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  #1  
Old 05-17-2004, 08:02 PM
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Moderato Moderato is offline
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How does SMG engage the clutch from a standstill?

I've never driven an SMG before and with all this talk about only SMG being offered in the new M5 and *possibily* all subsequent M's, I've been wondering what it's like just getting going from a standstill with SMG. I've read some threads about launching and it's my understanding that it has somekind of launch mode where it revs up to 1800rpms , but how does it engage the clutch? Does it ever dump the clutch when launching or does it always slip the clutch? and what about just getting started at a slow pace, does it rev the engine to a certain rpms and slip the clutch in, or does it simultaneously engage the clutch as it brings up the rpms? Does it rev match at all on the slow programs while upshifting, or does it always slip the clutch to bring the rpms down to the next gear? If you're giving it too much or too little throttle, will it override your throttle input to properly bring the rpms to where they need to be? I know the best thing to do would be to drive one but I'm not in the market for a new car now and I don't know anyone who has SMG, but if any of you SMG owners could describe the experience and answer some of my questions, I'm curious to know. Thanks.
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  #2  
Old 05-17-2004, 09:27 PM
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RKT BMR RKT BMR is offline
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The best qualitative answer is not very illuminating: It does basically the same thing you do (assuming you operate your clutch properly -- no dumping!). It just does it more consistently and therefore faster.

The technical answer is a hydraulic actuator controlled by a microprocessor programmed with a sophisticated algorithm that lets out the clutch based on a variety of inputs from a cadre of sensors, most of which were already in the vehicle to begin with (groundspeed, gear, crankshaft speed, etc. etc.)

The main advantage of SMG over a human is precision and speed.

Note that the tranny is the same as that in the manual. The difference is replacement of the manual hydraulic actuator with an automatic one, and the addition of a computer to control the actuator.
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Old 05-17-2004, 10:50 PM
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Quote:
Originally Posted by RKT BMR
Note that the tranny is the same as that in the manual. The difference is replacement of the manual hydraulic actuator with an automatic one, and the addition of a computer to control the actuator.
And, I would assume, no CDV.
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Old 05-18-2004, 09:58 AM
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Quote:
Originally Posted by Moderato
I've never driven an SMG before and with all this talk about only SMG being offered in the new M5 and *possibily* all subsequent M's, I've been wondering what it's like just getting going from a standstill with SMG. I've read some threads about launching and it's my understanding that it has somekind of launch mode where it revs up to 1800rpms , but how does it engage the clutch? Does it ever dump the clutch when launching or does it always slip the clutch? and what about just getting started at a slow pace, does it rev the engine to a certain rpms and slip the clutch in, or does it simultaneously engage the clutch as it brings up the rpms? Does it rev match at all on the slow programs while upshifting, or does it always slip the clutch to bring the rpms down to the next gear? If you're giving it too much or too little throttle, will it override your throttle input to properly bring the rpms to where they need to be? I know the best thing to do would be to drive one but I'm not in the market for a new car now and I don't know anyone who has SMG, but if any of you SMG owners could describe the experience and answer some of my questions, I'm curious to know. Thanks.

I've only had my car a couple days, so I can't really answer some of this, but I'll give you the ones that I know. By the way this is SMG and not SMGII, fyi, but for most of what your asking I think the basic functions are the same.

First your talking about the "acceleration assistant" function. Obviously I have not done this as my car has only 200 miles, but from what I understand its like this. From a stop, DSC off, and in sport mode, put it to the floor. The car will wait and launch at about 2k rpm, feathering the clutch as to not let your wheels spin at all. I have no idea how good this works, I will in a month or so I guess. I'll be posting my personal SMG review once I experience all these things after break in.

Second, starting slowly, like from a stop light or something, just driving normally is like this.
When your stopped the car is clutched, period. You have to hold your foot on the brake to not roll. The light turns green, switch the foot over to the accelerator real quick and the car begins to roll back just barely (depending on incline etc), but as soon as your foot touches the accelerator, and I mean you barely have to touch it, you feel the clutch desengage instantly and from that point you give it some gas just like any manual and go.
So I guess the answer is, the clutch lets go within about a mm of accelerator depression, or simultaneously to the driver hitting the gas.

In auto mode the tranny WILL clutch and kick me down a gear if I depress the accelerator hard in a low rpm situation, however I hardly ever use that, and in manual it will not do that, it will simpy bog the car out.

Outside of your questions, one thing I always heard and worried about before I got my car is jerkiness/lurchyness/rough shift, etc. Just so everyone knows, It took me a grand total of about 4 hours in the car to understand how to make it shift as smooth as butter in ANY mode, even auto without sport, so I just dont understand these comments. Fine if you went for a 5 minute test drive and you nailed it from a stop in auto mode with no sport and kept your foot on the floor the whole time, hell yea I bet it jerked you good, but with just a very simple understanding of it, the thing changes dramatically. Basically, once you learn that it MUST be driven like a MT and not an auto, you begin to understand it.

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  #5  
Old 05-18-2004, 10:22 AM
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Fireman3 Fireman3 is offline
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There is more to Lauch Mode than what you discribe>

The procedure has been listed on this board before. Do a search on "launch Mode" for more info.

BobD
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