E60's active steering, from AutoBild :)

Micsor/DK · 23rd August 2002, 15:34

http://bilder.autobild.de/bilder/1/15576.jpg

"BMW active steering element Driver steers. Steering element thinks Uniquely: In the next fuenfer BMW offers a steering element, which has for the first time a variable speed ratio. Gokart Feeling and driving fun purely the active steering element think 100-mal per second Steering elements are a leidiges topic. Particularly for the technical designers. Reason: The speed ratio is rigid. Thus one decides for a compromise. That lies usually at approximately 1:18, i.e., a degree of angle change at the wheel means 18 degrees at the steering wheel. With this interpretation the driver must live, all the same whether he parks, over winding highways drives or with maximum speed on the motorway on the way is. It needed another, better fitting speed ratio exactly for these three scenarios in each case. In the city the steering element should be very direct (relationship until 1:10), so that at the steering wheel must be turned less, the wheels however far to hit. Also on winding terrain a more direct relationship is desired. The car feels knackig, reacts more spontaneously, drives more handily. Only with higher speed (over 120 km/h) a steering element must become more indirect (until 1:25), because small steering wheel movements are to involve not directly a jagged track switching in the Schumi format. In addition the indirect, slower-acting relationship improves the straight line discharge. The driver must so not constantly intervene correcting. On this background only the indirect interpretation of the steering element remains for engineer. With the disadvantage: less fun with driving along curves, too much cranking when parking and ranking. But the wrong has an end: BMW comes 2003 in the new fuenfer with a steering element, which becomes depending upon speed directly, neutral or indirect. In fractions of a second. Their name: Active steering element. First trial trips, which we undertook on the BMW test area, were impressing. Ever a series car is not more handily through suspension tower lanes wagged and gone through curves. Gokart Feeling, driving fun purely. The technology for this is relatively simply that one asks oneself, why the developers not already in former times on it came. The active steering element is an overlapping steering element. For this into the steering column a planetary gear (about as large as a coffee cup) was integrated, into which a small electrical actuator reaches. When parking for example or in close curves the electrical motor helps over the planetary gear to hit the wheels more than the driver actually turns at the steering wheel. The car works substantially more directly, more actively, more handily. With high motorway speed the electrical motor intervenes opposite, takes the turn back somewhat. The car becomes more indirectly, calmer. 100-mal the second are seized approximately the necessary data over sensors and again computed. The controller decides whether and how much is admitted or taken back at guidance angles. The principal reason for BMW to decide and the electronic way "Steer by Wire" not go for the active steering element, is the realistic feedback, because the mechanical connections between steering wheel and the wheels remain. Also the topic security (electronics loss, redundant systems) is a reason for AFS (Active front Steering). The steering system (only four Kilos excess weight) is even so intelligent that it holds the car with centrifuge danger course, before the DSC would begin its work. Costs will the active steering element somewhat more than 1000 euro, to have in the fuenfer, Sechser and in following models. The additional installation, for example in the Siebener or also in the coming Z4, is not possible. Those are not completely unfortunate Bavaria not to be able to use the abbreviation AFS. One wants eh away from the letters, is called it from Munich. AFS is occupied. Not only active front light stands, but also for the "working group suitor groups of quiet" for Hellas."

Take care,

AnthonySoete · 23rd August 2002, 19:55

Really interesting, thank you for posting.

One question remains : if the car accelerates along a constant radius curve (circle), does the driver have to increase the steering wheel angle (as the ratio is not constant) ?

kevin034 · 23rd August 2002, 22:24

I don't know about this new technology. A major part of how a car performs has to do w/ how the tire-to-road contact is fed back to the driver. I'm afraid that this technology may take that away? I also believe that many of us has gotten used to the fact of "when car go slow, steering more effective. when car goes fast, steering less effective" concept.

I am just not sure about this tech. I rather have the good old rack-n-pinon steering IMHO.