4.6is = Active Steering?

[Weasel]

For the best personal results, go test drive the 4.6is again and pay more attention to the steering response and feel at all speeds in various turns. I believe when comparing it to the 3.0i, you will find it to have the same stability and turning ratios, but an easier and sportier feel. Just trust that the highly accomplished engineers at BMW knew what they were doing when they incorporated these characteristics into the sport model

[chilliwilli]

Love the turning radius...steering in city is very responsive and even better on hwy. If possible, take it for a spin...it will grow on you.

[vinuneuro]

Originally Posted by weasel56

The pressure assist is speed based, not rpm based. Controlled by controlling valve positions. Also the teeth on the cross bar in the rack are different widths from the center towards the ends... this is becoming hard to describe as how involved our steering systems are, so I am geting tempted to scan some pages from the "chassis dynamics/undercar technologies" books obtained during training. But I can be lazy... Any specific areas of the steering system you need info on?

As far as I know there are three types of power assist steering types: input based on engine speed, vehicle speed, tire torque/slip. In some places I've read that the Servotronic system is vehicle speed based, others that it's based on the tire slip.

[Weasel]

Oh it goes soooo much deeper than that. The active steering system BMW developed uses every input possible, and does more than you know. It is a very sophisticated system. I'm sure you notice when you are driving and a tire catches a puddle on one side, the steering wheel jerks that way and you have to correct it. On a BMW with active steering, it senses that and corrects it by instantaneously turning the wheels up to 4 degrees to compensate for it, yet does this completely unnoticed to the driver. You can actually kick back and put your hands behind your head and hit puddles with active steering.

To put into perspective how intertwined our systems can be, look at this video... you will be amazed!

http://www.youtube.com/watch?v=fXmOZ34PcJs

[Weasel]

Holy shit look at this, I found some great videos that feature illustrations directly from the training manual. Now you can see the active steering principles!

http://www.youtube.com/watch?v=yfvbJMLG7hk

apparently they have videos for most bmw systems. check out the one for xdrive in post facelift X5's

http://www.youtube.com/watch?v=eT8nNFQ34WQ

and the xdrive in a demonstration

http://www.youtube.com/watch?v=3RAFseqhWN0

[Icer006]

Originally Posted by AzNMpower32

I believe the 4.6is still had the old-style recirculating ball type steering (as opposed to rack-and-pinion); I remember driving someone's X5 4.6is at the DC meet which was ages ago. It really is light and a vague.

It's definitely not Active Steering since that wasn't introduced until the E70.

My 4.8is has active/adaptive steering.

[Weasel]

Originally Posted by Icer006

My 4.8is has active/adaptive steering.

But you must understand the differences between active and adaptive steering. Yes you have adaptive steering, but it a completely different beast from what BMW has sanctioned the name "active steering" to. Adaptive does actively adapt to steering situations and change variables while the active steering actually takes physical control and is... well, active.

Play with the videos that made it to youtube and if there are still questions, I'd might have to scan some pages from the training books on the E53 steering systems to demonstrate.

[LeMansX5]

4.8is steering is Servotronic
Effortless agility when parking, light-footed responsiveness and stability at higher speeds: Servotronic adjusts the amount of steering assistance to suit the current speed, enhancing driver comfort by lowering the effort needed to turn the steering wheel.

The Servotronic control unit adjusts the amount of steering assistance to suit the speed of the vehicle. An electromagnetic valve accurately controls the amount of force applied by the steering hydraulics, enabling outstandingly precise steering that suits your current driving situation. Conventional power steering systems, by contrast, regulate the power steering in relation to the engine's RPM. The electromechanical steering system EPS uses an electric motor to achieve the same effect.
Thanks to Servotronic, driving along narrow streets or parking becomes easier as it requires minimum effort to turn the steering wheel. The power assist progressively decreases when the vehicle speeds up, ensuring greater stability, improved precision and smoother vehicle behaviour.

Here's the difference on steerings for 3.0i, 4.4i & 4.8is:

3.0i and 4.4i models – according to engine speed, providing a moderate reduction of steering effort at very low speeds and in parking (engine speed below 1500 rpm) while preserving ultra-precise road feel at normal to high driving speeds.

4.8is – according to vehicle speed (Servotronic), which reduces steering effort in parking and at very low speeds more than the engine-speedsensitive assist does.

And this is what Active Steering(not on E53) is in detail:
The new dimension in steering comfort: Active Steering offers precision, agility and comfort in every driving situation.

At the heart of the new Active Steering system is the planetary gear set integrated into the steering column. An electric motor in the joint adjusts the front wheels' steering angle in proportion to the Sedan's current speed.

When driving at lower speeds - such as in city traffic, when parking or on winding mountain roads, Active Steering increases the size of the steering angle. The front wheels respond immediately to small movements of the steering wheel, enabling the driver to manoeuvre through tight spaces without needing to make multiple turns of the steering wheel. Parking is easier and agility enhanced.

At medium speeds, steering is also easier. And to ensure smoothness at higher speeds, as of around 120 to 140 km/h (depending on the model) Active Steering becomes more indirect.

Active Steering therefore reduces the amount of change in the steering angle for every movement of the steering wheel. This gives the driver the advantage of more precise steering at higher speeds, and ensures great stability and more comfort.

If the vehicle is threatened with instability, such as by oversteering or braking on a changeable surface, DSC identifies the problem and can use Active Steering to help overcome it. For example, in order to reduce unsafe yaw, Active Steering can increase the angle of steering wheels faster than even the most expert driver.

Active Steering does not interrupt the direct connection between steering wheel and front wheels, so that even in the unlikely event of a complete failure of the electronic systems, the BMW remains completely controllable at all times. This is because at the first sign of any problems, an adaptation mechanism blocks the Active Steering immediately using a pivot so that the driver is permanenty in control of the situation.

[Icer006]

^^Great info! Thanks.

[ljnlaw]

Holy shit look at this, I found some great videos that feature illustrations directly from the training manual. Now you can see the active steering principles!

http://www.youtube.com/watch?v=yfvbJMLG7hk

apparently they have videos for most bmw systems. check out the one for xdrive in post facelift X5's

http://www.youtube.com/watch?v=eT8nNFQ34WQ

and the xdrive in a demonstration

http://www.youtube.com/watch?v=3RAFseqhWN0

Wow that is some crazy cool stuff, thanks for posting!