JP2013032732A - Control device for egr valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such the problem that there is a possibility that an EGR rate in actual intake does not agree with a target EGR rate by a recirculated exhaust amount control based on only the flow rate of the recirculated exhaust gas when passing through an EGR valve.SOLUTION: A control device 10 includes an EGR valve 14 and a control unit 20. The control unit 20 calculates the predicted value of a recirculated exhaust gas amount Mwhen passing through the intake valve 16 of an internal combustion engine 22, on the basis of a recirculated exhaust amount Mand its change amount δMwhen passing through the EGR valve 14. The control unit: calculates an evaluation value on the basis of the difference between the predicted value and a target value Mof the recirculated exhaust amount Mof the recirculated exhaust gas when passing through the intake valve 16, and the change amount δMof the recirculated exhaust gas when passing through the EGR valve 14; obtains a change amount δMas an optimal value that gives the minimum of the evaluated value under the restricted conditions of the recirculated exhaust amount Mand its change amount δMof the gas when passing through the EGR valve 14 and of the recirculated exhaust amount Mof the gas when passing through the intake valve 16; and thereby determines the opening of the EGR valve 14.

Description

  The present invention relates to a control device for an EGR valve.

  2. Description of the Related Art A technique called exhaust gas recirculation (EGR) that reduces air pollutants in exhaust gas by returning a part of the exhaust gas discharged from the internal combustion engine to the intake side has been known. By mixing a part of the exhaust gas into the intake air, the combustion temperature in the combustion chamber of the internal combustion engine is suppressed, thereby suppressing the generation of air pollutants such as nitrogen oxide (NOx) that increases as the combustion temperature increases. It becomes possible. In addition, the pumping loss during low load operation can be reduced, and the fuel consumption can be improved.

  If the proportion of exhaust gas in the intake air is too low, the effect of reducing air pollutants will be reduced. On the other hand, if the proportion of exhaust air in the intake air is excessively high, it may lead to a phenomenon called misfire that does not cause a combustion reaction in the internal combustion engine. . Therefore, a target value (target EGR rate) and an upper limit value (misfire limit EGR rate) are determined for the EGR rate indicating the ratio of exhaust gas in intake air.

  In order to adjust the EGR rate to the target EGR rate, an EGR valve that adjusts the flow rate of exhaust gas that is returned to the intake side (hereinafter referred to as recirculated exhaust gas) is used. The EGR valve is provided in an exhaust gas recirculation pipe that connects the exhaust pipe and the intake pipe, and the amount of recirculated exhaust gas flowing through the exhaust gas recirculation pipe is adjusted by adjusting the opening thereof.

  For controlling the opening degree of the EGR valve, for example, in Patent Document 1, the recirculation exhaust amount when passing through the EGR valve is obtained by measurement or the like, and the opening degree of the EGR valve is controlled based on this recirculation exhaust amount. For example, the target recirculation exhaust amount is obtained from the target EGR rate and the fresh air amount, and the opening degree of the EGR valve is controlled so that the recirculation exhaust amount passing through the EGR valve becomes the target recirculation exhaust amount.

JP 2007-113563 A JP 2007-32462 A

  By the way, the exhaust gas recirculation amount at the time of passing through the EGR valve is not necessarily maintained and flows into the internal combustion engine. For example, during the transition period of EGR control, the exhaust gas recirculation amount that passes through the EGR valve may differ from the exhaust gas recirculation amount that flows into the internal combustion engine. Further, for example, the flow of the recirculated exhaust gas is disturbed by the inflow pressure of the fresh air amount, the opening / closing cycle of the intake valve of the internal combustion engine, and the like, and the exhaust gas recirculation amount actually flowing into the internal combustion engine may be different from that when passing through the EGR valve. In these cases, even if the recirculation exhaust amount when passing through the EGR valve is reduced to the target recirculation exhaust amount based on the target EGR rate, the flow rate may be different from the target recirculation exhaust amount when the internal combustion engine flows in. As described above, when the recirculated exhaust gas amount is controlled based only on the flow rate when passing through the EGR valve, the EGR rate of the intake air actually flowing into the internal combustion engine may be different from the target EGR rate.

  The present invention relates to a control device for an EGR valve. The control device includes an EGR valve that adjusts a recirculation exhaust amount for mixing a part of the exhaust gas of the internal combustion engine with the intake air. Further, a predicted value of the recirculation exhaust amount when passing through the intake valve for adjusting the intake amount flowing into the internal combustion engine is calculated based on the recirculation exhaust amount when passing through the EGR valve and its change amount, and A control unit is provided that calculates an evaluation value obtained based on a difference between the target value of the recirculation exhaust amount and the predicted value and a change amount of the recirculation exhaust when passing through the EGR valve. Further, the control unit gives a minimum value of the evaluation value in a range satisfying a constraint condition regarding a recirculation exhaust amount when the EGR valve passes and a change amount thereof and a recirculation exhaust amount when the intake valve passes. The amount of change in the recirculated exhaust gas is acquired as an optimum value, and the opening degree of the EGR valve is determined based on the optimum value.

  The present invention also relates to a control device for an EGR valve. The control device includes an EGR valve that adjusts a recirculation exhaust amount for mixing a part of the exhaust gas of the internal combustion engine with the intake air. Further, a predicted value of the recirculation exhaust amount when the intake valve passes is calculated based on the recirculation exhaust amount when the intake valve passes to adjust the amount of intake air flowing into the internal combustion engine and the change amount thereof. A control unit is provided for calculating an evaluation value obtained based on a difference between the target value of the recirculation exhaust amount and the predicted value and the amount of change. Further, the control unit converts the first restriction condition for the recirculation exhaust amount when the EGR valve passes and the change amount thereof into the second restriction condition for the recirculation exhaust amount and the change amount when the intake valve passes, A change amount of the recirculation exhaust gas when the intake valve passes that gives the minimum value of the evaluation value in a range satisfying the second constraint condition is acquired as an optimum value, and the optimum value is obtained as a recirculation exhaust gas amount when the EGR valve passes. Convert to change. Further, the opening degree of the EGR valve is determined based on the change amount of the recirculation exhaust amount when passing through the converted EGR valve.

  The present invention also relates to a control device for an EGR valve. The control device includes the EGR valve that adjusts the recirculation exhaust amount that mixes a part of the exhaust gas of the internal combustion engine with the intake air, and the variable of the optimization problem that includes a variable coefficient that is generated to obtain the opening degree of the EGR valve. And a controller that converts the coefficient into a constant coefficient and solves the optimization problem after the conversion to obtain the opening degree of the EGR valve.

  According to the present invention, the controllability of EGR control is improved as compared with the prior art.

It is a figure which illustrates the control apparatus of the EGR valve which concerns on this embodiment. It is a figure explaining model prediction control. It is a figure explaining the recirculation exhaust amount at the time of intake valve passing.

  FIG. 1 illustrates a control device for an internal combustion engine according to the present embodiment. The control device 10 includes a throttle valve 12, an EGR valve 14, an intake valve 16, an intake pressure sensor 18, a control unit 20, a throttle position sensor 24, and an EGR valve position sensor 25. Note that the control device 10 according to the present embodiment is mounted on a vehicle using, for example, the internal combustion engine 22 as a drive source.

  The throttle valve 12 includes a valve body capable of adjusting the flow rate of intake air (fresh air) supplied to the internal combustion engine 22, and is configured of, for example, a butterfly valve. The throttle valve 12 is driven by driving means such as a motor 21, and the opening degree of the throttle valve 12 changes according to this driving. The amount of intake air that passes through the throttle valve 12 is adjusted in accordance with this change in opening.

  The throttle valve 12 can be provided in an intake pipe 28 that feeds intake air into the combustion chamber 26 of the internal combustion engine 22. In the present embodiment, the throttle valve 12 is provided between an air cleaner 30 provided near the air intake port 29 of the intake pipe 28 and a surge tank 32 provided downstream thereof.

  Further, the throttle position sensor 24 transmits the opening degree of the throttle valve 12 to the control unit 20. For example, the throttle position sensor 24 measures the rotation speed of the motor 21, calculates the opening degree of the throttle valve 12 from the rotation speed, and transmits the opening degree to the control unit 20.

  The EGR valve 14 includes a valve body that can adjust a recirculation exhaust amount that recirculates a part of the exhaust discharged from the internal combustion engine 22 to the intake side, and includes, for example, a needle valve. The EGR valve 14 is driven by driving means such as a motor 36, and the opening degree of the EGR valve 14 changes according to this driving. The recirculation exhaust amount passing through the EGR valve 14 is adjusted in accordance with the change in the opening degree.

  Further, the EGR valve 14 can be provided in the exhaust gas recirculation pipe 40. For example, in the present embodiment, the EGR valve 14 is provided downstream (intake pipe side) from the EGR cooler 42 that cools the recirculated exhaust gas flowing through the exhaust recirculation pipe 40.

  The exhaust gas recirculation pipe 40 functions as a recirculation path for recirculating a part of the exhaust gas to the intake side. For example, in the present embodiment, the exhaust gas recirculation pipe 40 connects the exhaust pipe 38 and the intake pipe 28. In the present embodiment, the exhaust gas recirculation pipe 40 is connected upstream of the catalyst 44 for removing air pollutants in the exhaust gas in the exhaust pipe 38 and downstream of the surge tank 32 of the intake pipe 28. Has been.

  Further, the EGR valve position sensor 25 transmits the opening degree of the EGR valve 14 to the control unit 20. For example, the EGR valve position sensor 25 measures the rotation speed of the motor 36, calculates the opening degree of the EGR valve 14 from the rotation speed, and transmits the opening degree to the control unit 20.

  The intake pressure sensor 18 includes a sensor capable of measuring the intake pressure in the surge tank 32 and transmitting it to the control unit 20. The intake pressure sensor 18 can be composed of, for example, a semiconductor pressure sensor. In the present embodiment, the intake pressure sensor 18 can convert an absolute pressure with an absolute vacuum of 0 [kPa] into an electric signal and transmit the pressure signal to the control unit 20.

  The intake valve 16 introduces intake air mixed with fresh air sent via the throttle valve 12 and recirculated exhaust gas sent via the EGR valve 14 from the intake pipe 28 to the combustion chamber 26 of the internal combustion engine 22. The intake valve 16 is constituted by a needle valve, for example. In the present embodiment, the intake valve 16 is provided so as to close the intake port 27 of the internal combustion engine 22 in the closed state. The intake valve 16 may be driven by a variable valve system that can adjust the lift (opening), or may be driven by a valve system with a fixed lift.

  The control unit 20 includes a calculation processing unit for calculating information and a storage unit for storing information. The arithmetic processing unit can receive and process information received from measuring instruments such as the intake pressure sensor 18, the throttle valve position sensor 24, and the EGR valve position sensor 25, and can also perform arithmetic processing on the motor 21 for the throttle valve 12 and the EGR valve 14. It is comprised from the apparatus which can transmit an opening degree instruction | command with respect to peripheral devices, such as the motor 36. FIG. For example, the control unit 20 includes a microcomputer. This microcomputer can be composed of, for example, an electronic control unit (ECU) mounted on a vehicle.

  In addition, the opening degree of the throttle valve 12 corresponding to the fresh air amount, the opening degree of the EGR valve 14 corresponding to the recirculation exhaust amount, and the like are stored as a function or a map (table) in the storage unit. Further, the storage unit stores an air-fuel ratio and a target EGR rate corresponding to a drive mode (eco mode, power mode, etc.) for the internal combustion engine, various mathematical formulas used for opening control of the EGR valve 14 described later, and the like. . The storage unit may be any device capable of storing such information, and may be configured by one or a combination of a ROM, a RAM, an EPROM, a hard disk device, and the like.

  The opening degree control of the EGR valve 14 by the control unit 20 will be described. The control unit 20 determines the opening degree of the EGR valve 14 based on the recirculation exhaust amount that passes through the intake valve 16 (flows into the internal combustion engine 22). Specifically, a mathematical expression representing a relationship from the recirculation exhaust amount when passing through the intake valve to the opening degree of the EGR valve 14 is created, and the opening degree of the EGR valve 14 is determined based on this mathematical expression.

  The control unit 20 obtains the opening degree by performing model predictive control when the opening degree of the EGR valve 14 is controlled. In model predictive control, in a discrete time system in which the time is discretized in units of control steps, manipulated variables (input variables, opening and flow rate changes in EGR valve control, etc.) and controlled variables (output variables, flow rate in EGR valve control, etc.) ) Is used to create a model expression related to the dynamic characteristics (dynamics) and constraints of the system to be controlled, and a predicted value until the controlled variable converges to the target value is calculated based on this model expression. Further, the operation amount of the current value (the most recent operation amount) is determined according to the predicted value.

The basic procedure of model predictive control is shown below. Moreover, the schematic diagram of model prediction control is shown in FIG.
Procedure 1: Obtain the current value of the controlled variable.
Procedure 2: A set value that is a target value of the control amount is acquired.
Procedure 3: A target trajectory (reference trajectory) in the prediction interval [t + 1, t + N] is obtained. The target trajectory is an ideal trajectory where the control amount reaches the set value in the prediction interval. The target trajectory is set in consideration of both control responsiveness and robustness (stability). For example, the target trajectory is obtained from a model formula using dead time and first-order delay.
Procedure 4: The optimal value u (t)... U (t + N−1) of the manipulated variable is obtained so that the predicted value of the controlled variable is as close as possible to the reference trajectory in the prediction interval [t + 1, t + N].
Procedure 5: Let u (t) be the current operation amount.
Procedure 6: Move to the next control step t + 1 and return to Procedure 1.

  In the procedure 4, for example, an evaluation function is used as a method for bringing the predicted value of the controlled variable as close as possible to the reference trajectory. For example, an evaluation function J as shown below (Formula 1) is used.

Here, A, B, C, and D represent coefficients. Also, z ₀ (t) and x ₀ (t) represent initial values of control amounts, Z _ref represents target values (target trajectory values), Z and X represent control amounts, and U represents manipulated variables. Q and R represent weighting matrices (weighting coefficient matrices). In the model predictive control, the operation amount U that minimizes the evaluation function J is the optimum value of the operation amount. In this case, the first term of the evaluation function J has an effect of bringing the predicted value and the target value closer to each other, and the second term has an effect of suppressing a rapid change in the operation amount.

As one method for obtaining the manipulated variable U for minimizing the evaluation function J, for example, there is a method for obtaining a gradient に 関 す る_U related to the manipulated variable U of the evaluation function J. In executing this method, the evaluation function J is transformed into a form in which U is summarized as shown in the following (Formula 2).

However, H, F, and Y are coefficients, and P (t) is a variable that does not depend on U. The gradient に 関 す る_U related to the manipulated variable _U is obtained for (Formula 2). Specifically, the following (Formula 3) is obtained.

In (Equation 3), the manipulated variable U that satisfies _{Ｕ U} = 0 gives a minimum value to the evaluation function J. That is, the operation amount U at this time becomes an optimum value.

In some cases, restrictions may be imposed on the operation amount U and the control amount X. For example, a range of values that can be taken by the operation amount U may be defined. In this case, there may be a case where there is no U that satisfies ∇ _U = 0 in the range (allowable range) of the operation amount U (that is, the minimum point is not within the allowable region). In such a case, the minimum value in the allowable region can be obtained by using Lagrange multiplier theory in quadratic programming.

  Next, a model formula for obtaining the operation amount of the EGR valve 14 will be specifically described. As described above, the EGR valve 14 is a means for adjusting the recirculation exhaust amount, and its final purpose is to control the recirculation exhaust amount when it flows into the internal combustion engine 22, that is, when it passes through the intake valve 16. Therefore, in the present embodiment, an equation is created that defines the relationship between the opening degree of the EGR valve 14 and the recirculation exhaust amount when passing through the intake valve.

  Here, since the opening degree of the EGR valve 14 and the recirculation exhaust amount when passing through the EGR valve can be converted by a conversion formula described later, in this embodiment, instead of using the opening degree of the EGR valve 14 as a main parameter. The recirculation exhaust amount when passing through the EGR valve is used as a main parameter.

  As described above, in the present embodiment, the dynamics (dynamic characteristics) model equation of the EGR valve 14 uses the recirculation exhaust amount passing through the EGR valve 14 and the recirculation exhaust amount passing through the intake valve 16 as main parameters. .

  The storage unit of the control unit 20 stores two dynamic characteristic formulas, that is, a dynamic characteristic formula for the EGR valve 14 and a dynamic characteristic formula for the intake valve 16 (at the time of inflow of the internal combustion engine). The former dynamic characteristic formula is shown in (Formula 4), and the latter dynamic characteristic formula is shown in (Formula 5).

Here, in (Expression 4), t represents the current time, k represents the number of control steps (k = 0,... N−1), and h represents the control step period (for example, 8 ms). In addition, the control step in this embodiment shall point out the timing which the control part 20 sends an opening degree command to the motor 36 which drives the EGR valve 14. M _egr represents the recirculation exhaust amount passing through the EGR valve 14. In (Equation 4), this parameter is the controlled variable. δM _egr represents a change in flow rate in one step of the recirculation exhaust amount passing through the EGR valve 14. In (Equation 4), this parameter is the manipulated variable.

Further, regarding (Equation 5), M _egr ^cyl represents the recirculation exhaust amount when passing through the intake valve 16. D (t) represents a dead time, e represents a natural logarithm, and T (t) represents a time constant.

(Formula 5) will be described. FIG. 3 shows how the recirculated exhaust gas that has passed through the EGR valve 14 passes through the intake valve 16. Here, a state in which the recirculated exhaust gas having a flow rate M _egr (t0) that has passed through the EGR valve 14 at the current time t0 reaches the intake valve 16 (flows into the internal combustion engine 22) is shown. The recirculated exhaust gas that has passed through the EGR valve 14 passes through the intake valve 16 via the exhaust recirculation pipe 40 and the intake pipe 28. At this time, the recirculated exhaust amount passing through the intake valve 16 gradually approaches the flow rate M _egr (t) with a time delay. This flow rate change is approximated by a dead time + first order lag system.

The dead time d (t) is a time during which no change occurs, and represents a delay until the influence of the input is reflected in the output. The first-order lag system is a model formula that determines the rate of increase until the recirculated exhaust amount reaches the flow rate M _egr (t0). Specifically, the rate of increase is 1−e ^{−t / T (t0)} using the natural logarithm e. ⁾ In the present embodiment, the dead time d (t) and the time constant T (t) are represented as parameters that change according to the current time t. For example, when the rotational speed of the internal combustion engine 22 increases and the opening / closing cycle of the intake valve 16 becomes faster, the amount of intake air drawn into the internal combustion engine 22 increases. Along with this, the dead time d (t) and the time constant T (t) are shortened. In the present embodiment, the correspondence relationship between the rotational speed of the internal combustion engine 22 and the dead time and time constant is stored in the storage unit in the form of a function or a map (table, table) in advance and at the current time t for each control step. Calling the corresponding dead time and time constant.

  Thus, in the (Equation 5) modeled by the dead time + first-order lag system, the first term on the right side represents the remainder of the recirculation exhaust amount from the previous control step, and the second term is derived from the EGR valve 14. The amount of recirculated exhaust gas that has reached the intake valve 16 is represented.

Further, the following conditional expressions (Formula 6) to (Formula 8) are given with respect to the recirculation exhaust amount M _egr when passing through the EGR valve 14 and the recirculation exhaust amount M _egr ^cyl when flowing into the internal combustion engine.

Here, regarding (Equation 6), M _egr ^min and M _egr ^max represent the minimum value and the maximum value of the recirculation exhaust amount when passing through the EGR valve 14, respectively. Further, M _egr ^min and M _egr ^max can be obtained from the following (Equation 9) and (Equation 10), respectively.

Here, c _min and d _min each represent a coefficient when the opening degree of the EGR valve 14 is minimum, and c _max and d _max each represent a coefficient when the opening degree of the EGR valve 14 is maximum. P _m represents the pressure in the intake section. These values can be obtained in advance by actual measurement or the like.

In (Expression 7), β ^upper represents the upper limit value of the EGR rate. For example, an EGR rate that is likely to cause misfire of the internal combustion engine is set. Further, _Mc represents the total intake amount (new air + recirculation exhaust amount) passing through the intake valve 16.

Further, in (Equation 8), δM _egr ^min and δM _egr ^max represent the minimum value and the maximum value of the flow rate change per control step with respect to the recirculation exhaust amount when passing through the EGR valve 14, respectively. Furthermore, δM _egr ^min and δM _egr ^max can be obtained from the following (Equation 11) and (Equation 12), respectively.

Here, δc _min and δd _min each represent a change in coefficient corresponding to the maximum closing speed of the EGR valve 14, and δc _max and δd _max each represent a change in coefficient corresponding to the maximum opening speed. These values can be obtained in advance by actual measurement or the like.

  Furthermore, an evaluation function J relating to (Formula 4) and (Formula 5), which are dynamic characteristic formulas, is shown in the following (Formula 13).

Here, q and r represent weighting coefficients, and M _egr ^{cyl, ref} represents a target value of the recirculation exhaust amount that passes through the intake valve 16.

The control unit 20 performs an operation that minimizes the value (evaluation value) of the evaluation function (Equation 13) related to the dynamic characteristic equations (Equations 4 and 5) under the restriction by the constraint condition equations (Equations 6 to 8). The optimum value of the quantity δM _egr is determined. The optimum value of the manipulated variable can be obtained by transforming the evaluation function into a form in which the manipulated variable is summarized as in (Expression 2) described above. Hereinafter, a procedure for modifying (Formula 13) will be described.

  When (Formula 13) is converted into a vector display, the following (Formula 14) is obtained.

The vectors Z, Z _ref , Q, U, and R in (Expression 14) are respectively expressed as (Expression 15) to (Expression 19) below.

  Further, when dynamic expressions (Formula 4) and (Formula 5) are displayed as vectors, they are expressed as (Formula 20) and (Formula 21) below.

In (Equation 20), x ₀ (t) represents an initial value, and x ₀ (t) = M _egr (t−h). In (Expression 21), z ₀ (t) represents an initial value, and z ₀ (t) = M _egr ^cyl (t + d (t)). Further, the vectors X, A, and B in (Expression 20) and the vectors C (t) and D (t) in (Expression 21) are expressed as the following (Expression 22) to (Expression 25).

  Further, (Expression 6) to (Expression 8) which are constraint condition expressions are displayed as vectors as shown in (Expression 26) to (Expression 28) below, respectively.

X _min and X _max in (Equation 26) are expressed as (Equation 29) below.

U _min and U _max in (Equation 27) are expressed as (Equation 30) below.

Also, Z _upper in (Equation 28) is expressed as (Equation 31) below.

  Next, the evaluation function (formula 14) converted to vector display is summarized for U. From (Equation 20) and (Equation 21) which are dynamic characteristic equations, (Equation 14) can be transformed as (Equation 32) below.

  Here, the vectors H (t), P (t), F (t), and Y (t) are each expressed as (Equation 33) below.

  Further, when the constraint condition expressions (Expressions 26 to 28) are summarized for U using (Expression 20) and (Expression 21), they are expressed as (Expression 34) below.

  Here, the vectors G (t), W (t), and E (t) are expressed as the following (Formula 35).

  Eventually, the model formula relating to the EGR valve 14 is summarized as the following (Formula 36). The control unit 20 executes the calculation according to (Equation 36) for each control step, and obtains the optimum solution U.

From the optimal solution U, the operation amount δM _egr (t) at the current time t is obtained. The control unit 20 converts the manipulated _{variable into} the opening degree A _egr (t) of the EGR valve 14 using the following equation (Equation 37) which is a conversion equation.

As described above, in the present embodiment, since the constraint condition is explicitly considered, it is possible to avoid the possibility that the engine will misfire more accurately than in the past. Therefore, a value closer to the ^upper limit value β ^upper of the EGR rate than before can be used, and control at a high EGR rate is possible.

Here, P _m represents the intake pressure and can be obtained by the intake pressure sensor 18 or the like. Φ (P _m ) represents a function having the intake portion pressure P _m as a parameter. This function can be acquired in advance by actual measurement or the like. Further, instead of using (Equation 37), the following (Equation 38) obtained by linearly approximating (Equation 37) may be used.

In (Equation 38), a ₁ , b ₁ , and γ are arbitrary constants and can be obtained by actual measurement or the like. _Pe represents the exhaust pressure and can be obtained by providing a pressure sensor or the like on the exhaust side.

  In Equation 36, there are H (t), F (t), Y (t), G (t), W (t), and E (t) as coefficients that depend on the current time (t). That is, the control unit 20 solves an optimization problem having variable coefficients H (t), F (t), Y (t), G (t), W (t), and E (t). The variable coefficient needs to be updated for each control step, and the calculation load corresponding to that is imposed on the control unit 20. Therefore, in order to reduce the calculation load, model prediction control may be performed in which the variable coefficient is converted into a constant coefficient that does not depend on the current time (t).

In the following embodiment, model prediction based on a dynamic characteristic equation, a constraint condition equation, and an evaluation function with a recirculation exhaust amount M _egr ^cyl passing through the intake valve 16 as a control amount and a change amount δM _egr ^cyl as an operation amount. Take control. Since the model does not consider the flow of the recirculated exhaust gas flow from the EGR valve 14 to the intake valve 16, the dead time d (t) and the time constant T (t) described above are omitted from the model formula (included in the shade). Can do. As a result, there is no coefficient depending on the current time (t), and it is possible to make the evaluation function only a constant coefficient.

  A dynamic characteristic equation of the recirculation exhaust amount flowing into the internal combustion engine 22 is shown in the following (Equation 39).

  Moreover, the evaluation function J regarding the said dynamic characteristic formula is shown in the following (Formula 40).

Further, a constraint condition expression of the control amount M _egr ^cyl and the operation amount δM _egr ^cyl is shown in the following Expression 41.

Here, the first expression and the second expression of the above (Expression 41) are obtained by converting the constraint condition for the EGR valve 14 into the constraint condition for the intake valve 16. That is, the minimum value δM _egr ^min and the maximum value δM _egr ^max with respect to the recirculation exhaust amount when passing through the EGR valve 14 are expressed (Formula 11), and the minimum value δM _egr ^min and the maximum value with respect to the change amount of the recirculation exhaust when passing through the EGR valve 14. (Expression 12) representing δM _egr ^max is converted using the following (Expression 42).

  Furthermore, a mathematical formula when the evaluation function (Mathematical formula 40) is displayed in vector is shown in the following mathematical formula 43.

  Further, the dynamic characteristic equation (Equation 39) and the constraint condition equation (Equation 41) in vector form are shown in the following (Equation 44) and (Equation 45), respectively.

  Here, in (Equation 43) to (Equation 45), the definitions of the vectors X and U are changed to the above (Equation 18), (Equation 22), (Equation 29), and (Equation 30) in accordance with the change of the model equation. It is different. Specifically, the vector X is defined as shown below (Formula 46), and the vector U is defined as shown below (Formula 47).

  Next, the evaluation function J (Formula 43) is summarized for the manipulated variable U. Using (Equation 44), (Equation 43) can be transformed as (Equation 48) below.

  In (Formula 48), vectors H, F, Y, and P (t) are shown in the following (Formula 49).

  Further, the constraint condition formula (Formula 45) is summarized for U. Specifically, (Equation 45) is transformed into (Equation 50) below using (Equation 44).

  In (Formula 50), the vectors G, W, and E are shown in the following (Formula 51).

  Eventually, the model formula relating to the EGR valve 14 is summarized as the following (Formula 52).

As shown in (Formula 52), the coefficients H, F, Y, G, W, and E are all expressed as constant coefficients. Therefore, it is not necessary to update the coefficient for each control step, and the calculation load is reduced. The control unit 20 executes the calculation according to (Equation 52) for each control step,
An optimum solution of the operation amount that minimizes the value (evaluation value) of (Formula 52) is obtained. Further, the operation amount at the current time t is acquired from the optimal solution. Since the optimal solution of (Equation 52) is the change amount δM _egr ^cyl of the recirculation exhaust amount when passing through the intake valve, the control unit 20 converts this to the change amount δM _egr of the recirculation exhaust flow passing through the EGR valve 14. Specifically, δM _egr ^cyl (t) is converted to δM _egr (t) using (Equation 4) and (Equation 5) representing the relationship between M _egr ^cyl and δM _egr . Furthermore the control unit 20 converts the (Formula 37) or the opening A _egr of the EGR valve 14 .DELTA.M _egr (t) using (Equation 38) (t).

DESCRIPTION OF SYMBOLS 10 Control apparatus, 12 Throttle valve, 14 EGR valve, 16 Intake valve, 18 Intake pressure sensor, 20 Control part, 21 Throttle valve motor, 22 Internal combustion engine, 24 Throttle valve position sensor, 25 EGR valve position sensor, 26 Combustion chamber , 27 Intake port, 28 Intake pipe, 29 Air intake, 30 Air cleaner, 32 Surge tank, 36 EGR valve motor, 38 Exhaust pipe, 40 Exhaust recirculation pipe, 42 EGR cooler, 44 Catalyzer.

Claims (3)

An EGR valve for adjusting a recirculation exhaust amount for mixing a part of the exhaust gas of the internal combustion engine with the intake air;
A predicted value of the recirculation exhaust amount when the intake valve passes to adjust the intake amount flowing into the internal combustion engine is calculated based on the recirculation exhaust amount when the EGR valve passes and its change amount, and the recirculation exhaust when the intake valve passes An evaluation value calculated based on a difference between the target value of the amount and the predicted value and a change amount of the recirculated exhaust gas when passing through the EGR valve is calculated, and the recirculated exhaust gas amount and its change amount when passing through the EGR valve A change amount of the recirculation exhaust gas that passes through the EGR valve that gives a minimum value of the evaluation value in a range that satisfies a constraint condition regarding the recirculation exhaust gas amount when the intake valve passes is acquired as an optimal value, and the EGR is based on the optimal value A controller that determines the opening of the valve;
An EGR valve control device comprising: An EGR valve for adjusting a recirculation exhaust amount for mixing a part of the exhaust gas of the internal combustion engine with the intake air;
A predicted value of the recirculation exhaust amount when the intake valve passes is calculated based on the recirculation exhaust amount when the intake valve passes to adjust the intake amount flowing into the internal combustion engine and the change amount thereof, and the recirculation exhaust when the intake valve passes An evaluation value obtained based on the difference between the target value of the amount and the predicted value and the amount of change is calculated, and a first restriction condition on the amount of recirculated exhaust gas and the amount of change when passing through the EGR valve is defined as the intake valve. The amount of change in the recirculated exhaust gas when passing through the intake valve is converted into a second constraint condition for the recirculated exhaust gas amount during passage and the amount of change thereof, and gives the minimum value of the evaluation value in the range satisfying the second constraint condition. The optimal value is acquired, and the optimal value is converted into a change amount of the recirculation exhaust amount when passing through the EGR valve. Based on the converted change amount of the recirculation exhaust amount when passing through the EGR valve, the E value is changed. And a control unit which determines the degree of opening of the R valves,
An EGR valve control device comprising: An EGR valve for adjusting a recirculation exhaust amount for mixing a part of the exhaust gas of the internal combustion engine with the intake air;
The variable coefficient of the optimization problem including the variable coefficient generated to obtain the opening degree of the EGR valve is converted into a constant coefficient, and the opening degree of the EGR valve is determined by solving the optimization problem after the conversion. The desired control unit;
An EGR valve control device comprising:

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