JP6245114B2 - Control device for compression ignition engine - Google Patents

Description

  The technology disclosed herein relates to a control device for a compression ignition engine.

  For example, Patent Document 1 describes an engine that performs compression ignition combustion of an air-fuel mixture in a cylinder in a compression ignition combustion region set on a low load side. In the compression ignition combustion region, this engine performs internal EGR control for reintroducing combustion gas (burned gas) into the cylinder by opening the exhaust valve again during the intake stroke. Patent Document 1 also discloses that the internal EGR rate, which is the ratio of the combustion gas amount to the total gas amount in the cylinder, is relatively high on the low load side in the compression ignition combustion region, but relatively low on the high load side. It is described to do. This makes the temperature state in the cylinder almost constant regardless of the engine load, mainly improving the ignitability and stability of compression ignition combustion on the low load side, while mainly compressing on the high load side. Slow ignition combustion to avoid increased combustion noise.

  Further, Patent Document 2 discloses that when driving at an air-fuel ratio leaner than the theoretical air-fuel ratio, the vehicle acceleration is determined based on a predetermined target waveform based on the depression amount or depression speed of the driver's accelerator pedal. A technique for increasing the fuel injection amount is described.

JP 2014-47644 A JP 2006-328957 A

  As described in Patent Document 1, in an engine in which an air-fuel mixture in a cylinder is combusted by compression ignition (CI) or controlled auto ignition (CAI), the engine load The internal EGR rate is changed according to the engine load so that the internal EGR rate is high when the engine load is low and the internal EGR rate is low when the load is low. When the engine load is high, the fuel injection amount is relatively large, the temperature state in the cylinder is relatively high, and the temperature of the exhaust gas is also relatively high. Therefore, by setting the internal EGR rate low and reducing the amount of exhaust gas introduced into the cylinder, the temperature state in the cylinder is prevented from becoming too high.

  In this way, the internal EGR rate is changed according to the engine load. Therefore, when the driver depresses the accelerator pedal and the engine load changes from low to high, the internal EGR rate is changed from high to low. Must be changed.

  Here, at the time of transition when the engine load changes from low to high, the temperature state in the cylinder has not yet increased, and the temperature of the exhaust gas has not yet increased. Therefore, if the amount of exhaust gas introduced into the cylinder is reduced, the temperature state in the cylinder will be significantly lowered, leading to a reduction in the ignitability of compression ignition combustion and a reduction in stability. .

  The technology disclosed herein has been made in view of such a point, and the object of the technology is to achieve a high load engine operation state in a compression ignition engine that changes the internal EGR rate in accordance with the engine load. This is to avoid the deterioration of the ignitability and the stability of the compression ignition combustion during the transition to the side.

  The technology disclosed herein relates to a control device for a compression ignition engine, which has a fuel supply mechanism that supplies fuel to each of a plurality of cylinders, and in a preset compression ignition combustion region, An engine body configured to perform compression ignition combustion of an air-fuel mixture in each cylinder, an intake valve configured to open and close an intake port that sucks gas into the cylinder, and exhaust gas that discharges combustion gas from the cylinder An exhaust valve configured to open and close a port, and an internal EGR configured to introduce combustion gas into the cylinder together with fresh air by controlling a valve opening mode of at least one of the intake valve and the exhaust valve Control means.

  When the load on the engine body is low in the compression ignition combustion region, the internal EGR control means has a high internal EGR rate, which is a ratio of the amount of the combustion gas to the total gas amount in the cylinder, and the load When the engine is high, the internal EGR rate is made low, and in the compression ignition combustion region, the transition of the operating state of the engine body to the high load side so that the internal EGR rate is changed from high to low. Sometimes, the engine body increases the amount of fuel supplied into the cylinder in a range where the excess air ratio of the air-fuel mixture in the cylinder satisfies λ ≧ 1, and the internal EGR control means By performing a prior opening that opens the valve, combustion gas having a temperature higher than that during the exhaust stroke is discharged to the intake port, and the intake valve is opened during the intake stroke. By, via the intake port, for introducing the combustion gas together with fresh air into the cylinder.

Further, the internal EGR control means, during steady operation in the compression ignition combustion region, without opening the intake valve in advance, the main valve that opens the exhaust valve in the exhaust stroke, and in the intake stroke A part of the combustion gas is introduced into the cylinder through the exhaust port by performing a restart valve for opening the exhaust valve .

  Here, the internal EGR rate is “a ratio of the amount of the combustion gas to the total gas amount in the cylinder”, but the combustion gas here is a combustion gas (burned gas) substantially remaining in the cylinder. In addition to the combustion gas reintroduced into the cylinder through the intake port, the combustion gas remaining in the cylinder is included.

  According to this configuration, the internal EGR control means increases the internal EGR rate when the load on the engine body is low in the compression ignition combustion region. By increasing the internal EGR rate when the load on the engine body is low, the temperature state in the cylinder is increased, and the ignitability and stability of the compression ignition combustion are increased. On the other hand, when the load on the engine body is high, the internal EGR rate is made low. When the load on the engine body is high, it is avoided that the temperature state in the cylinder becomes too high, and the pressure rise of compression ignition combustion becomes steep and combustion noise increases.

  Thus, when the operating state of the engine body shifts to the high load side, the internal EGR rate is changed from high to low, but at the time of transition, the intake valve is opened in the expansion stroke. Do the valve. By doing so, the high-temperature combustion gas in the cylinder during the expansion stroke is discharged to the intake port side.

  Here, in the configuration in which the combustion gas is introduced into the cylinder by performing the prior opening of the intake valve, the prior opening is generally performed in the exhaust stroke. Thereby, it is possible to avoid a reduction in work rate. On the other hand, with the above-described configuration, the intake valve is opened in the expansion stroke at the time of transition. Thereby, it becomes possible to contribute high temperature combustion gas to combustion as soon as possible.

  This will be described in detail. Here, it is assumed that the engine body is a four-stroke four-cylinder engine that performs intake, compression, expansion, and exhaust processes while the crankshaft rotates twice. In this configuration, assuming that the ignition order is 1 → 3 → 4 → 2, the cylinder in the intake stroke when the first cylinder is in the exhaust stroke is the second cylinder, whereas the first cylinder is in the expansion stroke. The cylinder that is in the intake stroke when the engine is at is the fourth cylinder. As described above, when the first opening of the intake valve is performed in the expansion stroke in the first cylinder, the combustion gas discharged to the intake port side at that time is introduced into the fourth cylinder. On the other hand, when the preceding opening of the intake valve is performed in the exhaust stroke, the combustion gas discharged to the intake port at that time is introduced into the second cylinder. Therefore, by performing the preceding opening of the intake valve in the expansion stroke, it is possible to introduce the combustion gas discharged to the intake port side into the cylinder in the earlier combustion order than in the case of performing the preceding opening in the exhaust stroke. This is true regardless of the number of cylinders of the 4-stroke engine.

  Further, at the time of transition, by increasing the fuel amount, the combustion temperature becomes high, the temperature state in the cylinder is increased, and the temperature of the combustion gas introduced into the cylinder by the internal EGR control means is also increased. Further, by discharging a part of the combustion gas in the cylinder to the intake port side during the expansion stroke, the combustion gas having a temperature higher than that when performing the preceding valve opening in the exhaust stroke can be discharged to the intake port side. It becomes possible.

  Therefore, as the engine body load changes from low to high, the internal EGR rate changes from high to low, resulting in a higher temperature when the temperature state in the cylinder decreases. It is possible to introduce this combustion gas into the cylinder with the earlier combustion order, and to suppress the decrease in the temperature state in the cylinder as much as possible. As a result, it is possible to prevent the ignitability of compression ignition combustion from being lowered or the combustion stability from being lowered during a transition in which the operating state of the engine body shifts to the high load side, and to the high load side. The transition can be completed quickly.

  In addition, although the amount of fuel is increased, by reducing the expansion work by the prior valve opening in the expansion stroke, it is possible to avoid the generation of excessive torque during the transition, and the relative opening by the prior valve opening in the expansion stroke. By reintroducing the high-temperature combustion gas into the cylinder, it is possible to suppress an increase in the amount of fuel for ensuring the temperature of the combustion gas.

In addition, according to the above-described configuration, a part of the combustion gas is introduced into the cylinder through the exhaust port by opening the exhaust valve twice during steady operation in the compression ignition combustion region.

In other words, during steady operation, if the intake valve is opened in the expansion stroke, the expansion work is reduced. Therefore, the opening of the exhaust valve in the intake stroke is resumed without performing the pre-opening of the intake valve during a transient state. Run the valve. When the combustion gas is introduced into the cylinder by the restart valve, it is possible to ensure the thermal efficiency of the engine as compared to when the intake valve is opened in the expansion stroke.

On the other hand, during the transition when the operating state of the engine body shifts to the high load side, as described above, the intake valve is opened in advance in the expansion stroke, so that the high-temperature combustion gas is changed to the cylinder with the earlier combustion order. It becomes possible to introduce. This makes it possible to introduce a combustion gas having a temperature higher than that in the preceding opening in the exhaust stroke into the cylinder, and to ensure the ignitability and stability of the compression ignition combustion. Here, at the time of transition, the exhaust valve may be opened twice or the exhaust valve may be opened twice continuously.

In this way, the engine control mode is used differently so that the intake valve is opened twice during a transition to a high load side, while the exhaust valve is opened twice during steady operation. And thermal efficiency during steady operation can be achieved.

  The internal EGR control means may adjust the lift amount of the preceding valve opening of the intake valve so that the internal EGR rate is lower than the internal EGR rate before the transition during the transition.

  After the operating state of the engine body shifts to the high load side, the internal EGR rate is set lower than before the transition. However, by reducing the internal EGR rate during the transition than before the transition, It becomes possible to quickly shift the state to the high load side. At the time of transition, the lift amount of the preceding opening of the intake valve may be set relatively small. By doing so, the amount of combustion gas introduced into the cylinder is reduced, and the internal EGR rate can be lowered. On the other hand, as described above, since the temperature of the combustion gas introduced into the cylinder is relatively increased, the temperature state in the cylinder becomes high even if the amount of the combustion gas introduced into the cylinder is small. As a result, it is possible to prevent the temperature state in the cylinder from being lowered during a transition in which the operating state of the engine body shifts to the high load side.

  Also, if the amount of combustion gas reintroduced into the cylinder during the transition is reduced, the amount of fresh air introduced into the cylinder increases. As described above, the fuel amount increases during the transition, but it becomes possible to secure a fresh air amount corresponding to the increase in the fuel amount.

Thus, the temperature state in the cylinder is prevented from lowering during a transition in which the operating state of the engine body shifts to the high load side, and the amount of fresh air introduced into the cylinder increases, ignitability and stability of the compression ignition combustion Ru heightened.

Before SL internal EGR control means, in the compression ignition combustion region, it performs a preceding opening which opens the intake valve in the exhaust stroke, by opening the intake valve in the intake stroke, via the intake port The combustion gas is introduced into the cylinder together with fresh air, and the internal EGR control means advances the valve opening timing of the preceding valve opening of the intake valve more than before the transition at the time of the transition. In the expansion stroke, the preceding valve opening may be performed.

  According to this configuration, in the compression ignition combustion region, the intake valve is opened in advance in the exhaust stroke, that is, the intake valve is opened twice, so that a part of the combustion gas passes through the intake port in the cylinder. To be introduced. On the other hand, at the time of a transition in which the operating state of the engine body shifts to a high load side, the valve opening timing of the preceding opening of the intake valve is advanced so that the preceding opening of the intake valve is performed in the expansion stroke. This makes it possible to introduce a high-temperature combustion gas into a cylinder with a fast combustion order as described above. Here, at the time of transition, the opening timing of the preceding opening may be advanced by advancing the phase of the entire opening period of the preceding opening of the intake valve, or only the opening timing of the preceding opening. The phase of the valve closing timing does not have to be substantially changed. Alternatively, the intake valve may be opened in advance during the expansion stroke, and then the intake valve may be opened during the exhaust stroke, and the intake valve may be opened during the intake stroke. That is, the intake valve may be opened in the expansion stroke in addition to the double opening of the intake valve that performs the preceding valve opening in the exhaust stroke and the main valve opening in the intake stroke.

  The internal EGR control means may stop the preceding valve opening of the intake valve in the expansion stroke after the operating state of the engine body shifts to the high load side.

  When the transition to the high load side is completed (that is, when the transient state ends and the steady state transitions), the preceding opening of the intake valve in the expansion stroke is stopped. After the transition, as described above, when the exhaust valve is opened twice or the intake valve is opened twice, a part of the combustion gas is introduced into the cylinder, but the combustion gas is introduced into the cylinder. The temperature of is lower than during transients. As a result, when the load on the engine body is high, it is possible to prevent the temperature state in the cylinder from becoming too high and to prevent an increase in combustion noise.

  The engine body may increase the amount of fuel during a transition in which the operating state shifts from a preset region where the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio to a high load side. Good.

By doing so, the fuel amount can be increased in the range where the excess air ratio becomes λ ≧ 1, and the temperature state in the cylinder may be lowered during the transition without causing deterioration of the exhaust emission performance. It is suppressed .

  As described above, according to the control device for the compression ignition engine, the fuel amount is increased and the intake valve is opened during the expansion stroke at the time when the operating state of the engine body shifts to the high load side. By performing the preceding valve opening, it becomes possible to introduce as high a combustion gas as possible into the cylinder with the fastest combustion order, suppressing the temperature state in the cylinder from decreasing, and compression ignition combustion in a transient state The ignitability and stability of the engine can be improved, and the operating state of the engine body can be quickly shifted to the high load side.

It is the schematic which shows the structure of an engine. It is a block diagram concerning control of an engine. It is sectional drawing which shows schematically the structure of the drive mechanism of an intake valve. It is a figure which illustrates the lift curve of an intake valve and an exhaust valve. It is a figure which shows notionally the channel | path structure on the intake side and exhaust side. It is a figure which illustrates the operation control map of an engine. (A) It is a figure which illustrates the relationship of the EGR rate with respect to the level of engine load, and (b) the relationship of the combustion gas temperature with respect to the level of engine load. (A) The figure which illustrates the transition of the valve opening state of an intake valve and an exhaust valve when an engine operating state shifts to a high load side in the conventional configuration, (b) In this configuration, It is a figure which illustrates the transition of the valve opening state of an intake valve and an exhaust valve when shifting to the high load side. (A) change in internal EGR temperature, (b) change in compression end temperature, (c) change in internal EGR rate, (d) in the conventional configuration when shifting from a low load region to a medium load region in the CAI region (E) a change in fuel amount, (e) a change in air-fuel ratio, and (f) a time chart illustrating a change in the valve opening period of the exhaust valve, and (g) a change in internal EGR temperature in this configuration, (h ) A change in compression end temperature, (i) a change in internal EGR rate, (j) a change in fuel amount, (k) a change in air-fuel ratio, and (l) a change in the valve opening period of the preceding valve opening of the intake valve. It is each time chart illustrated. It is a timing chart which shows the cylinder which introduce | transduced the combustion gas at the time of the transition which shifts from the low load area | region to a medium load area | region in a CAI area | region at the time of a prior | preceding valve opening in an exhaust stroke. It is a timing chart which shows the cylinder which introduce | transduced the combustion gas at the time of the transition which shifts from the low load area | region to a medium load area | region in a CAI area | region at the time of a prior | preceding valve opening in an expansion stroke. FIG. 9 is a diagram illustrating the transition of the open state of the intake valve and the exhaust valve when the engine operating state shifts to a high load side in a configuration different from FIG.

  Hereinafter, an embodiment of a control device for a compression ignition engine will be described with reference to the drawings. The following description of preferred embodiments is exemplary.

(Entire engine configuration)
1 and 2 show a schematic configuration of an engine (engine body) 1. The engine 1 is a four-stroke engine mounted on a vehicle and a gasoline engine to which a fuel containing at least gasoline is supplied. Here, the engine 1 includes a cylinder block 11 provided with four cylinders 18 (only one cylinder is shown in FIG. 1), a cylinder head 12 provided on the cylinder block 11, and a cylinder. The oil pan 13 is disposed below the block 11 and stores lubricating oil. A piston 14 connected to the crankshaft 15 via a connecting rod 142 is fitted in each cylinder 18 so as to be able to reciprocate. On the upper surface of the piston 14, a cavity 141 like a reentrant type in a diesel engine is formed. The cavity 141 is opposed to an injector 67 described later when the piston 14 is positioned near the compression top dead center. The cylinder head 12, the cylinder 18 and the piston 14 having the cavity 141 define a combustion chamber. The shape of the combustion chamber is not limited to the shape illustrated. For example, the shape of the cavity 141, the upper surface shape of the piston 14, the shape of the ceiling portion of the combustion chamber, and the like can be changed as appropriate.

  The gasoline engine 1 is set to a relatively high geometric compression ratio of 15 or more for the purpose of improving the theoretical thermal efficiency and stabilizing combustion by compression autoignition described later. The geometric compression ratio may be set as appropriate in the range of about 15 to 20, and may be 18, for example.

  The cylinder head 12 is formed with an intake port 16 and an exhaust port 17 for each cylinder 18. The intake port 16 and the exhaust port 17 include an intake valve 21 and an exhaust valve that open and close the opening on the combustion chamber side. 22 are arranged respectively. As conceptually shown in FIG. 5, in the engine 1, two intake ports 16 and two exhaust ports 17 are connected to one cylinder 18. Two valves 22 are also provided for each cylinder 18.

  Of the valve systems that drive the intake valve 21 and the exhaust valve 22, respectively, a phase variable mechanism (hereinafter referred to as VVT (Variable Valve Timing) capable of changing the rotation phase of the intake camshaft with respect to the crankshaft 15 is provided on the intake side. 71) and a hydraulic variable drive mechanism 72 capable of changing the valve opening mode of the intake valve 21 are provided. The VVT 71 may adopt a known hydraulic or electric structure as appropriate, and the detailed structure is not shown. Details of the variable drive mechanism 72 will be described later. The drive mechanism of the intake valve 21 includes a VVT 71 and a variable drive mechanism 72.

  Also on the exhaust side, a VVT 73 capable of changing the rotation phase of the exhaust camshaft with respect to the crankshaft 15 and a hydraulic variable drive mechanism 74 capable of changing the valve opening mode of the exhaust valve 22 are provided. The VVT 73 on the exhaust side may adopt a hydraulic or electric known structure as appropriate, and the detailed structure is not shown. Details of the variable drive mechanism 74 will be described later. The drive mechanism of the exhaust valve 22 includes a VVT 73 and a variable drive mechanism 74. The variable drive mechanism 74 of the exhaust valve 22 can be omitted.

  FIG. 3 shows the configuration of the variable drive mechanism 72 of the intake valve 21. Although not shown, the configuration of the variable drive mechanism 74 of the exhaust valve 22 is substantially the same as the configuration of the variable drive mechanism 72 of the intake valve 21 shown in FIG. The variable drive mechanism 72 includes a camshaft 721, a cam 722 provided on the camshaft 721, a tappet 723 on which the cam 722 slides, a pump unit 724 coupled to the tappet 723, and a hydraulic pressure communicating with the pump unit 724. And a discharge path 725.

  The cam 722 for driving the intake valve 21 has two cam lobes 7221 and 7222 in this configuration example. The cam 722 pushes the tappet 723 down twice by two cam lobes 7221, 7222 during one revolution, in other words, during one combustion cycle of intake, compression, expansion and exhaust.

  The pump unit 724 includes a cylinder 7241 filled with hydraulic oil, and a plunger 7242 inserted in the cylinder 7241 and capable of reciprocating in the cylinder 7241. The plunger 7242 is also coupled to the tappet 723, and the plunger 7242 and the tappet 723 are biased toward the cam 722 by the spring 726. When the tappet 723 is pushed down by the cam lobes 7221 and 7222, the plunger 7242 moves down in the cylinder 7241, and the pressure of the hydraulic oil increases. The hydraulic oil pressure rises as the crank angle progresses and then falls to correspond to the profile of the cam 722. As described above, since the cam 722 has the two cam lobes 7221 and 7222, the hydraulic oil pressure rises twice during one combustion cycle.

  The hydraulic pressure discharge path 725 communicates with the cylinder 7241 of the pump unit 724, and a solenoid valve 7251 is interposed in the middle of the hydraulic pressure discharge path 725. The solenoid valve 7251 is a flow rate adjustment valve controlled by the PCM 10 to be described later, and its opening degree can be arbitrarily set between fully closed and fully open. When the solenoid valve 7251 is fully opened, the hydraulic oil pressure is not substantially increased because the hydraulic oil is discharged through the hydraulic pressure discharge passage 725 even when the plunger 7242 is lowered as described above. On the other hand, when the solenoid valve 7251 is fully closed, the hydraulic oil pressure is increased because the hydraulic oil is not discharged through the hydraulic pressure discharge path 725. Further, as will be described in detail later, the hydraulic oil pressure can be adjusted by adjusting the opening of the solenoid valve 7251 in accordance with the driving of the cam 722.

  The cylinder 7241 of the pump unit 724 is also in communication with a chamber 727, and a piston 728 connected to the upper end of the stem of the intake valve 21 is disposed in the chamber 727. The piston 728 is disposed so as to be able to reciprocate in the chamber 727. When the hydraulic oil whose pressure has been increased by the pump unit 724 is supplied, the piston 728 descends in the chamber 727 and is urged in the valve closing direction by the spring 729. The intake valve 21 is pushed down to open the intake valve 21.

  FIG. 4 shows an example of lift curves that the intake valve 21 and the exhaust valve 22 can take. 4 correspond to the lift curves of the intake valve 21 and the exhaust valve 22 when the solenoid valve 7251 is normally fully closed. If the solenoid valve 7251 is fully closed, the hydraulic oil whose pressure has been increased by the two cam lobes 7221 and 7222 is supplied to the chamber 727 as it is. The first valve opening L1 and the second valve opening L2 are opened twice.

  The fact that the intake valve 21 and the exhaust valve 22 are opened twice during one combustion cycle is used in the control of the internal EGR in the engine 1. Although details will be described later, in the engine 1, the intake valve 21 is basically opened twice during the control related to the internal EGR. Note that the exhaust valve 22 may be opened twice.

  When the intake valve 21 is opened twice, “internal EGR” means that the combustion gas discharged from the cylinder 18 to the intake port 16 side is reintroduced into the cylinder 18. That is, the intake valve 21 opens during the period from the expansion stroke to the exhaust stroke (that is, the first valve opening L1 corresponds to the preceding valve opening) and at least also during the intake stroke (that is, the second valve opening). L2 corresponds to the main valve opening). A part of the combustion gas in the cylinder 18 is discharged to the intake port 16 side when the first valve is opened, and the combustion gas and fresh air are introduced into the cylinder 18 when the second valve is opened. As will be described in detail later, the combustion gas is mainly introduced into different cylinders 18.

  On the other hand, when the exhaust valve 22 is opened twice, “internal EGR” means that the combustion gas discharged from the cylinder 18 to the exhaust port 17 side is reintroduced into the cylinder 18. That is, the exhaust valve 22 opens during the period from the expansion stroke to the exhaust stroke (that is, the first valve opening L1 corresponds to the main valve opening) and at least also during the intake stroke (that is, the second valve opening). L2 corresponds to a restart valve). When the first valve is opened, the combustion gas in the cylinder 18 is discharged to the exhaust port 17 side, and part of the combustion gas is introduced into the cylinder 18 when the second valve is opened. Combustion gas is mainly introduced into different cylinders 18.

  Further, if the solenoid valve 7251 is fully opened while the cam lobe 7221 pushes down the tappet 723 (in other words, while the cam lobe 7221 is operating) of the two cam lobes 7221 and 7222, the pressurized hydraulic oil is increased. Is not supplied to the chamber 727, the first valve opening L1 is not performed. Thereafter, when the solenoid valve 7251 is fully closed while the cam lobe 7222 pushes down the tappet 723 (in other words, while the cam lobe 7222 is operating), the second valve opening L2 is executed as described above. The In the intake valve 21, if the cam lobe 7221 is not substantially functioned and only the cam lobe 7222 is functioned, the intake valve 21 can be opened only once in the intake stroke during one combustion cycle. become. This is used during normal engine operation without internal EGR control.

  On the contrary, if the solenoid valve 7251 is fully closed while the cam lobe 7221 pushes down the tappet 723 (in other words, while the cam lobe 7221 is activated) of the two cam lobes 7221 and 7222, As described above, the first valve opening L1 is executed. After that, if the solenoid valve 7251 is fully opened while the cam lobe 7222 pushes down the tappet 723 (in other words, while the cam lobe 7222 is operating), the pressurized hydraulic oil is not supplied to the chamber 727. 2 Valve opening L2 is not performed. In the exhaust valve 22, if the cam lobe 7222 is not substantially functioned and only the cam lobe 7221 is functioned, the exhaust valve 22 can be opened only once in the exhaust stroke during one combustion cycle. become. This is used during normal engine operation without internal EGR control.

  Therefore, the variable drive mechanism 72 of the intake valve 21 and the variable drive mechanism 74 of the exhaust valve 22 can switch execution / non-execution of internal EGR control.

  Further, by controlling the opening and closing of the solenoid valve 7251 during the operation of the cam lobe 7221, the valve opening lift amount and the valve opening timing of the intake valve 21 or the exhaust valve 22 are changed with respect to the first valve opening. Specifically, if the solenoid valve 7251 is fully opened at the beginning of the operation of the cam lobe 7221, the intake valve 21 or the exhaust valve 22 can be maintained in the closed state, while the cam lobe 7221 is in operation (more To be exact, when the solenoid valve 7251 is closed (until the nose of the cam lobe 7221), the pressure of the hydraulic oil starts to push the piston 728, so that the intake valve 21 or the exhaust valve 22 is opened. Thus, with respect to the first valve opening, the opening timing of the intake valve 21 or the exhaust valve 22 can be delayed and the lift amount can be reduced (see L11 in FIG. 4). By further delaying the switching timing from opening to closing of the solenoid valve 7251, the opening timing of the intake valve 21 or the exhaust valve 22 can be further delayed, and the lift amount can be further reduced ( (See L12 in FIG. 4).

  Furthermore, when the operation of the cam lobe 7221 is started, if the solenoid valve 7251 is fully closed, the intake valve 21 or the exhaust valve 22 is opened in accordance with the increase in the hydraulic oil pressure, while the cam lobe 7221 By opening the solenoid valve 7251 during operation, the pressure of the hydraulic oil is reduced, so that the intake valve 21 or the exhaust valve 22 is closed by the biasing force of the spring 729. Thus, with respect to the first valve opening, it becomes possible to advance the closing timing of the intake valve 21 or the exhaust valve 22, and the lift amount and the operating angle of the intake valve 21 or the exhaust valve 22 are reduced (L13 in FIG. 4). reference). The closing timing and the lift amount of the intake valve 21 or the exhaust valve 22 are respectively changed according to the switching timing of the solenoid valve 7251 from closing to opening. For example, comparing L12 and L13 in FIG. 4 is equivalent to changing the valve opening timing while the lift amount of the intake valve 21 or the exhaust valve 22 is substantially the same. This makes it possible to change the phase of the first valve opening without changing the phase of the second valve opening L2.

  Further, if the rate of change of the opening of the solenoid valve 7251 from fully closed to fully opened is increased, the closing operation of the intake valve 21 or the exhaust valve 22 can be quickly performed with respect to the first valve opening. On the contrary, if the rate of change in the opening degree of the solenoid valve 7251 is lowered, the intake valve 21 or the exhaust valve 22 can be slowly closed. The variable drive mechanism 72 can also adjust the closing timing of the intake valve 21 or the exhaust valve 22.

  As with the first valve opening, it is possible to change the lift amount and valve opening timing of the intake valve 21 or the exhaust valve 22 for the second valve opening (L21 in FIG. 4). L22, see L23).

  In addition, an injector 67 that directly injects fuel into the cylinder 18 is attached to the cylinder head 12 for each cylinder 18. The injector 67 is arranged so that its nozzle hole faces the combustion chamber from the center portion of the ceiling surface of the combustion chamber. The injector 67 directly injects an amount of fuel corresponding to the operation state of the engine 1 at an injection timing set according to the operation state of the engine 1 into the combustion chamber. In this example, the injector 67 is a multi-hole injector having a plurality of nozzle holes, although detailed illustration is omitted. Thereby, the injector 67 injects the fuel so that the fuel spray spreads radially from the center position of the combustion chamber. At the timing when the piston 14 is positioned near the compression top dead center, the fuel spray injected radially from the central portion of the combustion chamber flows along the wall surface of the cavity 141 formed on the upper surface of the piston. It can be paraphrased that the cavity 141 is formed so that the fuel spray injected at the timing when the piston 14 is located near the compression top dead center is contained therein. This combination of the multi-hole injector 67 and the cavity 141 is an advantageous configuration for shortening the mixture formation period and the combustion period after fuel injection. In addition, the injector 67 is not limited to a multi-hole injector, and may be an outside-opening type injector.

  A fuel tank (not shown) and the injector 67 are connected to each other by a fuel supply path. A fuel supply system 62 including a fuel pump 63 and a common rail 64 and capable of supplying fuel to the injector 67 at a relatively high fuel pressure is interposed on the fuel supply path. The fuel pump 63 pumps fuel from the fuel tank to the common rail 64, and the common rail 64 can store the pumped fuel at a relatively high fuel pressure. When the injector 67 is opened, the fuel stored in the common rail 64 is injected from the injection port of the injector 67. Here, although not shown, the fuel pump 63 is a plunger type pump and is driven by the engine 1. The fuel supply system 62 configured to include this engine-driven pump enables the fuel with a high fuel pressure of 30 MPa or more to be supplied to the injector 67. The fuel pressure may be set to about 120 MPa at the maximum. The pressure of the fuel supplied to the injector 67 is changed according to the operating state of the engine 1. The fuel supply system 62 is not limited to this configuration.

  A spark plug 25 for forcibly igniting the air-fuel mixture in the combustion chamber is also attached to the cylinder head 12. In this example, the spark plug 25 is disposed through the cylinder head 12 so as to extend obliquely downward from the exhaust side of the engine 1. The tip of the spark plug 25 is disposed facing the cavity 141 of the piston 14 located at the compression top dead center.

  As shown in FIG. 1, an intake passage 30 is connected to one side of the engine 1 so as to communicate with the intake port 16 of each cylinder 18. On the other hand, an exhaust passage 40 for discharging burned gas (exhaust gas) from the combustion chamber of each cylinder 18 is connected to the other side of the engine 1.

  As described above, in this engine 1, two intake ports 16 are provided for one cylinder 18 (see FIG. 5), and the two intake ports 16, 16 of each cylinder 18 are gathered in the cylinder head 12. doing. Accordingly, four openings corresponding to the four cylinders 18 are provided on one side surface of the cylinder head 12, an independent passage that branches into each of the four openings, and a collective portion in which the independent passages gather. Is attached to one side of the engine 1. Thus, in the engine 1, the four cylinders 18 communicate with each other on the intake side, but the distance of the path for communicating between the cylinders is configured to be as short as possible. The configuration on the intake side is merely an example.

  An air cleaner 31 that filters intake air is disposed at the upstream end of the intake passage 30. A surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passage 30 on the downstream side of the surge tank 33 is an independent passage branched for each cylinder 18 as described above, and the downstream end of each independent passage is connected to the intake port 16 of each cylinder 18. .

  Between the air cleaner 31 and the surge tank 33 in the intake passage 30, a water-cooled intercooler / warmer 34 that cools or heats the air and a throttle valve 36 that adjusts the amount of intake air to each cylinder 18 are arranged. It is installed. An intercooler bypass passage 35 that bypasses the intercooler / warmer 34 is also connected to the intake passage 30. The intercooler bypass passage 35 is connected to an intercooler for adjusting the flow rate of air passing through the passage 35. A bypass valve 351 is provided. Adjusting the temperature of fresh air introduced into the cylinder 18 by adjusting the ratio between the passage flow rate of the intercooler bypass passage 35 and the passage flow rate of the intercooler / warmer 34 through the opening degree adjustment of the intercooler bypass valve 351. Is possible. It should be noted that the intercooler / warmer 34 and its associated members can be omitted.

  As shown in FIG. 5, in this engine 1, two exhaust ports 17 are provided for one cylinder 18, and the two exhaust ports 17, 17 of each cylinder 18 are gathered in the cylinder head 12. . For the second cylinder and the third cylinder whose exhaust order is not adjacent to each other (note that the exhaust order is the first, third, fourth, and second order), the exhaust ports 17 and 17 are further provided. As a result, three openings are provided on the other side surface of the cylinder head 12, and an exhaust manifold having an independent passage branched into each of the three openings and a collecting portion where the independent passages gather. Is attached to the other side of the engine 1. As described above, the engine 1 is configured such that the four cylinders communicate with each other even on the exhaust side, but the distance of the path for communicating between the cylinders is shorter than that on the intake side. The exhaust side configuration is merely an example.

  As shown in FIG. 1, a direct catalyst 41 and an underfoot catalyst 42 are connected to the downstream side of the exhaust passage 40 connected to the exhaust manifold as exhaust purification devices for purifying harmful components in the exhaust gas. Has been. Each of the direct catalyst 41 and the underfoot catalyst 42 includes a cylindrical case and, for example, a three-way catalyst disposed in a flow path in the case. The engine 1 does not include a NOx purification catalyst.

  A portion between the surge tank 33 and the throttle valve 36 in the intake passage 30 and a portion upstream of the direct catalyst 41 in the exhaust passage 40 are used for returning a part of the exhaust gas to the intake passage 30. They are connected via a passage 50. The EGR passage 50 includes a main passage 51 in which an EGR cooler 52 for cooling the exhaust gas with engine coolant is disposed, and an EGR cooler bypass passage 53 for bypassing the EGR cooler 52. ing. The main passage 51 is provided with an EGR valve 511 for adjusting the amount of exhaust gas recirculated to the intake passage 30, and the EGR cooler bypass passage 53 has a flow rate of exhaust gas flowing through the EGR cooler bypass passage 53. An EGR cooler bypass valve 531 for adjustment is provided.

  The engine 1 is controlled by a powertrain control module (hereinafter referred to as PCM) 10. The PCM 10 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units. This PCM 10 constitutes a controller.

As shown in FIGS. 1 and 2, detection signals from various sensors SW <b> 1 to SW <b> 16 are input to the PCM 10. The various sensors include the following sensors. That is, the air flow sensor SW1 that detects the flow rate of fresh air, the intake air temperature sensor SW2 that detects the temperature of fresh air, the downstream side of the intercooler / warmer 34, and the intercooler / warmer 34 downstream of the air cleaner 31. A second intake air temperature sensor SW3 for detecting the temperature of fresh air after passing through the EGR gas temperature sensor SW4, which is disposed in the vicinity of the connection portion of the EGR passage 50 with the intake passage 30 and detects the temperature of the external EGR gas. An intake port temperature sensor SW5 that is attached to the intake port 16 and detects the temperature of the intake air just before flowing into the cylinder 18, and an in-cylinder pressure sensor SW6 that is attached to the cylinder head 12 and detects the pressure in the cylinder 18. The exhaust passage 40 is disposed in the vicinity of the connection portion of the EGR passage 50 and has an exhaust temperature and exhaust gas Exhaust temperature sensor SW7 and exhaust pressure sensor SW8 for detecting a force, and is disposed on the upstream side of the direct catalyst 41, the linear O ₂ sensor SW9, direct catalyst 41 and underfoot catalyst 42 for detecting the oxygen concentration in the exhaust gas The lambda O ₂ sensor SW10 that detects the oxygen concentration in the exhaust gas, the water temperature sensor SW11 that detects the temperature of the engine coolant, the crank angle sensor SW12 that detects the rotation angle of the crankshaft 15, and the vehicle An accelerator opening sensor SW13 for detecting an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown), intake-side and exhaust-side cam angle sensors SW14, SW15, and a common rail 64 of the fuel supply system 62 are attached. The fuel pressure sensor SW16 detects the fuel pressure supplied to the injector 67. The

  The PCM 10 performs various calculations based on these detection signals to determine the state of the engine 1 and the vehicle, and in response to this, the injector 67, the spark plug 25, the intake-side VVT 71 and the variable drive mechanism 72, the exhaust side Control signals are output to the VVT 73, the variable drive mechanism 74, the fuel supply system 62, and the actuators of various valves (throttle valve 36, intercooler bypass valve 351, EGR valve 511, EGR cooler bypass valve 531). The PCM 10 estimates a combustion state including the temperature and pressure in the combustion chamber based on a preset model and the various detection signals described above, and outputs each control signal based on the combustion state. The engine 1 is operated.

(Engine operation control)
FIG. 6 shows an example of the operation control map of the engine 1. In order to improve fuel efficiency and exhaust emission performance, the engine 1 is controlled ignition (CAI) without performing ignition by the spark plug 25 in a low load region where the engine load is relatively low. To burn. In the example of FIG. 6, a region lower than the combustion switching load indicated by a solid line corresponds to a self-ignition region (CAI) in which CAI combustion is performed.

  As the load on the engine 1 increases, in CAI combustion, the combustion becomes too steep, causing problems such as combustion noise. Therefore, in the engine 1, in a high load region where the engine load is relatively high, the CAI combustion is stopped and the combustion is switched to the combustion by forced ignition (here, spark ignition (SI)) using the spark plug 25. In the example of FIG. 6, a region equal to or greater than the combustion switching load indicated by a solid line corresponds to a spark ignition region (SI) in which spark ignition combustion is performed. Thus, the engine 1 is configured to switch between the CAI mode and the SI mode in accordance with the operating state of the engine 1, in particular, the load of the engine 1. However, the boundary line for mode switching is not limited to the illustrated example.

  FIG. 7A shows a change in the EGR rate (that is, a change in the gas composition in the cylinder 18) with respect to the load of the engine 1 when the engine speed is constant at a predetermined speed on the low speed side. Yes. FIG. 7B shows changes in the combustion gas temperature with respect to the load of the engine 1. Hereinafter, the change in the gas composition in the cylinder 18 will be described in order from the low load side to the high load side.

(From minimum load to a specific load _{T 1)}
Low-load region to a certain load T ₁ corresponds to a low load region of the CAI mode, in order to improve the ignitability and stability of the CAI combustion, introducing a relatively high temperature hot EGR gas into the cylinder 18 . This is because the internal EGR gas is introduced into the cylinder 18. The introduction of hot EGR gas increases the compression end temperature in the cylinder 18 (that is, the temperature in the cylinder 18 when the piston 14 reaches compression top dead center), and the ignitability and stability of CAI combustion in a low load range. To increase.

In the CAI mode, the internal EGR gas amount is adjusted while keeping the throttle valve 36 fully open, and the fresh air amount is also adjusted. This is advantageous for reducing pump loss. Further, in the low load region to a certain load _{T 1,} the EGR rate is set to maximum EGR rate _{r max.} As described below, in certain load above T ₁ of the load area, in accordance with the load of the engine 1 becomes higher, when it EGR rate is set to be lower, the load on the engine 1 than the specific load T ₁ is low, the engine Regardless of the level of the load of 1, the EGR rate is made constant at the maximum EGR rate r _max . Limiting the EGR rate to the maximum EGR rate r _max means that if the EGR rate is made higher than that and a large amount of exhaust gas is introduced into the cylinder 18, the specific heat ratio of the gas in the cylinder 18 becomes low. Thus, even if the gas temperature at the start of compression is high, the compression end temperature is conversely lowered.

That is, exhaust gas contains a large amount of triatomic molecules such as CO ₂ and H ₂ O, and has a lower specific heat ratio than air containing nitrogen (N ₂ ) and oxygen (O ₂ ). Therefore, when the EGR rate is increased and the exhaust gas introduced into the cylinder 18 increases, the specific heat ratio of the gas in the cylinder 18 decreases.

Since the exhaust gas temperature is higher than fresh air, the higher the EGR rate, the higher the temperature in the cylinder 18 at the start of compression. However, the higher the EGR rate, the lower the specific heat ratio of the gas. Therefore, even if compression is performed, the temperature of the gas does not increase so much. As a result, the compression end temperature becomes the highest at a predetermined EGR rate r _max , and EGR Even if the rate is increased, the compression end temperature is lowered.

Therefore, in this engine 1, the compression end temperature is set to the highest becomes EGR rate to a maximum EGR rate _{r max.} Then, when the load of the engine 1 is lower than the specific loads T ₁ sets the EGR rate to a maximum EGR rate r _max, by the compression end temperature is avoided lowered. The maximum EGR rate r _max may be set to 50 to 90%. The maximum EGR rate r _max may be set as high as possible as long as a high compression end temperature can be secured, and is preferably 70 to 90%. In this engine 1, the geometric compression ratio is set to a high compression ratio of 15 or more so that a high compression end temperature can be obtained. Thus, in the engine 1 configured to ensure the highest possible compression end temperature, the maximum EGR rate r _max may be set to about 80%, for example. Setting the maximum EGR rate r _max as high as possible is advantageous in reducing the unburned loss of the engine 1. That is, since the unburned loss tends to increase when the load on the engine 1 is low, setting the EGR rate as high as possible when the load on the engine 1 is lower than the specific load T ₁ is effective in reducing the fuel consumption due to the reduction of the unburned loss. It is extremely effective for improvement.

In the region lower than this particular load T _1, 4, as shown for example L11, performed prior opening of the intake valve 21 of a relatively large lift amount. Thus, the amount of internal EGR gas introduced into the cylinder 18 is maximized. Thus, in this engine 1, when the load of the engine 1 is lower than the specific loads T _1, by ensuring a high compression end temperature, to ensure the ignitability and combustion stability of CAI combustion.

In the region lower than this particular load T _1, within a period of at least the intake stroke until the first half of the compression stroke, the injector 67 injects fuel into the cylinder 18. As a result, a homogeneous air-fuel mixture is formed in the cylinder 18.

(From a particular load _{T 1} to a predetermined load _{T 2)}
Region from a particular load T ₁ to a predetermined load T ₂ are equivalent to the load range in the CAI mode. In this region, the air excess ratio λ of the air-fuel mixture is made larger than 1. Therefore, the amount of fresh air introduced into the cylinder 18 is larger than the line of λ≈1 indicated by the one-dot chain line in FIG. It is less than the line of λ≈1. The excess air ratio λ of the air-fuel mixture is preferably made to be lean at least 2.4. Making the air-fuel mixture lean is advantageous for improving the fuel efficiency by improving the thermal efficiency, and by making the excess air ratio λ 2.4 or more, the generation of RawNOx is suppressed. This makes it possible to ensure the exhaust emission performance in the engine 1 that does not include the NOx purification catalyst. Note that the predetermined load T _2, between the switching load T ₃ to be described later, is provided a section for gradually changing the excess air ratio λ of the gas mixture.

In the region above a certain load T _1, since the fuel injection amount in accordance with the load of the engine 1 is increased to increase the excess air ratio lambda, in maintaining the so 2.4 above, as described above, the required fresh air amount The amount of hot EGR gas gradually decreases with the increase. When the load on the engine 1 is low, the temperature in the cylinder 18 at the start of compression is increased by increasing the amount of hot EGR gas introduced, and accordingly, the compression end temperature is increased to increase the ignitability of compression self-ignition and the compression. This is advantageous in increasing the stability of auto-ignition combustion. On the other hand, as the load on the engine 1 increases, the amount of fuel injection increases, and as shown in FIG. 7B, the combustion gas temperature increases, and the exhaust gas temperature increases with the temperature state in the cylinder 18. Therefore, even if the amount of hot EGR gas introduced is reduced, the ignitability and stability of compression self-ignition can be ensured.

  In this CAI region, the amount of hot EGR gas introduced corresponding to the load of the engine 1 is adjusted by adjusting the lift amount of the preceding valve opening of the intake valve 21. That is, when the EGR rate is changed from high to low as the load of the engine 1 increases, the lift amount of the preceding valve opening is reduced. Conversely, when the EGR rate is changed from low to high as the load on the engine 1 decreases, the lift amount of the preceding valve opening of the intake valve 21 is increased. As described above, this is performed by adjusting the opening / closing of the solenoid valve 7251 of the variable drive mechanism 72. In other words, when the EGR rate is changed from high to low as the load of the engine 1 increases, the timing of switching from opening to closing of the solenoid valve 7251 is delayed with respect to the start of operation of the cam lobe 7221 to advance the valve. Reduce the lift amount. Conversely, when the EGR rate is changed from low to high as the load of the engine 1 decreases, the lift amount of the preceding valve is opened by bringing the switching timing from opening to closing of the solenoid valve 7251 closer to the start of operation of the cam lobe 7221. Increase

(From the predetermined load _{T 2} to the switching load _{T 3)}
The predetermined load _{T 2} or more load region in CAI mode, corresponding to a high load region of the CAI mode. In the high load range in the CAI mode, the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio (λ≈1). As a result, a three-way catalyst can be used, and exhaust emission performance can be ensured. As shown in FIG. 7B, the combustion gas temperature becomes higher than that during lean combustion.

In this high load region, the temperature state in the cylinder 18 is further increased. Therefore, if hot EGR gas is introduced into the cylinder 18 while maintaining the air-fuel ratio of the air-fuel mixture at the stoichiometric air-fuel ratio (λ≈1), the temperature state in the cylinder 18 becomes too high and pre-ignition etc. May occur, or the pressure increase (dP / dθ) in the cylinder 18 may become steep during CAI combustion, resulting in a problem of combustion noise. Therefore, in the region from the predetermined load _{T 2} to switch the load _{T 3,} together with the hot EGR gas is introduced cooled EGR gas into the cylinder 18. The cooled EGR gas is basically an external EGR gas cooled by passing through the EGR cooler 52. The external EGR gas that bypasses the EGR cooler 52 may be included in the cooled EGR gas.

  Also in the high load side region of the CAI mode, the hot EGR gas introduction amount corresponding to the load of the engine 1 is adjusted by adjusting the lift amount of the preceding valve opening of the intake valve 21. As described above, the lift amount of the preceding valve is adjusted by opening / closing control of the solenoid valve 7251 of the variable drive mechanism 72. For example, as shown by L12 in FIG. 4, the preceding valve opening is performed with a relatively small lift amount and a relatively short valve opening period. The opening timing of the preceding valve opening in the high load side region is delayed from the opening timing of the preceding valve opening in the low load side region.

  Thus, in the region on the high load side of the CAI mode, the temperature state in the cylinder 18 is a combination of a small amount of hot EGR gas and a decrease in temperature and the introduction of the cooled EGR gas into the cylinder 18. Is prevented from becoming too high, which is advantageous for avoiding abnormal combustion and combustion noise. In the CAI mode, unlike the SI mode described later, there is no restriction on the EGR rate related to combustion stability. Therefore, it is possible to make the EGR rate as high as possible while setting the excess air ratio λ of the air-fuel mixture to substantially 1. Increasing the EGR rate is also advantageous for avoiding abnormal combustion and combustion noise in the high load region of the CAI mode.

Threshold engine load _{T 3} relates to switching between the CAI mode and SI-mode, the SI mode in the switching load _{T 3} or more high-load side. In the CAI mode, the internal EGR gas (that is, hot EGR gas) is introduced into the cylinder 18 by performing the pre-opening of the intake valve 21, while the pre-opening of the intake valve 21 is not performed in the SI mode. To stop the introduction of internal EGR gas. Therefore, by switching the load T ₃ as the boundary, execution and non-execution of the preceding opening of the intake valve 21 is switched. This is also done by controlling the opening and closing of the solenoid valve 7251.

(From the switching load _{T 3} up to a maximum load _{T max)}
Region of a load higher than the switching load T ₃ corresponds to SI mode. In the SI region, as described above, the hot EGR gas is substantially zero, and only the cooled EGR gas is introduced into the cylinder 18. Note that the fact that the hot EGR gas is substantially zero means that the internal EGR control is not performed. Since a part of the combustion gas remains in the cylinder 18 due to the structure, the hot EGR gas can remain in the cylinder 18 even in the SI mode.

  In the SI mode, basically, the opening of the throttle valve 36 is kept fully open, and the opening of the EGR valve 511 is changed according to the engine load. Thus, in the SI mode, the EGR rate is set to the maximum under the condition that the air-fuel ratio of the air-fuel mixture is set to the theoretical air-fuel ratio (λ≈1). This is advantageous for reducing pump loss. In addition, setting the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio makes it possible to use a three-way catalyst. Specifically, the EGR valve 511 gradually closes as the engine load increases, and closes at the fully open load. This is advantageous in improving controllability because the gas composition in the cylinder 18 is continuously changed when the engine load changes continuously.

In SI combustion, if the amount of exhaust gas introduced into the cylinder 18 is too large, the combustion stability is lowered. Therefore, there is a maximum EGR rate (that is, an EGR limit) that can be set in SI combustion. As described above, since the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio (λ≈1), the EGR rate changes continuously according to the engine load level, and when the engine load is low in the SI mode, the fuel amount and less, by fresh air amount is reduced, although the EGR rate can be high, from the switching load T ₃ to a predetermined load T _4, the EGR rate is limited to EGR limit. Thus, during the threshold engine load T ₃ to a predetermined load T ₄ it is, the EGR rate becomes constant at EGR limit, thus, when the EGR rate is limited by the EGR limit, the stoichiometric air-fuel ratio of the mixture (lambda In setting ≈1), the amount of fresh air introduced into the cylinder 18 must be reduced. Here, the amount of fresh air introduced into the cylinder 18 is reduced by delaying the closing timing of the intake valve 21 after the intake bottom dead center. Note that fresh air introduced into the cylinder 18 can be reduced by controlling the opening degree of the throttle valve 36, for example, instead of controlling the closing timing of the intake valve 21. However, controlling the closing timing of the intake valve 21 is advantageous in reducing pump loss.

(Adjustment of internal EGR gas amount accompanying changes in engine load)
As described above, in the CAI mode, the internal EGR gas amount is changed according to the engine load. Specifically, when the engine load is low, the amount of internal EGR gas introduced into the cylinder 18 is large (that is, the internal EGR rate is high), and when the engine load is high, the amount of internal EGR gas introduced into the cylinder 18 is small. (In other words, the internal EGR rate is low). Here, consider a case where the driver accelerates by depressing the accelerator pedal. At the time of acceleration, since the operating state of the engine 1 shifts to the high load side, the internal EGR rate is changed from high to low by changing the lift amount of the preceding valve opening of the intake valve 21. However, since the temperature state in the cylinder 18 and the exhaust gas temperature increase with a delay, a relatively small amount of internal EGR gas is introduced into the cylinder 18 at the transition transition of the operating state of the engine 1. As a result, the temperature state in the cylinder 18 becomes significantly low, and the ignitability and compression stability of compression ignition combustion may be reduced. Therefore, in the engine 1, during the transition in which the operating state of the engine 1 shifts to the high load side, transient control is performed to avoid a decrease in ignitability of compression ignition combustion and a decrease in stability.

  FIG. 8 shows the lift curve (see the solid line) of the intake valve 21 and the exhaust valve 22 at the time of transition when the operating state of the engine 1 shifts to the high load side so that the internal EGR rate changes from high to low. A lift curve (see broken line) is shown. FIG. 8A shows a conventional configuration, and FIG. 8B shows this configuration. In this configuration, the internal EGR control is performed by the prior opening of the intake valve 21 as described above. Unlike the present configuration, the conventional configuration performs internal EGR control by opening the exhaust valve 22 even in the intake stroke according to a preset profile, and also uses the VVT for the opening period of the exhaust valve 22. The amount of combustion gas introduced into the cylinder 18 is adjusted by changing the phase. Thereby, by opening the exhaust valve 22 during the intake stroke, a part of the exhaust gas discharged to the exhaust port 17 side during the exhaust stroke is reintroduced into the cylinder 18. In the example of FIG. 8A, the exhaust valve 22 opened during the exhaust stroke is kept open until the intake stroke. In the conventional configuration in which the exhaust valve 22 is opened twice, if the internal EGR gas amount is increased to increase the internal EGR rate, the opening period of the exhaust valve 22 is increased as shown on the left side of FIG. , Thereby increasing the opening time area of the exhaust valve 22 that opens during the intake stroke (that is, the value obtained by integrating the lift amount of the exhaust valve 22 over time). Conversely, if the internal EGR gas amount is decreased to reduce the internal EGR rate, the phase of the valve opening period of the exhaust valve 22 is advanced as shown on the right side of FIG. The opening time area of the exhaust valve 22 that opens during the stroke is reduced. As described above, in the conventional configuration in which the exhaust valve 22 is opened twice using VVT, as shown by an arrow in FIG. 8A during a transition in which the operating state of the engine 1 shifts to the high load side, The phase of the valve opening period of the exhaust valve 22 is gradually changed from the retarded angle side to the advanced angle side. In this configuration, as described above, the internal EGR gas must be gradually reduced in order to avoid the temperature in the cylinder 18 from being excessively lowered during the transition transition, and the operating state of the engine 1 is shifted. Become slow.

  On the other hand, this configuration is characterized in that the temperature of the combustion gas introduced into the cylinder 18 and the amount of the combustion gas are independently adjusted during a transition in which the operating state of the engine 1 shifts to the high load side. To do. This is because changing the internal EGR rate in accordance with the load level of the engine 1 makes the temperature state in the cylinder 18 almost constant regardless of the load level of the engine 1. .

  Specifically, when the operating state of the engine 1 is in the low load range and the internal EGR rate is set high, the lift amount of the preceding valve opening of the intake valve 21 as shown on the left of FIG. Is increased, and accordingly, the valve opening period of the preceding valve opening is lengthened (see L11). As described with reference to FIG. 4, the lift amount and the valve opening period of the preceding valve opening are performed by adjusting the opening / closing timing of the solenoid valve of the variable drive mechanism 72.

  In this configuration, during the transition when the operating state of the engine 1 shifts to the high load side, the lift amount of the preceding valve is not reduced gradually from large to small, but the lift amount of the preceding valve is greatly reduced. However, the valve opening timing is made earlier than the valve opening timing of the exhaust valve 22. As a result, as shown in the center of FIG. 8B, the pre-opening L13 of the intake valve 21 is performed during the expansion stroke at the time of transition. By performing the preceding valve opening during the expansion stroke, the high-temperature combustion gas in the cylinder 18 can be discharged to the intake port 16 side. As a result, even if the lift amount of the preceding valve opening is reduced and the amount of internal EGR introduced into the cylinder 18 is reduced, the temperature state in the cylinder 18, particularly the compression end temperature, can be increased. Since a high compression end temperature can be ensured in this way, the ignitability of CAI combustion decreases due to a decrease in the temperature state in the cylinder 18 during a transition in which the operating state of the engine 1 shifts to a high load side, It is possible to avoid a situation where stability is lowered.

  Further, in this configuration, after the operating state of the engine 1 shifts to the high load range, as shown on the right side of FIG. Retard. The opening timing of the preceding opening is delayed from the opening timing at the time of low load. Thereby, the temperature of the combustion gas introduced into the cylinder 18 is lower than that at the time of transition. Further, the lift amount of the preceding valve opening of the intake valve 21 is made smaller than when the load is low, and accordingly the opening period of the preceding valve opening is made shorter than when the load is low (see L12). The lift amount and the valve opening period are a lift amount and a valve opening period that are set according to the operating state in the high load range, and the internal EGR rate is set low. Thus, the temperature state in the cylinder 18 is prevented from becoming too high in the high load range. Thereby, an increase in combustion noise is avoided and abnormal combustion such as premature ignition is avoided.

  In the control example of FIG. 8B, the lift amount and the phase of the valve opening period of the main valve opening L2 of the intake valve 21 are not changed during the transition of the operating state of the engine 1. Further, the exhaust amount of the exhaust valve 22 and the phase of the valve opening period are not changed during the transition of the operating state of the engine 1.

Next, changes in various parameters when the operating state of the engine 1 shifts to the high load side will be described with reference to the time chart shown in FIG. In the time chart shown in FIG. 9, the load of the engine 1 rises from _{T 1} less than the initial load (1) shown in FIG. _7, to the target load between the T 1 through T ₂ (2). That is, the load of the engine 1 shifts from the low load region, which is a lean region in the CAI mode, to the medium load region. At the target load (2), only the internal EGR gas is introduced into the cylinder 18 and no external EGR gas is introduced.

  Each diagram on the left side of FIG. 9 exemplifies a change in parameters in the conventional configuration in which the exhaust valve 22 is opened twice using the VVT shown in FIG. FIG. 9A shows the change in the internal EGR temperature, FIG. 9B shows the change in the TDC temperature, FIG. 9C shows the change in the internal EGR rate, FIG. 9D shows the change in the fuel amount, and FIG. And (f) show the phase change during the valve opening period of the exhaust valve 22, respectively.

  In the conventional configuration, as described above, the phase of the valve opening period of the exhaust valve 22 is advanced when the internal EGR rate is changed from high to low. Here, as shown by a broken line in FIG. 9 (c), when the internal EGR gas is greatly reduced at the time of transition of the operating state of the engine 1, the combustion gas temperature and thus the exhaust gas temperature until then are low (in addition, In the conventional configuration, since the exhaust gas discharged to the exhaust port 17 side during the exhaust stroke is introduced into the cylinder 18, the exhaust gas temperature and the internal EGR gas temperature shown in FIG. As shown by a broken line in FIG. 9B, the temperature state in the cylinder 18 is lowered, and the ignitability and stability of CAI combustion are lowered.

  Therefore, in the conventional configuration, the combustion gas temperature is increased as much as possible, and the internal EGR rate is decreased as the gas temperature increases. Specifically, as shown in FIG. 9 (d), the fuel amount is gradually increased as the load of the engine 1 increases. Since the internal EGR gas cannot be rapidly reduced and a sufficient amount of fresh air cannot be secured, the amount of fuel is gradually increased. As the fuel amount increases, the air-fuel ratio of the air-fuel mixture is changed to the rich side (see FIG. 9E), and the combustion gas temperature rises. Accordingly, as shown in FIG. 9A, the temperature of the internal EGR gas introduced into the cylinder 18 gradually increases. Then, the phase of the valve opening period of the exhaust valve 22 is gradually advanced in accordance with the temperature rise of the internal EGR gas (see FIG. 9F). As a result, the internal EGR rate gradually decreases (see FIG. 9C). As a result, as shown in FIG. 9B, the compression end temperature can be maintained substantially constant during the transition.

  As described above, in the conventional configuration in which the exhaust valve 22 is opened twice using VVT, when the operating state of the engine 1 shifts to the high load side, the fuel amount increases, the exhaust temperature rises, the exhaust valve The advance angle of the valve opening period 22 and the internal EGR rate are sequentially decreased. Then, when the internal EGR rate and fuel flow rate corresponding to the target load are reached, the transient control ends. In the conventional configuration, during transient control, the increase in fuel amount and the advance angle of the valve opening period of the exhaust valve 22 must be gradually changed, so it takes a long time to complete the transition to the high load side. (See the white arrow in FIG. 9).

  On the other hand, each of the drawings on the right side of FIG. 9 exemplifies changes in parameters in this configuration in which the intake valve 21 shown in FIG. 9 (g) shows the change in the internal EGR temperature, (h) shows the change in the TDC temperature, (i) shows the change in the internal EGR rate, (j) shows the change in the fuel amount, and (k) shows the A / F of the air-fuel mixture. And (l) show the phase change during the preceding valve opening period of the intake valve 21, respectively.

  In this configuration, as described above, the phase of the preceding valve opening of the intake valve 21 is greatly advanced during transition transition, and the preceding valve is opened during the expansion stroke (see FIG. 9L). Also, the lift amount of the preceding valve opening is made sufficiently small (that is, the valve opening period is shortened). As a result, the internal EGR rate is made substantially the same as the internal EGR rate at the target load (see FIG. 9I). As a result, a sufficient amount of fresh air can be secured in the cylinder 18, so that the excess air ratio λ of the air-fuel mixture can be made 1 or more even if the amount of fuel is greatly increased. In the illustrated example, as shown in FIG. 9J, the fuel amount has increased to the fuel amount corresponding to the target load after the start of the transition.

  By increasing the fuel amount in this way, the temperature of the combustion gas increases. The amount of fuel can be increased in the range of λ ≧ 1. The amount of fuel may be increased as long as the combustion noise does not increase during the transition. As described above, by performing the preceding valve opening in the expansion stroke, it is possible to discharge the high-temperature combustion gas to the intake port 16 side. As a result, as shown in FIG. 9A, the temperature of the internal EGR gas introduced into the cylinder 18 can be significantly increased. In the illustrated example, the temperature of the internal EGR gas is temporarily higher than the internal EGR temperature after the transition to the middle load region during the transition. By increasing the internal EGR temperature, even if the internal EGR rate is low, the compression end temperature is suppressed from decreasing (see FIG. 9H).

  In this configuration, the temperature state in the cylinder 18 is rapidly increased and the exhaust gas temperature is also rapidly increased due to the increase in the fuel amount. In this configuration, during the transient control, the phase of the valve opening period of the preceding valve opening is delayed so that the compression end temperature does not become too high (see FIG. 9 (l)). Thus, the temperature of the internal EGR gas introduced into the cylinder is adjusted (see FIG. 9A). As a result, the compression end temperature can be maintained substantially constant during the transient control. In this configuration, as indicated by a white arrow in FIG. 9, the transient control can be ended quickly, and the operating state of the engine 1 can be quickly shifted to the middle load range. After completion of the transition to the middle load range, the valve opening timing of the preceding valve opening is further delayed than during the transient control. As a result, the valve opening timing of the preceding valve opening is delayed from the valve opening timing in the low load region (see IVO in FIG. 9 (l)). Thus, it is avoided that the temperature state in the cylinder 18 becomes too high in the middle load range.

  In this way, this configuration uses the preceding valve opening of the intake valve 21 to independently adjust the temperature of the internal EGR gas, thereby shortening the transient control and shifting the high load region compared to the conventional configuration. Complete promptly.

  Here, in this configuration, during the transient control, the preceding opening of the intake valve 21 is performed in the expansion stroke. In contrast to this, it is also conceivable to perform the prior opening of the intake valve 21 in the exhaust stroke during transient control. However, by performing the prior opening of the intake valve 21 in the expansion stroke, in addition to suppressing the temperature drop in the cylinder, after the start of the transient control, the high-temperature combustion gas is quickly introduced into the cylinder with the earlier combustion order. There is an advantage that it becomes possible. This point will be described with reference to the timing charts of FIGS.

  First, FIG. 10 shows the stroke transition of each of the first to fourth cylinders 18 when the intake valve 21 is opened in the exhaust stroke during transient control. In this figure, as shown in the upper left, it is assumed that the increase of the fuel injection amount is started from the first cylinder 18 with the start of the transient control.

  After fuel injection is performed in the first cylinder 18, combustion is performed in the first cylinder 18 as indicated by a white arrow in the figure. When the first cylinder 18 is in the exhaust stroke, the intake valve 21 is opened in advance. As a result, the combustion gas discharged to the intake port side is introduced into the cylinder 18 in the intake stroke at this timing due to the short communication distance between the cylinders on the intake side of the engine 1. The As indicated by a black arrow in FIG. 10, the cylinder in the intake stroke when the first cylinder 18 is in the exhaust stroke is the second cylinder 18. Therefore, the relatively high-temperature combustion gas is used to increase the temperature of the second cylinder 18. The effect of increasing the temperature of the combustion gas by increasing the fuel injection amount in the first cylinder 18 is reflected only when the second cylinder 18 is combusted. In a four-stroke four-cylinder engine, the period from when the fuel injection amount is increased until the effect is reflected corresponds to about two and a half rotations of the crankshaft.

  On the other hand, FIG. 11 shows a stroke transition of each of the first to fourth cylinders 18 when the intake valve 21 is opened in the expansion stroke during the transient control. Also in this figure, it is assumed that the increase in the fuel injection amount is started from the first cylinder 18 with the start of the transient control, as in FIG. Since the change in the opening mode of the intake valve 21 and the exhaust valve 22 is delayed with respect to the increase in the fuel injection amount, when the increase in the fuel injection amount in the first cylinder 18 is started, the first cylinder 18 is included. The opening modes of the intake valve 21 and the exhaust valve 22 are not changed. Thereafter, after the combustion of the first cylinder 18 is performed, the preceding valve opening of the intake valve 21 advances to the expansion stroke.

  The cylinder in the intake stroke when the first cylinder 18 is in the expansion stroke is the fourth cylinder. Combustion gas discharged to the intake port side by the first valve opening in the expansion stroke in the first cylinder 18 in the engine 1 having a short communication path distance between the cylinders as indicated by a black arrow in FIG. It is introduced into the four cylinder 18. Thus, the temperature of the fourth cylinder 18 is raised, and compression ignition combustion is performed. Therefore, the effect of increasing the temperature of the combustion gas by increasing the fuel injection amount in the first cylinder 18 is reflected at the time of combustion in the fourth cylinder 18, which is earlier in combustion order than the second cylinder 18, Corresponds to the degree of rotation. Thus, by performing the prior valve opening in the expansion stroke, it is possible to further suppress the temperature drop in the cylinder 18 during the transient control, and to quickly complete the transition of the operating state of the engine 1. Is possible.

  Here, as shown in FIG. 8, during the transient control, the phase of the entire valve opening period of the preceding valve opening is advanced than before the transition (see L11 and L13 in FIG. 8). Sometimes a pre-opening valve in the expansion stroke may be added. For example, in the example of FIG. 8, at the time of transient control, the intake valve 21 may be opened at L13 in the expansion stroke, and may be opened at L11 in the exhaust stroke, so that the preceding valve opening is performed twice. . The lift amount of the preceding valve opening can be changed as appropriate. Although illustration is omitted, only the opening timing of the preceding opening of the intake valve 21 is advanced, and the valve closing phase is not substantially advanced, so that the intake valve 21 is opened in the expansion stroke. You may do it.

  Also, for example, as shown in FIG. 12, during steady operation, the exhaust valve 22 is opened twice, and internal EGR control is performed, and only when the operating state of the engine 1 shifts to the high load side, the intake valve 21 A prior valve opening may be performed.

  That is, the left side of FIG. 12 corresponds to a case where the operating state of the engine 1 is in a low load range and the internal EGR rate is set high. At this time, the lift amount of the restart valve of the exhaust valve 22 is increased, The opening time area of the exhaust valve 22 during the intake stroke is increased (see L21). The exhaust valve 22 opens in both the exhaust stroke and the intake stroke, while the intake valve 21 opens only once during the intake stroke (see L2). As described with reference to FIG. 4, the opening of the intake valve 21 and the exhaust valve 22 is performed by adjusting the opening / closing timing of the solenoid valves of the variable drive mechanisms 72 and 74.

  At the time of transition in which the operating state of the engine 1 shifts to the high load side, as shown in the center of FIG. The main valve opening (L2) is performed. The exhaust valve 22 opens only during the exhaust stroke (see L1). Since this is the same as the opening mode of the intake valve 21 and the exhaust valve 22 shown in the center of FIG. 8B, the temperature state in the cylinder 18 is suppressed from decreasing during transient control, and compression ignition is performed. Combustion ignitability and combustion stability are improved. Further, it is possible to reflect the increase in the combustion gas temperature due to the increase in fuel in the cylinders with the earlier combustion order.

  Then, after the operating state of the engine 1 shifts to the high load side, as shown on the right side of FIG. 12, the pre-opening of the intake valve 21 in the expansion stroke is stopped, and the exhaust valve 22 is turned twice. The opening is changed again (see L1 and L22). At this time, the lift amount of the restart valve L22 of the exhaust valve 22 that opens in the intake stroke is set to be relatively small so as to correspond to the low EGR rate set on the high load side.

  In the example of FIG. 12, during transient control, the exhaust valve 22 is stopped from opening twice and the intake valve 21 is opened in advance, but the exhaust valve 22 is kept open twice, You may make it perform the prior | preceding valve opening (L13) of the intake valve 21. FIG.

  The technique disclosed here is not limited to application to the engine configuration described above.

  The drive mechanism of the intake valve 21 is not limited to the configuration including the VVT 71 and the variable drive mechanism 72. For example, the drive mechanism of the intake valve 21 may further include a switching mechanism capable of switching between two types of cams in addition to the VVT 71 and the variable drive mechanism 72. For example, the cam switching mechanism may switch between a cam having one cam peak and a cam having two cam peaks. A cam having one cam peak may be used when the internal EGR control is not performed, and a cam having two cam peaks may be used when the internal EGR control is performed.

  In addition, the drive mechanism of the intake valve 21 may include the cam switching mechanism instead of the variable drive mechanism 72. That is, the drive mechanism of the intake valve 21 may include a VVT and a cam switching mechanism. Even with this configuration, the lift curves shown in FIG. 4 can be realized.

  Further, the drive mechanism of the intake valve 21 may include a mechanical variable valve lift (CVVL) capable of continuously changing the lift amount of the intake valve and a VVT. Even with this configuration, the lift curves shown in FIG. 4 can be realized.

  It should be noted that a modification similar to the drive mechanism of the intake valve 21 described above can also be adopted for the drive mechanism of the exhaust valve 22.

  In the above configuration, the drive mechanism of the intake valve 21 includes the variable drive mechanism 72 and the drive mechanism of the exhaust valve 22 includes the variable drive mechanism 74. However, the variable drive mechanism 72 is provided only for the drive mechanism of the intake valve 21. You may make it prepare. That is, the mechanism that enables the first valve opening and the second valve opening twice may be provided only on the intake valve 21 side.

  The operation control map shown in FIG. 6 is merely an example, and various other maps can be provided.

  In addition, the exhaust passage is provided with only a three-way catalyst, but it is provided with a NOx purification catalyst, so that the excess air ratio λ is smaller than 2.4 and larger than 1.0, and A / F can be operated with Lean. May be.

  The technique disclosed here is not limited to being applied to a four-cylinder engine, and the number of cylinders can be any number. In a four-stroke engine, regardless of the number of cylinders, the prior opening of the intake valve 21 in the expansion stroke during transient control reflects the effect of increasing the temperature of the combustion gas due to the increase in fuel in the cylinders with the earlier combustion order It is possible.

  Furthermore, the technology disclosed herein can be applied to a diesel engine.

1 Engine (Engine body)
16 Intake port 17 Exhaust port 18 Cylinder 21 Intake valve 22 Exhaust valve 62 Fuel supply system 67 Injector 72 Variable drive mechanism (internal EGR control means)
74 Variable drive mechanism (internal EGR control means)
L11, L12, L13 Advance valve opening

Claims (5)

An engine main body having a fuel supply mechanism for supplying fuel to each of the plurality of cylinders and configured to perform compression ignition combustion of the air-fuel mixture in each cylinder in a preset compression ignition combustion region;
An intake valve configured to open and close an intake port for sucking gas into the cylinder;
An exhaust valve configured to open and close an exhaust port for discharging combustion gas from within the cylinder;
Internal EGR control means configured to introduce a combustion gas into the cylinder together with fresh air by controlling a valve opening mode of at least one of the intake valve and the exhaust valve, and
In the compression ignition combustion region, the internal EGR control means has a high internal EGR rate that is a ratio of the amount of the combustion gas to the total gas amount in the cylinder and a high load when the load of the engine body is low. Sometimes the internal EGR rate is lowered,
In the compression ignition combustion region, the engine body moves the air-fuel mixture in the cylinder during a transition in which the operating state of the engine body shifts to a high load side so that the internal EGR rate is changed from high to low. In the range where the excess air ratio is λ ≧ 1, the amount of fuel supplied into the cylinder is increased, and the internal EGR control means performs the preceding valve opening to open the intake valve in the expansion stroke, Combustion gas having a temperature higher than that in the exhaust stroke is discharged to the intake port, and the intake valve is opened in the intake stroke, whereby the combustion gas is introduced into the cylinder together with fresh air through the intake port. And
The internal EGR control means includes a main valve that opens the exhaust valve in the exhaust stroke without performing the prior opening of the intake valve during steady operation in the compression ignition combustion region, and the exhaust valve in the intake stroke. A control device for a compression ignition engine configured to introduce a part of the combustion gas into the cylinder through the exhaust port by performing a restart valve for opening the valve . The control apparatus for a compression ignition engine according to claim 1,
The internal EGR control means controls the compression ignition engine that adjusts the lift amount of the preceding valve opening of the intake valve so that the internal EGR rate is lower than the internal EGR rate before transition during the transition. apparatus. The control apparatus for a compression ignition engine according to claim 1 or 2,
In the compression ignition combustion region, the internal EGR control means opens the intake valve in the exhaust stroke and opens the intake valve in the intake stroke, thereby opening the intake valve via the intake port. The combustion gas is introduced into the cylinder together with fresh air,
The internal EGR control means controls the compression ignition engine that performs the preceding valve opening in the expansion stroke by advancing the opening timing of the preceding valve opening of the intake valve more than before the transition during the transition. apparatus. In the control apparatus of the compression ignition type engine according to any one of claims 1 to 3 ,
The internal EGR control means is a control device for a compression ignition type engine that stops the preceding opening of the intake valve in the expansion stroke after the operating state of the engine body has shifted to the high load side. In the control device for the compression ignition engine according to any one of claims 1 to 4 ,
The engine main body is a compression ignition type that increases the fuel amount at the time of transition when the operating state transitions from a preset region where the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio to the high load side. Engine control device.

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