Engine Control Unit

Abstract

To suppress a variation of an actual air-fuel ratio caused by the opening and closing of an EGR valve, related to an engine control device.SOLUTION: There is disclosed an engine control device 10 for controlling a combustion state of an engine 1 according to an opening / closing state of an EGR valve 9 which is interposed in an EGR passage 7 of the engine 1. The engine control device 10 comprises a setting part 12 for setting a correction amount with respect to an amount of fuel injection from a fuel injection valve 2, or an amount of suction air passing through a throttle valve 6 when an EGR opening is changed to an open state from a full-closed state, and a control part 13 for suppressing a variation of an actual air-fuel ratio of the engine 1 by reflecting the correction amount to the fuel injection amount or the suction air amount. The correction amount is set so that the correction amount takes an initial value at which an absolute value becomes maximum immediately after a change of the EGR opening, and the absolute value is decreased along the lapse of time, and also set so that a reduction speed of the absolute value becomes higher as a change amount of the EGR opening is larger.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an engine control device that controls the combustion state of an engine (internal combustion engine) to which an EGR system (exhaust gas recirculation system) is applied. [Background technology]

[0002] Conventionally, in engines to which an exhaust gas recirculation system is applied, a technique has been proposed for suppressing fluctuations in the actual air-fuel ratio caused by opening and closing an EGR valve. For example, a technique is known in which, when switching an EGR valve from a closed state to an open state, a throttle valve is controlled according to the amount of fresh air present in an EGR passage on the intake passage side of the EGR valve, thereby adjusting the amount of fresh air introduced from the outside. By such control, for example, when the EGR valve is opened, it is possible to suppress the air-fuel ratio in the cylinder from becoming leaner than the desired air-fuel ratio due to the fresh air in the EGR passage, thereby improving the controllability of the actual air-fuel ratio (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-152122 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the inflow speed of fresh air flowing from the EGR passage into the intake passage when the EGR valve is open can differ depending on the EGR opening (the degree of opening of the EGR valve). For example, if the EGR opening is small, the fresh air in the EGR passage flows slowly into the intake passage over a relatively long period of time. Conversely, if the EGR opening is large, the fresh air in the EGR passage flows quickly into the intake passage in a relatively short period of time. However, in conventional technology, such characteristics of the inflow speed of fresh air are not fully taken into consideration, and therefore fluctuations in the actual air-fuel ratio may not be suppressed, leaving room for improvement.

[0005] One of the objectives of the present invention, which has been devised in light of the above-mentioned problems, is to provide an engine control device capable of suppressing fluctuations in the actual air-fuel ratio caused by opening and closing the EGR valve. Note that the present invention is not limited to this objective. Another objective of the present invention is to achieve effects that cannot be obtained by conventional techniques and that are derived from the configurations shown in the "Description of Embodiments" to be described later. [Means for solving the problem]

[0006] The disclosed engine control device can be realized as the aspects or application examples disclosed below, and solves at least some of the above problems. This application discloses an engine control device that controls the combustion state of an engine according to the open / close state of an EGR valve installed in an EGR passage of the engine. The engine control device includes a setting unit that sets a correction amount for the fuel injection amount injected from a fuel injection valve or the intake air amount passing through a throttle valve when the EGR opening changes from a fully closed state to an open state, and a control unit that suppresses fluctuations in the actual air-fuel ratio of the engine by reflecting the correction amount in the fuel injection amount or the intake air amount. The correction amount is set to have an initial value whose absolute value is maximized immediately after the EGR opening changes, and to decrease with time, and is set so that the rate of decrease in the absolute value becomes faster as the amount of change in the EGR opening increases. Effect of the Invention

[0007] According to the disclosed engine control device, when the EGR opening changes from a fully closed state to an open state, the rate at which the absolute value of the correction amount decreases is set to be faster as the EGR valve opening becomes larger, making it easier to maintain the actual air-fuel ratio of the engine at the desired target air-fuel ratio and suppressing fluctuations in the actual air-fuel ratio due to the opening and closing of the EGR valve. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram showing an engine control device according to an embodiment; [Diagram 2]13(A) to 13(C) are graphs showing characteristics of the correction coefficient. [Diagram 3] 6A and 6B are graphs showing characteristics related to the correction of the fuel injection amount. [Figure 4] 13(A) to 13(C) are graphs for explaining the functions and effects of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [1. Configuration] An engine control device 10 as an embodiment is applied to an engine 1 (internal combustion engine) shown in FIG. 1. This engine 1 is, for example, a gasoline engine or a diesel engine, and can be installed in automobiles, ships, power generation facilities, and the like. A fuel injection valve 2 is provided in a cylinder of the engine 1. In addition, an EGR system (exhaust gas recirculation system) is applied to this engine 1. The EGR system is a system that improves the exhaust performance and thermal efficiency of the engine 1 by recirculating exhaust gas generated in the cylinder from an exhaust passage 3 to an intake passage 4. An EGR passage 7 (exhaust gas recirculation passage) for recirculating a part of the exhaust gas (EGR gas) is provided between the exhaust system and the intake system of the engine 1.

[0010] An EGR cooler 8 (exhaust gas recirculation cooling device) for cooling the EGR gas and an EGR valve 9 (exhaust gas recirculation valve) for controlling the flow rate of the EGR gas are provided in the EGR passage 7. The position of the EGR valve 9 can be set at any position in the EGR passage 7. For example, based on the flow of the EGR gas, it can be disposed downstream of the EGR cooler 8 or upstream (position indicated by the dashed line in FIG. 1).

[0011] The downstream end of the EGR passage 7 is connected to a surge tank 5. The surge tank 5 is a container-shaped portion interposed in the intake passage 4 between the throttle valve 6 and the cylinders of the engine 1. An intake manifold (intake manifold) that supplies intake air to each cylinder of the engine 1 is interposed between the surge tank 5 and the engine 1. The operating states of the fuel injection valve 2 and the throttle valve 6 are controlled by a control device 10.

[0012] The control device 10 is a computer (electronic control unit, ECU) that controls the combustion state of the engine 1 according to the open / closed state of the EGR valve 9, and has at least a processor (arithmetic processing unit) and a memory (storage device) built in. The contents of the control (control program) performed by the control device 10 are stored in the memory and executed by the processor. The control device 10 of this embodiment performs control to suppress fluctuations in the actual air-fuel ratio of the engine 1 when the opening degree of the EGR valve 9 (EGR opening degree) changes from a fully closed state to an open state. The fluctuations in the actual air-fuel ratio are suppressed by correcting the amount of fuel injection and the amount of intake air introduced into the cylinder.

[0013] 1, the control device 10 is provided with an estimation unit 11, a setting unit 12, and a control unit 13 as elements for implementing the above control. These elements are a convenient classification of the functions of the control device 10, and can be realized by software (programs) or hardware (electronic control circuits). Furthermore, these elements may be integrated into one piece of software or hardware, or may be distributed across multiple pieces of software or hardware.

[0014] The estimation unit 11 estimates the amount of remaining fresh air that is predicted to be unintentionally introduced from the EGR passage 7 into the cylinder of the engine 1 immediately after the EGR valve 9 is opened from a fully closed state. The remaining amount of fresh air is the amount (mass) of fresh air remaining in the EGR passage 7, and is one of the parameters used to set the correction amount of the fuel injection amount and the intake air amount when the EGR valve 9 is opened.

[0015] For example, if the EGR valve 9 is kept fully closed for a long period of time, the EGR passage 7 (specifically, the path from the EGR valve 9 to the downstream end of the EGR passage 7) should be filled with fresh air. Therefore, when the EGR valve 9 is subsequently opened, a large amount of fresh air remaining in the EGR passage 7 is first introduced into the surge tank 5, and the actual air-fuel ratio in the cylinder unintentionally becomes lean. Such fluctuations in the actual air-fuel ratio are temporary and are eliminated after all the remaining fresh air reaches the cylinder. However, in order to suppress such fluctuations in the actual air-fuel ratio, the fuel injection amount and the intake air amount must be corrected while the remaining fresh air is affecting the actual air-fuel ratio. The amount of remaining fresh air is used to determine the amount of these corrections.

[0016] The amount of remaining fresh air is estimated based on at least the volume of the EGR passage 7. The volume of the EGR passage 7 here is given as a constant determined according to the structure of the EGR passage 7, and is the volume from the EGR valve 9 to the downstream end of the EGR passage 7.

[0017] The above-mentioned remaining fresh air amount is preferably estimated taking into consideration the pressure and temperature of the EGR passage 7. For example, the higher the pressure of the EGR passage 7, the larger the estimated remaining fresh air amount is. Also, the lower the temperature of the EGR passage 7, the larger the estimated remaining fresh air amount is. The pressure and temperature of the EGR passage 7 may be detected by a pressure sensor and a temperature sensor installed inside the EGR passage 7, or may be estimated based on detection values ​​of sensors installed elsewhere (e.g., pressure in the surge tank, temperature in the surge tank, outside air pressure, outside air temperature, pressure in the intake passage, temperature in the intake passage, etc.).

[0018] The remaining fresh air amount is preferably estimated based on the elapsed time from the full closure of the EGR valve 9. The reason is that if the EGR valve 9 is in an open state for a long period of time, the remaining fresh air amount is 0, and it is only when the EGR valve 9 is in a fully closed state that the fresh air amount (i.e., the remaining fresh air amount thereafter) starts to increase.

[0019] Here, the volume of the EGR passage 7 is V, and the pressure correction coefficient set according to the pressure in the EGR passage 7 (from the EGR valve 9 to the downstream end of the EGR passage 7) is K. ATM The temperature correction coefficient set according to the temperature of the EGR passage 7 (from the EGR valve 9 to the downstream end of the EGR passage 7) is K TMP In addition, a time correction coefficient set according to the elapsed time from the full closure of the EGR valve 9 is K CL The remaining fresh air amount can be calculated based on the following formula 1. In this formula 1, the higher the pressure in the EGR passage 7 is, or the lower the temperature in the EGR passage 7 is, the larger the remaining fresh air amount is estimated to be. Note that, when the time correction coefficient K CL is a parameter used for calculating the remaining fresh air amount (a slightly smaller remaining fresh air amount) that should be taken into consideration when the EGR valve 9 is opened again in a comparatively short time after being fully closed. Residual fresh air amount=V×K ATM ×K TMP ×K CL … Formula 1

[0020] 2(A) to (C) are graphs illustrating the characteristics of the correction coefficient included in the formula 1. The pressure correction coefficient K ATM is set to 1 when the pressure in the EGR passage 7 is a predetermined pressure (for example, standard atmospheric pressure), and is set to a larger value as the pressure increases and to a smaller value as the pressure decreases. TMP is set to 1 when the temperature of the EGR passage 7 is a predetermined temperature (for example, standard atmospheric temperature), and is set to a smaller value as the temperature is higher and a larger value as the temperature is lower.

[0021] The time correction coefficient K shown in Figure 2(C) CL becomes 0 when the EGR opening changes from an open state to a fully closed state, increases as time elapses, and becomes 1 when the elapsed time is equal to or greater than a predetermined elapsed time. The predetermined elapsed time can be set according to the speed at which the residual fresh air accumulates in the EGR passage 7. For example, the predetermined elapsed time may be shortened as the amount of intake air of the engine 1 increases. The amount of intake air of the engine 1 may be calculated from the opening of the throttle valve 6, for example.

[0022] The setting unit 12 sets a correction amount for the amount of fuel injected from the fuel injection valve 2 or the amount of intake air passing through the throttle valve 6 when the EGR opening changes from a fully closed state to an open state. The correction amount is set to have an initial value whose absolute value is at least maximum immediately after the change in the EGR opening, and to decrease with time. A graph of the correction amount shows an inverse sawtooth wave (or sawtooth wave) in which the correction amount increases (or decreases) suddenly immediately after the change in the EGR opening, and then gradually decreases (or increases) to 0. Also, the correction amount is set so that the greater the change in the EGR opening, the faster the rate at which the absolute value decreases (the steeper the gradient).

[0023] 3A and 3B are graphs showing an example of characteristics related to the correction of the fuel injection amount. When the EGR opening degree changes from a fully closed state to an open state, the correction amount of the fuel injection amount is set so as to increase immediately after the EGR valve 9 opens and then gradually decrease. For example, the correction coefficient K F 3A, is set to change in an inverse sawtooth wave shape. In other words, the fuel injection amount is largely increased and corrected immediately after the EGR valve 9 is opened, and then the correction amount is linearly decreased.

[0024] FIG. 3B is a graph illustrating the change over time in the correction amount of the fuel injection amount. The solid line indicates the increase correction immediately after the EGR valve 9 is opened. The magnitude (absolute value) of the correction amount is maximum at the time when the correction is started (initial value) and becomes 0 when the correction time P has elapsed. Note that the area S of the hatched triangle (initial value F 1 and the correction time P) corresponds to the total correction amount that is increased when the EGR valve 9 is opened. 1 is a positive value.

[0025] E When the GR opening degree changes from a fully closed state to an open state, the correction amount of the intake air amount is set to decrease immediately after the EGR valve 9 opens and then to gradually increase. For example, the correction coefficient K A teeth ,ofThat is, the intake air amount is largely reduced immediately after the EGR valve 9 opens, and then the amount of correction increases linearly.

[0026] Sucking Air intake correction amount ( Reduction correction immediately after opening of EGR valve 9 )of The magnitude (absolute value) is maximum when the correction starts (initial value), and becomes 0 when the correction time Q has elapsed. Although not shown in the figure, Area of ​​triangle R (initial value A 1 and the correction time Q) corresponds to the total correction amount that is reduced when the EGR valve 9 is opened. 1 is a negative value. The correction time Q of the intake air amount may be the same as the correction time P of the fuel injection amount, or may be slightly different.

[0027] Strictly speaking, the correction amount does not have to be set to the initial value immediately after the EGR opening changes (the moment the EGR becomes fully closed). The absolute value of the correction amount may be increased rapidly so that the correction amount is set to the initial value within a very short time after the EGR opening changes (the moment the EGR becomes fully closed). ) inside If we use the hatched triangle in FIG. 1 to explain this, the position of the apex may be moved slightly backward (to the right in the drawing).

[0028] The setting unit 12 sets the correction amount so that the absolute value decreases faster as the change in the EGR opening becomes larger, i.e., as the target opening when the EGR opening changes from a fully closed state to an open state becomes larger. In other words, the slope of the correction amount that changes over the correction times P and Q is set to be steeper as the change in the EGR opening becomes larger. In other words, the correction times P and Q are shortened as the change in the EGR opening becomes larger. Note that, as shown in Figs. 3(A) and (B), )in Although the characteristic that the correction amount changes linearly is shown, the change in the correction amount does not need to be strictly linear, and the correction amount may change, for example, in a broken line or curved line.

[0029] The initial value of the correction amount may be set to a larger value as the change in the EGR opening amount increases. For example, the initial value F 1 The absolute value of the initial value may be set to a positive value with a larger absolute value as the opening degree of the opened EGR valve 9 increases. Also, the absolute value of the initial value may be set to a larger value as the outside air pressure increases. Alternatively, the absolute value of the initial value may be set to a larger value as the outside air temperature decreases. .first time Period A 1 The same applies to.

[0030] Regarding the correction times P and Q of the correction amount, these values ​​may be fixed values ​​set in advance, but preferably the larger the initial value of the correction amount, the shorter the correction time is, and the smaller the initial value of the correction amount, the longer the correction time is. For example, in setting the correction amount (increasing correction amount) shown by the solid line in FIG. 3(B), the correction time P is set so that the area S is constant regardless of the amount of change in the EGR opening. In other words, the correction time P is set so that the total correction amount (area S) is maintained regardless of the magnitude of the EGR opening. . Sucking The same applies to the setting of the correction amount (reduction correction amount) of the intake air amount.

[0031] Moreover, the total correction amount (area S, R) may be set to a value corresponding to the remaining fresh air amount estimated by the estimation unit 11. That is, the areas S, R when the EGR valve 9 is open may be set according to the remaining fresh air amount. For example, the areas S, R may be increased as the remaining fresh air amount increases, thereby setting the absolute value of the total correction amount when the EGR valve 9 is open to a large value.

[0032] In this embodiment, the total correction amount (area S, R) is set according to the residual fresh air amount estimated by the estimation unit 11, and the initial value is set according to the change in the EGR opening. Then, when gradually decreasing the correction amount from the initial value, the decrease speed (correction time P, Q) is set so that the correction amount becomes the previously set total correction amount (area S, R). When changing the total correction amount (area S, R) according to the elapsed time from the full closure of the EGR valve 9 or the pressure and temperature of the EGR passage 7, the total correction amount (area S, R) may be changed by changing only the decrease speed (correction time P, Q) without changing the relationship between the change in the EGR opening and the initial value. However, it is preferable to change the total correction amount (area S, R) by changing the relationship between the change in the EGR opening and the initial value, that is, to change the total correction amount (area S, R) to a larger value. As described above, in FIG. 3(B ) inside The triangle with area S is shown in the hatched area. (or area R ) As a method for changing the value, the following methods can be considered. Change only the length of the base (do not change the height) Change the height only (do not change the length of the base) Change both the base length and the height

[0033] The control unit 13 suppresses fluctuations in the actual air-fuel ratio of the engine 1 by implementing control to reflect the correction amount set by the setting unit 12 in the actual fuel injection amount and intake air amount. In this embodiment, the following controls can be implemented. These controls are selected and used in combination depending on the operating state of the engine 1, the open / close state of the EGR valve 9, instructions from an operator, etc. - When the EGR valve 9 is opened, the fuel injection amount is increased. - When the EGR valve 9 is opened, the intake air volume is reduced and corrected.

[0034] [2. Effect] Figure 4 13(A) to 13(C) are graphs for explaining the functions and effects of the embodiment. Figure 4 (A) is the EGR opening, Figure 4(B) is the time correction coefficient K used to calculate the residual air volume CL The change over time is also shown. Figure 4 (C) is the correction coefficient K set when correcting the fuel injection amount. F The change over time is shown.

[0035] Time T 0 When the EGR opening changes from a fully closed state to an open state, the time correction coefficient K CL The value of is referenced. 0 Time correction factor K CL The value of the pressure correction coefficient is 1. number K ATM and temperature compensation number K TMP Based on these values, the remaining fresh air amount is calculated in the estimation unit 11 according to the formula 1.

[0036] The setting unit 12 sets the time T 0 The correction amounts of the fuel injection amount and the intake air amount are set according to the amount of change in the EGR opening in the EGR opening. For example, the fuel injection amount is corrected to be increased, and the intake air amount is corrected to be decreased. The setting unit 12 sets the initial value (absolute value) of the correction amount to be larger and sets the reduction rate (the reduction rate of the absolute value of the correction amount) to be faster as the amount of change in the EGR opening increases. In other words, the larger the amount of change in the EGR opening, the steeper the change gradient of the correction amount becomes, and the shorter the correction time P of the fuel injection amount is.

[0037] Figure 4 Time T in (C) 0 ~T 2 The correction coefficient K shown by the solid line in F The graph of Figure 4 This shows the time-dependent variation when the EGR opening shown in (A) changes as shown in the solid line graph. Figure 4 Time T in (C) 0 ~T 2 The correction coefficient K shown by the dashed line in F The graph of Figure 4 This shows the time-dependent variation when the EGR opening shown in (A) changes as shown in the dashed line graph. Figure 4The solid line graph and the dashed line graph shown in (A) are assumed to be under the same conditions except for the EGR opening.

[0038] The total correction amount may be set to a value according to the remaining fresh air amount. For example, at the first time T 0 The total correction amount is set according to the amount of remaining fresh air in the EGR opening. Next, an initial value is set according to the amount of change in the EGR opening. After that, a correction time P is set that is proportional to the value obtained by dividing the total correction amount by the initial value. By using this method, the correction amount can be reduced at a gradient (decrease rate) according to the amount of change in the EGR opening. Figure 4 Time T in (C) 0 ~T 2 The total correction amount according to the solid line graph in is the same as the total correction amount according to the broken line graph.

[0039] Time T 3 When the EGR opening changes from the open state to the fully closed state, the time correction coefficient K CL teeth, Figure 4 As shown in (B), at time T 3 The predetermined elapsed time is set to 0 at the beginning of the EGR passage 7, and then gradually increases to return to 1 after a predetermined elapsed time. As described above, the predetermined elapsed time may be changed according to the speed at which the remaining fresh air accumulates in the EGR passage 7. For example, when the speed at which the remaining fresh air accumulates in the EGR passage 7 is slow, Figure 4 As shown by the solid line in (B), the predetermined elapsed time is time T 3 ~Time T 6 When the speed at which the remaining fresh air accumulates in the EGR passage 7 is fast, the predetermined elapsed time is set to time T 3 ~Time T 4 Hereinafter, the predetermined elapsed time is set as time T 3 ~Time T 6 The case where the above is set will be described.

[0040] Time T 5 When the EGR opening changes from a fully closed state to an open state, the time correction coefficient K CL The EGR opening at this time is0 ~T 3 On the other hand, at time T 5 Time correction factor K CL Since the value of is less than 1, the remaining fresh air volume calculated by Equation 1 is 0 Therefore, the total correction amount set according to the residual air volume is also small. Figure 4 Time T in (C) 5 ~Time T 7 Correction factor K in F The graph of time T 0 ~Time T 2 Correction factor K in F The waveform is a reverse sawtooth wave with a smaller size than that of the graph in (a). 3 ~Time T 4 If you set it as above, the time correction factor K CL Since the value of is 1, at time T 0 ~Time T 2 Correction factor K in F The graph is similar to that of

[0041] [3. Effects] (1) The control device 10 (engine control device) of this embodiment is provided with a setting unit 12 and a control unit 13. The setting unit 12 sets a correction amount for the fuel injection amount injected from the fuel injection valve 2 or the intake air amount passing through the throttle valve 6 when the EGR opening changes between a fully closed state and an open state. The control unit 13 reflects the correction amount in the fuel injection amount or the intake air amount to suppress fluctuations in the actual air-fuel ratio of the engine 1. In addition, the correction amount is set to take an initial value whose absolute value is maximized immediately after the EGR opening changes, and the absolute value decreases over time, and is set so that the rate at which the absolute value decreases increases as the amount of change in the EGR opening increases.

[0042] Immediately after the EGR opening changes from the fully closed state to the open state, the actual air-fuel ratio temporarily becomes lean because the remaining fresh air in the EGR passage 7 flows into the cylinder. On the other hand, according to this embodiment, by performing an increase correction of the fuel injection amount or a decrease correction of the intake air amount, it is possible to prevent the actual air-fuel ratio from becoming lean.

[0043] Also, the amount of remaining fresh air in the EGR passage 7 is greater immediately after the change in the EGR opening degree, and decreases with time. At this time, if the change in the EGR opening degree is large, the speed at which the remaining fresh air in the EGR passage 7 flows into the cylinder is faster, so the rate at which the remaining fresh air in the EGR passage 7 decreases is faster. On the other hand, according to this embodiment, the absolute value of the correction amount is set to decrease faster as the change in the EGR opening degree is larger, so that the correction amount can be set according to the actual change in the remaining fresh air. Therefore, the actual air-fuel ratio of the engine 1 is more likely to be maintained at the desired target air-fuel ratio, and the fluctuation of the actual air-fuel ratio due to the opening and closing of the EGR valve 9 can be suppressed. In other words, a correction appropriate to the inflow speed of the remaining fresh air into the cylinder can be performed, and the fluctuation of the actual air-fuel ratio can be efficiently suppressed.

[0044] (2) In this embodiment, the greater the change in the EGR opening, the greater the absolute value of the initial correction amount can be set. As the change in the EGR opening becomes greater, all of the remaining fresh air in the EGR passage 7 flows into the cylinder in a short time, which makes it easier for a sudden change (rise) in the actual air-fuel ratio to occur immediately after the change in the EGR opening. However, by setting the correction amount in this way, it is possible to suppress a sudden change (rise) in the actual air-fuel ratio.

[0045] (3) In this embodiment, the higher the outside air pressure, the larger the absolute value of the total correction amount can be set. In an environment where the outside air pressure is high, the mass of the remaining fresh air in the EGR passage 7 increases. Therefore, by setting the absolute value of the total correction amount to a large value, a correction commensurate with the amount of remaining fresh air flowing into the cylinder can be performed, and fluctuations in the actual air-fuel ratio can be efficiently suppressed.

[0046] In this embodiment, the lower the outside air temperature, the larger the absolute value of the total correction amount can be set. In a low outside air temperature environment, the mass of the remaining fresh air in the EGR passage 7 increases. Therefore, by setting the absolute value of the total correction amount to a large value, a correction commensurate with the amount of remaining fresh air flowing into the cylinder can be performed, and fluctuations in the actual air-fuel ratio can be efficiently suppressed.

[0047] (4) The control device 10 of this embodiment is provided with an estimation unit 11. The estimation unit 11 estimates the amount of remaining fresh air introduced from the EGR passage 7 into the cylinder of the engine 1 when the EGR valve 9 is opened, based on at least the volume of the EGR passage 7. The absolute value of the total correction amount when the EGR valve 9 is opened is set to a larger value as the amount of remaining fresh air increases. With this setting, a correction commensurate with the inflow amount of remaining fresh air can be implemented, and fluctuations in the actual air-fuel ratio can be efficiently suppressed.

[0048] (5) In this embodiment, the remaining fresh air amount is estimated based on the elapsed time from the full closure of the EGR valve 9. For example, as shown in FIG. 2C, a time correction coefficient K CL is set. This value is reflected in the remaining fresh air amount as shown in Equation 1. In this way, by considering the elapsed time since the EGR valve 9 was fully closed, the increase in the remaining fresh air amount due to the replacement of the EGR gas with fresh air can be accurately grasped, and the estimation accuracy of the remaining fresh air amount can be improved. Therefore, the effect of suppressing the fluctuation of the actual air-fuel ratio can be improved.

[0049] (6) In this embodiment, the higher the pressure in the EGR passage 7, the larger the estimated residual fresh air amount is. For example, as shown in FIG. 2A, the higher the pressure in the EGR passage 7, the larger the estimated pressure correction coefficient K ATM is set to a large value. This value is reflected in the remaining fresh air amount as shown in Equation 1. In this way, by taking the pressure of the EGR passage 7 into consideration, the estimation accuracy of the remaining fresh air amount can be further improved, and the effect of suppressing fluctuations in the actual air-fuel ratio can be enhanced.

[0050] (7) In this embodiment, the lower the temperature of the EGR passage 7, the larger the estimated residual fresh air amount is. For example, as shown in FIG. 2B, the lower the temperature of the EGR passage 7, the smaller the temperature correction coefficient K TMP is set to a large value. This value is reflected in the remaining fresh air amount as shown in Equation 1. In this way, by taking the temperature of the EGR passage 7 into consideration, the estimation accuracy of the remaining fresh air amount can be further improved, and the effect of suppressing fluctuations in the actual air-fuel ratio can be enhanced.

[0051] [4.Other] The above embodiment is merely illustrative, and is not intended to exclude various modifications or application of techniques not explicitly stated in the embodiment. Each configuration of the embodiment can be modified in various ways without departing from the spirit of the embodiment. Furthermore, each configuration of the embodiment can be selected as necessary, or can be combined appropriately.

[0052] In the above embodiment, the control device 10 including the estimation unit 11 is illustrated, but the estimation unit 11 may be omitted if the correction amount based on the amount of remaining fresh air is not set. At least when setting the correction amount as shown in FIG. 3(B) and FIG. 4(B), the correction amount is set so that the absolute value of the correction amount decreases faster (so that the gradient becomes steeper) as the amount of change in the EGR opening becomes larger, so that a correction appropriate to the inflow speed of the remaining fresh air into the cylinder can be performed, and the same effect as the above embodiment can be achieved. In the above embodiment, the correction when the EGR opening changes from a fully closed state to an open state has been described, but the same correction may also be performed when the EGR opening changes from an open state to a fully closed state. In this case, the positive and negative of the correction amount are reversed. [Explanation of symbols]

[0053] 1 Engine 2 Fuel Injection Valve 3 Exhaust passage (exhaust system) 4. Intake passage (intake system) 5. Surge Tank 6 Throttle valve 7 EGR passage (exhaust recirculation passage) 8 EGR cooler (exhaust gas recirculation cooling device) 9. EGR valve (exhaust gas recirculation valve) 10 Control device (engine control device) 11 Estimation part 12 Setting section 13 Control section

Claims

1. An engine control device that controls a combustion state of an engine in accordance with an open / close state of an EGR valve provided in an EGR passage of the engine, a setting unit that sets a correction amount for a fuel injection amount injected from the fuel injection valve or an intake air amount passing through the throttle valve when the EGR opening degree changes from a fully closed state to an open state; a control unit that reflects the correction amount in the fuel injection amount or the intake air amount to suppress a fluctuation in an actual air-fuel ratio of the engine, The correction amount is set to have an initial value whose absolute value is maximum immediately after the change in the EGR opening, and to decrease in absolute value over time, and is set so that the rate of decrease in the absolute value becomes faster as the change in the EGR opening becomes larger. An engine control device comprising:

2. The setting unit sets the absolute value of the initial value to a larger value as the amount of change in the EGR opening degree when the EGR opening degree is changed from a fully closed state to an open state increases.

2. The engine control device according to claim 1.

3. an estimation unit that estimates a remaining amount of fresh air in the EGR passage when the EGR opening is in a fully closed state; The setting unit sets the absolute value of the total correction amount when the EGR valve is opened to a larger value as the remaining fresh air amount increases.

3. The engine control device according to claim 1 or 2.

4. The estimation unit estimates the residual fresh air volume based on the elapsed time from when the EGR valve was fully closed.

4. The engine control device according to claim 3.

5. The estimation unit estimates the remaining fresh air amount to be larger as the pressure in the EGR passage increases.

5. The engine control device according to claim 3 or 4.

6. The estimation unit estimates the remaining fresh air amount to be larger as the temperature of the EGR passage decreases.

6. The engine control device according to claim 3, wherein the first and second inputs are connected to the first and second inputs.

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