JP2015113804A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably form a target value even in a case where the running condition for an internal combustion engine suddenly changes in a future estimation using a reference governor.SOLUTION: In one embodiment, for a correction target value candidate w, there are performed in parallel an estimation based on a current exhaust flow rate condition and an estimation based on an exhaust flow rate condition during an idle running time. By repeating calculation of an object function using those estimation results by a finite number, the correction target value candidate w to minimize an evaluation function J(w), as expressed in formula (2), is selected and determined as the final correction target value w.

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 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 predicts future values of state quantities to which constraints are imposed by the prediction model. Then, the target value of the control amount of the internal combustion engine is corrected based on the predicted value of the state quantity and the constraints imposed thereon.

  The inventor of the present application has already disclosed the prior art in which the reference governor is applied to the control of the internal combustion engine in the following Patent Document 1. In this prior art, the reference governor uses a plant model in which the dynamic characteristics of a closed-loop system related to feedback control is modeled by “dead time + secondary vibration system”, and uses a plant model in the future with specific state quantities such as supercharging pressure and charging efficiency. The trajectory is predicted, and the target value is shaped so as to satisfy the constraints imposed on the specific state quantity. Further, the range in which the future trajectory is predicted using the reference governor is set to the total time of the dead time in the plant model and the half of the vibration period of the secondary vibration system.

JP2013-084091A

  By the way, in the future prediction using the reference governor of Patent Document 1, it is assumed that the future information of the external input such as the operating condition of the internal combustion engine is constant within the prediction range. However, it is not realistic that the operating condition does not change over the predicted range. Therefore, an improvement that can cope with a case where the operating condition changes suddenly is desired.

  The present invention has been made in view of the above-described problems. That is, in the future prediction using the reference governor, the object is to stably shape the target value even when the operating condition of the internal combustion engine changes suddenly.

In order to achieve the above object, a control device for an internal combustion engine according to the present invention comprises:
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 preset prediction interval using a model of a closed loop system including the internal combustion engine and the feedback controller, and the calculated predicted value and the specific state A reference governor that modifies the target value provided to the feedback controller based on constraints imposed on the quantity;
The specific state quantity is a temperature of a device for removing particulates contained in the exhaust gas of the internal combustion engine,
The reference governor calculates the first future predicted value of the temperature calculated on the assumption that the operating condition of the internal combustion engine at the start time of the prediction interval is not changed until the end time of the prediction interval, and the start of the prediction interval The target value is corrected based on a second future predicted value of the temperature calculated on the assumption that the internal combustion engine is idling from the time point to the end time point, and a restriction imposed on the temperature. To do.
The “idle operation” means an operation state in which the load of the internal combustion engine is almost zero and the driving force generated by the internal combustion engine is not used to drive a vehicle equipped with the internal combustion engine. To do.

  According to the control device of the present invention, the future predicted value (first future predicted value) of the specific state quantity calculated on the assumption that the operating condition of the internal combustion engine at the start time of the predicted section is continued until the end time of the predicted section. ) As well as the future predicted value (second future predicted value) of the specific state quantity calculated on the assumption that the idling operation of the internal combustion engine is continued from the start point to the end point of the prediction interval. Since the given target value is corrected, even when the operating condition of the internal combustion engine changes suddenly, the target value of the temperature of the particulate removal device, which is the specific state quantity, can be stably shaped.

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 which shows the example of the control input and control output of a diesel engine which can apply the control apparatus of this invention.

Embodiment 1 FIG.
First, Embodiment 1 of the present invention will be described with reference to the drawings.

  The control device according to the present embodiment controls a post-processing system for a diesel engine mounted on a vehicle. FIG. 1 is a schematic view showing the configuration of a diesel engine aftertreatment system. The aftertreatment system shown in FIG. 1 includes a DOC (diesel oxidation catalyst) and a DPF (diesel particulate removal device) in an exhaust passage, and a fuel addition valve in an exhaust port of the cylinder head.

  An upper limit is set for the temperature (specific state quantity) of the DPF as a restriction on hardware or control. The control device of 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. As shown in FIG. 2, the target value tracking control structure includes a target value map (MAP), a reference governor (RG), and a feedback controller.

  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 and the exhaust gas temperature upstream of the DPF (downstream of the DOC). 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. The control input u to be given to the control object is determined. Since the control target in 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 is a diagram showing a feedforward structure obtained by equivalently deforming the target value tracking control structure shown in FIG. In the feedforward structure shown in FIG. 3, the closed-loop system surrounded by a broken line in FIG. 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 calculates the predicted value y ^ of the control output y of the controlled object using the prediction model represented by the above equation (1). The control output y in the present embodiment is the DPF temperature, and a restriction is imposed on the control output y. 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 ⁻ . In order to calculate the control output predicted value y ^, the corrected target value w is used in addition to the state quantity x and the exogenous input d. The reference governor calculates the corrected target value w using the evaluation function J (w) expressed by the following equation (2) based on the control output predicted value y ^ and the control output upper limit value y ⁻ .

The first term on the right side of the evaluation function J (w) shown in Expression (2) is an objective function with the corrected target value candidate w as a variable. This objective function 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 and third terms on the right side of the evaluation function J (w) are based on the weighted sum of the predicted output value y ^ predicted in the future by the above formula (1) under two different operating conditions (exhaust flow rate conditions). This is the term to be calculated. ρ _constant and ρ _worst are weighting factors.

Specifically, the two operating conditions are an exhaust flow rate condition at the present time and an exhaust flow rate condition at the time of idle operation. J _constant is the sum of the constraint conflict amounts calculated based on the predicted output value y ^ _const predicted using the prediction model, assuming that the current exhaust flow rate continues from the start time to the end time of the prediction interval, It is represented by the following formula (3). J _worst is the sum of the constraint conflicts calculated based on the predicted output y ^ _worst predicted using the prediction model, assuming that the exhaust flow during idle operation continues from the start to the end of the prediction interval. Yes, it is represented by the following formula (4).

  In the control device of the present embodiment, the correction target value candidate w that minimizes the evaluation function J (w) shown in the equation (2) is used as the final correction target value w. The evaluation function J (w) shown in Equation (2) can be solved as an unconstrained optimization problem. However, when the target value tracking control structure using the reference governor is applied to an actual engine, it is desirable that the evaluation function J (w) can be optimized online. For this reason, the control device according to the present embodiment employs the steepest descent method, which is a known method, as a method for searching for the minimum value of the evaluation function J (w).

  FIG. 4 is a diagram showing a reference governor algorithm according to the present embodiment. As shown in FIG. 4, in the present embodiment, prediction based on the current exhaust flow rate condition and prediction based on the exhaust flow rate condition during idle operation are performed in parallel with respect to the corrected target value candidate w. Then, by repeating the calculation of the objective function using these prediction results a finite number of times, the correction target value candidate w that minimizes the evaluation function J (w) shown in the equation (2) is selected, and the final correction is performed. The target value w is determined.

  The exhaust flow rate is small during idle operation. Therefore, the exhaust flow rate decreases when switching from normal operation to idle operation, and the exhaust flow rate increases when switching from idle operation to normal operation. Therefore, according to the present embodiment in which future prediction is performed by combining the current operating conditions and the operating conditions during idle operation, it is possible to realize target value tracking control provided for the worst case. Therefore, for example, when the clutch is suddenly disengaged by the driver and the exhaust flow rate suddenly decreases, it is possible to prevent the occurrence of a problem such as a thermal runaway of the DPF. In addition, the DPF temperature can be increased without a conservative prediction in a steady state.

In the embodiment described above, the output predicted value y ^ _{constant corresponds} to the "first future predicted value" of the present invention, and the output predicted value y ^ _worst corresponds to the "second future predicted value" of the present invention. ing.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described. The control device according to the second embodiment is premised on the configuration of the first embodiment, and is characterized in the weight coefficient ρ _constant and ρ _worst updating method described in the first embodiment. Therefore, in the following description, only this characteristic part will be described.

Optimum values of the weighting coefficients ρ _constant and ρ _worst are initially set by simulation. In the present embodiment, this initial set value is corrected based on the past engine operating state. Specifically, when the engine operating state within a predetermined time until the present is a steady state, there is a high possibility that the steady state will continue after the present. Therefore, a weight is added to the weighting factor ρ _constant rather than the weighting factor ρ _worst . On the other hand, if the engine operating state within a predetermined time until the present is a transient state, there is a high possibility that the transient state will continue after the present. Therefore, a weight is added to the weighting factor ρ _worst rather than the weighting factor ρ _constant . By performing such correction, it becomes possible to stably increase the DPF temperature in the steady state and complete the regeneration of the DPF at an early stage. In a transient state, it is possible to follow the target value while suppressing an excessive increase in the DPF temperature.

  By the way, in each above-mentioned embodiment, the aftertreatment system of the diesel engine was made into the controlled object. 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. 5A, 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. 5B, the control input can be a variable nozzle opening and a diesel throttle opening (D opening).

  Further, as shown in FIG. 5C, 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. 5 (d), the control input can be an EGR valve opening and a diesel throttle opening.

  Furthermore, as shown in FIG. 5E, 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. 5 (f), the control input is the EGR valve opening (LPL-EGR valve opening) of the low pressure EGR system. 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. 5G, the control input can be an EGR valve opening of the low pressure EGR system, an EGR valve opening of the high pressure EGR system, a variable nozzle opening, and a diesel throttle opening. Further, as shown in (h) and (i) of FIG. 5, 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 internal combustion engine to which the control device of each embodiment is applied is not limited to a diesel engine. For example, the present invention can be applied to a fuel cell system in addition to other in-vehicle power such as a gasoline engine or a hybrid system.

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 preset prediction interval using a model of a closed loop system including the internal combustion engine and the feedback controller, and the calculated predicted value and the specific state A reference governor that modifies the target value provided to the feedback controller based on constraints imposed on the quantity;
The specific state quantity is a temperature of a device for removing particulates contained in the exhaust gas of the internal combustion engine,
The reference governor calculates the first future predicted value of the temperature calculated on the assumption that the operating condition of the internal combustion engine at the start time of the prediction interval is not changed until the end time of the prediction interval, and the start of the prediction interval The target value is corrected based on a second future predicted value of the temperature calculated on the assumption that the internal combustion engine is idling from the time point to the end time point, and a restriction imposed on the temperature. A control device for an internal combustion engine.

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