Cylinder cylinder intersection: Design of a starter crank.

• To: mathgroup at smc.vnet.net
• Subject: [mg104594] Cylinder cylinder intersection: Design of a starter crank.
• From: Matthias Bode <lvsaba at hotmail.com>
• Date: Wed, 4 Nov 2009 01:39:15 -0500 (EST)

Dear Groupmembers:

I have made futile attempts at designing a "simple" starter crank to start an internal combustion engine.

The starter crank has a short transversal rod that pierces the crank perpendicularly and engages in the starter ratchet mounted on the engine's cranks haft. The crank's longitudinal axis intersects the rod's longitudinal axis.

The crank's lever measures 320 mm in length, the transversal rod measures 40 mm in length which is equal to ratchet's outer diameter.

The diameter of the crank must not exceed 18 mm (min. 16 mm), the diameter of the transversal rod must not exceed 9 mm (min. 6 mm). - (A thinner crank disengages more easily from the ratchet when the engine starts.)

I estimate the maximum force to be exerted on the crank's handle (just before the engine's crankshaft will start to rotate) to be ~ 700 N.

I studied  http://mathworld.wolfram.com/SteinmetzSolid.html  to find out how much material of the crank would be left given the bore for the transversal rod.

I got completely stuck at equation (12) - which I originally intended to solve using MATHEMATICA.

Given the tensile strengths of the crank and the rod (some high tensile str ength steels) the task is to determine the diameter of the transversal rod in such a way that crank and rod will withstand about the same forces. - Obviously a very thin rod will yield to the shear strain whilst too thick a rod will leave too little material of the crank, and alter the lever ratio rod to crank to the detriment of the latter.

(I already made such a starter crank using mild steel: The rod (diameter 6 mm) was shorn off AND the transversal hole in the crank (diameter 16 mm) be came more or less elliptic. - Torsion and bend of the crank itself are minimal and pose no problem.)

Solutions or references to (engineering) litterature will be highly appreciated.

Best regards,

MATTHIAS BODE
COCHABAMBA/BOLIVIA
S 17.35775=B0, W 066.14577=B0

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