JP4877857B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine having a compression ignition combustion mode as a combustion mode, and more particularly to a control device for an internal combustion engine in which a low temperature gas and a high temperature gas are stratified and burned by self ignition in the compression ignition combustion mode.

  As this type of conventional control device, for example, one disclosed in Patent Document 1 is known. In this control device, in the compression ignition combustion mode, the exhaust valve is completely closed by changing the closing timing of the exhaust valve to the advance side and changing the opening timing of the intake valve to the retard side. The burned gas remains as high-temperature gas in the cylinder by a negative overlap between the so-called exhaust valve and the intake valve, which is later opened. Further, in the compression ignition combustion mode, the swirl valve provided in the intake passage is controlled to be fully closed, and fresh air swirl is generated in the cylinder. As a result, the burned gas is distributed in the center of the cylinder, and the fresh air is distributed as a low-temperature gas having a temperature lower than that of the burned gas so as to surround it, and the burned gas and the fresh air are stratified.

  Further, in this control device, fuel is injected into the fresh air layer at the beginning of the intake stroke or the compression stroke, and fuel is injected into the burned gas layer near the compression top dead center. Along with the injection of fuel into the burned gas layer, first, combustion by self-ignition is started from the vicinity where the fuel in the burned gas layer is injected, thereby increasing the pressure and temperature of the fresh air layer, Thereafter, combustion by self-ignition is also started in the fresh air layer.

JP 2001-323828 A

  As described above, in the conventional control device for an internal combustion engine, the fuel is injected into the burned gas layer near the compression top dead center. In the vicinity of the compression top dead center, the temperature of the burned gas layer rises to an extremely high temperature, so that the combustion of the fuel injected into the burned gas layer starts immediately. For this reason, the combustion state is likely to change rapidly, and drivability deteriorates. In addition, since the fuel is injected while the inside of the cylinder is very hot, the combustion temperature tends to be high, and in this case, the exhaust gas characteristics deteriorate.

  The present invention has been made to solve such a problem, and in the compression ignition combustion mode, the concentration of the fuel in the cylinder is appropriately controlled, and the combustion by the self-ignition is stably performed. An object of the present invention is to provide a control device for an internal combustion engine that can improve the performance and exhaust gas characteristics.

  In order to achieve the above object, the invention according to claim 1 is a control device 1 for an internal combustion engine 3 that has a compression ignition combustion mode as a combustion mode and controls the internal combustion engine 3 in the compression ignition combustion mode. First fuel supply means (in-cylinder fuel injection valve 10 in the embodiment (hereinafter, the same applies to this section)) and fuel is supplied via the intake valve 12 during the intake stroke during the stroke. Intake means (intake side valve mechanism 40) for sucking the gas into the cylinder C, and the second fuel that generates fresh air mixed with the fuel as a low temperature gas by supplying the fuel into the cylinder C during the intake stroke By controlling the operation of the exhaust valve 13 at the end of the intake stroke with the supply means (port fuel injection valve 9, in-cylinder fuel injection valve 10), the exhaust gas discharged into the exhaust passage 5 is sent by the first fuel supply means Supplied A high-temperature gas suction means (ECU 2, EGR suction mechanism 80, step 11 in FIG. 8) for sucking again into the cylinder C as a high-temperature gas together with the fuel, and a stratification means for stratifying the low-temperature gas and the high-temperature gas in the cylinder C (Guide wall 3d, convex part 3e).

  According to the present invention, in the compression ignition combustion mode, the internal combustion engine is controlled as follows. First, fuel is supplied into the cylinder during the exhaust stroke by the first fuel supply means. Thereby, the fuel supplied during the exhaust stroke is once discharged to the exhaust passage together with the exhaust gas, and is sufficiently warmed by the heat of the exhaust gas in the exhaust passage, evaporated, and mixed with the exhaust gas.

  Also, during the intake stroke, fresh air is sucked into the cylinder by the intake means via the intake valve, and fuel is supplied into the cylinder by the second fuel supply means, so that the fresh air mixed with the fuel is cooled to a low temperature. Produced as a gas. Further, at the end of the intake stroke, the operation of the exhaust valve is controlled by the high temperature gas suction means, and the exhaust gas discharged into the exhaust passage and mixed with the fuel is again sucked into the cylinder as a high temperature gas. These low temperature gas and high temperature gas are stratified by the stratification means. Then, the stratified low temperature gas and high temperature gas burn by self-ignition in the subsequent compression stroke. This combustion is started from a higher temperature hot gas layer, and accordingly, the pressure and temperature of the low temperature gas layer are increased to reach the low temperature gas layer. Thus, in the compression ignition combustion mode, combustion by self-ignition propagates from the high-temperature gas layer to the low-temperature gas layer, so that the combustion by self-ignition can be performed slowly. As a result, it is possible to avoid a sudden increase in pressure and temperature in the cylinder, thereby improving exhaust gas characteristics.

  Further, since the fuel from the first fuel supply means is directly supplied to the exhaust gas and mixed with the exhaust gas in advance during the exhaust stroke before the intake of fresh air in the intake stroke, the mixing time of the fuel and the exhaust gas is long. By ensuring, the concentration of the fuel in the high temperature gas layer can be made more uniform, and can be controlled with high accuracy. Furthermore, since the fuel from the first fuel supply means is supplied during the exhaust stroke, the amount of fuel adhering to the piston is increased by supplying the fuel near the exhaust top dead center, for example. Thereby, more latent heat generated when the fuel is vaporized can be obtained, and the temperature reduction of the exhaust gas due to the fuel can be suppressed. As described above, as a result of appropriately controlling the combustion due to self-ignition in the high-temperature gas layer, a stable combustion state can be obtained, and thereby drivability can be improved.

  According to a second aspect of the present invention, in the control device 1 for the internal combustion engine 3 according to the first aspect, the second fuel supply means includes an in-cylinder fuel injection valve 10 that directly injects fuel into the cylinder C, an in-cylinder It is one of the fuel injection valve 10 and the port fuel injection valve 9 that injects fuel into the intake passage 4.

  According to this configuration, during the intake stroke, fuel is directly injected into the cylinder by the in-cylinder fuel injection valve, or in addition, fuel is injected into the intake passage by the port fuel injection valve, The injected fuel is mixed with fresh air. In particular, when a port fuel injection valve is used in combination, the fuel and fresh air mixing time is ensured for a long time, so that the fuel concentration in the low temperature gas layer can be made more uniform. It can be performed more stably.

  According to a third aspect of the invention, in the control device 1 for the internal combustion engine 3 according to the first or second aspect, the fuel in the high temperature gas layer T1 by the high temperature gas is assumed when supplied by the first fuel supply means. The first fuel supply amount calculating means (ECU2, ECU2) calculates the fuel amount such that the concentration of the fuel becomes equal to the concentration of the fuel in the low temperature gas layer T2 by the low temperature gas as the first fuel supply amount (first fuel injection amount QEX1). Step 22) in FIG. 9 and the amount of fuel such that the minimum amount of oxygen necessary for the combustion of the hot gas is present in the hot gas layer T1 is assumed to be supplied by the first fuel supply means. 2 fuel supply amount (second fuel injection amount QEX2) second fuel supply amount calculation means (ECU2, step 23 in FIG. 9) and fuel supply amount supplied by the first fuel supply means (exhaust fuel injection amount) QINJEX) Fuel supply amount determining means for determining the one small more of the first fuel supply amount and the second fuel supply amount, characterized by further comprising a, and (ECU 2, step 24 to 26 in FIG. 9).

  According to this configuration, the first fuel supply amount and the second fuel supply amount are calculated as the fuel amount supplied by the first fuel supply means during the exhaust stroke. The first fuel supply amount is a fuel amount such that the concentration of fuel in the high temperature gas layer is equal to the concentration of fuel in the low temperature gas layer, and the second fuel supply amount is the minimum required for combustion of the high temperature gas. The amount of fuel is such that there is oxygen present.

  If the fuel concentration in the cylinder is uniform, a stable combustion state can be obtained. However, for example, when the air-fuel ratio in the cylinder before combustion is close to the stoichiometric air-fuel ratio, the oxygen in the exhaust gas after combustion decreases. . In such a case, for example, if a large amount of fuel is supplied to the exhaust gas in order to make the fuel concentration uniform, oxygen necessary for combustion may be insufficient, and in that case, a large amount of unburned fuel is discharged. As a result, the exhaust gas characteristics deteriorate. Based on this point of view, according to the present invention, the fuel supply amount supplied into the cylinder during the exhaust stroke is the smaller of the first fuel supply amount and the second fuel supply amount calculated as described above. Decide on one side. For this reason, even in a situation where oxygen is insufficient, the minimum oxygen necessary for combustion can be secured, and the discharge of unburned fuel can be suppressed.

  According to a fourth aspect of the present invention, in the control device 1 for the internal combustion engine 3 according to any one of the first to third aspects, the smaller the amount of high-temperature gas sucked into the cylinder C (re-intake EGR amount GE), the first 1 further includes fuel supply timing setting means (ECU 2, step 13 in FIG. 8) for setting the fuel supply timing (exhaust injection timing TINJEX) by the fuel supply means to a later timing.

  When the amount of hot gas re-intaked into the cylinder is large, even if fuel is supplied at an early timing during the exhaust stroke, the fuel discharged into the exhaust passage is not discharged from the exhaust passage and re-entered into the cylinder. Inhaled. On the other hand, when the amount of hot gas to be re-inhaled is small and the fuel is supplied at an earlier timing, the fuel is discharged into the atmosphere from the exhaust passage without being re-inhaled along with the exhaust gas. End up. From this point of view, according to the present invention, as the amount of the high-temperature gas sucked into the cylinder is smaller, the supply timing of the fuel supplied during the exhaust stroke is set to a later timing. Spilling into the inside can be suppressed, and fuel consumption and exhaust gas characteristics can be improved.

1 is a diagram schematically showing a configuration of an internal combustion engine to which the present invention is applied. It is a block diagram which shows schematic structure of a control apparatus. It is the elements on larger scale of FIG. It is a schematic diagram which shows schematic structure of a switching mechanism. It is a partial expansion perspective view of a piston. It is a main flow which shows a combustion control process. It is a figure which shows an example of the map used by the process of FIG. It is a subroutine which shows CI combustion control processing. It is a subroutine which shows the calculation process of exhaust fuel injection amount. It is a subroutine which shows the calculation process of exhaust injection timing. It is a figure which shows an example of the map used by the process of FIG. It is a figure which shows an example of the operation | movement in CI combustion mode. It is a figure which shows the valve lift curve of the intake valve obtained by the intake side valve mechanism, and the valve lift curve of the exhaust valve obtained by the EGR intake mechanism.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of a control device 1 according to an embodiment of the present invention and an internal combustion engine (hereinafter referred to as “engine”) 3 to which the control device 1 is applied. The engine 3 is a 4-cylinder diesel engine having # 1 to # 4 (1st to 4th) cylinders C, and is mounted on a vehicle (not shown).

  In this engine 3, the phase of the combustion cycle is shifted by 180 ° in the order of # 1 cylinder C → # 3 cylinder C → # 4 cylinder C → # 2 cylinder C → # 1 cylinder C. Are performed in this order.

  An intake passage 4 and an exhaust passage 5 are connected to the cylinder head 3a of the engine 3, and an in-cylinder fuel injection valve 10 and a spark plug 11 are attached to each cylinder C so as to face the combustion chamber 3b. . The in-cylinder fuel injection valve 10 is a direct injection type that is provided below the intake port 4a and configured to inject fuel directly into the combustion chamber 3b. The valve opening time and the valve opening timing of the in-cylinder fuel injection valve 10 are controlled by the ECU 2 described later, whereby the fuel injection amount and the fuel injection timing by the in-cylinder fuel injection valve 10 are controlled. The ignition timing of the spark plug 11 is also controlled by the ECU 2.

  The engine 3 is provided with a port fuel injection valve 9 for each cylinder C in addition to the in-cylinder fuel injection valve 10. Each port fuel injection valve 9 is attached to each branch passage 4b of the intake manifold and faces the intake port 4a. The valve opening time and the valve opening timing of the port fuel injection valve 9 are also controlled by the ECU 2, whereby the fuel injection amount and the fuel injection timing by the port fuel injection valve 9 are controlled.

  In this engine 3, as a combustion mode, a homogeneous mixture generated by injecting fuel from the port fuel injection valve 9 and the in-cylinder fuel injection valve 10 during the intake stroke is burned by spark ignition by the spark plug 11. A spark ignition combustion mode (hereinafter referred to as “SI combustion mode”) and a compression ignition combustion mode (hereinafter referred to as “CI combustion mode”) in which a stratified mixture generated as described later is combusted by self-ignition. The switching is controlled by the ECU 2.

  As shown in FIG. 1, the exhaust passage 5 includes # 1 to # 4 first exhaust passages 5a to 5d connected to # 1 to # 4 cylinders C, and # 1 and # 4 first exhaust passages 5a and 5d, respectively. And the second exhaust passages 6a and 6b connected to the joining portions of the # 2 and # 3 first exhaust passages 5b and 5c, respectively, and the second exhaust passages 6a and 6b connected to the joining portions of the second exhaust passages 6a and 6b. 3 exhaust passages 7 are provided.

  A filter 14 is provided in each of the second exhaust passages 6 a and 6 b and the third exhaust passage 7. The filter 14 reduces the amount of PM discharged into the atmosphere by collecting PM such as soot in the exhaust gas.

  As shown in FIG. 3, the cylinder C is provided with a pair of intake valves 12, 12 and a pair of exhaust valves 13, 13 (only one is shown). The intake valve 12 is opened and closed by an intake side valve mechanism 40, and the exhaust valve 13 is opened and closed by an exhaust side valve mechanism 60. The configurations of the intake side valve mechanism 40 and the exhaust side valve mechanism 60 are the same as those already proposed in Japanese Patent Application No. 2009-168228 by the applicant of the present application. .

  The intake side valve mechanism 40 is a variable mechanism that changes the lift and valve timing of the intake valve 12. Note that the lift of the intake valve 12 and the lift of the exhaust valve 13 to be described later represent the maximum lifts of the intake valve 12 and the exhaust valve 13, respectively.

  The intake side valve mechanism 40 includes a rotatable intake camshaft 41, a pair of intake cams 42 and 42 (only one shown) provided integrally with the intake camshaft 41, an intake control shaft 43, and the intake control shaft 43. Actuator 44 (see FIG. 2), a pair of swing cams 45 and 45 (only one is shown) supported swingably on a support shaft 47, a control arm mechanism 46, an intake cam phase variable mechanism 50, etc. It has. The intake cam phase varying mechanism 50 changes the relative phase of the intake camshaft 41 with respect to a crankshaft (not shown) in a stepless manner.

  The intake camshaft 41 is connected to the crankshaft via an intake sprocket and a timing chain (both not shown), and rotates once every two rotations of the crankshaft.

  The control arm mechanism 46 includes a control arm 46a, a roller 46b, an intake rocker arm 46c, and the like. The control arm 46a is rotatably supported on the eccentric shaft 43a of the intake control shaft 43 at the base end portion. A roller 46b is provided at the other end of the control arm 46a. The control arm 46a is in contact with the swing cam 45 via the roller 46b.

  The intake rocker arm 46c includes a main body portion 46d rotatably supported by the intake control shaft 43, an extension portion 46e extending from the main body portion 46d, and the like. In the extension portion 46e, the roller 46b and the intake valve 12 are provided. It is in contact.

  With the above configuration, when the swing cam 45 is not pressed by the intake cam 42, the intake valve 12 is held in the closed position shown in FIG. When the swing cam 45 is pressed by the intake cam 42 as the intake cam shaft 41 rotates, the swing cam 45 rotates about the support shaft 47 counterclockwise in FIG. At that time, when the roller 46b is pressed by the swing cam 45, the intake rocker arm 46c rotates about the intake control shaft 43 through the roller 46b in the counterclockwise direction in FIG. By pushing down, the intake valve 12 is opened.

  When the intake control shaft 43 is rotated via the actuator 44 described above, the control arm 46 a moves in the left-right direction in FIG. 3 about the eccentric shaft 43. Along with this movement, the contact position of the control arm 46a with the swing cam 45 is changed, whereby the lift and valve timing of the intake valve 12 are changed steplessly.

  The exhaust side valve mechanism 60 described above includes a rotatable exhaust cam shaft 61, a pair of exhaust cams 62 and 62 (only one shown) provided integrally with the exhaust cam shaft 61, an exhaust control shaft 63, and the exhaust control. A pair of rocker arms 64 and 64 (only one is shown) that are rotatably supported by the shaft 63 and abut against the upper ends of the exhaust valves 13 and 13, respectively, a roller 65 provided on the rocker arm 64, and an exhaust cam phase variable. A mechanism 70 and the like are provided. The exhaust cam phase varying mechanism 70 changes the relative phase of the exhaust cam shaft 61 with respect to the crankshaft in a stepless manner.

  The exhaust camshaft 61 is connected to a crankshaft (both not shown) via an exhaust sprocket and a timing chain, and rotates once every two rotations of the crankshaft. When the exhaust camshaft 61 rotates, the rocker arms 64, 64 are pressed by the exhaust cam 62, and rotate about the exhaust control shaft 63 in the clockwise direction in FIG. 3, thereby opening the exhaust valves 13, 13.

  Further, the engine 3 includes an EGR suction mechanism 80 for sucking exhaust gas into the cylinder C again.

  The EGR intake mechanism 80 opens the exhaust valve 13 during a predetermined period from the intake stroke to the compression stroke, thereby causing the exhaust gas once discharged into the first exhaust passages 5a to 5d of the exhaust passage 5 to Inhaled into C. As shown in FIGS. 3 and 4, the EGR suction mechanism 80 is provided between the two intake cams 42, 42 and is rotatably supported by the EGR cam 81 integrated with the intake camshaft 41 and the support shaft 47. A rocker cam 82, a control arm 83, a lever 84, a switching mechanism 85, and the like. The EGR cam 81 is in contact with the roller 82 a of the rocker cam 82.

  The control arm 83 is rotatably supported by the eccentric shaft 63a of the exhaust control shaft 63 at the base end portion. A roller 83 a is provided at the other end of the control arm 83. The control arm 83 is in contact with the rocker cam 82 via the roller 83a.

  The lever 84 is provided between the two rocker arms 64 and 64. The lever 84 has a triangular shape, and is pivotally supported by the exhaust control shaft 63 at the apex corner, and abuts against the pressing portion 83b of the control arm 83 at one bottom corner. Yes.

  With the above configuration, when the roller 82a is pressed by the EGR cam 81 as the intake camshaft 41 rotates, the rocker cam 82 rotates about the support shaft 47 in the clockwise direction in FIG. At this time, the roller 83a of the control arm 83 is pressed by the rocker cam 82, whereby the control arm 83 rotates about the exhaust control shaft 63 in the clockwise direction in FIG. 84 is pressed. Thereby, the lever 84 rotates around the exhaust control shaft 63 in the clockwise direction of FIG.

  As shown in FIG. 4, the switching mechanism 85 includes cylinders 86 a to 86 c formed on the rocker arms 64 and 64 and the lever 84, connecting pistons 87 and 88 housed in the cylinders 86 a to 86 c, and the like. The cylinder 86a is provided with a return spring 89 that biases the connecting pistons 87 and 88 toward the opposite cylinder 86c. Further, hydraulic pressure is supplied to the cylinder 86 c via an oil passage (not shown) formed in the exhaust control shaft 63. The hydraulic pressure is supplied to the cylinder 86c by the ECU 2 controlling supply / stop of the hydraulic pressure from a pump (not shown) to the oil passage.

  With the above configuration, when no hydraulic pressure is supplied to the cylinder 86c, the connecting piston 87 is accommodated in the cylinder 86b and the connecting piston 88 is accommodated in the cylinder 86c by the urging force of the return spring 89 (FIG. 4A). )). As a result, the rocker arm 64 and the lever 84 are disconnected from each other and become free, so that the movement of the lever 84 is not transmitted to the rocker arm 64 and only the lever 84 is driven by the EGR cam 81.

  On the other hand, when the hydraulic pressure is supplied to the cylinder 86c, the connecting pistons 87 and 88 move toward the cylinder 86a against the urging force of the return spring 89 by this hydraulic pressure, so that the connecting piston 87 is moved to the cylinder 86a and the cylinder 86b. The connecting piston 88 is engaged in a state of straddling the cylinder 86b and the cylinder 86c (FIG. 4B). As a result, the lever 84 and the rocker arm 64 are connected, and the movement of the EGR cam 81 is transmitted to the rocker arm 64 via the lever 84, whereby the exhaust valve 13 is opened.

  The lift and valve timing of the exhaust valve 13 by the EGR intake mechanism 80 are linked to the lift and valve timing of the intake valve 12. More specifically, the larger the lift of the intake valve 12, the smaller the lift of the exhaust valve 13, and the slower the closing timing of the intake valve 12, the later the opening timing of the exhaust valve 13 (see FIG. 13). Furthermore, the larger the required torque PMCMD described later, the greater the lift of the intake valve 12 and the later the closing timing of the intake valve 12 becomes.

  Further, the lift LFT of the exhaust valve 13 is detected by the lift sensor 26, and a detection signal indicating it is output to the ECU 2.

  A plurality of guide walls 3d are attached to the cylinder head 3a. As shown in FIG. 3, the guide wall 3d extends over each of the openings of the # 1 to # 4 exhaust ports 8a to 8d over a part of the circumferential direction and protrudes into the combustion chamber 3b. Each guide wall 3d is disposed on the intake port 4a side, and its length is smaller than the radius of the openings of # 1 to # 4 exhaust ports 8a to 8d. The protruding height of the guide wall 3d is substantially the same as the lift of the exhaust valve 13, and is set to 2 to 3 mm, for example.

  As shown in FIG. 5, a convex portion 3e is formed on the top surface of the piston 3c. The convex portion 3e is arranged so that the center thereof is on the intake valve 12 side. Further, the edge 3g on the intake valve 12 side of the convex portion 3e is formed in a substantially straight line, whereas the edge 3h on the exhaust valve 13 side is curved in a state of being recessed toward the intake valve 12 side. Yes.

  With the above configuration, when the exhaust valve 13 is opened by the EGR intake mechanism 80 in the CI combustion mode, the exhaust gas discharged to the exhaust passage 5 is re-intaken into the cylinder C via the exhaust valve 13. At this time, the exhaust gas is sucked into the cylinder C while being guided downward along the inner wall on the exhaust valve 13 side by the guide wall 3d, and the intake valve of the exhaust gas sucked by the convex portion 3e of the piston 3c. Outflow to the 12 side is prevented. As a result, the exhaust gas flows into the cylinder C as indicated by the solid line A in FIG. As a result, a high-temperature gas layer T1 of higher-temperature exhaust gas is formed on the exhaust valve 13 side in the cylinder C, and a low-temperature gas layer T2 of lower-temperature fresh air is formed on the intake valve 12 side. New air and exhaust gas are stratified.

  In addition, pressure is introduced through the first exhaust passages 5a to 5d from the cylinder C in the exhaust stroke in which the phase of the combustion cycle is shifted by 360 ° with respect to the cylinder C in which the exhaust valve 13 is opened by the EGR intake mechanism 80. Is done. For example, because the phases of the # 1 cylinder C and the # 4 cylinder C are shifted from each other by 360 °, when the # 1 cylinder C is between the intake stroke and the compression stroke, the # 4 cylinder C is in the expansion stroke to the exhaust stroke. Between. For this reason, when the exhaust gas is re-inhaled into the # 1 cylinder C, the exhaust gas is properly re-inhaled into the # 1 cylinder C by the pressure of the exhaust gas discharged from the # 4 cylinder C.

  The engine 3 is provided with a crank angle sensor 21. The crank angle sensor 21 outputs a CKR signal and a TDC signal, which are pulse signals, to the ECU 2 as the crankshaft rotates.

  The CRK signal is output every predetermined crank angle (for example, 30 °). The ECU 2 calculates the engine speed (hereinafter referred to as “engine speed”) NE of the engine 3 based on the CRK signal. The TDC signal is a signal indicating that the piston 3c is in a predetermined crank angle position slightly before the top dead center at the start of the intake stroke in any cylinder C, as in the present embodiment. When the engine 3 has four cylinders, it is output every crank angle of 180 °.

  An intake air temperature sensor 22 and an air flow sensor 23 are provided in the intake passage 4 in order from the upstream side. The intake air temperature sensor 22 detects a temperature TA (hereinafter referred to as “intake air temperature”) TA in the intake passage 4 and outputs a detection signal representing it to the ECU 2. The air flow sensor 23 detects a fresh air amount GAIR sucked into the engine 3 and outputs a detection signal representing it to the ECU 2.

  A water temperature sensor 24 is provided in the main body of the engine 3. The water temperature sensor 24 detects the temperature (hereinafter referred to as “engine water temperature”) TW of the cooling water circulating in the cylinder block 3 f of the engine 3, and outputs a detection signal indicating it to the ECU 2.

  The ECU 2 outputs a detection signal representing the depression amount (hereinafter referred to as “accelerator opening”) AP of an accelerator pedal (not shown) of the vehicle from the accelerator opening sensor 25.

  The ECU 2 is composed of a microcomputer including a CPU, a RAM, a ROM, an I / O interface (all not shown), and the like. The ECU 2 determines the operating state of the engine 3 according to the detection signals of the various sensors 21 to 25 described above, and sets the combustion mode of the engine 3 to the SI combustion mode or the CI combustion according to the determined operating state. The mode is determined and combustion control is executed in accordance with the determined combustion mode.

  In the present embodiment, the ECU 2 corresponds to a high-temperature gas suction unit, a first fuel supply amount calculation unit, a second fuel supply amount calculation unit, a fuel supply amount determination unit, and a fuel supply timing setting unit.

  FIG. 6 is a flowchart showing the combustion control process described above. This process is executed in synchronization with the generation of the TDC signal. In this process, first, in step 1 (illustrated as “S1”, the same applies hereinafter), it is determined whether or not the environmental condition flag F_ENV is “1”. This environmental condition flag F_ENV is set to “1” when it is determined that a temperature state suitable for combustion by self-ignition is secured in the combustion chamber 3b, and the intake air temperature TA and the engine water temperature are set. When TW is equal to or higher than each predetermined temperature, it is determined that such a temperature state is secured.

  When the determination result in step 1 is NO, assuming that the temperature state in the combustion chamber 3b suitable for self-ignition is not secured, the combustion mode is determined as the SI combustion mode, and SI combustion control is executed (step 3). Then, this process is terminated.

  On the other hand, when the determination result in step 1 is YES, it is determined whether or not the engine 3 is in an operation region (hereinafter referred to as “HCCI region”) in which CI combustion is to be performed (step 2). This determination is made according to the engine speed NE and the required torque PMCMD based on the map shown in FIG. In this map, the HCCI region is set to an operation region in which the engine speed NE is in the low to medium rotation region and the required torque PMCMD is in the low to medium load region.

  If the determination result in step 2 is NO and the engine 3 is not in the HCCI region, the combustion mode is determined to be the SI combustion mode, and after performing SI combustion control in the step 3, the present process is terminated.

  This SI combustion control is performed as follows. First, the fuel injection amount QINJ is calculated by searching a predetermined map (not shown) according to the engine speed NE and the required torque PMCMD. Next, when the engine speed NE is equal to or lower than a predetermined value and the required torque PMCMD is equal to or lower than the predetermined value, fuel of the fuel injection amount QINJ is injected from the in-cylinder fuel injection valve 10 into the cylinder C. On the other hand, at other times, a predetermined ratio (for example, 80%) of fuel is injected from the port fuel injection valve 9 to the intake port 4a with respect to the fuel injection amount QINJ, and the remaining ratio of fuel is injected from the in-cylinder fuel injection valve 10. Injection into the cylinder C. The required torque PMCMD is calculated by searching a predetermined map (not shown) according to the engine speed NE and the accelerator pedal opening AP.

  On the other hand, if the determination result in step 2 is YES and the engine 3 is in the HCCI region, the combustion mode is determined to be the CI combustion mode, and the CI combustion control is executed (step 4), and then this process is terminated.

  FIG. 8 shows a subroutine of this CI combustion control process. In this process, first, in step 11, the switching mechanism 85 is driven and the lever 84 and the rocker arm 64 are connected so that the exhaust valve 13 can be opened in the intake stroke.

  Next, by searching respective predetermined maps (not shown) according to the engine speed NE and the required torque PMCMD, the fuel injection amount QINJ and the fuel injection timing TINJ to be injected during the intake stroke are respectively calculated ( Steps 12, 13). This fuel injection timing TINJ is represented by a crank angle CA. The fuel injection amount QINJ calculated as described above is a predetermined ratio from the port fuel injection valve 9 and the in-cylinder fuel injection valve 10 in the above-described SI combustion mode in the operating state other than the low rotation and low load. It is injected separately.

  Next, an exhaust fuel injection amount QINJEX is calculated (step 14). The exhaust fuel injection amount QINJEX is a fuel amount injected during the exhaust stroke, and the calculation process will be described later. Next, the exhaust injection timing TINJEX is calculated (step 15), and this process is terminated. The exhaust injection timing TINJEX is also represented by a crank angle CA, and the calculation process will be described later.

ここで、ＧＲＥＳは、ピストン３ｃの排気上死点において、気筒Ｃ内に残留する排ガスの量であり、ＧＥＧＲは、排気通路５に排出され、気筒Ｃ内に再吸入される排ガスの量である。以上から、再吸入ＥＧＲ量ＧＥは、気筒Ｃ内に存在する排ガスの量、すなわち高温ガス層Ｔ１を構成する排ガスの量を表す。なお、ＧＲＥＳは、所定値に設定されており、ＧＥＧＲは、リフトセンサ２６で検出された排気弁１３のリフトＬＦＴに応じて算出される。 FIG. 9 shows a subroutine for calculating the exhaust fuel injection amount QINJEX. In this process, first, in step 21, the re-inhalation EGR amount GE is calculated according to the following equation (1).

Here, GRES is the amount of exhaust gas remaining in the cylinder C at the exhaust top dead center of the piston 3c, and GEGR is the amount of exhaust gas discharged into the exhaust passage 5 and re-intaked into the cylinder C. . From the above, the re-intake EGR amount GE represents the amount of exhaust gas existing in the cylinder C, that is, the amount of exhaust gas constituting the high temperature gas layer T1. Note that GRES is set to a predetermined value, and GEGR is calculated according to the lift LFT of the exhaust valve 13 detected by the lift sensor 26.

ここで、右辺中のＱＩＮＪ／ＧＡＩＲは、低温ガス層Ｔ２中の燃料の濃度を表す。このため、第１燃料噴射量ＱＥＸ１は、高温ガス層Ｔ１中の燃料の濃度が低温ガス層Ｔ２中の燃料の濃度に等しくなるような燃料量である。 Next, using the intake air amount GAIR, the fuel injection amount QINJ calculated in step 12, and the re-intake EGR amount GE calculated in step 21, the first fuel injection amount QEX1 is calculated according to the following equation (2) (step 22). ).

Here, QINJ / GAIR in the right side represents the concentration of fuel in the low temperature gas layer T2. Therefore, the first fuel injection amount QEX1 is a fuel amount such that the concentration of fuel in the high temperature gas layer T1 is equal to the concentration of fuel in the low temperature gas layer T2.

ここで、ＬＡＦは、理論空燃比であり、所定値に設定されている。ＬＡＦＡＣＴは、実空燃比であり、吸気量ＧＡＩＲと燃料噴射量ＱＩＮＪとの比（＝ＧＡＩＲ／ＱＩＮＪ）に等しい。また、右辺の（１−ＬＡＦ／ＬＡＦＡＣＴ）は、低温ガス層Ｔ２中の燃料が燃焼したときに、その燃焼ガス中に残存する酸素の割合を表し、この値に再吸入ＥＧＲ量ＧＥを乗算した右辺の分子は、高温ガス層Ｔ１中の酸素量を表す。したがって、この値と理論空燃比ＬＡＦとの比、すなわち第２燃料噴射量ＱＥＸ２は、高温ガス層Ｔ１中に排ガスの燃焼に必要な最少限の酸素が存在するような燃料量である。 Next, the second fuel injection amount QEX2 is calculated using the re-inhalation EGR amount GE according to the following equation (3) (step 23).

Here, LAF is the stoichiometric air-fuel ratio, and is set to a predetermined value. LAFACT is an actual air-fuel ratio, and is equal to a ratio (= GAIR / QINJ) between the intake air amount GAIR and the fuel injection amount QINJ. Further, (1-LAF / LAFACT) on the right side represents a ratio of oxygen remaining in the combustion gas when the fuel in the low temperature gas layer T2 is combusted, and this value is multiplied by the re-intake EGR amount GE. The molecule on the right side represents the amount of oxygen in the high temperature gas layer T1. Therefore, the ratio between this value and the stoichiometric air-fuel ratio LAF, that is, the second fuel injection amount QEX2 is such a fuel amount that the minimum oxygen necessary for combustion of the exhaust gas exists in the high temperature gas layer T1.

  Next, it is determined whether or not the first fuel injection amount QEX1 calculated as described above is smaller than the second fuel injection amount QEX2 (step 24). When the determination result is YES, the first fuel injection amount QEX1 is set as the exhaust fuel injection amount QINJEX (step 25), and this process is terminated.

  On the other hand, if the determination result in step 24 is NO and QEX1 ≧ QEX2, the second fuel injection amount QEX2 is set as the exhaust fuel injection amount QINJEX (step 26), and this process is terminated.

  FIG. 10 shows a subroutine for calculating the exhaust injection timing TINJEX. In this process, first, in step 31, the exhaust injection timing TINJEX is calculated by searching a predetermined map (not shown) according to the re-intake EGR amount GE calculated in step 21.

  Next, the limit value TLMT on the advance side of the exhaust injection timing TINJEX is calculated by searching the map shown in FIG. 11 according to the required torque PMCMD (step 32). This limit value TLMT is for limiting the exhaust injection timing TINJEX in order to suppress the outflow of fuel into the atmosphere. In this map, the limit value TLMT is larger in order to suppress the outflow of fuel into the atmosphere because the lift of the exhaust valve 13 is smaller and the re-intake EGR amount GE is smaller as the required torque PMCMD is larger. That is, it is set on the more retarded side. Thereby, the exhaust injection timing TINJEX is set to a later timing.

  Next, it is determined whether or not the exhaust injection timing TINJEX calculated as described above is smaller than the limit value TLMT (step 33). When this determination result is NO, this process is terminated as it is.

  On the other hand, if the determination result in step 33 is YES and TINJEX <TLMT, the limit value TLMT is set as the exhaust injection timing TINJEX (step 34), and this process is terminated. Thus, the exhaust injection timing TINJEX is set between the limit value TLMT and the exhaust top dead center (a region indicated by hatching in FIG. 11), and fuel is injected in this region.

  Next, the operations obtained in the CI combustion mode will be collectively described with reference to FIG. First, in the exhaust stroke, the exhaust valve 13 is opened by the exhaust side valve mechanism 60, and the exhaust gas is discharged to the exhaust passage 5. Further, fuel is injected into the cylinder C from the in-cylinder fuel injection valve 10 during this exhaust stroke. This fuel is discharged into the exhaust passage 5 together with the exhaust gas. Then, the discharged fuel is sufficiently warmed by the heat of the exhaust gas in the exhaust passage 5, evaporated, and mixed with the exhaust gas, thereby generating a high-temperature gas.

  In the subsequent intake stroke, the intake valve 12 is opened by the intake side valve mechanism 40 and fresh air is drawn into the cylinder C. Further, during this intake stroke, fuel is supplied from the port fuel injection valve 9 and the in-cylinder fuel injection valve 10 into the cylinder C, and this fuel is mixed with fresh air, thereby generating low-temperature gas.

  Further, when the exhaust valve 13 is opened by the EGR intake mechanism 80 at the end of the intake stroke, the high-temperature gas generated in the exhaust passage 5 is re-inhaled into the cylinder C (hatching in the figure). The low-temperature gas and the high-temperature gas generated as described above are stratified into the high-temperature gas layer T1 and the low-temperature gas layer T2 in the cylinder C by the guide wall 3d and the protrusion 3e. The high temperature gas layer T1 is distributed on the exhaust valve 13 side, and the low temperature gas layer T2 is distributed on the intake valve 12 side. In the subsequent compression stroke, the high temperature gas layer T1 and the low temperature gas layer T2 are combusted by self-ignition. This combustion starts from a higher temperature hot gas layer T1 and reaches a lower temperature gas layer T2.

  As described above, according to the present embodiment, in the CI combustion mode, combustion due to self-ignition propagates from the high-temperature gas layer T1 to the low-temperature gas layer T2, so that the combustion due to self-ignition can be performed slowly. As a result, it is possible to avoid a sudden increase in the pressure and temperature in the cylinder C, thereby improving the exhaust gas characteristics.

  In addition, during the exhaust stroke before the intake of fresh air in the intake stroke, the fuel from the in-cylinder fuel injection valve 10 is directly supplied to the exhaust gas and mixed in advance, so that a long mixing time of the fuel and the exhaust gas is ensured. As a result, the concentration of the fuel in the high temperature gas layer T1 can be made more uniform, and can be controlled with high accuracy. Furthermore, since the fuel injection from the in-cylinder fuel injection valve 10 is performed on the exhaust top dead center side, the amount of fuel adhering to the piston 3c increases. Thereby, more latent heat generated when the fuel is vaporized can be obtained, and the temperature reduction of the exhaust gas due to the fuel can be suppressed. As described above, as a result of appropriately controlling the combustion by self-ignition in the high temperature gas layer T1, a stable combustion state can be obtained, and thereby drivability can be improved.

  Further, since the port fuel injection valve 9 is used in addition to the in-cylinder fuel injection valve 10 during the intake stroke, a long mixing time of the fuel and fresh air is ensured, so that the temperature in the low temperature gas layer T2 is increased. As a result of more uniform fuel concentration, combustion by self-ignition can be performed more stably.

  Further, the first fuel injection amount QEX1 and the second fuel injection amount QEX2 are calculated as the fuel amount injected from the in-cylinder fuel injection valve 10 during the exhaust stroke (steps 22 and 23), and the exhaust fuel injection amount QINJEX is set to Since it is determined to be one of the first fuel injection amount QEX1 and the second fuel injection amount QEX2, the minimum oxygen necessary for combustion can be secured, and the discharge of unburned fuel can be suppressed.

  Further, the limit value TLMT is set to a more advanced side as the re-inhalation EGR amount GE is smaller. Therefore, by limiting the exhaust injection timing TINJEX using the limit value TLMT, it is possible to suppress the outflow of fuel into the atmosphere and improve the fuel consumption and exhaust gas characteristics.

  In addition, this invention can be implemented in various aspects, without being limited to the described embodiment. For example, in the embodiment, the guide wall 3d for stratifying the high-temperature gas layer T1 and the low-temperature gas layer T2 is attached to the cylinder head 3a, but instead, it may be attached to the exhaust valve.

  In the embodiment, the high-temperature gas layer T1 is formed on the exhaust valve 13 side in the cylinder C and the low-temperature gas layer T2 is formed on the intake valve 12 side. For example, the high temperature gas layer T1 may be formed on the side opposite to the cylinder head, and the low temperature gas layer T2 may be formed on the cylinder head side.

  Furthermore, in the embodiment, the fuel injection during the intake stroke is performed by using the in-cylinder fuel injection valve 10 and the port fuel injection valve 9 together, but may be performed by the in-cylinder fuel injection valve 10 alone.

  Moreover, although embodiment is an example which applied this invention to the diesel engine mounted in the vehicle, this invention is not restricted to this, You may apply to various engines, such as gasoline engines other than a diesel engine. Also, the present invention can be applied to engines other than those for vehicles, for example, engines for marine propulsion devices such as outboard motors having a crankshaft arranged vertically. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

1 control device 2 ECU (high temperature gas suction means, first fuel supply amount calculation means, second fuel supply amount calculation means,
Fuel supply amount determination means and fuel supply timing setting means)
3 Engine 3d Guide wall (stratification means)
3e Convex (stratification means)
4 intake passage 5 exhaust passage 9 port fuel injection valve (second fuel supply means)
10 In-cylinder fuel injection valve (first fuel supply means and second fuel supply means)
12 Intake valve 13 Exhaust valve 40 Intake side valve mechanism (intake means)
80 EGR suction mechanism (hot gas suction means)
C cylinder QEX1 first fuel injection amount (first fuel supply amount)
QEX2 Second fuel injection amount (second fuel supply amount)
QINJEX Exhaust fuel injection amount (fuel supply amount)
TINJEX Exhaust injection timing (fuel supply timing)
T1 Hot gas layer T2 Low temperature gas layer GE Re-intake EGR amount (amount of hot gas sucked into the cylinder)

Claims (4)

A control device for an internal combustion engine that has a compression ignition combustion mode as a combustion mode and controls the internal combustion engine in the compression ignition combustion mode,
First fuel supply means for supplying fuel into the cylinder during the exhaust stroke;
An intake means for sucking fresh air into the cylinder through the intake valve during the intake stroke;
Second fuel supply means for generating fresh air mixed with the fuel as a low-temperature gas by supplying fuel into the cylinder during the intake stroke;
By controlling the operation of the exhaust valve at the end of the intake stroke, the exhaust gas discharged into the exhaust passage together with the fuel supplied by the first fuel supply means is re-intaken into the cylinder as a high temperature gas. Gas suction means;
Stratification means for stratifying the low temperature gas and the high temperature gas in the cylinder;
A control device for an internal combustion engine, comprising:   The second fuel supply means is one of an in-cylinder fuel injection valve that directly injects fuel into the cylinder, and a port fuel injection valve that injects fuel into the in-cylinder fuel injection valve and the intake passage. The control apparatus for an internal combustion engine according to claim 1, wherein the control apparatus is characterized in that: Assuming that the fuel is supplied by the first fuel supply means, the amount of fuel is such that the concentration of the fuel in the high temperature gas layer by the high temperature gas becomes equal to the concentration of the fuel in the low temperature gas layer by the low temperature gas. First fuel supply amount calculating means for calculating the fuel supply amount;
When it is assumed that the fuel is supplied by the first fuel supply means, a fuel amount such that a minimum amount of oxygen necessary for combustion of the hot gas is present in the hot gas layer is calculated as the second fuel supply amount. Second fuel supply amount calculating means for
And a fuel supply amount determining means for determining a fuel supply amount supplied by the first fuel supply means as a smaller one of the first fuel supply amount and the second fuel supply amount. The control apparatus for an internal combustion engine according to claim 1 or 2.   The fuel supply timing setting means for setting the fuel supply timing by the first fuel supply means to a later timing as the amount of the high-temperature gas sucked into the cylinder is smaller. The control apparatus for an internal combustion engine according to any one of claims 1 to 3.

Images