Piston for internal combustion engine, and internal combustion engine using the piston

A piston for an internal combustion engine, comprising:

• a top surface having a valve recess for avoiding interference with a valve and a tumble flow maintaining depression;
• and
• an outer peripheral part having a piston pin hole through which a piston pin is to be inserted,
• wherein a region where the valve recess is formed and a region where the depression is formed are adjacent to each other, and an edge line defined between the region where the valve recess is formed and the region where the depression is formed includes a changing edge line along which a dimension of the depression in a width direction perpendicular to an axis of the piston pin hole becomes smaller from a center in a direction along the axis of the piston pin hole toward a piston outer periphery in the direction along the axis of the piston pin hole, a constant edge line along which the dimension of the depression in the width direction is maintained to be generally constant toward the piston outer periphery in the direction along the axis of the piston pin hole, and an inflection part connecting the changing edge line and the constant edge line.

A piston for an internal combustion engine, comprising a top surface having a tumble flow maintaining depression,

• wherein the depression includes a center region formed at a center in a longitudinal direction of the depression and a side region continuously formed on both outer sides of the center region in the longitudinal direction,
• the center region has a reduction part in which a dimension of the center region in a width direction perpendicular to the longitudinal direction is gradually reduced toward a piston outer periphery in the longitudinal direction,
• the side region has a constant part in which a dimension of the side region in the width direction is substantially uniform in the longitudinal direction, and
• wherein the top surface further includes a valve recess adjacent to the depression, and an edge line defined between the valve recess and the depression includes a changing edge line along which a dimension of the depression in the width direction becomes smaller from a center in the longitudinal direction toward the piston outer periphery in the longitudinal direction, a constant edge line along which the dimension of the depression in the width direction is maintained to be generally constant toward the piston outer periphery in the longitudinal direction, and an inflection part connecting the changing edge line and the constant edge line.