DCT does rev match?
Le Mans Master
Joined: Mar 2006
Posts: 5,775
Likes: 585
From: Texas
I don't know the specs on the new Tremec DCT, but the Audi DCT upshifts in 8 milliseconds and downshifts in 60 milliseconds. I would guess that part of that extra downshift time would be for rev matching. Just faster than a human could do it.
Drifting
Joined: Jan 2019
Posts: 1,494
Likes: 703
From: Raleigh, NC
Yes on the ZF 7DCT. You hit the paddle as many times as you want & get an instant shift to the lowest safe gear. ECU prevents a money shift if you pull too many gears on a downshift.
Last edited by BEAR-AvHistory; Jul 26, 2019 at 01:55 PM.
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Melting Slicks
Joined: Sep 2012
Posts: 2,058
Likes: 1,906
Not sure if you would call it rev match. As I understand DCT (not an expert) one gear is always engaged as the next takes over so it is more of a gear hand off which is why it is so much better than manual. There is NO lag /delay or loss of forward momentum as you shift. It is always under power.
Experts please confirm or destroy ! ; )
Experts please confirm or destroy ! ; )
Last edited by firstvettesoon; Jul 26, 2019 at 01:55 PM.
Drifting
Joined: Jan 2019
Posts: 1,494
Likes: 703
From: Raleigh, NC
ZF 7DCT rev matches typically in the upper gears. Agree the next gear is always ready but you still have the ratio step up or down. If it did not match the shifts would be very jerky. Generally the ECU is programed to vary the matching depending on what gear you select. Going down in the very low gears will give you engine braking
Racer
Joined: Aug 2018
Posts: 443
Likes: 464
I'm not sure I would even call it rev matching in my GT3RS. It's so fast it just seems like an instant downshift. It's certainly not jerky though. Very smooth and sounds great.
You can hear some downshifts on a GT3 in this video to get a sense:
You can hear some downshifts on a GT3 in this video to get a sense:
Pro
Joined: Sep 2006
Posts: 608
Likes: 259
From: Louisiana
By definition, when you engage the next gear, it's going to be 'rev-matched' to the transmission speed.
But yeah, long story short, it's blipping the throttle on the downshift to keep the downshifts smooth.
It's not like an early, clunky F1 or e-gear box, for example.
But yeah, long story short, it's blipping the throttle on the downshift to keep the downshifts smooth.
It's not like an early, clunky F1 or e-gear box, for example.
Instructor
Joined: May 2014
Posts: 217
Likes: 126
From: San Diego
Yes, there is rev matching otherwise downshifts would be pretty harsh even though the clutch is supposed to be spinning as fast as the flywheel. Even a lot of cars with newer automatics rev match too such as in applications with the ZF8 in the big mopars.
Conversely, on upshifts, there's a split moment where the engine pulls timing and fuel to let the revs fall down easy vs the engine fighting against the transmission and gear shift and the revs falling only because the transmission is pulling it back. There's where "DSG farts" come from, but really it's from the engine pulling timing and the combustion being spit out the exhaust valves while the upshift is happening.
Conversely, on upshifts, there's a split moment where the engine pulls timing and fuel to let the revs fall down easy vs the engine fighting against the transmission and gear shift and the revs falling only because the transmission is pulling it back. There's where "DSG farts" come from, but really it's from the engine pulling timing and the combustion being spit out the exhaust valves while the upshift is happening.
Last edited by stingray87xx; Jul 26, 2019 at 03:43 PM.
Burning Brakes
Joined: Apr 2018
Posts: 1,051
Likes: 690
Not sure if you would call it rev match. As I understand DCT (not an expert) one gear is always engaged as the next takes over so it is more of a gear hand off which is why it is so much better than manual. There is NO lag /delay or loss of forward momentum as you shift. It is always under power.
Experts please confirm or destroy ! ; )
Experts please confirm or destroy ! ; )
Just because it's a DCT doesn't mean that the engine does not have to spin up to meet the next gear DOWN. Say you're in 4th gear, and let's assume 4th is 1:1, and 3rd is 1.5:1, and you're cruising at 50mph at 3.000RPM (theoretical).Iif all the transmission is doing is downshifting without revving the engine up first, you'd end up with a very jerky shift from 4th to 3rd because the wheel speed of 50mph @ 3,000RPM in 4th, would mean a wheel speed of 50mph @ 4,500RPM in 3rd. The instantaneous engagement would mean the engine is spinning much slower than the transmission is and you would get a strong jolt as the transmission slows down to meet the engine at 3,000 RPM while the engine is being spun by the flywheel to try and speed up to 4,500RPM.
In fact you'll likely suffer a momentary loss of rear traction as the difference in wheel and engine speed causes the rear to "lock up".
Any form of automated manual would need the Rev Match functionality built in otherwise they can not function smoothly.
Melting Slicks
Joined: Sep 2012
Posts: 2,058
Likes: 1,906
Destroy.
Just because it's a DCT doesn't mean that the engine does not have to spin up to meet the next gear DOWN. Say you're in 4th gear, and let's assume 4th is 1:1, and 3rd is 1.5:1, and you're cruising at 50mph at 3.000RPM (theoretical).Iif all the transmission is doing is downshifting without revving the engine up first, you'd end up with a very jerky shift from 4th to 3rd because the wheel speed of 50mph @ 3,000RPM in 4th, would mean a wheel speed of 50mph @ 4,500RPM in 3rd. The instantaneous engagement would mean the engine is spinning much slower than the transmission is and you would get a strong jolt as the transmission slows down to meet the engine at 3,000 RPM while the engine is being spun by the flywheel to try and speed up to 4,500RPM.
In fact you'll likely suffer a momentary loss of rear traction as the difference in wheel and engine speed causes the rear to "lock up".
Any form of automated manual would need the Rev Match functionality built in otherwise they can not function smoothly.
Just because it's a DCT doesn't mean that the engine does not have to spin up to meet the next gear DOWN. Say you're in 4th gear, and let's assume 4th is 1:1, and 3rd is 1.5:1, and you're cruising at 50mph at 3.000RPM (theoretical).Iif all the transmission is doing is downshifting without revving the engine up first, you'd end up with a very jerky shift from 4th to 3rd because the wheel speed of 50mph @ 3,000RPM in 4th, would mean a wheel speed of 50mph @ 4,500RPM in 3rd. The instantaneous engagement would mean the engine is spinning much slower than the transmission is and you would get a strong jolt as the transmission slows down to meet the engine at 3,000 RPM while the engine is being spun by the flywheel to try and speed up to 4,500RPM.
In fact you'll likely suffer a momentary loss of rear traction as the difference in wheel and engine speed causes the rear to "lock up".
Any form of automated manual would need the Rev Match functionality built in otherwise they can not function smoothly.
I guess my point was that the two transmission gears involved are spinning together and automatically and naturally (built in) match speed to make the switch of gears smooth and fast that the rev match per se is not a seperate function. I appreciate your explanation. Thanks!