Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
So what is with the dog clutch transmissions? 2
- Thread starter dicer
- Start date
-
2
- #2
BrianPetersen
Mechanical
Are you talking about:
- Motorcycle transmissions, ALL of which use dog-clutches and have done so pretty much forever?
- Aftermarket, generally rally-car, manual transmissions that use dog-clutches in place of synchro units? (these are in no way production transmissions nor will they ever be)
- Tractor-trailer transmissions, which have used dog-clutches forever?
- The ZF 9-speed front-drive transmission, which contains two dog-clutches (and four conventional clutch packs in addition to the lock-up clutch for the torque converter)?
Since you mention future multi-speed automatics, I presume you're referencing the latter situation. The ZF 9-speed has not gone over well; there are many complaints about driveability problems and slow shifting although supposedly these have been fixed (somehow) for 2016; I don't know what they've done inside, but the 2016 transmission has a different part number. The ZF has two awkward shift situations - downshifting from 8th or 9th into 7th or below, and downshifting from any higher gear into 4th or below. Both of those require the engine to disconnect output torque and "match revs" before the dog clutch can be engaged. A really ugly one is 8th into 3rd (e.g. if the driver mashes the accelerator to the floor somewhere near or just over 100 km/h) because then it has to do this rev-matching for BOTH dog clutches. I've driven a car with this transmission and found it to be fine, but I didn't try to intentionally catch it out.
I know a thing or two about the upcoming GM/Ford 10-speed rear-drive because a customer of mine is building parts for those. It contains six conventional hydraulically-actuated multi-plate clutches, in addition to the torque converter lock-up unit. This is promising to be very good.
I know there's an upcoming GM/Ford 9-speed front-drive but I don't know anything about it at this point.
The other choice is the dual-clutch transmission which uses manual-transmission synchro units. VW/Audi is likely to continue using them, because they seem to be the only ones who have figured them out properly (and even at that, some people don't like them because they have a different feel). I understand that Ford is going to be discontinuing theirs (Fiesta/Focus) and it will be replaced with some sort of conventional automatic; which one isn't known yet. Hyundai seems to be moving forward with theirs.
A big chunk of the automotive world is set on using CVT, like it or not. I don't like them, but I will grant that in a normal daily-driver vehicle driven by a non-enthusiast, they have become a decent solution.
- Motorcycle transmissions, ALL of which use dog-clutches and have done so pretty much forever?
- Aftermarket, generally rally-car, manual transmissions that use dog-clutches in place of synchro units? (these are in no way production transmissions nor will they ever be)
- Tractor-trailer transmissions, which have used dog-clutches forever?
- The ZF 9-speed front-drive transmission, which contains two dog-clutches (and four conventional clutch packs in addition to the lock-up clutch for the torque converter)?
Since you mention future multi-speed automatics, I presume you're referencing the latter situation. The ZF 9-speed has not gone over well; there are many complaints about driveability problems and slow shifting although supposedly these have been fixed (somehow) for 2016; I don't know what they've done inside, but the 2016 transmission has a different part number. The ZF has two awkward shift situations - downshifting from 8th or 9th into 7th or below, and downshifting from any higher gear into 4th or below. Both of those require the engine to disconnect output torque and "match revs" before the dog clutch can be engaged. A really ugly one is 8th into 3rd (e.g. if the driver mashes the accelerator to the floor somewhere near or just over 100 km/h) because then it has to do this rev-matching for BOTH dog clutches. I've driven a car with this transmission and found it to be fine, but I didn't try to intentionally catch it out.
I know a thing or two about the upcoming GM/Ford 10-speed rear-drive because a customer of mine is building parts for those. It contains six conventional hydraulically-actuated multi-plate clutches, in addition to the torque converter lock-up unit. This is promising to be very good.
I know there's an upcoming GM/Ford 9-speed front-drive but I don't know anything about it at this point.
The other choice is the dual-clutch transmission which uses manual-transmission synchro units. VW/Audi is likely to continue using them, because they seem to be the only ones who have figured them out properly (and even at that, some people don't like them because they have a different feel). I understand that Ford is going to be discontinuing theirs (Fiesta/Focus) and it will be replaced with some sort of conventional automatic; which one isn't known yet. Hyundai seems to be moving forward with theirs.
A big chunk of the automotive world is set on using CVT, like it or not. I don't like them, but I will grant that in a normal daily-driver vehicle driven by a non-enthusiast, they have become a decent solution.
- Thread starter
- #4
It is very funny how they keep trying something that is destined to fail, and end up back at the good old band and clutch planetary automatic transmission. The reason for CVT is trying to bring manufacturing costs down. Problem is to sell them they have to increase the warranty period, and after installing 3 or 4 transmissions, that tanks any savings.
EdStainless
Materials
For general driving the CVT look fine. The one in my wife's Subaru will last a long time. I wouldn't want one in a larger/more powerful car (that was going to be driven aggressively).
Many of the new 7-8-9 speed autos have shift ranges that leave them hesitating and hunting for the correct shift. It is just that the ZF does it at a very noticeable speed.
My daughter worked at Allison while they were developing the new 10 for over the road trucks. A lot of broken pieces along the way (and broken budgets also).
They go back to these designs because they are robust and they work.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
Many of the new 7-8-9 speed autos have shift ranges that leave them hesitating and hunting for the correct shift. It is just that the ZF does it at a very noticeable speed.
My daughter worked at Allison while they were developing the new 10 for over the road trucks. A lot of broken pieces along the way (and broken budgets also).
They go back to these designs because they are robust and they work.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
- Thread starter
- #6
It laughable using basically a motorcycle transmission in a car or truck application and shifting it electronically.
If you want a reliable CVT just go with a multi element torque converter, and tune the lockup clutch to better synchronize with shifts and not to go into torque converter mode so much. Initial cost of a normal automatic is more but if it is more durable its a huge savings in recalls and warranty work.
If you want a reliable CVT just go with a multi element torque converter, and tune the lockup clutch to better synchronize with shifts and not to go into torque converter mode so much. Initial cost of a normal automatic is more but if it is more durable its a huge savings in recalls and warranty work.
dicer said:
Going to go ahead and disagree with that.
The Ferraris, Porsches, and Lamborghinis of the world have used pretty superb electronically controlled manuals for quite some time- the only thing keeping them from being more common has been cost, which is coming down.
That's not to say that a 'traditional' automatic is ever going to be obsolete, or is ever going to be a smaller part of the market- but the technology is going to continue to develop for both systems.
BrianPetersen
Mechanical
The automated-manual and dual-clutch automotive transmissions that I'm aware of, use conventional synchromesh units like those of manual transmissions ... not dog clutches.
The only mass production automotive transmission that I know of that uses dog clutches, is the ZF 9-speed transverse.
The only mass production automotive transmission that I know of that uses dog clutches, is the ZF 9-speed transverse.
LionelHutz
Electrical
Aren't transport trucks using automated manuals without synchros?
You apparently hate CVT transmissions for some reason and believe they are completely unreliable. But, a few manufacturers have been selling them for many years now and they appear to still be doing well at their business with no indication they are going to drop them. So, you really need to put up some hard data showing how they are not reliable if you want anyone to take you seriously. Actually, you seem to think that any transmission not using clutch packs is inferior and will never make it in the marketplace.
I expect to see the popularity of computer shifted manuals and the use of dog clutches (since the computer can shift without a synchro) to increase in the quest to build vehicles that can meet the ever increasing fuel mileage standards.
You apparently hate CVT transmissions for some reason and believe they are completely unreliable. But, a few manufacturers have been selling them for many years now and they appear to still be doing well at their business with no indication they are going to drop them. So, you really need to put up some hard data showing how they are not reliable if you want anyone to take you seriously. Actually, you seem to think that any transmission not using clutch packs is inferior and will never make it in the marketplace.
I expect to see the popularity of computer shifted manuals and the use of dog clutches (since the computer can shift without a synchro) to increase in the quest to build vehicles that can meet the ever increasing fuel mileage standards.
EdStainless
Materials
There are a number of over-the road truck trans that are actually automatics.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
NormPeterson
Structural
Lionel - I'll have to ask my son what the story is on automated manual transmissions in 18-wheel over the road trucks.
Be aware that Nissan has had some teething pains with the CVTs in some of their product lines, and I understand that it gets expensive when the CVT does take a dump (last I knew, replacement was the only method of repair).
Aggressive torque management when the drive pulley is at its smaller diameters isn't going to be terribly appealing to those who are looking for high performance at low(ish) road speeds.
Norm
Be aware that Nissan has had some teething pains with the CVTs in some of their product lines, and I understand that it gets expensive when the CVT does take a dump (last I knew, replacement was the only method of repair).
Aggressive torque management when the drive pulley is at its smaller diameters isn't going to be terribly appealing to those who are looking for high performance at low(ish) road speeds.
Norm
BrianPetersen
Mechanical
Bringing this thread back ... I've got a Ford Focus rental (Powershift automatic) right now on a business trip - and for the first time, I understand what the owners are complaining about. I've had several in the past which have worked fine. This one has higher mileage than the ones I've previously rented (just short of 40,000 miles) - and it feels like the transmission is on its last legs. Anything resembling moderate or harder acceleration makes it lurch away from a stop and nasty grinding noise emanates from up front somewhere. Sometimes it sounds like grinding synchros in a manual transmission. I know this transmission uses normal manual-transmission-type synchro units to engage each gear.
If this was my car, I'd be complaining. Fortunately, it only needs to make it another 10 miles or so back to the rental agency, at which point it becomes "someone else's problem".
If this was my car, I'd be complaining. Fortunately, it only needs to make it another 10 miles or so back to the rental agency, at which point it becomes "someone else's problem".
- Status
Similar threads
- Locked
- Question
- Question
