Tansmissions-Powertrains

[user removed]

The EPA documents published on hydraulic hybrid research in 2006 included some projections about the potential improvements in mileage from various system improvements.

The greatest improvemnt with a peak projection of 80% was in the powertrain itself, with all other engine, aero, and tire rolling resistance increasing that 80% to a total of 120%. This has been coinfirmed by developments from various sources in the 6 years since the document was first published and has verified the accuracy of the original projection.
These projections also assume testing will be in exactly the same method as current EPA tests, which would eliminate extreme cases of hypermiling which do not match those same testing standards.

In thise series of threads I am going to discuss what I believe will be the future of powertrains. I will also relate my experiences with some of the newer developments in Continuously Variable and automated manual transmissions.

I fully understand that many of the best hypermilers use manual transmissions exclusively.

ANY HUMAN VEHICLE INTERACTION CAN BE RECORDED AND PROGRAMMED AND RENDERED AUTOMATIC.

The human interaction demonstrates the fact that the manual transmission is still king as far as efficiency, but only becasue of the unique way a highly skilled hypermiler can make it function, as well as using techniques that in the hands of less skilled operators, without a lot of practice could be dangerous and in some cases are technically illegal in some states in the US, even though the exact same techniques are considered legal when they are incorporated into a hybrid or pure electric vehicle design.

regards
Mech

[user removed]

CVTs are basically a device to engage or disengage the drive, with a very strong segmented steel belt connected between two pullys that have one of the pulley faces on each pully adjustable in realtion to the other. This allows both pulleys effective diameter to be adjusted in minute increments.

Years of development, especially by Nissan and Jatco (transmission manufacturer) in Japan have adressed many early issues with CVTs. They now use a "push belt" with around 400 segmented hardened steel "shoes" that are compressed against each other, and special fluids that provide lubrication while still allowing friction between the belt segments and the faces of the pulleys. The 2003 Nissan Murano was capable of towing 3500 pounds and the transmission could handle the torque and horsepower of the 3.5 liter engine providing a 3800 pound vehicle with acceleration of 0-60 in 8 seconds and 25 MPG highway. I have driven one at 70 MPH average speed, while fully loaded, and averaged 25 MPG.

In the latest model years, the most recent Nissan Sentra, Altima, and Versa model have recieved the latest versions of their CVTs and the Altima is rated at 38 MPG highway, while the Sentra and Versa are rated at 40, with the Versa rated at 35 combined, one of the highest non hybrid combined ratings of any comparable vehicle.

My personal experience with Nissan CVTs includes the Murano, Rogue, Sentra, and Altima. Their CVTs will provide you with good acceleration without the engine speed and load changing significantly, meaning you start off at 1800 RPM and the engine stays at 1800 RPM while the cars speed increases until it is going as fast as it will at 1800 RPM. In the first Murano we owned 1800 RPM was right at 70 MPH. More accelerator input increases the RPM speed which will still remain constant as long as the pedal pressure is constant.

Throttle by wire, combined with computer controlled CVTs means your gas pedal is actually an accelerator pedal that controls the drivers request for a rate of acceleration. The system compensates for minor fluctuations in pedal imput, as well as enhanced DFCO using thr CVTs wider ratios to keep the engine speed up during deceleration, but as low as possible to engage DFCO.

The torque converter on my 2008 Altima locked up at 12 MPH, basically it was used as a clutch and locked once the vehicle speed allowed the CVT pulleys to be used exclusively.

feel free to add any information that might be constructive.

regards
Mech

[mechman600]

Great thread, old mech.
I was wondering about the torque converter and when it locked in a CVT.
I also wonder what is better - a CVT or a 6 speed auto shifting "manual" like in your Fiesta, but I know you are going to elaborate on that soon enough. I am looking forward to what you have to say about it.

[nemo]

Why not just vary the amount or hydraulic flow to hub drive motors, keep the engine at one load setting or off and eliminating the need for belt and pulleys.

[mechman600]

Originally Posted by nemo

Why not just vary the amount or hydraulic flow to hub drive motors, keep the engine at one load setting or off and eliminating the need for belt and pulleys.

Hydraulic/hydrostatic drives lose a lot of energy to friction/heat compared to the belt in a CVT transmission.

[user removed]

http://www.innas.com/Assets/files/Hydrid%20brochure.pdf

WARNING!!!!!!!!! link is to a PDF file of about 1.5 MB

Hydrostatic drive losses can be significant, In wheel drives are the best option and reduce the inefficiency in a swashpalte type axial pump significantly, if compared to propshaft speeds of 3 to 4 times the RPM of wheel speeds. At speeeds below 1000 RPM and lower hydraulic drive efficiencies can exceed manual transmissions. The limked reference is a fixed displacement in wheel drive with a transformer to control pressure and volume.

We are getting a little ahead of ourselves here. Let's let the hydraulic discussion wait a while until after the dual clutch 6 speed automated manuals are presented. Thanks for the interest and responses.

[user removed]

The wifes current 2012 Kia Sorento as well as my 2011 Ford Fiesta both have dual clutch 6 speed transmissions.

Fiesta:
Remember this car was totalled and rebuilt.
The Fiesta is nice and the transmission works fairly well, but it seems a little cluncky at times and certain scenarios like my steep driveway can catch it in a funky shift. I have to be careful because I drive with one foot on the gas and the other on the brake (lets not dilute this thread with a debate on that).
When I get a little lazy and let my left foot touch the brake pedal it drives the transmission crazy and it starts doing crazy stuff, so I have to be aware of that.

Good performance, a little noisy, and it seems less perfected than the Sorento, which is as smooth as glass and likes to keep the engine at lower RPMs. The Kia is a great vehicle for what it is. I was surprized at how good it has held up and we have had absolutely no problems with it, and it's built in Gerogia. The transmission in the Kia seems far more refined than the Ford. I know Ford had service bulletins about "relfashing" the computer for the transmission, but mine is not eligible for any service bulletin dealer work due to the salvage title. It is still eligible for any recalls.

The biggest aggravation for me was after we got the Sorento I tried to see if I could easily beat highway MPG like I could in the Fiesta. I found it almost impossible unless I went 55 MPG with no accessories on a deserted road with virtually no traffic. Later Hyundai-Kia admitted they had "errred" in their highwway mileage testing and they dropped the EPA highway from 32 to 29.
Personally I would have kept the 2009 Rogue and it really ticks me off that they think paying her $100 a year for the difference in fuel mileage is fair.
We probably would not have bought the Sorento had it not been rated at 32 highway. She averages around 26.5 to 28 MPG.

I haven't really tried to much neutral coasting in her Sorento, just a few times with no problem, but I don't want them to have a warranty denial excuse. The Fiesta I neutral coast everywhere I can, even saw 80 MPG reading coasting around the Wall Mart parking lot after the last fillup when I reset the MPG meter. I have neutral coasted downhills on Interstates and through the mountians on two lane roads. The throttle by wire does a great job of rev matching on renegagement of the gears and selects the highest gear above 40 MPH with a smooth reengagemment of the engne.

The Fiesta transmission does not really go into neutral if you are moving. It will stay in 6th gear above 40 MPH but below that speed it shifts down to the lower gears when the engine speed would drop below 1500 RPM in the higher gear. It took me a while to realize it was doing that, but I could feel the transmission shifting, even though the shifter was in neutral.

regards
Mech

[California98Civic]

Subscribed.

[niky]

The advantage of dual clutch is the removal of torque converter losses. But it's clunky to use, and DCTs are heavy buggers. On-paper, they can match or exceed manuals, though.

But that's on-paper. In my experience, over several cars, including the Focus diesel, the Fiesta and the new Focus GDI, dual-clutches can match a well-driven manual on the highway, but in-traffic driving sees them suffer from the extra drivetrain weight. And the non-serviceable "lifetime" units are a nightmare. It's telling that Ford started offering replacement clutch packs for the Fiesta. They cost twice as much as traditional clutches (heck, there are two of them, so it makes sense), but at least you have the option.

CVTs are either as good or better than manuals or almost as good, depending on the implementation. By far the MOST economical automatic non-hybrid I've ever driven has been the Honda Fit 1.3 iDSi with the CVT. Ultra-light, ultra-low friction drivetrain, fantastic motor and car. 70 mpg easy. The only cars I've driven can do better are sub-liter cars.

BUT: Honda's CVT has a reputation for fragility, especially since they designed the stupid clutch packs to be non-serviceable items. Mitsubishi and Nissan get around this by using stronger steel belts and torque converters for smoothness. Adding a torque converter takes away from the efficiency bonuses, but if it has electronic locking (so it can lock up just off idle in high gears), it's not such a big issue. Mitsubishi's Mirage CVT with the 1.2 supposedly does almost 50 mpg on the highway.

New "traditional" automatics still have a lot of life left in them. Super-low-friction fluids, locking torque converters and lots and lots of ratios make for pretty good economy. They're not as fiddly as DCTs or as "unnatural" as CVTs, but once you have seven or eight speeds, the ratios are so close together that they start feeling like CVTs. Call it the "uncanny valley" of transmission ratios, but I can't imagine any criticism against CVTs that doesn't apply to these new eight-speed plus boxes. I drove a new Genesis Coupe for a week, and the eight speed box felt less "exciting" than the old six. That "kick" when you dropped two thousand rpm between gears was completely gone, replaced by nearly seamless acceleration.

Personally, I think CVTs, despite the "unnatural" feel, are the way to go. You avoid the jerky feel of DCTs in traffic, and adding a torque converter preserves clutch pack life. If you go for a dry clutch pack, you can still make it smoother than a DCT, and with clever programming, you can keep the dry system economy benefits while giving it longer clutch pack life. And if you really need the "feel" of gearchanges for one reason or another, a simulated five/six/seven speed mode will give you that, with less lag than in a traditional auto.

[user removed]

I have read a bit about the 1.3 IDSI equipped Fit. I only wish you could get that motor in a Honda in the USA that was not a hybrid. They are known to get mileages as good as the original Civic VX engines, and the CVT seems to work well with the fairly low horsepower output of the 1.3 which I think is a dual plug 2 valve head, with good swirl due to the offset valve locations, without any lean burn.

regards
Mech