Just for my own enlightenment, I'd like to hear about the designs you have come up with, and how you justified those designs...did you run single reduction, how did you find pulleys, how did you counteract any lever forces on the transmission output (if there were any), etc. I just haven't seen much intelligent discussion on this topic, but i know that teams have run them.
--casey

"I get to go to lots of overseas places, like Canada." - Britney Spears

We've run a CVT setup twice now, and we're going to do it again in 2003.

We use Polaris CVT clutches (pulleys) that are designed for quads and snowmobiles. The secondary clutch runs on a jack shaft which drives the final chain. The jack shaft has to withhold a hefty overhanging load, but with proper packaging within the chassis it's quite manageable.

This setup can prove to be pretty efficient if it's setup and tuned properly, and it makes the car a whole lot easier to drive (in this competition at least).

Nigel Lavers

Are you talking about belt drive on the engine crank side or on the LSD side?

I run both a belt drive CVT and a Gates Polychain belt final drive for the LSD on my AMod car. The CVT, unlike a stepped ratio gear box, is great for overall efficiency as well as eliminating driver's error in shifting. The problem is packaging. It increases the distance between the crank centreline and the diff's CL, hence a longer wheelbase car. I do think that a FSAE car would benefit with a final belt drive instead of a chain because of higher efficiency (about 3% claimed by Gates).

Joe

I'm talking about a direct connection from the output of the engine to the final drive, basically in place of the traditional chain drive. CVT's are a different story altogether. I don't think the tiny increase in efficiency is enough justification for what I see as huge packaging, part availability, and maintenance problems...any comments on these issues?
--Casey

"I get to go to lots of overseas places, like Canada." - Britney Spears

With a CVT and being able to keep the engine at peak power while gaining speed gives a substantial increase in efficiency. Parts, durability and maintenence are not a problem. Snowmobiles have been running them for years. Packaging is a BIG problem for a smaller car like the typical FSAE cars.

As far as the final drive belt. I have been using one since 1995. With close to 200 hp and two drivers running a very active autox program, I have broken 2 belts all these years. Both times, there were prior stone damage to the belt before breakage. Alignment is critical to avoid over stressing one edge of the belt. Harley Davidson has been using them for years on their bikes.

Joe

What do you do for pulleys? Have you found a wide selection of off-the-shelf parts? I suppose the CVT reduces the need for ratio changes, but in a car using a sequential tranny, it would obviously be different. Then throw in the different belt sizes needed....
I guess I'm asking this because I cannot see obvious benefits to the belt, other than the gain in efficiency, which I've even seen debated to a draw.
--Casey

"I get to go to lots of overseas places, like Canada." - Britney Spears

quote:

---

Originally posted by cdorneman:

I cannot see obvious benefits to the belt, other than the gain in efficiency, which I've even seen debated to a draw.

---

Obviously, you and all these people have never driven one or seen one run. All the dominating A-Mod cars at SCCA's Nationals are running a CVT. The snowmobile industry has standardize the CVT design to two belt lengths. Clutches (you call them pulleys) are available readily off the shelves. My prediction is that once the 4 stroke snowmobile engines start to appear (and they are coming because of EPA), FSAE will see more cars with CVT.


Joe

You do realize, I belive he's not talking about a CVT at all, he's talking about a belt drive in place of a standard chain. As far the the effiency comment anyway.

-Charlie Ping
Auburn University FSAE 1999-present

Yeah, Charlie.
I can see the benefit of a CVT (I am originally from the land of snowmobiles...built a go-kart in 7th grade with a Kawi440 and CVT out of an Arctic Cat) I'm talking about a belt that takes the place of a chain, with no other extras on the drivetrain. Maybe I'm wrong and no-one on this board has any experience with that situation.
--Casey

"I get to go to lots of overseas places, like Canada." - Britney Spears

As I mentioned earlier, I used a belt for final drive since 1995. The drive and driven sprockets (in aluminium) are available from any Formula 440 dealers. The belts are available in a whole range of sizes. The only thing about using a belt is that if it breaks, you need to remove the diff to put the new one on. As far as efficiency goes, I noticed the 2002 UTA car has no grease seal for the front hub bearing. I was told by a team member that this would eliminate the friction between the seal lip and the spindle. I guess the top teams are worrying about efficiency.

Joe

Joe,
I was not trying to imply that efficiency is a non-factor in FSAE...I'm just adding that factor into the equation containing packaging, maintenance, weight...it becomes a lot less important to me to gain a reported 3% less friction when I can't change my belt between autocross runs. Or to have less friction in my wheel bearings when they could get junked because we go off-track in testing and get sand in them...
I'm an engineer, so I'm a pessimist
--Casey

"I get to go to lots of overseas places, like Canada." - Britney Spears

Nigel, what kind of engine are you running? I'm curious because adapting a CVT to a typical bike engine/transmission package is no simple task...

Lehigh Formula SAE

www.lehigh.edu/~insae/formula