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From: pwv@fluke.UUCP (Pat Vilbrandt)
Newsgroups: net.auto.tech
Subject: Re: trivia question
Message-ID: <1015@vax2.fluke.UUCP>
Date: Mon, 18-Nov-85 12:38:48 EST
Article-I.D.: vax2.1015
Posted: Mon Nov 18 12:38:48 1985
Date-Received: Tue, 19-Nov-85 03:52:11 EST
References: <3173@hplabsb.UUCP>
Distribution: na
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 24

> Why do cars (i.e., motor vehicles) have clutches?  Hint, it's NOT so you
> can shift gears.

Outside of the obvious answer that the engine would quit when you stop,
the real reason is that an internal combustion engine produces torque that 
is relatively proprotional to engine rpm (up to a point).  At low rpm (idle) 
the engine is producing very little torque.  You need a "clutch" (the torque 
converter in an automatic transmission) to allow the rpm to increase to 
a point to where the engine is producing enough torque to move the car.

An external combustion engine (ie. steam engine) can produce full torque at
zero rpm, so you don't see clutches on old steam locomotives.  Electric
motors (depending on drive electronics) can also be made to put out enough
torque at zero rpm that a clutch isn't needed to start up an electric car.

-- 

   Pat Vilbrandt
   John Fluke Mfg. Co., Inc.
   Everett, Washington USA
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