CVT manipulation for perfect gear ratios

[blueflame]

In scooters you can use heavier weights to up the overall ratios, or pulleys with different ramp angles. Wider belts give you greater top speeds.

I'm sure the cars are different but I have no idea

[bwilson4web]

Originally Posted by Daox

Yeah, its definitely a different beast. I didn't know that the planetary setup did the entire work of the tranny. I kind of get what you're talking about Bob. Thanks for the explination.

No problem although it took awhile to wrap my head around it.

Originally Posted by Daox

It is quite an amazing package over all. I took my first drive this weekend in an 04 Prius, and with the wife driving at a steady 65 mph down the highway, we were getting about 55 mpg. Thats pretty hard to beat. No special driving, just a smooth foot on the accelerator.

I'm sure we learned things the Chief designer didn't know. The Prius is really a nice, technical puzzle.

Bob Wilson

[The Atomic Ass]

Originally Posted by Christ

What a CVT should be = two mechanical centrifugal clutches, one that opens with speed, one that closes with speed, and an idler pulley.

This is what my PUG had... 3200 RPM, in high gear, was about 28 MPH.

Lose some drag and drop the idler pulley. My Burgman doesn't have one.

[dremd]

My first thought would be an ecu tune . . . . .

Not sure what ecu's have been cracked as of now . . . .

[malibuguy]

our Caliber has a CVT....less throttle = taller gearing, when i floor it it just holds redline as it gradually adds in more ratio to maintain it & add speed

[Daox]

I guess I'd need to drive a CVT with a scangauge installed to watch rpm vs tps vs load to see how they react.

[malibuguy]

its very weird at first, but eventually i got used to it & kinda liked driving it, it pulls mph on the top end really good, out of the hole tho...its a slug, i pulled something like a 2.6 or 2.7 60ft, but ran a 16.99@83mph with a 15mph headwind on a cool day, its like driving a large rubber band

[MechEngVT]

Originally Posted by Christ

What a CVT should be = two mechanical centrifugal clutches, one that opens with speed, one that closes with speed, and an idler pulley.

This is what my PUG had... 3200 RPM, in high gear, was about 28 MPH.

I've seen a PUG, but it's been years. As I recalled it had a garden-variety "snowmobile clutch" mechanical CVT, but you're either misunderstanding this type of trans or describing something entirely different.

Rubber belt CVTs have a centrifugal drive clutch that closes with speed against spring pressure and a driven clutch that is not centrifugal in nature that opens along a ramp against a spring responding to belt tension. Sometimes the post of the drive clutch has an idler bearing to reduce transmitted torque at idle speed. Sometimes the centrifugal clutch is mounted to a go-kart-like starter clutch to disengage it from the engine at idle speed. Neither of these last two are specifically required nor common on low-end machines like PUGs and similar contraptions.

Coming off idle the centrifugal drive closes a little putting pressure on the sides of the V-shaped drive belt, transmitting torque along a small radius of the sheave faces. Because belt tension is low, the belt rides along the largest radius of the driven clutch sheaves yielding a numerically low transmission ratio. This allows the vehicle to begin moving as the engine spins up to "shift RPM" (where the clutch begins to shift ratios) at which point you are typically generating as much horsepower as you can for the conditions (speed/load). Assuming you keep your foot planted to the floor the vehicle speed increase allows the engine to begin to speed up above shift RPM at which point the drive clutch's centrifugal force increases, increasing belt tension, pushing the belt up the drive sheave faces and pulling the belt down the driven sheave face, continuously decreasing the numerical drive ratio. This increases load, pulls engine speed in line with shift RPM, and so continues the cycle. Once maximum drive ratio is achieved (assuming WOT all the way) the engine can speed above shift RPM up to engine governed RPM.

If you settle into part-throttle cruise as some speed between idle and full RPM at full shift-out, the decrease in horsepower (and therefore torque) of the engine decreases the tension in the drive belt allowing the drive clutch to balance the rpm-specific centrifugal forces against the driven-clutch's spring pressure and ramp angle. This shifts into numerically lower ratios, pulling down engine RPM. Engine load as a percentage of available torque will increase as the RPM decreases and CVT shifts out, all while the vehicle is traveling at a steady speed on flat ground. Encountering a hill or increasing throttle changes this equation and the CVT back-shifts to bring up engine RPM and increase reserve torque.

Automotive CVTs are all computer-controlled electro/hydraulic contraptions these days. Computer programming controls how they respond, whereas with snowmobile clutches it's all simple physics and geometry. I've driven a Caliber CVT rental and I adapted to it quickly since in my experience it behaves very much like a mechanical rubber belt CVT. I would definitely recommend driving such a vehicle with a scangauge. I think throttle modulation and driving style, along with frequent neutral coasting, would benefit you greatly. I do recall the Caliber had a bit too much engine braking dialed in (something CVTs rarely do well, so some computer controlled ones over-simulate it).