JPH0517369B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a pent roof type piston employed in a direct injection internal combustion engine that directly injects fuel into a combustion chamber, and particularly relates to a pent roof type piston that has a cavity shape recessed in the crown surface of the piston. Concerning an improved pent roof type piston.

[Prior Art] In general, in internal combustion engines, the cross-sectional area of the flow path of the intake and exhaust ports is increased by increasing the diameter of the intake and exhaust valves or by increasing the number of intake and exhaust valves per cylinder. By increasing , the intake and exhaust efficiency can be improved.

However, if the cross-sectional areas of the intake and exhaust ports are increased in this way, the valve shafts of the intake and exhaust valves must be inclined in a V-shape to avoid interference between them. Then, due to the arrangement of the valve mechanism, the combustion chamber formed on the lower surface of the cylinder head is recessed upward at the center along the axis of the crankshaft, and gradually slopes on both sides to form a combustion chamber that is approximately perpendicular to the valve axis. It becomes necessary to create a pent roof shape (roof shape) formed so that In order to ensure this, as shown in ``Diesel Engine Combustion Chamber Structure'' proposed in Utility Application No. 143456/1980, the piston crown surface must be made to correspond to the shape of the bottom surface of the cylinder head, and conversely upwards. It would be necessary to create a pent roof shape with a protruding part.

[Problems to be Solved by the Invention] Incidentally, in the case of a direct injection internal combustion engine, a cavity for forming a substantial combustion chamber is recessed approximately in the center of the crown surface of the piston. As shown in FIG. 6, in the conventional pent roof piston a, the cavity b has a circular cross section, and the bottom d at the lower end of the inner circumferential wall c is parallel to the piston ring groove e (t = constant). ) was formed. Therefore, when the inner circumferential wall surface c of the cavity b is developed, it becomes as shown in FIG. The height hb was changing. For this reason, the inside of the cavity b is A, B on two vertical planes A and B that form an angle of θ=45° with respect to the roof direction of the pent roof (the axial direction of the piston pin hole g).
When divided into four areas B, C, and D, the capacities V of these areas were VA=VC>VB=VD, and were different from each other. In addition, the same amount of fuel was injected into each area A, B, C, and D at an angle of 90° from the injection nozzle e located above the center of cavity b. . Therefore, the fuel spray F injected from the injection nozzle e swirls S.
When the air-fuel mixture rotates in cavity b, a rich air-fuel mixture is generated in areas B and D where the height of the inner peripheral wall c of the cavity is low and the volume is small, while on the other hand, the height of the inner peripheral wall c of the cavity is high and the volume is small. A lean mixture is generated in large areas A and C,
A partially non-uniform air-fuel mixture was generated within cavity b. As a result, sufficient air utilization could not be achieved, leading to the generation of a large amount of smoke, and sufficient output could not be obtained.

The present invention was made in view of the above problems, and its purpose is to be able to generate a uniform air-fuel mixture throughout the cavity, thereby increasing the air utilization rate and reducing the amount of smoke generated. It is an object of the present invention to provide a pent roof type piston for a direct injection internal combustion engine which is capable of achieving sufficient output.

[Means for Solving the Problems] In order to achieve the above object, the present invention protrudes directly above the piston pin hole on the piston crown surface along the axial direction, and both sides thereof are inclined. In a pent-roof type piston that is formed in a pent-roof shape and has a cavity recessed in the center of the piston crown surface along the axial direction of the piston, the cavity is formed from each point on the piston crown surface before the cavity is recessed. They are formed at approximately the same depth.

[Function] With the above configuration, the volume of the cavity becomes substantially uniform in the circumferential direction, and the bottom surface of the cavity changes in a undulating manner in the circumferential direction.

[Embodiment] A preferred embodiment of the pent roof piston according to the present invention will be described in detail below with reference to the accompanying drawings.

Figure 1 is a side sectional view of a pent roof type piston used in a direct injection internal combustion engine, and Figure 2 is a side sectional view of the pent roof type piston used in a direct injection internal combustion engine.
It is a sectional view taken along the line.

As shown in the figure, the piston 1 has a piston crown surface 3 directly above the piston pin hole 2 that protrudes upward along the axial direction of the piston pin hole 2 (i.e., the crankshaft direction), and both sides thereof are inclined. It is formed into a pent roof shape (roof shape),
Although this pent roof shape is not shown, it corresponds to the shape of the combustion chamber on the cylinder head side, which is formed on the lower surface of the cylinder head.

Incidentally, a cavity 4 is recessed approximately in the center of the piston crown surface 3 to form a substantial combustion chamber with the cylinder head at the end of the compression stroke. , from the opening periphery 5 to the bottom 6 of the cavity 4
The height h ₇ of the inner circumferential wall surface 7 is formed substantially uniformly over its circumferential side.

That is, in this embodiment, the cavity 4 has a circular cross section;
The height of the opening periphery 5 changes continuously along the circumference with the piston ring groove 8 as a reference, and the level is highest at the position directly above the piston pin hole 2, and the level on both sides thereof is the highest. The level at the 90° position is the lowest. The inner peripheral wall surface 7 of the cavity 4 has a height h ₇ as shown in the developed view of FIG.
are formed uniformly along the circumferential side, so that the bottom portion 6 is parallel to the level variation of the height of the opening peripheral portion 5 and has a wavy shape.

On the other hand, as shown in FIG. 3, above the approximate center of the cavity 4 is an injection nozzle 9 that is attached to the cylinder head and injects fuel into the cavity 4.
will be placed. The injection nozzle 9 has four injection ports (not shown) facing the inner circumferential wall surface 7 of the cavity 4 and opening diagonally downward. Four areas A, B, C,
The same amount of fuel is injected and supplied to the upstream side of the swirl S in D at an angle of 90 degrees to each other.

Therefore, as shown in FIGS. 3 and 4, the fuel spray F and its mixture G injected into each area A, B, C, and D in the cavity 4 are flowed into the swirl S and sent to the cavity. At this time, in the cavity 4 of the present invention, since the height _h7 of the inner peripheral wall surface 7 is formed uniformly along its peripheral side as described above, the opening Areas A and C where the height level of the peripheral portion 5 is high,
The volume of the lower part with areas B and D is VA, VB,
VC and VD are all the same.

Therefore, the amount of air existing in each area A, B, C, and D is equal, and as a result, each area A, B,
The concentrations of the air-fuel mixtures G generated in C and D are approximately equal, so that the air-fuel mixture G having the same concentration as a whole can be uniformly present in the cavity 4. As a result, the air utilization rate is improved, the amount of smoke generated is suppressed as much as possible, and the output can be increased.

Moreover, since the bottom part 6 of the cavity 4 has a wavy shape, the swirl S generated in the cavity 4 has a vertical micro-swirl in the part 6a where the bottom part 6 descends with respect to the flow direction. S
can be generated, making it possible to further improve the mixing of fuel and air.

Note that the swirl S in the cavity 4 is generated by intake air from the intake port.

[Effects of the Invention] In summary, according to the present invention, the following excellent effects are achieved.

(1) Even if the inside of the cavity is divided into a plurality of areas at the same angle along the circumferential direction, the volume of each area can be made the same.

(2) As a result, even if the same amount of fuel is injected and supplied to each area, it is possible to maintain a substantially uniform air-fuel mixture within the cavity as a whole, increasing the air utilization rate and reducing smoke. It becomes possible to reduce the amount of generation as much as possible and increase the output.

(3) Vertical microswirls can be generated in the descending portion of the bottom of the cavity with respect to the flow direction of the swirl, making it possible to achieve even better mixing of fuel and air.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view of a pent roof type piston according to the present invention, Fig. 2 is a side sectional view taken from the - line arrow in Fig. 1, Fig. 3 is a plan view of the crown surface of the piston, and Fig. 4 is a cavity inner peripheral wall. FIG. 5 is a plan view of a conventional piston crown surface, FIG. 6 is a sectional view taken along the line -- in FIG. 5, and FIG. 7 is a developed view of a conventional inner peripheral wall surface of a cavity. In the figure, 1 is a piston, 2 is a piston pin hole, and 3 is a piston.
is the piston crown surface, 4 is the cavity, 5 is the opening periphery, 6 is the bottom, 7 is the inner peripheral wall surface, and _h7 is the height of the inner peripheral wall surface.

Claims (1)

[Claims] 1. The piston crown surface directly above the piston pin hole protrudes along its axial direction, and its both sides are sloped to form a pent roof shape, and the piston crown surface extends along the axial direction of the piston at the center of the piston crown surface. A pent roof type piston having a recessed cavity, characterized in that the cavity is formed at approximately the same depth from each point on the crown surface of the piston before the cavity is recessed.