Primary Balance of Multi-Cylinder In-Lane Engine:
In multi-cylinder in-line arrangement all of the cylinder centre lines are parallel and in the similar plane that is on the similar side of the crank shaft centre line. This seems to be the most common configuration in use.
For the reciprocating parts weighing R & crank rotating at ω rad/s, the condition for balanced state shall be defined by two statements. These statements are following:
(i) Algebraic sum of all of forces must be zero.
(ii) Algebraic sum of all of the moments about any point in the plane of the forces must be zero.
These statements are expressed as
∑ (R/g) ω2 r cos θ = 0 -----------(1)
∑ (R/g) ω2 ra cos θ = 0 ---------------(2)
Where a is the distance from reference plane to plane of rotation of a crank. Already we have seen in previous unit that a mass revolving at crank radius r shall generate a force component along the line of stroke in Equation (1) and (2). r refer for the radius of crank and θ is for the angle made by crank along with cylinder line of centre. If the above equations are not satisfied then the right hand side shall not be zero but have some of magnitude giving unbalanced force & couple on the engine frame. Following instance will described how we may find if an engine is balanced.