# Power-split planetary gear set power calculation

## Main Question or Discussion Point

I think we have a problem with this rule. This is my understanding of the existing rule. Am I close?

The rule for calculating the power distribution on a power split planetary gear system is based on the equal force rule.
To calculate the power on the sun and ring of a planet set with input on the carrier we first determine the power in on the carrier. From the torque on the carrier we determine the force on the carrier based on its radius.
Now we apply the equal force rule.
Because of the planet gear’s independence it maintains its equilibrium between the carrier and the sun and ring. The rule is that the forces on the sun and ring from the carrier are always equal to one half each of the carrier force.
The torques on the sun and ring are proportional to their radius. The power distribution between the ring and sun is rpm dependent.

## Answers and Replies

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Baluncore
Science Advisor
2019 Award
I think we have a problem with this rule.
Where is the equal force rule defined? Under what conditions does it hold?

Thanks Baluncore,
I don't know where it originally came from. It is just what I have been told and what the engineers use when calculating torque through a power split planet set.
I will try to find an official source.
The second part of your question is very key. In my analysis it only holds true when either the ring or the sun is fixed. I think the engineering people have just interpreted this to mean always. We have just started to really look at the planet set as a power split device. I have a 6 page pdf of my analysis with what I think the right rule should be, if you would like me to attach.
John