JP5621632B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine provided with an in-cylinder injection valve that directly injects fuel into a cylinder.

  A direct injection internal combustion engine having an in-cylinder injection valve that directly injects fuel into a cylinder is known. According to this internal combustion engine, it is possible to directly cool the intake air in the cylinder using the latent heat of vaporization of the fuel, thereby improving the charging efficiency of the intake air and increasing the output, and spark ignition like a gasoline engine. In the internal combustion engine, knock resistance can be improved.

JP 2004-218603 A

  By the way, in a direct injection internal combustion engine, in which fuel is injected obliquely downward toward the piston, piston wet occurs in which the piston is wetted by the fuel when the fuel spray collides with the piston. Due to this piston wetness, there are concerns about problems such as an increase in the number of PM (particulate matter) particles, a decrease in volumetric efficiency ηv, a decrease in fully open (WOT) performance, and an increase in combustion fluctuations. In particular, there is a further concern about the problem of an increase in the number of PM particles during engine warm-up when the piston is not yet sufficiently warm.

  Accordingly, the present invention has been invented in view of the above circumstances, and an object thereof is to provide a control device for an internal combustion engine capable of solving various problems caused by piston wet.

According to one aspect of the invention,
A control device for an internal combustion engine including an in-cylinder injection valve that directly injects fuel into a cylinder,
From the first distance H from the start point to the end point of the fuel spray along the spray axis of the fuel spray injected from the in-cylinder injection valve when there is no piston, and from the start point of the fuel spray along the spray axis The ratio L / H with respect to the second distance L to the piston and the fuel from the in-cylinder injection valve so that the ratio L / H at 1 ms after the start of fuel injection becomes a predetermined value of 0.5 or more. There is provided a control device for an internal combustion engine comprising control means for injecting fuel.

  Preferably, the in-cylinder injection valve injects a fan-shaped fuel spray in which a first angle formed by the fuel spray in a plan view is larger than a second angle formed by the fuel spray in a side view.

  Preferably, the control means starts fuel injection from the in-cylinder injection valve during an intake stroke.

  Preferably, the control means sets the fuel injection start timing from the in-cylinder injection valve to a predetermined timing after 310 ° CA before compression top dead center and before 180 ° CA.

Preferably, the internal combustion engine has an oil jet for injecting cooling oil to the piston,
The predetermined value is set to a value larger than a predetermined value set for an internal combustion engine not having the oil jet.

  According to the present invention, an excellent effect that various problems due to piston wet can be solved is exhibited.

1 is a schematic side cross-sectional view showing a control device for an internal combustion engine according to an embodiment of the present invention. 1 is a schematic plan sectional view of an internal combustion engine. It is a graph which shows the relationship between injection time and the number of PM particles. It is a graph which shows the relationship between predetermined time distance ratio and the number of PM particles. It is a graph which shows the relationship between an injection angle and predetermined time-distance ratio.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 schematically shows a control device for an internal combustion engine according to the present embodiment. The illustrated internal combustion engine (engine) 1 is a direct-injection and spark-ignition internal combustion engine (gasoline engine). Although only one cylinder is shown in the figure, it is actually configured as a multi-cylinder engine. Although the use of the engine 1 is not ask | required, it is an object for motor vehicles, for example. An in-cylinder injection valve 4 that directly injects fuel into the combustion chamber 3 in the cylinder 2 is provided for each cylinder.

  The engine 1 has a cylinder block 5 and a cylinder head 6, and a cylinder 2 is defined in the cylinder block 5. A piston 7 is accommodated in the cylinder 2 so as to be movable up and down, and the piston 7 is connected to a crankshaft (not shown) via a connecting rod (not shown). The cylinder central axis is indicated by C in the figure.

  The cylinder head 6 is fastened to the top of the cylinder block 5 so as to close the cylinder 2 from above, and a gasket 8 is interposed between the cylinder block 5 and the cylinder head 6. The cylinder head 6 is provided with two intake ports 9 and exhaust ports 10, and an intake valve 11 and an exhaust valve 12, two for each cylinder. The cylinder head 6 is provided with a spark plug 13 for igniting the air-fuel mixture in the combustion chamber 3 for each cylinder.

  FIG. 1 shows a cross section in a side view of the engine, whereas FIG. 2 shows a cross section in a plan view of the engine. The former is a cross section parallel to the cylinder central axis C, and the latter is a cross section perpendicular to the cylinder central axis C.

  Here, in the plan view shown in FIG. 2, orthogonal coordinates with the cylinder center axis C as the origin are defined, and the axis extending in the horizontal direction in the figure is defined as the X axis and the axis extending in the vertical direction in the figure is defined as the Y axis. The Y axis is parallel to the center axis of the crankshaft, and the X axis is orthogonal to the Y axis. The left side of the figure is the intake side and the right side is the exhaust side from the Y axis. Also, with the X axis as the boundary, the upper side of the figure is the front and the lower side is the rear. 1 along the cylinder center axis C (upward side in the paper thickness direction in FIG. 2) is up, and the lower side in FIG. 1 (back side in the paper thickness direction in FIG. 2) is down.

  As shown in the drawing, two intake ports 9 are extended along the X-axis direction on the intake side substantially bordering on the Y-axis. Two intake valves 11 for opening and closing the outlets of the intake ports 9 are arranged in parallel.

  Similarly, two exhaust ports 10 are extended along the X-axis direction on the exhaust side substantially bordering on the Y-axis. Two exhaust valves 12 that open and close the inlets of the exhaust ports 10 are arranged in parallel. Thus, the engine 1 is configured with four valves per cylinder.

  The outlet of the intake port 9 and the intake valve 11 are larger in diameter than the inlet of the exhaust port 10 and the exhaust valve 12, and an intermediate position therebetween is slightly offset to the exhaust side with respect to the Y axis. Similarly, the spark plug 13 is arranged slightly offset to the exhaust side with respect to the Y axis. However, the center axis of the spark plug 13 is parallel to the cylinder center axis C and is on the X axis.

  The in-cylinder injection valve 4 is disposed substantially parallel to the lower side of the intake port 9 and is attached to the cylinder head 6. A mounting hole 14 is provided in the cylinder head 6, and the in-cylinder injection valve 4 is inserted and fixed in the mounting hole 14.

  The in-cylinder injection valve 4 is disposed obliquely downward and injects the fuel obliquely downward from the injection hole 4A. That is, the in-cylinder injection valve 4 injects fuel into the cylinder 2 obliquely downward from the upper end side of the cylinder 2. The injected fuel forms a fuel spray F. A recess 15 for causing the fuel spray F to collide is formed on the top surface of the piston 7. The recess 15 has a bottom surface 15A perpendicular to the cylinder center axis C and a side surface 15B rising from the bottom surface 15A. The fuel spray F colliding with the bottom surface 15A is wound up along the side surface 15B and diffused into the cylinder 2. It has become.

  The in-cylinder injection valve 4 is opened when energized (turned on) by an electronic control unit (hereinafter referred to as ECU) 30 as control means, injects fuel, and is de-energized (off) by the ECU 30. Close the valve and stop fuel injection. The spark plug 13 also performs ignition based on the ignition signal from the ECU 30.

  As shown in FIGS. 1 and 2, the fuel spray F has a spray axis P that is the central axis thereof. Further, the angle formed by the fuel spray F in the side view shown in FIG. 1 is α, and the angle formed by the fuel spray F in the plan view shown in FIG. 2 is β. The former is referred to as a side view spray angle, and the latter is referred to as a plan view spray angle, which corresponds to the second angle and the first angle of the present invention, respectively. Furthermore, as shown in the side view of FIG. 1, the angle formed by the spray axis P with respect to a plane perpendicular to the cylinder center axis C is γ, which is called the injection angle. As shown in the plan view of FIG. 2, the spray axis P is parallel to the X axis, and particularly on the X axis.

  The in-cylinder injection valve 4 injects a fan-shaped fuel spray F having a planar view spray angle β larger than a side view spray angle α.

  The fuel spray F has a starting point f1 along the spray axis P at the outlet position of the injection hole 4A of the in-cylinder injection valve 4. Further, the fuel spray F has an end point f2 along the spray axis P at the maximum arrival position of the fuel spray F. The distance from the start point f1 to the end point f2 along the spray axis P of the fuel spray F is referred to as a spray distance H. The spray distance H corresponds to the first distance of the present invention.

  On the other hand, the distance from the starting point f1 of the fuel spray F along the spray axis P to the piston 7 is referred to as a piston distance L. The piston distance L corresponds to the second distance of the present invention. In the example of FIG. 1, the distance from the starting point f1 of the fuel spray F to the bottom surface 15A of the recess 15 of the piston 7 forms the piston distance L.

  As described above, in the direct injection engine 1, piston wet occurs in which the piston 7 is wetted with fuel when the fuel spray F collides with the piston 7. Due to this piston wetness, there are concerns about problems such as an increase in the number of PM (particulate matter) particles, a decrease in volumetric efficiency ηv, a decrease in fully open (WOT) performance, and an increase in combustion fluctuations. In particular, there is a further concern about the problem of an increase in the number of PM particles during engine warm-up when the piston is not yet sufficiently warm.

  The combustion fluctuation refers to a change in the combustion state for each combustion cycle of each cylinder. Even during equal power operation, if the combustion fluctuation is large, the combustion state changes for each combustion cycle of each cylinder, which causes fuel consumption deterioration and vehicle vibration.

  In the present embodiment, in order to solve these various problems caused by piston wet, the fuel injection timing by the in-cylinder injection valve 4 is optimized based on the following viewpoints.

  In FIG. 3, the test result which investigated the relationship between the injection timing and the PM particle number N is shown. In this case, with respect to four types of in-cylinder injection valves a, b, c, and d having different at least one of the side view spray angle α, the plan view spray angle β, and the injection angle γ, the relationship between the injection timing and the number of PM particles N is respectively shown. Examined. The injection timing here is the injection start timing. The injection timing is indicated by the crank angle (° CA) before compression top dead center (BTDC).

  As shown in the figure, the characteristic changes at 310 ° CA as a boundary, and when the injection timing is 310 ° CA or later, the number of PM particles N is at an allowable level, but the injection timing is before 310 ° CA. It can be seen that the number N of PM particles tends to be extremely deteriorated.

  Here, the injection timing is in a range after 360 ° CA and before 180 ° CA, that is, during the intake stroke (or during piston lowering). Fuel injection performed during such an intake stroke is called intake stroke injection. This is because, when performing partial load combustion or EGR combustion (particularly large-volume EGR combustion), there is a demand for advancing the injection timing much more than fuel injection performed during a normal compression stroke (referred to as compression stroke injection).

  In the partial load combustion, the homogeneity of the air-fuel mixture is important, and the homogeneity of the air-fuel mixture becomes particularly important when improving fuel efficiency using the internal EGR as in recent years.

  In addition, EGR combustion is normally performed after the warm-up is completed, but it has been studied to set the start temperature of EGR combustion to a lower temperature side and perform the EGR combustion even before the warm-up is completed. Note that EGR combustion refers to combustion performed in a state where EGR gas is contained in a cylinder, and EGR includes internal EGR and external EGR.

  In order to obtain a more homogeneous air-fuel mixture during partial load combustion and EGR combustion before the end of warm-up, and to solve the above problems caused by piston wet, the injection timing is set within a range of 360 to 180 ° CA, Intake stroke injection is performed. Note that it is preferable to continuously change the injection timing before and after the end of warm-up.

  In particular, in this embodiment, the injection timing is set to a predetermined timing after 310 ° CA before compression top dead center and before 180 ° CA based on the result of FIG. As a result, at least the number N of PM particles can be suppressed to an allowable level or less.

  In order to obtain the optimal injection timing within this range, the present inventor has focused on the ratio of the piston distance L and the spray distance H at a predetermined time point. This ratio is called distance ratio R. R = L / H. In particular, the predetermined time point here is a time point of 1 ms after the start of fuel injection. Hereinafter, the distance ratio at 1 ms after the start of fuel injection is referred to as “predetermined time distance ratio”.

  FIG. 4 shows the relationship between the predetermined point distance ratio R and the number of PM particles N created based on the result of FIG. As can be seen, the number N of PM particles tends to decrease as the predetermined point distance ratio R increases. In particular, when the predetermined point distance ratio R is 0.5 or more, the number of PM particles N decreases to an allowable level.

  Therefore, in the present embodiment, the ECU 30 injects fuel from the in-cylinder injection valve 4 so that the predetermined time point distance ratio R becomes a predetermined value of 0.5 or more. More specifically, the ECU 30 starts fuel injection by the in-cylinder injection valve 4 at the injection timing such that the predetermined time point distance ratio R becomes a predetermined value of 0.5 or more.

  As a result, problems such as an increase in the number of PM particles, a decrease in volumetric efficiency ηv, a decrease in fully open (WOT) performance, and an increase in combustion fluctuations due to piston wet can be solved. In particular, the problem of an increase in the number of PM particles can be solved even during engine warm-up when the piston is not yet sufficiently warm.

  In the case of partial load combustion or EGR combustion, even when the intake stroke injection is performed with the injection timing advanced by a considerable amount compared to the normal compression stroke injection, good homogeneity of the air-fuel mixture can be ensured. Furthermore, even when EGR combustion is performed before the warm-up is completed, a homogeneous air-fuel mixture can be obtained, and the above-described problems caused by piston wet can be solved. In this way, it is possible to optimize the injection timing when fuel injection is started during the intake stroke.

  It should be noted here that the spray distance H that forms the denominator of the distance ratio or the predetermined time-distance ratio R is the spray distance H (from the start point f1 along the spray axis P to the end point f2 when it is assumed that there is no piston 7). Distance). On the other hand, the piston distance L that forms a numerator of the distance ratio or the predetermined time distance ratio R is the piston distance L (from the starting point f1 along the spray axis P to the piston 7 when the piston 7 is present, as in the present embodiment). Distance).

  At some point, when the distance ratio R is less than 1, the spray distance H is longer than the piston distance L. That is, the fuel spray F collides with the piston 7. When the piston 7 is present as in the present embodiment, the distance ratio R cannot actually be smaller than 1. This is because when the distance ratio R becomes 1, the fuel spray F collides with the piston 7 and the spray distance H cannot exceed the piston distance L.

  However, the spray distance H when the distance ratio R is 1 or less here means the spray distance H when it is assumed that there is no piston 7. Such a spray distance H can be obtained or grasped by removing the piston from the engine at the development stage. That is, separately from the presence or operation of the piston, the behavior of the fuel spray F is grasped individually, and the presence or operation of the piston 7 is combined with this to make the above-described predetermined point distance ratio R 1 or less. It is possible to set the time.

  At a certain point in time, when the distance ratio R is greater than 1, the spray distance H becomes shorter than the piston distance L, and the fuel spray F does not reach the piston 7.

  The predetermined time distance ratio R of 1 or less represents the strength of the fuel spray F hitting the piston 7. As the predetermined time distance ratio R of 1 or less increases, the spray distance H becomes relatively shorter than the piston distance L, and the hitting strength becomes weaker. In other words, as the predetermined point distance ratio R of 1 or less becomes smaller, the spray distance H becomes relatively longer than the piston distance L, and the hitting strength becomes stronger.

  The result of FIG. 4 shows that if fuel injection is performed at an injection timing such that the predetermined time distance ratio R is 0.5 or more, the strength of the fuel spray F hitting the piston 7 becomes relatively weak, and the number of PM particles N is It means that it can be lowered to an acceptable level.

  In the case of the sector fuel spray as in the present embodiment, the diameter and speed of the fuel droplets are large immediately after injection and the penetrating power of the spray is large. It diffuses in the direction of the visual spray angle β and the penetrating power of the spray becomes weaker. If the injection timing is such that the predetermined time distance ratio R is less than 0.5, the hitting strength of the fuel spray F is too strong, the piston wet becomes noticeable, and there are problems caused by the piston wet such as an increase in the number N of PM particles. Realize. However, at the injection timing such that the predetermined time distance ratio R is 0.5 or more, the hit strength of the fuel spray F can be moderately reduced, and the problem caused by the piston wet can be solved. is there.

  This embodiment is particularly suitable when the predetermined time distance ratio R is 1 or less, that is, when the spray distance H is equal to or greater than the piston distance L at the predetermined time and the fuel spray F reaches the piston 7. Accordingly, the injection timing is preferably determined so that the predetermined time distance ratio R is a predetermined value of 0.5 or more and 1 or less.

  By the way, as shown in FIG. 1, in the engine 1 of this embodiment, the oil jet 16 for injecting the cooling oil to the bottom surface portion of the piston 7 may be provided. In this case, the predetermined value related to the distance ratio R is set to a value larger than a predetermined value set for an engine having no oil jet. For example, when the predetermined value when there is no oil jet is 0.6, the predetermined value when there is an oil jet can be set to 0.7 or the like. In any case, the predetermined value is 0.5 or more.

  Under the same operating conditions, the piston temperature is lower when the oil jet is present than when the oil jet is absent. For this reason, it is preferable to increase the predetermined value as in this embodiment. This is because the strength of the fuel spray F hitting the piston 7 can be reduced to compensate for the decrease in evaporation of the fuel adhering to the piston 7.

  Conversely, since the piston temperature is higher in the case without oil jet than in the case with oil jet, it is preferable to reduce the predetermined value. This is because the fuel adhering to the piston 7 evaporates more positively, so that the strength of the fuel spray F can be increased.

  FIG. 5 shows the relationship between the injection angle γ and the predetermined point distance ratio R. Here, the relationship between three injection timings e, f, and g was examined. e is 300 ° CA BTDC, f is 310 ° CA BTDC, and g is 320 ° CA BTDC. e is the most retarded side. The spray distance H at a predetermined time (1 ms after the start of fuel injection) is constant.

  As shown in g, when the injection timing is set to 320 ° CA BTDC, in order to obtain a predetermined time point distance ratio R of 0.5 or more, the injection angle γ must be γ1 or less. As shown in f, when the injection timing is 310 ° CA BTDC, in order to obtain a predetermined time point distance ratio R of 0.5 or more, the injection angle γ must be γ2 (> γ1) or less. As shown in e, when the injection timing is set to 300 ° CA BTDC, the predetermined time point distance ratio R is always 0.5 or more within the range of the injection angle γ in the figure, so the injection angle γ is arbitrarily set. Can be determined.

  Thus, when trying to obtain the predetermined time point distance ratio R of 0.5 or more, the upper limit value of the injection angle γ tends to increase as the injection timing is retarded. This means that as the injection timing is retarded, the piston position at the injection timing is lower, so that fuel can be injected downward. That is, when the injection timing is relatively early, the fuel spray F is applied thinly (with a small injection angle γ) to the recess bottom surface 15A of the piston 7, and conversely when the injection timing is relatively late, the fuel spray F is applied to the recess bottom surface 15A of the piston 7. F can be applied thickly (with a large injection angle γ). Thus, the relationship between the injection timing and the injection angle γ can be optimized.

  Although the preferred embodiment of the present invention has been described in detail above, various other embodiments of the present invention are possible. For example, the engine may be a so-called dual injection type internal combustion engine provided with an intake passage injection valve for injecting fuel into the intake passage, particularly, the intake port, in addition to the in-cylinder injection valve.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

1 Internal combustion engine
2 Cylinder 4 In-cylinder injection valve 7 Piston 16 Oil jet 30 Electronic control unit (ECU)
F Fuel spray f1 Start point f2 End point P Spray axis α Side view spray angle β Plane view spray angle γ Injection angle

Claims (5)

A control device for an internal combustion engine including an in-cylinder injection valve that directly injects fuel into a cylinder,
From the first distance H from the start point to the end point of the fuel spray along the spray axis of the fuel spray injected from the in-cylinder injection valve when there is no piston, and from the start point of the fuel spray along the spray axis The in-cylinder injection valve such that the ratio L / H with respect to the second distance L to the piston is a predetermined value of 0.5 or more and less than 1 at 1 ms after the start of fuel injection. A control device for an internal combustion engine, comprising control means for injecting fuel from the fuel. The in-cylinder injection valve injects a fan-shaped fuel spray in which a first angle formed by the fuel spray in a plan view is larger than a second angle formed by the fuel spray in a side view. Control device for internal combustion engine. The control device for an internal combustion engine according to claim 1 or 2, wherein the control means starts fuel injection from the in-cylinder injection valve during an intake stroke. The internal combustion engine according to claim 3, wherein the control means sets the fuel injection start timing from the in-cylinder injection valve to a predetermined timing after 310 ° CA before compression top dead center and before 180 ° CA. Control device. The internal combustion engine has an oil jet for injecting cooling oil to a piston;
The internal combustion engine according to any one of claims 1 to 4, wherein the predetermined value is set to a value larger than a predetermined value set for the internal combustion engine not having the oil jet. Control device.

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