View Full Version : It works in my mind-

08-10-2004, 10:39 PM
I've had this idea popping in and out for a while now for a variable hydraulic motor/pump where the fluid presses directly on the crank journal, and not on a piston, vane, or connecting rod. There's no swash plate. There are no rollers riding in a cam shape, and the stroke is immediately variable at any time, meaning the thing doesn't have to be turning to change the stroke. It looks like it can be made compact, and in a little more complicated form, the forces within it are balanced, so there wouldn't need to be a huge force on the bearings. The stroke is variable thru zero and there's room for some negative stroke, for an easy reverse. Only problems I can see in this early stage, besides not having a full torque in reverse without a separate reversing valve, is that there needs to be about a dozen seals riding on the main shaft, and they need to be of a low friction, low leakage design. Also there will be some flow variation with rotation. This could be the killer right there. The main shaft also has to pass the fluid through it's center axially, in one end out the other. This increases the diameter requirement of the shaft as well as the seals, so friction losses might be significant. A fluid line to carry the control pressure for the stroke has to be in the shaft also. This is an outer rotor motor, where the shaft is stationary, so it would allow fixed hydraulic hose couplings to the non-rotating shaft. I imagine using a simple metal expanding ring type of seals for the pressure, and a polymer type seal after the last outer metal rings, to keep the seepage going to the sump and not all over the place. Valving is automatic with rotation, and is also pressure balanced, so no side or end forces there. All I need to make this idea viable is low friction high pressure low leakage seals internally. In my proposed application, the motor would be able to have full pressure feeding it, while the torque can be reduced to zero, at zero stroke. In this mode, the output shaft can freewheel, or it can be stopped. Dialing in some stroke makes it start to put torque to the output. Or it can be set with some fixed stroke, and operated by the presence or absence of fluid pressure. The only external valving would be a shut-off valve, which would remain fully open when it's operating. And maybe a reversing valve. Nothing internal needs fluid pressure to remain in place, but it does rely on the fluid for lubrication.

Sorry for yet another long post. I just had to toss this idea out there (in case anyone had need of something else to think about) http://bbs.homeshopmachinist.net//smile.gif