Dual clutch transmissions
Discussion
Driving one of these at the moment, Getrag box twin Haldex clutches, very similar to the VW/Audi DSG concept.
I could necro that thread on driving autos where the discussion on sitting on the brakes in traffic got heated so I won't.
The accepted wisdom seemed to be, keep on footbrake until somebody pulls up behind then handbrake on and foot off brakes to extinguish brake lights. Only slip box into neutral if it's areally long stop as that causes more wear than just letting the torque converter quietly churn away.
However this DCT disengages the clutch if you sit with foot on brake, yet as soon as you engage hand brake and come off foot brake it engages the clutch on the 1-3-5-shaft to what I would describe as the biting point.
Seems with a DCT transmission you are potentially in a lose-lose situation. Keep foot on brake, inconsiderate to vehicles behind. Handbrake on, poor mechanical sympathy. Keep slipping into neutral, again poor mechanical sympathy.
Other than this the Getrag version of the DCT works well and I have not managed to ctach it out yet, much more driveable than a slush box, yet concerns about clutch life.
I could necro that thread on driving autos where the discussion on sitting on the brakes in traffic got heated so I won't.
The accepted wisdom seemed to be, keep on footbrake until somebody pulls up behind then handbrake on and foot off brakes to extinguish brake lights. Only slip box into neutral if it's areally long stop as that causes more wear than just letting the torque converter quietly churn away.
However this DCT disengages the clutch if you sit with foot on brake, yet as soon as you engage hand brake and come off foot brake it engages the clutch on the 1-3-5-shaft to what I would describe as the biting point.
Seems with a DCT transmission you are potentially in a lose-lose situation. Keep foot on brake, inconsiderate to vehicles behind. Handbrake on, poor mechanical sympathy. Keep slipping into neutral, again poor mechanical sympathy.
Other than this the Getrag version of the DCT works well and I have not managed to ctach it out yet, much more driveable than a slush box, yet concerns about clutch life.
I'm not trying to be smart-arse here, but what does the handbook suggest/recommend for such events as being staionary at traffic lights?
I would have thought the likes of Getrag would have designed/developed the transmission to cope with normal stop/start city driving, without prematurely wearing out if you use the handbrake?
I would have thought the likes of Getrag would have designed/developed the transmission to cope with normal stop/start city driving, without prematurely wearing out if you use the handbrake?
What car is this F I F? My newly acquired M3 DCT does not seem to engage the clutch when stopped either with foot on footbrake or with handbrake on. To engage the clutch and creep you touch the accelerator and then release it. You can use the footbrake to slow, but if you bring the car to a halt the clutch disengages. I find it convenient to use the handbrake if stopped for a while, with a stable situation behind.
It's nothing exotic just a Volvo V50 and is on an extended test direct from the manufacturer. Just released and I reckon they have not delivered one to a real customer yet. Not even sure if dealers have got them yet, my local one was still waiting last week anyway.
Re the handbook it still just refers to the Geartronic which is conventional auto with torque converter. The general funcionality is the same.
If you pull up at lights, keep foot on brake after a few seconds the clutch disengages. Pull on handbrake, foot off brake pedal, you can feel the back of the car drop a bit as the clutch takes up the biting point. Press the pedal again and it disengages again. On and off the brake and you could get the back of the car bouncing up and down a little.
This does not seem right to me and will put it in my test report back to the manufacturer.
Might have a bit of a test today and see if disengages after a long while in D and just sitting with handbrake on, but reckon if it were used in a very congested area that it would get very hot on that clutch. Have to take 'er indoors shopping to Bridgenorth in a bit for some nefarious random item she's seen but round our way if there is more than 20 cars in a queue the locals scream gridlock and want a bypass so will have to looking for trouble.
Interesting about the M3, as wondered what other systems did.
Re the handbook it still just refers to the Geartronic which is conventional auto with torque converter. The general funcionality is the same.
If you pull up at lights, keep foot on brake after a few seconds the clutch disengages. Pull on handbrake, foot off brake pedal, you can feel the back of the car drop a bit as the clutch takes up the biting point. Press the pedal again and it disengages again. On and off the brake and you could get the back of the car bouncing up and down a little.
This does not seem right to me and will put it in my test report back to the manufacturer.
Might have a bit of a test today and see if disengages after a long while in D and just sitting with handbrake on, but reckon if it were used in a very congested area that it would get very hot on that clutch. Have to take 'er indoors shopping to Bridgenorth in a bit for some nefarious random item she's seen but round our way if there is more than 20 cars in a queue the locals scream gridlock and want a bypass so will have to looking for trouble.
Interesting about the M3, as wondered what other systems did.
waremark said:
My newly acquired M3 DCT does not seem to engage the clutch when stopped either with foot on footbrake or with handbrake on. To engage the clutch and creep you touch the accelerator and then release it.
Sorry missed commenting on this bit.If you are in D or manual and stopped with handbrake on, foot off brake, to creep just release the handbrake and you're away.
If you are sat as above but with foot on brake, then touching the accelerator causes the clutch to engage quicker but only marginally so.
Edited by F i F on Saturday 14th June 07:24
Sounds to me as if they have tried to reproduce conventional mush box behaviour, but with (presumably) a friction plate clutch. That sounds like a recipe for a very short clutch life, to me. The only way I can see to avoid it from your description is to hold it on the foot brake, too bad for the drivers following you.
Edited by GreenV8S on Sunday 15th June 00:08
If the Volvo has a mechanism whereby the footbrake causes the clutch to disengage, it should not be too difficult for them to make the handbrake also cause the clutch to disengage.
The BMW handbook tells you that if you start the car creeping with the accelerator, and then make too much use of the footbrake to slow it down, 'the gearbox will get hot'. If it gets too hot there will be a warning light (which I have not seen), and if you cause it to go on getting hotter it will stop you driving until it has cooled down. So basically they are saying that there is a safety mechanism to stop you causing damage; and clearly the BMW system whereby the clutch is disengaged if the car is braked to a halt is kinder to the clutch. I have still only had the car for a week so I don't know all the ins and outs. The only time I felt that I might be working the clutch hard was reversing up a steep hill, where I was probably causing the clutch to slip by the way I used the accelerator - but I would probably have been slipping the clutch in the same circumstances in a manual. I am finding the gearbox great.
The BMW handbook tells you that if you start the car creeping with the accelerator, and then make too much use of the footbrake to slow it down, 'the gearbox will get hot'. If it gets too hot there will be a warning light (which I have not seen), and if you cause it to go on getting hotter it will stop you driving until it has cooled down. So basically they are saying that there is a safety mechanism to stop you causing damage; and clearly the BMW system whereby the clutch is disengaged if the car is braked to a halt is kinder to the clutch. I have still only had the car for a week so I don't know all the ins and outs. The only time I felt that I might be working the clutch hard was reversing up a steep hill, where I was probably causing the clutch to slip by the way I used the accelerator - but I would probably have been slipping the clutch in the same circumstances in a manual. I am finding the gearbox great.
I guess it would be possible to check if the handbrake sensor does cause the clutch to disengage by applying the handbrake only just enough to illuminate the warning light (usually possible to achieve long before they is any real braking force applied) and see if the car will still creep forward.
Let me know if this is the case since the condition you describe, i.e. stationary in traffic with vehicle in D and handbrake applied is not an unreasonable one and you are right if the clutch remains engaged then this is generating unnecessary wear. If this is the case I may be able to help sort it out
. That said the clutch durability cycles and misuse/abuse tests for these things are so severe that I very much doubt the additional wear would make itself apparent within normal vehicle lifespans.
Let me know if this is the case since the condition you describe, i.e. stationary in traffic with vehicle in D and handbrake applied is not an unreasonable one and you are right if the clutch remains engaged then this is generating unnecessary wear. If this is the case I may be able to help sort it out
. That said the clutch durability cycles and misuse/abuse tests for these things are so severe that I very much doubt the additional wear would make itself apparent within normal vehicle lifespans.If you don't apply the handbrake firmly enough it still creeps against the handbrake. Does that answer your question?
I added a bit more in the report in the Volvo forum but will add it here too.
If you have been sat with the handbrake on a long time and then release it, the vehicle still creeps forward but only just. The place where I tried that it was on a slight upslope though.
I also sat the vehicle in D hand brake on idling away for about 45 mins while I hoovered, washed it and leathered off. Still crept and not a smidgin of complaint, ie no transmission warning light.
Also took it round a town with lots of steep hills and various junctions. They've got the hill start thing off pat. You can drive to the top of a hill with a T-junction, get up to the give way line still on the slope, and it gets the clutch hold position cock on every time. Very impressive, tbh I'd rather have that feature than a question mark about this clutch biting point thing. Did a few reverse parallel parks up a fair old hill into a tight space, and it was a p.o.p to do it, very controllable. It did make me wonder if it has some means of sensing just how much clutch slip to use to hold the vehicle, thus handbrake on = not much needed so hardly any engagement. Dunno just thinking aloud really.
edited due to spooling misstonks
I added a bit more in the report in the Volvo forum but will add it here too.
If you have been sat with the handbrake on a long time and then release it, the vehicle still creeps forward but only just. The place where I tried that it was on a slight upslope though.
I also sat the vehicle in D hand brake on idling away for about 45 mins while I hoovered, washed it and leathered off. Still crept and not a smidgin of complaint, ie no transmission warning light.
Also took it round a town with lots of steep hills and various junctions. They've got the hill start thing off pat. You can drive to the top of a hill with a T-junction, get up to the give way line still on the slope, and it gets the clutch hold position cock on every time. Very impressive, tbh I'd rather have that feature than a question mark about this clutch biting point thing. Did a few reverse parallel parks up a fair old hill into a tight space, and it was a p.o.p to do it, very controllable. It did make me wonder if it has some means of sensing just how much clutch slip to use to hold the vehicle, thus handbrake on = not much needed so hardly any engagement. Dunno just thinking aloud really.
edited due to spooling misstonks
Edited by F i F on Friday 27th June 13:40
There are sensors to measure both the amount of clutch slip and the wheel speed (common sensors with the ABS/ESP system). The TCM can then infer from this data the relationship between clutch engagement and wheel speed hence figure out how much clutch slip to allow to achieve the desired amount of creep. You may be interested to know that one of the issues encountered early in the development is that the normal ABS wheel speed sensors can't sense the direction of rotation which created some issues with maneuvering on a slope when the car couldn't tell the difference between creeping forwards and rolling backwards down the slope - net result was a quick search for some bi-directional sensors.
I haven't driven an MPS6 for a while but when I do I'll keep and eye for what you're describing and see what the development team have to say on the subject of unecessary clutch wear. It's possible that the answer is with it being a wet clutch system it isn't a concern - does raise an interesting question for the next generation of transmissions which will use a dry clutch though.
I haven't driven an MPS6 for a while but when I do I'll keep and eye for what you're describing and see what the development team have to say on the subject of unecessary clutch wear. It's possible that the answer is with it being a wet clutch system it isn't a concern - does raise an interesting question for the next generation of transmissions which will use a dry clutch though.
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