Why CVTs Won, Direct-Shift Gearboxes Lost Fuel-Economy Fight

The Prius does not use any of those three transmissions. While it physically uses some 'traditional' automatic hardware, its software emulates the CVT to the driver.

 

IMO, this may be the best. Toyota Corolla's CVT has simulated synthetic shifts and even Paddle Shifters for up & Downshift revs, Nice!

Watch between 3 - 4 minutes of this video.

 

I suspect a manual transmission with a motor-generator powered idler could be the price-performance winner:

• absolute crankshaft encoder
• idler encoder - part that shifts from gear-to-gear
• drive shaft encoder

The idler motor can drive it to support clutch-less, 'hot shifts', by using high-speed, absolute position encoders. The tricky part is starting from a dead stop but that can be handled by 'dragging the engine along' to start.

Bob Wilson

 

My only manual shift car is my Corvette, where I prefer to control the shift points for performance. However, even most performance cars, particularly the high end ones, are only offering paddle shifters and abandoning manual shift transmissions.

This is not because of laziness, but instead because of faster shifting capability, which translates to improved track times.

 

And I wonder if eCVTs, like Toyota and Ford hybrids, are counted as CVTs in such reports.

I think it is kind of early to call the end of the dual clutch auto. There are issues with them at this point, but CVTs had issues too when they first came out. Then some individual step automatic models can still have issues on introduction. Honda has to overcome their battery history, but they have dropped the CVT for a dual clutch in the IMA replacement hybrid system.

 

I'm not sure how the article can claim the direct-shift transmissions "lost" when Chrysler, Honda, Volkswagen, and several others have announced replacing their CVTs or torque-converter automatics w/ 8, 9, or even 10 speed DSGs.

 

I would say it comes down to reliability and software ....

With proper software, virtual gears can be added to cvt's and ecvts. Ford has had trouble getting software right on its dual clutch for drivers to like the driving feel. vw has had reliability problems on its transmissions.

I would say we are a long way from cvts "winning", but we know some advantages for each

low torque engines seem to be more suitable to cvts and ecvts (ford and toyota hybrids). If prices are brought down as nissan seems to have been able to do. If purchase price is less of a problem and there is room for a battery exvt has and advantage.

High torque engines -> trucks, luxury cars, sporty cars are better suited to automatics especially with 6 or more gears or manual transmissions. The dct with paddle shifter really has no disadvantage versus manuals other than cost and weight.

Inbetween there is still a lot of room for both.

The VW is a dual clutch transmission (dct) not a clutch less. It is an automated manual.
To Save Gas, VW Introduces the World’s First 10-Speed Transmission | Autopia | WIRED

That zf 9 speed in the chrysler is quite interesting, it uses some dog clutches like the dct and traditional friction clutches.
ZF’s 9-Speed 9HP Transmission Puts Dog Clutches On The Leash | The Truth About Cars

 

Incorrect. Chrysler/Honda's 9-speed cars will use "dog teeth" just like you find in a manual car & no torque converter. Please read the other thread for more detail

 

I owned two VWs with the DSG trans and I wouldn't own another. They're expensive to maintain and mine just never worked right. That's one of the main reasons I got rid of the cars. I'm very happy with an eCVT.

 

A manual gearbox is better for towing and heavy cargo.
Fuel efficiency depends on the proper mating of the power plant to a high transmission gear ratio



A Hypermiling POV

One traditional hypermiling technique (not legal in all states) which cannot be done on an automatic transmission but can be done on certain manual transmission vehicles is dropping into Neutral (NICE) to decrease the internal drag caused by the power plant and coasting/gliding the car until its speed drops to a predetermine bottom speed then reconnecting the transmission to the power plant while the car is still moving and speeding up the car before disconnecting the power plant again when a desired speed is reached. To deployed NICE with conventional gas car, hypermilers had to drive "Flat towable" cars. A "Flat towable" car has a electronically controlled ON state that allows the brakes and steering to work even when the gasoline engine was be turned OFF and more importantly allows the driver to turn the gasoline engine OFF and ON while the transmission is in Neutral and the car is still moving - certain cars like the Honda Civic/Fit with a Manual Transmission could do this.... Still, NICE requires a bit of skill because the driver must coordinate the clutch-transmission stick correctly. Like drafting (slipstreaming) - NICE is illegal many jurisdictions - especially when going downhill - because older manual transmission cars can be difficult to switch from neutral to drive while the car is still in motion - giving the driver less time to react.. In addition, on many non-Flat Towable cars, the steering or brakes may be harder to use or may not work when the engine is turned off during the coasting cycle.

Unlike older manual and automatic transmission cars, NICE on the Prius CVT can be done safely and easily. The Prius stop idle technology keeps the car electrically ON when the gas engine is OFF so the Prius never lose power to the steering or brakes even when the gas engine is turned OFF or when transmission is in Neutral (like a "Flat Towable" car). Just a flick to the transmission stick and the Prius switches back from Drive to Neutral to Drive back again.

 

How well does coasting in "N work for:

• Honda IMA drives
• Hyundai/VW "blue motion"
• Honda Accord
• Volt/Caddy drives

Do those cars have the same, synthetic drag as the Prius system? It never made sense why Toyota implemented a non-optional, synthetic drag. I could not find a government regulation that requires it.

BTW, I understand from Wiki some SAAB and a few other cars once came with a freewheeling clutch. Getting rid of the latent transmission drag when the accelerator is off remains 'low hanging fruit.' This transmission associated drag is in effect, riding the brakes.

BTW, I have no problem with "B" but only as a selected option. That is the only way engine/transmission drag makes sense.

Bob Wilson

 

This can be done on step(traditional) automatics. I've done it for years with multiple cars without issue. It's when you get into turning off the engine that whether or not the transmission is flat-towable(behind a RV on all four wheels) or not. It is not because power is cut to steering and brakes, which applies with manual transmissions also, but because a non-towable transmission isn't properly getting lubricated with the engine off.

With the engine off, you don't lose steering. Just the hydraulic power assist. Which is only an issue at low speeds. Electric power steering stays on for most cars. The brakes will hold vacuum for a couple uses, and then if the car has an electric acclimater, the assist may never be lost.

I have never driven those cars, so I can not comment on them, but here is the overview on using neutral coasting to save gas.

When it comes whether it is better to use N or not when depends on the transmission behavior and the upcoming road. While in gear and coasting, the car will enter decelleration fuel cut off(DFCO) where fuel is no longer being injected into the engine. When DFCO engages varies between cars. Newer ones will likely engage it quickly in order to meet rising mpg requirements. Older automatics will only enter it under a certain set of conditions(speed, rpm, temp., etc.), or not at all. In N, the engine will burn some fuel to keep spinning.

Now, when in DFCO, the engine is pumping air and braking the car. This where the upcoming road is important. If you are going to need to slow down or stop up ahead, leave it in gear if it means entering DFCO. If not, putting it in N may mean burning less gas than leaving it in gear and then having the accelerate back up to speed.

There are some other variables to consider like the cars behavior on shifting back into drive, but you see it is one of those YMMV things.

The synthetic drag never made sense to an engineer, but it made sense in making the new thing less scary to the general populace. I agree, it should have a shut off switch. Many EVs have that, and a dgree of its strength when on.

The freewheeling clutch is an old idea. In the days before power brakes, it lead to accidents on steep declines. Which is why it isn't on cars now, and why, in part, N coasting is against the law in some ares. It is something that needs to be revisited do to current technology.

 

I believe it is important to distinguish two distinct forms of this:
N-ICE-off: Neutral glide with engine shut off;
N-ICE-on: Neutral glide wide engine on and idling.

The former saves more fuel, but brings much more driver workload and risk. Turning the ignition switch off is cumbersome and risks locking the steering wheel if the switch is turned one notch too far. And it adds much extra wear on the switch itself. Some hard core users add a push button kill switch on their shift knob, simplifying this method and cutting much risk.

I used this method (sans kill switch) just barely enough to demonstrate that it works, but that it was not practical or reasonable for me and for the car I had at that time.

The later method, N-ICE-on, is far easier and I still use regularly in my current manual transmission vehicle.

Agreed, as I felt many times in a couple older cars that stalled on a whim. Steering without power assist is difficult only at parking lot speeds, just like the old fashioned manual steering cars.

Even the brakes still work without power assist, even after the vacuum has been depleted or electric power fails. This is even a federal requirement, though the required pedal force rises enormously, to essentially one's full body weight. Again, just like the old fashioned manual braking cars. Those old cars that frequently stalled on me, also had leaky vacuum storage in the booster and quickly reverted to manual mode.

Didn't some cars have a freewheeling overdrive? Engine compression braking was still available in regular gears.

 

And it takes little force to make a lane change.

Didn't some cars have a freewheeling overdrive? Engine compression braking was still available in regular gears.[/QUOTE]
That may be it. All I heard was that a system of decoupling the engine from the wheels was implemented. Resulting lack of engine braking combined with manual brakes resulted insufficient braking force on some declines. I don't know if it was actually banned in the regulations, but its use stopped.

 

My SAAB 93B had free-wheeling and would coast very nicely down hills due to its teardrop shape, partly achieved by installing a very small engine in front of the radiator. But the 93B model featured a 3-cylinder, in-line, 2-stroke engine (750 cc), so I think the freewheel was primarily to avoid over-leaning that engine on long descents which would cause engine seizure. However , there was a lock-out mechanism for the freewheel operated by pulling on a small white plastic T handle at the base of the firewall IIRC. Being wary of engine seizure, I did not try that option. I did not feel the coasting was dangerous because even though that car had drum brakes, it was extremely light weight.

 

• In the Honda IMA you can hold-in the clutch pedal, which will make the engine run in idle mode (about 400 mpg when coasting downhill). Or you can stay in gear so the engine will stop burning gasoline (infinite MPG) and battery will recharge. If the battery is full, then the car just coasts downhill w/o braking.

VW bluemotion is not a hybrid technology. It acts just like any other car going downhill.

The Accord G2 Hybrid ties the engine directly to the wheels at 44+ miles/hour. It uses the same "disconnect 3 cylinders" technology as the Civic hybrid, in order to reduce engine braking. Below 44 mph the Accord would have no engine connected & freewheel (like an electric car)