| 摘要 |
PURPOSE:To largely reduce the weight and lower the vibration level by reducing the number of counterweights fitted to a crank shaft to the minimum and arranging the center of gravity at the optimum position. CONSTITUTION:No counterweight is provided on the 3rd, 4th, 6th, 7th arms 33, 34, 36, 37. Counterweigths 61, 69 with the same shape, same weight, same section modulus are provided on the 1st and 9th arms 31, 39 so that the balance is kept by only both counterweights. The 2nd, 5th, 8th arms 32, 35, 38 are arranged line-symmetrically against the arm 35. Accordingly, counterweights 62, 68 with the same weight, same shape, same section modulus are provided on the 2nd and 8th arms 32, 38 so that the balance is kept by only these counterweights together with the 5th arm 35 and its counterweight 65. Furthermore, the counterweight 62 is arranged to be located above the horizontal level of the axis and the counterweight 68 below it respectively when the first pin 41 is at the top position.
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