| 摘要 |
PROBLEM TO BE SOLVED: To provide a piston structure for an engine capable of achieving both of suppression of erosion caused by knocking and improvement of emission performance while suppressing the production cost.SOLUTION: In the piston structure for an engine E having a crown part 30 forming a top part of a piston 1 and a top land part 23 continued to an outer periphery of the crown part 30, a diameter-contracted step part contracted inward in a radial direction is provided at least in a part of the vicinity of a boundary between the crown part 30 and the top land part 23 in a circumferential direction in order to upward reflect a pressure wave caused by self ignition. The diameter-contracted step part includes a first diameter-contracted step part 29 on the top land part 23 side, and a second diameter-contracted step part 35 positioned on an upper side of the first diameter-contracted step part 29 and having a diameter smaller than that of the first diameter-contracted step part 29. Accordingly, intrusion of the pressure wave into a clearance between the top land part 23 and a wall surface of a cylinder 4 can be prevented, and direct impact to the top land part 23 by the amplified pressure wave can be prevented. |
