DCT shift mechanism speed

[Tomm3]

Anybody knows if the shifting speed is different (S1,S2,S3)?

I am asking about an actual shift speed of the pushrods in the gearbox, not about clutch engagement. It's obvious that the clutch engaging speed is way different for every mode. I just want to find the best mode for the longest lifetime in daily driving when performance is not required at all.

Thanks and have a Happy New Year!

[paliknight]

No idea, but I know most forum members prefer S2.

[CanAutM3]

Good question. The only item that would really suffer from the shift speed you mention are the sychros. Since the gears are "pre-engaged", I have always assumed that the gear engagement speed is the same in all modes while it is the clutch engagement and engine power that is varied depending on Drivelogic modes, but I could be wrong.

[Super Spartan]

Originally Posted by Tomm3

Anybody knows if the shifting speed is different (S1,S2,S3)?
I am asking about an actual shift speed of the pushrods in the gearbox, not about clutch engagement. It's obvious that the clutch engaging speed is way different for every mode. I just want to find the best mode for the longest lifetime in daily driving when performance is not required at all.

Thanks and have a Happy New Year!

From an Arabic review of the M4 that I saw they mention that changing the shift levels doesn't make the car faster but actually increases the strength a in how ferocious the gear shifts are, for example with the level 1, the gear shifts are smooth and silent, level 2 are a bit wilder while with level 3 every heat shift throws you back in your seat with strong feedback

[GrussGott]

Originally Posted by CanAutM3

Good question. The only item that would really suffer from the shift speed you mention are the sychros. Since the gears are "pre-engaged", I have always assumed that the gear engagement speed is the same in all modes while it is the clutch engagement and engine power that is varied depending on Drivelogic modes.

That was my thought too, but I have no idea what I"m talking about so I kept it to myself ... but now that you've said it ...

Seems like IF there's a change in shift speed that the only parts affected would be the faster meshing synchros, although I have a hard time believing there'd be a shift speed change as that seems needlessly complicated. It also seems like there are going to be other drivetrain parts that fail way before those synchros; i.e., mean-time-to-failure is going to happen before the synchros wear out but, again, I really don't know what I'm talking about.

I'm including this picture of an M-DCT to make it look like I'm supporting my point, but really there's no reason for it:

[CanAutM3]

Originally Posted by Snappy Phoenix

From an Arabic review of the M4 that I saw they mention that changing the shift levels doesn't make the car faster but actually increases the strength a in how ferocious the gear shifts are, for example with the level 1, the gear shifts are smooth and silent, level 2 are a bit wilder while with level 3 every heat shift throws you back in your seat with strong feedback

In theory, the higher Drivelogic settings should yield slightly faster acceleration because they execute more aggressive "power shifts". By keeping the engine on full boil during the shift with an aggressive clutch engagement, the DCT is able to recuperate a portion of the inertia from the engine RPM drop and convert it in the car's forward momentum yielding a momentary surge in acceleration (the jerk we feel during the shift). Further, a "power shift" also better matains boost in the next gear.

However, I have never seen actual acceleration measurement comparing Drivelogic modes.

[Tomm3]

Originally Posted by CanAutM3

The only item that would really suffer from the shift speed you mention are the sychros.

This was exactly my thinking. Maybe additionally the "servos" driving the pushrods. By the way are they electrical or hydraulical? Or probably electrically controlled - hydraulically driven.

[captainaudio]

The best shifts are smooth shifts. I don't understand why anyone would want a computer controlled transmission that emulates a poorly driven manual transmission. Shifts should be smooth whether they are accomplished automatically or manually. Rough shifts can unsettle the car and an unsettled car is not a fast car.

[wzj519]

I remember one video on YouTube of M cars explained DCT shift behaviors in manual and auto modes. In manual, you change the shift position does change the shift speed, but you switch shift positions in auto made would just bring you a higher shift point.

[trackm4]

Originally Posted by GrussGott

I'm including this picture of an M-DCT to make it look like I'm supporting my point, but really there's no reason for it:

[lukej]

Originally Posted by GrussGott

That was my thought too, but I have no idea what I"m talking about so I kept it to myself ... but now that you've said it ...

Seems like IF there's a change in shift speed that the only parts affected would be the faster meshing synchros, although I have a hard time believing there'd be a shift speed change as that seems needlessly complicated. It also seems like there are going to be other drivetrain parts that fail way before those synchros; i.e., mean-time-to-failure is going to happen before the synchros wear out but, again, I really don't know what I'm talking about.

I'm including this picture of an M-DCT to make it look like I'm supporting my point, but really there's no reason for it:

Thanks for the pic,, don't have that one..

[Tomm3]

Agree to all previous posts but what you mainly describe - is the speed of cluch engagement - which makes the shifting process smooth or abrupt.

My concern is - at what speed (always constant or maybe different) the synchros in the gearbox are being engaged.

[mkoesel]

Originally Posted by captainaudio

The best shifts are smooth shifts. I don't understand why anyone would want a computer controlled transmission that emulates a poorly driven manual transmission. Shifts should be smooth whether they are accomplished automatically or manually. Rough shifts can unsettle the car and an unsettled car is not a fast car.

Definitely agree on that. However, as far as I can reason, the actual speed of the gear engagement itself should have no bearing on the smoothness of the shift.

Think of it like this: if, when driving a car with a manual transmission, you could somehow shift from one gate to another in zero time, while not changing your foot/clutching action at all, would you do it? Absolutely you would, right? It would definitely shorten your overall total shift time while, since you wouldn't be changing your clutch-in/clutch-out procedure at all, the smoothness of the shift would be identical to your normal (slow by comparison) movement of the shifter from one gate to the other.

[CanAutM3]

Originally Posted by captainaudio

The best shifts are smooth shifts. I don't understand why anyone would want a computer controlled transmission that emulates a poorly driven manual transmission. Shifts should be smooth whether they are accomplished automatically or manually. Rough shifts can unsettle the car and an unsettled car is not a fast car.

While there is some truth to it, that is somewhat of a motherhood statement.

I always use S3 at the track and never had an issue with smoothness. The beauty of DCT is that it can sense when the car is under lateral load and will execute a seamless shift when needed even in S3. You get the best of both words, a power shift when going straight to maximize acceleration and a smooth shift when under lateral load to keep the car perfectly planted .

[captainaudio]

Originally Posted by mkoesel

Definitely agree on that. However, as far as I can reason, the actual speed of the gear engagement itself should have no bearing on the smoothness of the shift.

Think of it like this: if, when driving a car with a manual transmission, you could somehow shift from one gate to another in zero time, while not changing your foot/clutching action at all, would you do it? Absolutely you would, right? It would definitely shorten your overall total shift time while, since you wouldn't be changing your clutch-in/clutch-out procedure at all, the smoothness of the shift would be identical to your normal (slow by comparison) movement of the shifter from one gate to the other.

Originally Posted by CanAutM3

While there is some truth to it, that is somewhat of a motherhood statement.

I always use S3 at the track and never had an issue with smoothness. The beauty of DCT is that it can sense when the car is under lateral load and will execute a seamless shift when needed even in S3. You get the best of both words, a power shift when going straight to maximize acceleration and a smooth shift when under lateral load to keep the car perfectly planted .

I agree that the faster a shift can be executed the better up to the point at which it becomes moot. For an (extreme) example if a shift could be executed in 50 nanoseconds improving shift speed to 10 nanoseconds would be theoretically 5 times faster shifts but would no effect on real world performance. There is certainly nothing wrong with fast shifts and the faster the better but shift speed should not come at the expense of smoothness.

What I was referring to are comments I have seen that equate jerky shifts to high performance. I have a friend who is a driving instructor for Ferrari. He told me that Ferrari actually programmed some of the smoothness out of the paddle shift transmissions on their street cars (at the expense of performance) because owners liked the feeling of jerky shifts and equated them to higher performance.

[CanAutM3]

Originally Posted by captainaudio

I agree that the faster a shift can be executed the better up to the point at which it becomes moot. For an (extreme) example if a shift could be executed in 50 nanoseconds improving shift speed to 10 nanoseconds would be theoretically 5 times faster shifts but would no effect on real world performance. There is certainly nothing wrong with fast shifts and the faster the better but shift speed should not come at the expense of smoothness.

What I was referring to are comments I have seen that equate jerky shifts to high performance. I have a friend who is a driving instructor for Ferrari. He told me that Ferrari actually programmed some of the smoothness out of the paddle shift transmissions on their street cars (at the expense of performance) because owners liked the feeling of jerky shifts and equated them to higher performance.

I agree with what you are saying where there is a point where greater shift speed becomes moot. But did you read my prior post about recuperating the engine inertia? This does have a benefit on acceleration performance and will inherently make the shift "less smooth".

[CanAutM3]

Originally Posted by Tomm3

By the way are they electrical or hydraulical? Or probably electrically controlled - hydraulically driven.

This is what I have always assumed, but did not find anything official to back up my assumption.

[CanAutM3]

Originally Posted by Tomm3

Agree to all previous posts but what you mainly describe - is the speed of cluch engagement - which makes the shifting process smooth or abrupt.

My concern is - at what speed (always constant or maybe different) the synchros in the gearbox are being engaged.

I am pretty sure that BMW and Getrag did their homework on that one. I would not be worried .

[Tomm3]

Just curiosity but do you have any idea if there is a way (probably a kind of scanner or computer connected) to check in what gear is currently the "other" part of the DCT?

[horsepower_and_hounds]

Originally Posted by wzj519

I remember one video on YouTube of M cars explained DCT shift behaviors in manual and auto modes. In manual, you change the shift position does change the shift speed, but you switch shift positions in auto made would just bring you a higher shift point.

Do you think we can find that video? Was it someone from M engineering?

[aboulfad]

Originally Posted by Tomm3

Just curiosity but do you have any idea if there is a way (probably a kind of scanner or computer connected) to check in what gear is currently the "other" part of the DCT?

OT, Yes, using ISTA/D, and calling up the ECU functions for DKG, there's tons of data accessible that is available in realtime.

[Tomm3]

I got an OBT2 bluetooth dongle.
Connecting with my iphone. It is quite interesting to see many DCT parameters.
For example - if stationary and trasmission in N - the DCT is actually always in 7th gear / Neutral. Both clutches open (zero pressure) so you may rev the engine and the car stays still.
For Reverse is alway R/4th gear.
When driving constant speed the other halve is usually in Neutral (probably for fuelsaving).
Of course you can also see the temp of transm oil, clutches temp and pressures etc..