Structure of combustion chamber for direct injection engine

A structure of a combustion chamber for a direct-injection engine, the structure comprising:

• a piston inserted into a cylinder and having a cavity formed by recessing a top surface of the piston;
• a surface of a cylinder head forming a ceiling portion of the combustion chamber and having an intake-side inclined surface and an exhaust-side inclined surface, the ceiling portion being configured to define, along with the cylinder and the piston, a pent-roof-shaped combustion chamber, the intake-side inclined surface being provided with openings of two intake ports arranged side by side along an engine's output shaft, the exhaust-side inclined surface being provided with an opening of an exhaust port;
• and
• a fuel injection valve arranged on a ridge line of a pent roof at which the intake-side and exhaust-side inclined surfaces intersect with each other, the pent roof forming the ceiling portion of the cylinder head, the fuel injection valve being shifted, with respect to a bore center of the cylinder, toward one end of the engine's output shaft, the fuel injection valve having an injection axis that extends along an axis of the cylinder, the fuel injection valve being configured to inject fuel through an injection tip thereof into the cavity facing the injection tip, wherein
• the top surface of the piston has inclined surfaces on an intake side and an exhaust side, and is raised by the inclined surfaces to correspond to the intake-side and exhaust-side inclined surfaces of the ceiling portion,
• the cavity is shifted toward the one end of the engine's output shaft to face the injection axis of the fuel injection valve, the cavity being formed by hollowing out portions of the inclined surfaces, and
• in a vertical cross section taken along a plane passing through a particular location in an intake other-side region and a location of the fuel injection valve, a distance from the injection tip of the fuel injection valve to a wall surface of the cavity at the particular location is longer than a distance from the injection tip to the wall surface of the cavity at a diametrically opposed location from the particular location with respect to the fuel injection valve, where the interior of the combustion chamber is divided, around the location of the fuel injection valve, into the four regions of:
• (1) an intake one-side region located on the intake side with respect to the ridge line of the pent roof and closer to the one end of the engine's output shaft;
• (2) an intake other-side region located on the intake side and closer to the other end of the engine's output shaft;
• (3) an exhaust one-side region located on the exhaust side with respect to the ridge line of the pent roof and closer to the one end of the engine's output shaft;
• and
• (4) an exhaust other-side region located on the exhaust side and closer to the other end of the engine's output shaft.