JP2015197087A - Internal combustion engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make feasible a control operation at a corrected target value closer to a restriction in a case of correcting a target value using a reference governor.SOLUTION: A second term on a right side of an equation (3) is configured to add a penalty based on not only a difference between a prediction value y^(k+i|k) and an upper limit value yif a prediction value is above a restriction but also a difference between the prediction value y^(k+i|k) and the upper limit value yif the prediction value is below the restriction and the penalty is added to a first term on the right side of the equation (3). That is, the penalty based on a sum of a part over the upper limit valueand a part below the upper limit valueis added to the first term on the right side of the equation (3). Owing to this, a corrected target value w over an original target value rcan be determined as an optimum value. It is, therefore, possible to correct the corrected target value w to a higher value even if the prediction value y^(k+i|k) does not conflict the restriction at all in a prediction interval.

Description

  The present invention relates to a control device for an internal combustion engine.

  When a target value is given for a control amount of an internal combustion engine, a general control device for an internal combustion engine determines a control input of the internal combustion engine by feedback control so that the output value of the control amount follows the target value. It is configured. However, in actual control of the internal combustion engine, there are many cases where various constraints on hardware or control exist regarding the state quantity of the internal combustion engine. If these restrictions are not satisfied, there is a risk that hardware breakage or control performance will be degraded. Satisfaction of the constraint is one of important performances required in the control of the internal combustion engine, as is the followability of the output value with respect to the target value.

  The reference governor is one effective means for satisfying the above requirements. The reference governor includes a prediction model that models a closed loop system (feedback control system) including an internal combustion engine to be controlled and a feedback controller, and when the control amount is controlled according to a target value, the state quantity of the internal combustion engine The future value of is predicted by a prediction model. Then, the target value of the control amount of the internal combustion engine is corrected based on the predicted state quantity and the imposed constraints.

  The inventor of the present application has already disclosed a technique for correcting a target value of a supercharging pressure as a control amount of an internal combustion engine with a supercharger by online calculation using a reference governor in Japanese Patent Application Laid-Open No. 2013-084091. .

JP2013-084091A

  By the way, what is important in the design of the reference governor is the content of the objective function used for calculating the corrected target value. Various objective functions can be adopted if only the satisfaction of constraints is considered. However, depending on what objective function is used to determine the corrected target value, the output value tracking characteristic for the controlled variable target value changes greatly, and the output value transient response characteristic for the controlled variable target value change Will change greatly. Particularly in the case of an internal combustion engine, the transient response characteristic of the output value with respect to a change in the target value of the controlled variable varies depending on the operating conditions. Therefore, in a control device that controls an internal combustion engine, it is an important issue to achieve good transient response characteristics while satisfying the constraints.

  Regarding the solution of the above problem, the inventor of the present application has already based on the first term relating to the difference between the original target value and the candidate for the corrected target value, and when the predicted value of the output value exceeds the constraint, It has been confirmed that the method of selecting a correction target value that minimizes the objective function represented by the second term that adds the penalty to the first term from the candidates is effective. However, since the second term becomes zero when the predicted value of the output value never conflicts with the constraint, the original target value is selected as the corrected target value that minimizes the objective function. Therefore, there is a problem that the control operation cannot be performed with a corrected target value that is closer to the restriction.

  The present invention has been made in view of the above-described problems. That is, an object of the present invention is to realize a control operation with a corrected target value that is closer to the constraint in the target value correction using the reference governor.

The present invention provides a feedback controller that determines a control input of the internal combustion engine by feedback control so that an output value of a control amount of the internal combustion engine approaches a target value;
A future predicted value of the specific state quantity of the internal combustion engine is calculated over a predetermined prediction interval using a model of a closed loop system including the internal combustion engine and the feedback controller, and is imposed on the predicted value and the control output. A reference governor for correcting the target value given to the feedback based on the constraints
The reference governor sets a penalty based on a first term relating to a difference between an original target value and a candidate for a corrected target value and a sum based on a sum of absolute values of differences between the predicted value and the constraint calculated in the prediction interval. A candidate for a correction target value that minimizes the objective function represented by the second term added to the term is searched, and a candidate for the correction target value that minimizes the objective function is used as a correction target value for correcting the target value. It is characterized by selecting.

  According to the present invention, not only when the predicted value of the output value exceeds the constraint, but also when the predicted value falls below the constraint, the difference between the predicted value and the constraint is integrated. Therefore, even when the predicted value never conflicts with the constraint, a candidate for a corrected target value larger than the original target value can be determined, so that a control operation with a corrected target value closer to the constraint can be realized. .

It is the schematic which shows the structure of the aftertreatment system of a diesel engine. It is a figure which shows the target value tracking control structure of the diesel engine which the control apparatus of embodiment has. FIG. 3 is an equivalent modification of the target value tracking control structure shown in FIG. 2. It is a figure which shows the reference governor algorithm which concerns on embodiment. It is a figure for demonstrating the objective function which concerns on embodiment. It is a figure which shows the example of the control input and control output of a diesel engine which can apply the control apparatus which concerns on this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The control device according to the present embodiment is a control device that controls a post-processing system of a diesel engine mounted on an automobile. FIG. 1 is a schematic view showing the configuration of a diesel engine aftertreatment system. The aftertreatment system includes a DOC (diesel oxidation catalyst) and a DPF (diesel particulate removal device) in the exhaust passage, and a fuel addition valve in the exhaust port of the cylinder head. A temperature sensor for measuring the exhaust gas temperature upstream of the DPF (downstream of the DOC) is attached between the DOC and the DPF.

  The control device according to the present embodiment includes a control structure for following the target value while maintaining the DPF temperature below the upper limit value. The control structure is the target value follow-up control structure shown in FIG. The target value tracking control structure according to the present embodiment includes a target value map (MAP), a reference governor (RG), and a feedback controller (FBC).

  The target value map outputs a target value r of the DPF temperature, which is a control amount, when an exogenous input d indicating the operating condition of the diesel engine is given. The exogenous input d includes the exhaust gas mass flow rate, the exhaust gas temperature upstream and downstream of the DPF, the amount of PM deposited on the DPF, and the atmospheric temperature. These physical quantities included in the exogenous input d may be measured values or estimated values.

  When the target value r of the DPF temperature is given, the reference governor corrects the target value r so that the constraint on the DPF temperature is satisfied, and outputs the corrected target value w of the DPF temperature. Details of the reference governor will be described later.

  When the correction target value w of the DPF temperature is given from the reference governor, the feedback controller acquires the state quantity x indicating the current value of the DPF temperature, and performs feedback control based on the deviation e between the correction target value w and the state quantity x. A control input u to be given to the diesel engine is determined. Since the control target according to the present embodiment is the post-processing system, the amount of fuel added to the exhaust gas by the fuel addition valve, that is, the amount of fuel addition is used as the control input u. The specification of the feedback controller is not limited, and a known feedback controller can be used. For example, a proportional-integral feedback controller can be used.

FIG. 3 shows a feedforward structure obtained by equivalently modifying the target value tracking control structure shown in FIG. In the feed-forward structure shown in FIG. 3, the closed loop system surrounded by a broken line in FIG. 2 is already designed, and is a single model (P). The model of the closed loop system is expressed by the following model equation (1). In Expression (1), f and h are functions of the model expression. K represents a discrete time step.

The reference governor prepares candidates (w ₁ , w ₂ ,..., W _Ng ) of the corrected target value w based on the given target value r of the DPF temperature. N _g represents the number of candidates for the correction target value w. The reference governor inputs each of the candidates for the corrected target value w into the model of the closed loop system and predicts the future value of the DPF temperature. Since the prediction model used by the reference governor is expressed by Expression (1), the future values of the state quantity x and the control output y are expressed by Expression (2) below.

X (i | k) and y (i | k) shown in the equation (2) are future state quantities i steps ahead estimated based on the information at time k and predicted values of control outputs. Further, a _{N h} is predicted number of steps shown in Equation (2) (predicted horizon). A value obtained by multiplying the number of prediction steps by the time interval of discrete time steps is a prediction length (prediction section) from the present to the future. Here, it is assumed that the value d (k) of the exogenous input at time k continues during the prediction interval.

The restriction imposed on the control output y is that the control output y is equal to or less than the upper limit value y ⁻ . The reference governor uses the objective function J (w) expressed by the following equation (3) based on the predicted value y (i | k) of the control output and the upper limit value y ^{− of the} control output, and the corrected target value w. Calculate

The first term on the right side of the objective function J (w) shown in Expression (3) is a term with the corrected target value candidate w as a variable. The first term is configured to take a smaller value as the distance between the original target value r and the corrected target value candidate w is smaller. The second term on the right side of the objective function J (w) is a penalty term. The penalty term is configured such that when the predicted value y ^ (k + i | k) conflicts with a constraint, a penalty corresponding to the conflict is added. Note that y ^ (k + i | k) represents the predicted value of the control output at time k + i based on the information at time k. In the penalty term, a weight constant ρ for weighting the penalty is set. According to this penalty term, the control output prediction value y ^ and constraints at a control output upper limit value y ^- value obtained by multiplying the weight constant ρ in the absolute value of the difference is added to the first term on the right side of equation (3).

  The objective function J (w) shown in the expression (3) is constrained to select the target function J (w) that minimizes the objective function J (w) from among the corrected target value candidates w that satisfy the restriction of the control output y at each time k. It can be solved as an optimization problem. Specifically, as described in Expression (3), a corrected target value candidate w that minimizes the objective function J (w) is searched over a finite prediction horizon. FIG. 4 is a diagram showing a reference governor algorithm according to the present embodiment. As shown in FIG. 4, in this embodiment, the objective function J (w) shown in Equation (3) is minimized by repeating the prediction value y (i | k) predicted by the closed loop system a finite number of times. The correction target value candidate w to be searched is searched and selected as the final correction target value w. In this embodiment, the steepest descent method, which is a known method, is employed as a method for searching for the minimum value of the objective function J (w).

The advantage of the objective function J (w) of Expression (3) will be described in comparison with the conventional objective function with reference to FIG. The following equation (4) is a conventional objective function as a comparative example of the objective function employed in the present embodiment.

Equation (4) in the second term on the right side of the predicted value y ^ (k + i | k) is the predicted value y when exceeding the constraint ^ (k + i | k) and the upper limit y ^- penalty the first based on the difference of the Added to the term. That is, a penalty based on the sum exceeding the upper limit value y ⁻ shown in FIG. 5 is added to the first term on the right side of Equation (4). On the other hand, the predicted value y ^ | if (k + i k) is below the constraints max {y ^ (k + i | k) -y -, 0} is 0. Therefore, if the predicted value y ^ (k + i | k) never violates the constraint in the prediction interval, the second term on the right side of Equation (4) is zero. Then, the corrected target value w for minimizing the objective function J (w) is r _k, i.e., so that the original target value is determined as the optimum value.

In contrast, in the second term on the right-hand side of equation (3), the predicted value y ^ when exceeding the constraint (k + i | k) and the upper limit y ^- not only the difference between the predicted value when below the constraints y ^ A penalty based on the difference between (k + i | k) and the upper limit value y ⁻ is added to the first term. That is, a penalty based on the sum of the upper limit y ⁻ and the lower limit y ⁻ shown in FIG. 5 is added to the first term on the right side of Equation (3). Therefore, the corrected target value w exceeding the original target value r _k can be determined as the optimum value. Therefore, even when the predicted value y ^ (k + i | k) never conflicts with the constraint in the prediction interval, the correction target value w is corrected upward, and the DPF temperature control on the high temperature side closer to the constraint can be realized. .

  By the way, in the above-mentioned embodiment, the control apparatus which concerns on this invention was applied to the aftertreatment system of the diesel engine. However, the control apparatus which concerns on this invention can make a control object into a diesel engine main body (DE), as shown to (a)-(i) of FIG.

  When the control target is a diesel engine body, as shown in FIG. 6A, the control input can be a variable nozzle opening (VN opening), and the control output can be a supercharging pressure. That is, the present invention can be applied to supercharging pressure control of a diesel engine. In this case, as shown in FIG. 6B, the control input can be a variable nozzle opening and a diesel throttle opening (D opening).

  Further, as shown in FIG. 6C, the control input can be an EGR valve opening, and the control output can be an EGR rate. That is, the present invention can be applied to EGR control of a diesel engine. In this case, as shown in FIG. 6 (d), the control input can be an EGR valve opening and a diesel throttle opening.

  Furthermore, as shown in FIG. 6E, the control input can be a variable nozzle opening, an EGR valve opening, and a diesel throttle opening, and the control output can be a supercharging pressure and an EGR rate. That is, the present invention can also be applied to cooperative control of the supercharging pressure and the EGR rate in a diesel engine.

  When the diesel engine to be controlled has a low-pressure EGR system and a high-pressure EGR system, as shown in FIG. And the EGR valve opening (HPL-EGR valve opening) and the variable nozzle opening of the high-pressure EGR system. Further, as shown in FIG. 6 (g), the control inputs can be the EGR valve opening of the low pressure EGR system, the EGR valve opening of the high pressure EGR system, the variable nozzle opening, and the diesel throttle opening. Further, as shown in (h) and (i) of FIG. 6, the control output includes an EGR amount (LPL-EGR amount) of the low pressure EGR system, an EGR amount (HPL-EGR amount) of the high pressure EGR system, and a supercharging pressure. It can also be.

  Furthermore, the plant to which the control device according to the present invention is applied is not limited to a diesel engine. For example, the present invention can be applied to other in-vehicle power plants such as gasoline engines and hybrid systems, as well as fuel cell systems.

Claims (1)

A feedback controller that determines a control input of the internal combustion engine by feedback control so that an output value of a control amount of the internal combustion engine approaches a target value;
A future predicted value of the specific state quantity of the internal combustion engine is calculated over a predetermined prediction interval using a model of a closed loop system including the internal combustion engine and the feedback controller, and is imposed on the predicted value and the control output. A reference governor for correcting the target value given to the feedback based on the constraints
The reference governor sets a penalty based on a first term relating to a difference between an original target value and a candidate for a corrected target value and a sum based on a sum of absolute values of differences between the predicted value and the constraint calculated in the prediction interval. A candidate for a correction target value that minimizes the objective function represented by the second term added to the term is searched, and a candidate for the correction target value that minimizes the objective function is used as a correction target value for correcting the target value. A control device for an internal combustion engine, wherein the control device is selected.

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