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Date: Sat, 18 Jan 2003 18:20:37 +0000 (UTC) From: amesnopsamrak.demon.co.uk (Andrew Stephenson) Subject: Re: Seatbelt Locking Problem
In article <b0basm$n5pnt$1nopsam52899.news.dfncis.de> grunffnopsam.com "Grunff" writes: > Paul wrote: > > > [his seat belts lock when parked on a slope -- SAAB baffled] > > I'm amazed that they're baffled by it. The belts, like all > retractable belts, use an inertia reel mechanism, so that when > the belt is pulled quickly (as it might be in a collision), it > locks up. This is done with a finely balanced spring setup. If > the spring is weak, then simply moving the belt relative to the > direction of gravity would also cause a lockup. > > [...] Possibly the design has changed; but years (decades) ago someone told me it works this way: imagine two circular metal plates set to rotate around the same vertical axis and almost touching each other. The lower plate is dished, the upper flat. In the space between them are trapped some ball bearings. When the belt is unwound or wound, one of these plates rotates if the balls can move freely. Otherwise, if the axis around which the plates turn seems to be non-vertical, the balls roll towards one edge, causing the plates to bind together. This happens in two cases: when the car is (1) accelerating (as in a crash) or (2) on a slope. Of course a combination of 1 and 2 can lead to odd effects; but let's keep it simple. -- Andrew Stephenson
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