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Voir la version complète : Systeme SMG BMW M3 2003: gadget ou fantastique?



jeffrey1972
23/11/2004, 17h42
Est ce un gadget tout simplement ou une invention vraiment incroyable?

L'avez vous essayé?

Merci :D

guy_geo
23/11/2004, 20h45
Si tu suis la F1, tu devrais avoir ta réponse.

la boîte SMG de BMW ets plus rapide que la manuelle...

Et c un beau petit gadget...
Un peu de lecture :

Le lien:

http://www.europeancarweb.com/tech/0212ec_bmwtech/

The SMG M3 uses exactly the same transmission and clutch, but they are actuated by an electro-hydraulic control system, which also has authority over the throttle. There is no clutch pedal in the car, and the conventional shift lever is replaced by a complex switch, supplemented by paddles mounted to the back of the steering wheel. Shifting can be accomplished using either control. Sequential mode responds to driver input. In automated mode, the computer does its own thing, as if emulating an automatic transmission. There are five settings for shift aggressiveness (speed) in each mode, plus a "maximum-attack" sixth level available only in sequential mode with DSC turned off. BMW states that SMG, in its fastest settings, is faster and more precise than any human could be.

Around town, the SMG car moves away from a stop smoothly, but one must understand that "automated" mode is not the same as an "automatic" transmission. Up- and downshifts are annoying if the car is driven like an automatic. On an upshift, a lurch is felt as the clutch disengages and acceleration ceases, then a pause while the transmission shifts. Finally, acceleration resumes just as abruptly. On downshifts, the engine is often 500 to 1000 rpm short of having matched revs when the clutch engages, causing another lurch. These patterns are felt in sequential mode as well, but they are less annoying because they are responses to driver inputs.

To drive an SMG car smoothly in everyday conditions, you must realize that even though you are not moving a shift lever, you still have to drive it. Lift the throttle lightly for upshifts, rev it a little extra for downshifts. Then it is smooth. Still, it seems as if BMW missed the mark on this part of the calibration and didn't quite deliver all the technology's promise. The pause while shifting in the less aggressive settings is often longer than even gentle shifts with a manual transmission. One solution that seems natural is, instead of lengthening the shift actuation so much, use the extra shift time to breathe off and back on the throttle more gradually.

On a mountain road or racetrack, however, the situation is entirely different. SMG feels as good as advertised. Put it on setting 6, or 5 if you want DSC on, and you quickly feel you couldn't match its speed or precision, whether shifting down or up. Certainly, the art of driving, the complexity and beauty of the dance we love, is diminished, but letting the car do the shifting allows the driver to focus more on his/her line and controlling the chassis. Given equal drivers, an SMG M3 will be faster than the six-speed.

Only two issues arose when driving fast with SMG. First, it ignores downshift requests rather than storing them. If the downshift paddle is pulled too early in braking to be completed without over-revving the engine, the request is ignored. When getting back on the throttle, the driver finds he/she is still in the higher gear--which quickly leads to the other issue: column- versus wheel-mounted shift paddles. In a very tight, autocross-type turn, the wheel may be upside down, switching which side to pull to shift up or down. So when intending to shift from third to second, it becomes easy to inadvertently shift to fourth instead. With column-mounted paddles, they would be exactly where they always are.

One solution (besides the obvious one of not downshifting early) is to make a habit of using the lever on the transmission tunnel. Unfortunately, that would eliminate many of SMG's advantages. In WRC cars, which must be shifted with the steering wheel doing crazy things, the shifter is usually either a dash-mounted lever or a push-pull ring behind the steering wheel. Overall, I find SMG to be an excellent system from the driver's seat. If I only drove on the street, I might stick with the manual, but for track use against a clock, I'd go for SMG every time. I'd like to see a software revision within a year or two, but it's very good right now.