JPH08319833A - Direct injection type diesel engine - Google Patents

Abstract

PURPOSE: To provide a diesel engine of direct jet type equipped with such a wall surface shape as producing a complex vortex of squish and swirl in a combustion chamber and maintaining strong turbulence till the later stage of combustion. CONSTITUTION: A suction valve 9 and exhaust valve 10 are inclined with respect to the center line of a cylinder in such a way that the valve faces are opposing, and the ceiling wall 22 of a combustion chamber is composed of a spherical portion 24 of such a curvature as substantially contacting with each valve face 9a and a plane portion 23 positioned around the spherical portion 24 and spreading in the form of plane perpendicularly intersecting the center line of the cylinder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection type diesel engine having a wall surface shape which produces a squish-swirl composite vortex flow in a combustion chamber and maintains a strong turbulence until the latter stage of combustion.

[0002]

2. Description of the Related Art A conventional direct injection diesel engine having two intake / exhaust valves in one cylinder is shown in FIG.
Gazette, reference).

In the figure, 1 is a cylinder, 2 is a piston, 4 is a cylinder head, 5 is a cavity opened in the top surface 21 of the piston 2, 3 is an intake port formed in the cylinder head 4, and 8 is a cylinder head 4. It is the formed exhaust port. The reciprocating motion of the piston 2 is converted into a rotary motion of the crankshaft via a connecting rod 7 (not shown).

Two intake valves 9 and two exhaust valves 10 are provided so as to surround the fuel injection valve 33. As each intake valve 9 is opened, air is taken into the cylinder 1 from each intake port 3, and this air is compressed by the piston 5 and ignited and burned. The burned gas is discharged to each exhaust port 8 as each exhaust valve 10 is opened. Each of these steps is continuously repeated.

The intake / exhaust valves 9 and 10 are arranged so as to be inclined at a predetermined angle with respect to the cylinder center line so that the valve faces 9a and 10a face each other.

The combustion chamber ceiling wall 22 has a valve face 9
It is formed to be inclined in a pent roof type along a and 10a. The top surface 21 of the piston 2 is formed to be inclined so as to face the combustion chamber ceiling wall 22 and the valve faces 9a, 10a in parallel. The bottom surface 5c of the cavity 5 is also formed to be inclined so as to face the combustion chamber ceiling wall 22 and the valve faces 9a, 10a in parallel.

Two camshafts 13 and 14 are provided on the cylinder head 4 for opening and closing the intake and exhaust valves 9 and 10. The camshafts 13 and 14 have suction / exhaust cams 15 and 16 for opening / closing the suction / exhaust valves 9 and 10, respectively.

The intake / exhaust cams 15 and 16 of the camshafts 13 and 14 are rotated by the rotation of the lifters 1.
2 is slid so that each lifter 12 causes each intake / exhaust valve 9, 1
0 is opened and closed against each valve spring 19. Further, the cam 31 formed on the exhaust cam shaft 14 swings the rocker arm 32 to open / close the fuel injection valve 33.

[0009]

However, in such a conventional apparatus, the pent roof type is adopted so that the top surface 21 of the piston 2 faces the combustion chamber ceiling wall 22 and the valve faces 9a, 10a. Since it is formed so as to be raised, the gap volume between the piston 2 and the cylinder 1 defined above the top ring 34 increases, the volume of the combustion chamber cannot be concentrated in the cavity 5, and the air utilization rate decreases. Then, there is a problem that the emission amount of smoke such as HC and SOF increases.

Further, since the top surface 21 of the piston 2 is formed to be raised in a pent roof type, when the piston 2 reaches the vicinity of the top dead center, the top surface 21 of the piston 2 and the combustion chamber ceiling of the cylinder head 4 are formed. There is a problem that the air in the cylinder 1 cannot be compressed between the walls 22 and the force of the squish flow flowing into the cavity 5 cannot be sufficiently secured, the air utilization rate decreases, and the smoke discharge amount increases. is there.

It is an object of the present invention to solve the above problems and to provide a direct injection diesel engine having a wall surface shape which produces a squish and swirl vortex flow in a combustion chamber and maintains a strong turbulence until the latter stage of combustion. To do.

[0012]

According to a first aspect of the present invention, there is provided a direct injection type diesel engine, which has a cavity recessed in a top surface of a piston and a combustion chamber ceiling wall defining a combustion chamber between the piston and the cavity. A fuel injection valve that is attached to the center of the combustion chamber ceiling wall to inject fuel, a plurality of intake ports that open to the combustion chamber ceiling wall to introduce intake air, and a plurality of intake valves that open and close each intake port, In an engine including a plurality of exhaust ports that open to the ceiling wall of a combustion chamber to discharge exhaust gas and a plurality of exhaust valves that open and close each exhaust port, the intake and exhaust valves are arranged so that their respective valve faces face each other. Is inclined with respect to the cylinder center line, and the combustion chamber ceiling wall is located around the spherical surface and a spherically curved spherical surface that is in close contact with each valve face of the intake / exhaust valve at the valve closing position. And a flat portion extending in a plane perpendicular to the cylinder centerline.

According to a second aspect of the present invention, in the direct injection type diesel engine, the radius of the spherical surface portion is set to be substantially equal to the radius of the cavity.

According to a third aspect of the present invention, in the direct injection type diesel engine according to the first or second aspect of the invention, a cylinder center line passing through a portion where adjacent valve faces of the combustion chamber ceiling wall are closest to each other is centered. When the circular arc to be performed is the reference circular arc S, the radius of the spherical portion is set to be larger than the radius of the reference circular arc S.

A direct injection diesel engine according to a fourth aspect of the present invention is the direct injection diesel engine according to any one of the first to third aspects, wherein two intake / exhaust valves for opening / closing each of the intake / exhaust valves are driven.
The exhaust camshafts are provided side by side above the intake / exhaust valves.

A direct injection diesel engine according to a fifth aspect of the present invention is the direct injection diesel engine according to any one of the first to fourth aspects, in which a swirl ratio is increased in a low speed low load range from a medium speed medium load range, and fuel injection is performed. Combustion control means for delaying the timing is provided.

[0017]

The direct injection diesel engine according to claim 1, wherein the flat portion of the combustion chamber ceiling wall is located above the spherical portion and spreads in a flat shape orthogonal to the cylinder center line. The volume of the space between the piston and the cylinder that is defined in Fig. 2 is kept small, the volume of the combustion chamber is concentrated in the cavity, and the air utilization rate is increased.
The amount of smoke emission such as F can be reduced.

The spherical portion of the ceiling wall of the combustion chamber has a spherically curved structure which is substantially in contact with each valve face of the intake / exhaust valve at the valve closing position, so that the intake / exhaust valves arranged so that the valve faces face each other. The volume of the valve recess that is recessed around the exhaust valve is reduced, and the wall surface of the combustion chamber defined by the spherical portion and each valve face is made smooth.
This suppresses the swirl and squish forces generated in the combustion chamber from being attenuated by the depression of the valve recess, and also suppresses the fuel spray radially injected from the fuel injection valve into the combustion chamber from entering the valve recess, Smoke emissions can be reduced.

In the direct-injection diesel engine according to the present invention, the radius of the spherical portion is set to be substantially equal to the radius of the cavity so that combustion is defined between the spherical portion and the cavity near the top dead center of the piston. The surface area of the chamber is minimized, and the amount of heat released from the combustion gas to the combustion chamber ceiling wall and the cylinder is suppressed.

On the other hand, when the radius of the spherical portion becomes much larger than the radius of the cavity, a wedge-shaped space is defined between the outer peripheral portion of the spherical portion and the piston top surface near the top dead center of the piston. Therefore, the swirl force generated in the combustion chamber may be attenuated, or the diffusion of the fuel spray radially injected from the fuel injection valve into the combustion chamber may be deteriorated, and the smoke emission amount may increase. .

In the direct-injection diesel engine according to the third aspect of the present invention, a portion of the combustion chamber ceiling wall where adjacent valve faces are closest to each other has a cross-section included in a spherical portion and curved in an arc shape. Thus, the concentration of thermal stress is relieved, and cracks and the like can be prevented from occurring at high speed and high load.

In the direct injection diesel engine according to the present invention, since the intake / exhaust valves are inclined with respect to the cylinder center line so that their valve faces face each other, they are parallel to each other on the intake / exhaust valves. A space between the two extending cam shafts is ensured, and interference between the cams is avoided. As a result, a valve operating mechanism such as a rocker arm provided between the intake / exhaust valve and the cam becomes unnecessary, and the number of parts can be reduced, and the weight and cost can be reduced.

In the direct injection diesel engine according to the fifth aspect of the present invention, in the low speed low load region, the combustion control is performed so that the swirl ratio is increased and the fuel injection timing is delayed in the low speed low load region compared with the medium speed medium load region. Since the combustion becomes gradual and the ignition delay period becomes long, the NOx concentration can be reduced, the swirl power can be increased, and the air utilization rate of the combustion chamber can be sufficiently obtained to reduce the smoke concentration.

The spherical portion of the combustion chamber ceiling wall increases the force of the swirl generated in the combustion chamber, so that it is not necessary to bend the tip of the intake port in a spiral shape on the plan view to strengthen the swirl, Higher output is achieved by reducing the passage resistance of the intake port.

[0025]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, 1 is a cylinder, 2 is a piston, 4 is a cylinder head, 5 is a cavity opened at the top surface 21 of the piston 2, 3 is an intake port formed in the cylinder head 4, and 8 is a cylinder head 4. It is an exhaust port formed in. The reciprocating motion of the piston 2 is converted into a rotary motion of the crankshaft via a connecting rod (not shown).

The top surface 21 of the piston 2 is formed flat with respect to the cylinder center line C. The toroidal cavity 5 is defined by a cylindrical side surface 5a centered on the cylinder center line C and a conical bottom surface 5b also centered on the cylinder center line C.

The piston top surface 21 extends annularly around the cavity 5 and compresses the air in the cylinder 1 between the combustion chamber ceiling walls 22 of the cylinder head 4 when the piston 2 reaches the vicinity of the top dead center. Forming a squish area that causes a squish flow to flow into the cavity 5.

As shown in FIG. 2, the cylinder head 1 is provided with a fuel injection valve 11 for radially injecting fuel into the cavity 5. The fuel injection valve 11 has a cylinder center line C.
It is located above and faces the center of the cavity 5.

Two intake valves 9 and two exhaust valves 10 are provided so as to surround the fuel injection valve 11. As each intake valve 9 is opened, air is taken into the cylinder 1 from each intake port 3, and this air is compressed by the piston 5 and ignited and burned. The burned gas is discharged to each exhaust port 8 as each exhaust valve 10 is opened. Each of these steps is continuously repeated.

Each intake port 3 has a straight shape with its tip extending linearly in a plan view.

A swirl control valve (not shown) for adjusting the opening area of one intake port 3 is provided as means for adjusting the swirl force generated in the cylinder 1.

The intake / exhaust valves 9 and 10 are arranged so as to be inclined at a predetermined angle with respect to the cylinder center line C so that the valve faces 9a and 10a face each other.

The angle between the intake / exhaust valves 9 and 10 is determined by the intake / exhaust valves that open / close the intake / exhaust valves 9 and 10, as will be described later.
The exhaust cams 15 and 16 are set to have the smallest value within a range in which they do not interfere with each other. In this case, the intake / exhaust valves 9 and 10 are arranged such that the angle between the intake / exhaust valves 9 and 10 is set to 6 °, and the intake / exhaust valves 9 and 10 are each inclined by 3 ° with respect to the cylinder center line C.

The combustion chamber ceiling wall 22 is provided with a flat surface portion 23 that spreads in a plane shape orthogonal to the cylinder center line C at the outer peripheral portion thereof, and a spherical surface portion 24 that is recessed into a spherical shape at the center portion thereof.

Valve seats 17, 18 on which the intake / exhaust valves 9, 10 are seated are fitted to the combustion chamber ceiling wall 22 of the cylinder head 4. The combustion chamber ceiling wall 22 is formed with valve recesses 27 and 28 that are recessed to accommodate the valve seats 17 and 18, respectively.

The spherical portion 24 of the combustion chamber ceiling wall 22 is provided with
The exhaust valves 9 and 10 are formed in a spherical shape with a predetermined radius of curvature so as to come into contact with the valve faces 9a and 10a of the exhaust valves 9 and 10. Therefore, the center of curvature of the spherical surface portion 24 substantially coincides with the intersection of the center lines I and E of the intake / exhaust valves 9 and 10.

Two camshafts 13 and 14 are provided on the cylinder head 4 to open and close the intake and exhaust valves 9 and 10. The camshafts 13 and 14 have suction / exhaust cams 15 and 16 for opening / closing the suction / exhaust valves 9 and 10, respectively.

The rotational force of the crankshaft (not shown) is transmitted to each of the camshafts 13 and 14 through the pulley and the timing belt at a reduced speed of 1/2.

As the cam shafts 13 and 14 rotate, the intake / exhaust cams 15 and 16 are moved to the lifter 1 respectively.
2 is slid so that each lifter 12 causes each intake / exhaust valve 9a,
9b, 10a, 10b are opened and closed against each valve spring 19.

Since the intake / exhaust valves 9 and 10 are arranged with an included angle of 6 °, the intake / exhaust valves 9 and 10 are arranged.
The space between the two cam shafts 13 and 14 extending parallel to each other is ensured to prevent the cams 15 and 16 from interfering with each other. As a result, a valve mechanism such as a rocker arm is not required, the number of parts can be reduced, and the weight and cost can be reduced.

In FIG. 3, reference numeral 60 denotes a fuel injection pump whose fuel injection timing and fuel injection amount are electronically controlled.
The fuel pumped from the fuel injection pump 60 is guided to the injection valve 11 through the pipe 58.

Reference numeral 63 is an intake passage, 65 is an exhaust passage, 76 is a filter for collecting particulates in the exhaust, and 7
An exhaust muffler 7 reduces exhaust noise.

Reference numeral 66 is an EGR passage that connects the exhaust passage 65 and the intake passage 63, and 67 is a diaphragm type EGR valve that responds to the control negative pressure.

Reference numeral 68 denotes a negative pressure control valve, which adjusts the constant negative pressure from the vacuum pump 69 in three stages according to the duty signal from the control unit 71. For example, when the OFF duty to the negative pressure adjusting valve 68 (OFF time ratio of a constant cycle) is the maximum value and a constant negative pressure is directly introduced to the EGR valve 67, 50% of the exhaust gas is recirculated. This means that the EGR rate (= EGR amount / fresh air amount x 100%) is 10
It corresponds to 0%. When the OFF duty gradually decreases, the control negative pressure to the EGR valve 67 decreases, so that the EGR valve opening decreases and the EGR flow rate decreases. That is,
The EGR rate is 60 each time the OFF duty is reduced.
% And 30%.

Reference numeral 61 is the above-mentioned swirl control valve, and 62 is an actuator for opening and closing the swirl control valve 61.

A control unit 71 including a microcomputer is provided for controlling the EGR rate, the swirl ratio, the fuel injection timing and the like according to the operating conditions of the engine. The control unit 71 has a sensor for detecting an accelerator opening (accelerator pedal opening), a signal from an air flow meter 73 for detecting an intake air amount Q taken into the intake passage 63 via an air cleaner 75, an engine speed, an engine speed, and an engine speed. Input the detection signal such as water temperature.

The control unit 71 controls the EGR rate to be higher than the medium speed to medium load range in a predetermined low speed and low load range to increase the swirl ratio and to delay the fuel injection timing to near the top dead center. By delaying the fuel injection timing to near the top dead center in the low speed and low load region, the proportion of premixed gas combustion is made larger than that of diffusion combustion, and both the NOx concentration and the smoke concentration are reduced.

The characteristics of the fuel injection timing according to the operating conditions are shown in FIG. 6. At high speed and high load, the fuel injection timing is advanced to 8 ° before top dead center, and the fuel injection timing is delayed stepwise as the rotation speed or load decreases. Delay at top dead center at low speed and low load.

The EGR rate is set as shown in FIG. 4 according to the operating conditions. In the figure, the EGR rate is 100% in the medium-speed / medium-load range and the low-speed full-load range. On the other hand, in the high speed and high load region, the combustion period is long and the generation of smoke cannot be completely suppressed. Therefore, the intake air temperature rises due to the increase in the exhaust gas temperature and the increase in the EGR flow rate. Since the effect of reducing NOx is reduced, the EGR rate is gradually reduced to 60% and 30%.

In order to obtain the characteristics of the EGR rate (target EGR rate) shown in FIG. 4 with respect to the torque generated by the engine and the engine speed, the accelerator opening (engine load equivalent amount) Acc and the engine speed Ne. Is set as a parameter (not shown) and the map is looked up to obtain the target EGR rate at that time. The EGR flow rate is calculated from this and the air flow meter flow rate (new air amount) by EGR flow rate = air flow meter flow rate × target EGR rate, and the OFF duty to the negative pressure control valve 68 is determined so that the EGR gas of this flow rate flows. Of.

The characteristics of the swirl ratio according to the operating conditions are shown in FIG.
As shown in, the swirl ratio is increased as the speed decreases.
In the high speed range, the volume efficiency decreases with the high swirl ratio, and the improvement of combustion by increasing the injection pressure weakens the need for swirl. Therefore, the swirl control valve 61 is opened stepwise as the rotation speed increases. It reduces the swirl ratio.

With the above construction, the operation will be described below.

In the case of a direct injection diesel engine, the fuel injected from the fuel injection valve 11 into the combustion chamber is combusted through atomization, evaporation and mixing with air.

As shown in FIG. 7, 5 ° before the piston top dead center
In the case of the conventional DI method in which fuel is injected from the fuel injection valve into the combustion chamber at a crank angle of, the diffusion combustion is rapidly performed as the piston reaches the top dead center, and exhaust gas NO
The x concentration increases.

Further, in the direct injection type diesel engine having the combustion chamber structure in which the swirl force generated in the combustion chamber is not sufficiently obtained, the conventional DI system corresponding to the exhaust control for delaying the fuel injection timing to near the top dead center In the case of NO, the ratio of premixed combustion is larger than that of diffusion combustion, and NO
Although the x concentration can be reduced, the swirl's power is insufficient and the air utilization rate in the combustion chamber cannot be sufficiently obtained.
The smoke concentration of C, SOF, etc. increases.

On the other hand, the DI method of the present invention, which has a smooth combustion chamber wall surface shape, achieves combustion control in which the swirl ratio is increased in the low speed and low load range compared to the middle speed and middle load range, and the fuel injection timing is delayed to the top dead center. With this configuration, the combustion is gradual in the low-speed low-load range, and the ignition delay period becomes long, so NO
In addition to reducing the x concentration, a complex vortex flow of squish and swirl is generated in the combustion chamber, maintaining a strong turbulence until the latter stage of combustion, so that the air utilization rate of the combustion chamber is sufficiently obtained and the smoke concentration is reduced.

That is, the spherical portion 24 of the combustion chamber ceiling wall 22.
Is a valve face 9a of each intake / exhaust valve 9,10,
Since the valve recesses 27 and 28 that are concavely recessed in the combustion chamber ceiling wall 22 have a small volume, the spherical recess 24 and the valve faces 9a and 10a are formed. The wall surface of the combustion chamber defined by is smoothed, and damping of the swirl force generated in the combustion chamber by the depressions of the valve recesses 27 and 28 is suppressed.

As a result, it is not necessary to bend the tip of the intake port 3 in a spiral shape on the plan view to strengthen the swirl, and the passage resistance of the intake port 3 can be reduced to achieve high output.

The flat portion 23 of the combustion chamber ceiling wall 22 is located around the spherical portion 24 and spreads in a plane orthogonal to the cylinder center line C, so that the flat portion 23 is defined above the top ring 34. The clearance volume of the cylinder 1 is suppressed to be small, the volume of the combustion chamber is concentrated in the cavity 5, the air utilization rate is increased, and the smoke discharge amount is reduced.

The valve recesses 27, 2 are formed by the spherical portion 24.
The fuel injection valve 11
The fuel spray radially injected into the combustion chamber from the inside is prevented from entering the valve recesses 27 and 28, and the smoke emission amount is reduced.

Further, since the top surface 21 of the piston 2 is formed orthogonal to the cylinder center line C so as to face the combustion chamber ceiling wall 22 and the valve faces 9a, 10a in parallel, the piston 2 is formed. When reaching near the top dead center, the top surface 21 of the piston 2 and the combustion chamber ceiling wall 2 of the cylinder head 4
Between the two, the air in the cylinder 1 is compressed to sufficiently secure the force of the squish flow flowing into the cavity 5, the air utilization rate is increased, and the smoke discharge amount is reduced.

The sandwiching angle of the intake / exhaust valves 9 and 10 is determined by the intake / exhaust valves for opening and closing the intake / exhaust valves 9 and 10, as will be described later.
Since the exhaust cams 15 and 16 are set to have the smallest value within a range where they do not interfere with each other, the combustion chamber ceiling wall 22 that produces a squish flow with the piston top surface 21.
The maximum squish area area is secured, the squish flow power is increased, and the air utilization rate is improved.

Next, in another embodiment shown in FIG. 8, the radius of the spherical portion 24 of the combustion chamber ceiling wall 22 is set to be substantially equal to the radius of the cavity 5. The same parts as those in FIG. 1 are designated by the same reference numerals.

In this case, the combustion chamber defined between the spherical portion 24 and the cavity 5 in the vicinity of the top dead center of the piston 2 has its surface area minimized, and the combustion chamber is covered with the combustion chamber ceiling wall 22.
The amount of heat released to the cylinder 1 can be suppressed.

On the other hand, when the radius of the spherical surface portion 24 of the combustion chamber ceiling wall 22 becomes significantly larger than the radius of the cavity 5, the outer peripheral portion of the spherical surface portion 24 and the piston top surface 21 near the top dead center of the piston 2. Since a space having a wedge-shaped cross section is defined between them, the swirl force generated in the combustion chamber is attenuated, or the diffusion of fuel spray radially injected from the fuel injection valve 11 into the combustion chamber is deteriorated. As a result, smoke emissions may increase.

Next, in another embodiment shown in FIG. 9, an arc centered on the cylinder center line C is used as a reference, passing through a portion where the adjacent valve faces 9a, 10a of the combustion chamber ceiling wall 22 are closest to each other. When the arc S is set, the radius of the spherical surface portion 24 is set to be larger than the radius of the reference arc S. The same parts as those in FIG. 1 are designated by the same reference numerals.

In this case, since the section where the adjacent valve faces 9a, 10a of the combustion chamber ceiling wall 22 are closest to each other is curved in an arc shape with the cross section included in the spherical portion 24, thermal stress is generated. Concentration is relieved, and cracks and the like can be prevented from occurring at high speed and high load.

[0069]

As described above, in the direct injection diesel engine according to the first aspect of the present invention, the intake / exhaust valves are inclined with respect to the cylinder center line so that their valve faces face each other, and the combustion chamber ceiling wall is provided. Is a combustion chamber structure that has a spherically curved spherical surface that is almost in contact with each valve face of the intake / exhaust valve in the closed position, and a flat surface that extends around the spherical surface and extends in a plane orthogonal to the cylinder center line. Therefore, the volume of the combustion chamber is concentrated in the cavity to increase the air utilization rate, the damping of the swirl force generated in the combustion chamber by the depression of the valve recess is suppressed, and the radial direction from the fuel injection valve to the combustion chamber is increased. Suppresses the fuel spray injected into the valve recess from entering the H
Smoke emissions such as C and SOF can be reduced.

In the direct injection diesel engine of the second aspect, the radius of the spherical surface portion is set to be substantially equal to the radius of the cavity so that the piston is defined between the spherical surface portion and the cavity near the top dead center. The surface area of the combustion chamber is minimized, so that the amount of heat released from the combustion gas to the ceiling wall of the combustion chamber and the cylinder is suppressed, thereby reducing fuel consumption.

In the direct injection type diesel engine according to the third aspect of the present invention, a portion of the ceiling wall of the combustion chamber where adjacent valve faces are closest to each other is curved in an arc shape with its cross section included in the spherical portion. This alleviates the concentration of thermal stress and prevents the occurrence of cracks or the like at high speed and high load.

In the direct injection diesel engine according to the fourth aspect, since the intake / exhaust valves are inclined with respect to the cylinder center line so that their valve faces face each other, they are parallel on the intake / exhaust valves. Extending to 2
The spacing between the camshafts of the book is secured, and the interference of the cams is avoided. As a result, a valve operating mechanism such as a rocker arm provided between the intake / exhaust valve and the cam becomes unnecessary, and the number of parts can be reduced, and the weight and cost can be reduced.

In the direct injection type diesel engine according to the fifth aspect of the present invention, in the low speed low load region, the combustion control is performed so that the swirl ratio is increased and the fuel injection timing is delayed compared with the medium speed medium load region. Burning,
Since the ignition delay period becomes long, the NOx concentration can be reduced, the swirl power can be increased, and the air utilization rate of the combustion chamber can be sufficiently obtained to reduce the smoke concentration.

[Brief description of drawings]

FIG. 1 is a sectional view of an engine showing an embodiment of the present invention.

FIG. 2 is a plan view of a combustion chamber ceiling wall and the like.

FIG. 3 is a system diagram showing a control system of the engine.

FIG. 4 is a control characteristic diagram of the EGR rate.

FIG. 5 is a control characteristic diagram of a swirl ratio.

FIG. 6 is a control characteristic diagram of fuel injection timing.

FIG. 7 is an explanatory view of a combustion state of the same.

FIG. 8 is a sectional view of an engine showing another embodiment.

FIG. 9 is a plan view of a combustion chamber ceiling wall showing still another embodiment.

FIG. 10 is a sectional view of an engine showing a conventional example.

[Explanation of symbols]

 1 Cylinder 2 Piston 5 Cavity 8 Exhaust Port 9 Intake Valve 9a Valve Face 10 Exhaust Valve 10a Valve Face 11 Fuel Injection Valve 13 Camshaft 14 Camshaft 15 Intake Cam 16 Exhaust Cam 17 Valve Seat 18 Valve Seat 21 Piston Top 22 Combustion Chamber Ceiling wall 23 Plane part 24 Spherical part 27 Valve recess 28 Valve recess

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location F02B 23/06 F02B 23/06 B

Claims (5)

[Claims] Claim: What is claimed is: 1. A cavity that is recessed in a top surface of a piston, a combustion chamber ceiling wall that defines a combustion chamber between the piston, and a fuel that is attached to a central portion of the combustion chamber ceiling wall and injects fuel. Injection valves, multiple intake ports that open to the combustion chamber ceiling wall to introduce intake air, multiple intake valves that open and close each intake port, and multiple exhaust ports that open to the combustion chamber ceiling wall to discharge exhaust gas And a plurality of exhaust valves that open and close each exhaust port, the intake / exhaust valves are inclined with respect to a cylinder center line so that respective valve faces face each other, and the combustion chamber ceiling wall is It has a spherically curved spherical portion that is in close contact with each valve face of the intake / exhaust valve in the valve closing position, and a flat portion that is located around the spherical portion and spreads in a planar shape orthogonal to the cylinder center line. Direct-injection diesel engine, wherein the door. 2. The direct injection diesel engine according to claim 1, wherein the radius of the spherical surface portion is set to be substantially equal to the radius of the cavity. 3. A radius of a spherical portion is larger than a radius of a reference arc S when an arc centered on a cylinder center line passing through a portion where adjacent valve faces of the combustion chamber ceiling wall are closest to each other is defined as a reference arc S. The direct injection diesel engine according to claim 1 or 2, wherein the diesel engine is set. 4. The two intake / exhaust camshafts for driving the intake / exhaust valves to open and close are provided side by side above the intake / exhaust valves. Direct injection diesel engine described in. 5. The combustion control means for increasing the swirl ratio and delaying the fuel injection timing in the low speed and low load region compared to the medium speed and medium load region is provided, as claimed in any one of claims 1 to 4. Direct injection diesel engine.