All about Inline 4-cylinder engines
As commonly known, big straight-four engine requires twin-balancer shafts rotating at twice the frequency as the crankshaft to reduce vibration.
This is very different to 3-cylinder engines, which need a single balancer shaft running at the same frequency as crankshaft.
An inline 4 cylinder engine fires once every 720° / 4 = 180° crank angle, hence 2 of the pistons are in exactly the same position and move in the same direction, while the remaining 2 pistons are also a pair.
To avoid the end-to-end vibration as experienced in 3-cylinder engines, car makers always arrange the pistons symmetrical. In other words, piston 1 and 4 are a pair, while piston 2 and 3 form another pair.
Therefore movement of piston 1 will be balanced by the symmetric piston 4. The same goes for piston 2 and 3.
That’s just the end-to-end vibration with respect to the engine center but when it comes to upward/downward vibration the movement of piston 1 is counter balanced by piston 2, while piston 3 counters piston 4.
One of the most free vibration engine is the boxer engine which has the pair of pistons always in opposite positions, directions and speeds, thus all the forces can be balanced.
In contrast, in a straight-four engine, rotate the crankshaft a certain angle, the piston near the top end has a displacement larger than that of another piston near the bottom.
As vertical force is the product of displacement and mass of piston and divided by the time taken for such displacement, therefore complete cancellation is impossible.
Author: AL
Source: Autolatest & AZ
An inline 4 cylinder engine fires once every 720° / 4 = 180° crank angle, hence 2 of the pistons are in exactly the same position and move in the same direction, while the remaining 2 pistons are also a pair.
To avoid the end-to-end vibration as experienced in 3-cylinder engines, car makers always arrange the pistons symmetrical. In other words, piston 1 and 4 are a pair, while piston 2 and 3 form another pair.
Therefore movement of piston 1 will be balanced by the symmetric piston 4. The same goes for piston 2 and 3.
That’s just the end-to-end vibration with respect to the engine center but when it comes to upward/downward vibration the movement of piston 1 is counter balanced by piston 2, while piston 3 counters piston 4.
One of the most free vibration engine is the boxer engine which has the pair of pistons always in opposite positions, directions and speeds, thus all the forces can be balanced.
In contrast, in a straight-four engine, rotate the crankshaft a certain angle, the piston near the top end has a displacement larger than that of another piston near the bottom.
As vertical force is the product of displacement and mass of piston and divided by the time taken for such displacement, therefore complete cancellation is impossible.
Author: AL
Source: Autolatest & AZ
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Published date: 13.01.2009 | 05:01 EET
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