CVT- Continuously Variable Transmission

How to convert a CVT into a IVT

The problem:

CVTs only provide positive ratios.
Therefore, a reverse gear and a clutch (or a torque converter) are necessary.

IVTs (Infinitely Variable Transmissions) provide a full range of ratio from reverse, through stationary, and from extremely low speeds, up to high overdrive.
The engine is permanently connected to wheels. Clutch and reverse gear are not required.

A "solution":

A planetary gear set (epicyclic) can be used to convert a CVT intoa IVT by power split.

The planetary gear set "subtracts some RPMs" from the CVT output. Thus, the overall ratio spread can be freely customized.

The planetary gear set formula:

WP × (DR + DS) = WR × DR - WS × DS

(W: angular velocities; D: primitive diameters)

Note: in this page, the ratios are calculated as: input speed/output speed.Therefore, ratios are greater than one when speed reduces. And negative ratiosare used when the rotation sense is inverted.

What will be the IVT output speed?

(Win = engine speed ; Rcvt = CVT ratio)

What will be the IVT overall ratio?

( ratios are input speed/output speed )

_
You can get any ratio spread

Problem:
You want to build a IVT to vary the ratio continuously, from reverse speed of -km/h per 1000rpm, to the overdrive speed of km/h per 1000rpm.
You already have a CVT which varies the ratio from a lower Rcvt1= to an overdrive Rcvt2=.
And you also have a planetary gear set with a sun diameter of DS=mm and a ring diameter of DR=mm.
The vehicle has a differential ratio is and the tyre diameter is mm.
You can decide what will be the ratio between the engine and the sun gear: R1=. By default the CVT input ratio is R2=.

Solution:
Now you can the required values for the fixed gear ratios for R3= and R4=.
This "CVT + planetary gear set" will result in a "IVT" transmission.
This "IVT" will provide an overall ratio spread from Rivt1=(negative for reverse) to Rivt2=(overdrive).

().( Note: ratios are input speed/output speed )

Six combinations of a CVT and a planetary gear set:_

Some existing examples of transmissions with Power-split:

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Combination a) :
Luk: http://luktest1.ina.com/content/media/_companydb/products/library/downloads/luk_k7_chap07.pdf pg77 ;
Torotrak; http://torotrak.com/regime_change.html ;
Epilogics: http://cvt.com.sapo.pt/ratcheting/ratcheting.htm ;
CVPST: http://www.cke-tech.com/cvpst.htm ;
-

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Combination b) :
Prius: http://home.earthlink.net/~graham1/MyToyotaPrius/Understanding/PowerTrain.htm
http://auto.howstuffworks.com/hybrid-car9.htm
http://www.familycar.com/Classroom/AlternativePowerSystems.htm ;
Claas: http://www.sae.org/ohmag/toptech/01.htm .
-

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Combination c) :
...

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Combination d) :
Motorcycle CVT: http://nr.stic.gov.tw/ejournal/ProceedingA/v23n6/716-727.pdf .
-

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Combination e) :
...

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Combination f) :
...

web links about CVTs with Power Split

( Remark: this page is not intended forexperts because it is just a personal opinion. )

[created: 01 Jul 2003, updated: 19 Set 2008 ] [ designed by vb.web.pt ]

How to convert a CVT into a IVT

_
You can get any ratio spread

Six combinations of a CVT and a planetary gear set:_

web links about CVTs with Power Split

hydrostatic CVTs

electric CVTs

Prius

ratcheting CVTs

toroidal CVTs

v-belt CVTs

How to convert a CVT into a IVT

_ You can get any ratio spread

Six combinations of a CVT and a planetary gear set:_

web links about CVTs with Power Split

hydrostatic CVTs

electric CVTs

Prius

ratcheting CVTs

toroidal CVTs

v-belt CVTs

_
You can get any ratio spread