RX8Club.com - Rx-8 Cvt

RX8Club.com (https://www.rx8club.com/)

- Series I Tech Garage (https://www.rx8club.com/series-i-tech-garage-22/)

- - Rx-8 Cvt (https://www.rx8club.com/series-i-tech-garage-22/rx-8-cvt-2203/)

Let's hope that Mazda will replace the 4-speed automatic transmission with a CVT in the future.

Continuously Variable Transmission offers good acceleration and improves fuel economy.

CVT's are better for engines with very narrow powerbands. Since the Renisis has a very wide powerband, a CVT is not a good way to improve performance or economy.

I personally think the best idea for Mazda to explore would be a hybrid engine that would allow more low end torque, with increased fuel efficiency. Check out the NSX hybrid concept.

correct me if im wrong but i was under the impression that cvt's were restricted to lower output engines, like the equivalent of your typical 4 banger or was it ~200ish horsepower?

there isn't really a theoretical limit if you're trying to design a car within reason (i'm not saying that you could produce a CVT for a 3500hp top fuel dragster or whatever...), but how much weight and cost would go into making one for a 300hp car??
i wouldn't doubt, though, that a CVT is a far better solution than the old 4 speed autos, as far as mass and efficiency go... but they are pricey. hmmmm... also, there's the problem of these transmissions handling revs... i don't know much about the way in which they work: would it pose a problem to have such a wide range of rpm operation (ie: about 6000 rpm)??

Quote:

Originally posted by lefuton
correct me if im wrong but i was under the impression that cvt's were restricted to lower output engines, like the equivalent of your typical 4 banger or was it ~200ish horsepower?

That was true until recently. CVTs are now able to handle HP north of 200. I think the nissian Morado (sp) has a CVT and more than 200 HP. Correct me if I am wrong though.

THe Williams F1 team made one in 93 I think..
Worked really good but sounded very strange.. *s*
It was banned before they ran it in a race..

//magnus

Um, ok coming from the snowmobiling world, I have personally worked on a 332.3hp (we have a Dyno) Drag snowmobile, since that is where the CVT came from (they are the same thing) I know for a fact that they can handle well over 300hp. The ones on snowmobiles are typically designed for the engine to mainly run at a constant rpm (most effecient) but work well at all rpm's. They work by having a "drive clutch" and "driven clutch" one is spring tensioned closed "driven", the other is open "Drive", when the engine's rpm's increase, weights swing out and close the "drive clutch" which forces open the driven and the friction also spins the driven and ultimately the wheels/track. The higher the rpms, the more the drive opens and the more pressure on the driven and the more the gearing rations change. Hope that was not too confusing but that is the basics of it. There are alot of other factors also, like spring tensions, weights, angle of the helix (the path the weights swing out on), etc. If anyone has any specific questions on how that clutch works post here and I will try to answer as best I can. Remember all my knowledge comes from snowmobile clutches so take that into acct when asking.

The new Audi A4 has a CVT available with the 3.0 V6 wich is rated at 220 hp.

The only problem with CVT's is almost all the ones in use now are front wheel drive only.

CVT Car model Engine Max. Torque
------------------------------------------------------
Audi A4 3.0 221 lb-ft

Nissan Murano 246 lb-ft

The max. torque of the Renesis is 160 lb-ft. Torque capacity is not an issue for the rotary.

In fact, a good CVT can handle a Vortech supercharged Renesis; as long as the boost is kept below 6psi.

A CVT compensates for the Renesis's lack of low end torque by keeping the engine operating in its powerband. In other words, you can tune a supercharged rotary for a narrow powerband.

A CVT is lighter than a conventional gearbox. The weight saving is another bonus.

alright, sure. i'm impressed with that torque handling capability: can it handle the rev's though?? 9k input revs is a lot... and who would want to be at 60 degree throttle all the time anyways to keep the engine in its "optimal performing range"?? i mean, sure, you'd get great get-up-and-go... how well could this system really save you gas by keeping revs pinned at 2krpm and just decreasing the ratio?? basically, what i'm getting to is "Can a CVT really span the useful strata of gearing ratios that your average banger box can??"... i wouldn't bet on it.

Although a CVT might be "lighter than a conventional gearbox", at what cost level, what design, what materials, how many cogs?? i'm nearly positive that if cost was equal (not only in manufacturing but also R+D) that you could certainly make a synchro'd manual tranny that weighs much less than a CVT.

:D i'm not against them, just trying to come up with some interesting counter thoughts, trying to see the comprimises (as in engineering they are ever present).

Actually, a regular manual gearbox is lighter than a CVT.

Audi A4 1.8T:

5Spd FWD - 3252 lbs
CVT FWD - 3362 lbs

http://www.audiusa.com/features_spec...ode-1_,00.html

one can't really say it's a universal truth, but yeah, i'm sure it'd be easy to make comparable transmissions of the manual sort lighter, if not also smaller, than a CVT... that said, it may be worth that extra mass in its advantages ?? it's all a big trade off. :)

Audi's multitronic ratio span has exceeded 6:1, and they are up to almost 6.5:1 in the 'version 2' in the A4 cabriolet

It will handle the rev's, the snowmobile could spin 14k rpm's (it was a 2stroke!) reliably, just had better drag racing capabilities spining at 9800rpm's. The only issue I can see is on snowmobiles the belts are worn out in 200-300 miles, so the belts in the cvt's for cars are different somehow to last longer.

Toroidal CVT A highly efficient transmission is a significant factor in reducing fuel consumption of automobiles. An automatic transmission that skilfully draws the power out of the engine, faithfully matching the driver's intentions allows every driver to enjoy driving in comfort. Starting from this premise, Mazda has conducted the R&D of Toroidal CVT (Continuously Variable Transmission) as a next-generation transmission, which is highly efficient, lightweight, compact and can deliver larger engine output.

The Mazda Toroidal CVT combines the half-toroidal CVT with a geared neutral starting system. This highly efficient system is an ideal transmission for FWD vehicles, delivering excellent response, quiet operation and superb fuel economy. Combined with a 3.0 liter engine, it achieves about 20% improvement in fuel economy in Japanese 10-15 mode compared to a current 4-speed automatic transmission. Half-Toroidal CVT In the half-toroidal CVT, a large force presses a semicircular disc against the power roller, and the resulting shearing force of the ail film squeezed in the space between them transmits power. Changing the effective radius of the contact point enables the gear ratio to change continuously, resulting in step-less gear shifting. An exclusive traction oil is used for lubricating the system; when this oil between the disc and power roller is placed under high pressure, its viscosity rises momentarily. As the oil becomes more viscous under pressure, it becomes harder, and transmits the power by the shearing force. An electro-hydraulic control tilts the shaft washer of the power roller, changing the effective radius of the contact point and making smooth, quick shifting possible.

In addition, the half-toroidal CVT has these key benefits: - It is possible to transmit high torque loads because of the high performance traction oil and high-surface-pressure material used in the disc and power roller. - It is very efficient because it does not require high hydraulic pressure to transmit power like a metal belt CVT. - It is much quieter than a metal belt CVT because power is transmitted via a smooth rolling contact surface and the shearing force of the oil. Geared-neutral starting system This transmission system uses a geared-neutral system. This dual-mode system which uses the CVT and planetary gears in low-speed mode, and the CVT alone in high speed mode. In low-speed mode, the planetary gears' differential function provides a large reduction gear ratio and also increases torque, for excellent starting acceleration. Because the engine can run at low rotational speeds, this system achieves excellent fuel economy and quiet operation. Switching between modes is automatically controlled by a computer, which synchronises the two clutches, one for low speeds and one for high speeds. The neutral-geared system also eliminates the need for a torque converter, further enhancing the overall compactness and efficiency of the car.

System torque capacity 300N - m
Reduction speed ratio Forward infinity to 0.415Reverse infinity to -2.789
Final drive gear ratio 4.375
CVT mechanism Dual cavity type, half-toroidal CVT
Starting system Geared neutral type
Shift control device Electronic hydraulic pressure control

holy shit, i'm impressed. if they could make those things smaller, lighter, and cheaper, it'd be all over!! :D wow. i'm sold.

Supercharger, engineers and fans of the CVT should give you a fricken' medal, man. great posts.

that said, i'm sure that manual trannies will always remain light enough, cheap enough, practical enough, and fun enough that there will always be a market for them; however, the 4 speed auto, and the recently-developed 5+ speed autos have their days numbered. :D

The engineers at Mazda deserve a medal. They know how to build affordable sportscars.:)

Mazda CVT's torque capacity of 300Nm = 221 lb-ft

Great posts, Supercharger!! I have been interested in these for years...now the technology and designs are catching up to the concepts.

The reason high rpms have been a problem with automatics was based on torque converter stator issues. Assigning a proper stall speed for an engine with a high rev powerband made streetability problematic. A CVT doesn't have the same design challenges.