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Question about coaster brake design

Posted: Jul 10 2018 10:39pm
by Dogu-ya
Hi guys,

I have a question regarding one component in coaster brakes, the clutch spring.
Also known as retarder spring, clutch tensioner, etc.

I've been reading H.P Townsend's coaster brake patent and in it, he describes his clutch spring, M as providing resistance needed for relative rotation between driver and clutch to provide translational motion needed to get the clutch to engage with hub or brake. And also to provide a bit of resistance such that the brake or hub are not accidentally engaged.

I see that he is tensioning the clutch against the hub.

But in almost all modern coaster brakes and freecoasters, I notice tensioning is between the axle and the clutch. This makes sense but then I wondered about Townsend's design.

If the clutch is tensioned to the hub, then during freewheeling, wouldn't the friction from the hub slowly push the clutch away from the clutch-hub engagement region and into the brake engagement area?

Am I wrong? Maybe the friction will not be able to give enough translational force to activate the braking, but this seems like a design flaw.

Also the wear on the clutch spring will be high because it is in contact with a moving component as opposed to the axle which is stationary.

Are there any modern coaster brakes which use a hub-clutch tension spring? As opposed to clutch-axle.