| 摘要 |
A cylinder block structure of a light alloy for use in a multicylinder internal combustion engine includes a cylinder-defining portion having a plurality of cylinder bores with a water jacket defined in surrounding relation to the cylinder bores, and a crankcase-defining portion integrally formed with the cylinder-defining portion and having a plurality of integral journal walls spaced in the direction in which the cylinder bores are arranged. Concavities are defined in opposite sides of the cylinder- and crankcase-defining portions between the adjacent cylinder bores, the concavities lying between the water jacket and journal walls. A plurality of reinforcing rib systems project from the opposite sides of the cylinder block and each rib system surrounds one of the concavities. The concavities reduce the amount of molten metal to be poured in casting the cylinder block structure, for thereby preventing casting defects such as cavities from being produced in the cylinder block. The reinforcing rib systems serve to provide the required degree of stiffness to the cylinder block. Since the reinforcing rib systems terminate short of the deck of the cylinder block, no vibration is transmitted through the reinforcing rib systems to the deck, whereby the deck is prevented from being subject to deflecting vibration.
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