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mud_dog450 -> Parasitic Drivetrain Loss and the Ultramatic CVT (9/4/2008 12:14:15 PM)
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Grizzly 660 42HP @ crank.
Grizzly 660 ~30HP @ rear wheels.
Parasitic Drivetrain Loss = ~29%
Only 29% of the available HP at the crank is transferred to the wheels via the internal wet clutch and CVT system!
Most all of the other manufacturers are focusing on building massive powerplants for their new machines instead of trying to develope more efficient ways to transfer this power. Instead of refining the clutching systems, they just throw a bigger, beefier, more powerful motor in so that the rear wheel power is greater, yet the loss between the crank and the wheels is still present.
Now only if there was a way to make the CVT system more efficient.
Automobiles using the CVT systems use stronger belts which incorporate steel belts and "keys" into the belts to allow them to withstand the HP and TQ of a 4-cylinder or V6 engine.
One thing that all CVT systems have in common is the sheave faces being smooth.
So why not knurl one or machine a pattern into the sheave faces to increase belt grip and reduce parasitic drivetrain loss?
The few problems I see with this are as follows:
A) Increased drivetrain wear and tear. Given the fact that wet-clutch systems are most likely the most efficient power distribution system out there, they slip very little once fully engaged. With the smooth sheave faces of the CVT system, they allow belt slippage to occur whether it uses the internal wet-clutch system that Yamaha utilizes, or the Polaris-style CVT system that uses a crankshaft mounted primary. Also, with the belt being mostly rubber, it stretches a certain amount. All of these factors act as a drivetrain "buffer" or "dampener" to decrease stress and wear on drivetrain components. This is much like the rubber dampening bushings (or "cush drive" system) in the sprockets or drive wheels of most motorcycles available these days.
B.) Belt/sheave wear. If you've ever had your belt off, you will see that the sheave faces will, over time, being to groove where the belt rides. They wear like this because they slip. Take away the slip, you take away the grooves. The belts will also wear due to this slippage. However, with the Ultramatic CVT systems, the primary always clamps on the belt. Because of this, I believe one could get away with running a slightly knurled or machined pattern on the sheave face because the majority of the slippage occurs in the wet clutch, and not so much on the belt/sheave faces. This is one of the biggest reasons why the Ultramatic CVT system is, in my opinion, the most reliable belt driven CVT system available. If you tried to knurl the sheave faces on a Polaris or Kawasaki system, the belt would be toast very quickly as the "teeth" would chew the belt very quickly.
Regardless, the knurles or machined patterns would increase belt wear. Without testing though, there's no telling how much wear would increase or how much more efficient the CVT system would be.
BUT, the way I see it, is that even if the parasitic loss is 10% less, that's only a 19% parasitic loss overall, which would come out to 8 more HP than the current setup.
8hp AT THE WHEELS is a HUGE increase in power especially since it's all felt at the wheels and not just "crank hp". Plus, the power is already there. It's practically "free" power.
Now, all of this is assuming that Yamaha or other manufacturers have experimented with this, and found it to be a lesser design compared to the smooth-faced sheave design. BUT, considering the fact that Ultramatic belts hardly ever need changing, I would be able to live with replacing the belt every 1500 miles or so, given the conditions were strictly mud riding.
Any thoughts?
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