Internal combustion engine control device

Abstract

An internal combustion engine control device that controls a fuel injection amount on the basis of a flow amount of air flowing in a plurality of cylinders of a multi-cylinder internal combustion engine having an exhaust pipe in which exhaust gas from each cylinder gets together is provided with a control unit that performs mass balance calculation for each of fuel and air at an entrance and an exit of each cylinder, estimates a fuel mass proportion for each cylinder while estimating an air-fuel ratio of the exhaust pipe from a result of each mass balance calculation, and calculates an air-fuel ratio of each cylinder from the air-fuel ratio of the exhaust pipe and the fuel mass proportion for each cylinder.

Description

Technical Field

[0001] The present invention relates to an internal combustion engine control device that controls an internal combustion engine based on an air-fuel ratio.

Background Art

[0002] In recent years, in order to cope with the strengthening of exhaust regulations for automobiles, it has become necessary to reduce the PN (Particulate Number) emissions, and measures have been taken for this purpose. In a DI (Direct Injection) engine, high fuel pressure and multi-stage injection are used in fuel injection. However, due to the frequent use of high fuel pressure multi-stage injection, variations occur in the injection amount for each cylinder of a multi-cylinder engine. As a result, even if the air-fuel ratio as a total (for the entire engine) is stoichiometric, there is a concern that the air-fuel ratio in some cylinders may become rich and the PN may deteriorate.

[0003]

[0004] Normally, an air-fuel ratio sensor attached to an exhaust pipe is used to measure the air-fuel ratio. However, the exhaust gases discharged from each cylinder are mixed in the exhaust pipe, and it takes time for the exhaust gases to reach the air-fuel ratio sensor, resulting in a delay. For this reason, the air-fuel ratio sensor cannot directly detect variations in the air-fuel ratio between cylinders.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] ​However, when the air quantity and fuel quantity change, the lag behavior of the air-fuel ratio itself changes. Therefore, it is difficult to accurately simulate the lag behavior of the air-fuel ratio by the method using the transfer function described in Patent Document 1. Further, in the method using the above transfer function, a large amount of fitting man-hours is required to obtain model constants.

[0007] From the above situation, in a multi-cylinder engine adopting multi-stage injection, in order to suppress the variation in injection quantity between cylinders, a method for accurately calculating the air-fuel ratio for each cylinder has been demanded.

Means for Solving the Problems

[0008] In order to solve the above problems, an internal combustion engine control device according to an aspect of the present invention is an internal combustion engine control device that controls a fuel injection amount based on an air flow rate flowing into a plurality of cylinders of a multi-cylinder internal combustion engine having an exhaust pipe where exhaust gas from each cylinder converges, and performs a mass balance calculation of fuel and air at the inlet and outlet for each cylinder, estimates the air-fuel ratio of the exhaust pipe from the results of each mass balance calculation, estimates the fuel mass ratio for each cylinder, and includes a control unit that obtains the air-fuel ratio of each cylinder from the air-fuel ratio of the exhaust pipe and the fuel mass ratio for each cylinder.

Effects of the Invention

[0009] According to at least one aspect of the present invention, in a multi-cylinder engine adopting multi-stage injection, the air-fuel ratio can be accurately calculated for each cylinder, so that the variation in injection quantity between cylinders can be suppressed. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] Hereinafter, examples of embodiments for carrying out the present invention (hereinafter referred to as "embodiments") will be described with reference to the accompanying drawings. In this specification and the accompanying drawings, the same components or components having substantially the same functions are denoted by the same reference numerals, and redundant descriptions are omitted.

[0012] [Configuration of Fuel Injection System] A fuel injection system including a fuel injection control device according to an embodiment of the present invention and a fuel injection device to be controlled will be described with reference to FIGS. 1 to 16.

[0013] First, the fuel injection system in this embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic diagram showing an example of the fuel injection system in this embodiment. The fuel injection system 1 shown in FIG. 1 is a system for performing fuel injection in an in-cylinder direct injection engine (an example of an internal combustion engine) that directly injects fuel into the cylinder, but the fuel injection system is not limited to this example. In this specification, the in-cylinder direct injection engine is simply referred to as "engine".

[0014] The in-cylinder direct injection engine in this embodiment includes four cylinders 108 (engine cylinders). The fuel injection system 1 includes four fuel injection devices 101A to 101D corresponding to the four cylinders 108, and an ECU (Engine Control Unit) 104 as an example of a fuel injection control device. The ECU 104 includes a CPU (Central Processing Unit) 120 and a memory 121 (an example of a storage medium). The memory 121 can be configured using a main storage device such as a RAM (Random Access Memory) or an auxiliary storage device such as a flash memory. In the following description, when it is not necessary to distinguish between the fuel injection devices 101A to 101D, they are referred to as the fuel injection device 101.

[0015] In each cylinder 108 of the fuel injection system 1, fuel injection devices 101A to 101D for side injection are installed such that atomized fuel is directly injected into the combustion chamber 107 from their fuel injection holes 219 (see FIG. 2 described later). The fuel stored in a fuel tank (not shown) is pressurized by a fuel pump 106 and sent to a rail-shaped fuel pipe 105 via a high-pressure pipe 115, and is then delivered from the fuel pipe 105 to each of the fuel injection devices 101A to 101D. A pressure sensor 102 for measuring the pressure of the fuel in the fuel pipe 105 is installed at one end of the fuel pipe 105.

[0016] The fuel pressure in the fuel pipe 105 varies depending on the balance between the flow rate of the fuel discharged by the fuel pump 106 and the injection amount of the fuel injected into each combustion chamber 107 by each fuel injection device 101. In this embodiment, the ECU 104 controls the fuel discharge amount of the fuel pump 106 based on the sensor information (information indicating the fuel pressure value) output from the pressure sensor 102 so that the fuel pressure in the fuel pipe 105 becomes a predetermined target pressure value.

[0017] The injection of fuel by the fuel injection device 101 is controlled by an injection pulse sent from the CPU 120 (an example of a control unit) of the ECU 104. For example, a command by an injection pulse (pulse signal) with an adjusted pulse width is input to a drive circuit 103 provided for each fuel injection device 101. The drive circuit 103 determines the waveform of the drive current based on the command (injection pulse) from the CPU 120, and supplies the drive current of the above waveform to the fuel injection device 101 for a time based on the pulse width. The drive circuit 103 is formed, for example, as a drive IC (Integrated Circuit).

[0018] When the control unit (CPU 120 of ECU 104) of the fuel injection control device changes the injection amount during fuel injection in one combustion cycle described later, it changes the current waveform for driving the fuel injection device (fuel injection device 101) based on the pulse width of the injection pulse. In this way, by changing the current waveform based on the pulse width of the injection pulse, the injection amount of the fuel injected by the fuel injection device can be adjusted. For example, by changing the current value of the drive current supplied to the fuel injection device, the lift amount of the fuel injection valve (valve body 214 in FIG. 2) changes, and the injection amount is adjusted. Also, by changing the timing (switching between off / on) of the injection pulse sent from the CPU 120 to the drive circuit 103, the timing at which the fuel injection device injects fuel can be adjusted.

[0019] Note that the drive circuit 103 may be implemented as a component or board integrated with the ECU 104. An apparatus in which the drive circuit 103 and the ECU 104 are integrated is referred to as a control device 150.

[0020] Next, the configurations and basic operations of the fuel injection device 101 and the ECU 104 will be described with reference to FIGS. 2 and 3. FIG. 2 is a diagram showing an example of a longitudinal section of the internal structure of the fuel injection device 101. FIG. 3 is an enlarged sectional view showing an example of the drive unit structure (in the vicinity of the mover and the valve body) of the fuel injection device 101.

[0021] The CPU 120 of the ECU 104 takes in signals indicating the state of the engine from various sensors into the ECU 104, and performs calculations on the width of the injection pulse, the current value of the drive current, and the injection timing for controlling the injection amount of the fuel injected from the fuel injection device 101 according to the operating conditions of the engine. The CPU 120 outputs an injection pulse corresponding to the calculation result to the drive circuit 103.

[0022] The ECU 104 is equipped with an A / D converter (not shown), an I / O port, etc. for capturing signals from various sensors. Examples of the various sensors include a temperature sensor for measuring the temperature of the engine's cooling water (an example of the engine's ambient temperature), a sensor for measuring the engine speed (rotation speed) (e.g., a sensor for detecting the rotation angle of the engine's crankshaft (not shown)), a pressure sensor 102 for measuring the fuel pressure in the fuel pipe 105, and an exhaust temperature sensor for measuring the exhaust temperature, etc.

[0023] The injection pulse output from the ECU 104 is input to the drive circuit 103 through the signal line 110. The drive circuit 103 controls the voltage applied to the solenoid 205 (an example of a coil) of the fuel injection device 101 and supplies current to the solenoid 205. The ECU 104 can communicate with the drive circuit 103 through the communication line 111. The ECU 104 can switch the drive current generated by the drive circuit 103 or change the set value of the drive current and the set value of the time for outputting the drive current according to the pressure of the fuel supplied to the fuel injection device 101, the operating conditions, etc.

[0024] The fuel injection device 101 shown in FIG. 3 is a normally closed solenoid valve (electromagnetic fuel injection device), and includes a solenoid 205 as an example of a coil, a mover 202, a fixed core 207, and a substantially rod-shaped valve body 214 (an example of a fuel injection valve). When the solenoid 205 is not energized, the valve body 214 is biased in the valve closing direction (downward in the drawing) by the spring 210, which is the first spring, and the valve body 214 is in a state of being in close contact with the valve seat 218 (closed valve state).

[0025] In the closed valve state, a force acting in the valve opening direction is applied to the mover 202 by the return spring 212, which is the second spring. At this time, since the force acting on the valve body 214 by the spring 210 is greater than the force by the return spring 212, the upper end surface 202A of the mover 202 contacts the flange portion 302 of the valve body 214, and the mover 202 is in a stationary state.

[0026] The valve body 214 and the mover 202 are configured to be relatively displaceable and are both enclosed in the nozzle holder 201. The nozzle holder 201 has an end face 303 that serves as a spring seat for the return spring 212 inside it. The biasing force by the spring 210 is adjusted during assembly by the amount of pushing-in of the spring retainer 224 fixed to the inner diameter of the fixed core 207.

[0027] In the fuel injection device 101, a magnetic circuit is formed by the fixed core 207, the mover 202, the nozzle holder 201, and the housing 203. A gap 301 is provided between the mover 202 and the fixed core 207. A magnetic throttle 211 is formed in a portion of the nozzle holder 201 corresponding to the gap 301 (the outer peripheral side of the gap 301), where a circumferential groove is formed on the outer peripheral surface of the nozzle holder 201.

[0028] The solenoid 205 is attached to the outer peripheral side of the nozzle holder 201 in a state of being wound around the bobbin 204. A rod guide 215 is fixed to the nozzle holder 201 at a position near the tip of the valve body 214 on the valve seat 218 side. With such a configuration, the valve body 214 is guided to move in the valve axis direction (the vertical direction in the drawing) by two sliding portions: the portion where the flange portion 302 of the valve body 214 and the fixed core 207 slide, and the portion where the valve body 214 and the rod guide 215 slide.

[0029] An orifice 216 having a valve seat 218 and a fuel injection hole 219 is fixed to the tip of the nozzle holder 201. With such a configuration, when the tip of the valve body 214 contacts the valve seat 218 of the orifice 216, the internal space (fuel passage) between the nozzle holder 201 and the tip of the valve body 214 can be sealed (closed valve state).

[0030] The fuel supplied from the fuel pipe 105 to the fuel injector 101 flows through the fuel passage hole 231 to the tip side of the valve body 214 when the fuel injector 101 is in the valve-closed state. However, the tip portion of the valve body 214 on the valve seat 218 side contacts the valve seat 218 of the orifice 216 to seal the fuel injection hole 219. At this time, the fuel is not injected to the outside from the fuel injection hole 219. When the fuel injector 101 is in the valve-closed state, a differential pressure is generated between the upper and lower parts of the valve body 214 due to the fuel pressure, and the valve body 214 is pushed in the valve-closed direction by the differential pressure force obtained by multiplying the fuel pressure by the pressure-receiving area at the valve seat position and the load of the spring 210.

[0031] When the supply of current to the solenoid 205 is started while the fuel injector 101 is in the valve-closed state, a magnetic field is generated in the magnetic circuit, a magnetic flux passes between the fixed core 207 and the mover 202, and a magnetic attraction force acts on the mover 202. At the timing when the magnetic attraction force acting on the mover 202 exceeds the load due to the differential pressure force and the spring 210, the mover 202 starts to displace in the direction toward the fixed core 207. Then, after the valve body 214 starts the valve-opening operation as the mover 202 moves, the mover 202 moves so as to approach the fixed core 207, and the mover 202 collides with the fixed core 207.

[0032] After the mover 202 collides with the fixed core 207, the mover 202 bounces back under the reaction force from the fixed core 207. However, the mover 202 is attracted to the fixed core 207 by the magnetic attraction force acting on the mover 202 and eventually stops to end the valve-opening operation. At this time, since a force acts on the mover 202 in the direction of the fixed core 207 by the return spring 212, the time until the bounce-back converges can be shortened. Since the bounce-back operation is small, the time during which the gap between the mover 202 and the fixed core 207 becomes large is shortened, and stable operation can be performed even for injection pulses with a shorter pulse width.

[0033] The mover 202 and the valve body 214 that have completed the valve opening operation in this way come to rest in the valve open state. In the valve open state, a gap is formed between the valve body 214 and the valve seat 218, and fuel is injected from the fuel injection holes 219. Note that the fuel supplied through the fuel passage hole 231 passes through the central hole provided in the fixed core 207 and the lower fuel passage hole 305 provided in the mover 202, and flows in the downstream direction (toward the fuel injection holes 219).

[0034] After that, when the power supply to the solenoid 205 of the fuel injection device 101 is cut off, the magnetic flux generated in the magnetic circuit disappears, and the magnetic attraction force acting on the mover 202 also disappears. When the magnetic attraction force acting on the mover 202 disappears in this way, the mover 202 and the valve body 214 are pushed back to the valve closed position where they contact the valve seat 218 by the load of the spring 210 and the differential pressure force.

[0035] Also, when the valve body 214 changes from the valve open state to the valve closed state, after the valve body 214 contacts the valve seat 218, the mover 202 separates from the valve body 214 and moves in the valve closing direction. After moving for a certain period of time, it is returned to the initial position in the valve closed state by the action of the return spring 212. That is, the mover 202 separates from the valve body 214 at the moment when the valve body 214 becomes the valve closed state. As a result, the mass of the movable member at the moment when the valve body 214 collides with the valve seat 218 can be reduced by the mass of the mover 202, so it is possible to reduce the collision energy when the movable member (substantially the valve body 214) collides with the valve seat 218. Therefore, it is possible to suppress the bounce of the valve body 214 caused by the valve body 214 colliding with the valve seat 218.

[0036] In the fuel injection device 101 according to the present embodiment, relative displacement occurs between the valve body 214 and the mover 202 in a short period of time at the moment when the mover 202 collides with the fixed core 207 during valve opening and at the moment when the valve body 214 collides with the valve seat 218 during valve closing. Thereby, it is possible to suppress the bounce of the mover 202 with respect to the fixed core 207 and the bounce of the valve body 214 with respect to the valve seat 218.

[0037] Next, the configuration inside the cylinder 108 of the engine and around the engine in the present embodiment will be described with reference to FIG. 4. FIG. 4 is a schematic diagram showing an example of the configuration inside the cylinder 108 of the in-cylinder direct injection engine and around the engine in the present embodiment. FIG. 4 shows an example of a schematic cross-section at the center inside the cylinder 108 of the engine.

[0038] The engine includes a fuel injection device 101, a spark plug 604, an intake port 607, an exhaust port 608, a piston 609, an intake valve 605, and an exhaust valve 610. In a general in-cylinder direct injection engine having two intake valves 605 and two exhaust valves 610, the intake valve 605 and the exhaust valve 610 are not normally visible in a cross-section passing through the central axis inside the cylinder 108. However, in FIG. 4, the intake valve 605 and the exhaust valve 610 are shown for explanatory purposes.

[0039] In the engine, the fuel injection device 101 is arranged to inject fuel toward the combustion chamber 107 from a direction (angle) intersecting the stroke direction of the piston 609 on the intake port 607 side. Fuel is injected into the cylinder 108 (combustion chamber 107) from the tip of the orifice 216 of the fuel injection device 101. In an in-cylinder direct injection engine, fuel is directly injected into the cylinder 108.

[0040] On the surface (crown surface) of the piston 609 on the spark plug 604 side, a cavity 606 (recess) is formed that is lower than the upper end (right side in the figure) of the piston 609 on the spark plug 604 side. This cavity 606 has a function of temporarily holding at least a part of the air-fuel mixture composed of the air intake from the intake port 607 and the fuel injected from the fuel injection device 101.

[0041] Here, in the present embodiment, the cavity 606 refers to the deepest part (the farthest from the ignition plug 604 side) on the crown surface of the piston 609 on the ignition plug 604 side. The cavity 606 is formed in a range such that the extension line 618 drawn in the stroke direction (sliding direction) of the piston 609 from the center gap 617 between the minus electrode 612 and the plus electrode 613 of the ignition plug 604 is within the cavity 606. The center gap 617 is an area including the ignition position where a spark is generated between the minus electrode 612 and the plus electrode 613.

[0042] For example, in the direction perpendicular to the stroke direction, the cavity 606 is formed from the intake port 607 side (left side of the drawing) to a range up to the exhaust port 608 side (right side of the drawing) from the intersection point with the extension line 618 passing through the center gap 617 of the ignition plug 604. With such a configuration, the air-fuel mixture held in the cavity 606 will be located directly below (on the extension line 618) the center gap 617 of the ignition plug 604. With such a configuration, the air-fuel mixture in the cavity 606 can be pushed upward toward the ignition plug 604 side, and the air-fuel mixture can be effectively burned by ignition with the ignition plug 604.

[0043] A fixed partition wall 602 that divides the air flow between the upper flow path (first flow path) 620 and the lower flow path (second flow path) 611 of the intake port 607 is attached to the intake port 607. An upstream of the lower flow path 611, a valve 601 that opens and closes (opens / shuts off) the lower flow path 611 side is provided. This valve 601 is configured such that the CPU 120 of the ECU 104 can control the valve opening / closing. In FIG. 4, a state where the valve 601 is closed is shown.

[0044] Next, a part of the configuration related to intake and exhaust in the engine will be described with reference to FIG. 5. FIG. 5 is a configuration diagram showing a part of the intake system and the exhaust system of the engine including the cylinder 108 shown in FIG. 4.

[0045] Into the cylinder 108 (combustion chamber 107) of the engine, air is inhaled from an intake port (not shown) through an air cleaner 701, a supercharger chamber 704, an intercooler 705, a throttle valve 706, and an intake port 607. The air cleaner 701 provided at the entrance of the supercharger chamber 704 removes dust in the inhaled air and prevents dust from being inhaled into the engine. Thereby, wear and the like inside the engine are suppressed.

[0046] The supercharger chamber 704 is equipped with a supercharger 702. The supercharger 702 includes a compressor 702A arranged on the intake side for compressing air, a turbine 702B arranged on the exhaust side and rotated by the flow of exhaust gas, and a shaft 707 connecting the compressor 702A and the turbine 702B. In the supercharger 702, the turbine 702B is rotated according to the flow velocity of the exhaust gas, and further the compressor 702A is rotated via the shaft 707. As a result, the air that has passed through the air cleaner 701 is compressed by the rotation of the compressor 702A and flows toward the intercooler 705 side. Thereby, the amount of air flowing into the combustion chamber 107 of the engine can be increased, and the output of the engine can be improved.

[0047] Note that since the air that has passed through the supercharger chamber 704 is compressed by the compressor 702A, its temperature rises. The intercooler 705 cools the air compressed by the compressor 702A and whose temperature has risen.

[0048] The throttle valve 706 adjusts the amount of air flowing from the intake port 607 into the cylinder 108 (combustion chamber 107). The opening degree of the throttle valve 706 is controlled by the ECU 104 based on the opening degree of an accelerator (not shown) and the like.

[0049] An intake valve 605 is provided in the intake port 607. The lift amount of the intake valve 605 (and the exhaust valve 610) with respect to the reference position is controlled by the ECU 104. When the intake valve 605 opens at a predetermined timing, air flows into the combustion chamber 107 of the engine.

[0050] In the combustion chamber 107 of the engine, the inflowing air and the fuel injected from the fuel injection device 101 are mixed to form an air-fuel mixture, and the air-fuel mixture is combusted by ignition by the spark plug 604. The force generated by the combustion of this air-fuel mixture is transmitted to a crankshaft (not shown) via the piston 609 and the connecting rod 711.

[0051] The engine is provided with a cooling device for cooling the heat of the engine and maintaining it at an appropriate temperature. For example, in a water-cooled cooling device, the cooling water passes through a water jacket (reference numeral omitted) provided around the cylinder 108 of the engine to take away the heat generated in the engine and maintain an appropriate temperature. The temperature of the cooling water of the engine (hereinafter referred to as the engine water temperature) is adjusted by a thermostat 712 provided in the water jacket. The engine water temperature is an example of the ambient temperature. A coupler for a temperature sensor is attached to the upper part of the thermostat 712. A temperature sensor (not shown) detects a change in the resistance value of the thermostat 712 via the coupler and outputs the detection result (output signal) to the ECU 104. The cooling water is led to a radiator (not shown) via the water jacket, the thermostat 712, and the radiator hose 713 to dissipate heat.

[0052] The exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber 107 rotates the turbine 702B of the supercharger 702 when the exhaust valve 610 is opened during the expansion stroke by passing through the exhaust port 608. The exhaust gas that has rotated the turbine 702B passes through the catalyst 703 provided in the exhaust pipe 722, and HC (hydrocarbon), NOx (nitrogen oxide), and CO (carbon monoxide) are reduced and discharged to the outside. In a multi-cylinder engine, the exhaust ports 608 of each cylinder 108 are connected, and the exhaust gas discharged from each cylinder 108 converges and then flows into the catalyst 703.

[0053] The catalyst 703 is a three-way catalyst having a catalyst made of, for example, palladium, rhodium, platinum, etc. The catalyst 703 removes HC, NOx, and CO contained in the exhaust gas by causing a reduction reaction and an oxidation reaction by the catalyst. When the temperature is low, this catalyst 703 has low reduction ability. Therefore, for example, at low temperature conditions such as at engine startup, combustion (catalyst warm-up) is required to warm up the temperature of the catalyst 703 at an early stage.

[0054] Also, in the engine configuration shown in FIG. 5, an air-fuel ratio sensor 710 is installed downstream of the exhaust port 608 and upstream of the catalyst 703. Further, between the intercooler 705 and the throttle valve 706 of the intake pipe 721, an air flow rate sensor 708 and an intake pipe pressure sensor 709 for detecting the pressure in the intake pipe 721 are provided.

[0055] In FIGS. 4 and 5, a reciprocating engine in which the piston 609 reciprocates in the cylinder 108 has been described, but a rotary engine in which a rotor rotates instead of the piston may be used.

[0056] As described in the background art section, in order to cope with the recent strengthening of exhaust gas regulations, it has become necessary to reduce the PN emission amount. In order to reduce the adhesion of the injected fuel to the combustion chamber wall surface, which is a cause of PN generation, instead of performing fuel injection once in one cycle, multi-stage injection that divides the fuel injection into a plurality of times is increasingly adopted. Since the injection amount per injection is reduced by multi-stage injection, the penetration (injection time) of the spray becomes short, and there is an effect of suppressing the adhesion to the opposing wall. However, by frequently using multi-stage injection, subtle differences between individuals occur in the operation of the fuel injection device as described above, and air-fuel ratio variations between cylinders occur.

[0057] As shown in FIG. 6, usually, an air-fuel ratio sensor 710 attached to an exhaust pipe 722 is used to measure the air-fuel ratio. In this case, the exhaust gases discharged from each cylinder are mixed in the exhaust pipe 722, and it takes time for the exhaust gas to reach the air-fuel ratio sensor 710, resulting in a delay. In FIG. 6, an example is shown in which a time delay occurs in the detected value y s (t - 1) of the air-fuel ratio sensor 710 with respect to the air-fuel ratio u(t) of the exhaust gas flowing into the exhaust pipe 722. For example, when the behavior of the air-fuel ratio in the exhaust gas collecting section is approximated by a second-order delay system such as the mathematical formula (1) described in Patent Document 1, the transmission delay of the air-fuel ratio changes under transient conditions. Therefore, in order to accurately estimate the air-fuel ratio, it is necessary to determine the coefficients k1 to k4 of the mathematical formula (1) by adaptation, but the man-hours required to obtain the model constants of the air-fuel ratio transmission delay model increase significantly.

[0058] [Number]

[0059] In response to such problems, the present invention proposes a correction control for suppressing the variation in the air-fuel ratio between cylinders caused by multi-stage injection. Here, FIG. 7 shows the air-fuel ratio to be estimated in the exhaust pipe 722 at a certain point in time (here, the state where the exhaust gas of the fourth cylinder has completely flowed to the downstream side of the air-fuel ratio sensor 710) when the combustion cycles are rotated in the order of the first cylinder, the third cylinder, the fourth cylinder, and the second cylinder. The air-fuel ratio to be estimated is the ratio of the mass of air contained in the exhaust gas collected from the first cylinder, the second cylinder, and the third cylinder to the mass of fuel contained in the same exhaust gas. In the figure, air is represented by diagonal lines and fuel is represented by dots for each cylinder. By simulating mixing and delay through the mass balance calculation of fuel and air and the fuel mass ratio calculation for each cylinder as shown in FIG. 7, the variation in the air-fuel ratio for each cylinder can be estimated with high accuracy.

[0060] Hereinafter, the air-fuel ratio control for each cylinder for suppressing the variation in the air-fuel ratio between cylinders in a multi-stage injection engine according to an embodiment of the present invention will be described in detail.

[0061] [Air-fuel ratio control for each cylinder] FIG. 8 is a block diagram showing functions for achieving cylinder-by-cylinder air-fuel ratio control in the ECU 104 according to an embodiment of the present invention. By the CPU 120 (FIGS. 1 and 2) of the ECU 104 reading and executing a control program recorded in the memory 121, the functions of each block shown in FIG. 8 are realized.

[0062] The ECU 104 includes an intake air amount calculation unit 801 for each cylinder, a fuel injection amount calculation unit 802 for each cylinder, an air mass balance calculation unit 803 for each cylinder, a fuel mass balance calculation unit 804 for each cylinder, an exhaust pipe air-fuel ratio estimation unit 805, and a fuel mass ratio calculation unit 806 for each cylinder. Further, the ECU 104 includes a Kalman filter 807, an air-fuel ratio estimation unit 808 for each cylinder, and a fuel injection amount correction unit 809 for each cylinder. This embodiment is particularly characterized by including the air mass balance calculation unit 803 for each cylinder, the fuel mass balance calculation unit 804 for each cylinder, the exhaust pipe air-fuel ratio estimation unit 805, the fuel mass ratio calculation unit 806 for each cylinder, the Kalman filter 807, and the air-fuel ratio estimation unit 808 for each cylinder.

[0063] In the intake air amount calculation unit 801 for each cylinder, the intake air amount for each cylinder is calculated from the intake pipe state (the state inside the intake manifold not shown) such as the detection value (intake air amount) of the air flow sensor 708 and the detection value (intake pipe pressure) of the intake pipe pressure sensor 709, and the calculation result is output to the fuel injection amount calculation unit 802 for each cylinder and the air mass balance calculation unit 803 for each cylinder. When the engine is equipped with an EGR (Exhaust Gas Recirculation) system, the EGR rate is reflected in the calculation of the intake air amount for each cylinder.

[0064] In the fuel injection amount calculation unit 802 for each cylinder, the fuel injection amount for each cylinder 108 is calculated using the calculation result of the intake air amount for each cylinder by the intake air amount calculation unit 801 and the target air-fuel ratio of each cylinder 108.

[0065] The air mass balance calculation unit 803 for each cylinder a plurality of for the cylinder 108 flowing into the air mass flow rate and the fuel a mixed gas with a mass flow rate flow rate are taken as the "inlet flow rate", from cylinder 108 the discharged exhaust gas with an air mass flow rate and a fuel mass flow rate When the gas flow rate is taken as the "outlet flow rate", the inlet flow rate the air mass flow rate of and the outlet flow rate the air mass flow rate of are used to per cylinder 108 calculate the air mass balance. For example, the air mass balance calculation unit 803 for each cylinder calculates the air mass balance for each cylinder 108 based on the calculation result of the cylinder inlet air amount by the cylinder inlet air amount calculation unit 801 the exhaust of the combustion gas the air mass flow rate for calculate. From this cylinder inlet air amount and the air mass flow rate of the exhaust gas each cylinder 108 the air of air mass balance of calculation. The exhaust gas the air mass flow rate is considering the mixing and arrival time delay of the exhaust gas in the exhaust pipe 722 simulated etc. in advance to the created model, the cylinder inlet air amount and operating conditions input to obtain. cylinder 108 Another air mass balance will be described later inlet flow rate of air mass flow rate m ai from the dot of the above-mentioned exhaust gas air mass flow rate for subtract this purpose calculate can be done.

[0066] The fuel mass balance calculation unit 804 for each cylinder calculates the fuel mass balance using the above-mentioned inlet flow rate the fuel mass flow rate of and the outlet flow rate the fuel mass flow rate of For example, the fuel mass balance calculation unit 804 for each cylinder calculates based on the calculation result of the cylinder fuel injection amount by the cylinder fuel injection amount calculation unit 802, per cylinder 108 mixing of exhaust gas in the exhaust pipe 722 calculate the fuel mass flow rate included in the exhaust gas flow rate, and perform the calculation of the fuel mass balance per cylinder 108 from this cylinder fuel injection amount and the fuel mass flow rate of the exhaust gas discharged from cylinder 108. The fuel mass flow rate of the exhaust gas is exhaust pipe 722 inside exhaust gas mixing, arrival time delay taken into account done simulated etc. in advance to the created model, the cylinder fuel injection amount and operating conditions input to obtain to it. For example, for the fuel mass balance calculation for each cylinder 108, the following formula 2 can be used.

[0067]

Equation

[0068] of Equation 2 The dot on the left side of m ex,fi represents the fuel mass balance of the i-th (i is a natural number from 1 to n) cylinder 108 (the difference between the fuel mass flow rate of the inlet flow and the fuel mass flow rate of the outlet flow) and in this embodiment, the dot represents the mass flow rate [kg / s]. m on the right side fi The dot is the cylinder fuel injection amount, that is the mass flow rate [kg / s] of the fuel that has flowed into the i-th cylinder 108 fuel quality . Also, r i ×m cat The dot is the mass flow rate of the exhaust gas discharged from the i-th cylinder 108 to the exhaust pipe 722 of catalyst 703 position . Here, r fuel is the fuel mass ratio for each cylinder shown in Equation 5 described later. m i . The dot is cat the total mass flow rate [kg / s] of the exhaust gas discharged from the exhaust pipe 722 to the shown in Equation 5 described later exhaust pipe 722 downstream of the collecting part of catalyst 703 position . It can be calculated using the following Equation 3. m 。

[0069] The exhaust pipe air-fuel ratio estimation unit 805 calculates the total mass balance, which is the difference between the above-mentioned inlet flow and outlet flow. For example, in the calculation of the total mass balance is. m ex The dot is is the total mass balance the total cylinder of the outlet flow rate the difference between the exhaust gas flow rate and the mixed gas flow rate, which is the inlet flow rate of all cylinders . m ai The dot is the mass flow rate of the air that has flowed into the i-th cylinder 108 air quality .

[0070]

Number

[0071] The exhaust pipe air-fuel ratio estimation unit 805 estimates the exhaust pipe air-fuel ratio based on total the mass balance operation result and of the cylinder-by-cylinder fuel mass balance calculation unit 804 the fuel mass balance operation result . For example, the exhaust pipe air-fuel ratio estimation unit 805 uses the calculation result of the fuel mass of the cylinder-by-cylinder fuel mass balance calculation unit 804 and the following Equation 4 to calculate the air air-fuel ratio φ of the exhaust gas in the exhaust pipe 722 flow rate . at the position of the inlet of the catalyst 703 the right side of Equation 4 ex . the right side of Equation 4 m ex,fi is the exhaust gas at the position of the inlet of the catalyst 703 in the exhaust pipe 722 Fuel mass is a value based on the calculation result of the fuel mass flow rate [kg / s] of the exhaust gas of the cylinder-by-cylinder fuel mass balance calculation unit 804, that is, the value based on the calculation result of "r i ×m cat dot" of Equation 2 described above. m on the right side of Equation 4 ex is the total mass of the exhaust gas at the position of the inlet of the catalyst 703 in the exhaust pipe 722, and is a value based on the calculation result of the total mass flow rate [kg / s] of the exhaust gas of the cylinder-by-cylinder fuel mass balance calculation unit 804, that is, the value based on the calculation result of "m cat dot" of the above-mentioned total mass balance. of the exhaust pipe air-fuel ratio estimation unit 805 The estimated result of the exhaust pipe air-fuel ratio is output to the air-fuel ratio estimator 808 for each cylinder and the Kalman filter 807.

[0072]

Number

[0073] The fuel mass ratio calculation unit 806 for each cylinder calculates the fuel mass ratio for each cylinder operation result of the exhaust pipe air-fuel ratio estimation unit 805 based on. For example, the fuel mass ratio calculation unit 806 for each cylinder the fuel mass of the exhaust gas at the position of the inlet of the catalyst 703 in the exhaust pipe 722 of the exhaust pipe air-fuel ratio estimation unit 805 the calculation result of, and total mass of the exhaust gas the calculation result of, and the following formula 5 to estimate the fuel mass ratio r of each cylinder 108 with respect to the fuel mass in the exhaust pipe 722 i

[0074]

Number

[0075] In the present embodiment, the calculation result of the fuel mass ratio for each cylinder by the fuel mass ratio calculation unit 806 for each cylinder is fed back to the fuel mass balance calculation unit 804 for each cylinder. As a result, the latest fuel mass ratio for each cylinder calculated by the fuel mass ratio calculation unit 806 is reflected in the fuel mass balance calculation for each cylinder in the fuel mass balance calculation unit 804 for each cylinder.

[0076] The exhaust pipe air-fuel ratio obtained by the exhaust pipe air-fuel ratio estimator 805 is input to the Kalman filter 807 as an input variable operation result, and the actual measurement of the air-fuel ratio sensor 710 is used as an output variable air-fuel ratio ​A value is input. Although not shown by an arrow, the exhaust pipe volume is input as a model constant to the Kalman filter 807. The exhaust pipe volume is a parameter related to the delay. Then, based on these variables, the Kalman filter 807 outputs the air mass and fuel mass in the exhaust pipe as state variables, and sends them to the cylinder-by-cylinder fuel mass ratio calculation unit 806. Thereby, the cylinder-by-cylinder fuel mass ratio calculation unit 806 corrects the calculation result of the cylinder-by-cylinder fuel mass ratio to improve the model accuracy. the mixing and arrival time of the exhaust gas in the exhaust pipe 722 described above a parameter related to the delay. And the Kalman filter 807 and constants based on these variables, as the state variable, the 722 inside the exhaust pipe at the inlet position of the catalyst 703 air mass and fuel quality quantity outputs and are sent to the exhaust pipe air-fuel ratio estimation unit 805. The exhaust pipe air-fuel ratio estimation unit 805 corrects the calculation result of the fuel mass of the exhaust gas and the calculation result of the total mass of the exhaust gas based on the output of the Kalman filter 807 sends to the cylinder-by-cylinder fuel mass ratio calculation unit 806. Thereby, the cylinder-by-cylinder fuel mass ratio calculation unit 806 in corrects the calculation result of the cylinder-by-cylinder fuel mass ratio to improve the model accuracy.

[0077] The cylinder-by-cylinder air-fuel ratio estimation unit 808 estimates the air-fuel ratio of the cylinder 108 using the change amount of the estimated air-fuel ratio in the exhaust pipe 722 from the exhaust valve opening timing to the exhaust valve closing timing at an arbitrary cylinder timing, and the cylinder-by-cylinder fuel mass ratio estimated by the cylinder-by-cylinder fuel mass ratio estimation unit 806 in the cylinder 108 at the exhaust valve closing timing. For example, at a certain cylinder timing, the cylinder-by-cylinder air-fuel ratio estimation unit 808 uses the exhaust pipe air-fuel ratio φ estimated by the exhaust pipe air-fuel ratio estimation unit 805 and the cylinder-by-cylinder fuel mass ratio r calculated by the cylinder-by-cylinder fuel mass ratio calculation unit 806, and from the exhaust pipe air-fuel ratios φ and φ at the EVO (exhaust valve open) and EVC (exhaust valve closed) timings and the fuel mass ratio of the cylinder 108, estimates the air-fuel ratio φ for each cylinder 108. The following formula 6 can be used for the estimation of the cylinder-by-cylinder air-fuel ratio. In formula 6, the average exhaust pipe air-fuel ratio φ in a plurality of combustion cycles is used as the exhaust pipe air-fuel ratio. ex and the cylinder-by-cylinder fuel mass ratio r i calculated by the cylinder-by-cylinder fuel mass ratio calculation unit 806, and from the exhaust pipe air-fuel ratios φ evo,i and φ evc,i at the EVO (exhaust valve open) and EVC (exhaust valve closed) timings and the fuel mass ratio of the cylinder 108, estimates the air-fuel ratio φ for each cylinder 108. The following formula 6 can be used for the estimation of the cylinder-by-cylinder air-fuel ratio. In formula 6, the average exhaust pipe air-fuel ratio φ in a plurality of combustion cycles is used as the exhaust pipe air-fuel ratio. cyl,i For the estimation of the cylinder-by-cylinder air-fuel ratio, the following formula 6 can be used. In formula 6, the average exhaust pipe air-fuel ratio φ in a plurality of combustion cycles is used as the exhaust pipe air-fuel ratio. ex,ave is used.

[0078]

Equation

[0079] The cylinder-specific fuel injection amount correction unit 809 corrects the fuel injection amount for each cylinder 108 using the output of the cylinder-specific air-fuel ratio estimation unit 808. For example, the cylinder-specific fuel injection amount correction unit 809 corrects the fuel injection amount for each cylinder 108 based on the difference between the air-fuel ratio estimated value for each cylinder 108 of the cylinder-specific air-fuel ratio estimation unit 808 and the target air-fuel ratio, that is, determines the injection pulse width of the fuel injection device 101. Thereby, the ECU 104 can correct the fuel injection amount for each cylinder 108 and control the combustion in each combustion chamber 107. The correction amount of the cylinder-specific fuel injection amount can be defined by the following mathematical formula 7. Further, the cylinder-specific fuel injection correction result is fed back to the cylinder fuel injection amount calculation unit 802. Then, by correcting the cylinder fuel injection amount by the cylinder fuel injection amount calculation unit 802, the variation in the air-fuel ratio between cylinders is corrected.

[0080] [Number]

[0081] [Control Model] Next, the functions used in constructing the control model for realizing the cylinder-specific air-fuel ratio control will be described. FIG. 9 is a conceptual diagram showing the functions used in constructing the control model in a block diagram. The estimator 910 obtains an output variable based on the input variable, the internal state variable and the model constant, and the static characteristics and dynamic characteristics defined by this model constant. Thereby, it is possible to estimate the output behavior with respect to the input and the behavior of the internal state.

[0082] While the estimator 910 describes the control object as a forward problem, it is necessary to solve the inverse problem in the control model. That is, the controller inputs the output variable as a target value and outputs the input variable (control amount) for realizing it. In deriving this controller, the following functional blocks are defined.

[0083] Here, the input-output relationship of the estimator 910 is changed to construct the observer 920. The observer 920 can be constructed by setting the input variables, output variables, and model constants to the block inputs and outputting the state variables. One of the methods for realizing the observer 920 is the Kalman filter adopted in this embodiment.

[0084] In this embodiment, as the input variables, for example, the cylinder intake air amount, the cylinder fuel injection amount, and the exhaust pipe exhaust gas amount are set. Also, as the state variables, for example, the exhaust pipe air amount and the exhaust pipe fuel amount are set. Further, as the output variable, for example, the exhaust pipe air-fuel ratio is set. The detected value of the air-fuel ratio sensor 710 is set as the exhaust pipe air-fuel ratio. Furthermore, as the model constant, for example, the exhaust pipe volume is set.

[0085] [State Space Model of Intake Pipe State] Next, a method for describing the intake pipe state by a state space model will be described. FIG. 10 is a diagram showing an equation representing the state space model of the intake pipe state. The time derivative of the state variable is defined as a discrete equation according to the first-order forward difference of Euler as shown in Equation (8).

[0086] [Equation]

[0087] Here, the subscript k attached to the upper right of x represents the current value when discretized on the time axis. Here, the first-order forward difference is used, but the present invention is not limited to this. Discretizing according to Equation (8), it is described by the state space models of the following Equations (9) and (10).

[0088] [Equation]

[0089] [Equation]

[0090] Here, in equations (9) and (10), A, B, and C represented by alphabets are matrices respectively. x k is a state vector, u k is an input vector, y k is an output vector, and they are given by the following equations (11), (12), and (13) respectively.

[0091]

Number

[0092]

Number

[0093]

Number

[0094] In the exhaust pipe air-fuel ratio estimation unit 805 (FIG. 8), the state equation is arranged in a state space model, and the vectors defined by equations (11) to (13) are passed to the processes executed in the Kalman filter 807.

[0095] [Internal Structure and Kalman Filter Algorithm of Kalman Filter] Next, the internal structure and Kalman filter algorithm of the Kalman filter 807 will be described with reference to FIGS. 11 and 12. FIG. 11 is a block diagram showing an example of the internal structure of the Kalman filter 807. FIG. 12 is a flowchart showing an example of the Kalman filter algorithm executed by the Kalman filter 807.

[0096] In the system of this embodiment, the linear Kalman filter algorithm is adopted, but the present invention is not limited thereto. That is, the same effect can be achieved by applying the extended Kalman filter known as a non-linear Kalman filter, the ensemble Kalman filter, or the like. Hereinafter, regarding the Kalman filter 807 which is one of the components of the air-fuel ratio correction control for each cylinder, the algorithm and the application method to this control will be described.

[0097] The Kalman filter 807 describes the state of the intake pipe which is the control target by a state equation, and defines the sensor measurement information for the output variable of the state equation. Then, based on the sensor measurement information defined for the output variable, a state variable (hereinafter referred to as "internal state variable") representing the state of the intake pipe that cannot be directly measured is estimated.

[0098] As shown in FIG. 12, when executing the Kalman filter 807, the CPU 120 of the ECU 104 first determines whether the Kalman filter 807 can be executed (S1201). As the determination index of whether execution is possible, the sensor state and the prediction range of the assumed state equation are considered. For example, as the sensor state, when it is determined by diagnosis that the sensor output cannot be obtained due to a sensor failure or disconnection, or that an unacceptable error has occurred in the sensor output due to sensor degradation, the Kalman filter 807 is not executed because accurate filter processing cannot be performed. The state quantities targeted by the state equation are the intake pipe pressure and the intake pipe EGR rate here. When any of the variables of the state equation exceeds the prediction range (the theoretical / physical range that can be taken by the state equation), that is, in a region that cannot be covered by the state equation, the Kalman filter 807 is not executed because accurate filter processing cannot be performed.

[0099] When the CPU 120 detects these situations, it determines that the Kalman filter 807 cannot be executed (NO in S1201), ends this process, and when it determines that the Kalman filter 807 can be executed (YES in S1201), it proceeds to step S1202. Note that when the CPU 120 determines that the Kalman filter 807 cannot be executed, it may set a fail-safe processing flag for the engine system.

[0100] The arithmetic expressions executed in steps S1202 to S1206 are specifically shown below. The Kalman filter 807 is premised on a state equation including system noise Q and observation noise R defined by the following mathematical formulas (14) and (15).

[0101]

Number

[0102]

Number

[0103] Here, "k" means the current value of discrete time. The processing of the Kalman filter 807 is divided into a prediction step and a filtering step. In the prediction step, based on the input variable and system noise Q, the internal state variable vector x and the covariance matrix P are calculated (updated) by the following mathematical formulas (16) and (17) (S1202, S1203).

[0104]

Number

[0105]

Number

[0106] Next, in the filtering step, the Kalman filter 807 calculates the Kalman gain K defined by the updated covariance matrix P and the observation noise R according to the following mathematical formula (18) (S1204). Note that the Kalman filter 807 may be configured to calculate the covariance matrix P in step S1203.

[0107] [Equation]

[0108] Furthermore, the Kalman filter 807 uses the Kalman gain K and the observation data (the detection value of the air-fuel ratio sensor 710) to update the internal state variable vector x and the covariance matrix P again according to the following mathematical formulas (19) and (20) (S1205, S1206). The alphabet "I" in the mathematical formula (20) is the identity matrix. After the processing of steps S1205 and S1206 is completed, the processing procedure returns to step S1201. In this way, the internal state variable vector x and the covariance matrix P are corrected by the actual observation data y(k) (the detection value of the air-fuel ratio sensor 710).

[0109] [Equation]

[0110] [Equation]

[0111] From the above calculations, the behavior of the cylinder-by-cylinder exhaust fuel mass and the total cylinder exhaust mass of the internal state variable x(k|k) that is difficult to measure directly can be estimated based on the output information of the measurable air-fuel ratio sensor 710. In this embodiment, the information of the internal state variable output from the Kalman filter 807 is used for internal state feedback control, that is, to improve the model accuracy.

[0112] [Measurement Results] Next, various measurement results or simulation results according to this embodiment will be described with reference to FIGS. 13 to 16. First, an example of the change in the exhaust pipe equivalent ratio (theoretical air-fuel ratio / air-fuel ratio) due to the variation in fuel injection amount between cylinders will be described with reference to FIG. 13.

[0113] FIG. 13 is a graph showing an example of the change in the equivalent ratio when there is variation in the fuel injection amount for each cylinder. In FIG. 13, the horizontal axis represents time, and the vertical axis represents the exhaust pipe equivalent ratio. In "Variation 1" on the left side of FIG. 13, it is the case where the injection amount variation of the first cylinder is "-10%", the second cylinder is "0%", the third cylinder is "+10%", and the fourth cylinder is "0%" with respect to the command value (target value) of the fuel injection amount for each cylinder, showing the change in the equivalent ratio as shown in the graph. Here, the injection amount variation for each cylinder is the difference (variation rate) between the command value (target value) of the fuel injection amount for each cylinder and the fuel injected in each cylinder. In "Variation 2" on the right side of FIG. 13, it is the case where the injection amount variation of the first cylinder is "-10%", the second cylinder is "0%", the third cylinder is "0%", and the fourth cylinder is "+10%", and similarly, the equivalent ratio changes as shown in the graph.

[0114] In addition, the timing of EVO and EVC is illustrated in the order of cylinder sequence 1-3-4-2 in each graph, and the amount of change at each timing can be seen. Here, the third cylinder in "Variation 1" and the fourth cylinder in "Variation 2" both have a variation of "+10%", but there is a difference in the peak values seen at each EVC.

[0115] Next, an example of the transition of the fuel mass ratio for each cylinder will be described with reference to FIG. 14. FIG. 14 is a graph showing an example of the transition of the fuel mass ratio for each cylinder, showing an example of the transition of the fuel mass ratio for each cylinder for "Variation 1" and "Variation 2" in FIG. 13. In FIG. 14, the horizontal axis represents time, and the vertical axis represents the fuel mass ratio for each cylinder. In FIG. 14, the solid line represents the fuel mass ratio of the first cylinder, the two-dot chain line represents the fuel mass ratio of the second cylinder, the broken line represents the fuel mass ratio of the third cylinder, and the one-dot chain line represents the fuel mass ratio of the fourth cylinder. Due to the variation in the fuel injection amount for each cylinder, there are differences in the waveforms of the fuel mass ratio for each cylinder.

[0116] [Estimation Results of In-Exhaust-Pipe Equivalence Ratio Behavior and Cylinder-by-Cylinder Equivalence Ratio] Next, an example of the estimation result of the in-exhaust-pipe equivalence ratio behavior due to the variation in fuel injection amount among cylinders and an example of the estimation result of the cylinder-by-cylinder equivalence ratio will be described with reference to FIG. 15. FIG. 15 is a graph showing an example of the estimation result of the in-exhaust-pipe equivalence ratio behavior due to the variation in fuel injection amount among cylinders and an example of the estimation result of the cylinder-by-cylinder equivalence ratio in one embodiment of the present invention. In FIG. 15, the estimation results of various equivalence ratios for "variation 1" and "variation 2" in FIGS. 13 and 14 are shown. The horizontal axis represents time, and the vertical axis represents the in-exhaust-pipe equivalence ratio and the cylinder-by-cylinder equivalence ratio. The estimation result of the in-exhaust-pipe equivalence ratio is obtained from the estimated value of the in-exhaust-pipe air-fuel ratio calculated by the in-exhaust-pipe air-fuel ratio estimation unit 805 and the theoretical air-fuel ratio. Further, the estimation result of the cylinder-by-cylinder equivalence ratio is obtained from the estimated value of the cylinder-by-cylinder air-fuel ratio calculated by the cylinder-by-cylinder air-fuel ratio estimation unit 808 and the theoretical air-fuel ratio.

[0117] In FIG. 15, the estimation results of the in-exhaust-pipe equivalence ratio behavior are obtained as changes shown by broken lines, and the estimation results of the cylinder-by-cylinder equivalence ratio become values shown by bar graphs.

[0118] [Correction Results of Cylinder-by-Cylinder Air-Fuel Ratio] Next, an example of the correction result by cylinder-by-cylinder air-fuel ratio control will be described with reference to FIG. 16. FIG. 16 is a graph showing an example of the correction result of the cylinder-by-cylinder air-fuel ratio in one embodiment of the present invention. In FIG. 16, the correction results of the cylinder-by-cylinder air-fuel ratio for "variation 1" and "variation 2" in FIGS. 13 and 14 are shown. The horizontal axis represents time, and the vertical axis represents the in-exhaust-pipe equivalence ratio. The correction result by cylinder-by-cylinder air-fuel ratio control corresponds to the estimated value of the cylinder-by-cylinder air-fuel ratio obtained by the cylinder-by-cylinder air-fuel ratio estimation unit 808 as a result of correcting the fuel injection amount for each cylinder in the cylinder-by-cylinder fuel injection amount correction unit 809.

[0119] In FIG. 16, the in-exhaust-pipe equivalence ratios before and after correction are indicated by a dashed line and a solid line, respectively. For both "variation 1" and "variation 2", the variation range of the air-fuel ratio in the exhaust pipe that occurred before correction is suppressed after correction. For example, in "variation 1", the air-fuel ratio variation range is reduced from 5.5% to 1%. Also, in "variation 2", the air-fuel ratio variation range is reduced from 5.7% to 2%.

[0120] As described above, the internal combustion engine control device (for example, ECU 104 or control device 150) according to the present embodiment is an internal combustion engine control device that controls the fuel injection amount based on the air flow rate flowing into a plurality of cylinders 108 of a multi-cylinder internal combustion engine (for example, a multi-cylinder in-cylinder direct injection engine) having an exhaust pipe 722 where the exhaust gases from each cylinder 108 gather. This internal combustion engine control device performs mass balance calculations of fuel and air at the inlet and outlet of each cylinder 108 (cylinder-by-cylinder air mass balance calculation, cylinder-by-cylinder fuel mass balance calculation), estimates the air-fuel ratio of the exhaust pipe 722 from the results of each mass balance calculation, estimates the cylinder-by-cylinder fuel mass ratio, and includes a control unit (for example, CPU 120) that obtains the air-fuel ratio of each cylinder 108 from the air-fuel ratio of the exhaust pipe 722 and the cylinder-by-cylinder fuel mass ratio.

[0121] According to the internal combustion engine control device according to the present embodiment, by performing the balance calculation and mass ratio calculation of fuel and air for each cylinder, it is possible to simulate the mixing and delay of the exhaust gases from a plurality of cylinders. Thereby, in the present embodiment, the air-fuel ratio of each cylinder can be estimated with high accuracy. As a result, the variation in the air-fuel ratio (fuel injection amount) between cylinders due to multi-stage injection can be suppressed. Therefore, PN can be reduced, and it becomes possible to comply with recent exhaust gas regulations. Also, in the present embodiment, the air-fuel ratio of each cylinder can be estimated with high accuracy without requiring a large amount of adaptation man-hours.

[0122] In addition, in the internal combustion engine control device according to the present embodiment (for example, ECU 104 or control device 150), the control unit (CPU 120) includes a fuel injection amount correction unit (cylinder-by-cylinder fuel injection amount correction unit 809) that corrects the fuel injection amount of the cylinder using the output of the cylinder-by-cylinder air-fuel ratio estimation unit (cylinder-by-cylinder air-fuel ratio estimation unit 808). Thus, in the present embodiment, by using the estimated high-precision cylinder-by-cylinder air-fuel ratio, the accuracy of fuel injection amount correction (fuel injection amount control) for each cylinder is improved.

[0123] In addition, in the internal combustion engine control device according to the present embodiment (for example, ECU 104 or control device 150), the control unit (CPU 120) is configured to correct the estimated value of the fuel mass ratio of each cylinder based on the output of the exhaust pipe air-fuel ratio estimation unit (cylinder-by-cylinder air-fuel ratio estimation unit 808) and the detection value of the air-fuel ratio sensor (air-fuel ratio sensor 710) provided in the exhaust pipe. For example, the control unit corrects the estimated value of the fuel mass ratio of each cylinder using the state variable output from a Kalman filter (Kalman filter 807) that takes the exhaust pipe air-fuel ratio estimated by the exhaust pipe air-fuel ratio estimation unit and the detection value of the air-fuel ratio sensor as inputs.

[0124] According to the internal combustion engine control device according to the present embodiment, by using the Kalman filter, it is possible to correct the model estimation result (for example, the fuel mass ratio of each cylinder) based on the actual measurement result of the air-fuel ratio sensor while considering the influence of sensor error and system error. And in the present embodiment, by correcting the model estimation result with the actual measurement result of the air-fuel ratio sensor, the robustness can be improved.

[0125] <Modification example> Note that the following forms can be considered as the correction control or diagnosis control by the ECU 104 according to the above-described present embodiment.

[0126] In the control unit (CPU 120) of the ECU 104, the correction of the estimated value of the fuel mass ratio of each cylinder is learned for each fuel pressure. Thereby, the ECU 104 can estimate the air-fuel ratio for each cylinder while appropriately considering the variation in the injection amount for each cylinder due to the fuel pressure.

[0127] Also, in the control unit (CPU 120) of the ECU 104, the correction of the estimated value of the fuel mass ratio of each cylinder is configured to be evenly reflected in each stage of the multi-stage injection. Thereby, the ECU 104 can reduce the injection period correction amount for correcting the variation in the injection amount between cylinders.

[0128] Also, in the control unit (CPU 120) of the ECU 104, the correction of the estimated value of the fuel mass ratio of each cylinder is configured to be added to the stage with the largest ratio of the fuel injection amount among the multi-stage injections. Thereby, the ECU 104 can prevent the shortage of the injection period caused by performing the correction on the stage with the smallest ratio of the fuel injection amount among the multi-stage injections.

[0129] Also, when the control unit (CPU 120) of the ECU 104 corrects the estimated value of the fuel mass ratio of each cylinder, if the total fuel injection amount by the multi-stage injection becomes equal to or less than a predetermined value due to the correction, the configuration is such that the number of injection times of the multi-stage injection is reduced. Thereby, the ECU 104 can prevent the shortage of the injection period during the correction of the injection amount variation.

[0130] Also, when the correction amount of the estimated value of the fuel mass ratio of each cylinder in the control unit (CPU 120) of the ECU 104 becomes equal to or greater than a predetermined value, it is diagnosed as an abnormality, and a fail-safe control is switched to, or a warning of replacing the fuel injection device is given to an instrument panel, an external terminal, or the like. Thereby, when an abnormality occurs in the fuel injection system, the ECU 104 can appropriately perform the abnormality diagnosis and the fail-safe control.

[0131] Furthermore, the present invention is not limited to the above-described embodiment, and it goes without saying that various other application examples and modification examples can be taken as long as the gist of the present invention described in the claims is not deviated from. For example, the above-described embodiment describes the configuration of the internal combustion engine system in detail and specifically for easy understanding of the present invention, and is not necessarily limited to the one having all the configured components described. Also, it is possible to add, replace, or delete some of the components of one embodiment with other components.

[0132] In the above-described embodiment, an example in which the present invention is applied to an engine system equipped with a supercharger has been described. However, the present invention is not limited to this example. For example, if a control model of an engine system without a supercharger is created, the present invention can be applied to an engine system without a supercharger. Further, for example, if a control model of an engine system equipped with an EGR system is created, the present invention can be applied to an engine system equipped with an EGR system.

[0133] In addition, each of the above-described configurations, functions, processing units, etc. may be realized in hardware by designing a part or all of them, for example, by using an integrated circuit. As the hardware, a processor device in a broad sense such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) may be used.

[0134] Also, in the flowchart shown in FIG. 12, a plurality of processes may be executed in parallel or the order of the processes may be changed as long as the processing result is not affected.

[0135] In addition, in the above-described embodiment, the control lines and information lines show those considered necessary for explanation, and not necessarily all the control lines and information lines are shown on the product. In reality, it may be considered that almost all components are interconnected.

Description of Reference Numerals

[0136] 1... Fuel injection system, 101... Fuel injector, 108... Cylinder, 104... ECU, 150... Control device, 120... CPU, 121... Memory, 710... Air-fuel ratio sensor, 721... Intake pipe, 722... Exhaust pipe, 801... Cylinder intake air amount calculation unit, 802... Cylinder fuel injection amount calculation unit, 803... Cylinder-by-cylinder air mass balance calculation unit, 804... Cylinder-by-cylinder fuel mass balance calculation unit, 805... Exhaust pipe air-fuel ratio estimation unit, 806... Cylinder-by-cylinder fuel mass ratio calculation unit, 807... Kalman filter, 808... Cylinder-by-cylinder air-fuel ratio estimation unit, 809... Cylinder-by-cylinder fuel injection amount correction unit

Claims

An internal combustion engine control device for an internal combustion engine having an air flow rate sensor capable of detecting an inflow air flow rate flowing into a plurality of cylinders, an exhaust pipe in which exhaust gas from the plurality of cylinders is collected at an exhaust gas collecting portion downstream of an exhaust port in the exhaust pipe and upstream of a catalyst, an air-fuel ratio sensor capable of detecting an actual air-fuel ratio downstream of the exhaust gas collecting portion and upstream of the catalyst, and a plurality of various sensors capable of detecting signals indicating states of other internal combustion engines, the internal combustion engine control device comprising a control unit that controls a fuel injection amount based on the inflow air flow rate, the actual air-fuel ratio, and signals indicating states of the other internal combustion engines, The control unit a cylinder inflow air amount calculation unit that calculates a cylinder inflow air amount flowing into the i-th cylinder (i is a natural number from 1 to n) based on the inflow air flow rate, a cylinder fuel injection amount calculation unit that calculates a fuel injection amount of fuel injected into the i-th cylinder in one combustion cycle of the internal combustion engine, with the target air-fuel ratio based on the operating conditions of the internal combustion engine and the cylinder inflow air amount as inputs, an air mass balance calculation unit that calculates a cylinder outlet air mass flow rate reaching the position of the air-fuel ratio sensor in the exhaust pipe from the i-th cylinder based on the cylinder inflow air amount and the operating conditions of the internal combustion engine, a fuel mass balance calculation unit that calculates a cylinder outlet fuel mass flow rate reaching the position of the air-fuel ratio sensor in the exhaust pipe using the fuel injection amount to the i-th cylinder and the operating conditions of the internal combustion engine, an exhaust pipe air-fuel ratio estimation unit that estimates an exhaust pipe air-fuel ratio at the position of the air-fuel ratio sensor in the exhaust pipe based on the cylinder outlet air mass flow rate and the cylinder outlet fuel mass flow rate for all cylinders, a Kalman filter in which the exhaust pipe air-fuel ratio is set as an input variable, the actual air-fuel ratio is set as an output variable, the exhaust pipe volume is set as a model constant, and the air mass and fuel mass of the exhaust gas at the position of the air-fuel ratio sensor in the exhaust pipe are output as state variables, a cylinder-by-cylinder fuel mass ratio calculation unit that estimates a cylinder-by-cylinder fuel mass ratio using the cylinder outlet fuel mass and the exhaust gas mass, and a cylinder-by-cylinder air-fuel ratio estimation unit that estimates a cylinder-by-cylinder air-fuel ratio using the exhaust pipe air-fuel ratio and the cylinder-by-cylinder fuel mass ratio. Internal combustion engine control device.

2. The control unit includes a cylinder-by-cylinder fuel injection amount correction unit that corrects the fuel injection amount of the cylinder using the target air-fuel ratio and the cylinder-by-cylinder air-fuel ratio. The internal combustion engine control device according to claim 1.

3. The control unit learns the correction of the estimated value of the cylinder-by-cylinder fuel mass ratio based on the output of the Kalman filter for each fuel pressure. The internal combustion engine control device according to claim 2.

4. The control unit equally reflects the correction of the estimated value of the cylinder-by-cylinder fuel mass ratio based on the output of the Kalman filter in each stage of the multi-stage injection. The internal combustion engine control device according to claim 2.

5. The control unit adds the correction of the estimated value of the cylinder-by-cylinder fuel mass ratio based on the output of the Kalman filter to the stage with the largest ratio of the fuel injection amount among the multi-stage injections. The internal combustion engine control device according to claim 2.

6. When the control unit performs the correction of the estimated value of the cylinder-by-cylinder fuel mass ratio based on the output of the Kalman filter, if the total fuel injection amount by the multi-stage injection becomes equal to or less than a predetermined value due to the correction, the control unit reduces the number of injection times of the multi-stage injection. The internal combustion engine control device according to claim 2.

7. When the correction amount of the estimated value of the cylinder-by-cylinder fuel mass ratio based on the output of the Kalman filter becomes equal to or greater than a predetermined value, the control unit diagnoses it as an abnormality and switches to fail-safe control or warns of the replacement of the fuel injection device. The internal combustion engine control device according to claim 2.

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