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FULL SPUR GEAR MEETS HALF SPUR GEAR - LOCKUP

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MRSSPOCK

Mechanical
Aug 29, 2010
303
Does anyone know of a way to minimise the possibility of gears locking in the following scenario.

Imagine a full ratcheted gear attached to a crankshaft. At a specific distance from the crankshaft axis is another gear axis, but this is only a quadrant of a gear, with a return spring. This is used to rotate the crankshaft, and then it is released and springs back to its parked position.

The crankshaft can be stopped at any point of rotation, so the problem arises when the first tooth on the quadrant coincides directly with a tooth on the ratcheted crank gear.

No rotation can be achieved since one gear tooth is pressing squarely on its counterpart tooth. Is there any way to minimise this likelyhood, other than making both of the teeth sets really pointy, and adding some correction to the root to accommodate the pointy teeth? Thanks
 
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This is used to rotate the crankshaft, and then it is released and springs back to its parked position.

Is this intended to turn the crankshaft backward as it springs back?
 
Ref TheTick

No. The gear on the crank has a ratchet to allow the quadrant to rotate backwards without influencing crank rotation. Its the starting mechanism for a two stroke engine, so once the crank has been turned forward, and the engine has started, (i.e. the crank is spinning), the quadrant is just returning back to its parked postion.
 
Could you try reliefing just the lead tooth edge on the quaudrant slightly
 
What hydro said. Cut the tooth shown in your figure as binding so that it is shorter in height than the others and can't bind on the reverse stroke. This will reduce the stroke angle where the last tooth is still engaged to the crank gear, but that is tradeoff for a non-binding mechanism.
 
I think it is common in car and bike kick and electric starters to use an axial motion of a gear or dog clutch. It is easy to provide some bevel on the engaging features so the full sized tooth etc is engaged before torque is applied.


I'd want a stout detent holding the gear segment securely, and safelyaway from the spinning gear.
 
I reckon taking any material off the tooth peak just makes the matter worse. A pointed tooth has the smallest landing area, so anything less than a point makes it more likely to bind. In reality the quadrant (which turns clockwise by the way, to cause crank rotation), is about twice the size of that which I have illustrated. I just made two gears of equal diameters to make the illustration easier to create. The standard crank gear and quadrant have really pointy teeth, but even then, they still lock peak to peak from time to time, causing teeth to chip, and then the problem just gets worse, once the pointiness has been lost.
 
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