Quote:
Originally Posted by footie
Enigma and Swamp,
You guys are still think of DCT like you would SMG, eg. one clutch controlling all of the gears. The jerk is engineered, please go and get a bit of advice on DCT and dual clutch technology before ranting.
Correct in your comments on why you don't what jerk but to think that the Veyron would suffer from traction issues, the Veyron can put all of it's 1160hp (yes that's right) to the road even in the rain. The reason jerk is unwanted is because it will cause unbalance the chassis during cornering.
ICT is the future, not CVT and BMW are a big player (among other car and gearbox manufacturers) in this technology as they are co-testing this technology with http://www.torotrak.com/, the company which invented it. Unlike CVT IVT can cope with more torque than is currently produced by any production vehicle and unlike CVT it uses special oil which increases friction, specially developed by Shell. The advantage of IVT is that it will optimise the engine's power and torque by acceleration at the optimum rev point unlike either a manual or automatic which has fixed ratios.
P.S.
And not a jerk in sight.  |
Well you have some OK points here but to insult either me or enigma in saying we do not understand how a DCT works is utter nonsense. Perhaps you should read my dozens of posts on the topic and the explanations I have provided to others before spouting such drivel. I think you have but maybe your memory just sucks as well.
You have continued to exhibit a clear lack of technical knowledge and grasp here on the forum. You do offer many valuable comments and opinions but your weakness is clear. I have my weaknesses as well, but generally technical understanding and ability isn't one of them.
It is a very interesting idea this whole jerk thing. Could BMW have possibly engineered the jerk back into the system when by its fundamental design there is no jerk? I just do not think it is possible. But in the future it may be. We have discussed extensively here on this forum the differences between speed (i.e. acceleration) and the perception of acceleration. It is a foregone conclusion that jerk is a more important factor in the perception of acceleration, but not actually in the measured acceleration and hence actual performance. Folks LOVE the SMG S6 smack, the jerk, it simply feels fast. But IT IS NOT AS FAST as it can be. It is not because it wastes time and bleeds speed by decelerating. The deceleration while the throttle is lifted and clutch is engaged with any MT or SMG system slows you down and produces less acceleration compared to an equivalent DCT design. We have explained why without some careful management even a DCT transmission will produce a spike/jerk. It is flywheel intertia and engine torque vs rpm.
Do you even have any idea what an accelerometer trace for a shift in a MT/SMG/DCT/AT will even look like and what they mean? Let me try help as much as possible. Below are some quick sketches of acceleration vs. time. There are not position vs. time, not velocity vs. time, but
acceleration vs. time. Qaulitatively the height of each curve represent how much push you feel on your back in the seat at any instant. These curves are not exact by any means, but do get all the main points across. Before clutching you are in a mode of acceleration dropping as engine torque does. When throttle is reduced and clutching the acceleration drops very sharply. If or how far you get below the x axis of zero accelertation depends on how fast you are going and how much air resistance there is. Here since you actually go to negative acceleration these shifts are likely above 50 mph or so. When you clutch out the accleration builds and you get the positive jerk as the flywheels momentum is conserved and the engine is transitioned to a lower rpm at a point it produces more torque. SMG exhibits both the dip and rise but they are very short. The AT smoothes everything over and generally lengthens the total shift time. Now with DCT you almost entirely eliminate the negative jerk via simultaneous clutching and are just left with the positive jerk (surge as BWM is calling it) from the flywheel effects and from the engine simply producing more torque at lower rpm.
Now much like an automatic transmission, but accomplished by very different means the Veyron and VW DSGs very much reduce the positive spike/jerk shown in my approximated DCT graph. As well lower A modes in DCT will similarly reduce the spike shown (and very likely stretch the time out, like the automatic but more on the time scale of a very good automatic, say the IS-F).
I think I am in part to blame for your misunderstanding here. I have talked much about how the BMW system will be very smooth yet still offer great performance. I was likely incorrect on their ability to have the ultimate performance with almost no jerk. My predictions here were based on both the Veyron and GTI DSG units as well.
It really seems like BMW has obtained the best of both worlds. There is less jerk than a MT or SMG, however there still is jerk but it is a surge rather than containing any deceleration. I would be very willing to live with little to no jerk myself if it meant more performance, but most would not. Almost no one can separate their perception of speed with obtaining true speed, hence everyone really wants the jerk. I guess that is why the forum seems to appreciate me and enigma!
Footie, please take some serious time and think this through. We are realyl trying to help you. Others: Correct my mistakes and predictions and let's keep the discussion going.
P.S. Thanks for the info on IVT, I am always keen on the emerging technologies. Some reading and research needed here for sure.