Continuously 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.

Reply to
will_usher
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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.

Reply to
<HLS

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.

Reply to
John S.

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.

Reply to
Pete C.

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.

Reply to
John S.

"Pete C." wrote

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.

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

Reply to
Thomas Schäfer

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.

Reply to
Kaz Kylheku

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:

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Reply to
Kaz Kylheku

Ich like das Deutsche-English! :)

Reply to
Kaz Kylheku

Perhaps the Audi Multitronic would fulfil most of your wishes?

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Reply to
Thomas Tornblom

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.

Reply to
John S.

"Pete C." wrote >

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

Reply to
Huw

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.

Reply to
Pete C.

I've not seen any planetary gearbox that was a CVT. Gears imply fixed ratios with steps between.

Pete C.

Reply to
Pete C.

That seems to have been the main limitation.

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.

Reply to
Pete C.

[ snip ]

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.

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This is what Mr. Sch=E4fer is referring to.

Reply to
Kaz Kylheku

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.

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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.
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Huw

Reply to
Huw

[ snip ]

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.

formatting link
This is what Mr. Schäfer is referring to.

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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

Reply to
Huw

sensation

increasing

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.

Reply to
Steve W.

"Steve W." wrote >

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

Reply to
Huw

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