Direct fuel injection-type spark-ignition internal combustion engine

A direct fuel injection-type spark-ignition internal combustion engine is disclosed. The engine comprises a spark plug, a fuel injector and a cavity formed on the top surface of the piston. The cavity has a bottom wall, a spark plug side wall and a fuel injector side wall. The fuel injector injects fuel toward the bottom wall of the cavity in stratified charge combustion. The fuel mainly proceeds toward the spark plug side wall of the cavity along the bottom wall, is deflected by the spark plug side wall and is led to the vicinity of the spark plug. In the engine, the fuel injector side wall of the cavity is provided with a deflecting portion. If a part of the injected fuel proceeds toward the fuel injector side wall along the bottom wall of the cavity, that part of the fuel is led to the vicinity of the spark plug by the deflecting portion.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a direct fuel injection-type
 spark-ignition internal combustion engine.
 2. Description of the Related Art
 There has heretofore been known the stratified charge combustion engine
 realized the directly injected fuel into a cylinder to form a mixture
 (hereinafter referred to as combustible mixture) that can be favorably
 ignited only in the vicinity of a spark plug, at the ignition timing, to
 burn a total lean mixture in the cylinder. To carry out stratified charge
 combustion, in general, the fuel injector injects fuel in the latter half
 period of the compression stroke. It is intended that the thus injected
 fuel proceeds into a concave cavity formed in the top of the piston, is
 vaporized by absorbing heat from the wall surfaces of the cavity, is
 deflected by the shape of the cavity toward the spark plug, and forms a
 combustible mixture near the spark plug.
 In the direct fuel injection-type spark-ignition internal combustion engine
 for performing the stratified charge combustion, in general, the spark
 plug is arranged nearly at the center in the upper part of the cylinder,
 and the fuel injector is arranged in the periphery in the upper part of
 the cylinder. The piston cavity is located from nearly the central portion
 of the top surface of the piston to the periphery of the top surface of
 the piston on the side of the fuel injector. The piston cavity has a
 bottom wall and side walls which are spark plug side and fuel injector
 side. Fuel injected into the cavity collides with the bottom wall of the
 cavity, thereafter proceeds toward the spark plug side wall along the
 bottom wall, and is deflected toward the spark plug by the spark plug side
 wall.
 In order to promote the fuel vaporization utilizing the heat of the wall
 surface of the cavity, the distance for moving fuel along the wall surface
 of the cavity must be lengthened so that the injected fuel stays in
 contact with the wall surface of the cavity for an extended period. In
 order to realize this without changing the shape of the cavity, it has
 been proposed to inject fuel at a relatively large acute angle with
 respect to the bottom wall of the cavity. This makes it possible to bring
 the position where fuel collides with the bottom wall away from the spark
 plug side wall of the cavity, maintaining the same injector hole position,
 compared with when the fuel is injected at a relatively small acute angle,
 and, hence, to extend the distance for moving fuel along the bottom wall
 of the cavity.
 When the fuel is injected at a relatively large acute angle with respect to
 the bottom wall of the cavity, however, fuel which has collided with the
 bottom surface is diverted and all of the fuel does not proceed toward the
 spark plug side wall along the bottom surface; i.e., a part of the fuel
 proceeds toward the fuel injector side wall along the bottom surface.
 Accordingly, the quantity of the combustible mixture formed near the spark
 plug via the spark plug side wall of the cavity is decreased, so that the
 engine output is also decreased. Furthermore, the mixture formed by fuel
 proceeded toward the fuel injector side wall of the cavity cannot be
 favorably burned, and unburned fuel may be emitted in increased amounts.
 SUMMARY OF THE INVENTION
 The objective of the present invention is to provide a direct fuel
 injection spark-ignition internal combustion engine which produces the
 engine output as intended in the stratified charge combustion mode; in
 this engine, fuel is injected toward the bottom wall of a cavity formed in
 the top surface of a piston so as to proceed mainly toward the spark plug
 side wall of the cavity along the bottom wall, and the fuel is led toward
 the vicinity of the spark plug and in which, even when the fuel that has
 collided with the wall surface of the cavity is diverted into toward the
 spark plug side wall of the cavity and toward the fuel injector side wall,
 all of the injected fuel is burned as the combustible mixture.
 According to the present invention, provided is a direct fuel
 injection-type spark-ignition internal combustion engine comprising a
 spark plug, a fuel injector and a cavity formed in the top surface of the
 piston, the cavity having a bottom wall, a spark plug side wall and a fuel
 injector side wall, the fuel injector injecting fuel toward the bottom
 wall of the cavity in stratified charge combustion, the fuel mainly
 proceeding toward the spark plug side wall of the cavity along the bottom
 wall, being deflected by the spark plug side wall and being led to the
 vicinity of the spark plug, wherein the fuel injector side wall of the
 cavity is provided with a deflecting portion, and if a part of the
 injected fuel proceeds toward the fuel injector side wall along the bottom
 wall of the cavity, the part of the fuel is led to the vicinity of the
 spark plug by the deflecting portion.
 The present invention will be more fully understood from the description of
 preferred embodiments of the invention set forth below together with the
 accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 FIG. 1 is a vertical sectional view schematically illustrating a direct
 fuel injection-type spark-ignition internal combustion engine according to
 a first embodiment of the present invention, and FIG. 2 is a plan view of
 a piston in FIG. 1. In these drawings, reference numeral 1 denotes an
 intake port and 2 denotes an exhaust port. The intake port 1 connects to
 the cylinder via an intake valve 3, and the exhaust port 2 connects to the
 cylinder via an exhaust valve 4. Reference numeral 5 denotes a piston
 having a cavity 8 formed in the top surface thereof, and 6 denotes a spark
 plug arranged near to the central upper part of the cylinder.
 A fuel injector 7 is arranged in the periphery of the upper part of the
 cylinder on the side of the intake port 1 and injects fuel whose spray
 pattern is flat fan shape with a relatively small thickness. The cavity 8
 is formed in the top surface of the piston, and located from near the
 central portion of the piston to the periphery of the piston on the side
 of the fuel injector. The cavity has a bottom wall 8a, a spark plug side
 wall 8b and a fuel injector side wall 8c. The spark plug 6 is positioned
 on the center line of the contained angle of the fan of the fan-shaped
 spray injected from the fuel injector 7, and faces the inside of the spark
 plug side wall 8b of the cavity 8.
 For example, in a uniform charge combustion region where a high engine
 output is required, the fuel injector 7 injects a required amount of fuel
 in the intake stroke thereby to form a uniform charge mixture in the
 cylinder at the ignition timing. On the other hand, in a stratified charge
 combustion region, a required amount of fuel is injected into the cavity 8
 in the latter half of the compression stroke. Fuel injected into the
 cavity 8 collides with the bottom wall 8a of the cavity 8 so as to proceed
 toward the spark plug side wall 8b along the bottom wall 8a. Fuel
 proceeding on the bottom wall 8a radially spreads within the contained
 angle of the fan of fuel, and is gradually vaporized by favorably
 absorbing heat from a wide area of the wall surface of the cavity.
 In addition to being smoothly connected to the bottom wall 8a, the spark
 plug side wall 8b of the cavity 8 has an arcuate shape in a plan view.
 Further, the distance from the center of the contained angle of the fan of
 fuel proceeding on the bottom wall 8a of the cavity to the spark plug side
 wall, is larger than the radius of the arcuate shape of the cavity.
 Therefore, each part of fuel in the width direction arriving at the spark
 plug side wall 8b does not lose much speed, and proceeds along the spark
 plug side wall 8b, gains an upward velocity component and further gains a
 velocity component in the direction of center line of the contained angle
 of the fan of fuel as fuel comes into collision with the spark plug side
 wall 8b at an acute angle in a plan view. Further, the spark plug side
 wall 8b is provided with a first deflecting portion 8d. Therefore, each
 part of fuel proceeding along the spark plug side wall 8b is finally
 deflected toward the inside of the cavity 8.
 Thus, if all of the injected fuel proceeds toward the spark plug side wall
 8b along the bottom wall 8a of the cavity 8 and is finally completely
 vaporized on the spark plug side wall 8b, then a combustible mixture is
 formed near the spark plug at the ignition timing, and favorable
 stratified charge combustion can be realized.
 In order to realize the favorable stratified charge combustion, first, it
 is important that all of the injected fuel is completely vaporized at the
 ignition timing. If a part of the fuel exists as liquid, it does not
 favorably burn and is exhausted as unburned fuel. In the present
 embodiment, the distance for moving fuel along the wall surface of the
 cavity is lengthened and the injected fuel is permitted to stay in contact
 with the wall surface of the cavity for an extended period in order to
 promote the vaporization of the fuel utilizing the heat of the wall
 surface of the cavity. Concretely speaking, the fuel injector 7 injects
 fuel at a relatively large acute angle with respect to the bottom wall 8a
 of the cavity 8, whereby the position where fuel collides the bottom wall
 8a is moved away from the spark plug side wall 8b of the cavity 8, making
 it possible to lengthen the distance for moving fuel on the bottom wall 8a
 of the cavity 8.
 However, when fuel 10 is injected at a relatively large acute angle with
 respect to the bottom wall 8b of the cavity 8, as shown in FIGS. 1 and 2,
 the fuel that has come into collision with the bottom wall 8a is diverted
 into a fuel 10a proceeding toward the spark plug side wall 8b along the
 bottom wall 8a and a fuel 10b proceeding toward the fuel injector side
 wall 8c along the bottom wall 8a.
 From the standpoint of quantity, a large proportion of fuel 10a proceeds
 toward the spark plug side wall 8b and a small proportion of fuel 10b
 proceeds toward the fuel injector side wall 8c. In stratified charge
 combustion, only a minimum required amount of fuel is injected in the
 present engine operating condition. Therefore, if a part of the injected
 fuel does not appear as a mixture near the spark plug 6, the engine output
 is not produced as intended. Besides, a part of the fuel is not favorably
 burned despite it being vaporized at the ignition timing, and it may be
 emitted as unburned fuel.
 In the present embodiment, the fuel injector side wall 8c of the cavity 8
 is provided with a second deflecting portion 8e for deflecting fuel toward
 the inside of the cavity 8. Therefore, even if a part of the injected fuel
 proceeds toward the fuel injector side wall 8c of the cavity 8 along the
 bottom wall 8a, this fuel is gradually vaporized by absorbing heat from
 the bottom wall 8a of the cavity 8 and from the fuel injector side wall
 8c, and is imparted with an upward velocity component due to the fuel
 injector side wall 8c and is further deflected toward the inside of the
 cavity 8 by the second deflecting portion 8e.
 At the ignition timing, as shown in FIG. 3, therefore, the mixture 10b'
 formed by fuel proceeding toward the fuel injector side wall 8c of the
 cavity 8 moves toward the spark plug 6 by use of the pentroof shape in the
 upper part of the cylinder, and merges with the mixture 10a' formed near
 the spark plug, due to fuel proceeding toward the spark plug side wall 8b,
 thereby to form a mass of combustible mixture, and thus favorable
 stratified charge combustion can be realized to produce the engine output
 as intended.
 The second deflecting portion 8e may be an inclined surface or an arcuate
 surface if it is capable of deflecting the fuel proceeding on the fuel
 injector side wall 8c of the cavity 8 toward the inside of the cavity 8.
 If the angle of the extended plane of the second deflecting portion 8e
 (when the second deflecting portion 8e is an arcuate surface, the plane
 extending in the tangential direction of the end thereof) with respect to
 the horizontal plane is selected to be relatively small, the mixture 10b'
 formed by fuel proceeding on the fuel injector side wall 8c of the cavity
 8 can be directly merged with the mixture 10a near the spark plug without
 employing the pentroof shape in the upper part of the cylinder.
 Further, as shown in FIGS. 1 and 3, at a piston position in the latter half
 of the compression stroke, the extended plane (P) of the second deflecting
 portion Be near the injection hole of the fuel injector 7 does not come
 into contact with the injection hole of the fuel injector 7, and the
 injection hole of the fuel injector 7 is positioned on the outer side of
 the extended plane (P).
 Therefore, even if fuel in the form of a liquid proceeds on the fuel
 injector side wall 8c of the cavity 8, the liquid fuel does not stick to
 the injection hole of the fuel injector 7 and does not form a deposit.
 This eliminates the problem in that the deposit is formed on the injection
 hole of the fuel injector 7 causing the fuel to be injected in a decreased
 amount per a unit time by the fuel injector 7.
 Further, if the fuel injector side wall 8c of the cavity 8 has an arcuate
 portion in a plan view and if the distance from the center of the
 contained angle of the fan of fuel proceeding toward the fuel injector
 side wall 8c along the bottom wall 8a of the cavity to the fuel injector
 side wall 8c is set to be larger than the radius of the arcuate portion of
 the fuel injector side wall 8c of the cavity, fuel proceeding toward the
 fuel injector side wall 8c can converge in the direction of center line of
 the contained angle of the fan of fuel as the spark plug side wall 8b, and
 the mixture formed by this fuel can be comfirmly led toward the spark plug
 6.
 In uniform charge combustion in which fuel is injected during the intake
 stroke, fuel injection amount becomes larger than that in stratified
 charge combustion since the engine load is high. In order to inject this
 large amount of fuel during the intake stroke, the fuel injection must be
 started from the initial stage of the intake stroke. In uniform charge
 combustion, the injected fuel is diverted as it comes into collision with
 the bottom wall 8a of the cavity 8 so as to be widely dispersed in the
 cylinder, offering an advantage from the standpoint of forming a favorable
 uniform mixture at the ignition timing.
 If fuel proceeds in large amounts toward the spark plug side wall 8b of the
 cavity 8 only, fuel tends to remain in a liquid form near the boundary
 between the bottom wall 8a of the cavity 8 and the spark plug side wall
 8b. The liquid fuel may not have been sufficiently vaporized at the
 ignition timing and may be emitted as unburned fuel. Fuel is diverted so
 as to proceed toward the fuel injector side wall 8c of the cavity 8,
 whereby fuel proceeds in a decreased amount toward the spark plug side
 wall 8b to solve the above problem. According to the present embodiment as
 described above, the problem caused by diversion of fuel in stratified
 charge combustion is solved, furthermore, diversion of fuel can be
 positively utilized for uniform charge combustion.
 In the present embodiment, the fuel injector 7 injects fuel in a flat fan
 shape having a relatively small thickness, however, this is not to limit
 the invention. The above-mentioned effects can be obtained even when fuel
 is injected in a conical shape or in a cylindrical shape, the fuel
 injector side wall 8c of the cavity 8 is provided with the above-mentioned
 second deflecting portion 8e and the fuel is diverted due to the collision
 with the bottom wall of the cavity.