Automated manuals and slow speeds?

[Palut]

How do automated manual transmissions handle slow speed driving? What is going on inside them when one is crawling along at two or three mph?

I would imagine that consumers would expect the new automated manuals to perform exactly like traditional torque converter automatics, and that includes being able to creep forward at very low speeds. How does an automated manual do that? Is it just slipping its clutches the entire time?

 

[JHZR2]

I recently drove friends' Jetta TDI with the DCT, and was NOT a fan.

It was just stupid to "shift" manually, because all the control of declutching and coasting in neutral essentially went away unless you took the lever to N in an awkward way. It wasnt faster to shift manually gear to gear, and didnt always let you do what you wanted.

Now in regular "drive", it was impressive how fast and clean it changed gears one to the next.

But none of this answers your question. I was under the impression that the precision of this device allows the transmission to sit right at the clutch point without causing any practical friction, and then applies directly. I didnt try to see if it crept in first, but I can make my MTs do that so Id imagine this could too. Still, Id bet the wear would be high.

Not a fan for the price and maintenance requirements.

 

[Shannow]

Originally Posted By: JHZR2
I recently drove friends' Jetta TDI with the DCT, and was NOT a fan.


Drove a workmate's golf a while back, and was similarly unimpressed...a torque converter gives you off the line torque multiplication and a little "thrust" which the turbodiesel VW just didn't display

 

[zloveraz]

Yeah slow speeds and smoothness has been the issue with DCT. GM is looking at adding a small TC to the DCT to solve the problem.

http://drivelinenews.com/transmission-insight/gm-explores-torque-converter-dct/

 

[SteveSRT8]

Originally Posted By: Shannow
Originally Posted By: JHZR2
I recently drove friends' Jetta TDI with the DCT, and was NOT a fan.


Drove a workmate's golf a while back, and was similarly unimpressed...a torque converter gives you off the line torque multiplication and a little "thrust" which the turbodiesel VW just didn't display


Yep, a TC isn't as bad as some think now that you can mechanically lock them down at any speed these days. And it's for sure the little motors benefit from some torque multiplication. Even my old NAG1 design based on the WA580 can infinitely vary the lockup in any gear but first and reverse.

GM has a patent on an algorithm for 'stuttering' the TC lockup to dampen driveline vibe which is not widely known. It's one of the reasons most of their slushboxes work quite smoothly these days. They are not as inefficient as many here believe.

Note that Merc has been using a wet clutch for ages in the big power AMG 7 speed slushboxes, it is a unique solution as well. There are many improvements to be made, cost is a huge factor. Remember that mfgrs will chase a one percent improvement in mileage these days...

 

[demarpaint]

Originally Posted By: JHZR2
I recently drove friends' Jetta TDI with the DCT, and was NOT a fan.

It was just stupid to "shift" manually, because all the control of declutching and coasting in neutral essentially went away unless you took the lever to N in an awkward way. It wasnt faster to shift manually gear to gear, and didnt always let you do what you wanted.

Now in regular "drive", it was impressive how fast and clean it changed gears one to the next.

But none of this answers your question. I was under the impression that the precision of this device allows the transmission to sit right at the clutch point without causing any practical friction, and then applies directly. I didnt try to see if it crept in first, but I can make my MTs do that so Id imagine this could too. Still, Id bet the wear would be high.

Not a fan for the price and maintenance requirements.


Funny you mentioned this, just yesterday I drove my buddies VW Jetta and had the exact same impression. Nice car, but if I wanted to shift the car manually I'd buy a stick. As an AT it was fine, shifting it manually, no thanks.

 

[supton]

I thought I read that some of the DSG's had a very deep 1st gear, so as to deal with this issue. At least in the case of the VW the often (and expensive) transmission fluid changes turned me off; well that and their failure of a DMF design. Toss in the question of what happens in very low speed operation, or say very low speed operation on a hill, and I think a TC is better.

 

[90crvtec]

Automated manuals handle low speed driving pretty much the same as you or I would with a traditional manual transmission. If we wanted to creep forward in traffic with a traditional manual, we'd give a few feet to the car in front of us first and that would allow us to let out the clutch entirely in 1st gear to keep slippage and heat to a minimum.

The problem is the automated manuals can't judge traffic and they can't predict when you're going to want more or less acceleration. They can only try to lock the clutch once you start moving. A good example here is when coasting through a right turn yield, you may almost come to stop while checking oncoming traffic to the left. Upon seeing no traffic, if you immediately stab the gas pedal to merge into traffic, the automated manual will usually take up the clutch quite quickly because it's trying to react to driver inputs. I always tell people to drive an automated manual with a similar throttle input to how they would drive a traditional manual, soft throttle inputs at low speeds. This solves 90% of the jerky feeling associated with them.

A lot of people drive dual clutch and single clutch automated manuals and expect that because the gear shift says PRND, it must behave just like an automatic. It doesn't. I think people need to manage their expectations of what these gearboxes are designed to do and will inherently do with a clutch system.

VW allows some creep function in their DSG gearboxes here in the states. My understanding is that this function is largely removed in Europe. Again, it comes down to driver perception "My car is in D, why doesn't it creep forward?!" I would be 100% OK with an automated manual with no creep function, my right foot can control how much creep I want. But we end up with a slightly compromised product to appease the masses who think it's just another automatic.

 

[brandini]

Mazda's SkyActiv transmissions have a tiny TC that locks up at 5mph and higher. Instead of having clutches AND a TC it probably saves a bit of weight and complexity. They also claim a wider lockup range so you get that TC torque multiplication before lockup. Nifty.

 

[dparm]

To clarify, a DCT is not an automated-manual. That would be be more of a sequential-manual/automated-single clutch like the BMW SMG or Ferrari F1 systems. Those aren't used anymore since they tend to be very clunky (it was the only reason I didn't buy an M5, for those who are curious).

I've owned two dual-clutch cars. My Audi had an S tronic, which is a rebranded VW DSG made by BorgWarner. My BMW has an M-DCT, which is made by Getrag (same unit as several Ferraris). I didn't find either one to be jerky. It's all about managing your own expectations. The take-off on both is a bit like a manual in that you have to feed it a bit of gas until the clutch grabs and then accelerate (this is pretty fast, actually). It's not like a torque converter where you can just punch the gas.

Low-speed driving can be weird depending on the programming. The Audi was a bit clunky in this regard because taking your foot off the brake makes the car start moving, just like in a torque-converter automatic. In my BMW, taking your foot off the gas does nothing, akin to having the clutch in on a manual transmission. BMW makes the low-speed driving easier with what they call a "low-speed assistant" -- by just tapping the gas pedal it will very slowly ease it into gear without any jerkiness or shuddering, and let you creep forward in traffic. BMW also offers "Drivelogic", which gives you 6 possible steps for aggressiveness/speed. The Audi basically has normal, sport, and full-manual...but will still shift at redline in manual mode and downshift if you floor the gas, whereas the M-DCT will happily bounce off the rev limiter and stay in gear when you apply more gas.



After owning the two dual-clutch cars, and driving many others, I am convinced that 95% of it comes down to the programming. I would advise you to drive the BMW M-DCT to see what the benchmark really is. Even though VW was the first-to-market with the DSG, I don't think their programming is sport-focused like BMW's.

BTW, the new ZF 8-speed transmission is excellent. I've driven it in a few different cars now and would gladly buy a vehicle with that.

 

[afoulk]

I can only comment on them from the heavy duty side of things. I'm a mechanic for a Mack dealership and everyonce in awhile we get new macks in the shop with either their own M Drive automated manual (its a Volvo transmission) or Eaton's automated version of their 10spd manual. The eaton is horrible. It uses a clutch with centrifical weights, so it does not grab until the rpms are brought up. This sounds fine, until your sitting on a hill at a red light, or trying to back a trailer up to a loading dock. it will start rolling until you bring the rpms up, unless you keep your left foot on the brake. They shift ok, but are programmed to pull out in second, unless you tell it to use 1st, and they will shift up through every gear. If any of you have ever driven a tractor trailer empty, or bobtail (no trailer) you know what a pain this is. The Mack M Drive is far better. It uses an air operated slave cylinder and must engage the clutch just enough to keep the truck from rolling on hills, and makes clutch engagement when backing a trailer up much smoother. It also has a sensor that tells it if the truck is loaded or not, so when unloaded, it will pull out in 3rd or 4th, and actually skip gears (I believe they are 12spds). Only down side to them is they drive the transmission oil pump off the input shaft, so if you are going to tow one from the front, you need to remove the drive shaft or keep the engine on it running, other wise the transmission will burn up.

 

[Nick R]

My focus has a DCT and for the most part it works perfectly. Low speeds can be odd, depending on how you drive it. You want to be smooth and light with throttle inputs at low speeds when you don't intend to accelerate. What will happen is if you give it hard throttle, and then let off, and then back on again, the transmission isn't exactly sure what to do. (Then again a lot of regular automatics do this today too) and can be jerkey. Low speed in stop and go can be fairly normal, but you have to get used to driving it so you know HOW to drive it.

Once you've gotten used to it, driving it at low speeds shouldn't feel awkward. Mine will creep if you ask it to and do so just fine. Takeoffs from a stop during normal operation also feel completely normal. The only difference is there is a slight "catch" of sorts when the clutch fully locks up. Which doesn't bother me, it's just different than a normal auto.

 

[Nick R]

Actually, I just made this video a week or two ago for someone as a demo for the DCT in my focus. And to the nannys, don't worry this was done later at night in a rural area so there wasn't any traffic :|

 

[Nick R]

If you want slow speeds, I did this one just after I got the focus, has more slow speed/stop and go. Though the trannsmission has gotten a lot better since it's broken in and gotten used to my driving style.

 

[Palut]

It seems that each different make's transmission behaves differently at slow speeds. Does anyone know how the transmission is wearing during this kind of operation?

One of these transmissions seems like a nice compromise between a traditional automatic and a stick, to get convenience during traffic and fun during normal driving. But would creeping along through a really bad traffic jam, the kind where you rarely ever achieve the speed that you could actually let out the clutch in a stick, be destroying the clutch faster than it would with a normal stick shift?

I know a torque converter wouldn't care, but it seems like consistently driving one of these transmissions in those conditions could get expensive very quickly.

 

[dparm]

Originally Posted By: Palut
It seems that each different make's transmission behaves differently at slow speeds. Does anyone know how the transmission is wearing during this kind of operation?

One of these transmissions seems like a nice compromise between a traditional automatic and a stick, to get convenience during traffic and fun during normal driving. But would creeping along through a really bad traffic jam, the kind where you rarely ever achieve the speed that you could actually let out the clutch in a stick, be destroying the clutch faster than it would with a normal stick shift?

I know a torque converter wouldn't care, but it seems like consistently driving one of these transmissions in those conditions could get expensive very quickly.



The verdict is still out. The early dual-clutch units were for low-power applications that don't exert high stress, nor are the drivers routinely rowing the gears on the track. It's true that a clutch job on a manual transmission is going to be cheaper, but at the same time, you have two clutches here meaning that the wear should (in theory) be halved.

Dual-clutches are also self-adjusting, meaning that as the mechatronics unit detects slippage (from wear), they are programmed to adjust take-up, shift speed, etc.

Anecdotally, they seem pretty resilient. There are a lot of VWs/Audis running around with 150k+ on their units, original clutches (maybe just one or two fluid changes). BMW has been putting them in the M cars since 2008 and there are again plenty of guys with 100k+ on the clock still humming along...and that's not exactly a pedestrian vehicle. It seems that these things either have catastrophic problems early, probably signifying poor QC, or they go for a very very long time without incident.

The only reports I ever saw were from the mechatronics units, not the transmissions themselves. A mechatronics unit is not cheap, but it is WAY cheaper than the transmission.

 

[Zako2]

One interesting new type of automatic transmission is the 6-speed in the new automatic Skyactiv Mazdas. It has a small torque converter for speeds up to 5pmh or so. After that, the transmission acts as a DSG or something like that. Anyways, the car supposedly has the most direct connection to the road, as if driving a manual transmission.

 

[79sunrunner]

Originally Posted By: dparm
To clarify, a DCT is not an automated-manual. That would be be more of a sequential-manual/automated-single clutch like the BMW SMG or Ferrari F1 systems. Those aren't used anymore since they tend to be very clunky (it was the only reason I didn't buy an M5, for those who are curious).

I've owned two dual-clutch cars. My Audi had an S tronic, which is a rebranded VW DSG made by BorgWarner. My BMW has an M-DCT, which is made by Getrag (same unit as several Ferraris). I didn't find either one to be jerky. It's all about managing your own expectations. The take-off on both is a bit like a manual in that you have to feed it a bit of gas until the clutch grabs and then accelerate (this is pretty fast, actually). It's not like a torque converter where you can just punch the gas.

Low-speed driving can be weird depending on the programming. The Audi was a bit clunky in this regard because taking your foot off the brake makes the car start moving, just like in a torque-converter automatic. In my BMW, taking your foot off the gas does nothing, akin to having the clutch in on a manual transmission. BMW makes the low-speed driving easier with what they call a "low-speed assistant" -- by just tapping the gas pedal it will very slowly ease it into gear without any jerkiness or shuddering, and let you creep forward in traffic. BMW also offers "Drivelogic", which gives you 6 possible steps for aggressiveness/speed. The Audi basically has normal, sport, and full-manual...but will still shift at redline in manual mode and downshift if you floor the gas, whereas the M-DCT will happily bounce off the rev limiter and stay in gear when you apply more gas.



After owning the two dual-clutch cars, and driving many others, I am convinced that 95% of it comes down to the programming. I would advise you to drive the BMW M-DCT to see what the benchmark really is. Even though VW was the first-to-market with the DSG, I don't think their programming is sport-focused like BMW's.

BTW, the new ZF 8-speed transmission is excellent. I've driven it in a few different cars now and would gladly buy a vehicle with that.



When you mentioned you had to add a small amount of throttle before the clutch kicked in, about how many rpms was the engine raised above idle (what is idle rpm) before the clutch engagement?

 

[dparm]

Originally Posted By: Zako2
One interesting new type of automatic transmission is the 6-speed in the new automatic Skyactiv Mazdas. It has a small torque converter for speeds up to 5pmh or so. After that, the transmission acts as a DSG or something like that. Anyways, the car supposedly has the most direct connection to the road, as if driving a manual transmission.



That's how the ZF 8-speed works. The torque converter is locked in 2nd gear and above. The shifts are indeed very quick.

 

[SteveSRT8]

Originally Posted By: dparm
Originally Posted By: Zako2
One interesting new type of automatic transmission is the 6-speed in the new automatic Skyactiv Mazdas. It has a small torque converter for speeds up to 5pmh or so. After that, the transmission acts as a DSG or something like that. Anyways, the car supposedly has the most direct connection to the road, as if driving a manual transmission.



That's how the ZF 8-speed works. The torque converter is locked in 2nd gear and above. The shifts are indeed very quick.


No offense to the legions of 'skyactiv' supporters but there is little new anything in mazda's slushbox. It is simply programmed well.

My 8 year old Chrysler has infinitely variable lockup in any gear but first and reverse. Many other cars do too, some much OLDER!

Computer operated manuals come in many flavors. All they require is proper programming and most would be comparable, this is the key difference from platform to platform. The above mentioned ZF 8 speed has become quite common in nearly everything from Bentley to Jeep...