Hydraulic speed governor

[Brian Rupnow]

In 50 years of designing machines and mechanical devices of all kinds, I kind of thought that I had "seen it all" in terms of "neat mechanical devices". Last week while researching a machine that is already on the market, I seen something which just blew me away. This is an absolutely brilliant solution to controlling the speed of a rotating shaft. I would have never thought of this in a hundred years. The machine in question runs down an inclined plane, under the force of gravity---but---the speed at which it rolls must be controlled, so that it doesn't "run away" under the force of gravity. The axle which the wheels are attached to, is actually shaped like a crankshaft. The blue cylinder has the rod end mounted on the "throw" of the axle/crankshaft. The clevis at the rear of the cylinder is attached to the framework which supports the rotating axle/crankshaft, in a manner which allows it to pivot. The cylinder is filled with hydraulic oil on both sides of the piston. As the wheels and axle rotate, the axle/crankshaft drives the piston rod in and out of the cylinder body, forcing the oil back and forth from one end of the cylinder to the other. The needle valve fitted to the line which runs to both ends of the cylinder can be adjusted to control how freely the hydraulic fluid can pass from one end of the cylinder to the other,thus making it possible to control the speed at which the axle can rotate.  Granted, I don't think it would be a totally constant "drag effect" on the axle, as there would be a bit of a "dead spot" as the piston went over "dead center" at both ends of the stroke, but overall, during the greatest linear part of the stroke in both directions the speed would definitely be controlled. There are probably 25 other ways of achieving the same result to "control speed", but this is the first time I have ever seen this. It is so uniquely "neat" that I just had to show it.---Brian

[ths]

The dash pot effect. That's a good one, thanks Brian. Hugh.

[b.lindsey]

That's an elegant solution to the problem Brian. What kind of machine did you see it on...just curious?

Bill

[Brian Rupnow]

It is on a device used for moving paralyzed patients from the upper floors of a home or hospital to the ground floor and outside in case of a fire or some other disaster, via stairways, not elevators. The 'speed limiter' is a device to keep it from running away out of control while descending the stairs..

[b.lindsey]

Thanks!  Yeah...that would seem to present a critical need for not letting speed get out of control for sure!!

Bill

[cobweb81]

That is the same device used on horizontal band saws and power hack saws to regulate down feed pressure. Simple to make your own for an old saw that maybe did not have one. Made one for an old power hack saw with an air cylinder and vegetable oil.

[JMcRae]

Interesting Brian! Eaton is using an interesting system for garbage trucks not quit the same but they are using a hydraulic pump to pump oil into an accumulator to help slow the truck drown, then the hi pressure oil is released from the accumulator to help get the truck moving again.

[Hugh Currin]

Brian:

Is there air left in the system? It seems the volume would change as the piston moves unless the piston rod is double ended. Some air in the system, or an accumulator, would make up this difference. The pressure would change but still create a drag though the needle valve.

I've thought of using something similar for motion. There air in the system would hamper motion so, I think, a double ended cylinder is needed.

Yep, I have one of these on my bandsaw but didn't think about its operation.

Thanks.

Hugh

[BillTodd]

A few years ago the makers of the Batman film wanted the 'Bat Car' to stop in a particularly fast and controlled way (in the correct place for the camera).  My brother's job was to buid the rig to do this. His solution was remarkably similar to the above.

He made a long cylinder with a  number of 'exhausts' each with a valve feeding back to behind the piston . The piston is pulled out  by a cable attached to the car . The valves can be adjusted to control the stop .  It works so well it now part of the Chris Corbould's special effect dept's standard rig.

[Brian Rupnow]

Brian:

Is there air left in the system? It seems the volume would change as the piston moves unless the piston rod is double ended. Some air in the system, or an accumulator, would make up this difference. The pressure would change but still create a drag though the needle valve.

I've thought of using something similar for motion. There air in the system would hamper motion so, I think, a double ended cylinder is needed.

Yep, I have one of these on my bandsaw but didn't think about its operation.

Thanks.



Hugh

Hugh--I don't think it would work with air in the system, just the same as your automobile brakes won't work if there is any air in the system. Air is compressible, while fluid is not. For consistent operation, you wouldn't want any air in the system.

[Dave Otto]

I purchased a used Roll-In band saw a number of years ago and the stock hydraulic cylinder to control the speed of the cut, leaked oil and was not made to be repaired (it was crimped together). The throttle was also built right into the end of the cylinder and it operated backwards. To top it off the nice folks at Roll-In wanted $600.00 for a replacement!

So I decided to make a new one; some DOM tubing a section of hard chromed shafting and some machine work we had a working cylinder. I even moved the throttle to a more convent location up on the table. It all worked great except for one small problem; there wasn't enough room in the upper part of the cylinder for the oil from the lower end because of the space the rod took up .

So a small tank was fabricated to give a little extra space; problem solved.

It's not hooked to a crankshaft; but the idea kind of goes along with the the banter.

Dave