Patent Application
20200072151
The disclosure of Japanese Patent Application No. 2018-160591 filed on Aug. 29, 2018 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
The disclosure relates to a control device for an internal combustion engine and a control method for an internal combustion engine, and specifically, relates to a control device and a control method that are suitably used for control of a controlled object having a stochastic dispersion.
In the case where a feedback control is applied to a controlled variable for a controlled object having a stochastic dispersion, it is necessary to inevitably perform a conservative control, for preventing an excessive control due to the stochastic dispersion. However, in the conservative control, it is difficult to secure a fast-response to a change in the controlled variable.
The change in the controlled variable includes a change due to an original stochastic dispersion of a system and a change due to a factor other than the stochastic factor. The change in the controlled variable that needs to be dealt with by the feedback control is the latter change due to the change in the state of the controlled object. Therefore, for securing the fast-response while preventing the excessive control, it is required to determine whether the change in the controlled variable is the former change or the latter change. However, generally, a lot of data is needed for statistically determining the cause for the change in the controlled variable. As the number of data increases, the accuracy of the determination increases, but the time for collection of the data increases, so that the fast-response decreases.
For increasing the fast-response, it is necessary to perform the determination with as little data as possible. In this regard, Jinwu Gao, Yuhu Wu, Tielong Shen, A statistical combustion phase control approach of SI engines, Mechanical Systems and Signal Processing 85 (2017) 218-235 discloses a control technique of feeding back the change in the controlled variable to a manipulated variable using a hypothesis test and a statistical decision. As a specific example, Jinwu Gao, Yuhu Wu, Tielong Shen, A statistical combustion phase control approach of SI engines, Mechanical Systems and Signal Processing 85 (2017) 218-235 discloses an example in which a crank angle (represented by LPP, hereinafter) maximizing the combustion pressure of an internal combustion engine is applied to a feedback control for controlling a reference expectation value. The combustion of the internal combustion engine is an example of the controlled object having the stochastic dispersion, and LPP is an example of the controlled variable.
If the expectation value of LPP is the reference expectation value, the value (represented by Z, hereinafter) obtained by dividing a deviation of an average value of LPP from the reference expectation value by a standard error of the average value accords with a standard normal distribution. When the data of LPP from the first cycle to the n-th cycle is obtained, the average value is the average value of n pieces of data from the first cycle to the n-th cycle. Further, the standard error of the average value is obtained by dividing a standard deviation of LPP by a square of the number of data.
Whether Z accords with the standard normal distribution can be determined by comparison to a threshold value that is calculated from a significant level. In the case where Z does not fall within a credibility interval that is specified by a negative threshold value and a positive threshold value, it is determined that Z does not accord with the standard normal distribution, that is, the expectation value of LPP is not equal to the reference expectation value. In the case where Z falls within the credibility interval, Z accords with the standard normal distribution, that is, the expectation value of LPP is equal to the reference expectation value.
In the case where the expectation value of LPP is equal to the reference expectation value, the change in LPP is the change due to the original stochastic dispersion of the system. On the other hand, in the case where the expectation value of LPP is not equal to the reference expectation value, the change in LPP is the change due to the factor other than the stochastic factor. Therefore, by calculating Z for each combustion cycle and checking whether Z falls within the credibility interval, it is possible to determine whether the change is a change in LPP that needs to be dealt with by the feedback control, for each combustion cycle.
In the specific feedback control disclosed in Jinwu Gao, Yuhu Wu, Tielong Shen, A statistical combustion phase control approach of SI engines, Mechanical Systems and Signal Processing 85 (2017) 218-235, a value obtained by adding a product of the positive threshold value and the standard error to the reference expectation value of LPP is set as an upper limit value of LPP, and in the case where the average value of LPP exceeds the upper limit value, ignition timing is advanced. Further, a value obtained by adding a product of the negative threshold value and the standard error to the reference expectation value of LPP is set as a lower limit value of LPP, and in the case where the average value of LPP exceeds the lower limit value, the ignition timing is advanced. In the control technique disclosed in Jinwu Gao, Yuhu Wu, Tielong Shen, A statistical combustion phase control approach of SI engines, Mechanical Systems and Signal Processing 85 (2017) 218-235, it is possible to make a statistical determination without requiring a lot of data. Therefore, by performing the feedback control based on the determination, it is possible to secure the fast-response to the change in the controlled variable due to the factor other than the stochastic factor, while preventing the excessive control to the change in the controlled variable due to the stochastic dispersion.
Japanese Patent Application Publication No. 2007-198313, Japanese Patent Application Publication No. 2002-322938 and Japanese Patent Application Publication No. 2011-089470 are exemplary literatures that show the state of the art in the technical field related to the disclosure.
However, in the control technique disclosed in Jinwu Gao, Yuhu Wu, Tielong Shen, A statistical combustion phase control approach of SI engines, Mechanical Systems and Signal Processing 85 (2017) 218-235, there is room for further improvement in terms of the fast-response to the change in the controlled variable due to the factor other than stochastic factor.
Hence, the disclosure further enhances the prevention of the excessive control to the change in the controlled variable due to the stochastic dispersion and the securement of the fast-response to the change in the controlled variable due to the factor other than the stochastic factor, by a control technique evolved from the control technique disclosed in Jinwu Gao, Yuhu Wu, Tielong Shen, A statistical combustion phase control approach of SI engines, Mechanical Systems and Signal Processing 85 (2017) 218-235.
A first aspect of the disclosure is a control device for an internal combustion engine. The control device includes: at least one processor; and a memory configured to store a program. The at least one processor is configured to execute a manipulated variable decision process, a sample value calculation process, an expectation value calculation process, a hypothesis test process and an adaptive control process by executing the program. The manipulated variable decision process decides a manipulated variable of the internal combustion engine from a control input value related to a controlled variable including a stochastic dispersion, in accordance with a predetermined conversion rule. The sample value calculation process calculates a sample value of the controlled variable for each sampling cycle based on information from a sensor that detects a state of the internal combustion engine. The expectation value calculation process calculates a reference expectation value of the controlled variable from the control input value using a normative model for the internal combustion engine. The hypothesis test process performs a hypothesis test for a null hypothesis that an average value of a predetermined number of recent sample values of sample values of the controlled variable is equal to the reference expectation value. The adaptive control process modifies the predetermined conversion rule by an adaptive control based on an error between the average value and the reference expectation value, when the null hypothesis is rejected.
With the above configuration, by combining the adaptive control with the determination of the stochastic dispersion by the hypothesis test, it is possible to expect a further enhancement of the prevention of the excessive control to the change in the controlled variable due to the stochastic dispersion and the securement of the fast-response to the change in the controlled variable due to the factor other than the stochastic factor.
In the control device, the hypothesis test process may include an acceptance region calculation process and a determination process. The acceptance region calculation process may calculate an upper limit value of a region of acceptance and a lower limit value of the region of the acceptance by multiplication of a standard error of a reference normal population of the controlled variable when a number of sample data is the predetermined number by a predetermined critical value. The determination process may reject the null hypothesis when the error between the average value and the reference expectation value does not fall within the region of the acceptance. The expectation value calculation process may be a process of calculating an average value of the reference normal population, as the reference expectation value.
In the control device, the reference normal population may be a set of sample values prior to the predetermined number of sample values of the controlled variable, and the reference expectation value and the standard error may be updated for each sampling cycle. In the control device, the reference normal population may be a set of sample values of the controlled variable, the sample values being obtained from a reference internal combustion engine, and the reference expectation value and the standard error may be predetermined values that are calculated from the reference normal population.
In the control device, the manipulated variable decision process may include a feedback process of calculating a feedback value of the manipulated variable from the error between the average value and the reference expectation value, and the adaptive control process may include a feedback gain modification process of modifying a feedback gain in the feedback process, depending on the error between the average value and the reference expectation value.
In the control device, the manipulated variable decision process may include a feedforward process of calculating a feedforward value of the manipulated variable from the control input value, and the adaptive control process may include a feedforward map modification process of modifying a feedforward map in the feedforward process, depending on the error between the average value and the reference expectation value.
A second aspect of the disclosure is a control method for an internal combustion engine. The internal combustion engine includes a memory configured to store a program, and at least one processor configured to execute the program. The control method includes: executing, by the at least one processor, a manipulated variable decision process of deciding a manipulated variable of the internal combustion engine from a control input value related to a controlled variable including a stochastic dispersion, in accordance with a predetermined conversion rule; executing, by the at least one processor, a sample value calculation process of calculating a sample value of the controlled variable for each sampling cycle based on information from a sensor that detects a state of the internal combustion engine; executing, by the at least one processor, an expectation value calculation process of calculating a reference expectation value of the controlled variable from the control input value using a normative model for the internal combustion engine; executing, by the at least one processor, a hypothesis test process of performing a hypothesis test for a null hypothesis that an average value of a predetermined number of recent sample values of sample values of the controlled variable is equal to the reference expectation value; and executing, by the at least one processor, an adaptive control process of modifying the predetermined conversion rule by an adaptive control based on an error between the average value and the reference expectation value, when the null hypothesis is rejected.
With the above configuration, by combining the adaptive control with the determination of the stochastic dispersion by the hypothesis test, it is possible to expect a further enhancement of the prevention of the excessive control to the change in the controlled variable due to the stochastic dispersion and the securement of the fast-response to the change in the controlled variable due to the factor other than the stochastic factor.
Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:
Hereinafter, an embodiment of the disclosure will be described with reference to the drawings. However, when a numerical value about each element, as exemplified by the number of elements, quantity, amount and range, is mentioned in the embodiment described below, the disclosure is not limited to the mentioned numerical value, except in a case where the numerical value is explicitly adopted particularly and a case where the numerical value is clearly adopted in principle. Further, structures, steps and the like in the embodiment described below are not always essential for the disclosure, except in a case where the structures, the steps and the like are explicitly adopted particularly and a case where the structures, the steps and the like are clearly adopted in principle.
The internal combustion engine 2 is an internal combustion engine that is mounted on an automobile, for example, a spark-ignited internal combustion engine that uses gasoline as fuel. The internal combustion engine 2 includes an ignition system that can adjust ignition timing by controlling energization period for an ignition coil. The plurality of sensors 4 includes at least a combustion pressure sensor and a crank angle sensor. The combustion pressure sensor, which is attached to each cylinder of the internal combustion engine 2, outputs a signal corresponding to the combustion pressure in a combustion chamber. The crank angle sensor outputs a signal corresponding to the crank angle of the internal combustion engine 2. In addition, the plurality of sensors 4 may include a knocking sensor, an air-fuel ratio sensor, or the like.
The control device 10, which is an electronic control unit for engine control, receives the signals of the sensors 4, and calculates a controlled variable of the internal combustion engine 2, based on information included in the signals of the sensors 4. The control device 10 includes a processor 12 and a memory 14 as physical constituents. The memory 14 stores a program for control of the internal combustion engine 2, and the processor 12 reads the program from the memory 14 and executes the program. The control device 10 may be constituted by a plurality of electronic control units.
First, the manipulated variable decision process 21 will be described. In the manipulated variable decision process 21, the control device 10 decides the manipulated variable for controlling a controlled object of the internal combustion engine 2. The controlled object of the internal combustion engine 2 includes a controlled object including a stochastic dispersion, as exemplified by combustion and exhaust emission. In the case where the controlled object includes the stochastic dispersion, the controlled variable, which is a state quantity, also includes the stochastic dispersion. Examples of the controlled variable relevant to the combustion include CA50, maximum-combustion-pressure crank angle (LPP), knocking-start crank angle, maximum-knocking-occurrence crank angle, and knocking intensity. Examples of the controlled variable relevant to the exhaust emission include air-fuel ratio and fuel equivalence ratio. In the case where the controlled object is the combustion, the manipulated variable is ignition timing, for example. In the case where the controlled object is the exhaust emission, the manipulated variable is fuel injection quantity, for example.
In the manipulated variable decision process 21, the manipulated variable of the internal combustion engine 2 is decided from a control input value in accordance with a predetermined conversion rule. The control input value is associated with a reference expectation value (target value) of the controlled variable. In the controlled technique disclosed in Jinwu Gao, Yuhu Wu, Tielong Shen, A statistical combustion phase control approach of SI engines, Mechanical Systems and Signal Processing 85 (2017) 218-235, the control input value needs to have the same dimension as the dimension of the controlled variable, and the reference expectation value itself of the controlled variable is input as the control input value. On the other hand, in the control device 10 according to the embodiment, a parameter having a different dimension from the dimension of the control input value can be used as the control input value, as described later. In the case where the controlled variable is CA50, for example, required torque or required efficiency can be used as the control input value. In the case where the controlled variable is air-fuel ratio, for example, required NOx concentration or required fuel efficiency can be used as the control input value. Here, the reference expectation value itself of the controlled variable can be input as the control input value.
The conversion rule for deciding the manipulated variable from the control input value, specifically, is configured by a map and/or a function. For example, in the case where a feedback control is used for deciding the manipulated variable from the control input value, the conversion rule includes a conversion function for a feedback process. A feedback gain of the conversion function can be varied, and can be modified by the adaptive control process 25 described later. For example, in the case where a feedforward control is used for deciding the manipulated variable from the control input value, the conversion rule includes a feedforward map for a feedforward process. In the feedforward map, the manipulated variable is associated with the control input value. The association between the control input value and the manipulated variable in the map can be modified, and is modified by the adaptive control process 25 described later.
Next, the sample value calculation process 22 will be described. In the sample value calculation process 22, the control device 10 calculates a sample value of the controlled variable for each sampling cycle based on the information from the sensors 4. The calculated sample value of the controlled variable is fed back to the manipulated variable decision process. Therefore, preferably, the sampling cycle should be equal to the cycle of the decision of the manipulated variable. For example, the combustion cycle of the internal combustion engine 2 may be used as the sampling cycle.
For example, in the case where the controlled variable is CA50, the control device 10, for each combustion cycle, calculates the value of CA50 from the pressure in the combustion chamber that is measured by the combustion pressure sensor. Specifically, CA50 means a crank angle at which combustion rate is 50%. The combustion rate means the rate of the mass of actually combusted fuel to the mass of fuel supplied into the combustion chamber per combustion cycle. The combustion rate at an arbitrary crank angle can be calculated as the rate of the heat production at the crank angle to the final heat production. The heat production is the total of heat quantity generated in the combustion chamber from the start of the combustion in one combustion cycle. Therefore, the heat production at the crank angle is calculated by integrating a heat production rate calculated for each crank angle in an integration range from a combustion start angle to the crank angle. The heat production rate is a heat quantity produced in the combustion chamber per unit crank angle, and can be calculated from the pressure in the combustion chamber that is measured by the combustion pressure sensor. In the case where the controlled variable is CA50, the value of CA50 is calculated for each combustion cycle in this way. The combustion rate of 50% is one criterion, and a crank angle at which the combustion rate is a predetermined rate other than 50% may be used as the controlled variable.
Next, the reference expectation value calculation process 23 will be described. In the reference expectation value calculation process 23, the control device 10 calculates the reference expectation value of the controlled variable from the control input value, using a normative model for the internal combustion engine 2. The normative model is a model that simulates an ideal input-output characteristic between the control input value as an input and the controlled variable as an output so as to satisfy a required performance of the internal combustion engine 2. In the normative model, dimension conversion is performed, and therefore, the dimension of the control input value may be different from the dimension of the controlled variable as described above.
For example, the normative model is configured by a function, and a parameter of the function is learned based on actual data of the control input value and the controlled variable. For example, the data to be used for the learning by the normative model may be data to be obtained from a reference internal combustion engine. The reference internal combustion engine is an internal combustion engine having a desired performance according to the design. In the case where the normative model performs the learning with such data, a deviation between the reference expectation value obtained from the normative model and the sample value calculated in the sample value calculation process 22 means that there is a gap between the current state and proper state of the internal combustion engine 2.
Further, for example, the data to be used for the learning by the normative model may be data to be obtained by an actual operation of the internal combustion engine 2. The data to be used for the learning is updated for each sampling cycle. In the case where the normative model performs the learning with such data, a deviation between the reference expectation value obtained from the normative model and the sample value calculated in the sample value calculation process 22 means that there is a gap between the current state and past state of the internal combustion engine 2. That is, the deviation means a change in the state of the internal combustion engine 2 (particularly, the state of the controlled object).
Next, the hypothesis test process 24 will be described. The internal combustion engine 2 has an individual difference, and changes over time. Therefore, even when the manipulated variable is identical, the obtained sample value of the controlled variable has a dispersion for each sampling cycle. However, the dispersion includes a stochastic dispersion in accordance with a normal distribution. Hence, in the hypothesis test process 24, the control device 10 performs a hypothesis test for a null hypothesis that an average value (referred to as an average recent sample value, hereinafter) of a predetermined number of recent sample values of the sample values of the controlled variable is equal to the reference expectation value calculated in the reference expectation value calculation process.
Here, as shown in
In the case of making the null hypothesis that the average recent sample value Xave is equal to the reference expectation value μo, data Z calculated by the following formula accords with a standard normal distribution if the null hypothesis is true. In the following formula, σo is a standard deviation of the reference normal population, and σo/nr1/2 a standard error of the reference normal population when the number of data is nr.
When a significance level is represented by α and a critical value for the data Z is represented by Zα/2, the critical value Zα/2 can be calculated by the following formula. The significance level a is a numerical value that is decided by adaptation at the time of design.
When the dispersion of the controlled variable for each sampling cycle in the internal combustion engine 2 is a stochastic dispersion in accordance with a normal distribution, the following formula is satisfied for the error between the average recent sample value Xave and the reference expectation value μo. The lower limit value of the error Xave−μo of the controlled variable is a value obtained by multiplying the standard error σo/nr1/2 by a negative critical value Zα/2, and the upper limit value of the error Xave−μo of the controlled variable is a value obtained by multiplying the standard error σo/nr1/2 by a positive critical value Zα/2. When the following formula is not satisfied, the dispersion of the sample value of the controlled variable includes a factor other than the stochastic factor.
As seen from the graph in
Finally, the adaptive control process 25 will be described. In the case where the null hypothesis that the average recent sample value Xave is equal to the reference expectation value μo is rejected in the hypothesis test process 24, the dispersion of the sample value of the controlled variable includes a factor other than the stochastic factor. The main factor is a change in the state of the controlled object due to a change in an environment condition, a temporal change in the internal combustion engine 2, that is, a deviation between the actual state of the controlled object and the state of the controlled object in the normative model. Hence, in the case where the above-described null hypothesis is rejected in the hypothesis test process 24, the control device 10, in the adaptive control process 25, modifies the conversion rule to be used for the decision of the manipulated variable in the manipulated variable decision process 21, by an adaptive control based on the error Xave−μo of the controlled variable.
In the adaptive control process 25, the conversion rule is modified based on the magnitude of the error Xave−μo of the controlled variable and whether the sign is positive or negative, such that the error Xave−μo of the controlled variable falls within the region of the acceptance. A specific modified object is a map or function that configures the conversion rule. For example, in the case where the conversion rule is configured by a function, gains of at least some members are modified depending on the magnitude of the error Xave−μo of the controlled variable. In the case where the feedback control is used for the decision of the manipulated variable, a conversion function for the feedback process is included in the conversion rule, and at least some feedback gains are adopted as the modified object in the adaptive control.
In the case where the conversion rule is configured by a map, some or all map values are modified, for example, depending on the magnitude of the error Xave−μo of the controlled variable and/or whether the sign is positive or negative. Thereby, the association between the control input value and the manipulated variable in the map is modified. In the case where the feedforward control is used for the decision of the manipulated variable, a feedforward map for the feedforward process is included in the conversion rule, and at least some map values are adopted as the modified object in the adaptive control.
The controller 31 executes the above-described manipulated variable decision process 21. The controller 31 receives the control input value from an unillustrated high-order system. The controller 31 decides the manipulated variable from the received control input value. The internal combustion engine 2 is operated in accordance with the manipulated variable decided in the manipulated variable decision process 21. For example, in the case where the controlled object is the combustion and the controlled variable is CA50, the internal combustion engine 2 is operated in accordance with the ignition timing decided by the controller 31.
The controlled variable sample value calculation unit 32 executes the above-described sample value calculation process 22. The controlled variable sample value calculation unit 32 acquires the sensor information output by the sensors 4, and calculates the sample value of the controlled variable from the acquired sensor information, for each sampling cycle. For example, in the case where the controlled variable is CA50, the controlled variable sample value calculation unit 32 acquires the combustion pressure in one combustion cycle from the combustion pressure sensor, and calculates the sample value of CA50 based on the acquired combustion pressure. Furthermore, the controlled variable sample value calculation unit 32 calculates the average value of a predetermined number nr of recent sample values of the controlled variable, that is, calculates the average recent sample value Xave. The predetermined number nr of recent sample values of the controlled variable includes the currently calculated sample value of the controlled variable.
The normative model 33 executes the above-described reference expectation value calculation process 23. The normative model 33 receives the control input value from the unillustrated high-order system. The normative model 33 calculates the reference expectation value μo of the controlled variable from the received control input value, based on a modeled ideal input-output characteristic. Further, the normative model 33 calculates the standard deviation σo of the reference normal population used for the learning by the normative model 33, and further calculates the standard error σo/nr1/2 of the reference normal population when the number of data is nr.
The hypothesis test unit 34 executes the above-described hypothesis test process 24. The hypothesis test unit 34 receives the error Xave−μo between the average recent sample value Xave calculated by the controlled variable sample value calculation unit 32 and the reference expectation value μo output from the normative model 33. Although not illustrated, the hypothesis test unit 34 receives also the standard error σo/nr1/2 of the reference normal population that is calculated by the normative model 33. The hypothesis test unit 34 sets the region of the acceptance and the region of the reject, using the standard error σo/nr1/2, and determines whether the error Xave−μo of the controlled variable is in the region of the acceptance or in the region of the reject. Further, as an update signal, the hypothesis test unit 34 receives a crank angle signal that is transmitted from the crank angle sensor in synchronization with the combustion cycle. In response to the update signal, the hypothesis test unit 34 updates the hypothesis test result.
The adaptive control unit 35 executes the above-described adaptive control process 25. In the case where the hypothesis test unit 34 determines that the error Xave−μo of the controlled variable is in the region of the reject, the adaptive control unit 35 receives the error Xave−μo of the controlled variable, from the hypothesis test unit 34. The adaptive control unit 35 applies an adaptation law of the adaptive control to the conversion rule of the controller 31, and modifies the conversion rule based on the received error Xave−μo of the controlled variable.
The feedback controller 42 receives the control input value and the error Xave−μo of the controlled variable. In
Next, a case where the adaptive control is applied to an ignition timing control will be described as a specific example of the adaptation law of the adaptive control. First,
In the above-described embodiment, a Z-test is used in the hypothesis test process 24. However, various test techniques such as a t-test and an H-test can be used in the hypothesis test process 24. For example, in the case of using the t-test instead of the Z-test, it is possible to extract samples from the reference normal population, and to perform the hypothesis test using the sample average and the standard deviation calculated from the sample average.
The disclosure can be also applied to a control device for a compression self-ignition engine. In this case, CA50, LPP or the like can be used as the controlled variable. Further, fuel injection timing, EGR valve opening degree or the like can be used as the manipulated variable.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-160591 | Aug 2018 | JP | national |
