JP6131847B2 - Control unit for direct injection engine - Google Patents

Description

  The present invention relates to a control device for a direct injection engine.

  Conventionally, for the purpose of improving fuel efficiency, compression auto-ignition combustion has been performed in a combustion chamber formed in a cylinder of an engine body.

  In compression self-ignition combustion, it is necessary to raise the temperature of the air-fuel mixture in the cylinder to a temperature at which self-ignition is possible. Therefore, normally, when performing compression auto-ignition combustion, the air-fuel mixture is heated by internal EGR or the like. However, if the fuel cut is performed to stop the fuel supply at the time of deceleration or the like, the wall surface temperature of the combustion chamber decreases as the combustion is stopped. There is a problem that it becomes difficult.

  To solve this problem, for example, in Patent Document 1, compression auto-ignition combustion is not performed at the time of return from the fuel cut, but spark ignition combustion is performed, and compression auto-ignition combustion is not performed until a predetermined time has elapsed after the return. The transition is disclosed.

Japanese Patent No. 4159918

  In the invention of Patent Document 1, since spark ignition combustion is performed instead of compression self-ignition combustion, fuel efficiency cannot be sufficiently improved.

  The present invention has been made in view of the above points, and provides a control device for a direct injection engine that can realize stable compression auto-ignition combustion at an earlier stage after restarting combustion after execution of fuel cut.

  In order to solve the above problems, the present invention includes a fuel injection device capable of injecting fuel into a combustion chamber formed in a cylinder, and reciprocating a piston by combusting a mixture of fuel and air in the combustion chamber. A control device for a direct-injection engine to be moved, comprising: determination means for determining an operating state of the engine; and at least an operation in a compression auto-ignition combustion region in which an engine load is set to a region lower than a predetermined load. Combustion control means for controlling each part of the engine including the fuel injection device so that the air-fuel mixture is combusted by self-ignition, and the combustion control means is a fuel cut in which fuel injection from the fuel injection device is stopped When the combustion is restarted in the compression auto-ignition combustion region after performing the above, the air-fuel mixture is combusted by auto-ignition and the required engine torque is generated in the fuel injection device. And a post-injection for injecting fuel into the combustion chamber at a predetermined timing in the expansion stroke after the main injection, and injection of the post-injection The timing is set to the advanced side as the in-cylinder state temperature that affects the combustibility of the air-fuel mixture containing the post-injected fuel burns, and the in-cylinder state temperature is lower. There is provided a control device for a direct injection engine characterized by timing.

  According to the present invention, stable compression auto-ignition combustion can be realized at an early stage by increasing the wall surface temperature of the combustion chamber at an early stage after resuming the combustion after the fuel cut is performed without giving a torque shock. This can achieve high combustion stability and leads to high fuel efficiency.

  Specifically, in the present invention, while performing the main injection according to the required engine torque, the post-injection is performed during the expansion stroke after the main injection, that is, at a timing at which the generated combustion energy is difficult to be converted into an effective engine torque. We are carrying out. For this reason, the required engine torque is appropriately generated by the main injection, and the combustion energy generated by the post injection avoids the generation of a torque higher than the required engine torque. The amount of heat generated can be increased, and the wall surface temperature of the combustion chamber can be raised.

  Moreover, in the present invention, the lower the in-cylinder state temperature that influences the combustibility of the air-fuel mixture, that is, the more the post-injected fuel is more difficult to burn, the more the post-injection injection timing is advanced. The Therefore, at least a part of the post-injected fuel can be reliably burned, and the wall surface temperature of the combustion chamber can be more reliably increased by this combustion energy.

  In the present invention, the combustion control means performs the post-injection over a plurality of cycles after resuming combustion in the compression auto-ignition combustion region after fuel cut, and increases the number of elapsed cycles from immediately after resuming combustion. It is preferable to set the injection timing of the post injection to the retard side (Claim 2).

  In this configuration, the number of cycles that have elapsed immediately after resuming combustion increases, the in-cylinder state temperature increases, and the post-injection delay of fuel in the case of post-injection at the same timing becomes shorter, the post-injection injection timing becomes retarded. To be. Therefore, it is possible to more reliably avoid the occurrence of torque shock due to the combustion energy generated by early combustion of the post-injected fuel being converted into an excessively effective engine torque.

  In the above-described configuration, a purification device capable of purifying the exhaust discharged from the direct injection engine is provided, and the combustion control means is configured to reduce a temperature in the purification device when combustion is resumed in the compression auto-ignition combustion region after a fuel cut. Is lower than a preset first reference temperature and higher than a second reference temperature, the injection timing of the post-injection is set to a timing at which a part of the post-injected fuel does not burn in the combustion chamber. (Claim 3).

  As described above, when the present invention is applied to a device equipped with a purification device, the purification device that has become low temperature as a result of fuel cut is activated early due to an increase in exhaust gas temperature due to an increase in combustion energy due to post injection. be able to.

  Further, in this configuration, the purification device having a temperature lower than the first reference temperature and higher than the second reference temperature, that is, a purification device that is capable of reacting in the purification device but is not sufficiently activated. Unburned fuel can be supplied, and the purification device can be heated and activated more effectively by reacting the unburned fuel in the purification device.

  In the present invention, the combustion control means may divide the fuel into a plurality of times during the compression process as the main injection when the combustion is restarted in the compression auto-ignition combustion region after the fuel cut. It is preferable to carry out the compression process divided injection for injection.

  In this way, in addition to the temperature rise effect of the wall surface temperature in the combustion chamber by the post injection, the combustion promotion effect by the compression stroke division injection makes the auto-ignition combustion more stable and stable when the combustion is restarted after the fuel cut. Can be realized.

  Specifically, in this configuration, by performing the compression stroke division injection, the fuel amount per injection and the fuel spray penetration (penetration force) are suppressed, and the fuel diffusion is suppressed, thereby the vicinity of the compression top dead center. In the combustion chamber, the air-fuel ratio is locally richer than the stoichiometric air-fuel ratio and an air-fuel mixture with a short ignition delay can be formed. And the combustion of the whole air-fuel mixture can be promoted by inducing the combustion of the other air-fuel mixture by early ignition and combustion of the locally rich air-fuel mixture formed in the combustion chamber.

  As described above, according to the present invention, at the time of resuming combustion in the compression auto-ignition combustion region from the fuel cut, more reliable and stable compression auto-ignition combustion can be realized, and high fuel efficiency can be obtained. .

1 is a schematic view showing an engine system according to an embodiment of the present invention. It is a block diagram which concerns on control of the engine system shown in FIG. It is sectional drawing which expands and shows the combustion chamber shown in FIG. (A) It is the figure which showed the lift characteristic of the exhaust valve in normal mode. (B) It is the figure which showed the lift characteristic of the exhaust valve in a special mode. It is a figure which illustrates the operation control map of an engine. (A) It is a figure which shows the injection pattern of intake stroke batch injection. (B) It is a figure which shows the injection pattern of main injection and post injection. It is a figure which shows the mode of the injection in a cavity. It is a flowchart which shows the flow of the fuel-injection control which concerns on embodiment of this invention. (A) It is the figure which showed distribution of the equivalent ratio at the time of collective injection. (B) It is the figure which showed distribution of the equivalent ratio at the time of collective injection. (C) It is the figure which showed distribution of the equivalent ratio at the time of division | segmentation injection. It is the figure which showed the relationship between the ignition delay of air-fuel | gaseous mixture, and an equivalent ratio. It is a figure for demonstrating the effect of the engine system which concerns on embodiment of this invention. It is a figure which shows the other example of an injection pattern. It is a figure which shows the other example of an injection pattern.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an engine system 100 to which a control device for a direct injection engine according to the present invention is applied. The engine system 100 is mounted on a vehicle and has an engine body 1.

  The engine body 1 is a gasoline engine to which a fuel containing at least gasoline is supplied, and is a four-cycle engine, that is, an engine in which an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke are sequentially performed. As will be described later, the engine body 1 is a direct injection engine configured such that fuel can be directly injected into a cylinder 10 (combustion chamber 11) by an injector (fuel injection device) 15. The engine body 1 is an engine that realizes compression self-ignition combustion, as will be described later.

  The engine body 1 has a cylinder block 12 in which a cylinder 10 is formed and a cylinder head 13. In the present embodiment, four cylinders 10 are formed in series with the cylinder block 12. In each cylinder 10, a piston 14 connected to a crankshaft via a connecting rod is fitted so as to be able to reciprocate. In each cylinder 10, a combustion chamber 11 surrounded by the inner surface of the cylinder 10, the crown surface of the piston 14, and the cylinder head 13 is formed.

  Hereinafter, the reciprocating direction of the piston 14 is referred to as the vertical direction, and the side on which the cylinder head 13 is disposed with respect to the cylinder block 12 is referred to as the upper side.

  In the present embodiment, the geometric compression ratio of the engine body 1 is set to a relatively high value of 15 or more for the purpose of improving the thermal efficiency and stabilizing the compression ignition combustion. The geometric compression ratio of the engine body 1 is not limited to this, but a range of about 15 or more and 20 or less is preferable.

  The piston 14 and the combustion chamber 11 have a configuration as shown in FIG. A cavity 11 a having a concave shape that is recessed in a direction away from the ceiling of the cylinder head 13 and the combustion chamber 11, that is, in the downward direction, is formed in the center in the radial direction of the piston 14. The cavity 11a has an opening facing the ceiling of the combustion chamber 11, that is, upward, at the upper end thereof. The opening area of the opening of the cavity 11a is set to be smaller than the maximum value of the area of the horizontal cross section at each height position inside the cavity 11a. That is, the cavity 11a is constricted so that the inner diameter becomes narrower in the range from the opening to a predetermined depth.

  An injector 15 that directly injects fuel into the combustion chamber 11 is attached to the cylinder head 13 for each cylinder 10. As shown in FIG. 3, the injector 15 is disposed so as to face the inside of the combustion chamber 11 from the radial center of the ceiling surface of the combustion chamber 11 so that the nozzle hole faces the radial center of the cavity 11 a. . In the present embodiment, the injector 15 is a multi-hole type having a plurality of nozzle holes, and the fuel spray injected from the injector 15 spreads radially downward from the radial center of the combustion chamber 11. The injector 15 injects relatively high-pressure fuel pumped from a fuel tank (not shown) by a fuel supply system (not shown) into the combustion chamber 11.

  A spark plug 16 that forcibly ignites the air-fuel mixture in the combustion chamber 11 is attached to the cylinder head 13 for each cylinder 10. Each spark plug 16 is arranged such that an electrode portion provided at the tip thereof is positioned in the vicinity of the nozzle hole of the injector 15.

  The cylinder head 13 is provided with an intake port 17 for introducing intake air into the cylinder 10 and an exhaust port 18 for discharging exhaust gas from the cylinder 10 for each cylinder 10. The intake port 17 and the exhaust port 18 are respectively provided with these ports 17, 18, and more specifically, an intake valve 21 and an exhaust valve 22 that open and close the openings of the ports 17, 18 formed in the cylinder head 13, respectively. It is installed.

  The exhaust valve 22 is driven by an exhaust valve drive mechanism 23. The exhaust valve drive mechanism 23 includes an exhaust valve lift variable mechanism (hereinafter referred to as an exhaust VVL (Variable Valve Lift)) 23a and an exhaust phase variable mechanism (hereinafter referred to as an exhaust VVT (Variable Valve Timing)) 23b.

  The exhaust VVL 23a switches the operation mode of the exhaust valve 22 between a normal mode shown in FIG. 4 (a) and a special mode shown in FIG. 4 (b). In the normal mode, the exhaust valve 22 is opened mainly during the exhaust stroke (the majority of the period from the start of valve opening to the valve closing overlaps with the exhaust stroke). At this time, the valve lift of the exhaust valve 22 gradually increases after the valve is opened, and when reaching the maximum lift, it gradually decreases again and reaches zero. In the special mode, the valve lift of the exhaust valve 22 gradually increases after the valve opening and reaches the maximum lift during the first valve opening period t_1 as in the normal mode. Without reaching zero as it is, the lift amount, that is, a lift lower than the maximum lift in the first valve opening period t_1 is maintained to zero after maintaining the second valve opening period t_2. The exhaust VVL 23a includes a first cam and a second cam having different cam shapes in order to realize these modes. The first cam has a shape corresponding to the lift characteristic shown in FIG. 4A and has one cam crest. The second cam has a shape corresponding to the lift characteristics shown in FIG. 4B, and has two cam peaks. The exhaust VVL 23 a includes a lost motion mechanism that selectively transmits the operating state of the first cam and the second cam to the exhaust valve 22. By transmitting the operating state of the first cam to the exhaust valve 22, the exhaust valve 22. The operation state is set to the normal mode, and the operation state of the exhaust valve 22 is set to the special mode by transmitting the operation state of the second cam to the exhaust valve 22. The exhaust VVL 23a is, for example, hydraulically operated.

  The exhaust VVT 23b changes the opening timing and closing timing of the exhaust valve 22 by changing the rotational phase of the exhaust camshaft with respect to the crankshaft. The exhaust VVT 23b changes the valve opening timing and the valve closing timing of the exhaust valve 22 while keeping the valve opening period of the exhaust valve 22 constant in each of the normal mode and the special mode. The exhaust VVT 23b may employ a hydraulic, electromagnetic, or mechanical known structure as appropriate, and a detailed description thereof is omitted.

  The exhaust VVT 23b sets the rotation phase of the exhaust camshaft so that the exhaust valve 22 opens in the intake stroke in addition to the exhaust stroke when the exhaust valve 22 is in the special mode. Further, when the exhaust valve 22 is in the special mode, the exhaust VVT 23b has an exhaust top dead center (TDC in FIG. 4B) during the second valve opening period t_2, that is, the exhaust VVT 23b is exhausted. The rotational phase of the exhaust camshaft is set so that the valve lift of the exhaust valve 22 at the top dead center becomes a relatively small value realized during the second valve opening period t_2. Thus, in the present embodiment, the exhaust valve 22 is opened during the intake stroke in addition to the exhaust stroke when the operating state of the exhaust valve 22 is set to the special mode. In particular, in the present embodiment, the exhaust valve 22 is continuously opened in the exhaust stroke and the intake stroke with the exhaust top dead center being sandwiched without closing in the middle. Here, when the exhaust valve 22 is continuously opened across the exhaust top dead center, the exhaust valve 22 and the piston 14 may interfere with each other. In contrast, in the present embodiment, as described above, the valve lift amount of the exhaust valve 22 near the exhaust top dead center is suppressed to a small value, so that interference between the exhaust valve 22 and the piston 14 is avoided. Can do. The exhaust double opening, that is, the special mode is performed in order to perform so-called internal EGR by leaving the high-temperature burned gas, that is, the internal EGR gas in the combustion chamber 11. Specifically, when the exhaust is opened twice and the exhaust valve 22 is opened even during the intake stroke, the exhaust once discharged to the exhaust port 18 during the exhaust stroke is in the combustion chamber 11 during the intake stroke. The exhaust gas, that is, the high-temperature burned gas remains in the combustion chamber 11.

  The intake valve 21 is driven by an intake valve drive mechanism 24. The specific configuration of the intake valve drive mechanism 24b is not particularly limited. For example, an intake VVL 24a that can change the valve lift of the intake valve 21 and an intake VVT 24b that changes the opening timing and closing timing of the intake valve 21 are provided. Including.

  An intake passage 30 is connected to each intake port 17. Specifically, branch passages that branch in correspondence with the cylinders 10 are formed at the downstream end of the intake passage 30, and these branch passages are connected to the intake ports 17.

  In the intake passage 30, an air cleaner 31, a throttle valve 32, and a surge tank 33 are arranged in this order from the upstream side.

  An exhaust passage 40 is connected to each exhaust port 18. Specifically, similarly to the intake passage 30, branch passages that branch to correspond to the cylinders 10 are formed at the upstream end of the exhaust passage 40, and these branch passages are connected to the intake ports 17. .

  A purification device that purifies harmful components in the exhaust gas is disposed in the exhaust passage 40. In the present embodiment, a direct catalyst 41 and an underfoot catalyst 42 are provided in order from the upstream side. The direct catalyst 41 and the underfoot catalyst 42 include a three-way catalyst.

  An EGR device 50 is provided between the intake passage 30 and the exhaust passage 40 to recirculate a part of the exhaust gas to the intake air, that is, to perform external EGR. The EGR device 50 includes an EGR passage 51 and an EGR cooler 52. The EGR passage 51 connects a portion of the intake passage 30 between the surge tank 33 and the throttle valve 32 and a portion of the exhaust passage 40 upstream of the direct catalyst 41. The EGR cooler 52 is for cooling the gas passing through the EGR passage 51, and is interposed in the EGR passage 51. In the present embodiment, the gas passing through the EGR passage 51 is necessarily cooled by the EGR cooler 52. The EGR passage 51 is provided with an EGR valve 53 that adjusts the flow rate of the exhaust gas that passes through the EGR passage 51. Hereinafter, recirculation of a part of the exhaust gas to the intake air using the EGR device 50 is referred to as external EGR, and the exhaust gas recirculated to the intake air by the EGR device 50 may be referred to as external EGR gas.

  Each of the devices is controlled by a powertrain control module (hereinafter referred to as PCM) 60. The PCM 60 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units.

  As shown in FIGS. 1 and 2, detection signals from various sensors SW <b> 1 to SW <b> 12 are input to the PCM 60.

The sensor SW1 is an air flow sensor SW1 that detects the flow rate of fresh air. The sensor SW2 is an intake air temperature sensor that detects the temperature of fresh air. The air flow sensor SW1 and the intake air temperature sensor SW2 are disposed on the downstream side of the air cleaner 31 in the intake passage 30. The sensor SW3 is an EGR gas temperature sensor for detecting the temperature of the external EGR gas. The EGR gas temperature sensor SW3 is disposed in the vicinity of the connection portion with the intake passage 30 in the EGR passage 51. The sensor SW4 is an intake port temperature sensor that detects the temperature of intake air immediately before flowing into the cylinder 10. The intake port temperature sensor SW4 is attached to the intake port 17. The sensor SW5 is an exhaust temperature sensor that detects the exhaust temperature. The sensor SW6 is an exhaust pressure sensor that detects the exhaust pressure. The exhaust temperature sensor SW5 and the exhaust pressure sensor SW6 are disposed in the vicinity of the connection portion of the EGR passage 51 in the exhaust passage 40. The sensor SW7 is a linear O ₂ sensor that detects the oxygen concentration in the exhaust gas. The linear O ₂ sensor SW 7 is disposed on the upstream side of the direct catalyst 41 in the exhaust passage 40. The sensor SW8 is a lambda O ₂ sensor that detects the oxygen concentration in the exhaust gas. The lambda O ₂ sensor SW8 is disposed between the direct catalyst 41 and the underfoot catalyst 42. The sensor SW9 is a water temperature sensor that detects the temperature of the engine cooling water. The sensor SW10 is a crank angle sensor that detects the rotation angle of the crankshaft. The sensor SW11 is an accelerator opening sensor that detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle. The sensor SW12 is a catalyst temperature sensor that detects the temperature of the catalyst included in the direct catalyst 41, that is, the temperature in the direct catalyst 41 that is a purification device. The catalyst temperature sensor SW12 is attached to the direct catalyst 41.

  The PCM 60 performs various calculations based on the detection signals of the sensors SW1 to SW11. The PCM 60 determines the operating conditions of the engine body 1 and the vehicle based on these detection signals. The PCM 60 outputs control signals to the actuators of the injector 15, spark plug 16, fuel supply system, intake VVT 24b, intake VVL 24a, exhaust VVT 23b, exhaust VVL 23a, and various valves (throttle valve 32, EGR valve 53) according to operating conditions. And control these. Thus, in this embodiment, the PCM 60 controls the determination means for determining the operating state of the engine from the engine speed, the engine load, and the like, the injector 15, the spark plug 16, and the like in the combustion chamber 11. The combustion mode of the air-fuel mixture is controlled and functions as a combustion control means for realizing compression auto-ignition combustion in the CI combustion region, as will be described later.

  The contents of control by the PCM 60 will be described next.

  FIG. 5 is a control map of the engine speed on the horizontal axis and the engine load on the vertical axis. In the engine system 100, in a high load region (SI (Spark Ignition) combustion region) in which the engine load is equal to or higher than a preset combustion switching load T1, combustion noise becomes a problem when performing compression auto-ignition combustion. Spark ignition combustion is performed by igniting the plug 16 to burn the air-fuel mixture. On the other hand, in the CI (Compression Ignition) combustion region (compression ignition combustion region) in which the engine load that suppresses combustion noise is set to a low load region less than the combustion switching load T1, the air-fuel mixture is not ignited by the spark plug 16. Compressed self-ignition combustion is performed in which self-ignition is performed.

  Detailed control contents in the CI combustion region will be described.

  In order to realize stable compression self-ignition combustion, it is necessary to raise the temperature of the air-fuel mixture to a temperature at which self-ignition is possible. Therefore, in the CI combustion region, internal EGR is performed to cause the internal EGR gas, which is a high-temperature burned gas, to remain in the combustion chamber 11, thereby increasing the temperature in the combustion chamber 11 and the air-fuel mixture. Specifically, in the CI combustion region, the exhaust valve 22 is opened twice with the operating state of the exhaust valve 22 as a special mode. However, in the CI combustion region where the engine load is relatively high (in the example shown in FIG. 5, the region where the engine load is equal to or higher than the EGR switching load T2), the temperature of the air-fuel mixture is sufficiently high and the internal EGR gas is excessive. If introduced, the air-fuel mixture may ignite prematurely or combustion noise may increase. Therefore, in the present embodiment, in the low load side CI combustion region CI_1 in which the engine load is set to be less than the EGR switching load T2, only the internal EGR is performed, and the engine load is equal to or higher than the EGR switching load T2 and less than the combustion switching load T1. In the set high load side CI combustion region CI_2, in addition to the internal EGR, the external EGR is performed to introduce the external EGR gas cooled by the EGR cooler 52, thereby suppressing the temperature of the mixture from rising excessively. . Specifically, in the high-load side CI combustion region CI_2 region, the exhaust valve 22 is opened twice while the operating state of the exhaust valve 22 is set to the special mode, and the EGR valve 53 is opened.

  In the CI combustion region, the air-fuel ratio of the entire air-fuel mixture is made leaner than the stoichiometric air-fuel ratio in order to further improve fuel efficiency. That is, in the CI combustion region, the excess air ratio λ of the entire air-fuel mixture is set to λ> 1.

  Here, for example, in the case of steady operation of an engine in which the vehicle is in power running, etc., and combustion continues, the wall surface temperature of the combustion chamber 11 and the temperature of the exhaust gas are kept high to some extent. Therefore, in this case, the temperature of the air-fuel mixture can be appropriately increased by introducing the internal EGR gas as described above. However, when a fuel cut that stops fuel injection and combustion is performed during deceleration or the like, the wall surface temperature of the combustion chamber 11 decreases. In addition, when the wall surface temperature of the combustion chamber 11 is low, the temperature of the generated exhaust gas is also kept low. Therefore, when returning from the fuel cut to the CI combustion region, that is, when resuming combustion in the CI combustion region after the fuel cut is performed, the temperature of the air-fuel mixture can be sufficiently increased even if the internal EGR gas is introduced. There is a problem that proper compression auto-ignition combustion cannot be realized.

  On the other hand, in the engine system 100, in the CI combustion region, the control of the air-fuel ratio and the control of EGR are performed at the time of return from the fuel cut and other operating conditions (hereinafter referred to as steady operation). Higher fuel economy performance during steady operation, etc., while maintaining the same, i.e., making the air / fuel ratio of the entire air-fuel mixture lean and opening the exhaust twice while varying the fuel injection control contents In addition to realizing the exhaust performance, stable compression auto-ignition combustion is realized at the time of return from the fuel cut, and compression auto-ignition combustion is performed in the CI combustion region regardless of whether or not the return from the fuel cut. Note that specific operating conditions for returning from the fuel cut to the CI combustion region are included in the CI combustion region when the idling operation set in the CI combustion region after the fuel cut is performed, or after the fuel cut. This is the case when relatively moderate acceleration is performed. The contents of the fuel injection control in the CI combustion region will be described next.

(1) Fuel injection control during steady operation, etc. When the engine is in steady operation in the CI combustion region, as shown in FIG. 6 (a), intake stroke collective injection that injects fuel during the intake stroke collectively. And perform premixed compression auto-ignition combustion. That is, the fuel and air are sufficiently mixed in advance by the compression top dead center so that the air-fuel ratio of the entire air-fuel mixture becomes substantially uniform lean, and self-ignition is performed in the vicinity of the compression top dead center. In FIG. 6A, the heat generation rate dQ / dθ when the intake stroke batch injection is performed is indicated by a broken line.

  In this way, in the engine system 100, high fuel efficiency and exhaust performance can be obtained by performing homogeneous premixed compression self-ignition combustion of air-fuel ratio lean during steady operation or the like.

(2) Fuel injection control at the time of return from the fuel cut When returning to the CI combustion region from the fuel cut, as shown in FIG. 6 (b), main injection for generating the required engine torque is performed, Later, during the expansion stroke, post injection is performed. In this embodiment, post injection is performed over a plurality of cycles immediately after return. As the number of elapsed cycles increases, the post injection timing is retarded. Further, the injection timing of the post injection (hereinafter sometimes referred to as post injection timing) is set so that at least a part of the post-injected fuel is burned, although it does not become an effective engine torque. Thus, the lower the in-cylinder state temperature, the more advanced the side. In FIG. 6B, the heat generation rate dQ / dθ when the intake stroke batch injection is performed is indicated by a broken line.

  Moreover, in this embodiment, the compression stroke division injection which injects the fuel according to a request | required engine torque in multiple times during a compression stroke is performed as main injection. In this embodiment, this compression stroke division injection is performed while post injection is being performed.

  Here, a part of the fuel may be injected into the intake stroke, and the remaining fuel may be divided and injected during the compression stroke. However, in the present embodiment, as shown in FIG. 6B, only during the compression stroke. Split injection of fuel. FIG. 6B shows a case where the fuel is injected four times during the compression stroke.

  Further, in the present embodiment, each fuel is injected at a timing when each fuel separately injected during the compression stroke is accommodated in the cavity 11a. Specifically, as shown in FIG. 7, the divided injection is performed at the timing when the tip of each fuel spray injected by the divided injection enters the inside of the cavity 11a. In this embodiment, each injection timing of the divided injection during the compression stroke is set in the latter half of the compression stroke. More specifically, it is preferable that the timing of the compression process divided injection is set between 20 ° CA before compression top dead center and 80 ° CA before compression top dead center.

  The fuel injection control flow and post injection timing setting procedure in the CI combustion region will be described with reference to the flowchart of FIG.

  First, in step S1, the PCM 60 determines whether or not it is time to return from the fuel cut to the CI combustion region. If this determination is NO, the process proceeds to step S2. In step S2, fuel injection control during steady operation, that is, intake stroke batch injection is performed.

  On the other hand, if the determination in step S1 is YES and it is the time of return from the fuel cut to the CI combustion region, the process proceeds to step S3. In step S3, the in-cylinder state temperature Tcyl_post is calculated. The in-cylinder state temperature Tcyl_post is an index representing the ease of combustion of the post-injected fuel, and is a temperature determined by the temperature of the wall surface of the combustion chamber and the temperature of the mixture in the combustion chamber immediately before the post-injection, It is the atmospheric temperature in the combustion chamber at a predetermined timing after the main injection. As the in-cylinder state temperature Tcyl_post is lower, the post-injected fuel becomes harder to burn. In the present embodiment, the in-cylinder state temperature Tcyl_post is determined by the wall surface temperature of the combustion chamber, the compression end temperature of the air-fuel mixture, and the amount of heat generated by the main injection. Specifically, each temperature and calorific value are calculated from the engine water temperature, intake air temperature, injection amount, engine speed, and the like, and the in-cylinder state temperature Tcyl_post is calculated based on these calculation results.

  In step S4, which proceeds after step S3, the injection timing of post injection to be performed immediately after the return is determined. As described above, the post-injection timing is determined at a timing at which at least a part of the post-injected fuel is combusted while the combustion energy generated by the post-injection is not converted into an effective engine torque. Here, as described above, the lower the in-cylinder state temperature Tcly_post, the less post-injected fuel is combusted. Therefore, in order to reliably burn the post-injected fuel, it is necessary to perform the post-injection under a higher temperature condition, that is, at an advanced angle side (a side closer to the compression top dead center). Therefore, in step S4, the post-injection timing is determined as the advance timing as the in-cylinder state temperature Tcly_post calculated in step S3 is lower. Specifically, it is a map of the post injection timing with respect to the in-cylinder state temperature Tcly_post in advance in the PCM 60, and at least a part of the post-injected fuel burns, while the combustion energy generated by the post injection is effective. The map of the post-injection timing set to the advance side value is stored as the in-cylinder state temperature Tcly_post is lower, and the post-injection timing corresponding to the in-cylinder state temperature Tcly_post is stored from this map. Extracted.

  In step S5, which proceeds after step S4, the elapsed cycle is initially set to 1.

  In step S6, which proceeds after step S5, it is determined whether or not the elapsed cycle is less than 2, that is, whether or not the elapsed cycle is 1 and immediately after return. When this determination is YES and immediately after the return, the process proceeds to step S11.

  On the other hand, if the determination in step S6 is NO and the elapsed cycle is 2 or more, the process proceeds to step S7. Here, if the number of elapsed cycles from the return increases, the in-cylinder state temperature rises, and the combustion energy of the post-injected fuel is easily converted into effective engine torque. Therefore, it is preferable that the post injection timing is retarded as the number of elapsed cycles increases. Therefore, in the present embodiment, the post injection timing is retarded each time the elapsed cycle increases. That is, in this step S7 that proceeds when the number of elapsed cycles is 2 or more, the post injection timing is retarded from the timing of the previous cycle.

  Here, depending on the operating conditions, etc., the in-cylinder state temperature Tcly_post may be raised to some extent, while the catalyst temperature Tcat, that is, the temperature in the purification device is low, and it may be desirable to preferentially warm the catalyst temperature early. In this case, if the temperature of the catalyst is raised to some extent so that self-reaction is possible, the catalyst temperature can be made earlier by supplying unburned fuel and allowing it to self-react rather than supplying high-temperature exhaust gas to the catalyst. Can be warmed. In the present embodiment, assuming the above-described case, the following steps S8 to S10 are performed to increase the in-cylinder state temperature Tcly_post to some extent, and when the catalyst temperature Tcat is within a predetermined range, post injection A part of the fuel that has been discharged is supplied to the catalyst device without burning.

  In step S8 that follows step S7, it is determined whether or not the in-cylinder state temperature Tcyl_post exceeds a preset first reference in-cylinder state temperature Tcyl_post_H1. If this determination is NO and it is determined that the in-cylinder state temperature Tcyl_post has not yet sufficiently increased, the following steps S9 and S10 are not performed, and the process proceeds to step S11.

  On the other hand, if the determination in step S8 is YES and it is determined that the in-cylinder state temperature Tcyl_post exceeds the first reference in-cylinder state temperature Tcyl_post_H1, the process proceeds to step S9. In step S9, it is determined whether the catalyst temperature Tcat is higher than the first reference catalyst temperature Tcat_L and lower than the second reference catalyst temperature Tcat_H. In the present embodiment, the catalyst temperature Tcat is the catalyst temperature in the direct catalyst 41 detected by the catalyst temperature sensor SW12. An estimated value may be used as the temperature in the purification device.

  If the determination in step S9 is NO and the catalyst temperature Tcat is equal to or higher than the second reference catalyst temperature Tcat_H and the catalyst is sufficiently activated, or the catalyst temperature Tcat is equal to or lower than the first reference catalyst temperature Tcat_L If the temperature of the catalyst is not high enough to allow self-reaction, the process proceeds to step S11 without performing step S10.

  On the other hand, the determination in step S9 is YES, and the catalyst temperature Tcat is lower than the second reference catalyst temperature Tcat_H and the catalyst is not yet fully activated, but the catalyst temperature Tcat is higher than the first reference catalyst temperature Tcat_L. If the temperature is high enough to allow the catalyst to self-react, the process proceeds to step S10. In step S10, the timing set in step S7 is corrected so that the post-injection timing becomes the timing at which part of the post-injected fuel is discharged without being burned. In addition, what is necessary is just to maintain the timing, when the timing set in step S7 is already the timing at which unburned fuel is discharged to the catalyst side by post injection. After step S10, the process proceeds to step S11.

  In step S11, post injection is performed at the post injection timing determined in step S4, step S7, or step S10, and split injection is performed during the compression stroke.

  After step S11, the process proceeds to step S12, and the number of elapsed cycles is counted up. After step S12, the process proceeds to step S13, and it is determined whether or not the in-cylinder state temperature Tcly_post exceeds a preset second reference in-cylinder state temperature Tcyl_post_H2. If this determination is NO, the process returns to step S6, and steps S6 to S13 are repeated. On the other hand, if this determination is YES and the in-cylinder state temperature Tcly_post exceeds the second reference in-cylinder state temperature Tcyl_post_H2, the temperature is raised to a temperature at which stable compression auto-ignition combustion is realized even when the intake stroke batch injection is performed. If so, the process proceeds to step S2, where the split injection and post injection during the compression stroke are stopped, and the routine proceeds to fuel injection control during steady operation, that is, intake stroke batch injection.

  Thus, in the present embodiment, at the time of returning from the fuel cut to the CI combustion region, the post injection is performed in the expansion stroke while generating the engine torque corresponding to the required engine torque by the main injection. The wall surface temperature of the combustion chamber 11 can be raised early by the combustion energy generated by post injection to improve the ignitability of the air-fuel mixture, and stable self-ignition combustion can be realized early after return. Then, the injection timing of the post injection is advanced as the in-cylinder state temperature is lower, and at least a part of the post-injected fuel is surely combusted, and the post injection is performed in the expansion stroke, and this combustion energy is reduced. Since almost no effective engine torque is converted, the temperature of the wall surface of the combustion chamber 11 can be raised early, and the occurrence of torque shock due to excessive engine torque can be avoided.

  Here, if the post-injected fuel is burned, the wall surface temperature of the combustion chamber 11 can be increased as described above, and the exhaust temperature and the temperature of the exhaust port 18 can be increased. And in this embodiment, internal EGR by exhaust twice opening is implemented. Therefore, in the present embodiment, the temperature of the internal EGR gas can be increased by the combustion of fuel that has been post-injected, and this can also improve the ignitability of the air-fuel mixture. Further, as the exhaust gas temperature rises, the temperature of the purification device can be raised early, and the early activation of the purification device can be realized. Further, in the present embodiment, the catalyst temperature Tcat is not less than the first reference catalyst temperature Tcat_L and less than the second reference catalyst temperature Tcat_H, and the catalyst is not sufficiently activated, while the catalyst temperature is not self-reacting with the catalyst. If it is increased to the extent possible, the post-injected fuel is supplied to the catalyst device unburned. Therefore, the catalyst device can be activated earlier due to the self-reaction of the catalyst.

  In the present embodiment, the compression stroke division injection is performed as the main injection after the return. Therefore, as described below, while the air-fuel ratio of the entire air-fuel mixture is made lean, an air-fuel mixture that is locally richer than the stoichiometric air-fuel ratio, has a short ignition delay, and is ignited early is formed in the combustion chamber 11. be able to. In particular, since the fuel is injected so as to fit in the cavity 11a, a rich air-fuel mixture can be surely formed in the cavity 11a. And, it is possible to trigger the ignition of the relatively lean air-fuel mixture by the early ignition and combustion of this rich air-fuel mixture, even if the temperature in the combustion chamber before the start of ignition immediately after the return is low, The entire mixture can be self-ignited.

  FIGS. 9A, 9B and 9C show the air-fuel ratio distribution of the air-fuel mixture when the injection amount is the same and the injection pattern is varied. 9 (a), 9 (b), and 9 (c) are the results of calculating the air-fuel ratio distribution of the air-fuel mixture, and the horizontal axis is the equivalence ratio φ and the vertical axis is the frequency (spatial frequency) graph. The equivalent ratio φ on the horizontal axis is the reciprocal of the excess air ratio λ, and the larger the equivalent ratio φ, the richer the fuel. The frequency of the vertical axis specifies the number of regions having an equivalent equivalence ratio φ based on the local equivalence ratio φ of each region when the space in the cavity 11a is divided into a plurality of regions. . FIG. 9A shows the result when the fuel is injected at 20 ° CA before compression top dead center. FIG. 9B shows the result when the fuel is injected at 14 ° CA before compression top dead center. FIG. 9C shows the results when fuel was injected at 14, 17 and 20 ° CA before compression top dead center, that is, when fuel was divided and injected three times during the compression stroke.

  9A and 9B, the frequency is concentrated around the equivalent ratio φ = 1, that is, the excess air ratio λ = 1. On the other hand, in the case of split injection during the compression stroke of FIG. 9C, the frequency spreads to the side where the equivalence ratio φ is high and the air-fuel ratio is rich in fuel, and the region is richer in the cavity 11a. Is shown to be formed. As described above, when the divided injection is performed during the compression stroke, a richer air-fuel mixture can be locally formed in the cavity 11a than when the fuel is collectively injected. This is because, in the case of split injection, the fuel spray penetration (penetration force) is suppressed and fuel diffusion is suppressed in comparison with the case where the same amount of fuel is injected all at once. It is.

  FIG. 10 shows the relationship between the ignition delay of the air-fuel mixture and the air-fuel ratio. FIG. 10 is a graph in which the horizontal axis is the logarithmic axis of time and the vertical axis is the temperature of the air-fuel mixture, and shows the temperature change of the air-fuel mixture when compressed self-ignition combustion is performed. FIG. 10 shows the temperature change when the air-fuel mixtures having different air-fuel ratios are self-ignited under the same initial temperature T0 (about 1300 K). Specifically, L1, L2, L3, and L4 in FIG. 10 are temperature changes with an equivalent ratio φ = 1.0, 3.0, 5.0, and 7.0, respectively. In FIG. 10, the timing at which the temperature rises from the initial temperature T0 is the ignition start timing, and the longer the rise is on the right side, the longer the ignition delay. As shown in FIG. 10, even when the pre-ignition temperature is the same temperature T0, the larger the equivalence ratio φ and the richer the air-fuel ratio, the shorter the ignition delay and the earlier the air-fuel mixture ignites and burns.

  11, the fuel injection amount and the combustion chamber wall temperature (combustion) when the injection control of the engine system 100 according to this embodiment described above is performed and when the intake stroke batch injection is performed immediately after the return. Changes in engine wall torque). In FIG. 11, the solid line is a change in the case of the engine system 100 according to the present embodiment, and the broken line is a change in the case where the intake stroke batch injection is performed immediately after the return. FIG. 11 shows a case where the fuel cut is performed at time t1, the accelerator opening is stepped on at time t2, a return request is made, and slow acceleration is performed.

  When the fuel cut is performed at time t1, the wall surface temperature of the combustion chamber gradually decreases. Here, as shown by the broken line, when the intake stroke batch injection is performed immediately after the return request at time t2, the fuel injection amount gradually increases in response to the slow acceleration request. However, in this case, although fuel injection is performed from time t2, since the temperature in the combustion chamber 11 is low, stable compression auto-ignition combustion is not realized, and effective engine torque is not generated. Then, only when the injection amount increases to some extent (time t3), stable compression auto-ignition combustion is realized and effective engine torque is generated. As described above, when the intake stroke batch injection is performed immediately after the return, effective engine torque is not generated until the injection amount increases to some extent, the response is deteriorated, and a relatively large injection amount is supported at time t3. Since a relatively large torque is suddenly generated, the torque shock becomes large, and the operability becomes very poor.

  In contrast, as shown by the solid line in FIG. 11, in the engine system 100 according to the present embodiment, after the return request at time t2, post injection is performed in addition to the main injection according to the requested engine torque. Accordingly, the fuel injection amount is increased. And the wall surface of a combustion chamber is heated up early with implementation of this post injection. In addition, as a result of the compression process division injection being performed, stable compression auto-ignition combustion is realized immediately after the return, and as a result, an effective engine torque can be generated at time t2 when the injection amount is smaller than time t3. Further, although not shown in FIG. 11, according to the engine system 100, the reaction of HC and CO is caused by the fact that stable compression auto-ignition combustion is realized early after the return in this way and the combustion temperature rises. The exhaust performance can be enhanced, and the influence of these unburned gases contained in the internal EGR on the combustion can be suppressed to a small extent so that the fluctuation of combustion between cycles can be suppressed.

  Thus, in the engine system 100 according to the present embodiment, when returning from the fuel cut to the CI combustion region, the main injection for injecting the fuel for generating the required engine torque into the combustion chamber 11 and the main injection Post-injection is performed in which fuel is injected into the combustion chamber 11 at a timing at which the combustion energy generated at a predetermined timing of the subsequent expansion stroke is unlikely to become effective engine torque. The temperature can be raised immediately after the return, and stable compression auto-ignition combustion can be realized earlier. As a result, the exhaust performance and the fuel consumption performance can be enhanced while improving the response and suppressing the torque shock to a small level and realizing high driving operability.

  In particular, since the injection timing of the post injection is set so that at least a part of the post-injected fuel burns, the combustion energy is surely generated by the post injection and the temperature in the combustion chamber 11 is reliably increased. Can do. Further, the injection timing of the post injection is advanced as the in-cylinder state temperature that affects the combustibility of the air-fuel mixture is lower, that is, the post-injected fuel is more difficult to burn. The burned fuel can be burned more reliably.

  Further, as the main injection, compression stroke division injection is performed to form a locally rich air-fuel mixture in the combustion chamber 11 so that the main injected fuel can be compressed and self-ignited and burned early after the return. Stable compression auto-ignition combustion can be realized.

  Further, the post-injection is performed over a plurality of cycles after the return, and the post-injection is performed as the number of cycles elapsed after the return is increased, that is, the post-injected fuel becomes easier to burn as the in-cylinder state temperature becomes higher Since the injection timing of the engine is retarded, it is possible to avoid that the combustion energy generated by the early combustion of the post-injected fuel is converted into an excessively effective engine torque. Generation of torque shock accompanying torque conversion can be avoided.

  Here, in the above-described embodiment, the case where the post injection timing is retarded every time the elapsed cycle is increased is described. However, the specific procedure for retarding the post injection timing as the number of elapsed cycles is not limited thereto. For example, the post injection timing may be retarded every predetermined cycle or every predetermined time, or the post injection timing may be appropriately retarded according to the in-cylinder state temperature.

  Here, in the above-described embodiment, the example in which the post-injection timing is corrected based on the catalyst temperature, that is, the temperature in the purification device, is shown only when the in-cylinder state temperature is increased to some extent. Regardless, the post injection timing may be corrected based on the catalyst temperature. That is, step S8 may be omitted in the flowchart shown in FIG. Further, correction of the post injection timing based on the catalyst temperature can be omitted. That is, steps S8 to S10 may be omitted in the flowchart. However, if the unburnt fuel is supplied in a state where the catalyst temperature, that is, the temperature in the purification device is within a predetermined range and the reaction with the catalyst is possible but the catalyst is not sufficiently activated, the purification device By reacting the unburned fuel inside, the purification device can be heated and activated more effectively. In the present embodiment, the case where a catalyst is provided in the purification device has been described. However, the present invention can also be applied to a purification device having no catalyst such as a particulate filter.

  In the above-described embodiment, the case where the compression stroke split injection is performed as the main injection when returning from the fuel cut to the CI combustion region has been described. However, the main injection is set to the same intake stroke batch injection as in the steady operation or the like. Also good. However, if the compression stroke division injection is performed, as described above, it is possible to realize more stable and stable compression auto-ignition combustion immediately after the return. Further, as shown in FIG. 12, by using the compression stroke split injection and the intake stroke injection together, a part of the injection amount corresponding to the required engine torque is injected into the intake stroke, and the rest is split during the compression stroke. May be. In addition, the number of compression stroke injections is not limited to four.

  In the above-described embodiment, the case where the execution cycle of the compression stroke split injection and the execution cycle of the post injection are made the same when returning from the fuel cut to the CI combustion region has been described. It may be allowed. For example, the compression stroke division injection may be terminated early and only the post injection may be continued. The number of execution cycles may be, for example, a fixed number set in advance, or an ignition delay time predicted from a fuel cut time, an engine water temperature, an intake air temperature, an exhaust temperature, an engine speed, and the like. It may be changed according to the prediction result.

  Further, the number of injections, the timing, the injection amount, and the like of the compression stroke division injection may be changed according to the number of elapsed cycles. For example, as shown in FIG. 13, split injection during the compression stroke is also performed while part of the fuel is injected during the intake stroke, and the fuel injected during the intake stroke is gradually increased and the split injection during the compression stroke is performed. The number of times may be gradually decreased. In FIG. 13, only main injection is shown, and post injection is omitted.

1 Engine (Engine body)
10 cylinders 11 combustion chambers 15 injectors (fuel injection devices)
60 PCM (determination means, combustion control means)

Claims (4)

A control device for a direct injection engine having a fuel injection device capable of injecting fuel into a combustion chamber formed in a cylinder, and reciprocating a piston by burning a mixture of fuel and air in the combustion chamber;
Determining means for determining the operating state of the engine;
Each part of the engine including the fuel injection device is controlled so that the air-fuel mixture in the combustion chamber burns by self-ignition during operation in a compression auto-ignition combustion region where the engine load is set to a region lower than a predetermined load. Combustion control means,
The combustion control means combusts the air-fuel mixture by self-ignition when resuming combustion in the compression auto-ignition combustion region after execution of a fuel cut in which fuel injection from the fuel injection device is stopped, and Main injection for injecting fuel for generating required engine torque into the combustion chamber to the fuel injection device, and post injection for injecting fuel into the combustion chamber at a predetermined timing of the expansion stroke after the main injection The in-cylinder state temperature that influences the combustibility of the air-fuel mixture containing at least a part of the post-injected fuel and the air-fuel mixture containing the post-injected fuel. A control device for a direct injection engine, characterized in that the timing is set on the advance side as the temperature is lower. The direct injection engine control device according to claim 1,
The combustion control means performs the post-injection over a plurality of cycles after resuming combustion in the compression auto-ignition combustion region after the fuel cut, and the post-injection injection increases as the number of elapsed cycles from immediately after the resumption of combustion increases. A control device for a direct-injection engine, characterized in that the timing is retarded. The direct injection engine control device according to claim 2,
A purification device capable of purifying the exhaust discharged from the cylinder;
The combustion control means is configured such that the temperature in the purification device is lower than a preset first reference temperature and lower than a preset second reference temperature when resuming combustion in the compression auto-ignition combustion region after fuel cut. When it is high, the post-injection injection timing is set to a timing at which a part of the post-injected fuel does not burn in the combustion chamber. It is a control apparatus of the direct injection engine in any one of Claims 1-3,
The combustion control means is a compression process divided injection for injecting fuel into the fuel injection device in a plurality of times during the compression process as the main injection upon resuming combustion in the compression auto-ignition combustion region after fuel cut The direct-injection engine control apparatus characterized by performing this.

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