The crankshaft position, speed and acceleration differ from a straight
sin/cos function by an extra term involving the connecting rod length.
This extra term accounts for the assymetry between the speed on the top
half and bottom halves of the stroke. An inline 4 cylinder engine is
inherently unbalanced due to this assymetry. A longer connecting rod
makes the top and bottom halves more nearly symmetric, giving better
balance. Some modern inline 4 cylinder engines use an extra balance
shaft to compensate. I've got the formula coded in a spreadsheet if
anyone is interested.
Larry Young
Bill Babcock wrote:
>I seem to remember that speed is a sine curve
>and acceleration is a cosine, but I really don't remember this stuff, but
>I'll pull out my ancient copy of Ricardo tonight and refresh my memory.
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