Fuel injection apparatus

1. A fuel injection apparatus used for an engine that includes:

a piston;

a cylinder that allows insertion of the piston;

an ignition plug disposed in the vicinity of a center axis of the cylinder, and

an intake port and an exhaust port disposed at positions where the ignition plug is interposed therebetween, the fuel injection apparatus comprising:

an injector that is disposed at a position offset from the ignition plug toward the intake port and injects a fuel spray toward a crown surface of the piston, and

an injection controller that causes the injector to perform injection in accordance with an amount of fuel injection and timing of fuel injection that are preset in accordance with an operating state of the engine,

wherein the piston includes:

a first recess formed by recessing a central portion of the crown surface; and

a second recess that is formed by recessing part of the first recess on an injector side further than the first recess,

wherein the injector injects 50% or more of fuel that is to be injected for the last fuel injection toward the second recess during a compression stroke of the engine, and injects part of the fuel to be injected for the last fuel injection toward an area of the first recess other than the second recess,

wherein the second recess has;

a bottom surface located lower with respect to other portions of the crown surface,

stepped portions formed along an outer peripheral edge of the bottom surface of the second recess continuously over the entire circumference and surrounding the bottom surface, and

a pair of lateral sides each formed straightly along an outer peripheral edge of the second recess so as to extend substantially in parallel to the straight line that connects the injector and the ignition plug when seen in a direction of an axial line of a cylinder bore of the cylinder,

wherein the stepped portions comprise:

a central-side step that constitutes an end of the recess on a bore central side and has a plan view having an arcuate shape protruding on an exhaust side when seen in the direction of the axial line of the cylinder bore,

an outer-diameter-side step that constitutes part of an end of the recess on a bore outer diameter side and has an arcuate shape protruding on an intake side in plan view when seen in the direction of the axial line of the cylinder bore, and

straight guide steps that constitute a pair of lateral portions provided in parallel to each other so as to linearly couple both ends of the central-side steps and both ends of the outer-diameter-side step, each of the straight guide steps being formed along each of the pair of lateral sides, and

wherein the injector comprises a multiple hole injector that forms multiple beams including fuel sprays and travelling in a radial fashion, and the injector injects a half or more of the multiple beams toward the second recess and injects one or more of the multiple beams toward the area of the first recess other than the second recess at the last fuel injection that is performed during the compression stroke of the engine, and

wherein the injector is configured to inject a half or more of the multiple beams toward a first area adjacent to an end of the outer-diameter-side step on the bore outer diameter side, a second area adjacent to one of the straight guide steps and a third area adjacent to another of the straight guide.

2. The fuel injection apparatus according to claim 1 , wherein, among the multiple beams, the injector injects one or more beams travelling along a straight line that connects the injector and the ignition plug and a plane including a center axis of the cylinder and two or more of the multiple beams in a pair travelling substantially symmetrically with respect to the plane toward the second recess at the last fuel injection performed during the compression stroke of the engine.

3. The fuel injection apparatus according to claim 1 , wherein the second recess includes a plurality of hitting areas, where beams injected from the injector hit, disposed substantially on a plane including the straight line that connects the injector and the ignition plug and the center axis of the cylinder,

wherein the plurality of hitting areas includes:

a first hitting area is disposed in the first area,

a first pair of hitting areas and a second pair of hitting areas disposed in the second area, and

a second hitting area is disposed in the first recess at a position deviated radially outward from the central-side step.

4. The fuel injection apparatus according to claim 3 , wherein the first pair of hitting areas and the second pair of hitting areas are disposed in substantially plane symmetry with respect to the plane.

5. The fuel injection apparatus according to claim 3 , wherein the fuel sprays reaching the first pair of hitting areas and the second pair of hitting areas from the injector proceed substantially symmetrically with respect to the plane.

6. The fuel injection apparatus according to claim 3 , wherein the first pair of hitting areas are disposed on a side closer to the first hitting area in a longitudinal direction of the straight guide steps than the second pair of hitting areas.

7. The fuel injection apparatus according to claim 3 , wherein the second pair of hitting areas are disposed on a side farther from the first hitting area in the longitudinal direction of the straight guide steps than the first pair of hitting areas.

8. The fuel injection apparatus according to claim 3 , wherein the first pair of hitting areas and the second pair of hitting areas are disposed offset from being in substantially plane symmetry with respect to a plane including the straight line that connects the injector and the ignition plug and the center axis of the cylinder.