M-DCT Semantics and Subtleties

[mkoesel]

Originally Posted by Danand85

Every time I put my foot down it bounces out of automatic into paddle shift mode, even at fairly low RPM. So I keep having to hit the DCT shifter right again - to put it back in auto.

Is this correct? How would do I keep it in auto?

Be aware that, when in auto (S) mode, if you pull one of the paddles on the steering wheel, the car automatically changes to manual (D) mode and stays there until you switch back using the shift lever, iDrive settings, or a suitably programmed M button.

So, what is almost surely happening here is the acceleration of the vehicle is causing your hands to tighten and accidentally pull one of the paddles in the process. Try accelerating in auto mode with your hands tight on the wheel and see if you can get the car to switch to manual mode. I suspect you'll find it does not.

[NPuter]

I know this question was asked on the last page, but I figure I might as well ask it again since it has been over a year.

Is there any way to disable low speed assistant (via coding or flashing)? (Tap the gas to make the car start creeping)
I find it makes parking or inching forward in traffic very difficult (having to tap the gas then immediately jump to the brake and use the brake to modulate how fast the car creeps). The creep w/o braking is not slow imo, and I find its pretty impossible to make maneuvers of just a couple of inches without risk. With a manual, I'm able to back within an inch of a wall. With the DCT, I start getting nervous a a couple of feet out.

It was said "drive it like a manual" with the right pedal acting as both throttle and clutch. That is just not a good analogy with this low speed assistant. You can modulate a clutch without ever touching the brake (on a flat surface) to have the car creep/stop. There's no easily modulating the clutch using a single pedal with this DCT.

I know the answer is probably still no, so this is a bit of a rant.
I think this gearbox would be perfect if it didn't keep the clutch engaged until you hit the brake.

[KevinGS]

I have to say, I love the way this DCT transmission is slightly clunky and "feels" like a manual, with how it engages 1st from a start, how it slows down when coming to a stop, how I can take my foot off the brake when stopped and the car doesn't creep, etc. I really like that it's not torque-converter smooth....yet in high velocity mode, the downshifts are fast and furious.

[mkoesel]

Originally Posted by NPuter

I know this question was asked on the last page, but I figure I might as well ask it again since it has been over a year.

Is there any way to disable low speed assistant (via coding or flashing)? (Tap the gas to make the car start creeping)

I don't understand what you want the car to do instead of behaving this way? How do you get the car moving if not via the gas pedal?

If you are asking for it to move slower, that's also not possible. It already creeps at idle speed, and anything less would lead to a stall. The reason you can move slower in a car with an MT is because you can ride the clutch to simulate a slower input-shaft speed than the engine's idle speed. Not possible with DCT.

I think this gearbox would be perfect if it didn't keep the clutch engaged until you hit the brake.

If you let it coast down to a stop, it will eventually disengage the clutch by itself to keep the car from stalling.

Other than in that case, there is no other function of the car you could use to tell it to disengage the clutch besides the brake pedal.

You are looking for software solutions to a problem that could only be solved by adding hardware (a clutch pedal, or rather two of them actually, or some ill-conceived button or slider switch to toggle the clutch engagement, which would be a disastrously poor interface).

[zohaibkhawaja]

For those of you who use the parking brake when turning the car off in D or S, do you pull the parking brake before or after turning the car off? Is there a correct order to do so? I usually pull the parking brake before but the owners manual seems to suggest turning the car off then pulling it.

[CanAutM3]

Originally Posted by zohaibkhawaja

For those of you who use the parking brake when turning the car off in D or S, do you pull the parking brake before or after turning the car off? Is there a correct order to do so? I usually pull the parking brake before but the owners manual seems to suggest turning the car off then pulling it.

When the car is parked, it is preferable for it to rest on the parking brake and not the on transmission parking pawl.

So it is not really a matter of when you shutdown the engine in the sequence but rather how you transition between the brakes. Ultimately, you want to engage the parking brake BEFORE you release the brake pedal.

[zohaibkhawaja]

Originally Posted by CanAutM3

When the car is parked, it is preferable for it to rest on the parking brake and not the on transmission parking pawl.

So it is not really a matter of when you shutdown the engine in the sequence but rather how you transition between the brakes. Ultimately, you want to engage the parking brake BEFORE you release the brake pedal.

In this case does it matter if you remove your foot from the brake after engaging the parking brake but before shutting off the car? Just want to make sure I'm not doing anything that's not good for the car.

[NPuter]

Originally Posted by mkoesel

I don't understand what you want the car to do instead of behaving this way? How do you get the car moving if not via the gas pedal?

If you are asking for it to move slower, that's also not possible. It already creeps at idle speed, and anything less would lead to a stall. The reason you can move slower in a car with an MT is because you can ride the clutch to simulate a slower input-shaft speed than the engine's idle speed. Not possible with DCT.



If you let it coast down to a stop, it will eventually disengage the clutch by itself to keep the car from stalling.

Other than in that case, there is no other function of the car you could use to tell it to disengage the clutch besides the brake pedal.

You are looking for software solutions to a problem that could only be solved by adding hardware (a clutch pedal, or rather two of them actually, or some ill-conceived button or slider switch to toggle the clutch engagement, which would be a disastrously poor interface).

I'm asking for it to not keep the clutch engaged indefinitely after releasing the gas. My R-Tronic R8 released the clutch when I released the gas at creeping speed (i.e. no "low speed assist" - if you wanted to keep moving, you had to keep on the gas), so I could inch the car by just repeatedly lightly tapping the gas, instead of having to jump between gas and brake in the F80. Albeit I was definitely not a fan of R-Tronic, but in terms of low-speed maneuverability, it was much easier to control than the F80 DCT.

I'm also not asking for the car to creep slower by slipping the clutch. I understand why that's not a viable solution. (Although I know the car can creep slower than it does without stalling - I can force it to by using the brake.) But without the low speed assist feature, you'd be able to make more precise maneuvers because you could just tap the gas to move up on inch, instead of having to tap the gas then immediately jump to the brake to stop the creep.

Also, from my experience, my car will never release the clutch and coast to a stop without you hitting the brake. It will go down to idle creep speed and stay there until I hit the brake.

Right now, two pedals control the clutch: the gas to engage it, and the brake to disengage it. I'm asking for the clutch to engage when depressing the gas and disengage when releasing it, giving you control over the clutch with one pedal (how I think it should be).

Overall, I'm definitely a fan of the DCT. It's just this small change that would make it perfect for me.

[SD ///M4]

Originally Posted by zohaibkhawaja

In this case does it matter if you remove your foot from the brake after engaging the parking brake but before shutting off the car? Just want to make sure I'm not doing anything that's not good for the car.

1. Come to a stop
2. Pull up the parking brake
3. Push the On/Off button once to turn off the engine
4. Take your foot off the brake
5. Push the On/Off button again to turn off the ignition or just get out of the car and lock it, which will also turn off the ignition.

You really want your foot on the brake until the engine has shut down. However, if you keep your foot on the brake and push the On/Off button twice, it will turn the engine off and then start it again.

[mkoesel]

Originally Posted by NPuter

I'm asking for it to not keep the clutch engaged indefinitely after releasing the gas.

I see. What confused me was your words "Tap the gas to make the car start creeping." I understand now that what you are looking for is to be able to release the gas to make it stop creeping.

I'm also not asking for the car to creep slower by slipping the clutch. I understand why that's not a viable solution. (Although I know the car can creep slower than it does without stalling - I can force it to by using the brake.)

Right, although that will still cause the computer to slip the clutch or at least ride on the edge of engagement (I believe the manual even has a warning about this type of behavior causing wear - or did in some revision). Either way, it's a course-grained way of artificially limiting the speed with possible undesired side-effects.

But without the low speed assist feature, you'd be able to make more precise maneuvers because you could just tap the gas to move up on inch, instead of having to tap the gas then immediately jump to the brake to stop the creep.

I see how that could be useful, sure.

Also, from my experience, my car will never release the clutch and coast to a stop without you hitting the brake. It will go down to idle creep speed and stay there until I hit the brake.

That makes more sense - probably my misremembering. There are definitely cases where the car will release the clutch without application of the brake, but it's probably limited to a spin or other extreme situations.

Right now, two pedals control the clutch: the gas to engage it, and the brake to disengage it. I'm asking for the clutch to engage when depressing the gas and disengage when releasing it, giving you control over the clutch with one pedal (how I think it should be).

It's not a bad idea. The drawback is that you can't creep without some pedal input. I appreciated the no-input behavior in traffic, particularly when combined with the ability to toggle from first to second gear.

Overall, I'm definitely a fan of the DCT. It's just this small change that would make it perfect for me.

What would be nice is if you could choose which way you wanted it to operate using iDrive settings. They could even add a third "auto-creep" mode allowing you to use the brake pedal for both engaging and disengaging the clutch.

[NPuter]

Originally Posted by mkoesel

I see. What confused me was your words "Tap the gas to make the car start creeping." I understand now that what you are looking for is to be able to release the gas to make it stop creeping.



Right, although that will still cause the computer to slip the clutch or at least ride on the edge of engagement (I believe the manual even has a warning about this type of behavior causing wear - or did in some revision). Either way, it's a course-grained way of artificially limiting the speed with possible undesired side-effects.



I see how that could be useful, sure.



That makes more sense - probably my misremembering. There are definitely cases where the car will release the clutch without application of the brake, but it's probably limited to a spin or other extreme situations.

We're on the same page now

It's not a bad idea. The drawback is that you can't creep without some pedal input. I appreciated the no-input behavior in traffic, particularly when combined with the ability to toggle from first to second gear.

I definitely find the low speed assist useful a lot of times (like you mention, in traffic, or just slowly driving through parking lots). It's just the difficulties that it causes with parking in really tight spaces that makes me rather not have it altogether.

What would be nice is if you could choose which way you wanted it to operate in iDrive. They could even add a third "auto-creep" mode allowing you to use the brake pedal for both engaging and disengaging the clutch.

A user-selectable option would be amazing (Teslas have the option to turn creep on/off), but I understand why BMW would avoid doing that. There are also alternatives I can think of (e.g. the car disabling low speed assist when the parking sensors are active/know when you're close to something).

Audi/Porsche DSG/PDK simulate a normal auto where the car starts/stops creeping with the brake pedal. I'm also not a huge fan of the way that works (I had an S7 with DSG). Mainly because it's weird having the car add throttle without touching the gas. It feels like the car is trying really hard to simulate a torque converter, but with it not doing a great job at it. It definitely does make the car easier to control when parking though.

[akkando]

Originally Posted by zohaibkhawaja

In this case does it matter if you remove your foot from the brake after engaging the parking brake but before shutting off the car? Just want to make sure I'm not doing anything that's not good for the car.

I pull the parking brake, put in neutral, let my foot off the brake so the car rests on the parking brake, then put my foot back on the brake, switch into gear and turn the car off.

[NPuter]

Originally Posted by akkando

I pull the parking brake, put in neutral, let my foot off the brake so the car rests on the parking brake, then put my foot back on the brake, switch into gear and turn the car off.

The switching to neutral and then back into gear is superfluous. You can leave the car in gear, pull the ebrake, take your foot off the brake (clutch won't engage without the gas, so the car will roll and sit on the ebrake), and then shut the car off to put it in park.

[NPuter]

Actually my last post made me think of something. Is there any difference between D and N (besides clutch engagement)? i.e. is there anything happening in the transmission when switching between D and N? There's the obvious clunking when switching in and out of R, but I'm not recalling hearing/feeling anything when going between N and D.

[akkando]

Originally Posted by NPuter

The switching to neutral and then back into gear is superfluous. You can leave the car in gear, pull the ebrake, take your foot off the brake (clutch won't engage without the gas, so the car will roll and sit on the ebrake), and then shut the car off to put it in park.

Hmm, you might be right.

[zohaibkhawaja]

Originally Posted by NPuter

The switching to neutral and then back into gear is superfluous. You can leave the car in gear, pull the ebrake, take your foot off the brake (clutch won't engage without the gas, so the car will roll and sit on the ebrake), and then shut the car off to put it in park.

So if one does not let off the brake after engaging the parking brake before shutting the car off is the weight of the car on the parking brake or the transmission?

[mkoesel]

Originally Posted by NPuter

Is there any difference between D and N (besides clutch engagement)? i.e. is there anything happening in the transmission when switching between D and N?

Although I don't know for absolute certain, I believe the TCU disengages all shift collars just as would be the case with a manual transmission with the shifter is in the neutral position.

It is true that the TCU could technically just open both clutches and call that state "neutral", leaving one or two shift collars engaged. However it makes more sense to put the transmission into a true neutral state, if for no other reason, in case a clutch were to be engaged due to some failure in the hydraulic system. One might put the transmission in neutral and exit the vehicle for an extended period of time, and merely relying on the clutch remaining open to keep the car from moving would be unnecessarily precarious.

Whether the TCU also keeps both clutches open at that point, I don't know.

[NPuter]

Originally Posted by zohaibkhawaja

So if one does not let off the brake after engaging the parking brake before shutting the car off is the weight of the car on the parking brake or the transmission?

I think mostly likely it'd still sit on the ebrake before putting load on the parking pawl.

Originally Posted by mkoesel

Although I don't know for absolute certain, I believe the TCU disengages all shift collars just as would be the case with a manual transmission with the shifter is in the neutral position.

It is true that the TCU could technically just open both clutches and call that state "neutral", leaving one or two shift collars engaged. However it makes more sense to put the transmission into a true neutral state, if for no other reason, in case a clutch were to be engaged due to some failure in the hydraulic system. One might put the transmission in neutral and exit the vehicle for an extended period of time, and merely relying on the clutch remaining open to keep the car from moving would be unnecessarily precarious.

Whether the TCU also keeps both clutches open at that point, I don't know.

Interesting question. A number of possibilities that all result in the same user experience. I bet you're right though. I'd also imagine that it would reduce wear vs it having to keep the clutches open a lot more frequently.

[CanAutM3]

Originally Posted by mkoesel

Although I don't know for absolute certain, I believe the TCU disengages all shift collars just as would be the case with a manual transmission with the shifter is in the neutral position.

It is true that the TCU could technically just open both clutches and call that state "neutral", leaving one or two shift collars engaged. However it makes more sense to put the transmission into a true neutral state, if for no other reason, in case a clutch were to be engaged due to some failure in the hydraulic system. One might put the transmission in neutral and exit the vehicle for an extended period of time, and merely relying on the clutch remaining open to keep the car from moving would be unnecessarily precarious.

Whether the TCU also keeps both clutches open at that point, I don't know.

As far as I know the clutches are “normally” open on the DCT and hydraulic pressure is required to close them. This is opposite to a standard manual transmission where the clutch is normally closed and outside force (the foot pressing on the clutch pedal) is required to open it. So when the engine is shut down, there is no more hydraulic pressure in the DCT and both clutches open.

Ragarding the neutral position for the transmission, the diagram in the F8X technical training doc shows a true neutral with none of the gear dogs engaged.

[mkoesel]

Originally Posted by CanAutM3

As far as I know the clutches are “normally” open on the DCT and hudraulic pressure is required to close them. This is opposite to a standard manual transmission where the clutch is normally closed and outside force (the foot pressing on the clutch pedal) is required to open it. So when the engine is shut down, there is no more hydraulic pressure in the DCT and both clutches open.

That is also my understanding, yes. With regard to my reply, I should have been clear that I was speaking in terms of the engine running. I assumed that was what the member I replied to was referring to, but admittedly, he did not specify.

It does make sense that, even with the engine running, in neutral there wouldn't necessarily be a reason to close the clutches. I don't know for sure if that's how it works though.

Regarding the neutral position for the transmission, the diagram in the F8X technical training doc shows a true neutral with non of the gear dogs engaged.

Thanks for the point of reference. Good to have confirmation that it behaves as one might expect.

[CanAutM3]

Originally Posted by mkoesel

It does make sense that, even with the engine running, in neutral there wouldn't necessarily be a reason to close the clutches. I don't know for sure if that's how it works though.

I've attached the diagram from the training doc in my previous post, it shows both clutches open in the neutral position. So it fair to assume that it is the case when the engine is running. Which also makes sense from an efficiency perspective, why waste engine power to keep clutch closed when it is not needed.

[NPuter]

Originally Posted by CanAutM3

That's the thing, by having the parking brake engaged before engaging "Park", there is NO load on the parking pawl .

The car still moves though after setting the ebrake and taking your foot of the brake (albeit very slightly), which is why I said most likely.

Also, is it advisable to not use the ebrake when you're on a flat surface (to avoid wearing it out)?

Interesting stuff regarding the neutral position. I did not know that the clutches are normally open.