JP2018003751A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To take measures against increase of a distance between a spray outline face and an electrode portion when activation control of an exhaust emission control catalyst is performed with an engine constitution in which a part of fuel spray from an injector is directed to a direction of an ignition plug positioned at a downstream side in a flowing direction, of tumble flow, and the electrode portion of the ignition plug is disposed in a range at an upper part with respect to the outline face of the fuel spray closest to the ignition plug.SOLUTION: In catalyst warming-up control, intake stroke injection and compression stroke injection are performed (upper stage in Fig. 7). During the catalyst warming-up control, a discharge timing in an electrode portion 34 is determined at a delayed angle side with respect to a compression top dead center, and expansion stroke injection is performed during the discharge timing. However, in a case when a distance between a spray outline face and the electrode portion 34 is increased, additional injection (first injection) is performed before the expansion stroke injection (second injection), and discharge (second discharge) corresponding to the expansion stroke injection, and discharge (first discharge) corresponding to the additional injection are performed (lower stage in Fig. 7).SELECTED DRAWING: Figure 7

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly, to a control device that controls an internal combustion engine that includes an injector and a spark plug in a combustion chamber and includes a catalyst that purifies exhaust from the combustion chamber (an exhaust purification catalyst).

  Japanese Patent Application Laid-Open No. 2011-106377 discloses a technique related to a configuration related to the positional relationship between an ignition plug provided at the upper portion of a combustion chamber and an injector, and a technique related to a control method for the ignition plug and the injector based on this configuration. Yes. Specifically, this configuration includes the distance from the center position of the discharge gap of the spark plug to the center position of the injector nozzle hole closest to the spark plug, and the fuel injected from the nozzle hole from the center position of the discharge gap. The distance to the central axis of spraying is set to a specific range.

  In addition, the control method based on this configuration is to apply a high voltage to the spark plug over the fuel injection period after a predetermined time has elapsed since the start of fuel injection from the injector. The fuel injected at a high pressure from the injector forms a low pressure part by taking away the surrounding air (entrainment). Therefore, according to the above control method for applying a high voltage to the spark plug during the fuel injection period, a low pressure part is formed around the fuel spray, and the discharge spark generated in the discharge gap is attracted to the low pressure part. Can do. Therefore, the ignitability of the air-fuel mixture formed around the spark plug can be improved.

  In addition, in the above publication, activation control of the exhaust purification catalyst at the time of starting the engine is given as an example of utilizing the above-described attraction action.

JP 2011-106377 A

  By the way, the present inventor is examining the activation control of the exhaust purification catalyst in an engine configuration different from the above publication. The engine configuration related to the examination is similar to the engine configuration described in the above publication in the configuration related to the positional relationship between the spark plug and the injector. However, the engine configuration involved in the study differs from the engine configuration in the above publication in that a tumble flow is formed from the intake air supplied to the combustion chamber, and when viewed in the flow direction of the tumble flow, it is located downstream of the injector. It has an engine configuration in which a spark plug is arranged.

  The tumble flow formed in the combustion chamber swirls from the upper part of the combustion chamber to the lower part on the exhaust port side and from the lower part of the combustion chamber to the upper side on the intake port side. Is assumed. Specifically, the control related to the examination is performed by performing injection in the intake stroke and swirling the fuel spray together with the tumble flow in the combustion chamber while starting the ignition by the spark plug (that is, the start timing of applying the high voltage to the spark plug). ) Is set on the retard side from the compression top dead center. In addition to this, in the control according to the examination, during the application of a high voltage to the spark plug, injection is performed in an expansion stroke such that the injection period ends.

  If injection is performed in the expansion stroke, the same action as the attracting action in the above publication can be obtained. That is, the discharge spark generated by the spark plug can be attracted to the low pressure portion formed around the fuel spray injected from the injector and directed toward the spark plug. Further, in addition to the attracting action in the above publication, according to the control related to the examination, not only the discharge spark but also the air-fuel mixture including fuel spray by the injection in the intake stroke and the initial flame generated from this discharge spark Can be attracted. Therefore, since the attracted initial flame can be brought into contact with the fuel spray by the injection in the expansion stroke and grown, the combustion for growing the initial flame can be stabilized and the combustion fluctuation can be suppressed.

  However, as mentioned in the above publication, the distance from the center position of the discharge gap of the spark plug to the center axis of the fuel spray injected from the injector injection hole is important for the attraction action described above. This also applies to the control concerned. That is, the distance between the outer surface of the fuel spray directed toward the spark plug by the injection in the expansion stroke and the spark plug is important. For this reason, when the distance between the outer surface and the spark plug is increased, there is a possibility that the action of attracting the discharge spark and the initial flame based on the injection in the expansion stroke is insufficient.

  Even if the attracting action by the injection in the expansion stroke is insufficient, it is possible to grow by bringing the initial flame into contact with the fuel spray by the injection. However, the fact that this attractive action is insufficient means that the initial flame is not sufficiently attracted to the fuel spray by the injection in the expansion stroke, and the concentration of the air-fuel mixture around the initial flame is not increased. means. Therefore, when the attracting action is insufficient, the growth of the initial flame is suppressed. If the number of cycles in which such a situation occurs in the combustion cycle under control related to the study increases, the fluctuation in combustion between cycles increases, which affects drivability.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to make a part of the fuel spray from the injector face a spark plug located downstream in the flow direction of the tumble flow and When the activation control of the exhaust purification catalyst is performed by the engine configuration in which the electrode portion of the ignition plug is arranged in a range above the outer surface of the fuel spray closest to the plug, the distance between the outer surface and the electrode portion It is to take measures when it expands.

An internal combustion engine control apparatus according to the present invention includes an injector provided at an upper portion of a combustion chamber for directly injecting fuel into a cylinder, and an ignition plug for igniting an air-fuel mixture in the cylinder using a discharge spark generated at an electrode portion The fuel spray is provided at the upper part of the combustion chamber and downstream of the injector in the flow direction of the tumble flow formed in the combustion chamber, and is injected from the injector toward the spark plug. An internal combustion engine including an ignition plug provided so that the position of the electrode portion is located above the outer surface and an exhaust purification catalyst for purifying exhaust from the combustion chamber is controlled.
The control device controls the spark plug so that a discharge spark is generated in a predetermined period that is retarded from the compression top dead center as control for activating the exhaust purification catalyst, and from the compression top dead center. Expansion stroke injection on the retard side, the injection period overlaps at least a part of the predetermined period, and the end time is an advance side relative to the end time of the predetermined period; The injector is controlled to perform the intake stroke injection in the same cycle as the cycle in which the expansion stroke injection is performed.
The control device further includes the intake stroke injection and the expansion stroke when it is determined that the growth rate of the initial flame generated from the air-fuel mixture including the fuel spray by the intake stroke injection and the discharge spark is lower than a predetermined determination value. It is additional injection in the same cycle as the cycle in which injection is performed, and is retarded from the compression top dead center, and advanced from the start timing of the expansion stroke injection and the start timing of the predetermined period. A discharge period in which the injector is controlled to perform the additional injection, and is started from the advance side with respect to the injection start timing of the additional injection and expires on the retard side with respect to the injection start timing of the expansion stroke injection The spark plug is controlled so as to generate a discharge spark at.

  Since the fuel spray by the additional injection is carried in the downstream direction by the tumble flow, it moves to the vicinity of the electrode portion when the expansion stroke injection is performed. During the movement of the fuel spray, a discharge spark is generated by the control of the spark plug, and a flame kernel is generated by contact between the discharge spark and the fuel spray by the intake stroke injection. Therefore, when the fuel spray moves to the vicinity of the electrode portion by the tumble flow, it comes into contact with the initial flame generated from the flame kernel. That is, when the injector is controlled to perform additional injection and the spark plug is controlled to perform discharge that starts from the advance side of the injection start timing of this additional injection, before the fuel spray by the expansion stroke injection is involved In addition, the initial flame grows with the fuel spray from the additional injection. Therefore, compared with the case where the control of the injector and the spark plug is not performed, the time until the initial flame entrains the fuel spray by the expansion stroke injection is shortened.

  According to the control device for an internal combustion engine of the present invention, when it is determined that the growth rate of the initial flame generated from the air-fuel mixture including the fuel spray by the intake stroke injection and the discharge spark is lower than a predetermined determination value, the expansion is performed. Prior to entraining the fuel spray from stroke injection, the initial flame can be brought into contact with the fuel spray from additional injection and entrained to grow. In other words, when the distance between the outer surface of the fuel spray closest to the spark plug and the electrode portion of the spark plug among the fuel spray by the expansion stroke injection increases, the initial flame entrains the fuel spray by the expansion stroke injection. It is possible to keep the time until in an appropriate range. Therefore, it is possible to satisfactorily suppress the influence on drivability by reducing the combustion fluctuation between cycles.

It is a figure explaining the system configuration | structure which concerns on embodiment of this invention. 2 is a diagram illustrating an example of a fuel injection pattern immediately after the internal combustion engine 10 is started. FIG. It is a figure which shows the injection start timing in catalyst warm-up control, the injection period, and the discharge period in the electrode part. It is a figure which shows the relationship between a combustion fluctuation rate and the fuel injection quantity in expansion stroke injection. It is a figure for demonstrating the attracting action of the discharge spark by expansion stroke injection. It is a figure explaining the problem of catalyst warm-up control. It is a figure explaining the outline | summary of the catalyst warm-up control of embodiment of this invention. It is a figure explaining the in-cylinder state in the case of performing twice injection and discharge twice in an expansion stroke. It is a figure which shows an example of the relationship between the valve opening period (tau) of an injector, and the amount of injected fuel. It is a figure which shows an example of the relationship between the number PN of particle | grains, a combustion fluctuation rate, and fuel injection amount. It is a figure which shows an example of the relationship between the engine cooling water temperature in the cold start of the internal combustion engine 10, and the injection period in the expansion stroke 1st time injection. It is a figure which shows an example of the relationship between an ignition probability and SA-CA10, and the discharge period in the expansion stroke 1st discharge. It is a figure which shows the relationship between a combustion fluctuation rate and SA-CA10. It is a figure explaining the judgment value about distance DT. It is a flowchart which shows an example of the process which ECU40 performs in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

[Description of system configuration]
FIG. 1 is a diagram illustrating a system configuration according to an embodiment of the present invention. As shown in FIG. 1, the system according to the present embodiment includes an internal combustion engine 10 mounted on a vehicle. The internal combustion engine 10 is a four-stroke one-cycle engine and has a plurality of cylinders. However, only one of the cylinders 12 is shown in FIG. The internal combustion engine 10 includes a cylinder block 14 in which a cylinder 12 is formed, and a cylinder head 16 disposed on the cylinder block 14. A piston 18 that reciprocates in the axial direction (vertical direction in the present embodiment) is disposed in the cylinder 12. The combustion chamber 20 of the internal combustion engine 10 is defined by at least the wall surface of the cylinder block 14, the lower surface of the cylinder head 16, and the upper surface of the piston 18.

  Two intake ports 22 and two exhaust ports 24 communicating with the combustion chamber 20 are formed in the cylinder head 16. An intake valve 26 is provided at an opening portion of the intake port 22 that communicates with the combustion chamber 20, and an exhaust valve 28 is provided at an opening portion of the exhaust port 24 that communicates with the combustion chamber 20. In addition, the cylinder head 16 is provided with an injector 30 so that the tip thereof faces the combustion chamber 20 from substantially the center of the upper portion of the combustion chamber 20. The injector 30 is connected to a fuel supply system including a fuel tank, a common rail, a supply pump, and the like. In addition, a plurality of injection holes are formed radially at the tip of the injector 30. When the injector 30 is opened, fuel is injected from these injection holes in a high pressure state.

  Further, the cylinder head 16 is provided with an ignition plug 32 above the combustion chamber 20 on the exhaust valve 28 side than the portion where the injector 30 is provided. The spark plug 32 includes an electrode portion 34 including a center electrode and a ground electrode at the tip. The electrode portion 34 protrudes above the outer surface of the fuel spray from the injector 30 (hereinafter also referred to as “spray outer surface”) (that is, the range from the spray outer surface to the lower surface of the cylinder head 16). Is arranged. More specifically, the electrode portion 34 is disposed so as to protrude in a range above the outer surface of the fuel spray closest to the ignition plug 32 among the fuel sprays injected radially from the injection hole of the injector 30. Yes. The outline drawn in FIG. 1 represents the outline of the fuel spray closest to the spark plug 32 in the fuel spray from the injector 30.

  The intake port 22 extends almost straight from the inlet on the intake passage side toward the combustion chamber 20, and a flow passage cross-sectional area is reduced at a throat 36 that is a connection portion with the combustion chamber 20. Such a shape of the intake port 22 generates a tumble flow in the intake air supplied from the intake port 22 to the combustion chamber 20. The tumble flow swirls in the combustion chamber 20. More specifically, the tumble flow is directed from the intake port 22 side to the exhaust port 24 side in the upper part of the combustion chamber 20 and from the upper part to the lower part of the combustion chamber 20 on the exhaust port 24 side. Further, the tumble flow is directed from the exhaust port 24 side toward the intake port 22 side at the lower part of the combustion chamber 20 and is directed upward from the lower part of the combustion chamber 20 at the intake port 22 side. A recess for holding the tumble flow is formed on the upper surface of the piston 18 that forms the lower part of the combustion chamber 20.

  Further, as shown in FIG. 1, the system according to the present embodiment includes an ECU (Electronic Control Unit) 40 as a control means. The ECU 40 includes a RAM (Random Access Memory), a ROM (Read Only Memory), a CPU (Central Processing Unit), and the like. The ECU 40 captures and processes signals from various sensors mounted on the vehicle. The various sensors include an in-cylinder pressure sensor 42 provided at the top of the combustion chamber 20, a crank angle sensor 44 that detects the rotation angle of the crankshaft connected to the piston 18, and a temperature that detects the coolant temperature of the internal combustion engine 10. A sensor 46 is included at least. The ECU 40 processes the signals of the acquired sensors and operates various actuators according to a predetermined control program. The actuator operated by the ECU 40 includes at least the injector 30 and the spark plug 32 described above.

[Control at start-up by ECU 40]
In the present embodiment, control immediately after the cold start of the internal combustion engine 10 by the ECU 40 shown in FIG. 1 is performed (hereinafter, also referred to as “catalyst warm-up control”) that promotes activation of the exhaust purification catalyst. . The exhaust purification catalyst is a catalyst provided in the exhaust passage of the internal combustion engine 10, and as an example, when the atmosphere of the activated catalyst is in the vicinity of stoichiometry, nitrogen oxide (NOx), hydrocarbon (HC) in the exhaust ) And carbon monoxide (CO).

  The catalyst warm-up control will be described with reference to FIGS. FIG. 2 shows an example of a fuel injection pattern immediately after the internal combustion engine 10 is cold started. As shown in FIG. 2, immediately after start-up, first, two injections in the intake stroke (hereinafter also referred to as “intake stroke injection”) and one injection in the compression stroke (hereinafter also referred to as “compression stroke injection”). And a fuel injection pattern in combination. Thereafter, the compression stroke injection is switched to the single injection in the expansion stroke (hereinafter also referred to as “expansion stroke injection”) in order to start the catalyst warm-up control as the engine speed increases. That is, in the catalyst warm-up control, a fuel injection pattern that combines intake stroke injection and expansion stroke injection is employed.

FIG. 3 shows the injection start timing, the injection period, and the discharge period at the electrode portion 34 during the catalyst warm-up control. As shown in FIG. 3, the first intake stroke injection is started at a crank angle A ₁ (as an example, near BTDC 300 °), and the second time is started at a crank angle A ₂ (as an example, near BTDC 260 °). The second intake stroke injection is performed for the purpose of improving the homogeneity of the air-fuel mixture in the combustion chamber 20. However, results in the injection at a time fuel crank angle A _2, becomes large amount of fuel adhering to the wall surface of the combustion chamber 20, which is one particle number PN (Particulate Number) of the target emission regulations increasingly End up. In order to avoid such a situation, in the present embodiment, the second part of the intake stroke injection is shared for the first time. In this embodiment Incidentally, since the by sharing the first injection quantity half the second injection amount of the intake stroke injection, the injection of the first shown in FIG. 3 period Q ₁ and second injection period Q ₂ Are equal. The second injection amount and the first injection amount in the intake stroke injection may be changed, or the total number of injections in the intake stroke may be three or more.

Further, as shown in FIG. 3, during the catalyst warm-up control, the discharge period T ₁ (predetermined period) at the electrode part 34 is set to the retard side with respect to the compression top dead center. What sets the discharge period T ₁ to the retard side of the compression top dead center is for raising the exhaust gas temperature, the expansion stroke injection is performed during the discharge period. More specifically, the expansion stroke injection is started at the crank angle a ₁ that is retarded from the discharge start timing SA ₁ (as an example, near ATDC 25 to 35 °) of the electrode 34, and the discharge at the electrode 34 is discharged. injection period q ₁ at the advance side than the end timing of the expiration.

Incidentally in FIG. 3, although the interval _{I 1} is present between the start timing SA ₁ to crank angle _{a 1,} may be the start timing SA ₁ and the crank angle _{a 1} is consistent (i.e., without an interval _{I 1} May be) Further, even when the discharge end time (that is, the crank angle (SA ₁ + T ₁ )) at the electrode portion 34 coincides with the expiration time of the injection period q ₁ (that is, the crank angle (a ₁ + q ₁ )). Good. If the injection period q ₁ overlaps at least a part of the discharge period T _{1 in} the electrode part 34 and the expiration time of the injection period q ₁ is more advanced than the discharge end time in the electrode part 34 The crank angle a ₁ may be on the more advanced side than the discharge start timing SA ₁ at the electrode portion 34. The reason why such expansion stroke injection is performed is to reliably burn the fuel from the expansion stroke injection by the attraction action. Details of the attracting action will be described later.

Injection period q ₁ shown in FIG. 3, the combustion fluctuation rate obtained in the catalyst warm-up control in the same operating conditions, is set based on a relationship between the fuel injection quantity in the expansion stroke injection. FIG. 4 shows an example of this relationship. As shown in FIG. 4, the combustion fluctuation rate obtained under the operating condition equivalent to that during the catalyst warm-up control is convex downward in a specific fuel injection amount range. The injection period q ₁ is set as an injection period corresponding to the fuel injection amount (for example, about 5 mm ³ / st) when the combustion fluctuation rate is the smallest.

[Catalyst warm-up control utilizing attraction and its problems]
FIG. 5 is a diagram for explaining an attracting action by the expansion stroke injection. In the upper and middle stages of FIG. 5, the in-cylinder state during the discharge period at the electrode part 34 is depicted. The upper stage of FIG. 5 corresponds to the case where the expansion stroke injection is not performed, and the middle stage and the lower stage of FIG. 5 correspond to the case where the expansion stroke injection is performed. For convenience of explanation, FIG. 5 shows only the fuel spray closest to the spark plug 32 among the fuel sprays by the expansion stroke injection. When the expansion stroke injection is not performed, the initial flame generated from the discharge spark generated at the electrode portion 34 and the air-fuel mixture including the fuel spray by the intake stroke injection and the discharge spark extends in the flow direction of the tumble flow (see FIG. 5 top). On the other hand, when the expansion stroke injection is performed, a low pressure portion is formed around the fuel spray (entrainment), and therefore, the discharge spark generated in the electrode portion 34 and the mixture and discharge including the fuel spray due to the intake stroke injection. The initial flame generated from the spark is attracted in the direction opposite to the flow direction of the tumble flow (middle stage in FIG. 5). Then, this initial flame grows by entraining the fuel spray by the expansion stroke injection (the lower stage in FIG. 5).

  The fuel spray due to the injection in the expansion stroke is affected by the tumble flow and the in-cylinder pressure. Therefore, even if the injection is such that the injection period expires on the advance side of the discharge start timing at the electrode portion 34 even on the retard side of the compression top dead center, the fuel spray by this injection Before reaching the electrode portion 34, its shape changes, and the combustion fluctuation tends to increase. In this regard, if the expansion stroke injection is performed under the injection period condition described with reference to FIG. 3, the attracting action shown in the middle of FIG. 5 can be utilized. For this reason, even if the shape of the fuel spray by the expansion stroke injection changes, the combustion for growing the initial flame (hereinafter also referred to as “initial combustion”) can be stabilized, and the combustion fluctuation can be suppressed. Furthermore, the combustion following the initial combustion, that is, the combustion in which the grown initial flame further entrains the air-fuel mixture containing the fuel spray by the intake stroke injection (hereinafter also referred to as “main combustion”) can be stabilized.

  However, the distance between the spray outer surface and the electrode part 34 (hereinafter also referred to as “distance DT”) is important for this attracting action. For this reason, when the distance DT increases due to aging or the like, the attracting action may be insufficient. FIG. 6 is a diagram for explaining a problem of catalyst warm-up control. As shown in the upper part of FIG. 6, when the central axis of the fuel spray by the expansion stroke injection moves in the lower direction of the combustion chamber 20 (that is, the upper surface direction of the piston 18), the spray outer surface and the electrode portion 34 The distance between them increases and the attracting action becomes insufficient. Then, as shown in the lower part of FIG. 6, the growth of the initial flame including the fuel spray by the expansion stroke injection is suppressed, and the growth speed of the initial flame, that is, the initial combustion speed is lowered. In the combustion cycle during the catalyst warm-up control, if the number of cycles in which such a situation occurs increases, the fluctuation in combustion between cycles increases, which affects drivability.

[Features of catalyst warm-up control of embodiment]
Therefore, in the present embodiment, determination regarding the distance DT is performed during catalyst warm-up control. Then, when it is determined that the distance DT has increased, two injections in the intake stroke, two injections in the expansion stroke, and two discharges in the expansion stroke are performed. The double injection in the intake stroke is basically the same as the intake stroke injection described above. The double injection in the expansion stroke includes the expansion stroke injection described above and the additional injection performed in a form prior to the expansion stroke injection. The additional injection is delayed from the compression top dead center and advanced from the start time of the second discharge at the electrode 34 (the expansion stroke injection is advanced from the start time of the second discharge). Is started on the retard side with respect to the compression top dead center and on the advance side with respect to the injection start timing of the expansion stroke injection. The twice discharge in the expansion stroke is composed of the discharge corresponding to the expansion stroke injection described above and the discharge corresponding to the additional injection.

  For convenience of explanation, in the following description, the additional injection is also referred to as “expansion stroke first injection”, and the expansion stroke injection is also referred to as “expansion stroke second injection”. The discharge corresponding to the additional injection is also referred to as “expansion stroke first discharge”, and the discharge corresponding to the expansion stroke injection is also referred to as “expansion stroke second discharge”.

  FIG. 7 is a diagram illustrating an overview of catalyst warm-up control according to the embodiment of the present invention. As in FIG. 3, FIG. 7 shows the injection start timing, the injection period, and the discharge period at the electrode unit 34 during the catalyst warm-up control. The upper part of FIG. 7 corresponds to the control when the distance DT is not enlarged or when the distance DT is enlarged but the determination is not made. In such a case, the same control as the control described in FIG. 3 (fuel injection control and discharge control) is performed.

The lower part of FIG. 7 corresponds to the control when it is determined that the distance DT has increased. In this case, the contents of the discharge control (discharge start timing and period) are partially changed. That is, the first discharge of the expansion stroke is started at the start time SA ₁ ′ and is performed over the discharge period T ₁ ′. Further, the second discharge of the expansion stroke is started at the start time SA ₂ ′ and is performed over the discharge period T ₂ ′ (<discharge period T ₁ ′). Here, the start time SA ₂ ′ coincides with the start time SA ₁ and is a period obtained by adding the discharge period of the first discharge of the expansion stroke and the discharge period of the second discharge of the expansion stroke (= T ₁ ′ + T ₂ ′). It is set to a period equal to the injection period T _1. In addition, the interval (15 ° as an example) between the expiration time of the discharge period T ₁ ′ and the start time SA ₂ ′ corresponds to the time required for charging the ignition coil (15 ° as an example). However, if the electric power charged in the ignition coil is distributed to the second discharge of the expansion stroke so as not to be used up only by the first discharge of the expansion stroke, the period can be compressed.

Further, when it is determined that the distance DT has increased, the content of the fuel injection control (start timing and period of fuel injection) is also partially changed. That is, the first injection in the expansion stroke is started at the crank angle a ₁ ′ and is performed over the injection period q ₁ ′. The second expansion stroke injection is started at the crank angle a ₂ ′ and is performed over the injection period q ₂ ′. Here, the crank angle a ₂ ′ coincides with the crank angle a ₁ , and the injection period q ₂ ′ is set to a period equal to the injection period q ₁ . Details of the injection period q ₁ ′ will be described later.

Note that the interval I ₁ ′ from the start of the first expansion stroke discharge to the start of the first expansion stroke injection and the interval I ₂ from the second expansion stroke discharge to the start of the second expansion stroke injection. 'Is set to a period equal to the interval I ₁ . Here, to start timing _'a crank angle a _1' SA 1 may coincide, which may start timing SA 2 _'and crank angle a _2' do not match (that is, the interval I ₁ ', I ₂ 'may be omitted). On the other hand, the end time of the first expansion stroke discharge (that is, the crank angle (SA ₁ ′ + T ₁ ′)) is the expiration time of the injection period q ₁ ′ of the _first expansion stroke injection (that is, the crank angle (a ₁ ′ + q _1)). The reason for this is that the initial flame generated by the first discharge of the expansion stroke is surely brought into contact with the fuel spray produced by the first injection of the expansion stroke. in 7, the discharging period T _{1 'is} discharging period T _2' is set to a period longer than the discharge time period T _{2 'is} shortened result, the expansion stroke the second discharge end timing (i.e., crank angle (SA ₂ ′ + T ₂ ′) is located on the more advanced side than the expiration time of the injection period q ₂ ′ of the expansion stroke second injection (that is, the crank angle (a ₂ ′ + q ₂ ′)).

In the lower part of FIG. 7, the first intake stroke injection is started at the crank angle A ₁ ′, and the second intake stroke injection is started at the crank angle A ₂ ′. Here, the crank angles A ₁ ′, A ₂ ′ coincide with the crank angles A ₁ , A ₂ . Further, the first injection period Q ₁ ′ and the second injection period Q ₂ ′ of the intake stroke injection are set to be equal. However, the injection periods Q ₁ ′ and Q ₂ ′ are set to a period shorter than the injection period Q ₁ (= Q ₂ ). The reason for this is to make the total injection amount in one combustion cycle equal in the upper and lower stages of FIG. Therefore, the injection periods Q ₁ ′ and Q ₂ ′ are shorter than the injection period Q ₁ (or the injection period Q ₂ ) by half of the injection period q ₁ ′ (Q ₁ ′ = Q ₁ −q ₁ ′ / 2). Note that the total injection amount in one combustion cycle is separately calculated in the ECU 40 so that the in-cylinder air-fuel ratio becomes equal to the stoichiometry.

  FIG. 8 is a diagram for explaining an in-cylinder state in a case where two injections and two discharges are performed in the expansion stroke. The four in-cylinder states depicted in FIG. 8 represent the in-cylinder states in the crank angle period during the expansion stroke shown in the lower part of FIG. “Fuel spray (i)” drawn in the first to third stages from the top of FIG. 8 corresponds to the fuel spray closest to the spark plug 32 in the fuel spray by the first injection in the expansion stroke. “Fuel spray (ii)” drawn in the fourth stage from the top in FIG. 8 corresponds to the fuel spray closest to the spark plug 32 in the fuel spray by the second injection in the expansion stroke.

As shown in the first and second stages from the top of FIG. 8, the fuel is injected from the crank angle a ₁ ′ to the crank angle (a ₁ ′ + q ₁ ′) (that is, during the first injection of the expansion stroke). The fuel spray (i) is conveyed downstream in the flow direction of the tumble flow formed in the combustion chamber 20. Further, as shown in the second stage, while the fuel spray (i) is being carried to the downstream side in the tumble flow direction, discharge sparks and flame nuclei are generated in the electrode section 34. This is because the crank angle (a ₁ '+ q ₁ ') to the crank angle (SA ₁ '+ T ₁ ') (that is, from the end of the first expansion stroke injection to the end of the first expansion stroke discharge). In this case, the first discharge of the expansion stroke is performed, and flame nuclei are generated from the discharge spark generated in the electrode part 34 by the first discharge of the expansion stroke and the air-fuel mixture including the fuel spray by the intake stroke injection. is there. This flame kernel further takes in the surrounding air-fuel mixture and becomes an initial flame.

The fuel spray (i) further transported downstream in the flow direction of the tumble flow reaches the vicinity of the electrode portion 34, thereby coming into contact with the initial flame generated from the flame kernel. As shown in the third stage from the top in FIG. 8, between the crank angle SA ₂ ′ and the crank angle a ₂ ′ (that is, from the start of the second discharge of the expansion stroke to the start of the second injection of the expansion stroke). When the initial flame comes into contact with the fuel spray (i), the initial flame grows with the fuel spray (i) involved. The flame kernel shown in the third stage is derived from the second discharge of the expansion stroke, and plays a role in assisting the initial flame to grow with the fuel spray (i). Then, as shown in the fourth stage from the top in FIG. 8, the discharge from the crank angle a ₂ ′ to the crank angle (SA ₂ ′ + T ₂ ′) (that is, from the start of the second expansion stroke injection to the second discharge of the expansion stroke). The grown initial flame can come into contact with the fuel spray (ii) injected until the end of (1).

  As described above, if the first expansion stroke injection and the first discharge of the expansion stroke are performed, the initial flame generated from the discharge spark by the first discharge of the expansion stroke and the air-fuel mixture including the fuel spray by the intake stroke injection is reduced to the fuel spray (i ) To grow. Therefore, it is possible to shorten the time until the initial flame entrains the fuel spray (ii) and keep it within an appropriate range. That is, it is possible to suppress an initial combustion speed reduction and realize an initial combustion speed equivalent to the case where it is determined that the distance DT has not increased.

[Details of first injection of expansion stroke]
Details of the injection period q ₁ ′ shown in FIG. 7 will be described with reference to FIGS. 9 to 11. FIG. 9 is a diagram showing an example of the relationship between the valve opening period τ of the injector and the amount of injected fuel. In order to realize the movement of the fuel spray (i) described in FIG. 8, in this embodiment, the injection period q ₁ ′ of the first expansion stroke injection is shorter than the injection period q ₂ ′ of the second expansion stroke injection. Set. However, as shown in FIG. 9, in the region where the valve opening period τ is extremely short, the valve opening period τ and the injected fuel amount do not show a linear relationship. This non-linearity is due to the structure of the injector. Therefore, when setting the injection period q ₁ ′, the fuel injection amount in the partial lift stable region (1 to 5 mm ³ / st (30 MPa) as an example) surrounded by the upper limit and the lower limit shown in FIG. 9 is adopted.

FIG. 10 is a diagram illustrating an example of the relationship between the number of particles PN, the combustion fluctuation rate, and the fuel injection amount in the first expansion stroke injection. The horizontal axis in FIG. 10 corresponds to the vertical axis in FIG. As shown in the upper part of FIG. 10, the particle number PN increases as the fuel injection amount increases. Further, when the combustion state is normal (normal) and the combustion state is deteriorated (combustion deterioration), the number of particles PN increases when the combustion state is worse than the normal case. On the other hand, as shown in the upper part of FIG. 10, the combustion fluctuation rate is convex downward in the injection amount range surrounded by the upper limit and the lower limit. Further, when the combustion state is normal (when normal) and the combustion state deteriorates (when combustion deteriorates), the combustion fluctuation rate becomes higher when the combustion state deteriorates than when it is normal. In the present embodiment, assuming that the particle number PN has a higher priority than the combustion fluctuation rate, the fuel injection amount corresponding to the lower limit of the partial lift stable region is adopted when setting the injection period q ₁ ′ (FIG. 10 top). Note that priority may be given to the combustion fluctuation rate instead of the particle number PN, or priority may be given to the balance between the particle number PN and the combustion fluctuation rate.

FIG. 11 is a diagram illustrating an example of the relationship between the engine coolant temperature during the cold start of the internal combustion engine 10 and the injection period in the first expansion stroke injection. As shown in the lower part of FIG. 11, the injection period q ₁ ′ of the _first injection in the expansion stroke is set to be constant regardless of the engine coolant temperature during the cold start. As shown in the upper and lower stages of FIG. 11, the injection period q ₂ ′ for the _second expansion stroke injection and the injection period q ₁ for the expansion stroke injection are also set to be constant regardless of the engine coolant temperature during the cold start. Is done. As described above, the injection period q ₂ ′ is set to a period equal to the injection period q ₁ .

[Details of first discharge of expansion stroke]
FIG. 12 is a diagram showing an example of the relationship between the ignition probability and SA-CA10 and the discharge period in the first discharge of the expansion stroke. The ignition probability referred to in FIG. 12 means the degree to which an initial flame sufficient to grow the fuel spray in the second injection of the expansion stroke is generated from the discharge spark generated in the electrode portion 34. , Evaluated by SA-CA10. Incidentally, SA-CA10 is defined as a crank angle period from the ignition timing (that is, the discharge start timing at the electrode portion 34) until the combustion mass ratio (MFB) reaches 10%. The MFB is calculated based on the analysis result of the in-cylinder pressure data obtained by using the in-cylinder pressure sensor 42 and the crank angle sensor 44, and SA-CA10 is calculated based on the calculated MFB. Note that the method for calculating MFB from the analysis result of the in-cylinder pressure data and the method for calculating SA-CA10 are described in detail in, for example, Japanese Patent Application Laid-Open Nos. 2015-094339 and 2015-098799. The description in this specification is omitted.

As can be seen from the definition of SA-CA10 described above, a small value of SA-CA10 means that the period until MFB becomes 0% to 10% is long. It means that there is not enough initial flame from the generated discharge spark to grow the fuel spray in the second expansion stroke injection. On the other hand, a large value of SA-CA10 means that the period until the MFB becomes 0% to 10% is short. From the discharge spark generated in the electrode part 34, the expansion stroke is injected for the second time. This means that there is enough initial flame to grow the fuel spray. As can be seen from FIG. 12, the longer the discharge period in the first discharge of the expansion stroke, the smaller the value of SA-CA10 and the higher the ignition probability. Based on such a viewpoint, the discharge period T ₁ ′ in the first discharge of the expansion stroke is set to a period as long as possible. Therefore, the discharge period T ₁ ′ in the first discharge of the expansion stroke is set to be longer than the discharge period T ₂ ′ in the second discharge of the expansion stroke.

[Determination on distance DT]
Whether or not the expansion stroke first injection and the expansion stroke first discharge are performed is determined based on the determination regarding the distance DT. In the present embodiment, this determination is performed using SA-CA10. FIG. 13 is a diagram showing the relationship between the combustion fluctuation rate and the SA-CA10. As shown in FIG. 13, the combustion fluctuation rate increases as the SA-CA 10 becomes longer. Here, as one of the causes of the increase in the combustion fluctuation rate, the distance DT is increased and the initial combustion speed is decreased as described above (see the description in the lower part of FIG. 6). Therefore, based on this, when the calculated SA-CA10 becomes longer than the SA-CA10 before the distance DT is expanded, that is, when the SA-CA10 is normal, one of the causes is an increase in the distance DT. It can be estimated that the initial combustion speed is reduced.

  FIG. 14 is a diagram illustrating determination values related to the distance DT. As shown in FIG. 14, in the present embodiment, the actually calculated SA-CA10 (hereinafter also referred to as “real SA-CA10”) is a predetermined crank angle period (as an example) than the normal SA-CA10. When it becomes longer than 5 °), it is determined that the distance DT is increased. It is assumed that the SA-CA10 longer than the normal SA-CA10 by a predetermined crank angle period is set after obtaining “normal SA-CA10” by prior adaptation.

[Specific processing in the embodiment]
FIG. 15 is a flowchart illustrating an example of processing executed by the ECU 40 in the embodiment of the present invention. Note that the routine shown in this figure is repeatedly executed while an operation mode for executing catalyst warm-up control (hereinafter also referred to as “catalyst warm-up mode”) is selected.

In the routine shown in FIG. 15, first, fuel injection control for injecting once in the expansion stroke and discharge control for discharging once in the expansion stroke are executed (step S100). Specifically, in step S100, the injection amount of the intake stroke injection (injection periods Q ₁ and Q ₂ ) and the injection start timing (crank angles A ₁ and A ₂ ) are set. Also, an injection amount (injection period q ₁ ) of the expansion stroke injection and an injection start period (crank angle a ₁ ) are set. Further, the start timing SA ₁ of the discharge of the expansion stroke, the discharge period T ₁ is set. The difference period between the discharge start timing in the expansion stroke after setting and the injection start timing in the expansion stroke injection after setting is the interval I ₁ described in FIG.

  Subsequent to step S100, it is determined whether the actual SA-CA10 is longer than the normal SA-CA10 by a predetermined crank angle period or more (step S102). In step S102, the actual SA-CA10 calculated separately in the ECU 40 is acquired and compared with the normal SA-CA10 (set value). As a result of the comparison, when it is determined that the actual SA-CA10 is longer than the normal SA-CA10 by a predetermined crank angle period or more (in the case of “Yes”), the process proceeds to step S104. On the other hand, if it is determined that this is not the case (“No”), the routine is exited.

In step S104, fuel injection control for injecting twice in the expansion stroke is executed. In step S104, the intake stroke injection amount (injection period Q ₁ ′, Q ₂ ′) and the injection timing (crank angle A ₁ ′, A ₂ ′) are specifically set. In addition, the injection amount (injection period q ₁ ′) of the first injection in the expansion stroke and the injection timing (crank angle a ₁ ′) are set. Further, the injection amount (injection period q ₂ ′) of the second injection in the expansion stroke and the injection timing (crank angle a ₂ ′) are set. In addition, a discharge period T ₁ ′ of the _first discharge of the expansion stroke and a discharge start time SA ₁ ′ are set. In addition, a discharge period T ₂ ′ for the second discharge of the expansion stroke and a discharge start time SA ₂ ′ are set. The difference period between the start timing of the first discharge in the expansion stroke after the setting and the injection start timing in the first injection in the expansion stroke after the setting is the interval I ₁ ′ described in FIG. 7, and the expansion stroke after the setting The difference period between the start time of the second discharge and the injection start time in the second injection in the expansion stroke is the interval I ₂ ′ described in FIG.

  According to the present embodiment described above, the following effects can be obtained. That is, if it is determined that the distance DT has not increased, the initial combustion can be stabilized by the expansion stroke injection described with reference to FIG. 3, and the combustion fluctuation can be suppressed. Even when it is determined that the distance DT has increased, the initial combustion is stabilized by the first expansion stroke injection and the first discharge of the expansion stroke described in the lower part of FIG. The combustion fluctuation can be suppressed similarly to the case where it is determined that there is no.

[Modification of Embodiment]
By the way, in the above embodiment, the tumble flow formed in the combustion chamber 20 is directed from the upper part to the lower part of the combustion chamber 20 on the exhaust port 24 side, and directed upward from the lower part of the combustion chamber 20 on the intake port 22 side. I tried to turn like this. However, the tumble flow swirls in the opposite direction, that is, from the upper side of the combustion chamber 20 toward the lower side on the intake port 22 side and from the lower side to the upper side of the combustion chamber 20 on the exhaust port 24 side. Also good. However, in this case, it is necessary to change the arrangement location of the spark plug 32 from the exhaust valve 28 side to the intake valve 26 side. If the location of the spark plug 32 is changed in this way, the spark plug 32 is positioned downstream of the injector 30 in the tumble flow direction. Therefore, it is possible to realize movement of the fuel spray (that is, fuel spray (i)) in the direction of the electrode portion 34 by the first injection of the expansion stroke described in FIG.

  Moreover, in the said embodiment, the determination regarding expansion of the distance DT was performed using SA-CA10. However, instead of SA-CA10, the determination regarding the expansion of the distance DT may be performed using a known parameter having a correlation with the initial combustion speed. That is, any known parameter that can compare the initial combustion speed with the determination value can be used instead of SA-CA10.

In the above-described embodiment, when it is determined that the distance DT has increased, the first discharge in the expansion stroke corresponding to the first injection in the expansion stroke and the second injection in the expansion stroke are performed as the second discharge in the expansion stroke. A corresponding second expansion stroke discharge was performed. However, the discharge in the expansion stroke may not be performed twice, and one discharge corresponding to both the first expansion stroke injection and the second expansion stroke injection may be performed in the expansion stroke. This is because the in-cylinder state described with reference to FIG. 8 can be realized even when the first discharge in the expansion stroke and the second discharge in the expansion stroke are continuously performed. When the discharge is performed once in the expansion stroke, for example, the discharge may start at the crank angle SA ₁ ′ described in FIG. 7 and end at the crank angle (SA ₂ ′ + T ₂ ′).

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Cylinder 14 Cylinder block 16 Cylinder head 18 Piston 20 Combustion chamber 22 Intake port 24 Exhaust port 30 Injector 32 Spark plug 34 Electrode part 36 Throat 40 ECU
42 In-cylinder pressure sensor 44 Crank angle sensor 46 Temperature sensor

Claims (1)

An injector provided at the top of the combustion chamber and directly injecting fuel into the cylinder;
An ignition plug for igniting an air-fuel mixture in a cylinder using a discharge spark generated in an electrode unit, the upper part of the combustion chamber, and downstream of the injector in the flow direction of a tumble flow formed in the combustion chamber An ignition plug provided on the side and provided such that the position of the electrode portion is above the outer surface of the fuel spray injected from the injector toward the ignition plug;
An internal combustion engine control device for controlling an internal combustion engine comprising an exhaust gas purification catalyst for purifying exhaust gas from the combustion chamber,
The control device controls the spark plug so that a discharge spark is generated in a predetermined period that is retarded from the compression top dead center as control for activating the exhaust purification catalyst, and from the compression top dead center. Expansion stroke injection on the retard side, the injection period overlaps at least a part of the predetermined period, and the end time is an advance side relative to the end time of the predetermined period; And controlling the injector to perform intake stroke injection in the same cycle as the cycle in which the expansion stroke injection is performed,
The control device further includes the intake stroke injection and the expansion stroke when it is determined that the growth rate of the initial flame generated from the air-fuel mixture including the fuel spray by the intake stroke injection and the discharge spark is lower than a predetermined determination value. It is additional injection in the same cycle as the cycle in which injection is performed, and is retarded from the compression top dead center, and advanced from the start timing of the expansion stroke injection and the start timing of the predetermined period. A discharge period in which the injector is controlled to perform the additional injection, and is started from the advance side with respect to the injection start timing of the additional injection and expires on the retard side with respect to the injection start timing of the expansion stroke injection A control device for an internal combustion engine, wherein the spark plug is controlled so that a discharge spark is generated in the engine.

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