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PatEff CVT ( Continuously Variable Transmission )

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#1 manolis

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Posted 23 May 2014 - 03:35


At http://www.pattakon....takonPatBox.htm it is presented the PatEff CVT.

The plot below shows the problem of the current state-of-the-art CVT for lightweight vehicles (the SECVT of Suzuki):


It is the Efficiency of the SECVT vs. the Load; the Over-Clamping is shown by the color bars (the data are from lab tests made in the Eindhoven University for a "Formula Student Racecar" project: at http://www.pattakon....atBox/SECVT.pdf).

Compare the "efficiency fall" with the "over clamping" of the belt.

The same problem exists in the conventional CVT's for scooters, ATV's etc that are based on a centrifugal governor (they call it "variator") for the control of the transmission ratio).

The above plot in stereoscopic form:


The following plot:


shows the thrust force applied to the V-belt and the necessary thrust force for the specific load.

In the "0% LOAD" curve of the above plot the torque-cam action is zero.
In the "25% LOAD", "50% LOAD" and "100% LOAD" curves, the thrust force caused by the "torque-cam" is added to the thrust force provided by the compressed spring of the rear pulley.
These curves are the "lab measured" ones.

A safety factor (like 30%) is necessary to avoid a "belt slipping" at all operational conditions.

The dashed lines S1, S2, S3 and S4 are "theoretical" and give the "necessary" thrust force for 100%, 50%, 25% and 0% load respectively (necessary in the sense that with such a thrust force there is no belt slipping; in the following it will be clarified how these lines result).

The left end of the "100% LOAD" "lab measured" curve is 30% higher (safety factor) than the left end of the S1 line.
The right end of the S1 line is 50% lower than the left end of the S1 line because at the highest gear, at right, the eccentricity of the V-belt in the front pulley is double as compared to the eccentricity of the V-belt in the front pulley at the lowest gear, at left.

In order to pass only 50% of the load, the necessary thrust force is half as compared to the 100% load case. This way the S2 line results from the S1 line. And so on for the S3 and S4 lines.

For a specific load (input torque) and gear ratio the difference between the "lab measured" curve and the "theoretical" one, gives the "over clamping", i.e. the surplus of thrust force that unnecessarily loads the V-belt.
For instance, between 25% and 50% load, at high gear (overdrive), i.e. wherein most of the time a typical CVT operates, the over clamping is between 250% and 600%, which means that the V-belt is compressed 2.5 to 6 times more than what is required in order to pass - without belt slipping - the input torque to the output shaft (according the "Efficiency vs. Load" plot, the efficiency of the CVT at these conditions is around 80%).

The following figure shows at top the radial forces caused on the V-belt by the thrust forces the conical pulleys apply on the V-belt.


It also shows how things now work in the SECVT and in the conventional variator-CVT's

In the following image it is shown the principle of operation of the PatEff CVT.

The ECU controls the axial displacement E (the distance from the casing) of a support (44) wherein the spring (29) of the rear pulley (4) abuts.


In the following images, at left is the SECVT, at right is the PatEff CVT:




Theoretically a good CVT is superior than a good manual gearbox, but in practice (and excluding the “easy of use”) the CVT proves worse.



Manolis Pattakos


#2 manolis

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Posted 26 May 2014 - 16:19


More productive than "generating" energy with "perpetual motion devices", is to minimize the energy loss from the internal combustion engine to the wheel(s).

This thread is about saving a good percentage (say 10%+) of the power passing through the transmission of scooters, ATV's etc lightweight vehicles.

Imagine how many fewer tons of CO2 would be emitted to the atmosphere per day, by just minimizing the over clamping of the V-belt of the scooters and ATV CVT's.

Manolis Pattakos

#3 manolis

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Posted 24 June 2014 - 15:23


A simpler (it needs not electronic control) version of the PatEff for the conventional "variator" CVT's:


was added lately at http://www.pattakon....takonPatBox.htm :


A centrifugal mechanism (like a variator) in the rear pulley counterbalances at medium / high speeds a good part of the force the compressed spring applies to the axially movable conical half of the rear pulley, and reduces this way the unnecessary over clamping of the V-belt.

While the CVT with the "automatic PatEff" operates, without belt slipping, with a belt clamping like the c1-c2-c3 line:


the present CVT's for scooters and lightweight vehicles (ATV's etc) cannot help running on a several times heavier belt clamping (like the s1-s2-s3-s4 line) that reduces the efficiency and the reliability of the transmission.

Manolis Pattakos