Browse Publications Technical Papers 2012-32-0106
2012-10-23

360° vs. 270° vs. 180°: The Difference of Balancing a 2 Cylinder Inline Engine: Design, Simulation, Comparative Measurements 2012-32-0106

Beside the automotive industry, where 2-cylinder inline engines are catching attention again, twin-cylinder configurations are quite usual in the small engine world. From stationary engines and range-extender use to small motorcycles up to big cruisers and K-Cars this engine architecture is used in many types of applications. Because of very good overall packaging, performance characteristics and not least the possibility of parts-commonality with 4-cylinder engines nearly every motorcycle manufacturer provides an inline twin in its model range.
Especially for motorcycle applications where generally the engine is a rigid member of the frame and vibrations can be transferred directly to the rider an appropriate balancing system is required. A 360° parallel twin engine does generate both: free 1st order mass forces and free 2nd order mass forces. 1st order mass forces can be compensated by a balancer shaft which is the most common, the implementation of a reciprocating balancer weight would eliminate both but has certain drawbacks like complexity, friction and additional excitations.
A 180° crank-pin offset does produce 1st order mass-moments and free 2nd order mass forces. In addition to that an uneven firing order gives drawbacks in orifice noise and excitations in other orders.
The option of a 90° crank-pin offset in an inline 2-cylinder engine features a design, without free 2nd order mass forces on the one hand but small mass moments and an uneven firing distribution on the other hand.
This paper investigates the difference on the NVH behavior between 360°, 270° and 180° inline 2-cylinder engines by the means of design and engine mount simulations and shows the comparative results of structural vibrations, airborne noise and orifice noise of these 2 versions having the same basic design and engine specifications measured on an acoustic chassis dynamometer.

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