Increasing Torque with Gerotor Design: Lengthening, Diameter, and Series

[Dano61]

How do you increase torque in gerotor design other than increasing flow. Will lengthening it increase torque? Will increasing diameter increase torque? What about running 2 or 3 in series?

 

[berkeman]

Welcome to the PF.

How do you increase torque in gerotor design other than increasing flow. Will lengthening it increase torque? Will increasing diameter increase torque? What about running 2 or 3 in series?

It looks like a Gerotor is a positive displacement pump: https://en.wikipedia.org/wiki/Gerotor

What do you mean by "increasing torque"? What flow rate do you want to achieve, and what is the working fluid (water? Oil?)? Thanks.

 

[jrmichler]

I assume you are referring to a gerotor hydraulic motor. Anything that increases volume per revolution (displacement) will increase torque. Increasing pressure will increase torque. Connecting three motors in series will increase torque, but could shear the shaft of the third motor. Increasing flow will increase speed, but not torque.

Note that all gerotor motors have a maximum rated pressure and speed. If you exceed either, bad things will happen. Leakage may increase, it may wear faster, bearings may fail, seals may leak or blow out, or it may fail catastrophically.

 

[Dano61]

jrmichler, thank you for the reply. I guess what I am trying to determine is: does length affect torque, does increasing diameter affect torque. I am currently working with a gerotor that puts out a certain torque at 150L/m. How can I maintain the same flow and increase torque?

 

[jrmichler]

The torque is proportional to the pressure differential across the motor. The pressure differential is the inlet pressure minus the back pressure at the outlet. If the flow stays the same, anything that increases torque will decrease speed, increase pressure, or both. If you want more torque at the same flow, you have three choices:
1) Add a gear reducer to slow it down.
2) A larger motor (more displacement per revolution) will behave the same as adding a gear reducer - more torque at a lower speed.
3) Increase the pressure differential by increasing the inlet pressure, decreasing the back pressure, or both.

 

[berkeman]

How can I maintain the same flow and increase torque?

Gears?

Given a set power source (your flow rate at whatever pressure/head), if you want more torque, you may need to gear down the output. Can you say what the application is?

 

[Tom.G]

See also this recent thread. https://www.physicsforums.com/threads/is-there-any-way-to-vary-the-torque-of-a-gerotor.967155/

 

[Dano61]

So length will not affect torque in a Gerotor?

 

[Baluncore]

How do you increase torque in gerotor design other than increasing flow.

You might be referring to a gerotor pump, or a gerotor motor.
I assume it is a motor. Correct me if I am wrong.

You need to specify whether the torque is now limited by movement of the physical load, or by the available hydraulic pressure. What load is being driven? And how is the speed being regulated?

The rate of fluid flow sets the speed of a gerotor motor. Fluid flow rate does not set the torque, unless turning the load at increased speed requires higher torque, and a greater fluid pressure is available.

So length will not affect torque in a Gerotor?

If you double the length of a gerotor motor, you will double the rotor area and so double the torque for the same fluid pressure. To maintain the same speed, you will then need double the volume of fluid flowing.
That is equivalent to joining two motor shafts, while supplying the same pressure fluid to the two motors in parallel, an arrangement that will require twice the volume of fluid flow.

The torque available from a gerotor motor is proportional to the fluid pressure across that motor.

What about running 2 or 3 in series?

If the same fluid flows in series through several gerotor motors, each motor will develop less torque, since the motors will share the total pressure available.

Connecting motors in series will not increase torque. Series connection of several motors is expensive and pointless, since it will be equivalent to one motor only.