Sent: Friday, October 26, 2007 9:08:27 PM

> Subject: [s-cars] active sway bar

>

> I was at a high-end body shop yesterday here in Seattle and got a

> chance to eye a BMW 5-series rear subframe up close and personal. The

> unit had been entirely removed from the car with the wheels and struts

> still attached and undamaged.

>

> I couldn't help but notice the servo lump with hydraulic lines located

> smack dab in the middle of the rear sway bar. It's an active

> suspension (anti-roll) mechanism that is controlled hydraulically.

> Assuming the rates were done properly, would be a pretty

> sweet-adjust-it-from-the-driver's-seat sort of gizmo.

>

> Otherwise, it would be a large sinkhole for Pentosin.

>

> I could see some here (hi Hap!) modifying such a beast for use in our cars...

>

> Steve Powers

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