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Post by urbanmadness on May 27, 2014 11:40:12 GMT -5
Maybe I am the Devil. Haha. I own a motorcycle and a scooter. The motorcycle has a steel chain and steel gears. This phenomena does not happen because the steel chain and gears cannot slip so there is a fixed relationship between the engine rpm and the rotation speed of the rear tire. One difference between the motorcycle and scooter is the transmission. As the referenced article states, the people who design these CVT's say the belt slips more when applying more torque. So under acceleration the belt slips more resulting in a higher rpm for the same 50 mph speed. Backing off the throttle and reapplying to maintain the 50 mph means applying less torque to maintain the same speed resulting in less slip so a lower rpm results in the same 50 mph. This is no different than using a wrench to loosen a nut. When the nut is not loose, you have to apply a lot of torque to loosen it, but once it is loose the amount of torque required to continue turning it is much reduced. On the other hand wrenches like strap wrenches based on a belt can slip under torque. This explanation also explains why this is less likely with smaller engines. Smaller engines have less available torque so they cannot cause as great an increase in slip. It also says that if you increase speed very gradually which applies less torque over a longer period of time the phenomena is less likely to occur. If you have a scientific explanation or a scientific paper to explain the process I am willing to listen. What is being described here is not belt slip. It's the variator changing ratios. To slip a belt on a scooter, would take more horse power then they generate unless there is something wrong with the bike. For example, my 500cc makes about 39BHP with a belt that is not much larger than what is used on a 150 or 250. It is a little thicker but that's about it. Think about it, if the belt slips too much, it is going to burn up or squel (and you'd smell it). They don't unless you have a clutch problem. The "Slippage" being described here is the CVT doing it's thing. Comparing it to a clutch and gears bike is like comparing apples to oranges. A closer comparison would be to a 10speed bike. The rear pully acts like a de-railer that is taking up the slack in the chain, and the varator like the front set of sprokets with the front sproket being completely automatic, depending on RPM. As RPM's increase, the Variator (front pully) closes and the belt ramps up, changing the ratio. Check out a couple Youtube vids on how a variator works and you will see, just how ingenous they really are. You really have to hand it to the engineers that designed these CVT's. They are cheap, relaible and brain dead simple in function. The fact that the design has been around for so many years, on everything from 50cc 2 strokes up to my 500cc Italian bike is a testoment to how well this style of transmission actually works. Is it as efficient as clutch and gears? Yes and no... For this type of bike, in stop and go traffic and in a down town situation, a bike with a properly tuned CVT can pull 75-100 mpg (150, 250 class). My 500cc, for example pulls about 58MPG in city stop and go driving... Get the 500 out on the open road, and it drops to 50MPG. This is because when a CVT bike with a properly tuned variator takes off, it's in the powerband thru acceleration, when crusing you may not be in the powerband (the 500cc runs on the freeway at about 6k rpms). A clutch and gears bike, ridden well, you can cruise at lower RPM's and get the milage numbers out of it on the open road, but you will take a hit when you accelerate as you are moving in and out of the torque curve. In case you are wondering where I got the MPG numbers for the 500cc, the touring computer on the bikes tells me and resetting it every tank gives me a very good idea on what riding style with that bike nets the best MPG numbers. I know, long winded, off topic, but I hope that at least sheds a little light on what you are saying vs what alley is saying. |
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Post by oldchopperguy on May 27, 2014 13:37:08 GMT -5
Hey Urbanmadness...
I'm with you on how amazing the CVT setup is, and how versatile. I think these have been used on high-performance snowmobiles for a LONG time... And they are used not only on the larger scoots like yours, but on those up to the 800cc class, and on some big motorcycles. Now to carry that to the next level, Ford uses it on some of their CARS! I believe other makers are doing it too... My neighbor has a performance Ford with it, and he's a pro jet-aircraft technician. He likes it because it's SO simple, trouble-free and, it seems Ford has combined it with TOTAL computer-control, tied into all the "black-box" gizmos that control the fuel-injection, etc. By doing that, he thinks they eliminated the few negatives like you spoke of at highway speeds. Hmmm... An infinitely variable CVT tranny that works in a 300 hp performance car? I'm thinking this type of transmission may be the wave of the future in a LOT more applications than scooters... Ford does NOT advertise the CVT... Neither do the other makers using it. At least one Japanese car maker uses it. The idea of "belt-drive" is a major "turn-off" to buyers, even if it's great... The old sixties/seventies Cadillac Eldorado and Olds Toronado used a monster chain-drive from the engine to the torque-converter on their front-drive trans-axles. They didn't tout that either because of the negative and "primitive" aspect of "chain-drive" on a modern car. Whatever their good and bad points, the CVT tranny is definitely here to stay!Enjoy em, no matter what they reside in!  Leo
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Post by bnc on May 27, 2014 14:54:33 GMT -5
Thanks for the welcome oldchopperg.
Urbanmadne
The problem is that Alleyoop eliminated that from the equation when he said,
but we were talking about two difference engine rpm's at 50 mph. When I asked if this is not belt slip, the answer was no. I think you can see the problem. If the variator has reached its highest gear, the belt is not slipping then how can two different input rpm's result in the same output rpm at the rear wheel?
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Post by urbanmadness on May 27, 2014 15:30:43 GMT -5
Thanks for the welcome oldchopperg. Urbanmadne The problem is that Alleyoop eliminated that from the equation when he said, but we were talking about two difference engine rpm's at 50 mph. And that is possible. I've seen it. I can cruise at about 500 rpm less then acclerating on my big bike. (the only one I have that has a tach) Alley was talking under acceleration only, I believe. What we are talking about is accleration, coast, then accleration. The gear ratio is going to be different depending on conditions, load and a given RPM and I notice it more on the larger bikes. Afterall CVT stands for Continously Variable Transmission. When coasting or cruising, the rear pully pushes the belt thru the variator, which keeps the belt up in the variator, lowering engine RPM, then when you goose it, it the engine pulls it tight, pulling it into a lower ratio until it throws the wights back out. <----- this may a more to the point answer to what you were asking. CVT's are pretty dynamic... |
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Post by urbanmadness on May 27, 2014 15:46:55 GMT -5
I didn't know Ford was using a CVT. I know Nissian does, and so does Mini.
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Post by bnc on May 27, 2014 16:04:33 GMT -5
Assuming this to be true, also that the belt reaches its outermost travel at 40 mph as he stated, and that the belt does not slip as he stated, implies that the lower rpm would occur on acceleration which is the opposite of his findings.
The reason I ask such questions is because in my first job, an experienced guy before me did a project without people asking him hard questions. The result was that the company invested more than a million dollars in production equipment only to find out that the prototype was the only unit that behaved the way it was required to behave. The company had to write it all off as a huge loss and the guy was terminated. Scared the daylights out of us new hires.
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Post by urbanmadness on May 27, 2014 16:33:53 GMT -5
Assuming this to be true, also that the belt reaches its outermost travel at 40 mph as he stated, and that the belt does not slip as he stated, implies that the lower rpm would occur on acceleration which is the opposite of his findings. The reason I ask such questions is because in my first job, an experienced guy before me did a project without people asking him hard questions. The result was that the company invested more than a million dollars in production equipment only to find out that the prototype was the only unit that behaved the way it was required to behave. The company had to write it all off as a huge loss and the guy was terminated. Scared the daylights out of us new hires. I think one source of confussion on this thread is we are talking three different class bikes with different set ups. Alley rides a trike (150cc I think), OCG rides a 250, and I ride a 500cc. My bike is good for over 95MPH stock so it has a much larger Variator, so much more surface to play with. The 250 that started this discussion also has a bigger variator then alley's bike. 250cc bikes are good for anywhere from 65mph to 75 mph stock depending on set up and the 150cc class bike that's usually good for 50-60. Alley will have the same thing happen at lower speeds. Two different RPM's at the same speed. It's just a different "gear".... But once you get to top of the variator, they don't loose rpm when you let off the gas. It's only when you are not at the top of the travel of the variator. That happens at 40mph on Alley's bike... I Don't know where it happens on my bike (don't want the ticket) and probaly around 60 on OCG's bike. Have you ridden a CVT bike? |
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Post by alleyoop on May 27, 2014 17:23:54 GMT -5
This all is amazing to me, but let me ask one simple question: Here is my CVT with the motor off and at IDLE the belt stays in the same position. Here is the question: Does anyone believe, IF the belt stays in that position and giving it throttle will it turn the rear wheel? If the answer is YES, explain why. If the answer is NO, explain why. Not to be a smart( ask) , BUT this is a test, I just want to see who knows how a CVT works. Alleyoop  |
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Post by urbanmadness on May 27, 2014 18:06:33 GMT -5
yes, if it spins the rear pully fast enough to engage the clutch but chances are the belt will move up the variator a little before that happens. (am I right?)
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Post by alleyoop on May 27, 2014 18:38:47 GMT -5
KUDOS, you can also make it turn the rear wheel by just taking the weights out the variator and it will not move out and the belt will stay there, so the magic word is CENTRIFUGAL force is all it needs to throw out the clutch pads to grab the bell and turn the wheel and to do that you need the motor to turn over fast enough to accomplish it(RPMS). I noticed a lot of lookers and no takers, tell you It does get tiring when someone that does not understand how things work jump on my case. So I am done with this and you guys can now battle with Urbanmadme  Thank you Urbanmadme I need a rest  Alleyoop |
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Post by urbanmadness on May 27, 2014 19:03:16 GMT -5
I'm pretty much done too. Hey, I tried . Figured if I missed something, you'd correct me Alley.
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Post by bnc on May 28, 2014 14:50:14 GMT -5
I just realized that I have been using a layman's term "slip" when engineers and scientists use the term "creep". Creep occurs for example, when a 1:1 ratio CVT has an input rpm of 1,000 so the output should be 1,000 but it measures 950 rpm. Creep and friction account for a good part of why a rubber belt CVT only as a typical efficiency of  %. From a paper titled "Kinematic Creep in Continuously Variable Transmission" by Professors Gillispie of U of Michigan, and Moore of U of Florida schools of mechanical engineering. I have a Yamaha Riva 125, a Honda Reflex, and a Kawasaki Ninja. |
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Post by jc on Sept 2, 2015 12:42:07 GMT -5
Of course all rubber driving surfaces will experience a extremely small percentage of slip. You see the results of that slip in the cvt case as a fine black powder. You see it on your tires as wear. Now about the wot situation where you can back off throttle a bit and hold the same speed. I understand Alleyoops explanation being a lean condition that may be happening, generating a little more power at the lower rpm . What about the possibility that the belt may be requires the belt to loosen up a certain amount before the belt starts to push up the rear driven face as the spring force overcomes the belts outward pushing force, And the difference between those 2 forces are a few hundred rpm? Be gentle, Im just trying to get my head around this.  I just noticed the date on the last post, I apologize for resurrecting an old thread. |
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Post by nulldevice on Sept 2, 2015 17:03:39 GMT -5
I have had the same faster at part throttle experience on my first Suzuki two stroke twin. After I put bigger jets in it ran even faster at full throttle. I know you said the dealer checked the mixture, but you have said your scooter runs better in extreme hot weather. That tells me you are running lean at WOT. Your density altitude is much higher at 100 degrees F than at 50 degrees F. Who are you going to believe, an instrument at a dealer on maybe a cool day during high pressure weather or your lying eyes?  Try a larger main jet. |
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Post by JoeyBee on Sept 3, 2015 9:35:05 GMT -5
I tested this out on my TaoTao Powermax 150 last night, and this "trick" worked for me. Here are my observations from the test.
Typically, at WOT my chinometer tops out at 100 with 7000RPMs. That's exactly what I tuned my CVT for to avoid the 8000RPMs. This was how she was running last night. So on a straight and level road I maxed her out. Once I was at that limit I eased off the throttle a 1/4ish for a moment then twisted back to WOT. To my surprise the chinometer climbed to 110 and RPMs reached 8000. Once I saw it worked I slowed down, but I was very surprised. My scooter has never gone that fast.
I don't think I will be doing that very often. I drive for reliability not speed. Plus the road I drive to work has a speed limit of 45. I don't want to be that guy pulled over for speeding on a scooter. But it was fun to push her limits.
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..BAD TO THE BONE..
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