×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

#### Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
To Your Posts
• Keyword Search
• One-Click Access To Your
Favorite Forums
• Automated Signatures
On Your Posts
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

# Planetary Gear Set - Hybrid drivetrain

 Forum Search FAQs Links MVPs

## Planetary Gear Set - Hybrid drivetrain

(OP)
Hey all,

I'm new to this forum, but hoping there is some kind person out there with experience analyzing hybrid drivetrains that might be able to help this rookie out!

I'm trying to get my head around a kinetic energy recovery system I came across in a paper the other day;
(this paper -->) http://openaccess.city.ac.uk/4057/
Basically, a planetary gear set is used to split power between the flywheel (sun), wheels (carrier) and a brake (applies braking torque to the ring).

Now here's the problem: Lets say the flywheel is initially stationary and the speed into the carrier is omc. Then the ring speed, omr is given by the kinetic relationship between the gears;
omr = (omc-B*oms)/A where A = rr/(2*rc) and B = rs/(2*rc). rr is the radius of the ring gear etc.
I apply a torque Tr to the ring gear, which changes the ring speed (omr). This adjusts the torques acting on the flywheel and wheels. But how will the flywheel respond?

I have the power balance;
Tc*omc = Tr*omr + Ts*oms

and then there is there are the dynamic equations for the two flywheels (modelling the car wheels as a flywheel);
Ts = Is*oms_dot (first derivative of oms)
Tc = Ic*omc_dot (first derivative of omc)

If we assume the inertia of the gears are small compared to the flywheel and car, then we can balance forces on the planet gears to give;
Tc/rc = Tr/rr + Ts/rs (I'm a little suspicious about this one)
That's five equations and five unknowns (2 torques and 3 speeds), so it should be solvable. I've tried modelling this with a step-wise approach in Matlab but my output doesn't make much sense. Can anybody see where I'm going wrong?

Thanks in advance!!
Lily

Replies continue below

### RE: Planetary Gear Set - Hybrid drivetrain

Your suspicions are justified. The relationship between the 3 torques is very simple. If any one is known the other 2 are defined by the EGB ratios. See equations 4 and 5 on page 5 of your linked paper.

je suis charlie

### RE: Planetary Gear Set - Hybrid drivetrain

(OP)
Thanks gruntguru for your reply!

I saw the torque equations in the paper, but I thougt they only applied when the ring or sun are stationary.

I put those equations in my Matlab model and they seem to give reasonable results, for as long as omr (ring speed) is positive. Seems almost too good to be true haha

Thanks again for your help!

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

### Reply To This Thread

#### Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!

Already a member? Close this window and log in.