An idea I had at work

Here's an idea I had while I was working the other day:

Ok, first off, a car accelerates hardest when its making its peak power at a certain RPM. Lets say that we have a car that makes its peak power at 5000 RPM. What if someone designed a transmition that when the car was at WOT, it automatically took it down to the lowest possible gear ratio for the speed they are going, while keeping the engine at 5000. Then as the car accelerates, the tranny constantly changed the gear ratios to keep the car at 5000 RPM while it accelerates. Which would mean that you never notice it actually "shifting." This would have to be done with some sort of continuously variable transmition. I'm really horrible at explaning things, so feel free to ask if sometimes isnt clear. My first question is, would it be possible? If it is, would it be beneficial? What is everyones thoughts on this?

yes, it's possible, it's called a continuously variable transmission (CVT), and there are several mass-produced vehicles on the road today that have CVTs available. Usually the controls on these CVTs aim to keep the engine operating near peak torque, but it's the same idee-er.

But what I'm saying is that the tranny would never actually "shift" but instead would gradually change the ratios while still delivering power and keeping the engine at whatever it makes it peak power at. So, you would be able to floor it, and have it keep it at 5000 all the way from 10 mph to 100 mph without ever stopping the delivery of power. I thought that CVTs were just like other transmitions, but just never shifted into a specific gear ratio.

they make cars liek that. The new audi A4 has a transmission that doesnt' shift in the traditional sense. Toyota also has something similar on there mr2

I talk out of my ass too much. :)

1) Not check if it already exists.
2) If it doesn't exist, post it on the internet.

This isn't a flame, just a suggestion that if you had thought up some kind of new gearbox, your best bet is to keep it secret until you've actually invented it ;)

454: While I haven't driven a car equipped with a CVT, I feel confident saying that they're anything but "just like autos and manuals."

Yellow: CVTs are always using one gear ratio or another... they just have an (almost) infinite spread to choose from. It's like having a 1,000,000 speed transmission instead of a 5-speed. Here are some quotes from articles about CVTs:

"Going WOT in any mode (E, D, or S) will cause Multimatic to use the highest possible engine rpm (>7000rpm for S) which delivers the optimum gear ratio for the highest possible acceleration from then onwards. This feature offers superior pick-up from 4AT and superior flexibility over 5MT during driving." http://asia.vtec.net/article/mmt/

"The "stepless" nature of its design is CVT's biggest draw for automotive engineers. Because of this, a CVT can work to keep the engine in its optimum power range, thereby increasing efficiency and gas mileage. " http://www.edmunds.com/ownership/techcenter/articles/45104/article.html

"Obviously, a CVT feels smooth in operation because no actual shifts occur, but the real advantage comes from its ability to vary gear ratios instead of engine rpm for a given driving situation. For example, if an engine's peak horsepower and torque occur at 3,200 rpm, a CVT would allow the engine to remain at this rpm even when climbing moderate hills or accelerating. While a traditional transmission must shift between multiple gears to try and keep an engine in its prime operating zone, a CVT just slides its belt between the narrow and wide ends of the pulleys to create a much more efficient drivetrain" http://www.edmunds.com/news/innovations/articles/43036/article.html

"during full throttle acceleration runs when engine revs are held almost constant while road speed increases rapidly" http://www.autobytel.com.au/consumer/Articles/usedcarreports/Civiccvt.htm


Does that sound a bit like what you were referring to?

Constantly keeping gears running at 5000rpm.. wouldn't this cause overheating eventually? An extra cooling system will be required if this concept really is used.

CVTs currently in mass-produced cars, that I know of are the hybrid cars, such as the Toyota Prius, which features the "Electronically controlled continuously variable transmission (ECVT)"... I forgot if the Honda Insight has the same system, but I would guess it would have something similar to increase efficiency.

http://web.ecomplanet.com/JONE4883/ServerContent/MyCustomImages/JONE4883CustomImage0157891

OMG that is the coolest picture i have ever seen :p

Originally posted by ivymike1031

"during full throttle acceleration runs when engine revs are held almost constant while road speed increases rapidly" http://www.autobytel.com.au/consumer/Articles/usedcarreports/Civiccvt.htm

That is what I was talking about. Seems it can and already has been done. Thanks Mike!

and R34GTRVspec2, that pic sure is an awesome red x.:silly2:

Now they just need to figure out how to strengthen the setup so that you can slap it onto a 1Khp+ car. :)

Originally posted by YellowMaranello
and R34GTRVspec2, that pic sure is an awesome red x.:silly2:

:jump: ya, my bad LOL

If a CVT tranny never really shifts, and keeps it at the optimum rpms, then it must sound REALLY goofy to hear a car that has a cvt with aftermarket exhaust....

The impression I get is that it would produce a flat, "BBBBAAAAAHHHHHHHHHHHHHHHHHHHHHHHH"

True??

yes and no... if you put a "standard" aftermarket exhaust on, it would probably not sound the way you wanted it to. I'm sure you could design an aftermarket exhaust for the CVT application that would give you a more desireable sound.

ok, theres one thing I'm not getting here still. On a cvt is there like and Economy and Performance selector or something, like instead of the standard 1,2,3,D? So would it be like P,R,N,P,E? Thanks for explaining this to me, I haven't read much on these trannys.

Maranello, think of a CVT as two cone shaped gears connected by a chain or belt. The belt or chain can move infintely up each gear, creating an almost inifinite range of useful gear ratios.

And they can be tuned to either boost performance (staying at max power RPM all the time) or bost economy (staying at max fuel economy RPM all the time). The only disadvantages of a CVT are the inability to adapt to different drive systems (such as AWD) and the inability to handle large amounts of power or torque.

Well, if you dig REEAAL deep into the patent office website, you'll find that about every major car manufacturer in the world is currently trying to develope a practical CVT. Some of those patents are under the name of that actual company, others by their subsidieries. One I found is patented to Timken, a bearing company that supplies a LOT of stuff to Ford, so do the math.

Truth is, as has already been discussed, they're only any good at really low power applications in the form they are right now. Most of them revolve around two pulleys that, in one way or another, vary their sizes to change the ratio between them. There's at least a dozen different forms of that particular setup, and they all have wear and slip issues. Ford recently publicized an effort to develop one that uses a beefed up chain in between a series of pullies, but I don't think it's working out. It's just too big for practical use, the smallest thing Ford could put it in is the F-250. The smaller ones are practical for transverse mounted engines because the pulley type CVT is very large in diameter, but very short. Again, though, it wont accept large amounts of power because the belt slips and wears out.

Other attempts are based on geometric shapes: discs, bell-shaped devises, and cones. The one I found that seemed the most promising used a pair of cones with a wheel in between them. The cones moved back and forth with the weel in place to change the ratio, but it stated right in the patent that it didn't work due to vibration problems. I know all of this because I'm currently trying to begin the patent process on a completely different setup (or at least as far as I know so far). My buddy and I have been thinking through all the bugs in it for about 2 years now, and have a working model, but patents are expensive and time-consuming. And being stuck out here in the middle of Iraq isn't helping move things along any.

Anyway, the theory is still the same, and the origional post had it right: the idea is that when you want to accelerate that the CVT will downshift untill you reach max-output on the engine, then upshift continuously throughout the acceleration, keeping at that exact RPM. Then, when you've reached the speed you want, it upshifts to the ratio that will render maximum efficiency. If/when it works out, it'll be an absolute breakthrough in both performance and efficiency. We'll just have to wait to see who wins the race to be the first to make it work in a sports car like a Mustang or Corvette.

Similar stuff has existed for industrial applications for years. As others have stated these involve changing the pitch diameters of the drive and driven pulleys. The other method is to use hydraulics with bent axis pumps and motors. Yet another is using power electonics. The problem is is that just because you operate the engine at peak efficiency doesn't mean its economical. There are many times you don't need the power. This is where flywheel, hydraulic, battery, and other storage devices come into play when designing a system built around a power source running at one setting.

Dude,

This post is like four years old,

CVTs have been around for a while. Subaru Justys had them in the 80s. I drove one and it was powerless (but that was the fault of the 1.5L four)

It is just as described. The justy CVT used belts and conical pulleys. Based on the position of your right foot and engine speed, the drive pulley changed the position of the belt - effectively changing the ratios on a sliding rate. The acclerator (in addition to opening the throttle) controlled where the pulleys were. If you put your foot to the floor, the justy would rev to 4000, and the transmission would adjust the cones as you acclerated to keep the same RPM. Then when you back off the acclerator, it "shifts" up to a higher ratio seamlessly. It still transfers power, just that the cones are now adjusted for 1500 rpms.