Controlling planetary ratio by braking sun gear

[ChrisEng1]

I have an application where a planetary gearbox is being driven on the ring gear and the speed is reduced to the carrier with the sun gear being held stopped by a torque arm with the torque being monitored by the system. If torque is too high the system is shutdown to protect the equipment. The maximum torque allowed is about 2100 ft lbs on the sun gear shaft. It also includes a "shear pin" that breaks if that torque is exceeded allowing the sun gear to freely rotate at the same speed as the ring gear.

I want to take the sun gear shaft and control its speed so that i can adjust the gear ratio between the ring gear and the carrier.

If my ring gear is spinning at 1000 rpm, i want to be able to control the speed of the sun gear from between 0 rpm and 1000 rpm by applying a braking force which would be a maximum of 2100 ft lbs at the stopped speed.

Ive looked at different ways to do this and not sure if its something that is already done a certain way. Some things ive considered are:
- A friction disc brake, which i think would work but im not sure how long and reliable it would be.
- Some type of fluid coupling like a torque converter seems like it could work but im not sure it could be made infinitely adjustable between something like 0 and 1000 RPM.
- A motor connected to the shaft and used to generate braking with a VFD, seems like this could work as well but probably not at the lower speeds.

Anyone have any knowledge as to whether this is already commonly done in some application? Or what would be a suitable way to achieve this?

Thanks, Chris

 

[SwinnyGG]

Two methods I'd want to investigate:

1) Eddy current brake. The torque level and amount of power you're talking about are not prohibitive. This may be expensive, depending on the exact configuration and range of control you need.

2) A friction brake - but wet, with an active cooling system. Effectively a wet clutch. This is an arrangement that can be made to last a very long time, if there is enough cooling in the system.

 

[mfgenggear]

OP
please provide what is the driver, EG electric motor, gas motor ect.
please provide the object driven EG prop drive shaft, mulcher.
what is the starting torque and rpm
and the output shaft torque and rpm.

the reason to have a shear neck is to prevent damage to the motor and gear box.
i am thinking on your issue.

can you make a hand sketch.

 

[GregLocock]

You seem to be talking about a hundred hp, on dynos we either used a water brake or an eddy current brake, or these days a motor/generator. The water brake is comparatively cheap and simple and adjustable, and has no wearing parts. However it won't do 0 rpm and I suspect you'd need to gear it up to get the rotor moving at a sensible speed. You are more or less reinventing the Prius' driveline.

Dynamometer absorber selection - Perek

Eddy brake, powder brake, motor, water brake or hydraulic pump? How to select the best absorber for your dyno.

perek.it

is quite interesting

 

[ChrisEng1]

This is for a centrifuge where the drive is an electric motor (500 HP), driving the bowl of the centrifuge and conveyor of the centrifuge at different speeds through the planetary gearbox. A lot of newer designs drive each independently so that the differential between bowl and conveyor can be controlled by VFD, or hydraulic speed control, or other means, but this is an existing piece of equipment with the fixed speed gear box, and having variability would be beneficial to the process.

As I had been looking in to it it just seemed like controlling the speed of that sun gear would be an "easy" way to control that differential by changing the ratio.

RPM is about 900 RPM at the bowl, the differential is only about 25 RPM so the screen operates at about 875 RPM. The gear box has a torque limit of 1 million inch pounds on the differential output side which would be about 2100 ft lbs on the sun gear side where torque is monitored. The shear pin is between the sun gear shaft and the torque arm such that if 2100 ft pounds is exceeded the pin shears and the sun gear is allowed to rotate freely.

The actual amount of torque applied to the sun gear would be variable depending on how much load the machine is under. I was also wondering if something like a hydraulic pump/motor could be attached to the output shaft to act as a brake with valving to control the restriction on the hydraulic fluid flow.

A wet friction break sounds like it might be the most simple, ill do some reading about eddy current breaks. This is just an idea and may not be feasible but if we found a solution that worked it might be something that could be retrofit to other machines in the same application.

I don't think I would need control all the way down to zero RPM, if I could keep it at zero with a mechanical brake and then control it between something like 300 and 750 RPM I think that would give me the range id need.

I attached a poorly drawn sketch.

Thanks for the replies so far.

 

[mfgenggear]

An automatic transmission will not stall a motor. Yet will allow the output shaft to stop.
By means of a clutch, and Torque converter.
They sell gear boxes with brakes.