JP2011179448A - Egr valve control device and program - Google Patents

Abstract

The EGR rate is prevented from exceeding an upper limit value in the process of converging the EGR rate to a target value.
An operation unit 24 of an EGR valve control device 10 opens an EGR valve 14 during a delay period from the current time when an opening command of the throttle valve 18 is received to an operation time when the throttle valve 18 opens according to the opening command. Calculate the degree. The storage unit 26 of the EGR valve control device 10 stores the target value of the EGR rate and the upper limit value of the EGR rate as a constraint condition, and the calculation unit 24 converges the EGR rate to the target value. Therefore, the opening degree of the EGR valve 14 is calculated within a range that does not deviate from the constraint conditions.
[Selection] Figure 3

Description

  The present invention relates to an EGR valve control device and a program for controlling the opening of an EGR valve.

  Exhaust gas recirculation that mixes exhaust gas into intake air by recirculating part of the exhaust gas to the intake side as one of the means to reduce the concentration of harmful gas in exhaust gas discharged from internal combustion engines such as vehicles A technique called “Exhaust Gas Recirculation” (hereinafter referred to as “EGR”) is known.

  EGR is performed by connecting an intake side and an exhaust side of an internal combustion engine with an EGR pipe and returning a part of exhaust gas on the exhaust side to the intake side via the EGR pipe. The EGR pipe is provided with an EGR valve that controls the flow rate of exhaust gas recirculated to the intake side.

  By mixing exhaust gas into the intake air and sending the intake air to the combustion chamber of the internal combustion engine, the combustion temperature in the combustion chamber can be lowered. Nitrogen oxide (NOx), which is one of the exhaust gases, is known to reduce the generation amount when the combustion temperature decreases, and NOx is reduced by increasing the EGR rate (ratio of exhaust gas to intake air). Can be made.

  In order to converge the EGR rate to a desired value, a technique for controlling the opening degree of an EGR valve provided in a vehicle or a throttle valve for adjusting an intake air amount has been conventionally known. For example, in Patent Document 1, target values are set for a plurality of parameters (intake air amount, supercharger pre-pressure, scavenging pressure) that determine the EGR rate, and a throttle valve, EGR is used to set these parameters toward the target values. Controls the opening of valves and waste gate valves.

JP 2008-248863 A

  By the way, when the EGR rate becomes excessively high (when the ratio of exhaust gas becomes high), the oxygen concentration in the intake air decreases, and as a result, a phenomenon called misfire in which combustion does not occur in the combustion chamber of the internal combustion engine may occur. For this reason, an upper limit value is set for the EGR rate, and the target value of the EGR rate is set to be equal to or lower than the upper limit value.

  Here, generally, in the process of converging the control target to the target value, the value of the control target fluctuates up and down with respect to the target value. That is, the EGR rate fluctuates up and down with respect to the target value in the process of converging the EGR rate to the target value. At this time, the EGR rate fluctuated to a value equal to or higher than the target value in the process of convergence, exceeding the maximum EGR rate, and there was a risk of misfire in the internal combustion engine.

  Accordingly, an object of the present application is to provide an EGR valve control device that prevents the occurrence of misfire in the process of converging the EGR rate to a target value.

  The present invention relates to an EGR valve control device that controls the opening degree of an EGR valve that adjusts the flow rate of exhaust gas to be recirculated when a part of exhaust gas discharged from an internal combustion engine to an exhaust portion is recirculated to an intake portion. Is. The EGR valve control device includes a storage unit in which a target value of the EGR rate is stored and an upper limit value of the EGR rate is stored as a constraint condition. Further, the EGR valve control device opens the EGR valve within a range that does not deviate from the constraint condition in order to converge the EGR rate to the target value when the opening degree command for the throttle valve for adjusting the intake amount of the intake portion is received. A calculation unit for calculating the degree is provided, and the opening degree of the EGR valve is controlled to the calculated opening degree.

  In the above invention, the calculation unit calculates the opening degree of the EGR valve at each time between the time when the throttle valve opening command is received and the operation time when the throttle valve opens to the opening command opening degree. Is preferred.

  Moreover, in the said invention, it is suitable for the memory | storage part to memorize | store the operation | movement restriction | limiting of an EGR valve in addition to the upper limit of an EGR rate as a constraint condition. Further, when the opening of the EGR valve that satisfies the constraint conditions cannot be calculated, the calculation unit issues a command for setting the opening of the throttle valve at the operating time to an opening lower than the throttle opening command. It is preferable to send it to a throttle valve control device for controlling the degree.

  Moreover, in the said invention, it is suitable that the constraint conditions are comprised as a function which uses the variation | change_quantity of the flow volume with respect to the time of an EGR valve as an input variable.

  In the above invention, the function of the constraint condition is that the pressure of the intake portion and the flow rate of the EGR valve are state variables, and the opening command for the throttle valve and the pressure of the discharge portion are variables that are not dependent on constants or state variables and input variables. It is preferable to be configured as a function including Further, it is preferable that the calculation unit calculates the opening degree of the EGR valve based on the opening degree command for the throttle valve, the pressure of the intake part and the exhaust part, the flow rate of the EGR valve, and the function.

  The present invention also provides an EGR valve control that controls the opening of an EGR valve that adjusts the flow rate of the exhaust gas to be recirculated when a part of the exhaust gas discharged from the internal combustion engine to the exhaust portion is recirculated to the intake portion. The present invention relates to a program for executing opening degree control on an apparatus. The storage unit of the EGR valve control device stores the target value of the EGR rate and the upper limit value of the EGR rate as a constraint condition. When the calculation unit of the EGR valve control device receives an opening degree command for the throttle valve that adjusts the intake air amount of the intake unit, the program sets the constraint condition so that the calculation unit converges the EGR rate to the target value. The opening degree of the EGR valve is calculated within a range that does not deviate. Further, the program causes the EGR valve control device to control the opening degree of the EGR valve to the calculated opening degree.

  The present invention also relates to a valve control device that controls the opening of a first valve among a plurality of valves provided in a gas passage communicating with an internal combustion engine. The valve control device includes a storage unit that stores the target value of the state quantity of the first valve and stores the constraint condition of the state quantity of the first valve. Further, the valve control device is provided in the gas passage, detects a change in the state quantity of the second valve different from the first valve, and converges the state quantity of the first valve to the target value. A calculation unit that calculates the opening of the first valve within a range that does not deviate from the constraint conditions, and controls the opening of the valve to the calculated opening.

  The present invention also relates to a program for controlling the opening degree of a valve control device that controls the opening degree of a first valve among valves provided in a gas passage communicating with an internal combustion engine. . The storage unit of the valve control device stores the target value of the state quantity of the first valve and the constraint condition of the state quantity of the first valve. The program is provided in the gas passage, and when the calculation unit of the valve control device detects a change in the state quantity of the second valve different from the first valve, the calculation unit sets the state quantity of the first valve to the calculation unit. In order to converge to the target value, the opening degree of the first valve is calculated within a range that does not deviate from the constraint condition. Further, the program causes the valve control device to control the opening degree of the first valve to the calculated opening degree.

  According to the present invention, in calculating the EGR valve opening to converge the EGR rate to the target value, the upper limit value of the EGR rate is set as a constraint condition for calculating the EGR valve opening. The calculation unit of the EGR valve control device determines the opening of the EGR valve within a range that does not deviate from this constraint. As a result, the EGR rate can be converged to the target value without departing from the upper limit value of the EGR rate.

  Further, the present invention can be applied not only to the control of the EGR valve but also to various valve controls in the internal combustion engine. In other words, by defining the upper limit value of the state quantity of a predetermined valve provided around the internal combustion engine as a constraint condition when calculating the opening, the valve opening for converging the state quantity of the predetermined valve to the target value is established. In the degree calculation, the opening degree of the valve can be calculated without departing from the constraint condition.

It is a figure explaining the structure of the EGR valve control apparatus concerning this embodiment, and its periphery. It is a system configuration figure of an EGR valve control device. It is a conceptual diagram of the opening degree control which an EGR valve control apparatus performs. It is a figure which illustrates the flowchart of opening degree control. It is a figure which illustrates the functional block diagram of an EGR valve control apparatus. It is a figure explaining the division linear process with respect to a flow volume model. It is a figure which illustrates the simulation result of the opening degree control concerning this embodiment. It is a figure which illustrates the simulation result of the opening degree control concerning this embodiment.

  FIG. 1 shows an EGR valve control device according to an embodiment of the present invention and the surrounding configuration. In FIG. 1, the gas flow path and the flow direction are indicated by solid arrows, and the signal flow is indicated by broken arrows. The EGR valve control device 10 can communicate with an engine control unit (ECU) 12 that controls various parameters around the internal combustion engine 5. The EGR valve control device 10 is connected to the EGR valve 14. The EGR valve control device 10 is connected to a surge tank pressure sensor 16 that detects the pressure of the surge tank 15. The EGR valve control device 10 is connected to an exhaust gas collecting portion pressure sensor 20 that detects the pressure of the exhaust gas collecting portion 17. Further, the EGR valve control device 10 can receive an opening degree command of the throttle valve 18 calculated by the engine control unit 12 based on the depression angle of the accelerator pedal.

  Next, a system configuration diagram of the EGR valve control device 10 is shown in FIG. The EGR valve control device 10 includes a receiving unit 22, a calculation unit 24, a storage unit 26, and an output unit 28. These units can communicate with each other.

The function of each part of the EGR valve control device 10 will be described. Receiver 22, the pressure value transmitted from the surge tank pressure sensor 16, receives as an intake section pressure P _a. Also, the pressure value transmitted from the exhaust gas collecting portion pressure sensor 20, receives as a discharge section pressure P _e. The receiving unit 22 receives the opening command _{A t} of the throttle valve 18 from an engine control unit 12. Further, the receiving unit 22 receives an opening degree signal indicating the opening degree A _egr of the EGR valve 14 from the EGR valve 14. Here, the opening represents the opening area.

The storage unit 26 is configured to include storage means such as a semiconductor memory and a hard disk, and includes an opening degree control program for controlling the opening degree A _egr of the EGR valve 14, a target value for the EGR rate, and various kinds of opening degree control. The constraint conditions are stored. For example, information including an EGR rate upper limit value γ _{a, max} and an operation limit of the EGR valve 14 is stored as a constraint condition. Here, the EGR rate upper limit value indicates the maximum EGR rate at which the internal combustion engine 5 does not misfire. For example, the EGR rate upper limit value γ is 20 to 30% when the internal combustion engine is a gasoline engine and 30 to 40% when the diesel engine is a diesel engine. It is set as _{a, max} . The operation restriction of the EGR valve 14 defines a maximum value δA _{egr, max of an} amount that the EGR valve 14 can be opened and closed per unit time, a maximum opening A _{egr, max of} the EGR valve 14, and the like. Incidentally, EGR rate upper limit, in addition to the operation limit of the EGR valve 14, intake section pressure P _a may be stored intake unit pressure limit such that to be less than or equal to the exhaust unit pressure P _e in the storage unit 26.

  Further, the target value of the EGR rate is set to a value equal to or less than the maximum EGR rate. For example, a value of 15 to 30% is set for a gasoline engine, and a value of 25 to 40% is set for a diesel engine. Here, the maximum EGR rate may be set as the target value.

Calculation unit 24, as shown in FIG. 3, the observed amount 32 (e.g. EGR valve flow _{M egr} and the intake unit pressure _{P a)} if and necessary other observables 34 (e.g. temperature, etc. which are output from the controlled object 30 fetches the disturbance component or exhaust unit pressure P _e) of taking the target value 36 (for example, a maximum EGR rate) for the output of the controlled object 30. Further, the EGR rate converges to the target value with reference to constraint conditions such as the input constraint 38 (for example, the maximum EGR rate is not exceeded) for the control target 30 and the state constraint 40 (for example, the operation constraint of the EGR valve 14) of the control target 30. And the input value 42 (for example, EGR opening degree A _egr ) satisfying the constraint condition is calculated.

The calculation unit 24 is a so-called CPU and can access the storage unit 26. The calculation unit 24 captures various values received by the reception unit 22, reads out the target value, the constraint condition, and the opening degree control program stored in the storage unit 26, and executes the opening degree control program, thereby performing EGR. The opening degree A _{egr of the} valve 14 is calculated. Here, the calculation unit 24 is from the time when the receiving unit 22 receives the throttle valve opening command from the engine control unit (current time) to the operating time when the throttle valve 18 is actually opened to the opening command. The degree of opening at each time during the period (hereinafter referred to as a delay period) is calculated.

The delay period will be described. A slight delay period of about 30 msec to 80 msec occurs from the time when the receiving unit 22 receives the opening command of the throttle valve 18 (current time) to the operation time when the throttle valve 18 opens to the opening of the opening command. The calculation unit 24 divides this delay period into a plurality of steps. For example, 1 step = 8 msec, and the opening degree A _egr of the EGR valve 14 at each step is calculated. For example, assuming that the step of the delay period is divided into N steps, the calculation unit 24 calculates EGR valve opening _degrees A _{egr, t} , A _{egr, t + 1} ,..., A _{egr, t + N.} In calculating the opening degree, the restriction condition stored in the storage unit 26 is referred to, and the opening degree A _egr of the EGR valve 14 is set so that the EGR rate converges to the target value without departing from the restriction condition. Calculated.

The output unit 28 transmits an opening degree command for the EGR valve 14 during the delay period to the EGR valve 14 based on the calculation result of the calculation unit 24. With the EGR valve 14 changes the opening degree _{A egr} receiving opening command, feeds back the opening _{A egr} after the change to the receiving unit 22.

Next, the contents of the opening degree calculation program executed by the calculation unit 24 will be described with reference to the flowchart of FIG. Calculation unit 24 obtains the opening degree command _{A t} of the throttle valve 18 via the reception section 22 (S1). The arithmetic unit 24, the opening _{A egr} of the EGR valve 14 at the current time through the receiver 22 obtains the pressure _{P a} and the pressure _{P e} of the discharge portion of the intake section (S2). The calculation unit 24 executes the opening degree calculation program based on these input values, the target value and the constraint conditions stored in the storage unit 26 (S3). The opening degree calculation program is composed of a so-called constrained optimal control problem, and the calculation unit 24 obtains the EGR valve opening degree A _egr in each step of the delay period by solving the optimal control problem. A constrained optimal control problem is a state equation that includes an input variable, a state variable whose state changes according to the input variable, a constraint expression that defines the constraint condition of the input variable, and a state under the constraint condition Of the solutions satisfying the equations (executable solutions), the evaluation function is composed of three mathematical expressions. The state equation, constraint equation, and evaluation function will be described later.

The calculation unit 24 substitutes each value sent in S1 and S2 for each mathematical expression, and determines whether there is an executable solution that satisfies the constraint (S4). If the feasible solutions is not present, the opening degree A _t the operation time of the throttle valve 18 is lower than the opening command (i.e., a small opening deviation) a command to the engine control unit 12 so as to opening Send (S5). As the opening degree deviation becomes smaller, the restriction becomes looser, and the probability of obtaining an executable solution increases. Computing section 24 determines the presence or absence of feasible solutions again based on the throttle opening degree A _t becomes smaller deviation (S4). The processes from S1 to S5 are performed until an executable solution is found. When an executable solution is found, the calculation unit 24 calculates an evaluation function in order to obtain an optimal solution from a plurality of executable solutions (S6). The evaluation function can derive an optimal solution in light of a predetermined evaluation condition. For example, condition 1 that the smaller the difference between the EGR rate and the target value is better and the condition 2 that the smaller the operation amount of the EGR valve 14 is better are reflected in the evaluation function. To derive.

  When the optimal solution is obtained, the calculation unit 24 sends an opening command of the EGR valve in each step of the delay period to the output unit 28 according to the optimal solution (S7). The output unit 28 transmits the opening degree command to the EGR valve 14. Thereafter, the processing of S1 to S7 is repeated every time the time advances by one step.

  In step 5 (S5), the engine control unit 12 that has received a change command for the opening command of the throttle valve 18 from the calculation unit 24 has changed the opening of the throttle valve 18 at the operating time, that is, an opening deviation. An opening degree command is sent to the throttle valve 18 so that the opening is reduced. Further, the opening degree of the throttle valve 18 is controlled so that the opening degree before the change is reached after several steps (1 step to 3 steps) after the operation time.

  FIG. 5 shows a functional block diagram of the EGR valve control device 10 that executes the opening degree calculation process described above. The EGR valve control apparatus 10 executes input data acquisition means 44 that executes S1 and S2, executable solution determination means 46 that executes S3, S4, and S5, and optimal solution determination means 48, S7, and S8 that execute S6. The opening transmission means 50 is comprised.

  Next, the optimal control problem with restrictions executed in the opening degree calculation program will be described. As described above, the optimal control problem includes a state equation, a constraint condition expression, and an evaluation function. The general form of the state equation and the constraint equation is shown in the following equations 1 and 2.

Here, x is a state variable (for example, flow rate in a valve), u is an input variable (for example, valve opening), x and u suffix k is a discrete time step (a delay period divided into a plurality of time steps), p Indicates a target value (for example, maximum EGR rate), an external input (for example, throttle valve opening M _t ), a boundary condition, and the like. Here, p represents a constant that does not change with the discrete time step k, or a variable that does not depend on the state variable or the input variable.

  Equations 1 and 2 are non-linear equations and take a long time for the calculation process. Since the delay period is a short period of about 30 msec to 80 msec, it is preferable to correct to a linear format or a secondary linear format that is simpler and requires less calculation processing time. Here, the state equation and the constraint condition equation are generated based on the flow rate model in the EGR valve 14 that is the control target. Therefore, the mathematical formulas 1 and 2 are transformed into a linear format by transforming the flow rate model into a linear or secondary linear format.

  A flow rate model in the EGR valve 14 is shown below.

Here, M _egr represents the gas flow rate (mass flow rate) in the EGR valve 14, and A _egr represents the opening area of the EGR valve 14. Further P _a represents the air intake pressure. In other _words, since the _{M egr} is represented by the product of the variables _{A egr} and variables _{P a,} Equation 3 is understood to be a non-linear equation. The outline of Equation 3 is shown by the solid line in FIG. 6, the horizontal axis represents the ratio between the intake portion pressure P _a and the exhaust unit pressure P _{e (constant),} the vertical axis represents the value of M _egr (relative value).

  Here, piecewise linear processing is performed on Equation 3. Piecewise linear processing refers to processing in which the horizontal axis is divided into a plurality of sections and Equation 3 is approximated by a linear function for each section. Equation 4 after the piecewise linear processing is shown below, and its outline is indicated by a dotted line in FIG.

Here, a ₁ , c ₁ , and γ are arbitrary constants. A constraint condition formula is generated based on Formula 4. In the following, the input variable is changed from A _egr which is the opening degree of the EGR valve to an amount of change in flow rate with respect to time of the EGR valve 14 (hereinafter referred to as flow rate deviation) δM _egr . Furthermore, the state variable intake portion pressure _{P a} and the EGR valve flow _{M egr.} As will be described later, the constraint condition can be described linearly by changing the input variable to the flow rate deviation δM _egr . First, the constraint condition of the EGR valve opening degree A _egr is shown in the following formula 5.

Based on Expression 4 and Expression 5, a constraint condition for the EGR valve flow rate M _egr (state variable) as shown in Expression 6 below is obtained.

Next, the constraint condition of the EGR valve opening deviation δA _egr is shown in the following Expression 7.

Equation 7 is modified to obtain the constraint condition of EGR valve flow rate deviation δM _egr (input variable) as shown in Equation 8 below.

The above formulas 6 and 8 are constraint condition formulas that determine the operation constraint of the EGR valve 14. Here, in Equation _{6 A egr, min, A egr} , max, δA egr, min, δA egr, max can be determined in advance as a constant, further or _{P e} is set as a constant, the input variables and the state variables It becomes possible to obtain from the exhaust gas collecting portion pressure sensor 20 as a variable which does not depend on it. Therefore, Equation 6 and 8 is the linear equation together input variables .DELTA.M _egr, state variables _M egr, with respect to _{P a.}

Furthermore, the upper limit value of the EGR rate is determined as a constraint condition. When the maximum EGR rate is γ _{a, max} , the upper limit value of the EGR rate is expressed by the following formula 9.

Here, M _t indicates the gas flow rate in the throttle valve 18. Is this M _t is also set as a constant as with P _e, it can be set based on the throttle opening command sent from the engine control unit 12 as a variable which is not dependent on the input variables and the state variables. In Equation 9, EGR rate = (M _egr / M _t ), but EGR rate = (M _egr / M _t + M _egr ) may be used.

Further, as the other constraints, it defines the relationship between the gas pressure P _ics of the intercooler 52 on the upstream of the intake section pressure P _a relationship and intake unit pressure between the discharge portion pressure P _e P _a and the surge tank 15 An expression may be added. Incidentally, be set by either the P _ics set as constants like the P _e, the EGR valve control apparatus 10 the value of the pressure sensor 54 of the intercooler 52 as a variable which is not dependent on the input variables and the state variables to obtain it can. Relationship between P _a and _{P e,} and show the relation between _{P a} and _{P ics} the following equation 10.

  When the conditional expressions of Expressions 6, 8, and 9 are put together and the step k (t to t + N) in the delay period is further considered, the following Expression 11 is obtained.

Here, C, D, and E are arbitrarily defined constant matrices, which can be set in advance. Further, when M _egr and P _a are collectively expressed as a state variable vector x _k , δM _egr as an input variable vector v _k , a constant term on the right side, or a variable not dependent on an input variable or a state variable is expressed as a vector p, Expression 11 Can be transformed as shown in Equation 12 below.

Next, a state equation for the state variable vector x _k and the input variable vector v _k is shown in the following Equation 13.

It can be understood from Equation 13 that the state variable vector x _k is obtained recursively from the initial values v _t and x _t of the input variable vectors v _K and x _K. Therefore, Equation 12 can be transformed from a shape that explicitly includes the state variable vector x _k to a shape that is implicitly included as shown in Equation 14 below.

Here, G and W are arbitrary constant matrices and can be set in advance. Furthermore V are those represented collectively input variable vector v _K in each step.

From Expressions 11 to 14, the input variable vector V (δM _{egr, t to} δM _{egr, t + N} ) is the EGR valve flow rate M _{egr, t} (= x _t ) and the intake part pressure P _{a, t} ( = X _t ), throttle opening command M _t (included in p), and exhaust pressure P _e (included in p) can be obtained.

  As described above, Equation 13 shows the state equation, and Equation 14 shows the constraint condition equation. Next, an evaluation function J for obtaining an optimal solution among the executable solutions of the state equation in the executable region that satisfies the constraint equation is expressed by the following mathematical formula 15.

Here, Q, H, and F are arbitrary constant matrices and can be set in advance. Further, x _{t + N | t} indicates a state variable vector that is N steps ahead from the current sample time t (current time) when the delay period is divided into time segments (horizontal) of N steps. Further, r _t represents the target value, the sample time t a value corresponding to the throttle opening command the receiver 22 received in (current time) (throttle valve flow M _t and the intake unit pressure P _a in the present embodiment) Represents.

In Equation 15 _represents the difference between the terms input variable vector and the target value of _{| | (t -r t x t} + k) (x t + N t -r t) or. That is, this term represents the above-described condition 1 (the smaller the difference between the EGR rate and the target value, the better). In addition, the term (v ^T _{t + k} Rv _{t + k} ) represents the manipulated variable of the input variable vector. That is, this term represents the above-described condition 2 (the smaller the operation amount of the EGR valve 14 is, the better). From this, it is understood that the value of the input variable vector V that minimizes the value of the evaluation function J is the optimal solution.

  Here, in the lower part of Expression 15, the terms including the input variable vector V are the first term and the second term, and the third term can be regarded as a constant term. Therefore, it is understood that the evaluation function J takes the minimum value when the first term + second term in the lower part of Expression 15 is the minimum. From this, the constrained optimal control problem for which the calculation unit 24 performs the calculation can be finally summarized into the following Expression 16.

  As a solution of Expression 16, various conventionally known solutions can be used. For example, the parameter space can be divided into a plurality of regions using multiparametric programming, and the optimum gain F in each region can be derived using the optimality condition (KKT condition). For example, the optimum flow rate deviation in the parameter area i can be expressed as in the following Expression 17, and the parameter area i can be expressed as in the following Expression 18.

Here, F ⁱ represents an optimum gain, and g ⁱ represents a constant matrix. In addition, in order to apply a so-called reverse horizon strategy, the input variable vector (flow rate deviation) v and the suffix t of the state variable vector x indicate the current time.

In practice, first, the current state x _t (for example, EGR valve flow rate M _{egr, t} , intake air pressure _{Pa , t} ) and constant p (for example, throttle opening command M _t ) are specified from among a plurality of parameter regions. Specify the parameter area. Next, an optimum input variable (for example, flow rate deviation) is calculated using the optimum gain F ⁱ corresponding to the specified parameter region. Next, an optimal flow rate deviation is added to the current EGR valve flow rate to calculate the EGR valve flow rate in the next step, and the corresponding EGR valve opening is calculated using the flow rate model described above. Finally, the command for the calculated EGR valve opening is transmitted to the EGR valve. This is repeated every step.

  In general, it is known that the division of the parameter area increases exponentially with the number of prediction steps and the number of constraint conditions, and it is difficult to select the parameter area i in real time. Therefore, the number of parameter regions can be greatly reduced by determining candidates for constraints (active constraints) that satisfy the equation from the constraint conditions.

  The simulation result by the above-mentioned EGR valve opening degree control is shown in FIG. In FIG. 7, the output in the present embodiment is indicated by a square marker, and the output in the prior art that does not have the EGR rate as a constraint is indicated by a circle marker. The transition of the throttle opening is shown in the upper part of FIG. Here, 8 steps are set as a delay period, and the opening degree is set to be rapidly closed after 8 steps from the present time. The middle row shows the transition of the EGR rate. Here, the target EGR rate is indicated by a broken line, and the maximum EGR rate is indicated by a one-dot chain line. Here, in order to clarify the difference between the present embodiment and the prior art, the target value is set to a value slightly lower than the maximum EGR rate.

  The lower part shows the operation restriction of the EGR valve flow rate. The maximum EGR increase (maximum increase that can be increased in one step), which is the upper limit of the EGR valve operation limit, is indicated by a one-dot chain line, and the maximum EGR decrease (can be reduced in one step), which is the increase / decrease of the operation limit. The maximum reduction amount is indicated by a dotted line. A possible value of the flow rate deviation of the EGR valve is limited between the maximum EGR increase and the maximum EGR decrease.

  In the prior art, it is understood that the maximum EGR rate greatly deviates at the 8th step and then converges to the target value. That is, it is understood that the maximum EGR rate deviates greatly in the process of convergence to the target value. On the other hand, in the EGR valve control according to the present embodiment, since the maximum EGR rate is a constraint, it is understood that the fluctuation of the EGR rate is within a range not exceeding the maximum EGR rate. As described above, in the EGR valve control according to the present embodiment, the maximum EGR rate is set as a constraint condition. Therefore, the EGR rate is set to the target value while suppressing the fluctuation of the EGR rate within a range not exceeding the maximum EGR rate. It is possible to converge to.

  Further, FIG. 8 shows another simulation result by the EGR opening degree control according to the present embodiment. In this example, when there is no solution that satisfies the constraint conditions, processing is performed to reduce the opening of the throttle valve 18 at the operating time from the command.

  The roles of the dotted line, the alternate long and short dash line, and the marker in FIG. 8 are the same as those in FIG. In this embodiment, when the calculation unit 24 calculates that there is no feasible solution that satisfies the constraint condition, the calculation unit 24 opens the throttle valve 18 at the operation time to the engine control unit 12. A command to reduce the degree at a predetermined rate than the opening degree command is sent. Thereby, as shown in the upper part of FIG. 8, the opening degree of the throttle valve 18 is corrected in the eighth step. In the opening degree control in this embodiment, the restriction condition is relaxed by correcting the throttle opening degree, and the EGR rate increases up to the maximum EGR rate, but does not increase any more and satisfies the restriction condition. Is understood from the graph in the upper part of FIG. On the other hand, it is understood that in the prior art in which no upper limit is set for the EGR rate, the maximum EGR rate greatly deviates at the 8th and 9th steps.

  As described above, in the EGR valve control device according to the present embodiment, the EGR valve opening is determined within a range not exceeding the maximum EGR rate by setting a constraint condition that the maximum EGR rate is not deviated. Is possible. Furthermore, if a combination of openings that satisfies the constraint conditions cannot be derived, the throttle valve opening is commanded to the throttle valve control system, which is an external control system as seen from the EGR control system, and the constraint conditions are relaxed. This makes it possible to derive an executable solution.

  In the above-described embodiment, the control target is limited to the EGR valve control. However, the control and the control program may be applied to any valve control provided in the gas passage communicating with the internal combustion engine. Is possible. That is, in the above-described embodiment, the state equation and the constraint condition are derived based on the linear flow rate model (Equation 4) of the EGR valve, but this is replaced with the linear or secondary linear flow rate model of other valves. It is possible to control the valve by deriving a state equation and constraint conditions. Specifically, a state quantity of a predetermined first valve provided in a gas passage communicating with the internal combustion engine is provided in a gas passage of the internal combustion engine, and a state quantity of a second valve different from the first valve Consider the case of changing by When the state quantity change of the second valve is detected, when the state quantity of the first valve is converged to the target value, the upper limit value of the state quantity of the first valve is calculated for the opening degree of the first valve. By defining the restriction condition, the opening degree of the first valve can be calculated without departing from the restriction condition.

  As shown in FIG. 1, in addition to the EGR valve 14, there are a throttle valve 18 provided between the intercooler 52 and the surge tank 15, an intake valve 56 provided in the internal combustion engine 5, and an exhaust in the vicinity of the internal combustion engine. A waste gate valve 64 for controlling the flow rate of the valve 58 and the turbine 60 and the compressor 62 is provided. These valves can also be controlled as described above. Further, the application range of the valve control according to the present embodiment is not limited to individual valve control, and can be applied to integrated control in which these valves are integrated and controlled.

  The throttle valve flow rate is expressed by Equation 19 below.

Here, _{M t} is the throttle valve flow, _{A t} is the throttle valve _{opening, P ics} pressure of the intercooler _52, a _{2, c} 2 denotes an arbitrary constant. The waste gate valve flow rate is expressed by the following formula 20.

_{Here, M wg} is the waste gate valve _{flow, A wg} is the waste gate valve opening, _{P o} is the atmospheric _pressure, a _{5, c} 5 represents an arbitrary constant. Further, the intake valve flow rate can be expressed using an intake scavenging flow rate or an exhaust reverse flow rate. The exhaust reverse flow rate is expressed by Equation 21.

Here, M _ex represents the exhaust reverse flow rate, and I _AOL represents the effective opening area of the flow path when the intake valve 56 and the exhaust valve 58 overlap (when both valves are open and O / L). A ₃ and c ₃ represent arbitrary constants. Further, the intake scavenging amount is expressed by Equation 22.

Here, M _scav represents the intake scavenging amount, and a ₄ and c ₄ represent arbitrary constants. Further, the intake valve flow rate is expressed by Equation 23.

_{Here, M in} the intake valve _flow, the _{T out} represents a function of the gas temperature at the discharge valve 58, _{T a} is the gas temperature at the inlet _portion, k 1, _{k 4} is an arbitrary constant or speed and temperature. Here, because it is provided in a position close to each other and the discharge valve 58 and the exhaust gas collecting portion 17 may be determined to be equal to the temperature T _e of approximately exhaust gas gathering portion 17 and T _out.

  Further, the discharge valve flow rate is expressed by Equation 24.

Here, M _out represents the discharge valve flow rate, and M _f represents the fuel flow rate. That is, the right side represents the flow rate of the air-fuel mixture in which intake air and fuel are mixed. It is understood that all the flow rate models described above are linear or quadratic lines, and are simpler to calculate than non-linear equations.

Further, the turbine flow rate M _trb and the compressor flow rate M _cmp can be obtained based on a known turbine / compressor map expressed by Expression 25.

Here, Ω _tc represents the turbine speed. Further, the turbine temperature T _trb and the compressor temperature T _cmp are expressed by Expression 26. It can be determined based on a known turbine / compressor map.

Each flow model is shown above. Flow model of the EGR valve 14 from (Equation 4), the flow rate difference .DELTA.M _egr as input variables, the linear constraints that the air intake pressure _{P a} and the EGR valve flow _{M egr} and state variables (equations 6, 8, 9, 10) As described above, linear or quadratic linear constraints on the state quantities (flow rate, flow rate deviation, pressure, temperature) of each valve can be derived from each flow rate model.

Next, the equation of state using each flow model is shown below. Flow rate _{M cmp} outlet pressure _{P ics} and compressor 62 of the intercooler 52, showing the relationship between the flow rate _{M t} of the throttle valve 18 (input variable) to the following equation 27. Here, when considering the exit pressure P _ics of the intercooler 52 as a control object, a state variable outlet pressure P _ics. On the other hand, when not considered as a control target, it is handled as a variable that is not subordinate to the input variable and the state variable.

Here, κ is the specific heat ratio of the gas, R is the gas constant, T _ic is the temperature of the intercooler 52, V _ic is the volume of gas in the intercooler 52, Q _ic is the amount of heat transfer in the intercooler 52, and C _p is constant pressure. It represents specific heat.

Further, the relationship between the intake portion pressure P _a (state variable), the flow rate M _t (input variable) of the throttle valve 18, the flow rate M _egr (input variable) of the EGR valve 14, and the intake valve flow rate M _in (input variable) is shown below. It is shown in Formula 28.

Here, T _w is the volume of gas in the cooling water temperature, T _a is the gas temperature in the intake section, V _a is the intake portion of an internal combustion engine 5, Q _a represents the amount of heat transfer in the intake section.

Further, the exhaust pressure P _e and the waste gate valve flow rate M _wg (input variable), exhaust gas flow rate M _out , EGR valve flow rate M _egr (input variable), turbine flow rate M _trb (input variable if a turbine nozzle is attached) The following formula 29 shows the relationship. In addition, when considering discharge part pressure _Pe as control object, let discharge part pressure _Pe be a state variable. On the other hand, when not considered, it is treated as a variable that is not subordinate to the input variable and the state variable.

Here, T _out is the temperature of exhaust gas emitted to the atmosphere, T _e is the volume of gas in the gas temperature, V _e is discharged portion of the discharge portion (exhaust gas collecting portion 17), Q _e is the heat transfer at the discharge portion Represents quantity.

The relation between workload W _e and the load torque tau _d at the discharge portion engine speed Omega (state variables) the following equation 30.

  Further, instead of the second expression of Expression 30, the following Expression 31 may be applied.

_{Here, a Ω, a w1, a} w2, a w2 are _{constants, N cyl} represents the number of cylinders in the internal combustion engine 5. V _BDC is the cylinder volume at the bottom dead center (Bottom Dead Center), V _TDC is the cylinder volume at the top dead center (Top Dead Center), and M _IVC is the cylinder at the time when the intake valve is closed (Intake Valve Close). internal volume, g _w is a function of the ignition time, u _s ignition timing, the F _C cylinder fuel amount, the H _f lower heating value, alpha air-fuel ratio, d is up to the torque generated from the time the intake valve was closed The dead time step number is indicated, M _EVO is the mass in the cylinder when the exhaust valve is opened (Exhaust Valve Open), and M _f is the fuel flow rate.

Further, the relationship between the turbine rotational speed Ω _tc (state variable), the turbine flow rate M _trb (which becomes an input variable if a turbine nozzle is attached), and the compressor flow rate M _cmp is shown in Equation 32 below.

Here, J _tc represents the moment of inertia of the turbine 60 and the compressor 62, and L _tc represents the load of the turbine 60 and the compressor 62.

  The flow model and the state equation for each valve have been described above. As shown in Expressions 27 to 32, it is understood that the state equation can also be expressed in a linear or quadratic line format as well as the constraint condition. Further, similarly to EGR valve control, it is understood that if the current value can be acquired, the state variable after N steps can be calculated recursively. When actually performing valve control, when the valve control device or its calculation unit detects a change in the state quantity around the target valve, the constraint condition is obtained from the flow model and state equation of the valve to be controlled, A feasible solution is obtained by substituting current values into constraints and state equations. Furthermore, the target value for the state quantity stored in advance in the storage unit 26 is substituted into the evaluation function of Formula 14, and an optimal solution is derived from the feasible solutions based on the evaluation function. As a result, it is possible to control the valve opening to converge to the target value within a range that does not deviate from the constraint conditions.

  In all the embodiments described above, the optimum floor is derived from the feasible solutions when a target value (throttle opening degree, etc.) after N steps from the present time is input. Note that the algorithm for deriving the optimum floor is an offline algorithm, that is, a map (or table) having the current feedback value, target value, and other external variables as inputs, and outputting the optimum feedback gain, in consideration of the constraints in advance. Either an algorithm to be calculated or an offline algorithm, that is, an algorithm that solves a constrained control problem for each step as a linear programming problem (or a quadratic programming problem) may be used.

  5 internal combustion engine, 10 EGR valve control device, 12 engine control unit, 14 EGR valve, 15 surge tank, 16 surge tank pressure sensor, 17 exhaust gas collecting part, 18 throttle valve, 20 exhaust gas collecting part pressure sensor, 22 receiving part , 24 arithmetic unit, 26 storage unit, 28 output unit, 30 control target, 32 observation amount, 34 other observation amount, 36 target value, 38 input constraint, 40 state constraint, 42 input value, 44 input data acquisition means, 46 Executable solution determination means, 48 optimum solution determination means, 50 opening transmission means, 52 intercooler, 54 intercooler pressure sensor, 56 intake valve, 58 discharge valve, 60 turbine, 62 compressor, 64 waste gate valve.

Claims (8)

An EGR valve control device that controls the opening of an EGR valve that adjusts the flow rate of the exhaust gas to be recirculated when a part of the exhaust gas discharged from the internal combustion engine to the exhaust portion is recirculated to the intake portion.
A storage unit in which a target value of the EGR rate is stored and an upper limit value of the EGR rate is stored as a constraint;
In order to converge the EGR rate to the target value when receiving an opening degree command for the throttle valve that adjusts the intake air amount of the intake portion, the opening degree of the EGR valve is set within a range not deviating from the constraint condition. A computing unit to calculate,
And an EGR valve control device that controls the opening degree of the EGR valve to the calculated opening degree. The EGR valve control device according to claim 1,
The calculation unit calculates the opening degree of the EGR valve at each time between the time when the throttle valve opening command is received and the operation time when the throttle valve opens to the opening command opening degree. An EGR valve control device. The EGR valve control device according to claim 1 or 2,
In the storage unit, in addition to the upper limit value of the EGR rate, an operation limit of the EGR valve is stored as the constraint condition,
When the calculation unit cannot calculate the opening degree of the EGR valve that satisfies the constraint condition, the arithmetic unit issues a command to set the opening degree of the throttle valve at the operation time to an opening degree lower than the throttle opening degree command. The EGR valve control device is characterized by being sent to a throttle valve control device for controlling the opening of the throttle valve. The EGR valve control device according to claim 3,
The EGR valve control device, wherein the constraint condition is configured as a function having an amount of change in flow rate with respect to time of the EGR valve as an input variable. 5. The EGR valve control device according to claim 4, wherein the function of the constraint condition is that the pressure of the intake portion and the flow rate of the EGR valve are state variables, and an opening degree command for the throttle valve and the discharge portion Configured as a function including pressure as a constant or a variable independent of the state variable and the input variable,
The calculation unit calculates the opening degree of the EGR valve based on an opening degree command for the throttle valve, pressures of the intake and exhaust parts, a flow rate of the EGR valve, and the function. An EGR valve control device. For an EGR valve control device that controls the opening of an EGR valve that adjusts the flow rate of the exhaust gas to be recirculated when a part of the exhaust gas discharged from the internal combustion engine to the exhaust portion is recirculated to the intake portion. A program for executing the opening degree control,
In the storage unit of the EGR valve control device, a target value of the EGR rate is stored, and an upper limit value of the EGR rate is stored as a constraint condition,
When the calculation unit of the EGR valve control device receives an opening degree command for the throttle valve that adjusts the intake air amount of the intake unit, the calculation unit causes the calculation unit to converge the EGR rate to the target value. The opening of the EGR valve is calculated within a range that does not deviate from the constraints,
A program for causing the EGR valve control device to control the opening of the EGR valve to the calculated opening. A valve control device for controlling an opening degree of one or a plurality of first valves among a plurality of valves provided in a gas passage communicating with an internal combustion engine,
A storage unit in which a target value of a state quantity in the first valve is stored and a constraint condition of the state quantity of the first valve is stored;
In order to detect a change in the state quantity of a second valve that is provided in the gas passage and is different from the first valve, and to converge the state quantity of the first valve to the target value, the constraint condition And a calculation unit that calculates the opening degree of the first valve within a range that does not deviate from the above, and controls the opening degree of the valve to the calculated opening degree. A program for controlling the opening degree of one or a plurality of first valves among a plurality of valves provided in a gas passage communicating with an internal combustion engine, for causing the valve control device to execute the opening degree control. And
The storage unit of the valve control device stores a target value of the state quantity in the first valve, and stores a constraint condition of the state quantity of the first valve,
When the calculation unit of the valve control device detects a change in the state quantity of a second valve that is provided in the gas passage and is different from the first valve, the calculation unit has a state of the first valve. In order to converge the amount to the target value, the opening degree of the first valve is calculated within a range not departing from the constraint condition,
A program for causing the valve control device to control the opening degree of the first valve to the calculated opening degree.

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