JP7306832B2 - cylinder head - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cylinder head in a spark ignition internal combustion engine that uses an injector to inject fuel into an intake port.

2. Description of the Related Art In a PFI type internal combustion engine that uses an injector to inject fuel into an intake port, one of the problems is the port wet phenomenon in which fuel adheres to the inner surface of the intake port. If the fuel adheres to the inner surface of the intake port, it causes incomplete combustion and PM (particulate matter) is likely to be generated.

On the other hand, in order to improve the mixing of fuel, a tumble flow is formed in the cylinder bore during the intake/compression process. It is effective to bring the center line of the cylinder as close as possible to the axis of the cylinder bore.

Therefore, in Patent Document 1, in a configuration in which the injector is arranged above the intake port, the angle between the intake port and the axis of the cylinder bore is made as small as possible to promote the generation of tumble flow, and during cold operation of the engine. , the shutter valve is throttled to increase the flow rate of the intake air, while assist air is supplied to the injector to promote atomization of the fuel.

On the other hand, in Patent Document 2, in a structure in which an intake system member is arranged between cylinder banks of a V-type engine, an injector is arranged below an intake port, and the intake port is arranged in an S shape when viewed from the crankshaft center direction. A technique is disclosed for preventing fuel from adhering to the lower surface of the intake port by forming it into a gently curved shape.

Japanese Patent No. 3937547 Japanese Patent No. 2759334

As mentioned above, it is effective to raise the intake port as much as possible to generate a strong tumble flow. There's a problem.

Therefore, if the intake port is to be erected as much as possible with the injector positioned above the intake port, the injector must be attached to the intake manifold to separate it from the valve operating member, or the valve operating member must be positioned higher than the injector. In any case, the size and weight of the internal combustion engine is increased , which not only worsens fuel efficiency, but also increases the fuel scattering distance and reduces the flow velocity, causing the fuel to flow into the intake air. There is a possibility that it will become difficult to sufficiently achieve the purpose of preventing the port wetting phenomenon, because the tendency to adhere to the upper surface of the intake port along with the flow increases.

On the other hand, when the injector is arranged below the intake port as in Patent Document 2, the intake port can be erected as much as possible while preventing interference between the injector and the valve operating member. There is a risk that the straightness of the flow will decrease and the flow resistance will increase, which will be disadvantageous in strengthening the tumble flow.

The present invention is made to improve such a situation.

The present invention is directed to a cylinder head, and this cylinder head, as in claim 1,
"An intake port is formed in a straight line as a whole from the beginning to the end thereof, and below the intake port , an injector is arranged at a height toward the tip so that the direction of fuel injection is toward the upper surface of the intake port. a cylinder head arranged in a tilted posture in which the nozzle of the injector is exposed on the lower surface of the intake port,
The recess includes a first inclined bottom portion where the nozzle of the injector is arranged, a second inclined bottom portion located downstream of the first inclined bottom portion, and a third inclined bottom portion located upstream of the first inclined bottom portion. having a bottom and
When viewed in the axial direction of the crankshaft, the first inclined bottom portion and the third inclined bottom portion convexly intersect toward the intake port, and the first inclined bottom portion and the second inclined bottom portion extend toward the intake port. It intersects concavely."
It is configured.

In the present invention, since the injector is arranged below the intake port, the intake port can be erected on the side of the axis of the cylinder bore while preventing interference between the injector and the valve operating member. Therefore, the injector can be arranged as close to the intake valve as possible without increasing the height of the valve operating member, and the length of the intake port can be shortened as much as possible. This contributes to the generation of a strong tumble flow while promoting compactness and weight reduction of the internal combustion engine. As a result, it can contribute to the improvement of fuel efficiency.

In addition, since the intake port has a straight posture, the intake air flows into the cylinder bore with a strong directivity with almost no flow resistance. Therefore, the intake port can be erected as close to the axis of the cylinder bore as possible, and a strong tumble flow can be generated inside the cylinder bore. As a result, complete combustion can be achieved, contributing to improved fuel efficiency and reduced PM.

When the intake port is formed with a tapered tip as in the embodiment, the flow velocity of the intake air flowing into the cylinder bore increases, so that the tumble flow can be further strengthened. In addition, when the flow velocity of the intake air increases, the effect of pushing the fuel injected from the injector toward the cylinder bore increases, so there is an advantage that the fuel can be prevented from adhering to the upper surface of the intake port.

Now, whether the injector is placed above or below the intake port, the nozzle (tip) of the injector will be exposed in the recess formed in the intake port. is formed, a drift phenomenon occurs in which the intake air turns toward the interior of the recess, fuel is guided toward the inner surface of the intake port, and the fuel may adhere to the inner surface of the intake port.

Regarding this point, if the configuration of the present invention is adopted, the intake air flowing toward the first and second inclined bottom portions of the recess is guided downward by the third inclined bottom portion, so that the intake air flows over the recess. It is possible to prevent the drift phenomenon that tends to occur and involve the inside of the recess. This prevents the fuel from adhering to the lower surface of the intake port, thereby greatly suppressing the generation of PM.

It is a longitudinal front view of an embodiment. (A) is an enlarged view of the main part of FIG. 1, (B) is a cross-sectional view taken along the line BB of (A), and (C) is a longitudinal front view of the main part of a comparative example (another example). It is a figure which shows an effect|action. Both (A) and (B) are graphs for explaining the effect. It is a figure which shows a modification with (A) and (B).

Next, embodiments of the present invention will be described based on the drawings. In the following, the terms front-rear and left-right are used to specify directions, and the front-rear direction is the direction of the crank axis, and the left-right direction is the direction orthogonal to the crank axis and the cylinder bore axis. A front view is a crank axial direction view.

(1). Basic Structure First, the first embodiment shown in FIGS. 1 to 4 will be described. The basic structure of the internal combustion engine is the same as that of the conventional engine. and a cylinder head 3 fixed to the Naturally, the piston 4 is slidably arranged in the cylinder bore 1 . Further, the cylinder block 2 is formed with an annular block-side water jacket 5 surrounding the group of cylinder bores 1 .

On the other hand, a group of mountain-shaped combustion chambers 6 is formed in the cylinder head 3 so as to face each cylinder bore 1, and each combustion chamber 6 has an intake port 7 and an exhaust port 8 arranged in a pair on the left and right sides. The opening is closed. In this embodiment, the pair of front and rear intake ports 7 are each independently opened to the intake side surface 9 of the cylinder head 3, and below each intake port 7, an injector 10 for fuel injection is arranged. . Therefore, this embodiment is a dual-port dual-injector type.

A branch pipe 11 a of an intake manifold 11 is connected to the intake side surface 9 of the cylinder head 3 . , one branch pipe 11a and two intake ports 7 may be connected. Further, the pair of front and rear intake ports 7 may be configured such that the inlets are connected at a collective portion and separated from the middle by a partition wall.

On the other hand, the pair of front and rear exhaust ports 8 are assembled into one and open to the exhaust side surface of the cylinder head 3, and each intake port 7 communicates with a collective passage formed inside the cylinder head 3. can be adopted. In the former structure, exhaust ports corresponding to the number of cylinder bores 1 are opened in the exhaust side surface of the cylinder head 3, and in the latter structure, one exhaust port is opened in the exhaust side surface of the cylinder head 3.

A spark plug 12 is arranged in the central portion of the combustion chamber 6 . A head-side water jacket 15 through which cooling water flows is also formed in the cylinder head 3 .

A downstream end 7 b of the intake port 7 is opened and closed by an intake valve 13 , and an upstream end (starting end) of the exhaust port 8 is opened and closed by the intake valve 13 . Both valves 13 and 14 are opened and closed by cam shafts that constitute valve mechanisms, although it is not necessary to explain them. The valves 13 and 14 have valve shafts (valve stems) 13a and 14a and head portions, and the cylinder head 3 is fitted with a valve seat (not shown) against which the head portions come into contact.

(2). Injector The injector 10 has a body 18 with a nozzle formed at its tip, and the body 18 incorporates a solenoid valve for controlling fuel injection. The body 18 is formed with a downward facing socket 19, and a plug (not shown) connected to the socket 19 is connected to an ECU (engine control unit). Each injector 10 is also connected to a delivery pipe 21 that extends in the axial direction of the crankshaft.

A nozzle provided at the tip of the body 18 that constitutes the injector 10 is exposed in a recess 22 formed in the intake port 7 , and the fuel passes through the recess 22 and is injected into the intake port 7 . The fuel ejection area 23 is a conical space, but the tip of the ejection area 23 is significantly shifted upstream from the downstream end 7 b of the intake port 7 . Therefore, the fuel is jetted toward the upper surface of the intake port 7 and mixes with the intake air while flowing through the intake port 7 . A body 18 of the injector 10 is mounted in a mounting hole 25 with an O-ring 24 interposed therebetween.

As shown in FIG. 2B, the cross-sectional shape of the intake port 7 is basically circular, and the recess 22 has a substantially U-shaped cross section. Further, the recess 22 has a first inclined bottom portion 22a where the tip surface of the injector 10 is exposed, and a second inclined bottom portion 22b located downstream of the first inclined bottom portion 22a. extends to the downstream end 7b of the intake port 7 and gradually becomes shallower. Therefore, the recess 22 has a roughly triangular cross-sectional shape when viewed from the crank axial direction.

Further, the intake port 7 is tapered such that the cross-sectional area gradually decreases from the upstream end 7a toward the downstream end 7b, and the axis (center line) O1 is straight. . Therefore, the intake port 7 extends in a straight line. The cross-sectional shape of the intake port 7 can also be formed in a substantially rectangular, elliptical, or oval shape.

On the other hand, the injector 10 is arranged in a tilted posture that falls on the outlet side of the intake port 7 so as to rise toward the tip, and the axial center (center line) O2 of the injector 10 and the axial center O1 of the intake port 7 are aligned. An included angle .theta.1 widened (horizontally widened) toward the side of the intake side surface 9 is about 60.degree. Therefore, the downward widening included angle θ2 formed by the axis (center line) O2 of the injector 10 and the center line O1 of the intake port 7 is about 120°, which is an obtuse angle larger than 90°. . The fuel is injected obliquely upward toward the downstream side of the intake port 7 .

An upwardly widening included angle θ3 formed by the axis O1 of the intake port 7 and the axis O3 of the cylinder bore is slightly larger than 60° (approximately 65°). Therefore, an included angle θ4 formed by the axis O3 of the cylinder bore, the axis O2 of the injector 10, and the axis O3 of the cylinder bore is about 125°.

The portion of the lower surface (bottom surface) of the intake port 7 upstream of the first inclined bottom portion 22a of the recess 22 is the lower surface of the upstream end portion 7a of the intake port 7 and the lower surface of the downstream end portion (terminus) 7b. A third inclined bottom portion 27 is inclined so as to be lower toward the recess 22 with respect to a reference bottom line 26 connecting the . Note that the reference bottom line 26 may be rephrased as an imaginary bottom line (bottom surface) of the intake port 7 assuming that the recess 22 does not exist. The angle θ5 formed by the third inclined bottom portion 27 and the reference bottom line 26 is set to about 8°, but it is estimated that about 5 to 10° will suffice. Regarding the recess 22, when viewed from the crankshaft line direction, the first inclined bottom portion 22a and the third inclined bottom portion 27 intersect in a concave shape toward the intake port 7, and the first inclined bottom portion 22a and the third inclined bottom portion 27 intersect with each other. It intersects in a convex shape toward the intake port 7 .

(3) Summary As shown in FIGS. 2A and 3, when the intake valve 13 is opened, intake air flows into the cylinder bore 1 and fuel is injected from the injector 10 . Then, the fuel is jetted obliquely upward toward the upper surface of the intake port 7, and is pushed by the intake air to flow toward the cylinder bore 1 while being mixed with the intake air.

In this embodiment, since the injector 10 is arranged below the intake port 7, the intake port 7 is kept in an upright position as much as possible without interfering with a valve operating member such as a rocker arm that drives the intake valve 13. can be formed into Further, since the intake port 7 is of a straight type, the air flows into the cylinder bore 1 with strong directivity without resistance. Furthermore, since the intake port 7 is tapered, the flow velocity of the intake air entering the cylinder bore 1 is higher than the flow velocity of the intake air flowing into the intake port 7 .

In this way, the intake port 7 stands up as much as possible and the intake air tends to flow downward inside the cylinder bore 1, the intake air smoothly flows into the cylinder bore 1 without resistance, and the intake air increases the flow velocity and flows into the cylinder bore 1. , a strong tumble flow can be formed in the cylinder bore 1. As a result, the mixture of fuel with intake air can be improved, and complete combustion can be achieved.

The fuel is ejected from the injector 10 in a straight line, but is pushed by the intake air. As it transforms, it mixes with the intake air. In this case, since the injection amount of fuel is proportional to the amount of intake air, the fuel is sent to the cylinder bore 1 along with the intake air without adhering to the upper surface of the intake port 7 .

When comparing the case where the fuel adheres to the upper surface of the intake port 7 and the case where the fuel adheres to the lower surface, the fuel adhered to the upper surface tends to separate due to gravity. understood to be less.

Now, FIG. 2(C) shows a mode in which the bottom surface (bottom surface) of the intake port 7 is left at the reference bottom line 26 at the portion 29 on the upstream side of the recess 22 without forming the inclined bottom portion 27 . However, in this embodiment, according to computer analysis, the intake air flows into the recess 22 as indicated by an arrow 30, causing the intake air to flow into the second inclined bottom portion 22b of the recess 22 as indicated by an arrow 31. There was a case where a drift phenomenon flowing toward the

In particular, when the injector 10 is laid largely on the horizontal side, the drift phenomenon appears remarkably. When this drift phenomenon occurs, the fuel ejected from the injector 10 is likely to be pushed against the lower surface of the intake port 7 (the lower surface of the recess 22). There is concern that it will become easier to adhere.

On the other hand, if the third inclined bottom portion 27 is formed in the upstream portion of the recess 22 as in the embodiment, the intake air does not flow into the recess 22 as indicated by the arrow 32 in FIG. 2(A). It flows smoothly without any occurrence. Therefore, it is possible to prevent the fuel ejected from the injector 10 from adhering to the lower surface of the intake port 7 (the lower surface of the recess 22).

Now, in the case of FIG. 2(C) where the third inclined bottom portion 27 does not exist, the speed of the intake air drops sharply at the starting end of the first inclined bottom portion 22a , so that the intake air is sucked into the recess 22 due to the pressure drop. As a result, it is presumed that the above-described drift occurs (this drift is presumed to appear more remarkably as the crossing angle between the lower surface of the intake port 7 and the front end surface of the recess 22 increases).

On the other hand, when the slide -like third inclined bottom portion 27 is formed in the upstream portion of the recess 22, the cross-sectional area of the intake port 7 gradually increases, so that the flow velocity of the intake air flowing along the lower surface of the intake port 7 increases. As a result, the intake air flows smoothly to the downstream side without going around the recess 22 .

The inventors of the present application simulated the flow of intake air for a structure in which the bottom surface of the intake port 7 is formed with a jump table-like inclined surface 33 that rises toward the recess 22, as shown by the dashed line in FIG. 2(C). However, in this case, the drift phenomenon in which the intake air circulates into the recess 22 appears even more strongly. Therefore, it is understood that the phenomenon of drift is greatly influenced by the rapid change in the flow velocity (pressure) of the intake air.

FIG. 4A shows an embodiment in which a slide-shaped third inclined bottom portion 27 is provided, a comparative example 1 (normal shape) in which the bottom surface of the intake port 7 is left as the reference bottom line 26, and FIG. The result of analysis of the amount of fuel adhering to the intake port 7 is shown for Comparative Example 2 in which the inclined surface 33 in the shape of a jumping platform is formed as indicated by the dashed line.

Regarding FIGS. 4A and 4B, the relationship between the crank angle and the amount of fuel adhering to the intake port 7 is supplemented as follows. That is, assuming that the piston is positioned at the top dead center of the explosion process and the crank angle is 0°, the opening of the intake valve 13 and the fuel injection by the injector 10 are started at about 380°, and the fuel injection is stopped at about 480°. Assuming that the intake valve 13 is closed at about 540°, the amount of fuel adhered increases from the start to the end of injection, and then stabilizes at the maximum amount ignoring evaporation. there is The inner diameter of the intake port 7 was about 20 mm on average.

The embodiment in which the slide-shaped third inclined bottom portion 27 is formed has the smallest amount of adhered fuel, and the comparative example 2 in which the sloping surface 33 of the sloping stage is formed has the largest amount of adhered fuel. However, it is understood that such results are obtained depending on the presence or absence of drift as described above.

FIG. 4B shows the relationship between the angle θ4 formed between the axis O3 of the cylinder bore 1 and the axis O2 of the injector 10 and the amount of adhered fuel. From this graph, it can be seen that the amount of adhering fuel is the smallest when θ4 is about 110°, and the amount of adhering fuel increases as θ4 decreases (as θ2 increases). It is understood that this is because the tendency of the fuel to be pushed to the lower surface of the intake port 7 by the intake air increases as θ2 increases.

The amount of adhered fuel is slightly different between (A) and (B) in FIG. 4, but this is due to subtle differences in analysis conditions. According to the analysis results of the inventors of the present application, the fuel adhesion amount is minimum when θ1 is 68.5°, and when θ1 is smaller than 68.5°, the fuel tends to be pushed downward by the intake air. Therefore, the amount of adhering fuel increases.

It should be noted that θ1 and θ2 have an inverse correlation such that when one increases, the other decreases. When .theta.1 is larger than 90.degree., the penetration force of the fuel against the intake air becomes strong, and the fuel easily adheres to the upper surface of the intake port 7. Therefore, .theta.1 should be smaller than 90.degree. Conversely, in order to suppress adhesion of fuel, θ2 must be set to an obtuse angle larger than 90°.

On the other hand, if θ2 is too large, not only will the fuel easily adhere to the lower surface of the intake port 7, but the fuel will also gather at the lower portion of the intake port 7, thereby deteriorating the mixing of fuel and intake air. Therefore, θ2 also has a suitable upper limit. Regarding θ1, it can be said that a preferable angle is in the range of 10° up and down with a central value of about 70°. .).

Also, from the aspect of mixing the fuel and the intake air as much as possible in the intake port 7, the fuel injection area 23 is located upstream of the terminal end 7b of the intake port 7, and upstream of the intake port 7 as much as possible. It is preferably located in In the illustrated example, the fuel ejection area 23 is positioned upstream of the longitudinal middle portion of the intake port 7. With this extent, the fuel can be mixed with the intake air as evenly as possible even within the intake port 7. .

(4).Modified example/others Fig. 5 shows a modified example. In the example shown in (A), the terminal end of the second inclined bottom portion 22b is positioned in the middle of the intake port 7. As shown in FIG. In this embodiment, the volume of recess 22 is smaller than in the previous examples.

In the example shown in (B), on the lower surface of the intake port 7 on the upstream side of the recess 22, a slide-like fourth downward inclined bottom portion 34 inclined downward toward the downstream side and a fourth 4 and a third inclined bottom portion 27 rising from the end of the inclined bottom portion 34 toward the reference bottom line 26 is formed. Accordingly, a guide recess having a downward fourth inclined bottom portion 34 and an upward third inclined bottom portion 27 is formed in a portion of the lower surface of the intake port 7 upstream of the first inclined bottom portion 22a. ing.

In the example of (B), since the flow velocity of the intake air temporarily decreases due to the presence of the fourth downwardly inclined bottom portion 34 , it is presumed that the intake air flows so as to jump over the recess 22 . Therefore, unlike the form shown by the dashed line in FIG. 2C, it is presumed that the drift phenomenon in which the intake air flows into the recess 22 can be prevented or greatly suppressed.

Although the embodiments of the present invention have been described above, the present invention can be embodied in various other ways. For example, the intake port 7 can be made large so as to intersect the cylinder bore axis at about 45°.

The present invention can be embodied in a PFI internal combustion engine. Therefore, it can be used industrially.

REFERENCE SIGNS LIST 1 cylinder bore 2 cylinder block 3 cylinder head 6 combustion chamber 7 intake port 7a upstream end (starting end) of intake port
7b Downstream end of intake port (terminus)
10 injector 13 intake valve 18 injector body 22 recess
22a first inclined bottom
22b second inclined bottom
23 Fuel injection area 26 Reference bottom line 27 Third inclined bottom O1 Intake port axis (center line)
Axis of O2 injector Axis of O3 cylinder bore

Claims (1)

An intake port is formed in a straight line as a whole from its starting end to its terminal end, and below the intake port , an injector is arranged so that the fuel injection direction is directed toward the upper surface of the intake port. A cylinder head arranged in a rising inclined posture to form a recess in which the nozzle of the injector is exposed on the lower surface of the intake port,
The recess includes a first inclined bottom portion where the nozzle of the injector is arranged, a second inclined bottom portion located downstream of the first inclined bottom portion, and a third inclined bottom portion located upstream of the first inclined bottom portion. having a bottom and
When viewed in the axial direction of the crankshaft, the first inclined bottom portion and the third inclined bottom portion convexly intersect toward the intake port, and the first inclined bottom portion and the second inclined bottom portion extend toward the intake port. intersecting concavely,
cylinder head.

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