CVT idea

[Benzine]

Had an idea today after reading about CVTs on this forum, thought I'd bounce it around. Probably cloud cuckoo land stuff I read someone saying that the CVT units commonly used are designed for gokarts etc. Things with small rear wheels and higher revving engines.

As small diesel engines don't rev comparatively high, could you do something like in my crude diagram below:



A= engine crank sprocket
B= CVT driver unit (smaller sprocket than on the crank, mounted on a jackshaft behind the CVT unit)
Red line= chain
Other big black circle= CVT driven unit

A sprocket on the CVT driver unit slightly smaller than on the crank so that the CVT is effectively geared up so it can spin faster. Would the clutch then engage at a lower RPM? (i.e closer to idle than before) Basically a quick idea to try and mimic the higher revving engines that these CVTs were designed for. Benefits/pitfalls?

[coachgeo]

have proposed the same idea........ but for different reason. My proposed reason was so you could turn the bulbus drive pully inside out. The bulb would be protruding under the seat instead of sticking outboard. For example Heiko's "CVT"ed Triumph is wider than same bike with Ultima. CVT is a bit lighter though.

Will be interesting the replies on your proposal.

[AMB2012]

You can get kits of different springs and weights that will increase or decrease the engagement RPM of the CVT.

Google isn't playing nice atm otherwise I'd post the link, but you can get a kit to get the engagement down to 1400 rpm, which sounded about right for a Yan-clone.

AMB

[coachgeo]

You can get kits of different springs and weights that will increase or decrease the engagement RPM of the CVT.

Google isn't playing nice atm otherwise I'd post the link, but you can get a kit to get the engagement down to 1400 rpm, which sounded about right for a Yan-clone.

AMB

Think his point is beyond just the take off rpm. His idea affects the final ratio as well. The "cart" CVT's are manufactured and sold to operate in an RPM range outside of the range our diesels work. The added pully and chain/belt is introducted to bring it back into that higher range it was desinged for. My question though is can a cart pully handle the torque etc. of a diesel when Cart cvt is used this way.

Now it would be good to note though that the Cart systems are a matched Drive (engine side) and Driven (jack shafted to chain sprocket) in house under assumption it is going on a cart. You can buy them seperate and get a different Driven pully that creates a different span of infinite ratios between start and final ratio

[AMB2012]

Fair point - I'm hoping to do it "all in one" (engine - cvt in - cvt out - rear sprocket) without an intermediary, gearing etc permitting, if only to make the build simpler.

Flipping the CVT over so the "bulge" (I'm sure there is a technical term) is on the inside is an interesting idea - I guess it depends on your frame size (a longer-narrower engine and transmission vs. a shorter-wider version).

AMB

[pietenpol2002]

Just to clarify, "flipping" of either part requires that both drive and driven units are "flipped". As only one half of the sheave on either unit moves, they must move simultaneously in opposite directions to one another relative to the centerline of the belt to maintain correct alignment of the belt. But, it can certainly be done and by using the proposed 2 jackshafts, the CVT can be positioned behind the engine thus reducing the overall width.
If sufficient vertical space exists behind the engine, one could mount the cvt vertically with the primary drive angled from the crank to the drive shaft mounted topside. The shortest rendition of the Comet 40 requires something like 7 1/4 inches center-to-center between the shafts which translates to something like 15 inches overall. Thus, if using the little Yanclone singles, the vertically mounted cvt package would be shorter than the height of engine, which is in excess of 19 inches.
The obvious down side is the cumulative losses with the additional chains/belts, bearings, etc with what is already marginal power.
All with the usual disclaimer - easier said than done.

[coachgeo]

Just to clarify, "flipping" of either part requires that both drive and driven units are "flipped". ....

twas my assumption. Interesting thought is to have mounted onto the jackshaft of the driven pully an alternator that also acts as a reverse motor. In neutral (lower rpm) for a short period with the belt sliping..... drive the driven pully with the alternator/motor to reverse your heavy bike..... or in my case..... your not so heavy bike but the rider skinny whose own weight is way less than 1/2 the weight of the bike. (I way 150lb) Disel tiger is close to what 400lb?