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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / March 2006Continuously Variable Transmission
Could anyone tell me if it is possible to buy a small CVT off the shelf, or the components (preferably in the UK). Thanks. > Could anyone tell me if it is possible to buy a small CVT off the > shelf, or the components (preferably in the UK). > > Thanks. DAF used them in some of their cars. I suspect they are still available as rebuilds, and possibly as dealer items. Wrecking yards might be a source if you think the DAF unit would work for you. > Could anyone tell me if it is possible to buy a small CVT off the > shelf, or the components (preferably in the UK). > > Thanks. In addition to DAF, Subaru sold at least one car with a CVT, and of course Honda is currently selling one model with that transmission. So you might look in the wrecking yard for a used one or contact either company for a new one. The extent of electronic control will probably limit the alternative applications that transmission could be used in. It's an interesting concept that has been around for a long time, but one that never caught on. The sensation one encounters while driving a car with CVT is different enough that Honda apparently had to engineer in shift steps because consumers were used to the thunk of gear changes and the sound of the engine revving up. I have to think the sensation of driving a CVT must be like a Buick Dynaflow of many years ago. > > Could anyone tell me if it is possible to buy a small CVT off the > > shelf, or the components (preferably in the UK). [quoted text clipped - 13 lines] > and the sound of the engine revving up. I have to think the sensation > of driving a CVT must be like a Buick Dynaflow of many years ago. I've driven one of the Subaru Justys with the ECVT and it's quite interesting. Remarkable performance with it even from the tiny 50-something HP three cylinder engine they used with it. The main reason they haven't caught on is that it's too difficult to make one that will stand up to a decent amount of HP. Invent a reasonable weight CVT that can handle 600 HP reliably and you'll be a multi-billionare licensing it to the heavy trucking world where every .1 MPG counts. Pete C. > > > Could anyone tell me if it is possible to buy a small CVT off the > > > shelf, or the components (preferably in the UK). [quoted text clipped - 24 lines] > you'll be a multi-billionare licensing it to the heavy trucking world > where every .1 MPG counts. Yes, I understand that the CVT in it's current design can only handle a limited amount of power. I vaguely remember reading that one version of the CVT tended wear out belts. Was that the Subaru? I would think a hydrostatic type of transmission would give a similar result. If so those are used in construction equipment. > > > > Could anyone tell me if it is possible to buy a small CVT off the > > > > shelf, or the components (preferably in the UK). [quoted text clipped - 31 lines] > I would think a hydrostatic type of transmission would give a similar > result. If so those are used in construction equipment. I don't think so, the Subaru implementation had a very unique belt made of stacked steel plates with several steel cables threaded through to hold the plates in belt form. It also operated in a compression mode rather than the tension mode of conventional rubber belts. The hydrostatic transmissions are very inefficient in transmitting power with a lot of the power being converted to heat. They are common in construction equipment because they are easy to control at low speed and provide a completely flexible connection i.e. hose between the power source and the driven item. Pete C. >> > > Could anyone tell me if it is possible to buy a small CVT off the >> > > shelf, or the components (preferably in the UK). [quoted text clipped - 31 lines] > I would think a hydrostatic type of transmission would give a similar > result. If so those are used in construction equipment. This is not a hydrostatic transmission. I'll post a few links to the control centre and technical stuff and an example of what it is fitted to. http://www.fendt.com/index.php?id=dc903bbef155511b8c0d0dea001edc93ccb67ffe80df84 4e81&l=2 http://www.fendt.com/index.php?id=f46cabe198f7f645678e3f998b893ffc6e9598d13027d9 cd5c&l=2 http://www.fendt.com/index.php?id=1fb55cee2bde3f9534a31009e8d7f94db7ca990c0a71d6 a734&l=2 Click on this last one for technical specifications including power, torque and fuel consumption figures for the MAN engines which are, amazingly, less than 7litres swept volume. http://www.fendt.com/index.php?id=414cf66556288fdb157e1dbbcf713cec6292638839af81 be28&l=2 Huw > Invent a reasonable weight CVT that can handle 600 HP reliably A planetary gearbox (like the Prius has) can handle much more. They are also used in mills, power stations, airplanes etc. But for a full cvt the Prius also needs 2 electro engines. > 1 MPG counts. Unfortunately the planetary gearbox has more friction than standard gears. But also does the "Standard-CVT" with belts oder chains like Audi or countless small motorcycles. A CVT does not always save fuel. Cheers Thomas > > Invent a reasonable weight CVT that can handle 600 HP reliably > [quoted text clipped - 12 lines] > > Thomas I've not seen any planetary gearbox that was a CVT. Gears imply fixed ratios with steps between. Pete C. > > > Invent a reasonable weight CVT that can handle 600 HP reliably > > > > A planetary gearbox (like the Prius has) can handle much more. > > They are also used in mills, power stations, airplanes etc. > > But for a full cvt the Prius also needs 2 electro engines. [ snip ] > I've not seen any planetary gearbox that was a CVT. Gears imply fixed > ratios with steps between. That's correct. But if you have two sources of torque, you can use a differential gear to produce a rotation that is the difference of their RPMs. A planetary gear can be used as a differential. http://www.ecrostech.com/prius/original/PriusFrames.htm This is what Mr. Schäfer is referring to. Pete C. wrote: > "Thomas Schäfer" wrote: > > [quoted text clipped - 5 lines] > > They are also used in mills, power stations, airplanes etc. > > But for a full cvt the Prius also needs 2 electro engines. [ snip ] > I've not seen any planetary gearbox that was a CVT. Gears imply fixed > ratios with steps between. That's correct. But if you have two sources of torque, you can use a differential gear to produce a rotation that is the difference of their RPMs. A planetary gear can be used as a differential. http://www.ecrostech.com/prius/original/PriusFrames.htm This is what Mr. Schäfer is referring to. ***************************************************************** Have a look at the Fendt power-splitting schematic to which I have posted a link. In effect the CVT is actioned by the hydraulic pump and motor varying the speed of a the ring gear on an epicyclic [planetary] set. In this system the ring can be turned forward, backwards or indeed held stationary. Similar systems are used by ZF and Steyer but they have a narrower angle hydraulic set which means that they need four ratios in a conventional gear set, changed by conventional constant mesh powershift clutch packs, to acheive a broad speed band. These other two also need clutch packs to acheive a foward/reverse power shuttle. Huw >>Invent a reasonable weight CVT that can handle 600 HP reliably > [quoted text clipped - 12 lines] > > Thomas But is a planetary transmission continuously variable? I thought it was a two speed (for each planetary gear set). > But is a planetary transmission continuously variable? I thought it was > a two speed (for each planetary gear set). In the special configuration of the Prius it is a true CVT. http://www.wind.sannet.ne.jp/m_matsu/prius/ThsSimu/index_i18n.html Not applicable for every single-engined car. But still a genius invention. Thomas what is going on in that animation?! > what is going on in that animation?! - Select English/US (or the simulation will try to show japanese signs) - Check the Driving mode-Checkbox on the right - Select D-Range (like standard automatic) in the right Combobox (B[rake]-Range is special for Prius with more recuperation downhill) - Use the Accel and/or Brake-throttle with your mouse Thomas > Invent a reasonable weight CVT that can handle 600 HP reliably and > you'll be a multi-billionare licensing it to the heavy trucking world > where every .1 MPG counts. What limitation is responsible for that? Is it the use of a frictional belt? Are you familiar with the Anderson CVT? It uses sprockets and teeth, so the belt cannot slip. That should take a high horse power. Take a look: http://www.andersoncvt.com/ > > Invent a reasonable weight CVT that can handle 600 HP reliably and > > you'll be a multi-billionare licensing it to the heavy trucking world > > where every .1 MPG counts. > > What limitation is responsible for that? Is it the use of a frictional > belt? That seems to have been the main limitation. > Are you familiar with the Anderson CVT? It uses sprockets and teeth, so > the belt cannot slip. That should take a high horse power. > > Take a look: > > http://www.andersoncvt.com/ That's quite interesting, I haven't seen it before. I'm not sure how long it's been around, but as we all know things take quite a while to migrate to mass market applications. Certainly the picture on that site shows a pretty basic prototype and it would take some refinement to produce a vehicle ready unit. Perhaps it will eventually show up. Pete C. "Pete C." <aux3.DOH.4@snet.net> wrote > > Invent a reasonable weight CVT that can handle 600 HP reliably and > you'll be a multi-billionare licensing it to the heavy trucking world > where every .1 MPG counts. HP is not the problem. Torque is. To handle the torque the transmission must be extremely heavy duty which usually means heavy and expensive. However if you look at agricultural tractors which have similar engines though mainly limited to under 350hp, then you will find several manufacturers market power-splitting CVT's with success. Mind you, the requirement of the agricultural tractor is for a far more sophisticated and integrated system than is needed for road trucks but they have a narrower operating speed band, typically from 0 to 50kph, than is needed for a truck. With today's rising power engines with massive torque rise of up to 50% there is hardly a need for CVT for trucks I wouldn't have thought. Huw > and the sound of the engine revving up. I have to think the sensation > of driving a CVT must be like a Buick Dynaflow of many years ago. Indeed, some people report that a CVT during acceleration feels like a boat. In a boat, you increase the throttle and the revs go up and stay high as you accelerate. I'd love to have a CVT that has a manual stick: some kind of lever that slides from lowest to highest, plus,a way to select neutral and reverse. And of course a clutch pedal for starts and stopping. It would be interesting, finding different combinations of gear ratio and RPMS. Engine spinning a little too slow and working too hard going up a hill? Just nudge the gear ratio down a little bit while increasing throttle to maintain speed. Perhaps the Audi Multitronic would fulfil most of your wishes? http://www.audi.co.uk/experience/techdesign/multitronic.jsp > > and the sound of the engine revving up. I have to think the sensation > > of driving a CVT must be like a Buick Dynaflow of many years ago. [quoted text clipped - 13 lines] > up a hill? Just nudge the gear ratio down a little bit while increasing > throttle to maintain speed. I'm no mechanical engineer, so I'm going to ask a very basic question. Is the CVT is effective at transmitting power as a geared transmission. My mental image of a belt or chain turning two pulleys that are changing size regularly makes me think a fair amount of energy is lost in that process. > My mental image of a belt or chain turning two pulleys that are > changing size regularly makes me think a fair amount of energy is lost > in that process. Correct. To avoid slipping, the belt or chain must be firmly pressed on/between the pulleys. Imagine a bicycle chain pressed onto the toothed wheels (although in this case unneccessary). That must produce a noticeable amount of friction. In small motorcycles strong springs enforce a constant pressure, designed for maximum torque -> constantly maximum friction. In modern cars the electronic monitors torque and power needed, electric/hydraulic actuators apply the variable pressure. Cheers Thomas > > My mental image of a belt or chain turning two pulleys that are > > changing size regularly makes me think a fair amount of energy is lost [quoted text clipped - 4 lines] > Imagine a bicycle chain pressed onto the toothed wheels > (although in this case unneccessary). A chain that is so tight that it exerts pressure on the sprocket wheels could cause considerable friction --- in the hubs of those sprocket wheels. But also, because of the way the chain engages with the teeth, excessive tension could cause some friction at the points of engagement and disengagement where the chain is tangential to the sprocket. And of course, the bicycle chain is composed of links which bend and straighten and are lubricated. More chain tension means more friction in these links. A belt, such as a rubber fan belt, generates heat from being deformed as it bends around the pulleys and straightens. A CV transmission's V-belt minimizes the friction deformation of the belt by its composition of many thin steel bands that hold together trapezoidal pieces with enough gaps between them to allow for bending without compressing any material. You'd think that if the V-belt does not slip with respect to the pulleys, there wouldn't be frictional losses. But the details of the reality are different. :) Check out the Ph. D. paper of one Sam Akehurst, from the University of Bath: http://staff.bath.ac.uk/enssa/thesis.pdf "An Investigation into The Loss Mechanisms Associated with a Pushing Metal V-Belt Continuously Variable Transmission" > > and the sound of the engine revving up. I have to think the sensation > > of driving a CVT must be like a Buick Dynaflow of many years ago. [quoted text clipped - 13 lines] > up a hill? Just nudge the gear ratio down a little bit while increasing > throttle to maintain speed. A CVT does all the above with no user input. Reverse is selected through gearing. Starting and stopping is part of the CVT. As the RPMs of the engine drop the trans automatically selects higher ratios. No reason to have a mechanical lever since you cannot just switch the ratios UP/down in rapid steps without the engine bogging down. If you want to see widespread CVT use just look at every snowmobile built since about 1968, they all use a belt CVT. "Steve W." <Dugdug56@what.com> wrote > > A CVT does all the above with no user input. Reverse is selected > through gearing. Starting and stopping is part of the CVT. As the RPMs [quoted text clipped - 4 lines] > If you want to see widespread CVT use just look at every snowmobile > built since about 1968, they all use a belt CVT. A growing number of quad bikes as well, including the majority of those now sold in N America, or so I am told. Engine braking is a problem, the lack of engine braking that is. Some marques now use an electric motor actuated device to overcome this problem. Having said that, I am now left to wonder whether cars with belt CVT's have a similar problem. Huw > If you want to see widespread CVT use just look at every snowmobile > built since about 1968, they all use a belt CVT. Now that you mention it, several years ago I bought my son a Dingo (something like a go-kart) which had a variable belt type transmission. It was a bit problematic, but then when you give a young boy a hard use toy, you expect some problems. > Could anyone tell me if it is possible to buy a small CVT off the > shelf, or the components (preferably in the UK). > > Thanks. Sure. A lot of Cushman three-wheeled vehicles had (have) this. You know the little vehicles that meter-maids and zoo employees drive. They are small, simple and off the shelf. Two variable pulleys and a belt. Quite a few other manufacturers have this same design, especially golf cart manufacturers. Oh, you wanted one for a car. That's a little different....... no this is to use for a weight lifting system, so it can be any CVT... I just found a mini moto CVT which is quite cheap. Not too sure on the ratio between the diameter of the two pulleys though (what the max/min diameter of each pulley is). Also, what mechanism controls the distance between the two plates to vary the diameter of the pulleys? And how is this mechanism controlled? > Also, what mechanism controls the distance between the two plates to > vary the diameter of the pulleys? And how is this mechanism controlled? Engine RPM controls it. There is a cam system on the driven pulley that tries to hold the sheave together. The drive pulley is controlled by various methods, most use weights, either flyweights or roller weights, as the engine RPM rises these weights move the sheaves on the drive pulley tighter while springs try to keep them apart. By adjusting the weights, ramps and springs you can fine tune the clutch unit to whatever characteristics you need. http://www.gates.com/brochure.cfm?brochure=1033&location_id=542 > Also, what mechanism controls the distance between the two plates to > vary the diameter of the pulleys? And how is this mechanism controlled? On simpler machines like scooters it is a mechanical control. Below is an interesting and detailed discussion of how one works and how it may be modified. http://groups.google.com/group/alt.scooter/browse_frm/thread/9c0357deaef72e7e/72 0e63d3ced5ff6a?lnk=st&q=scooter+cvt&rnum=1&hl=en#720e63d3ced5ff6a do you think it would be possible to modify this mechanical control so that someone could vary the diameter of the pulley by hand (as I'm thinking of using one on a weight lifting system). Could I literally buy something like this and set it up easily; http://cgi.ebay.co.uk/MINI-DIRTBIKE-DIRT-BIKE-GEARBOX-CVT_W0QQitemZ7221714384QQc ategoryZ75221QQrdZ1QQcmdZViewItem > do you think it would be possible to modify this mechanical control so > that someone could vary the diameter of the pulley by hand (as I'm [quoted text clipped - 3 lines] > > http://cgi.ebay.co.uk/MINI-DIRTBIKE-DIRT-BIKE-GEARBOX-CVT_W0QQitemZ7221714384QQc ategoryZ75221QQrdZ1QQcmdZViewItem I think that it could be done with extensive modification. Remember that transmission is designed to have an engine spining at 5,000+ rpm on the input shaft and the output shaft is designed to run a scooter at 30mph. The rpm's you will be developing will be totally different. Also remember that because you will need to exert squeezing pressure on both pulleys to keep the belt in one position and fully tensioned. Consequently you will have some friction to overcome. I suspect that it will not be a very efficient way of lifting. I would look for a simple two speed gearbox and attach a drum to one end and a hand crank to the other. > Remember that transmission is designed to have an engine > spining at 5,000+ rpm on the input shaft and the output shaft > is designed to run a scooter at 30mph. The scooter vario itself has a ratio of about 0.75 to 2.4. A second fixed gear (near rear wheel) reduces the rpm by another ca. 1:10. Thomas > > Remember that transmission is designed to have an engine > > spining at 5,000+ rpm on the input shaft and the output shaft [quoted text clipped - 5 lines] > > Thomas That's quite a range of ratios and a very long fixed step-down gear. So that I understand it correctly, does the vario transmission input shaft vary from .75 to 2.4 revolutions for every revolution of the output shaft? >> The scooter vario itself has a ratio of about 0.75 to 2.4. >> A second fixed gear (near rear wheel) reduces the rpm >> by another ca. 1:10. >That's quite a range of ratios and a very long fixed step-down gear. >So that I understand it correctly, does the vario transmission input >shaft vary from .75 to 2.4 revolutions for every revolution of the >output shaft? Yes. Typical rpm varies from 2000 (idle) to 7000 (open throttle). Let's assume a wheel with 1m circumference. Minimum speed would be 2000rev/min -> 2000/60 rev/s / 2.4 (vario) / 10 (fixed) = 1.4 wheel-turns/s -> 5kph Maximum speed 7000/60/0.75/10 = 15.6 wheel-turns/s -> 56kph. Thomas > >> The scooter vario itself has a ratio of about 0.75 to 2.4. > >> A second fixed gear (near rear wheel) reduces the rpm [quoted text clipped - 13 lines] > > Thomas OK, that is useful information. I suspect that the range of ratios would suit the application described by the original poster. I would think that there would be extensive modifications required to allow a vario transmission to be used as a multi-speed pulley however. > do you think it would be possible to modify this mechanical control so > that someone could vary the diameter of the pulley by hand (as I'm > thinking of using one on a WEIGHT LIFTING system). Ah. So that's what you really want it for... a weight-lifting machine where you don't remove/replace individual plates, or move a pin from one hole to another in a vertical shaft, changing the number of plates lifted off the ground. > Could I literally buy something like this and set it up easily I doubt it. The shifting of the belt style CVT relies on the pullies constantly rotating along with the belt, while the side-pressure of the moveable half of the pulley makes the belt "climb" up out of the groove, allowing the pulley halves to get closer. You seem to want a more "static" system, where you change the leverage "ratio" while everything is sitting still, and then apply the force. I have also seen extremely simple CVT:s on small lawn mowers, that even give you a reverse for free. You have a driven flat round plate and a wheel that runs on the plate at a 90 degree angle. That wheel is axially adjustable so that it can sit at the center of the rotating plate, at which time the output shaft is not moving. The farther away from the center of the plate you move the wheel, the faster will the output shaft rotate. Moving the wheel to the other side of of the input shaft center will make the output shaft rotate in the other direction. Snowmobiles have CVT. Almost every major manufactur sells or has sold a vehicle with a CVT Here are some examples - Ford - 500/Freestyle, GM - Saturn Vue (and Ion?), Nissan - Murano, Honda - Civic Hybrid, Volvo (old DAF designs). Ed > Could anyone tell me if it is possible to buy a small CVT off the > shelf, or the components (preferably in the UK). > > Thanks. > Almost every major manufactur sells or has sold a vehicle with a CVT Here > are some examples - Ford - 500/Freestyle, GM - Saturn Vue (and Ion?), [quoted text clipped - 6 lines] > > > > Thanks. I know but I need a much smaller CVT than a car CVT. > I know but I need a much smaller CVT than a car CVT. Look at small motorcycles! Those CVTs are also sold seperately or in parts (tuning, ...). Thomas This is the gokart type drive, called a torque convertor. http://www.gokartsupply.com/comet.htm |
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