Balance and Smoothness
An inline six engine is in perfect primary and secondary mechanical balance, without the use of a balance shaft. The engine is in primary couple balance because the front and rear trio of cylinders are mirror images, and the pistons move in pairs. That is, piston #1 mirrors #6, #2 mirrors #5, and #3 mirrors #4, largely eliminating the polar rocking motion that would otherwise result. Secondary imbalance is avoided because the crankshaft has six crank throws arranged in three planes offset at 120°. The result is that the secondary forces that are caused by differences from purely sinusoidal motion sum to zero.
An inline four cylinder or V6 engine without a balance shaft will experience secondary dynamic imbalance, resulting in engine vibration. As a general rule, the forces arising from any dynamic imbalance increase as the square of the engine speed — for example, if the speed doubles, vibration will increase by a factor of four. In contrast, inline six engines have no primary or secondary imbalances, and with carefully designed crankshaft vibration dampers to absorb torsional vibration, will run more smoothly at the same crankshaft speed (rpm). This characteristic has made the straight-six popular in some European sports-luxury cars, where smooth high-speed performance is very desirable. As engine reciprocating forces increase with the cube of piston bore, straight-six is a preferred configuration for large truck engines.
Read more about this topic: Straight-six Engine
Famous quotes containing the words balance and, balance and/or smoothness:
“The perfect aphorism would achieve classical balance and then immediately upset it.”
—Mason Cooley (b. 1927)
“There is a delicate balance of putting yourself last and not being a doormat and thinking of yourself first and not coming off as selfish, arrogant, or bossy. We spend the majority of our lives attempting to perfect this balance. When we are successful, we have many close, healthy relationships. When we are unsuccessful, we suffer the natural consequences of damaged and sometimes broken relationships. Children are just beginning their journey on this important life lesson.”
—Cindy L. Teachey. “Building Lifelong Relationships—School Age Programs at Work,” Child Care Exchange (January 1994)
“Then, welcome each rebuff
That turns earth’s smoothness rough,
Each sting that bids nor sit nor stand but go!”
—Robert Browning (1812–1889)