wild and crazy gear teeth
wild and crazy gear teeth
In the attached file, the white parts are standard spur gears. I used 20 tooth, 20DP, 25 degree PA gears, but the gear size does not matter.
Then I extended the lands, as shown in black. These extensions are curved, but with a smaller radius than the tooth faces where they meet. They are not separate parts, just cut that way into the gear blank. I am assuming that this smaller radius would prevent any interference with normal operation of the otherwise standard involute teeth.
These extensions use one-half of the normal clearance, just an arbitrary choice to get started. So there is still some clearance. I am not worried about it if nobody else is. I suppose the gears could be designed with normal clearance, resulting in a slightly increased center distance, which might weaken the teeth a little, but that would be acceptable if it is necessary.
If this design would work, I also suppose that the problem would be cutting the gears. I don't know enough about it. I hope to get some comments and advice from the experts. Wouldn't these extensions increase the tip strength a little?
I am thinking that this design would allow easier meshing of the gears, not by sliding them together axially as in a car transmission, but by a radial approach. That is, in the same plane, with decreasing center distance until they meet and then mesh.
If the gears are not turning as they approach, and have normal lands which are about flat, they will sometimes be prevented from meshing because the lands meet. That stops the approach and the gears can't mesh. It helps if the gears are turning, the slower the better, but still the lands can meet and prevent meshing. Then it is just "grinding the gears" until the lands eventually separate enough to allow meshing.
That can take some time, because friction between the lands tends to hold the gears in the same orientation, and they turn together as though they were in mesh. If there is not much load on the gears, they will just rotate together without meshing until something good happens. If the gears are not turning in this situation, you are stuck. They will never mesh.
Now it will be clear why I would like to have these round land extensions. They should allow the teeth to slide by each other almost every time the gears are to be brought into mesh, instead of jamming way too often with flat lands.
A typical synchro-mesh would not work here, because the meshing direction is radial, not axial. If there is synchro-mesh for the radial direction, I have never seen one. If there is one, it would have to be extremely simple for my application, cheap and of very low volume and weight and high efficiency.
OK, it is a bicycle gearbox. If anyone gets any ideas, I can say with confidence that there is still a long way to go.