ENGINE UNIT


  1. CONSTRUCTION


    1. Balance shafts are used to reduce vibration.

    2. The crankshaft directly drives the No. 1 balance shaft.

    3. In addition, a resin gear is used on the driven side to suppress noise and offer a lightweight design.

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      *1 Balance Shaft Drive Gear *2 No. 2 Balance Shaft
      *3 No. 1 Balance Shaft Housing *4 No. 1 Balance Shaft
      *5 No. 2 Balance Shaft Housing *6 Crankshaft
      *a Resin Gear - -

    4. In an in-line 4-cylinder engine, the crankshaft angle for cylinders No. 1 and No. 4 is exactly the opposite (180°) from the position of cylinders No. 2 and No. 3. Therefore, the inertial force of the pistons and the connecting rods of the former 2 cylinders and of the latter 2 cylinders almost cancels each other out. However, because the position at which the piston reaches its maximum speed is located toward top dead center from the center of the stroke, the upward inertial force is greater than the downward inertial force. This unbalanced secondary inertial force is generated twice for each rotation of the crankshaft.

      Figure 1. Inertial Force Generated by In-line 4 Cylinders

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      *a Inertial Force of Cylinders No. 2 and No. 3 *b

      Combined Inertial Force of All Cylinders

      (Unbalanced Secondary Inertial Force)
      *c Inertial Force of Engine Balancer Assembly *d Force
      *e Inertial Force of Cylinders No. 1 and No. 4 *f -180°
      *g -90° *h 0°
      *i 90° *j 180°
      *k 270° *l Top Dead Center
      *m Point of Max. Speed *n Bottom Dead Center

    5. To cancel the unbalanced secondary inertial force, 2 balance shafts are provided that rotate twice for each rotation of the crankshaft. By doing this they generate an inertial force in the opposite direction. Also, in order to cancel the inertial force generated by the balance shafts themselves, there are actually 2 shafts rotating in opposite directions.

      Figure 2. Inertial Force of Balance Shafts

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      *a 0° *b 90°
      *c 180° *d 270°
      *e Direction of Mass of Balance Shaft *f Inertial Force of Balance Shafts
      *g Crankshaft Angle *h Secondary Inertial Force