JP2018003713A - Design method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a design method for internal combustion engine in which a superior combustion of mixture at a combustion chamber can be realized.SOLUTION: When a location of a wall surface 151 of a recess 15 of a cylinder head 11 that is positioned outside rather than an intake valve 19 and an exhaust valve is applied as an outer wall surface 152, a wall surface oblique angle ξ that is an angle formed by a connecting location 153 with a fixing surface 111 at the outer wall surface 152 at a section including a central axis of a cylinder 14 along an extending direction of a crank shaft and the fixing surface 111 is 90° or more. When an ignition time target value is more than a strength of a tumble flow at the intake stroke time, the wall surface angle ξ is set to an angle less than a reference oblique angle and in turn when the ignition time target value is less than a strength of the tumble flow at the intake stroke time, the wall surface oblique angle ξ is set to an angle larger than the reference oblique angle.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for designing an internal combustion engine for designing an internal combustion engine that generates a tumble flow in the combustion chamber by introducing intake air from an intake port into the combustion chamber.

  Patent Document 1 describes an example of an internal combustion engine that can generate a tumble flow in the combustion chamber by introducing intake air from the intake port into the combustion chamber. In such an internal combustion engine, it is possible to strengthen the tumble flow during the intake stroke by devising the shape of the intake port.

JP 2013-194585 A

  The intensity of the tumble flow during the intake stroke is made equal to the target value at that time (hereinafter also referred to as “target value during the intake stroke”), and the intensity of the tumble flow at the subsequent ignition timing is set to the target value (hereinafter referred to as “the target value”). When the tumble flow is appropriately controlled, the air-fuel mixture can be burned satisfactorily. However, when the shape of the intake port is designed so that the strength of the tumble flow during the intake stroke is equal to the target value during the intake stroke, the strength of the tumble flow during the subsequent ignition timing is not always equal to the target value of the ignition timing. . As described above, when the strength of the tumble flow at the ignition timing is deviated from the target value at the ignition timing, even if the strength of the tumble flow at the intake stroke is equal to the target value at the intake stroke, the air-fuel mixture cannot be burned well. There is a fear.

  An object of the present invention is to provide a design method of an internal combustion engine that can realize good combustion of an air-fuel mixture in a combustion chamber.

  An internal combustion engine design method for solving the above problem is a design method for designing an internal combustion engine that generates a tumble flow in the combustion chamber by introducing intake air from the intake port into the combustion chamber in the cylinder. is there. In the internal combustion engine manufactured based on the design method, the intake port is connected to the combustion chamber and is bent at a predetermined curvature, and is connected to the upstream end of the downstream passage and has a predetermined An upstream passage extending in the extending direction. The combustion chamber is configured by an internal space of the cylinder and a recess communicating with the internal space of the cylinder head. Further, in the cylinder head, when the surface attached to the cylinder block with the gasket sandwiched is used as the mounting surface, and the portion located outside the intake valve and the exhaust valve in the wall surface of the depression is the outer wall surface, A wall surface inclination angle, which is an angle formed by a connection portion of the outer wall surface with the mounting surface and the mounting surface in a cross section along the extending direction of the crankshaft of the engine and including the central axis of the cylinder, is 90 ° or more. . In the internal combustion engine design method, the tumble flow during the intake stroke is gradually reduced as the wall surface inclination angle becomes smaller and when the coefficient that becomes 1 when the wall surface inclination angle is equal to the reference inclination angle is defined as the specified coefficient. Assuming that the product of the strength of the engine and the specified coefficient is the strength of the tumble flow at the ignition timing, the target value of the tumble flow at the ignition timing is the target value of the tumble flow during the intake stroke. When the above is set, the wall inclination angle is set to an angle equal to or smaller than the reference inclination angle, while when the ignition timing target value is set to be less than the strength of the tumble flow during the intake stroke, the wall inclination angle is set to an angle larger than the reference inclination angle. .

  The intake port of the internal combustion engine has an upstream passage extending in a predetermined extending direction, and a downstream passage connected to the downstream end of the upstream passage and bent at a predetermined curvature radius. In this case, the strength of the tumble flow generated in the combustion chamber during the intake stroke is in accordance with the inclination angle of the upstream passage with respect to the central axis of the cylinder and the curvature radius of the downstream passage.

Further, in the internal combustion engine that generates the tumble flow in the combustion chamber in this way, the present inventor has obtained the following knowledge.
-The strength of the tumble flow at the ignition timing decreases as the wall inclination angle increases and the combustion chamber volume decreases.
When the wall inclination angle is equal to a certain angle, the strength of the tumble flow at the ignition timing can be made equal to the strength of the tumble flow at the intake stroke, and when the wall inclination angle is larger than the certain angle, the tumble flow at the ignition timing The strength of the flow can be made smaller than the strength of the tumble flow during the intake stroke, and when the wall inclination angle is smaller than a certain angle, the strength of the tumble flow at the ignition timing is greater than the strength of the tumble flow during the intake stroke. What you can do.

  Therefore, the present inventor defines a coefficient that gradually decreases as the wall surface inclination angle increases within a range where the wall surface inclination angle is 90 ° or more, and equals 1 when the wall surface inclination angle is equal to the reference inclination angle. In the case of a coefficient, the wall surface inclination angle is set on the assumption that the product of the tumble flow intensity during the intake stroke multiplied by the specified coefficient becomes the tumble flow intensity at the ignition timing. That is, when the ignition timing target value is made equal to the strength of the tumble flow during the intake stroke, the wall surface inclination angle is made equal to the reference inclination angle. Further, when the ignition timing target value is made smaller than the strength of the tumble flow during the intake stroke, the wall surface inclination angle is made larger than the reference inclination angle. When the ignition timing target value is made larger than the strength of the tumble flow during the intake stroke, the wall surface inclination angle is made smaller than the reference inclination angle. In this way, by setting the wall inclination angle based on the magnitude relationship between the intensity of the tumble flow during the intake stroke and the target ignition timing value, the target value of the tumble flow intensity during the intake stroke and the target ignition timing value are determined. Regardless of the size relationship, the inclination angle of the upstream passage of the intake port with respect to the central axis of the cylinder and the radius of curvature of the downstream passage of the intake port can be set.

  When an internal combustion engine is manufactured based on each value set in this manner, the internal combustion engine has the same tumble flow intensity during the intake stroke as the target value at that time, but the tumble flow at the subsequent ignition timing. Can be made equal to the ignition timing target value. Therefore, good combustion of the air-fuel mixture in the combustion chamber can be realized.

Sectional drawing which shows typically a part of internal combustion engine designed by the design method of the internal combustion engine of embodiment. The figure which shows the shape of the cross section along the extending | stretching direction of a crankshaft and including the central axis of a cylinder of the internal combustion engine. The graph which shows the relationship between a port inclination | tilt angle and a curvature radius normalization value, and the intensity | strength of the tumble flow in the intake stroke. The graph which shows the relationship between a wall surface inclination angle and a regulation coefficient.

An embodiment embodying a design method for an internal combustion engine will be described below with reference to FIGS.
FIG. 1 shows an internal combustion engine 10 designed and manufactured by the internal combustion engine design method of the present embodiment. As shown in FIG. 1, in the internal combustion engine 10, a cylinder head 11 is attached to a cylinder block 13 via a gasket 12. In the present specification, the surface of the cylinder head 11 that is attached to the cylinder block 13 via the gasket 12 (the lower surface in the figure) is also referred to as an “attachment surface 111”.

  The cylinder block 13 is provided with a plurality of cylinders 14 (only one is shown in FIG. 1) arranged in a direction orthogonal to the paper surface in FIG. The cylinder head 11 is provided with the same number of recesses 15 as the number of cylinders 14, and each recess 15 communicates with the internal space 141 of the corresponding cylinder 14. A combustion chamber 16 is constituted by the internal space 141 and the recess 15 of the cylinder 14 communicating with each other.

  As shown in FIG. 1, the cylinder head 11 is provided with an intake port 17 and an exhaust port 18 connected to the combustion chamber 16. Opening and closing of the intake port 17 with respect to the combustion chamber 16 is performed by an intake valve 19, and opening and closing of the exhaust port 18 with respect to the combustion chamber 16 is performed by an exhaust valve 20.

  The intake port 17 is connected to the combustion chamber 16 and is bent at a predetermined radius of curvature, and the upstream passage is connected to the upstream end of the downstream passage 171 and extends in a predetermined extending direction. 172. In this specification, the inclination angle of the upstream passage 172 in the extending direction with respect to the center line of the cylinder 14 is referred to as “port inclination angle θ”, and the curvature radius of the downstream passage 171 is referred to as “port curvature radius R”. .

  During the intake stroke, the intake valve 19 is opened, and intake air is introduced into the combustion chamber 16 via the intake port 17. Then, in the combustion chamber 16, the intake air is introduced through the intake port 17, thereby generating a tumble flow as indicated by an arrow in FIG. 1. In the compression stroke, which is the next stroke of the intake stroke, the air-fuel mixture containing intake air and fuel is compressed by moving the piston 21 toward the top dead center, and is mixed by ignition by the spark plug 22 shown in FIG. Qi is burnt. The force generated by the combustion of the air-fuel mixture is transmitted to the crankshaft extending in the direction orthogonal to the paper surface in FIG. In the subsequent exhaust stroke, the exhaust valve 20 is opened, and the exhaust generated in the combustion chamber 16 is discharged to the exhaust port 18.

  FIG. 2 shows a cross section of the internal combustion engine 10 along the extending direction of the crankshaft and including the central axis of the cylinder 14, that is, a cross section taken along the line 2-2 in FIG. As shown in FIG. 2, in the wall surface 151 of the recess 15 of the cylinder head 11, when the portion located outside the intake valve 19 and the exhaust valve 20 is the outer wall surface 152, the lower end portion of the outer wall surface 152 in the figure is The connection portion 153 is connected to the mounting surface 111 of the cylinder head 11. In the cross section shown in FIG. 2, when the angle formed by the connection part 153 of the outer wall surface 152 and the mounting surface 111 is the wall surface tilt angle ξ, the wall surface tilt angle ξ is 90 ° or more.

Next, a method for designing the internal combustion engine of the present embodiment will be described.
The internal combustion engine design method according to the present embodiment includes a first step of designing the intake port 17 and a second step of designing the combustion chamber 16. In the first step, the port curvature radius R and the port inclination angle θ are set so that the strength of the tumble flow during the intake stroke becomes equal to the target value during the intake stroke. In the second step, assuming that the strength of the tumble flow during the intake stroke is equal to the target value during the intake stroke, the wall inclination angle ξ is set so that the strength of the tumble flow during the ignition timing is equal to the target value during the ignition timing. Is done.

First, the first step will be described.
As a result of various experiments and simulations, the present inventor has obtained the following knowledge.
-Until the port inclination angle θ of the upstream passage 172 reaches a certain value, the strength of the tumble flow during the intake stroke increases as the port inclination angle θ increases, but after the port inclination angle θ exceeds a certain value As the port inclination angle θ increases, the strength of the tumble flow during the intake stroke decreases.
The strength of the tumble flow during the intake stroke increases as the port curvature radius R of the downstream passage 171 increases.
・ Decomposes the strength of the tumble flow during the intake stroke into a component where the port inclination angle θ contributes to the strength of the tumble flow during the intake stroke and a component where the port curvature radius R contributes to the strength of the tumble flow during the intake stroke Show it.

  The following relational expressions (Expression 1), (Expression 2), and (Expression 3) are obtained by formulating the above knowledge. That is, in relational expression (1), “F (θ)” is a component in which the port inclination angle θ contributes to the strength of the tumble flow during the intake stroke, and “Xa”, “Xb”, and “Xc” This is a constant determined from the cross-sectional shape of the passage 172, the friction coefficient of the wall surface of the upstream passage 172, and the like. In the relational expression (Expression 2), “F (R)” is a component in which the port curvature radius R contributes to the strength of the tumble flow during the intake stroke, and “D” is the diameter of the umbrella portion of the intake valve 19. is there. In the relational expression (Formula 2), “Ya” and “Yb” are constants depending on the structure and processing method of the valve seat for the intake valve 19, and are between the wall surface of the downstream passage 171 and the valve seat. The larger the step, the larger.

F (θ) = Xa · θ ² + Xb · θ + Xc (Formula 1)
F (R) = Ya · Ln (R / D) + Yb (Formula 2)
Ft_in = F (θ) × F (R) (Formula 3)
The value obtained by dividing the port curvature radius R by the diameter D of the umbrella portion of the intake valve 19 is a value obtained by normalizing the port curvature radius R (hereinafter also referred to as “curvature radius normalized value”). In this case, as the radius of curvature normalization value (= R / D) is increased from 1, the intensity of the tumble flow gradually increases during the intake stroke. This is because the larger the port curvature radius R, the lower the flow velocity when the intake air flows from the upstream passage 172 into the downstream passage 171 is suppressed. However, when the curvature radius normalized value reaches a certain level, the strength of the tumble flow during the intake stroke is unlikely to increase even after the curvature radius normalized value is further increased.

  And this inventor is the curvature radius normalized value when the strength of the tumble flow during the intake stroke becomes difficult to increase even if the curvature radius normalized value is increased, that is, the maximum value of the curvature radius normalized value, It was discovered that it can be expressed by the following relational expression (formula 4). In the relational expression (Formula 1), “RDMax” is the maximum value of the curvature radius normalized value. “Za” and “Zb” are constants that are set to larger values as the degree of decrease in the flow rate of the intake air in the intake port 17 is greater. As represented by this relational expression (Formula 4), the maximum value RDMax of the radius of curvature normalized value increases as the port inclination angle θ decreases.

RDMax = (Za / θ) + Zb (Formula 4)
Therefore, the range in which the strength of the tumble flow during the intake stroke can be changed by changing the curvature radius normalized value, that is, the port curvature radius R, can be expressed by the following relational expression (formula 5).

1 ≦ R / D ≦ (Za / θ) + Zb (Formula 5)
In the first step, the port inclination angle θ and the port curvature radius R are set using the above relational expressions (Expression 1), (Expression 2), (Expression 3), and (Expression 5). Specifically, the port inclination angle θ and the port curvature radius R are set after substituting the target value during the intake stroke into “Ft_in” in the relational expression (Expression 3).

  Incidentally, FIG. 3 shows a graph showing the relationship between the port inclination angle θ and the curvature radius normalized value (R / D) and the strength of the tumble flow during the intake stroke. In FIG. 3, a broken line DL is a line indicating the maximum value RDMax of the curvature radius normalized value. In FIG. 3, solid lines SL1, SL2, SL3, SL4, and SL5 represent the relational expression (Expression 3). That is, the solid line SL1 represents a relational expression (formula 3) when the target value during the intake stroke is set to the first value. The solid line SL2 represents the relational expression (formula 3) when the target value during the intake stroke is set to a second value larger than the first value, and the solid line SL3 represents the target value during the intake stroke. The relational expression (formula 3) when it is set to a third value larger than the value 2 is shown. A solid line SL4 represents a relational expression (equation 3) when the target value at the intake stroke is set to a fourth value larger than the third value, and a solid line SL5 represents the target value at the intake stroke. The relational expression (Formula 3) when set to a fifth value larger than the value of 4 is shown.

Next, the second step will be described.
The present inventor has found that the strength of the tumble flow at the ignition timing changes according to the wall surface inclination angle ξ. Specifically, when the wall surface inclination angle ξ is larger than a certain angle, the larger the wall surface inclination angle ξ, the smaller the volume of the combustion chamber 16, thereby maintaining the strength of the tumble flow as the piston 21 approaches the top dead center. It becomes difficult to do. That is, as the wall surface inclination angle ξ increases, the strength of the tumble flow at the ignition timing decreases. When the wall surface inclination angle ξ is equal to a certain angle, the strength of the tumble flow is maintained when the piston 21 is moving toward the top dead center. When the wall surface inclination angle ξ is smaller than a certain angle, the strength of the tumble flow is slightly increased when the piston 21 is moving toward the top dead center.

  Therefore, the present inventor created the following relational expression (formula 6) based on such knowledge. In the relational expression (Expression 6), “Ft_cmb” is the intensity of the tumble flow at the ignition timing, F (ξ) is a specified coefficient corresponding to the wall surface inclination angle ξ, and “Ft_in” is the value during the intake stroke. The strength of the tumble flow.

Ft_cmb = F (ξ) × Ft_in (Expression 6)
The specified coefficient F (ξ) has characteristics as shown in FIG. That is, as shown in FIG. 4, when the wall surface inclination angle ξ when the strength of the tumble flow at the ignition timing is equal to the strength of the tumble flow at the intake stroke is defined as the reference inclination angle ξTH, the specified coefficient F (ξ) Is 1 when the wall inclination angle ξ is equal to the reference inclination angle ξTH. Further, when the wall surface inclination angle ξ is an angle smaller than the reference inclination angle ξTH, the specified coefficient F (ξ) is larger than 1. When the wall surface inclination angle ξ is smaller than the reference inclination angle ξTH, the specified coefficient F (ξ) increases as the wall surface inclination angle ξ decreases. On the other hand, when the wall surface inclination angle ξ is larger than the reference inclination angle ξTH, the specified coefficient F (ξ) is smaller than 1. When the wall surface inclination angle ξ is larger than the reference inclination angle ξTH, the specified coefficient F (ξ) decreases as the wall surface inclination angle ξ increases.

  Therefore, when the ignition timing target value is made equal to the intake stroke target value, the wall surface inclination angle ξ is made equal to the reference inclination angle ξTH. When the ignition timing target value is set to be larger than the intake stroke target value, the wall surface inclination angle ξ is set to an angle smaller than the reference inclination angle ξTH. Further, when the ignition timing target value is made smaller than the intake stroke target value, the wall surface inclination angle ξ is made larger than the reference inclination angle ξTH.

Next, the operation of the internal combustion engine 10 manufactured based on each value set by the internal combustion engine design method of the present embodiment will be described together with effects.
The port curvature radius R and the port inclination angle θ in the intake port 17 are the values set in the first step. Therefore, during the intake stroke, the intake air is introduced from the intake port 17 as described above, so that a tumble flow having the same intensity as the target value during the intake stroke is generated in the combustion chamber 16. Since the wall inclination angle ξ is set to a value corresponding to the difference between the target ignition timing value and the target value during the intake stroke, the intensity of the tumble flow becomes equal to the target ignition timing value at the subsequent ignition timing. . Therefore, the strength of the tumble flow during the intake stroke can be made equal to the target value during the intake stroke, and the strength of the tumble flow during the subsequent ignition timing can be made equal to the target ignition timing value. Therefore, good combustion of the air-fuel mixture in the combustion chamber 16 can be realized.

  Thus, according to the design method of the internal combustion engine of the present embodiment, an internal combustion engine that can realize good combustion of the air-fuel mixture in the combustion chamber 16 can be designed.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Cylinder head, 111 ... Mounting surface, 12 ... Gasket, 13 ... Cylinder block, 14 ... Cylinder, 15 ... Depression, 151 ... Wall surface, 152 ... Outer wall surface, 153 ... Connection part, 141 ... Internal space , 16 ... combustion chamber, 17 ... intake port, 171 ... downstream passage, 172 ... upstream passage, 19 ... intake valve, 20 ... exhaust valve.

Claims (1)

An internal combustion engine design method for designing an internal combustion engine that generates a tumble flow in a combustion chamber by introducing intake air from an intake port into the combustion chamber in the cylinder,
The intake port is connected to the combustion chamber and is bent at a predetermined curvature, and an upstream passage is connected to the upstream end of the downstream passage and extends in a predetermined extending direction. With
The combustion chamber is composed of an internal space of the cylinder and a recess communicating with the internal space of a cylinder head.
When the surface of the cylinder head that is attached to the cylinder block with the gasket interposed therebetween is the mounting surface, and the portion located outside the intake valve and the exhaust valve among the wall surfaces of the depression is the outer wall surface, A wall surface inclination angle that is an angle formed by a connection portion of the outer wall surface with the mounting surface and the mounting surface in a cross section along the extending direction of the crankshaft of the internal combustion engine and including the central axis of the cylinder is 90 ° or more. And
When the wall surface inclination angle becomes gradually smaller and becomes a specified coefficient when the wall surface inclination angle is equal to the reference inclination angle,
Under the premise that the product of the tumble flow strength during the intake stroke multiplied by the specified coefficient is the strength of the tumble flow at the ignition timing,
When the ignition timing target value, which is a target value of the tumble flow intensity at the ignition timing, is set to be equal to or greater than the tumble flow intensity at the intake stroke, the wall surface inclination angle is set to an angle equal to or less than the reference inclination angle, while the ignition timing target value is set. A method for designing an internal combustion engine, wherein the wall surface inclination angle is set to an angle larger than the reference inclination angle when the value is less than the strength of the tumble flow during the intake stroke.

Images