Dual-Clutch Transmission: Wet or Dry?
transmissiondigest.com
transmissiondigest.com
* Hybrids are largely "Power Split Devices" (Toyota / Ford / etc. etc.) which use a planetary gearset to kinda-sorta make a CVT-like approach.
* CVTs with belts and/or cones are all available, to varying qualities.
* Dry DCTs have created sub-100ms shifts in automatic transmissions
* ZF8 (wet-clutch planetary gear / torque-converter traditional automatic) has sub 200ms shifts (~150ms or so for the typical ZF-8). Just old tech but done exceptionally well today.
Dig the ZF8 in my RAM a lot. Did not like the 10 speed in my F-150, ZF is much better.
The idea was that you need a certain velocity and torque to hold the drive train at a given speed, and instead of using reconfigurable gearsets for that, you use a differential, and one of the output shafts is sometimes an input shaft. One of the output shafts is attached to the wheels, the other to a motor. At some speeds output shaft B is stationary. To accelerate, you feed power into the motor and now it's speeding up shaft A. At lower speeds, you bleed power off of shaft B by running the motor as a dynamo, using it to charge the batteries and run auxiliary equipment.
In the hybrid version there was an ICE on the input shaft (or an ICE and a ganged electric motor) but on a full electric you could run two motors with different torque curves and balance the inputs for each speed.
Honda's old system, 'IMA', which was a traditional ICE drivetrain with a motor assist. They abandoned it because mild hybrids don't really deliver a good value. It's a lot more cost for not very much improvement in economy.
Honda's new system, E-drive, usually operates like an EV with a generator attached, but it also has a lock-up clutch to allow the engine to direct drive the wheels in cruising conditions.
3-motor actually. https://eahart.com/prius/psd/
2x Electric Motors + 1x ICE motor. Its a bit confusing but there's a lot of Youtube demos, webpage-demos, and simulations to help you understand how it all works.
And all that is without considering hybrid tech.
ZF-8 apparently removed a lot of the "slushbox" / wet-clutch problems with efficiency. Its apparently the best / peak automatic transmission technology with exceptionally good reviews and specifications, though the main problem seems to be downshifts. But upshifts (1->2->3->4...) are basically solved with ZF-8 and operate at high efficiency.
CVTs are manual-transmission/clutch-like levels of efficiency, though there's so much diversity in CVT implementations I feel like its hard to discuss.
Hybrid Vehicles are either directly-connected / 1-gear systems (ex: Honda: ICE Engine gets a gear and EV engine gets a 2nd gear, no transmission otherwise required), or the Toyota Power-split device (aka: Prius) that has exceptionally good efficiency as you're probably aware.
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Manual Transmission's main benefit is economy. Its just a bit of hydraulics controlling a drum-brake like system (aka: the Clutch) with a human controlling the gears, so no need for any complex logic.
I think economy cars / low-cost cars need to go back to manual transmissions. But maybe USA is just too rich and that the $20,000+ price point is high enough to just default to automatic transmissions.
There's a lot of "machine empathy" in manual transmissions, they're exceptionally simple, cheap, and reliable (when used properly).
People will often point out that you can use the override but I feel like that misses the point. There's what a person can do, and what they will do, and when we are talking about something like global fuel economy and carbon emissions, 'will do' is the only metric that actually matters. And hybrid electrics and DCTs fare better in the 'will do' category.
Some of these designs are mind-blowingly simple. My favorite is Honda's E-drive: https://www.youtube.com/watch?v=QLUIExAnNcE
Honda hybrids also have a clutch to connect gas engine directly to the wheels on motorway speeds to improve efficiency. And it simulates sound of gear changes during acceleration even if there are no gears whatsoever, since that's apparently what makes it more exciting and enjoyable to us petrolheads:
In some ways I'm surprised that more EVs don't have this as an option:
Batteries keep going down in price and weight
1. Change the engine to Atkinson Engine. This makes low-end torque terrible.
2. Make up for low-end torque by paring a small 80 horsepower electric motor (which handles 0rpm exceptionally well). Atkinson Engine does 2000+ rpm / highway speeds exceptionally well. Use a computer + a 3rd electric motor to configure the planetary gears to make the EV motor #1 and ICE engine cooperate best.
3. Beef up the alternator into a proper generator (to charge the battery when its low). Use the motors to hold the car still if stopped at a stop-light but keep the ICE engine on the generator to build up the charge you need to take off later.
4. Use the EV motor as the starter (hook it up to the engine to start it up, much like a traditional starter).
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As such: the Power Split Device removes the alternator, starter, and traditional transmission (with the EV motor#1 and EV motor#2 + computer allowing different configurations / rotations to recreate alternator / starter / transmission-like behaviors).
With... here's the big magic... the ICE + EV Motor being able to assist each other on the highway. (Honda's ICE as Generator approach leads to 100% ICE on the highways). Toyota Prius has a better ability to mix EV vs ICE (even the ability to run 100% EV at the push of a button, though at dramatically worse performance since IIRC its only a sub-100hp electric motor).
Well, it's 100% when load is between zero and a reasonable maximum torque at the fixed gear ratio. If you lift, the engine shuts off, and if you command significant acceleration, the engine will revert back to generator duties.
Honda's system has an advantage on the highway too -- because no motor ever spins faster than the output drive motor, there is no speed ceiling at which the engine must run to prevent either MGs from overspinning. You can take a Honda hybrid to the speed limiter, lift the throttle, and it will go into EV mode immediately. This is nice in areas where you might end up coasting a lot on the highway because you can get some time with the engine off, even at highway speeds.
Only the gearheads who don't understand torque and efficiency curves! I hate that Honda made this change on their latest generation of Hybrids. It is an intentional performance compromise made just to satisfy the expectations of an uninformed buyer. RPM fluctuation under acceleration is a drawback of fixed gear ratio transmissions, not an advantage.
The artificial audio is also a thing, but if they only did it with that, you'd also hear the engine droning a constant pitch in the background.
Also notice how the 'power' meter is dropping (accurately) from 100% each time.
I wish Honda made a Civic Type R with a DCT.
One cannot realistically expect urban regions to have drivers that leave large spaces of road empty, it wouldn’t back up the congestion even further onto other roads.
It’s especially exacerbated because all vehicles and drivers have different reaction times and acceleration, so it’s inevitable that gaps will increase and decrease. Taking advantage of the gaps actually increases the road’s throughput, and is a sufficient tradeoff to risk and energy efficiency for almost all drivers worldwide.
Read the above as a rant for better transit.
Even better is to get the cars off the road by having good flow and not jamming it up.
"Closing the gaps" means tailgating or switching lanes to get into those sweet, wide open spaces. These are the primary causes of phantom traffic jams on congested freeways. There's a pretty good deep dive covering this[1].
[1] https://www.autoblog.com/2022/11/03/phantom-traffic-jams-pre...
This is not practical in most cases of congestion, which are caused by the number of vehicles exceeding the road's capacity. There is no other choice after a certain point, vehicles will begin to pile up and speed up and slow down creating the traffic waves.
That video is correct for only a minority of times where the road capacity has not been met, but people are accelerating and decelerating too fast causing the traffic waves.
However, during times of too many vehicles on the road, such as rush hour, there is nothing anyone can do, other than use as much of the road as possible (i.e. less empty space).
Your analysis misses safety and so while your facts are correct your conclusion is wrong. When more cars want to use a section of road than the road can handle you must not put more cars into the empty space without all the cars slowing down (which in turn means the road can handle less cars per time). I know that is not what everyone does, but they (we) are wrong.
> Taking advantage of the gaps actually increases the road’s throughput, and is a sufficient tradeoff to risk and energy efficiency for almost all drivers worldwide.
> the road can handle you must not put more cars into the empty space without all the cars slowing down (which in turn means the road can handle less cars per time)
I agree that there is a range where cars weaving in and out causing people to brake unnecessarily causes more congestion, but there is also a point where there is so much congestion that “filling in the gaps” becomes the optimal move, because the road’s capacity has been reached and maintaining large gaps would simply push congestion further back onto other roads.
You don't even need to maintain large gaps - you just need about two seconds of time between you and the car in front of you, and that varies based on the speed of traffic. Everyone going ~30mph with gaps is going to have a lot more throughput than everyone averaging 10mph with short gaps. Of course this is before you get into the increased risk of collisions with smaller gaps. One fender bender is enough to bring everything to a halt, and statistically with enough cars and short enough gaps those are basically guaranteed.
I did my first 10 years of driving in a manual and when you get a hang of the gearbox you barely need the clutch at all. Just a light tap, barely disengage anything.
Nowadays the sequential dogbox in my motorcycle is my fav. Similar to what rally cars use. You only need the clutch when stopping, otherwise you can just jam between gears with a light flick of the throttle to relieve tension. No electronics.
Wish nonracing cars came with that option. I think some 90’s supercars have it.
I think in the mountains it’s the opposite. I wouldn’t want to drive 1km of elevation down without using the engine to control the speed. Brakes in most cars aren’t designed to engage continuously for long time, they overheat and may eventually fail.
Automatics are also just one more unfixable thing to go wrong. An automatic has so many moving parts, most of which are tiny little things buried deep inside. Manuals just run forever, needing at most new clutch plates or slave cylinders, things external to the actual transmission. Fixing anything to do with an automatic is akin to automotive heart surgery.
DCTs will absolutely give you this experience. Most don't expose a UI for shifting from directly to any gear arbitrarily, though.
Ya, I don't want to get into an argument with my car. I want a transmission that will actively allow the engine to stall, or let the rev limiter do its thing. I also want a clutch that I control, one that will engage when I ask it rather than a second later, which is a bigger deal in snow/mud/rock. A couple weeks ago I had to rock my car out of some deep snow (snowed-in parking spot). An automatic just will not engage/disengage fast enough on command for such trickery.
1-gear transmission seems... ill-suited. Its only possible on grossly-overpowered EVs (ex: Tesla). Economical cars like Leaf would likely benefit from a 2nd speed.
Honda Accord Hybrids have a silly design: EV Motor is permanently on low-gear, while ICE-engine is permanently on high-gear. You could call it a two-gear system, but perhaps its two motors each permanently attached to a single gear without any traditional "transmission" (aka: system to change gears). Just a computer that is deciding to take more (or less) power to the ICE vs EV.
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EVs are well known to have poor highway cruising economy. I do wonder if a 2nd gear would help them out.
Plus, a tuned Golf R/STI/Evo can throw people in their seats effortlessly too, and rolling antilag will always sound cool.
It's annoying that the VW manual suggests comically long service intervals for this stuff to make it look like the running costs are lower than they are. I want to just keep the car until it has 300k+ miles. But it's all about shifting those units initially.
Rebuilding the clutch packs themselves is a tedious and obnoxious process, because they're a giant stack of friction material that needs to be shimmed into tolerance, but you often just buy the clutch pack as a whole assembly.
I'd massively prefer a wet clutch even for long term serviceability - a few hundred dollars or less every year or two for fresh fluid and you've got a long service life before an expensive removal.
But seriously, they are a great second vehicle to have, or even main vehicle depending on where you live. They are simpler than cars and you can work on them using basic hand tools easily enough. They are cheap and good on gas. And they are just really really fun.
Made for a fun time of getting nowhere pretty quickly.