A Study on the Balancing of the Three-Cylinder Engine with Balance Shaft

For the three-cylinder engine whose crankshaft has a phase of 120 degrees, the total sum of unbalanced inertia forces occurring in each cylinder will be counterbalanced among the three cylinders. However, parts of inertia forces generated at the No.1 and No.3 cylinders will cause a primary moment about the No.2 cylinder. In order to eliminate this out-of-balance moment, a single balance shaft has been attached to the cylinder block so that engine durability and ride comfort may be further improved. Accordingly, the forced vibration analysis of the three-cylinder engine must be implemented to meet the required targets at an early design stage. In this paper, a method to reduce noise and vibration in the 800cc, three-cylinder LPG engine is suggested using the multibody dynamics simulation. The static and dynamic balances of the three-cylinder engine are investigated analytically. A multibody dynamic model of the three-cylinder engine is developed where the inertia properties of the connecting rod, crankshaft, and balance shaft are extracted from their FE-models. The combustion pressures within the No.1 cylinder in three operating conditions (1500rpm-full load, 4000rpm-full load, and 7000rpm-no load) are measured from the actual tests to excite the engine. The vibration velocities at the three engine mounts with and without the balance shaft are evaluated through the real-time vibration analysis. Obviously, it is shown that the vibrations of the three-cylinder engine with the balance shaft are reduced to an acceptable level.