Continuously Variable Transmission Idea

[rajava007]

I made a CVT (Continuously Variable Transmission) that uses two differentials to first split power between two gear ratios based on torque (1:1 and 2:1), and then recombine the separate rotations into a single output via a second differential. Yes, I did test this out, and it works. However, My Question Is: Why hasn't this cvt(the one that I just made) been implemented before? Yes, a reverse gear isn't implemented, and the completely automatic nature of it doesn't allow you to control it if needed, but why haven't vehicles like bikes used this before?
DISCLAIMER: The model below isn't fully proper; a 1:2 ratio isn't possible between the differentials, and is only possible by multiplying the output of the transmission by two.
Below is a power diagram:

And now this is the diagram of the CVT I made without edits ontop:

 

[Baluncore]

Welcome to PF.

Can you please name the input, control and output shafts.

 

[rajava007]

The carrier of the gray open differential is the input, and the carrier of the black open differential is the output

 

[berkeman]

I'm seeing straight-cut gears and differentials, but I'm not seeing anything that would imply continuous variability of the input/output gear ratio. Can you say more about what provides the continuously variable property? Thanks.

 

[rajava007]

So the idea is that the first differential will blend the power between both gear ratio paths. One path is a 1:1 gear ratio, and the other is a 2:1 gear ratio. By default, the open differential wants to send power with the 1:1 gear ratio. However, depending on the amount of torque required, the differential will send part, if not all of the power, to the 2:1 gear ratio. Finally, after the power has been split and either increased speed or torque, they are added back together into one rotation to use. This "blending" of gear ratios is what allows for that continuously variable property.
Some examples that can help:
First example(high load):
A motor rotates at 1 rpm, and the load is high - the differential will send all power through the 2:1 gear ratio(A); no power is given to the 1:1 gear ratio(B). Path A outputs 0.5 rpm(1/2 *1), and path B outputs 0(1/1 *0). The differential adds these outputs into one rotation(0.5+0); the final output is 0.5 prm.

Second example(no load):
A motor rotates at 1 rpm, and the load is low- the differential will send all power through the 1:1 gear ratio(B); no power is given to the 2:1 gear ratio(A). Path B outputs 1 rpm(1/1 *1), and path B outputs 0(1/2 *0). The differential adds these outputs into one rotation(1+0); the final output is 1 rpm.

Third example(medium load - half&half):
A motor rotates at 1 rpm, and the load is medium- the differential will send power through both path A and path B; each path is given equal rotation(0.5 rpm each). Path A outputs 0.5 rpm(1/1 *0.5), and path B outputs 0.25(1/2 *0.5). The differential adds these outputs into one rotation(0.5+0.25); the final output is 0.75 rpm.

 

[Halc]

From what I can see, the input and output are always identical. It seems to be an interesting alternative to a through-shaft. There is no variability at all to the thing. A video showing otherwise would put me in my place.

Both large gears turn at identical rates, slower than the smaller ones turning faster. The average is the same on both sides. By symmetry, 1:1 in to out.

 

[rajava007]

I did a little more digging and found my exact concept in this article: LINK
The article also shares a video in step 1 by Autstron: LINK
*Step 12 shares that the CVT might require friction in some places to work*

 

[jack action]

However, My Question Is: Why hasn't this cvt(the one that I just made) been implemented before? Yes, a reverse gear isn't implemented, and the completely automatic nature of it doesn't allow you to control it if needed, but why haven't vehicles like bikes used this before?

Although I haven't analyzed the design deeply, the link you provided in your last post might give some explanation in step 2:

Note that this transmission does not convert torque. But is designed to provide a constant torque though an infinite array of speeds. Any extra torque acquired at low gear is dissipated through friction. This friction is necessary to achieve the higher gears for more speed. Because of the friction at lower gears, this transmission is most efficient at its highest gear ratio.

Having higher torque at low speed is the desired effect of a transmission. This one seems to only lower the rpm and waste the extra torque that could be provided through friction, which is not only unhelpful but also very inefficient.

 

[Baluncore]

I think there are possibilities for such a configuration, but that it is too complex for an untrained brain to model immediately as a thought experiment. I get a feeling that complexity here leads easily to circularity, then to delusion, in the same way that a PMM is conceived.

There are different velocities and torques, that resolve to power. Those must follow the energy conservation laws, and the mechanical laws of gears. Since the input differential will share torque equally, as a good differential should, then that torque will be scaled by the following gears to be delivered to the output differential as two unequal torques, which defies the differential's equal sharing of torque assumption. Energy must therefore be circulating, down one side and up the other. I do not yet understand the occasion or magnitude of that circulating energy, but I suspect it may tend towards the maximum energy available. Power factor may be so poor, that no real work is being done.

Now is the time to build a numerical model, or to find an electrical analog.

 

[Averagesupernova]

It looks like each differential carrier wil rotate at identical speeds no matter what. The interesting thing is that if one changes the speed of the left or right set of black/yellow gear pairs by braking or applying power in either direction it makes no difference to the speed of the differential carriers. If the gray carrier is the input and the black carrier is the output then that's all it is. Applying a brake to one black/yellow gear pair will simply speed the other pair up as long as it is allowed to rotate freely. Nothing really new here. It's a type of power combiner. Real CVT transmissions have some sort of variable speed source such as a variable shieve pulley set or a hydrostatic drive. They often use a differential or planetary type combiner but that is secondary.

 

[rajava007]

Thank you so much! I have been stuck around this point for a very long time! So in summary, all this does is vary the speed?

 

[Averagesupernova]

Thank you so much! I have been stuck around this point for a very long time! So in summary, all this does is vary the speed?

It's a type of power combiner. Real CVT transmissions have some sort of variable speed source such as a variable shieve pulley set or a hydrostatic drive. They often use a differential or planetary type combiner but that is secondary.