CVT "manual shift "CVT?

Discussion in 'Transmission / Drivetrain' started by kallsop, Jan 7, 2010.

  1. kallsop

    kallsop Member

    Has anyone built a manually shifting symmetrical CVT? Meaning that, instead of relying on a spinning mass to adjust the width of the pulley, have a manual adjuster operated by cable and e.g. connected to a lever style shifter? So it becomes a stepless ratio manual gearbox. Seems like it could be dirt cheap and very reliable. One adjustable width crank mounted pulley, tensioner, output pulley with jackshaft to the final drive sprocket. The adjuster would need to be stationery and not rotating of course, but that should not be a big problem. Belt tension could be used to widen the pulley, and the adjuster would wind in to narrow the pulley. Open the pulley wide and select neutral.

    I'm just wondering if riders would prefer a fully automatic CVT or a manually shifting stepless gearbox? The automatics seem to have issues with engagement rpm's and constant maintenance.
     

  2. kallsop

    kallsop Member

    Here's a question. Looking at the Comet 340 symmetrical torque converter (e.g. http://www.jrdragsterplus.com/salsb.pdf ) the largest size of the driver pulley is 4.8", and the driven is fixed 6". At that extreme, the ratio is 6:4.8, or 1:0.8, meaning that one turn of the driver equals 0.8 turns of the driven. Note that 1:0.8 is the same as 1.25:1.

    The driver pulley can get wider such that it's effective diameter gets smaller. The ratio therefore reduces. If the driver halves to 2.4" diameter, the ratio is 1:0.4, alternately stated as 2.5:1.

    Why do Comet quote the "driving ratio" as 2.5:1 to 0.8:1? There is no way the driven pulley can go faster than the driver pulley to get 0.8:1. Yet they quote an overall ratio of 3.16:1 and 3.16 is approx. 2.5/0.8. Did I make a mistake somewhere?
     
  3. Youngbird

    Youngbird Member

    Because as the driver "decreases" in size, the driven "increases". Neither one is a fixed "size".
     
  4. Nuttsy

    Nuttsy Member

    I suppose it could be done with a fork type deal like on a manual car transmission for the clutch throw-out. I would like to see such an animal because one of the biggest complaints I have with my cvt is that it is REACTIVE instead of PROactive. By time they "feel" a load or hill coming on, you are already into it. Whereas, when you "SEE" a hill coming you could downshift ahead of time and even hold it there. I think an index type shifter would be a good match for that type shifting. The contra spring/pulley can stay to counteract the variator. It should be a simple enough concept. I have no complaints on the take off and acceleration from a stop. Only on hills or high wind conditions. I also don't have any maintenance problems. A couple of times per year I change the oil in the gear box; still the same belt for almost a year and thousands of miles.
    Have you got any plans to manufacture such a cvt, or you just fishin'?
    Nuttsy
     
  5. kallsop

    kallsop Member

    I get it now, thanks. Looking at only the first page, it seemed like the driven pulley was solid. Now it gets a lot more complicated to think about having two adjusters rather than one, or maybe just a single adjuster on the driver and a fixed driven but then the range of ratios is limited.


     
  6. kallsop

    kallsop Member

    Just thinking out loud at the moment. I don't really need an automatic. A stepless manual would be great.


     
  7. Youngbird

    Youngbird Member

    Why not just use the MaxTorque driver/driven and be done with it. Its a good setup as is the Comet, but they are out of business.
     
  8. loquin

    loquin Active Member

    The driven pulley is just a pair of spring-loaded sheaves. There aren't any weights causing them to move together or apart. So, if you could set up a manual adjustment for the drive side (as with a clutch throw-out fork,) the driven pulley just 'follows along.'
     
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