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The A35 AMG is listed as using a DCT transmission, however I have noticed that it creeps slowly on its own when you let off the brake pedal from a complete stopped position.
Normally DCT transmissions don't do this. Is it possible they're using a torque converter with a DCT??
It has just a simple Double Clutch mechanism. A complete stop, if is a very short one - the Gear 1 is not yet coupled - and starting from Gear 2 could be a little slow.
No, they are not using a torque converter. Many DCTs have creep. They start to engage the clutch when you take the foot off the brake. Most DCTs these days have wet multi plate clutches, so they don't wear nearly as much as dry clutches under partial engagement. These clutches operate in an oil bath, and the oil is actually partially responsible for producing friction, but at the same time it cools the clutch and reduces wear.
No, they are not using a torque converter. Many DCTs have creep. They start to engage the clutch when you take the foot off the brake. Most DCTs these days have wet multi plate clutches, so they don't wear nearly as much as dry clutches under partial engagement. These clutches operate in an oil bath, and the oil is actually partially responsible for producing friction, but at the same time it cools the clutch and reduces wear.
So if I’m stopped at a traffic light with my foot on the brake I’m still wearing the clutch since it really never disengages?
So if I’m stopped at a traffic light with my foot on the brake I’m still wearing the clutch since it really never disengages?
No, you don't. It fully disengages when you stay on the brakes. Hydraulic pressure is applied to the piston to start clamping the plates together as soon as you take the foot off the brakes, but with the foot on the brake there's no hydraulic pressure applied to the piston.
But I never really notice any drop in fluctuations in the RPM when fully stop. It doesn’t give me the impression it’s disengaged at all. Still feels like it wants to pull forward.
But I never really notice any drop in fluctuations in the RPM when fully stop. It doesn’t give me the impression it’s disengaged at all. Still feels like it wants to pull forward.
Drop in fluctuations? What are you referring to? No engine has a perfect idle. There's natural fluctuation, but if you start releasing the brakes it'll start to creep and get ready to fully engage the clutch as soon as you step on the throttle. Just make sure you apply enough brake pressure for it to not think that you wanna creep forward. The clutch disengages before you even come to a full stop. During the last few feet the car just rolls when you come to a stop. You should notice that at some point the rpm doesn't drop lower, even though you haven't fully stopped yet, but if the clutch didn't disengage the engine would stall or the car would come to a very jerky stop.
Last edited by superswiss; 05-30-2022 at 06:57 PM.
Ok great thanks. I’ll pay more attention to this tomorrow. But how do you explain that at a full stop, if I put the car in N it suddenly feels like it doesn’t want to pull forward… more like a regular slushbox transmission?
Ok great thanks. I’ll pay more attention to this tomorrow. But how do you explain that at a full stop, if I put the car in N it suddenly feels like it doesn’t want to pull forward… more like a regular slushbox transmission?
Without knowing how much brake pressure you are applying when you are stopped that's hard to say. It's very possible that you are not standing on the brakes firmly enough when stopped and so the clutch is slightly engaged. Do you take advantage of the HOLD function when stopped?
I have not driven the A35 specifically, but I've driven many DCT cars in the past and currently have a '19 C63S which has what AMG calls a multi clutch transmission. Like a dual clutch it uses a wet startup clutch instead of a torque converter. I feel no difference going from D to N to R or back. In fact, occasionally I don't push the gear stalk up far enough to reverse and end up in N instead and I won't notice it until I step on the gas and the car doesn't move and as said I've previously driven and owned many cars with dual clutch transmissions.
There are always slight differences in implementations obviously. It's very possible that the A35 very eagerly starts engaging the clutch even if you just slightly take your foot off the brake. Also, pretty much all transmissions adapt to your driving style and they do fine tune themselves over time. How many miles/kilometers do you have on it? The clutches have to wear in and the software has to fine tune itself based on your driving, so it may not feel completely right just yet and you have to give it some more time. Generally, if you feel forces in the drivetrain when going between D, N and R that's usually a sign that the transmission hasn't adapted properly yet.
The car is brand new, about 400 Km. I do use the hold function most of the time. Still feels like it’s wanting to pull forward.
Thanks for all your input. I don’t mind that it’s wanting to pull forward, I just hope it’s not adding extra wear for no apparent reason. Haven’t been able to find a reliable source of information on how DCT is implemented on the A35, and as usual the dealer is useless in these matters lol.
The car is brand new, about 400 Km. I do use the hold function most of the time. Still feels like it’s wanting to pull forward.
Thanks for all your input. I don’t mind that it’s wanting to pull forward, I just hope it’s not adding extra wear for no apparent reason. Haven’t been able to find a reliable source of information on how DCT is implemented on the A35, and as usual the dealer is useless in these matters lol.
In that case give it time. You are still in the break-in period. Everything has to wear in and loosen up first. My past cars, including my current C63, didn't start to wake up and feel properly until about 8k miles. I now have about ~26k miles on it and it drives better than on day 1. Everything from the suspension to the transmission to the engine has come together and feels like one piece now. New cars are much like a new pair of leather shoes. They have to be worn in.
In that case give it time. You are still in the break-in period. Everything has to wear in and loosen up first. My past cars, including my current C63, didn't start to wake up and feel properly until about 8k miles. I now have about ~26k miles on it and it drives better than on day 1. Everything from the suspension to the transmission to the engine has come together and feels like one piece now. New cars are much like a new pair of leather shoes. They have to be worn in.
There are a few patents out there that refence Producing vehicle creep through a transmission without a torque converter. It's safe to assume the A35 is perhaps using something similar to this technology.
Here is a direct quote:
"With the brake pedal fully depressed, the desired clutch torque capacity is determined from among completely-open, nearly-stroked, and slipping or slightly-engaged states using empirical data, from which desired clutch torque capacity is determined. By not applying excess clutch torque, this calibration prevents unnecessary wear on the clutch when vehicle creep movement is not desired. As the brake pedal is released, the desired clutch torque capacity increases as the brake pressure decreases."
There are a few patents out there that refence Producing vehicle creep through a transmission without a torque converter. It's safe to assume the A35 is perhaps using something similar to this technology.
Here is a direct quote:
"With the brake pedal fully depressed, the desired clutch torque capacity is determined from among completely-open, nearly-stroked, and slipping or slightly-engaged states using empirical data, from which desired clutch torque capacity is determined. By not applying excess clutch torque, this calibration prevents unnecessary wear on the clutch when vehicle creep movement is not desired. As the brake pedal is released, the desired clutch torque capacity increases as the brake pressure decreases."
Yes, this is essentially what I was getting at. During the break-in and beyond it will calibrate itself to various parameters. Things will also behave differently whether you are stopped on an incline or level surface. On an incline for example if steep enough it will not creep and instead you can roll backwards like with a manual transmission. To avoid this, there's a hill start assist feature that will automatically hold the brakes for a few seconds to give you time to switch from the brake pedal to the throttle pedal w/o the car rolling backwards. This usually kicks in on an incline of 3% or more.
Wet clutches are really quite amazing. We generally associate oil with lubrication, but these transmissions and other applications of wet clutches use oil with specific frictional properties that make these things work. The level of wear is very different from a typical dry clutch where you don't want to partially engage the clutch or it wears down. Some performance cars actually give you the option to have creep or not, for example the Nissan GT-R.
Yes, this is essentially what I was getting at. During the break-in and beyond it will calibrate itself to various parameters. Things will also behave differently whether you are stopped on an incline or level surface. On an incline for example if steep enough it will not creep and instead you can roll backwards like with a manual transmission. To avoid this, there's a hill start assist feature that will automatically hold the brakes for a few seconds to give you time to switch from the brake pedal to the throttle pedal w/o the car rolling backwards. This usually kicks in on an incline of 3% or more.
Wet clutches are really quite amazing. We generally associate oil with lubrication, but these transmissions and other applications of wet clutches use oil with specific frictional properties that make these things work. The level of wear is very different from a typical dry clutch where you don't want to partially engage the clutch or it wears down. Some performance cars actually give you the option to have creep or not, for example the Nissan GT-R.
Would you know how the Nissan GT-R implements the artificial creep? Would that not be detrimental to the clutch when fully stopped and hold the brake pedal engaged while the car wants to inch forward like a normal automatic? This is what I'm trying to fully understand.....
Would you know how the Nissan GT-R implements the artificial creep? Would that not be detrimental to the clutch when fully stopped and hold the brake pedal engaged while the car wants to inch forward like a normal automatic? This is what I'm trying to fully understand.....
It does it the same way as I've been describing. With foot on the brake the clutch is fully open and then it starts applying pressure to the clutch as you let go off the brakes. There is no clutch wear while fully stopped, at least once everything has calibrated.
I have not driven the A35 specifically, but I've driven many DCT cars in the past and currently have a '19 C63S which has what AMG calls a multi clutch transmission. Like a dual clutch it uses a wet startup clutch instead of a torque converter. I feel no difference going from D to N to R or back. In fact, occasionally I don't push the gear stalk up far enough to reverse and end up in N instead and I won't notice it until I step on the gas and the car doesn't move and as said I've previously driven and owned many cars with dual clutch transmissions.
05-30-2022, 09:13 AM
DCT with torque converter?
