JP2004239268A - Fuel injection device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent fluctuation of the engine output torque caused by secondary fuel injection in an expansion or exhaust stroke of an engine. <P>SOLUTION: A cylinder fuel injection valve 111 to directly inject fuel in a cylinder of an internal combustion engine is provided, and main fuel injection is performed in the cylinder intake stroke and/or the compression stroke, and secondary fuel injection not contributing to the combustion is performed in the expansion stroke or the exhaust stroke, respectively. An electronic control unit (ECU) 30 of the engine calculates the amount of remaining fuel in the cylinder by the secondary fuel injection based on the operating state of the engine, and the amount of the next main fuel injection is reduced by the amount of the remaining fuel. Therefore, even when the remaining fuel is present in the cylinder by the secondary fuel injection, the output torque is not fluctuated during the combustion at the next cycle. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a fuel injection device for an internal combustion engine, and more particularly, to a fuel injection device having an in-cylinder fuel injection valve for directly injecting fuel into an engine cylinder.

2. Description of the Related Art A fuel injection device including an in-cylinder fuel injection valve for directly injecting fuel into a cylinder and performing secondary fuel injection during an expansion stroke or an exhaust stroke of the cylinder in addition to main fuel injection contributing to normal in-cylinder combustion is known. Have been.
As this type of apparatus, for example, there is an apparatus disclosed in Patent Document 1.

The device of Document 1 absorbs NO _X in exhaust gas when the air-fuel ratio of the exhaust gas flowing into the exhaust passage of the diesel engine is lean, and releases the absorbed NO _X when the oxygen concentration in the exhaust gas flowing in decreases. _the NO _X storage reduction catalyst were placed, usually performs a main fuel injected into the cylinder at the compression top dead center near the engine cylinder, the time to emit NO _X from _the NO _X storage reduction catalyst, in addition to the main fuel injection cylinder The secondary fuel injection is performed during the expansion or exhaust stroke of the engine.

The fuel injected into the cylinder during the expansion or exhaust stroke is exposed to the high-temperature burned gas without contributing to the combustion in the cylinder. Decomposes into small hydrocarbons. Also, since the fuel injected by the secondary fuel injection does not contribute to the combustion and is discharged as it is with the exhaust gas, even in a diesel engine, it is necessary to make the exhaust gas rich air-fuel ratio without increasing the explosion pressure in the cylinder. A very large amount of fuel can be injected. Therefore, exhaust gas of a rich air-fuel ratio rich in hydrocarbons having a high active low molecular weight becomes to flow to the NO _X occluding and reducing catalyst in the exhaust passage by the secondary fuel injection, NO was absorbed from _the NO _X storage reduction catalyst _X Is released and reduced and purified by hydrocarbons in the exhaust gas.

JP-A-6-212961

  However, in an engine that performs secondary fuel injection as in Patent Literature 1, the fuel injected by secondary fuel injection sometimes remains in the cylinder without being completely discharged during the exhaust stroke. If a part of the fuel of the secondary fuel injection remains in the cylinder, the remaining fuel is burned in the cylinder in addition to the fuel supplied by the main fuel injection when the next main fuel injection is performed. There is a problem that the generated torque becomes excessive and the output torque of the engine fluctuates.

  The present invention has been made in view of the above circumstances, and has as its object to provide a fuel injection device for an internal combustion engine that can prevent engine output torque fluctuation due to residual fuel during secondary fuel injection.

  According to the first aspect of the present invention, an in-cylinder fuel injection valve for directly injecting fuel into a cylinder of an internal combustion engine, and the in-cylinder fuel injection valve are controlled to inject fuel contributing to combustion in the cylinder. Fuel injection control means for performing main fuel injection and, if necessary, performing secondary fuel injection for injecting fuel that does not contribute to combustion in the cylinder during an expansion stroke or an exhaust stroke after the main fuel injection, The fuel injection control means calculates the amount of fuel remaining in the cylinder among the fuel injected by the immediately preceding secondary fuel injection, and corrects the injection amount of the main fuel injection according to the remaining fuel amount. A fuel injection device for an internal combustion engine is provided.

  That is, in the first aspect of the invention, the fuel injection control means calculates the amount of fuel remaining in the cylinder due to the immediately preceding secondary fuel injection, and corrects the main fuel injection amount according to the remaining fuel amount. This correction is performed, for example, by reducing the main fuel injection amount by an amount corresponding to the residual fuel amount. As a result, the amount of fuel contributing to combustion during main fuel injection is maintained at the target amount. For this reason, even when fuel remains in the cylinder due to the secondary fuel injection, the output torque of the engine does not fluctuate.

  According to the second aspect of the present invention, an in-cylinder fuel injection valve for directly injecting fuel into a cylinder of an internal combustion engine, and the in-cylinder fuel injection valve are controlled to inject fuel contributing to combustion in the cylinder. Fuel injection control means for performing main fuel injection and, if necessary, performing secondary fuel injection for injecting fuel that does not contribute to combustion in the cylinder during an expansion stroke or an exhaust stroke after the main fuel injection, The fuel injection control means converts the main fuel injection as necessary into a first main fuel injection for generating a homogeneous mixture in a cylinder and a second main fuel injection for generating a layer of a combustible mixture. When the secondary fuel injection is executed, the fuel amount remaining in the cylinder among the fuel injected by the immediately preceding secondary fuel injection is calculated, and the second fuel injection is performed in accordance with the residual fuel amount. 1 Fuel for internal combustion engine that corrects the injection amount of main fuel injection Morphism apparatus is provided.

  That is, in the second aspect of the invention, when performing the main fuel injection twice, the fuel injection control means corrects the amount of the first main fuel injection according to the amount of residual fuel in the cylinder due to the secondary fuel injection. This correction is performed, for example, by reducing the first main fuel injection amount by an amount corresponding to the residual fuel amount. The first main fuel injection is for generating a homogeneous mixture in the cylinder, whereas the second main fuel injection is for stratifying the mixture. On the other hand, the fuel remaining in the cylinder generates a homogeneous mixture in the cylinder. Therefore, when the first main fuel injection amount is set as usual, the air-fuel ratio of the generated homogeneous mixture becomes richer than the target value. According to the present invention, by correcting the first main fuel injection amount according to the remaining fuel amount, the air-fuel ratio of the homogeneous mixture generated in the cylinder is maintained at the target value.

  In the invention described in each claim, the amount of fuel remaining in the cylinder at the time of performing the secondary fuel injection is calculated, and the main fuel injection amount is corrected according to the remaining fuel amount. Even when the residual fuel in the cylinder is generated, it is possible to prevent the fluctuation of the engine output from occurring.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an embodiment in which the fuel injection device of the present invention is applied to an internal combustion engine for a vehicle.
In FIG. 1, reference numeral 1 denotes an internal combustion engine for a vehicle. In the present embodiment, the engine 1 is a four-cylinder gasoline engine having four cylinders # 1 to # 4, and fuel injection valves 111 to 114 for directly injecting fuel into the cylinders are provided in the # 1 to # 4 cylinders. Is provided. As will be described later, the internal combustion engine 1 of the present embodiment is a lean burn engine that can operate at a higher (lean) air-fuel ratio than the stoichiometric air-fuel ratio.

  In the present embodiment, the cylinders # 1 to # 4 are grouped into two cylinder groups including two cylinders whose ignition timings are not continuous with each other. (For example, in the embodiment of FIG. 1, the cylinder ignition order is 1-3-4-2, and the cylinders # 1, # 4 and the cylinders # 2, # 3 each constitute a cylinder group. The exhaust port of each cylinder is connected to an exhaust manifold for each cylinder group, and is connected to an exhaust passage for each cylinder group. In FIG. 1, reference numeral 21a denotes an exhaust manifold for connecting the exhaust ports of a group of cylinders composed of # 1 and # 4 cylinders to the individual exhaust passage 2a, and reference numeral 21b denotes an exhaust port of a group of cylinders composed of # 2 and # 4 cylinders for the individual exhaust passage 2b. Exhaust manifold connected to the In the present embodiment, start catalysts (hereinafter, referred to as “SC”) 5a and 5b made of a three-way catalyst are arranged on the individual exhaust passages 2a and 2b, respectively. The individual exhaust passages 2a and 2b join the common exhaust passage 2 downstream of the SC.

On the common exhaust passage 2, a NO _X storage reduction catalyst 7 described later is arranged. In FIG. 1, reference numerals 29a and 29b denote air-fuel ratio sensors disposed upstream of the start catalysts 5a and 5b of the individual exhaust passages 2a and 2b, and reference numeral 31 denotes a NO _X storage reduction catalyst 7 of the exhaust passage 2. It is an air-fuel ratio sensor arranged at the outlet. The air-fuel ratio sensors 29a, 29b and 31 are so-called linear air-fuel ratio sensors that output a voltage signal corresponding to the exhaust air-fuel ratio in a wide air-fuel ratio range.

  In FIG. 1, the intake ports of the cylinders # 1 to # 4 of the engine are connected to a surge tank 10a via an intake manifold 10b, and the surge tank is connected to a common intake passage 10. Further, in this embodiment, a throttle valve 15 is provided on the intake passage 10. The throttle valve 15 of the present embodiment is a so-called electronically controlled throttle valve, and is driven by an actuator 15a of an appropriate type such as a stepper motor, and has an opening in accordance with a control signal from an ECU 30 described later. Reference numeral 15b in FIG. 1 denotes a throttle valve opening sensor for detecting the opening of the throttle valve 15.

  In the present embodiment, the in-cylinder fuel injection valves 111 to 114 are individually connected to a common rail (accumulator) 110 and inject high-pressure fuel in the common rail 110 into the cylinder. A fuel pump indicated by 130 in FIG. 1 is a high-pressure pump such as a plunger pump. The fuel pump 130 pumps high-pressure fuel to the common rail 110 every time fuel is injected from each of the fuel injection valves (111 to 114).

  A variable valve timing device that changes the valve timing of the engine 1 is shown at 200 in FIG. In this embodiment, the variable valve timing device 200 may be of any known type as long as it can change the valve timing of the engine 1 in response to a command signal from the ECU 30 described later. Alternatively, any of those that change only the opening / closing timing of the exhaust valve, those that change the valve lift together with the opening / closing timing, and the like can be used. Further, the change of the valve timing may be performed continuously or stepwise.

Reference numeral 30 in FIG. 1 denotes an ECU (engine control unit) that controls the engine 1. The ECU 30 includes a microcomputer having a known configuration in which a RAM, a ROM, and a CPU are interconnected by a bidirectional bus, and performs basic control such as main fuel injection control and ignition timing control of the engine 1. Further, in the present embodiment, the ECU 30 switches the combustion in the cylinder to a rich air-fuel ratio during the regeneration operation of the NO _X storage reduction catalyst described later, or performs the secondary fuel injection during the expansion or exhaust stroke of each cylinder, and performs the NO _X storage reduction catalyst. The secondary fuel injection control for switching the exhaust air-fuel ratio flowing into the fuel cell to the rich air-fuel ratio in a short time is performed.

The ECU30 input ports, air-fuel ratio sensor 29a, a signal representative of the exhaust air-fuel ratio SCs 5a, in 5b the entrance from 29 b, and a signal representing the exhaust gas air-fuel ratio in _the NO _X storage reduction catalyst 7 exit from the air-fuel ratio sensor 31, a surge tank In addition to a signal corresponding to the intake pressure of the engine from the intake pressure sensor 37 provided in 10a and a signal corresponding to the accelerator pedal depression amount (accelerator opening) of the driver from the accelerator opening sensor 33, respectively, A crank rotation angle pulse signal is input from the rotation speed sensor 35 arranged near the engine crankshaft (not shown) at every constant rotation angle of the engine crankshaft. The ECU 30 calculates the crankshaft rotation angle from the pulse signal and calculates the engine speed from the frequency of the pulse signal.

  Further, a signal corresponding to the fuel pressure in the common rail 110 from the fuel pressure sensor 120 disposed on the common rail 110 and a signal representing the opening of the throttle valve 15 from the throttle valve opening sensor 15b are input to input ports of the ECU 30. I have.

  In addition, an output port of the ECU 30 is connected to fuel injection valves 111 to 114 of each cylinder via a fuel injection circuit (not shown) in order to control a fuel injection amount and a fuel injection timing to each cylinder. It is connected to an actuator 15b of the valve 15 via a drive circuit (not shown) to control the opening of the throttle valve 15.

  In addition to the above control, the ECU 30 performs feedback control of the fuel pumping amount of the fuel pump 130 so that the fuel pressure in the common rail 110 becomes a target value in accordance with the fuel pressure signal in the common rail 110 input from the fuel pressure sensor 120. Note that the fuel pumping from the fuel pump 130 to the common rail 110 is performed every time fuel is injected from the fuel injection valves 111 to 114.

Further, the output port of the ECU 30 is connected to a variable valve timing device 200 via a drive circuit (not shown), and controls the valve timing of the engine 1 according to the engine load state (accelerator opening and engine speed). I have.
In the present embodiment, the main fuel injection of the engine 1, that is, the injection of fuel for combustion in the cylinder is controlled in the following five modes according to the engine load.

1) Lean air-fuel ratio stratified combustion (one compression stroke injection)
2) Lean air-fuel ratio homogeneous mixture / stratified combustion (intake stroke / compression stroke twice injection)
3) Lean air-fuel ratio homogeneous mixture combustion (single injection stroke)
4) Combustion of stoichiometric air-fuel ratio homogeneous mixture (injection of intake stroke once)
5) Combustion of rich air-fuel ratio homogeneous mixture (injection of the intake stroke once)

  That is, in the light load operation region of the engine 1, the lean air-fuel ratio stratified combustion of 1) is performed. In this state, in-cylinder fuel injection is performed only once in the latter half of the compression stroke of each cylinder, and the injected fuel forms a combustible mixture layer near the cylinder ignition plug. Further, the fuel injection amount in this operating state is extremely small, and the overall air-fuel ratio in the cylinder is about 25 to 30.

  Further, when the load increases from the state of the above 1) and becomes a low load operation region, the above 2) the lean air-fuel ratio homogeneous mixture / stratified combustion is performed. As the engine load increases, the amount of fuel injected into the cylinder increases. However, in the above-mentioned stratified combustion, since the fuel injection is performed in the latter half of the compression stroke, the injection time is limited, and the amount of fuel that can be stratified is reduced. Has limitations. Therefore, in this load region, a target amount of fuel is supplied to the cylinder by injecting in advance the amount of fuel that is insufficient only by fuel injection in the latter half of the compression stroke into the first half of the intake stroke.

  The fuel injected into the cylinder in the first half of the intake stroke produces an extremely lean homogeneous mixture by the time of ignition. In the latter half of the compression stroke, fuel is further injected into this extremely lean homogeneous mixture, and a layer of ignitable combustible mixture is generated near the ignition plug. At the time of ignition, the combustible air-fuel mixture layer starts burning, and the flame propagates to the surrounding lean air-fuel mixture layer, so that stable combustion is performed. In this state, the amount of fuel supplied by the injection in the intake stroke and the compression stroke is increased from 1), but the overall air-fuel ratio is slightly lower (for example, about 20 to 30 in air-fuel ratio).

  When the engine load further increases, the engine 1 performs the lean air-fuel ratio homogeneous mixture combustion described in 3) above. In this state, the fuel injection is executed only once in the first half of the intake stroke, and the fuel injection amount is further increased from the above 2). In this state, the homogeneous air-fuel mixture generated in the cylinder has a lean air-fuel ratio relatively close to the stoichiometric air-fuel ratio (for example, an air-fuel ratio of about 15 to 25).

  When the engine load further increases and enters the engine high load operation region, the amount of fuel is further increased from the state of 3), and the stoichiometric air-fuel ratio homogeneous mixture operation of 4) is performed. In this state, a homogeneous air-fuel mixture having a stoichiometric air-fuel ratio is generated in the cylinder, and the engine output increases. Further, when the engine load further increases and the engine becomes full load operation, the fuel injection amount is further increased from the state of 4), and the rich air-fuel ratio homogeneous mixture operation of 5) is performed. In this state, the air-fuel ratio of the homogeneous mixture generated in the cylinder becomes rich (for example, about 12 to 14 in air-fuel ratio).

  In this embodiment, the optimal operation modes (1 to 5)) are set in advance based on experiments and the like according to the accelerator opening (the amount of depression of the accelerator pedal by the driver) and the engine speed. Are stored as a map using the accelerator opening and the engine speed. During the operation of the engine 1, the ECU 30 determines which of the above 1) to 5) operation modes should be currently selected based on the accelerator opening detected by the accelerator opening sensor 33 and the engine speed. The fuel injection amount, the fuel injection timing, the number of times, and the throttle valve opening are determined according to.

  That is, when the mode 1) to 3) (lean air-fuel ratio combustion) is selected, the ECU 30 determines the accelerator opening and the engine based on the maps prepared in advance for the modes 1) to 3). The fuel injection amount is determined from the rotation speed. When the modes (4) and (5) (the stoichiometric air-fuel ratio or the rich air-fuel ratio homogeneous mixture combustion) are selected, the ECU 30 performs the operations based on the maps prepared in advance for the modes (4) and (5). Then, the fuel injection amount is set based on the intake pressure detected by the intake pressure sensor 33 and the engine speed.

When mode 4) (stoichiometric air-fuel ratio homogeneous mixture combustion) is selected, the ECU 30 further calculates the fuel injection amount calculated as described above so that the engine exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio. , 29b for air-fuel ratio control for feedback correction.
The start catalysts (SC) 5a and 5b use a honeycomb-shaped carrier such as cordierite to form a thin coating of alumina on the surface of the carrier, and form a platinum Pt, palladium Pd, rhodium Rh, etc. on the alumina layer. As a three-way catalyst supporting the noble metal catalyst component. Three-way catalyst for purifying HC at the stoichiometric air-fuel ratio near, CO, three components of the NO _X at a high efficiency. Three-way catalyst, the air-fuel ratio of the inflowing exhaust gas because the reducing capacity of the higher becomes the NO _X than the stoichiometric air-fuel ratio decreases, to sufficiently purify NO _X in the exhaust gas when the engine 1 is a lean air-fuel ratio operation It is not possible.

  In the present embodiment, the SCs 5a and 5b mainly perform exhaust purification during the rich air-fuel ratio operation of the engine 1 immediately after the cold start and exhaust purification when the engine 1 is operated at the stoichiometric air-fuel ratio during the normal operation. For this reason, the SCs 5a and 5b are arranged in portions of the exhaust passages 2a and 2b close to the engine 1 so as to be able to reach the activation temperature of the catalyst and start the catalytic action in a short time after starting the engine, thereby reducing the heat capacity. Therefore, it has a relatively small capacity.

Next, the NO _X storage reduction catalyst 7 of the present embodiment will be described. The NO _X storage-reduction catalyst 7 of the present embodiment uses, for example, alumina as a carrier, and on the carrier, for example, an alkali metal such as potassium K, sodium Na, lithium Li, or cesium Cs, or an alkaline earth such as barium Ba or calcium Ca. And at least one component selected from rare earths such as lanthanum La, cerium Ce and yttrium Y, and a noble metal such as platinum Pt. When the air-fuel ratio of the exhaust gas _the NO _X storage reduction catalyst is flowing is lean, NO _X in the exhaust gas (nitrogen oxides) nitrate ion NO ₂ ^- was absorbed in the form of inflow exhaust gas is less stoichiometric air-fuel ratio ( When the air-fuel ratio reaches a rich air-fuel ratio, a NO _X absorption / release operation is performed to release the absorbed NO _X.

  The mechanism of this absorption and release will be described below by taking platinum Pt and barium Ba as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.

When the oxygen concentration in the inflowing exhaust gas increases (that is, when the exhaust air-fuel ratio becomes lean), these oxygens are deposited on the platinum Pt in the form of O ₂ ⁻ or O ²⁻ , and the NO _X in the exhaust gas is reduced on the platinum Pt. Reacts with O ₂ ^— or O ²⁻ , thereby producing NO ₂ . Further, the inflow NO ₂ and NO ₂ produced by the above exhaust platinum Pt on the further absorbed into the absorbent while being oxidized barium oxide BaO and bound with nitrate ions NO ₃ ^- in the form of absorbent Spread. Therefore, so NO _X in the exhaust gas is absorbed in the form of nitrates into _the NO _X absorbent in the lean atmosphere.

Further, when the oxygen concentration in the inflowing exhaust gas is significantly reduced (that is, when the exhaust air-fuel ratio becomes smaller than the stoichiometric air-fuel ratio (rich)), the amount of NO ₂ generated on the platinum Pt decreases, so that the reaction proceeds in the reverse direction. And the nitrate ion NO ₂ ⁻ in the absorbent is released from the absorbent in the form of NO ₂ . In this case, if there are reducing components such as CO and components such as HC and CO ₂ in the exhaust gas, NO ₂ is reduced on the platinum Pt by these components.

In the present embodiment, in the normal operation, as described above, the engine 1 is operated at the lean air-fuel ratio in most of the load region except for the high load operation, and the NO _X storage reduction catalyst absorbs NO _X in the inflowing exhaust gas. I do. When the engine 1 is operated at the rich air-fuel ratio, the NO _X storage reduction catalyst 7 releases the absorbed NO _X and purifies it. Therefore, when the amount of NO _X absorbed in the NO _X occluding and reducing catalyst 7 in a conventional lean air-fuel ratio during operation increases, performs the rich spike operation for switching a short time the engine air-fuel ratio from a lean air-fuel ratio to a rich air-fuel ratio, NO _X Release of NO _X from the storage reduction catalyst and reduction purification (regeneration of the NO _X storage reduction catalyst) are performed.

However, it has been found that when the rich spike operation of the engine 1 is performed, unpurified NO _X is released from the NO _X storage reduction catalyst immediately after switching from the lean air-fuel ratio to the rich air-fuel ratio. This is considered to be because the HC and CO components in the exhaust gas may be insufficient when the engine is switched from the lean air-fuel ratio operation to the rich air-fuel ratio operation. That is, when switching from lean to rich, the exhaust air-fuel ratio changes continuously. At this time, the exhaust air-fuel ratio passes through a region where the rich air-fuel ratio is low but the degree of richness is low and the HC and CO components in the exhaust gas are relatively small. It is considered that the HC and CO components in the exhaust gas are insufficient in this region, and the total amount of NO _X released from the NO _X storage reduction catalyst cannot be reduced.

Therefore, in the present embodiment, when NO _X is to be released from the NO _X storage reduction catalyst, secondary air injection is performed during the expansion or exhaust stroke after the main fuel injection to sharply increase the exhaust air-fuel ratio to a considerable rich air-fuel ratio. This prevents the emission of unpurified NO _X from the NO _X storage reduction catalyst. The fuel injected into the cylinder by the main fuel injection during the expansion or exhaust stroke after combustion does not burn and comes into contact with the high-temperature burned gas to vaporize and generate low-molecular-weight HC. Further, since the fuel supplied by the secondary fuel injection does not contribute to the combustion in the cylinder, even if a relatively large amount of fuel is supplied by the secondary fuel injection, the engine output torque does not increase.

For this reason, by performing secondary fuel injection when NO _X is to be released from the NO _X storage reduction catalyst, it is possible to rapidly change the exhaust air-fuel ratio to a low value without causing a change in engine output torque. Thus, NO _X in the storage reduction catalyst without passing through the air-fuel ratio of the intermediate, unpurified in the NO _X release at the initial from possible and becomes _the NO _X storage reduction catalyst by supplying a high degree of rich exhaust NO _X Is prevented from being released. It should be noted that NO _X can be released from the NO _X storage reduction catalyst only by secondary fuel injection, or when the main fuel injection amount is increased to perform a normal rich spike, the secondary A fuel injection may be performed to rapidly switch the exhaust air-fuel ratio to the rich air-fuel ratio.

However, when a part of the fuel injected by the secondary fuel injection remains in the cylinder during the secondary fuel injection, the engine output torque may fluctuate. As described above, the ECU 30 calculates the required fuel amount based on the engine load state (accelerator opening, rotation speed) and supplies the fuel to the cylinder by main fuel injection. For this reason, when residual fuel is generated by the secondary fuel injection, in the next cycle, in addition to the fuel supplied by the main fuel injection, the above-described residual fuel burns in the cylinder. There is a problem that the engine output torque increases and torque fluctuation occurs.
This problem can be solved by the following two methods.

(A) The entire amount of fuel injected by the secondary fuel injection is discharged out of the cylinder during the exhaust stroke (while the exhaust valve is open) so that no residual fuel is generated.
(B) When residual fuel is generated, the fuel injection amount during the next main fuel injection is reduced and corrected by the residual fuel so that the fuel amount contributing to combustion matches the target injection amount of main fuel injection. .

Hereinafter, an embodiment in which each method is adopted will be described.
(1) First Embodiment This embodiment is a reference embodiment that is not directly related to the invention described in the claims.
In the present embodiment, fluctuations in engine output torque due to secondary fuel injection are prevented by discharging the entire amount of fuel injected by secondary fuel injection to the outside of the cylinder during the exhaust stroke.

FIG. 2 is a diagram showing a vertical section of a cylinder of the engine 1. FIG. 2 shows a cross section of the # 1 cylinder. The configuration of the # 2 to # 4 cylinders is the same as that of FIG.
2, reference numeral 10 denotes a cylinder combustion chamber, 11 denotes a piston, 13 denotes an intake port, 13a denotes an intake valve, 15 denotes an exhaust port, and 15a denotes an exhaust valve. Reference numeral 111 denotes an in-cylinder fuel injection valve, and reference numeral 17 denotes a spark plug provided at the center of the cylinder head cylinder. In the present embodiment, a concave piston cavity 11 a is provided on the top surface of the piston 11. The cavity 11a plays a role of concentrating the fuel injected from the fuel injection valve 111 in the vicinity of the ignition plug 17 in the latter half of the compression stroke in the lean air-fuel ratio operation to generate a combustible air-fuel ratio mixture layer in the vicinity of the plug 17. .

  That is, in the above-described main fuel injection of 1) lean air-fuel ratio stratified combustion (compression stroke single injection) and 2) lean air-fuel ratio homogeneous mixture / stratified combustion (intake stroke / compression stroke twice injection), the compression stroke When the piston comes to a position where it is sufficiently raised in the latter half, fuel having a relatively strong penetration force (high injection pressure) is injected from the in-cylinder fuel injection 111 toward the piston cavity 11a.

  At this time, the injected fuel reaches the surface of the piston cavity 11a and flows along the curved surface of the cavity 11a. The side surface 11b of the cavity 11a on the side remote from the fuel injection valve 111 has a relatively large curvature (small radius of curvature) so that the fuel flowing along the surface of the cavity 11a is deflected toward the vicinity of the spark plug 17. It has become. As a result, the fuel injected from the fuel injection valve 111 becomes stratified near the ignition plug 17.

  In the present embodiment, the entire amount of the fuel injected by the secondary fuel injection is discharged from the exhaust port 15 using the piston cavity 11a. That is, in the present embodiment, the fuel injection timing is set at a time later than the fuel injection timing at which the main fuel injection is performed by 360 degrees in crank angle in the latter half of the exhaust stroke. Thus, during execution of the secondary fuel injection, the piston 11 is at the same position as when the main fuel injection (hereinafter, referred to as “compression stroke fuel injection”) for stratifying the air-fuel mixture is performed. Therefore, the fuel injected by the secondary fuel injection is deflected by the curved surface 11b similarly to the main fuel injection, and flows toward the vicinity of the ignition plug 17 (that is, the exhaust port 13).

  However, since the exhaust valve 15a is open in the latter half of the exhaust stroke, the secondary injection fuel deflected by the above does not stratify around the spark plug 17 as shown by F in FIG. The gas is discharged from the port 13 to the outside of the cylinder. Therefore, the generation of residual fuel in the cylinder due to the secondary fuel injection is prevented. In this case, the injected fuel comes into contact with the surface of the piston cavity 11a. However, since the temperature of the piston is high during operation, the fuel that has come into contact with the surface of the cavity 11a is immediately vaporized and adheres to the surface of the cavity 11a. I will not.

  Incidentally, in order to discharge the entire amount of fuel injected by the secondary fuel injection to the outside of the cylinder as described above, all of the fuel must be exhausted to the exhaust port 15 until the intake valve 13a starts opening during the exhaust stroke. Need to be exhausted from If fuel remains in the cylinder during a period in which the exhaust valve 15a and the intake valve 13a are simultaneously opened (valve overlap period), a part of the fuel flows back to the intake port and the cylinder is re-started in the next intake stroke. This is because there is a possibility that a portion of the secondary injected fuel will remain in the cylinder. Further, the engine 1 of the present embodiment includes the variable valve timing device 200, and the valve timing is changed according to the engine load state. Thus, in the present embodiment, the fuel injected by the secondary fuel injection is read by reading the valve opening timing of the intake valve at the time of executing the secondary fuel injection and changing the secondary fuel injection amount according to the valve opening timing of the intake valve. This prevents the air from flowing back to the intake port and remaining in the cylinder.

FIG. 3 is a flowchart illustrating a fuel injection control operation according to the present embodiment. This operation is performed by a routine executed by the ECU 30 at every constant rotation angle of the crankshaft.
When the operation starts in FIG. 3, it is determined in step 301 whether or not the secondary fuel injection is requested. In the present embodiment, the amount of NO _X absorbed in the NO _X storage reduction catalyst 7 is estimated based on the engine operating state by a separately executed routine (not shown), and when the absorbed NO _X amount reaches a predetermined value. Secondary fuel injection (rich spike) is required.

Instead of estimating the NO _X absorption, when predetermined time has elapsed since the last of the NO _X emission operation execution, or when the engine speed integrated value from the previous NO _X emission operation execution has reached a predetermined value The secondary fuel injection may be requested on the assumption that the absorbed NO _X amount of the NO _X storage reduction catalyst has reached a predetermined value.

  If the secondary fuel injection is not requested in step 301, the operation immediately ends without executing steps 303 to 321 and the secondary fuel injection is not performed. On the other hand, if the secondary fuel injection is requested in step 301, step 303 is executed next to calculate the target value qinjex of the secondary fuel injection amount. In step 303, a secondary fuel injection amount qinjex required to obtain a desired air-fuel ratio is calculated from the air amount Q drawn into the cylinder per one revolution of the engine and the main fuel injection amount.

  In the present embodiment, the relationship between the engine speed N, the load (accelerator opening) ACCP, and the cylinder intake air amount Q per one engine revolution is obtained in advance by an experiment, and the ECU 30 is controlled in the form of a numerical map using N and ACCP. It is stored in ROM. The main fuel injection amount is also stored in the ROM of the ECU 30 as a numerical map of N and ACCP. Therefore, in step 303, the intake air amount Q and the main fuel injection amount are calculated from these numerical maps using the current load conditions (N, ACCP), and are required to set the exhaust air-fuel ratio to the target value. The secondary fuel injection amount qinjex is calculated.

After calculating the secondary fuel injection amount qinjex, in step 305, the calculated secondary fuel injection amount qinjex (ml) is calculated by using the fuel pressure in the common rail 110 and the characteristic value of the in-cylinder fuel injection valve. Valve opening time) Converted to tauex (ms).
Then, in step 307, the intake valve opening timing (crank angle) IO currently set by the variable valve timing device 200 is read, and in step 309, the currently allowable maximum secondary fuel injection time (guard value) tauexmax is calculated. .

In the present embodiment, as described above, the entire amount of fuel injected by the secondary fuel injection from the fuel injection valve needs to be discharged out of the cylinder before the intake valve opens. In the present embodiment, the timing of the secondary fuel injection is fixed (360 degrees behind the compression stroke injection timing). Therefore, it is necessary to limit the maximum value of the fuel injection amount in order to discharge the entire amount of the injected fuel out of the cylinder before opening the intake valve. In step 309, the difference between the intake valve opening crank angle IO read in step 307 and the secondary fuel injection start crank angle ainjc + 360 (ainjc is the compression stroke main fuel injection timing) and the current engine speed N are used. The time t ₁ (ms) from the start of fuel injection to the opening of the intake valve is calculated.

Further, the time t ₂ required for the flight from the fuel injection valve to the exhaust port becomes necessary for the fuel injected by the secondary fuel injection final stage is discharged from the exhaust port. Here, t ₂ is determined by the internal pressure of the common rail 110. Therefore, in the present embodiment, if the fuel injection from the fuel injection valve does not end within the time after the start (t ₁ -t ₂ ), there is a possibility that residual fuel is generated in the cylinder. Therefore, in step 309, the above t ₁ and t ₂ are calculated using the intake valve opening crank angle IO, the engine speed N, and the fuel pressure in the common rail, and the maximum fuel injection time tauexmax is calculated as tauexmax = t ₁ −t Calculated as ₂ .

Next, in steps 311 to 317, the target secondary fuel injection time tauex set in step 305 is limited by the maximum value tauexmax and the minimum value taumin, and the value of tauex is set in the range of taumin ≦ tauex ≦ tauexmax. The minimum value tauemin is a controllable minimum valve opening time of the fuel injection valve 111 and is a characteristic value of the fuel injection valve 111.
Then, in step 319, the secondary fuel injection start timing ainjex is set to ainjex = ainjc + 360, and in step 321, ainjex and tauex are set in a fuel injection circuit (not shown). As a result, the secondary fuel injection is started at the crank angle ainjex and the time injection of tauex is performed.

  As described above, in the present embodiment, the fuel injected by the secondary fuel injection is made to flow to the exhaust port 13 using the piston cavity 11a, and the fuel injection amount is controlled according to the engine load state and the valve timing. This makes it possible to discharge the entire amount of fuel injected by the secondary fuel injection to the outside of the cylinder during the exhaust stroke.

In the example of FIG. 2, the flow of the fuel injected by the secondary fuel injection by the cavity 11a formed on the top surface of the piston is deflected toward the exhaust port, but the flow of the fuel is changed by using other means. The flow may be deflected toward the exhaust port.
For example, the fuel injection valve is configured as an air assist valve that injects pressurized air together with fuel, and the injected fuel is discharged by the assist air by injecting the pressurized air toward the exhaust port only during secondary fuel injection. It is also possible to make it drift to the port side.

Further, when the fuel injection valve has a structure in which the injection direction can be switched between the main fuel injection and the secondary fuel injection with one fuel injection valve, the fuel injection direction is set to the exhaust port or the exhaust port at the time of the secondary fuel injection. The switching may be performed in accordance with the heading drift.
Further, in the example of FIG. 2, the main fuel injection and the secondary fuel injection are performed by the same fuel injection valve. However, an auxiliary fuel injection valve dedicated to the secondary fuel injection is provided separately from the fuel injection valve for the main fuel injection. Alternatively, the injection direction of the auxiliary fuel injection valve may be set toward the exhaust port.

Further, instead of the piston cavity, a drift plate is provided which protrudes into the cylinder only at the time of the secondary fuel injection. You may make it flow.
(2) Second Embodiment Next, a second embodiment will be described. This embodiment is a reference embodiment that is not directly related to the invention described in the claims.
As in the first embodiment described above, also in this embodiment, the variation in the engine output torque due to the secondary fuel injection is reduced by discharging the entire amount of the fuel injected by the secondary fuel injection to the outside of the cylinder during the exhaust stroke. It is preventing.

FIG. 4 is a view similar to FIG. 2 showing a cross section of a cylinder of the engine 1. 4, the same reference numerals as those in FIG. 2 indicate the same elements as those in FIG.
In the present embodiment, the secondary fuel injection is performed at an early stage of the exhaust stroke when the piston is near the bottom dead center, and the injection pressure (common rail pressure) of the secondary fuel injection is lower than the pressure at the time of the main fuel injection. Set. As described above, in the early stage of the exhaust stroke, the pressure of the burned gas in the cylinder is high, and a relatively strong exhaust flow toward the exhaust port is generated in the cylinder as shown by an arrow in FIG. When the secondary fuel injection is performed at a relatively low injection pressure at this time, the injected fuel passes through the exhaust flow in the cylinder and does not reach the cylinder wall or the piston as shown by F in FIG. Near the center, it gets on the exhaust stream and is transported to the exhaust port. Therefore, the entire amount of the fuel injected by the secondary fuel injection is discharged out of the cylinder during the exhaust stroke without the injected fuel adhering to the cylinder wall, the piston, the cylinder head, etc., and the residual fuel is generated in the cylinder. Absent.

  In the above-described embodiment, in order to discharge the entire amount of the fuel injected by the secondary fuel injection before the intake valve opens to the outside of the cylinder, the secondary fuel is set according to the engine operation state (load state) and the valve timing. Although the injection amount is controlled, the timing of the secondary fuel injection is important in the present embodiment. That is, if the fuel injection timing is delayed, a part of the injected fuel may flow back to the intake port, and if the fuel injection timing is too early, the injected fuel diffuses into the cylinder, and the entire amount rides on the exhaust flow. This is because there is a possibility that the gas will not be discharged out of the cylinder. Hereinafter, control of the fuel injection timing in the present embodiment will be described.

FIG. 5 is a flowchart illustrating a fuel injection control operation according to the present embodiment. This operation is performed by a routine executed by the ECU 30 at every constant rotation angle of the crankshaft.
When the operation starts in FIG. 5, it is determined in step 501 whether or not secondary fuel injection is necessary. In step 503, a target value qinjex of the secondary fuel injection amount is calculated. In step 505, the injection time tauex is calculated from the target injection amount qinjex. Is calculated. The calculation of the target injection amount qinjex in step 503 and the injection time tauex in step 505 are performed in the same manner as in steps 303 and 305 in FIG. 3, respectively. Since the pressure is controlled so as to decrease the pressure at 110, the injection time tauex is longer than in FIG. 3 even when the target injection amount qinjex is the same as in FIG.

After calculating qinjex and tauex as described above, in this embodiment, the current intake valve opening timing (crank angle) IO and exhaust valve opening timing (crank angle) EO are read in step 507, and in step 509 the fuel injection valve 111 is read. The flight time t ₂ until the fuel injected from the exhaust port is discharged from the exhaust port is calculated as t ₂ = α + β. Here, α is a time required for the fuel injected from the fuel injection valve 1112 to reach the center of the cylinder, and is a time proportional to the common rail 110 pressure (fuel injection pressure). Β is the time required for the fuel that has reached the central portion to get on the exhaust flow and be discharged from the exhaust port, and is a time proportional to the engine speed N.

After calculating the flight time t ₂ in step 509, the maximum value of the secondary fuel injection time in step 511 (guard value) Tauexmax is calculated as tauexmax = t ₃ -t _2.
Here, t ₂ is the time from the opening of the exhaust valve to the opening of the intake valve, using the valve opening timings IO and EO of the intake and exhaust valves read in step 507 and the engine speed N. Is calculated. That is, tauexmax is the injection time corresponding to the maximum fuel injection amount that allows the entire amount of the injected fuel to be discharged out of the cylinder without the backflow of the injected fuel to the intake port when the secondary fuel injection is performed simultaneously with the opening of the exhaust valve. It is.

After calculating tauexmax in step 511, in steps 513 to 517, the target injection time tauex calculated in step 505 is limited by the maximum value tauexmax and the minimum value taumin. In step 521, the intake valve opening timing IO and the engine speed N are set. Then, the secondary fuel injection start timing ainjex is calculated based on and the restricted tauex. That is, the secondary fuel injection start timing is earlier than the intake valve opening timing by (tauex + t ₂ ), that is, the fuel injected at the end of the secondary fuel injection is discharged from the exhaust port immediately before the intake valve opens. It starts at the timing. That is, in the present embodiment, the secondary fuel injection timing is advanced as the secondary fuel injection amount increases. As a result, the entire amount of the fuel injected by the secondary fuel injection reaches the exhaust port before the intake valve opens, and the fuel injected by the secondary fuel injection timing being too early becomes a cylinder. It is prevented from diffusing into.

  In the above-described second embodiment, the fuel injection direction of the in-cylinder fuel injection valve 111 is the same as that of the embodiment of FIG. 2, but, for example, as shown in FIG. If the in-cylinder fuel injection valve is provided to inject fuel toward the center of the cylinder at a low fuel injection pressure during secondary fuel injection, the residual fuel prevention effect is further enhanced.

(3) Third Embodiment Next, a third embodiment will be described.
This embodiment is an embodiment corresponding to the invention described in the claims.
In the present embodiment, the remaining fuel amount is calculated from the engine operating state on the assumption that a part of the fuel injected by the secondary fuel injection remains in the cylinder when performing the secondary fuel injection, and the next main fuel The fuel injection amount at the time of injection is corrected to be reduced by the amount of the residual fuel. As a result, the amount of fuel supplied to the cylinder (contributing to combustion) at the time of main fuel injection accurately matches the target injection amount of main fuel injection. This prevents the engine output torque from fluctuating even when residual fuel is generated during the execution of the secondary fuel injection.

First, a method of calculating the residual fuel amount in the secondary fuel injection according to the present embodiment will be described.
FIG. 7 is a graph showing the relationship between the engine output torque (vertical axis) and the main fuel injection amount (horizontal axis) when the engine is operated at a predetermined constant rotation speed. In FIG. 7, curve I shows the relationship between the output torque and the main fuel injection amount when only the main fuel injection is not performed and the secondary fuel injection is performed, and curve II shows the execution of the secondary fuel injection in addition to the main fuel injection. 4 shows the relationship between the output torque and the main fuel injection amount in the case of the above. As described above, the secondary fuel injection amount is set to an amount necessary for setting the exhaust air-fuel ratio to the target air-fuel ratio in each case, and is determined from the engine load (main fuel injection) and the rotation speed. Is done. In this case, the secondary fuel injection timing may be set by any of the above-described methods, or may be fixed at a constant appropriate crank angle.

As described above, the engine output torque is the same regardless of the presence or absence of secondary fuel injection unless residual fuel is originally generated by secondary fuel injection. However, when residual fuel is generated by the secondary fuel injection, the engine output torque at the time of performing the secondary fuel injection increases by an amount corresponding to the amount of the residual fuel (curve II in FIG. 7).
That is, it is assumed that the output torque is increased by the amount indicated by a in FIG. 7 during the secondary fuel injection at a certain main fuel injection amount. It is assumed that the amount of increase in the output torque at this time is equal to the case where the main fuel injection amount is increased by the amount indicated by b in FIG. In this case, since the output torque increase amount a is generated by the combustion of the residual fuel in the cylinder by the secondary fuel injection, the residual fuel amount is the main fuel injection amount necessary to increase the output torque by the same amount, that is, FIG. It should be equal to the fuel quantity shown in 7b. Therefore, in the present embodiment, when the amount of increase in the output torque due to the secondary fuel injection is the amount indicated by a in FIG. 7, it is assumed that the amount indicated by b in FIG. 7 is equal to the residual fuel amount in the cylinder. Estimate the amount of residual fuel.

  That is, in the present embodiment, a curve corresponding to FIG. 7 is created in advance for each combination of the engine speed and the fuel injection modes 1) to 5) to be described later, and the residual fuel in each main fuel injection amount is calculated. The fuel amount (FIG. 7, b) is calculated. The value of the residual fuel amount b is created for each fuel injection mode as a numerical map using the engine speed N and the main fuel injection amount (qinj = qinjei + qinjec) as parameters, and stored in the ROM of the ECU 30. During the operation of the engine, the ECU 30 calculates the residual fuel amount in the cylinder at the time of performing the secondary fuel injection based on the engine speed N and the main fuel injection amount qinj. Here, qinjei is the injection amount in the first main fuel injection during the intake stroke, qinjec is the injection amount in the second main fuel injection in the compression stroke, and qinj is the total amount of both.

Also in the present embodiment, the following five fuel injection modes of the engine 1 are provided.
1) Lean air-fuel ratio stratified combustion (one compression stroke injection)
2) Lean air-fuel ratio homogeneous mixture / stratified combustion (intake stroke / compression stroke twice injection)
3) Lean air-fuel ratio homogeneous mixture combustion (single injection stroke)
4) Combustion of stoichiometric air-fuel ratio homogeneous mixture (injection of intake stroke once)
5) Combustion of rich air-fuel ratio homogeneous mixture (injection of the intake stroke once)
In the present embodiment, in the case of mode 3) (two intake strokes / compression stroke injections), the correction is performed by reducing the fuel injection amount in the intake stroke injection by the residual fuel. The residual fuel diffuses into the cylinder and becomes a part of the homogeneous mixture, and the air-fuel ratio of the homogeneous mixture formed in the cylinder is directly affected. In the present embodiment, in order to prevent this, the air-fuel ratio of the actually generated homogeneous mixture is maintained at the target value by reducing the amount of intake stroke fuel injection for producing the homogeneous mixture by the amount of the residual fuel. That's how it works.

FIG. 8 is a flowchart illustrating the main fuel injection control operation of the present embodiment. This operation is executed at every constant rotation angle of the engine crankshaft.
In FIG. 8, when the operation starts, in step 801 the engine load (accelerator opening) ACCP and the rotation speed N are read. Then, in steps 803, 811, and 823, it is determined which of the fuel injection modes 1) to 4) is to be adopted based on the accelerator opening ACCP and the rotation speed N.

  That is, in step 803, the fuel injection mode 3) lean air-fuel ratio homogeneous mixture combustion (single-injection stroke injection) or 4) stoichiometric air-fuel ratio homogeneous mixture combustion (single intake stroke injection) or lean air-fuel ratio homogeneous mixture combustion ( It is determined from the ACCP and N whether or not to adopt the intake stroke (single injection), and if the mode 3) or 4) or 5) is to be adopted, the ECU 30 determines in advance in step 805 based on the ACCP and N. , The intake stroke fuel injection amount qinjei is calculated from the numerical map stored in the ROM, and in step 807, the compression stroke fuel injection amount qinjec is set to zero.

  Next, in step 809, the total qinj of qinjei and qinjec is calculated, and the residual fuel amount b in the cylinder when secondary fuel injection is performed is determined based on the rotation speed N and the main fuel injection amount qinj. ) Or 4) is calculated from the relationship in FIG. Then, in step 817, it is determined whether or not there is a request for the secondary fuel injection. If there is, the process proceeds to step 819, in which the intake stroke fuel injection amount qinjei is reduced and corrected by the residual fuel amount b. Then, the corrected intake stroke fuel injection amount qinjei and compression stroke fuel injection amount qinjec (in this case, qinjec = 0) are set in the fuel injection circuit, and the operation is terminated. As a result, when the secondary fuel injection is performed, the main fuel injection amount is corrected to be reduced by the residual fuel amount b. Therefore, even when the secondary fuel injection is performed, the fluctuation of the engine output torque is prevented.

  On the other hand, if none of the fuel injection modes 3), 4), and 5) are adopted in step 803, the process proceeds to step 811 and the fuel injection mode 2) (lean air-fuel ratio homogeneous mixture / stratified combustion (intake air) It is determined whether or not to adopt the stroke / compression stroke injection)). If the mode 2) is adopted, a numerical map stored in advance in the ROM of the ECU 30 based on ACCP and N in step 813 based on ACCP and N. An intake stroke fuel injection amount qinjei and a compression stroke fuel injection amount qinjec are calculated. Then, in step 815, the residual fuel amount b at the time of performing the secondary fuel injection is calculated from the relationship shown in FIG. That is, in this case as well, only the intake stroke fuel injection amount qinjei is corrected to be reduced by the residual fuel amount b, and the compression stroke fuel injection amount qinjec is not corrected.

  On the other hand, if none of the fuel injection modes 2) to 5) is adopted in steps 803 and 801, the fuel injection mode 1) (lean air-fuel ratio stratified combustion (compression stroke single injection)) is adopted, In step 823, the compression stroke fuel injection amount qinjec is calculated based on ACC and N, and the intake stroke fuel injection amount qinjei is set to zero. Also in this case, in step 827, the residual fuel amount b at the time of performing the secondary fuel injection is calculated from the relationship of FIG. 7 in mode 1), and in step 829, it is determined whether or not there is a secondary fuel injection request. Then, in this case, when there is a secondary fuel injection request, the compression stroke fuel injection amount qinjec is reduced by the residual fuel b in step 831 and step 821 is executed.

  In the present embodiment, as described above, the main fuel injection amount is corrected according to the residual fuel amount due to the secondary fuel injection, thereby preventing the secondary fuel injection from causing the engine output torque fluctuation. In addition, in mode 3) (when both the intake stroke and the compression stroke of fuel injection are performed) at the time of the above correction, only the intake stroke fuel injection amount is corrected, so that the homogeneous air-fuel ratio mixture is improved. The air-fuel ratio becomes equal to the target value.

  In the present embodiment, the correction is performed for each cycle using the relationship between the main fuel injection amount and the residual fuel amount in the cylinder, which is obtained in advance by an experiment, but the engine output torque actually generated by the residual fuel in the cylinder is A change (a change indicated by a in FIG. 7) is detected from a change in the engine speed, a change in the combustion pressure in the cylinder, and the like, and a correction amount b of the main fuel injection amount is calculated from the relationship in FIG. You may do it. In this case, the correction of the main fuel injection amount is performed in the cycle following the cycle in which the torque change is detected.

Further, in each of the embodiments described above, the engine in which the fuel injection mode is switched according to the engine operating state is described. However, the fuel injection mode is fixed to the intake stroke fuel injection, the compression stroke fuel injection, or both (two injections). It is needless to say that the present invention can be applied to an institution that has been established.
Further, in each of the above embodiments, the case where the NO _X storage reduction catalyst is disposed in the exhaust passage has been described as an example. However, the present invention is not limited to this embodiment, and all cases where the secondary fuel injection is performed are described. It is needless to say that the present invention is applicable. For example, in a case where a selective reduction catalyst that reduces NO _X by selectively reacting HC (or HC adsorbed on the catalyst) and NO _X in the exhaust gas under a lean air-fuel ratio in the exhaust passage is provided. Although it becomes necessary to supply HC to the selective reduction catalyst, the present invention is also applicable to a case where HC is supplied to the selective reduction catalyst by secondary fuel injection.

FIG. 1 is a diagram illustrating a schematic configuration of an embodiment in which the present invention is applied to an automobile gasoline engine. FIG. 2 is a vertical sectional view of a cylinder illustrating a reference embodiment of the present invention. 3 is a flowchart illustrating a secondary fuel injection control operation according to the reference embodiment of FIG. 2. FIG. 7 is a vertical sectional view of a cylinder illustrating another reference embodiment of the present invention. 5 is a flowchart illustrating a secondary fuel injection control operation according to the reference embodiment of FIG. 4. FIG. 9 is a view similar to FIG. 4, illustrating a modification of the reference embodiment of FIG. 4. It is a figure explaining the calculation method of the amount of residual fuel of the embodiment of the present invention. 8 is a flowchart illustrating a main fuel injection control operation of the embodiment of FIG. 7.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Engine body 11 ... Piston 11a ... Piston cavity 15 ... Exhaust port 15a ... Exhaust valves 111-114 ... In-cylinder fuel injection valve 200 ... Variable valve timing device 30 ... Engine control unit (ECU)
7 ... NO _X occluding and reducing catalyst F ... injected fuel

Claims (2)

An in-cylinder fuel injection valve that injects fuel directly into a cylinder of an internal combustion engine,
The in-cylinder fuel injection valve is controlled to perform main fuel injection for injecting fuel contributing to combustion in the cylinder and, if necessary, to perform combustion in the cylinder during an expansion stroke or an exhaust stroke after the main fuel injection. Fuel injection control means for performing secondary fuel injection that injects fuel that does not contribute to the
The fuel injection control means calculates the amount of fuel remaining in the cylinder among the fuel injected by the immediately preceding secondary fuel injection, and corrects the injection amount of the main fuel injection according to the remaining fuel amount. A fuel injection device for an internal combustion engine. An in-cylinder fuel injection valve that injects fuel directly into a cylinder of an internal combustion engine,
The in-cylinder fuel injection valve is controlled to perform main fuel injection for injecting fuel contributing to combustion in the cylinder and, if necessary, to perform combustion in the cylinder during an expansion stroke or an exhaust stroke after the main fuel injection. Fuel injection control means for performing secondary fuel injection that injects fuel that does not contribute to the
The fuel injection control means converts the main fuel injection as necessary into a first main fuel injection for generating a homogeneous mixture in a cylinder and a second main fuel injection for generating a layer of a combustible mixture. When the secondary fuel injection is executed, the fuel amount remaining in the cylinder among the fuel injected by the immediately preceding secondary fuel injection is calculated, and the second fuel injection is performed in accordance with the residual fuel amount. (1) A fuel injection device for an internal combustion engine that corrects an injection amount of main fuel injection.

Images