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"Liquid Drive" bike prototype at auction
It looks like the fella behind this CVT hydraulic bike is trying to
raise some capital by selling off his prototype: http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3641257316 http://www.powerengine.com It seems like a cool artifact, if not particularly practical. I know this particular bike has come up for discussion before, with a certain amount of pooh-poohing of the general concept. Since this thing surfaced again, I've been reflecting on what hypothetical advantages a hydraulically driven bike could have over a chain driven bike, which might offset the drawbacks of what is almost certainly a heavier, lossier, and more expensive system than chain drive. So far I've come up with: 1) True continuously variable transmission ratio, which this bike has Some people insist we want CVT, but hydraulically driven vehicles have always had it available and are still rather uncommon. For instance, Hondamatic motorcycles never caught on, though their system seemed to work as intended. I'm unconvinced that it's really as desirable as its proponents say. How did CVT become associated with the HPV community, when human power seems to tolerate a wide range of RPM? 2) Two-wheel drive, which this bike does not have This is another feature that some have tried to provide, while others wonder why. The benefits of four-wheel-drive in cars look similarly esoteric to me, yet many people opt to pay a premium for 4WD or AWD cars. If such a thing were available for bikes (and without glaring shortcomings), I wonder whether there would be any noteworthy handling benefits. I don't ride my bikes in the muck, but perhaps those who do would appreciate 2WD? 3) Integral braking, which the inventor's website mentions, but which does not appear to be incorporated into this bike I think that having a bike's drive and braking functions integrated into the same apparatus is the most desirable potential feature of a hydraulic drivetrain. Check valves could be adjusted to match available maximum braking torque to the load, and the force required to close the braking valves would be miniscule compared to that required to actuate normal rim or hub brakes. 4) Possibly less regular maintenance and system wear Many hydraulically powered machines work around the clock for years between breakdowns in the hydraulic systems. (I am reminded of various forklifts I've worked with, whose batteries always seemed to be troublesome but whose hydraulics were seemingly invincible.) Hydraulic systems by their nature run in a lubricant bath, and much of the mechanical wear in them occurs to the fluid. I am sure that not every cyclist would be willing to give up a noticeable amount of efficiency to have a service interval measured in years, but some certainly would if the cost were not offensive. 5) No intrinsic configuration constraints This seems most relevant to suspension bikes, where chain drive and suspension components compete for space and exert forces upon each other, and to recumbents, where the rider's behind often interrupts the straight line between drive sprocket and driven sprocket. But the hydraulic "driveline" is just a pair of hoses, and can be fitted around (or through) other mechanisms. It could be routed under the cargo bed of a carrier bike, for instance, or within a frame tube to a drive wheel far removed from the crank. Even a crank is not a given; it could just as well be treadles or something else yet. The possibilities outrun my ability to imagine good uses for them-- so much about the bikes we know is just corollary to the chain drive, that it's difficult to imagine what a "normal" bike would be like in the absence of one. The high wheeler is what you get when you assume that a bike's cranks will drive its axle directly, and the diamond frame with derailleurs is what you get when you assume the use of a chain drive. If you don't assume either of those things, then what? I suppose the answer to that will have to await another feasible alternative, if there is one. Chalo Colina |
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"Liquid Drive" bike prototype at auction
"Chalo" wrote in message om... It looks like the fella behind this CVT hydraulic bike is trying to raise some capital by selling off his prototype: http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3641257316 http://www.powerengine.com It seems like a cool artifact, if not particularly practical. snip 3) Integral braking, which the inventor's website mentions, but which does not appear to be incorporated into this bike I think that having a bike's drive and braking functions integrated into the same apparatus is the most desirable potential feature of a hydraulic drivetrain. Check valves could be adjusted to match available maximum braking torque to the load, and the force required to close the braking valves would be miniscule compared to that required to actuate normal rim or hub brakes. snip Chalo Colina Thanks Chalo, I really find these things fun - wish I had time to have a go at building such impracticalities.... Theoretically instead of dispersing the braking energy through turbulence in the hydraulic fluid you COULD use the pressure (via an accumulator) to store the energy for future use. Not suggesting its at all practical, but makes an interesting mind project. Hugh Fenton |
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"Liquid Drive" bike prototype at auction
"Chalo" wrote in message om... It looks like the fella behind this CVT hydraulic bike is trying to raise some capital by selling off his prototype: http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3641257316 http://www.powerengine.com Some people insist we want CVT, but hydraulically driven vehicles have always had it available and are still rather uncommon. For instance, Hondamatic motorcycles never caught on, though their system seemed to work as intended. I'm unconvinced that it's really as desirable as its proponents say. The 750cc Honda with the CVT transmission was a dog. If I recall correctly, it produced about half the horsepower at the rear wheel that the regular model did. Not many people are willing to buy a 750cc bike that performs like a 250. Another issue against it was that the motorcycle community, with it's higher than average level of machismo posturing, did not warm up to the introduction of something as un-manly as a full-sized automatic motorcycle. Ed Chait |
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"Liquid Drive" bike prototype at auction
(Chalo) writes:
It looks like the fella behind this CVT hydraulic bike is trying to raise some capital by selling off his prototype: http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3641257316 http://www.powerengine.com It seems like a cool artifact, if not particularly practical. Quick summary of the mechanism as I understand it from reading the website : The basic unit consists of an opposed two cylinder 'boxer' layout. The unit can be used either as a pump or as a motor. Two 'bottom bracket' actuators are illustrated, one with a single two cylinder unit, and the other with two units mounted at ninety degrees to one another, and thus presumably providing substantially smoother flow as at least one piston is on its pump stroke at all times. So far I've described components of a fixed ratio transmission. The CVT bit comes from a very cool idea: a variable offset crank-pin at the pump end. As the crankpin offset increases, so the volume of fluid moved per rotation increases, so the effective ratio increases. So far so good. But now for the disappointing bit: It's manual. You have a lever on your handlebar which varies the offset on the crankpin. I really don't see that that's a significant benefit over, say, a Rohloff. Yes, I appreciate that the transmission is stepless, but as you have to move the lever to change the ratio, you experience a step, and the difference between 14 steps and stepless isn't much. It surely shouldn't be beyond the wit of man to manage feedback from the high-pressure side of the system to the crankpin offset to get fully automatic CVT, which would be a significant win. -- (Simon Brooke) http://www.jasmine.org.uk/~simon/ For office use only. Please do not write or type below this line. |
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"Liquid Drive" bike prototype at auction
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"Liquid Drive" bike prototype at auction
Chalo,
Thanks for the interesting link and comments. Last time I looked many powered vehicles in the world were hydraulically driven at least part-time. May I present the humble "Torque Convertor". Marcus |
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"Liquid Drive" bike prototype at auction
"Simon Brooke" wrote in message
. uk... All wheel drive on an off-road vehicle is generally a good thing, provided that you have limited-slip differentials or the equivalent. If one wheel spinning brings the whole vehicle to a halt there isn't a lot of point. However, a pushbike is much lighter than other off road vehicles. If you do get into a situation where the back wheel just can't grip the usual solution is to put the bike on your shoulder and walk a bit. So AWD isn't that big an issue, although it might be useful on loose, gravelly climbs. Again, I'd be most interested to try an AWD off-road bike, but, once again, I suspect losses in the system would outweigh any advantage. Find a dealer to test out this all-wheel-drive bike: http://www.christini.com/ AWD is a great addition to a car in slippery conditions. The Audi Quattro was banned from European touring car racing because they were deemed to have an unfair advantage. http://www.audiworld.com/news/02/unf.../content.shtml While this is great press for cars, I doubt all wheel drive would make much difference in bicycle racing. -Buck |
#9
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"Liquid Drive" bike prototype at auction
Some people insist we want CVT, but hydraulically driven vehicles have
always had it available and are still rather uncommon. For instance, Hondamatic motorcycles never caught on, though their system seemed to work as intended. I'm unconvinced that it's really as desirable as its proponents say. How did CVT become associated with the HPV community, when human power seems to tolerate a wide range of RPM? Many years ago my father drove a little DAF car which had a CVT system which operated through pairs of opposed cones with a belt linking them; the belt was automatically moved from one end of the cones to the other to vary the ratio. The system was remarkably effective and seemed quite a good thing, but as you say hasn't been widely adopted (I think there were limitations on how much power it could transmit). Similarly, hydraulic CVT gearboxes were around on farm tractors when I was a boy, but the vast majority of tractors continue to have mechanical gearboxes. CVTs like you are describing on the DAF have been used successfully in snowmobiles for about 50 years. 186,000 snowmobiles, all with CVTs, were sold last year so I would say they are quite widespread. The biggest snowmobiles are currently putting out 170+ HP, made possible by advances in belt and clutch technology. The CVT is a simple, effective, and efficient transmission. The biggest hurdle to clear for automotive use has been building a belt that can handle high loads. Snowmobilers think nothing of putting a new belt on every 2000 miles or so, as 2000 miles is a long way by snowmobile. That is not acceptable in a car, I believe all current automotive applications are using some form of steel link belt. Polaris also uses a CVT in most of their ATVs. I'm not sure exactly what they are, as I don't ATV, but I think they are belt driven. They sell a ton of them. In a bike? That is an interesting idea, but I don't think we could pedal fast enough to get good clamping force on the belt. The hydraulic CVT would be fun to try. |
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"Liquid Drive" bike prototype at auction
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