JP2016188628A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly adjust an opening of an EGR valve by using frequency analysis to bring an actual EGR rate close to a target EGR rate.SOLUTION: By using a frequency analysis, exciting force is calculated from an output signal of an in-cylinder pressure sensor 14 for each frequency. A value obtained by subtracting a target resonance primary frequency determined according to a target EGR rate from a resonance primary frequency at which the calculated exciting frequency becomes a peak is set as a first difference, a value obtained by subtracting target exciting force determined according to the target resonance primary frequency from exciting force at the resonance primary frequency is set as a second difference, and a value obtained by subtracting target low frequency range exciting force determined according to the target EGR rate with respect to a low frequency, from low frequency range exciting force at the low frequency that is lower in frequency than the resonance primary frequency, is set as a third difference. When the first difference is a positive value, the second difference is a negative value and the third difference is a negative value, the opening of an EGR valve is set larger than the present opening. When the first difference is a negative value, the second difference is a positive value and the third difference is a positive value, the opening of the EGR valve is set smaller than the present opening.SELECTED DRAWING: Figure 3

Description

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

  Conventionally, as disclosed in Patent Document 1, for example, an EGR (Exhaust Gas Recirculation) device is known in which a part of exhaust gas of an internal combustion engine is recirculated to the intake side as EGR gas and introduced into the combustion chamber again. . The EGR device includes an EGR passage that connects the exhaust passage and the intake passage. In the EGR passage, an EGR valve capable of opening and closing is provided. Patent Document 1 discloses a configuration for controlling the EGR rate based on the estimated value of the premixed combustion ratio.

  The applicant has recognized the following documents including the above-mentioned documents as related to the present invention.

Japanese Patent Laid-Open No. 2002-161796 JP 58-62349 A JP-A-3-39184 JP 2011-43125 A Japanese Patent Laid-Open No. 9-228899

  In the future, more precise EGR control will be required as exhaust restrictions become more severe. In order to realize highly accurate EGR control, it is desired that the actual EGR rate in each cylinder can be calculated. As for the calculation method of the EGR rate for each cylinder, the inventor has studied the frequency characteristics (relationship between frequency and excitation force) when only the EGR rate is changed without changing other combustion states after earnest research. I found a change. Specifically, when the EGR rate is increased, the peak position of the resonance primary frequency determined based on the combustion chamber diameter moves to the low frequency side, and the excitation force at the peak position increases. Conversely, when the EGR rate is lowered, the peak position of the resonance primary frequency moves to the high frequency side, and the excitation force at the peak position becomes smaller. In addition to this, it has also been found that the excitation force in the low frequency region near 3 kHz increases as the EGR rate increases and decreases as the EGR rate decreases.

  The present invention has been made to solve the above-described problems. By using frequency analysis, a deviation between the actual EGR rate and the target EGR rate is determined from the output signal of the in-cylinder pressure sensor, and the actual EGR rate is calculated. It is an object of the present invention to provide a control device for an internal combustion engine that can appropriately adjust the opening degree of an EGR valve so as to approach a target EGR rate.

In order to achieve the above object, the present invention provides a control device for an internal combustion engine,
An in-cylinder pressure sensor that outputs a signal corresponding to the pressure in the cylinder of the internal combustion engine;
An EGR valve provided in an EGR passage that recirculates a part of the exhaust flowing through the exhaust passage connected to the cylinder to the intake passage;
Frequency analysis means for calculating an excitation force for each frequency from the output signal of the in-cylinder pressure sensor using frequency analysis;
A value obtained by subtracting the target resonance primary frequency determined according to the target EGR rate or the target EGR amount from the resonance primary frequency at which the excitation force calculated by the frequency analyzing means reaches a peak is the first difference, and the resonance A value obtained by subtracting the target excitation force determined according to the target resonance primary frequency from the excitation force at the primary frequency is a second difference, and a low frequency region at a low frequency lower than the resonance primary frequency. A value obtained by subtracting the target low-frequency region excitation force determined according to the target EGR rate or the target EGR amount for the low frequency from the excitation force is set as a third difference, and the first difference is a positive value, Means for making the opening of the EGR valve larger than the current opening when the second difference is a negative value and the third difference is a negative value;
Means for making the opening of the EGR valve smaller than the current opening when the first difference is a negative value, the second difference is a positive value, and the third difference is a positive value; It is characterized by providing.

  According to this invention, it is possible to determine the deviation between the actual EGR rate and the target EGR rate from the output signal of the in-cylinder pressure sensor using frequency analysis. Then, the opening degree of the EGR valve can be appropriately adjusted so that the actual EGR rate approaches the target EGR rate according to the state of deviation. Therefore, deterioration of exhaust performance and fuel consumption can be suppressed. In particular, according to the present invention, frequency analysis can be performed for each cylinder, so that the actual EGR rate with variation for each cylinder can be individually measured, and the EGR valve corresponding to each cylinder can be individually controlled. . Therefore, the actual EGR rate in each cylinder can be brought close to the target EGR rate. Therefore, highly accurate EGR control will be possible in the future as exhaust restrictions become stricter. In addition, by using the output signal of the in-cylinder pressure sensor, the EGR valve can be controlled with high frequency (for example, every cycle), and highly accurate EGR control can be performed.

It is a figure for demonstrating schematic structure of the internal combustion engine which concerns on Embodiment 1 of this invention, and its intake / exhaust system. It is a figure which shows an example of the result of having analyzed the frequency of the output signal of the cylinder pressure sensor. 4 is a flowchart of a control routine executed by an ECU 50 in the system according to Embodiment 1 of the present invention. It is a figure for demonstrating the driving | operation area | region where condensed water is easy to generate | occur | produce. 6 is a flowchart of a control routine executed by an ECU 50 in the system according to Embodiment 2 of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a schematic configuration of an internal combustion engine and an intake / exhaust system thereof according to Embodiment 1 of the present invention. The system shown in FIG. 1 includes an internal combustion engine 10. The internal combustion engine 10 has four cylinders 12. Although four cylinders 12 are shown in FIG. 1, the number of cylinders is not limited to this. Each cylinder 12 is provided with a cylinder pressure sensor 14 that outputs a signal corresponding to the cylinder pressure.

  An intake manifold 16 and an exhaust manifold 18 are connected to the internal combustion engine 10. An intake passage 20 is connected to the intake manifold 16. An exhaust passage 22 is connected to the exhaust manifold 18. In the present embodiment, intake manifold 16 and intake passage 20 correspond to the intake passage according to the present invention, and exhaust manifold 18 and exhaust passage 22 correspond to the exhaust passage according to the present invention.

  A compressor 24 a of a turbocharger 24 is installed in the intake passage 20. A turbine 24 b of the turbocharger 24 is installed in the exhaust passage 22.

  An intercooler (not shown) and a throttle valve (not shown) are provided downstream of the compressor 24 a in the intake passage 20. An air flow meter (not shown) is provided upstream of the compressor 24 a in the intake passage 20.

  A catalyst (not shown) is provided downstream of the turbine 24 b in the exhaust passage 22.

  The intake / exhaust system of the internal combustion engine 10 is provided with an EGR system for introducing a part of the exhaust gas flowing through the exhaust system into the intake system as EGR gas for recirculation. The EGR system according to this embodiment includes a high pressure EGR device 26 and a low pressure EGR device 28.

  The high pressure EGR device 26 includes a high pressure EGR passage 30, a high pressure EGR cooler 32, and a high pressure EGR valve 34. The high pressure EGR passage 30 has an upstream end connected to the exhaust manifold 18 and a downstream end connected to the intake manifold 16. Specifically, a plurality of passages branched for each cylinder are formed in the downstream portion of the high pressure EGR passage 30. Similarly, a plurality of passages branched for each cylinder are formed in the downstream portion of the intake manifold 16. Each passage formed in the downstream portion of the high-pressure EGR passage 30 is connected to each passage formed in the downstream portion of the intake manifold 16. A high-pressure EGR valve 34 is provided in each passage formed in the downstream portion of the high-pressure EGR passage 30.

  In the present embodiment, the EGR gas introduced from the exhaust manifold 18 to the intake manifold 16 through the high pressure EGR passage 30 may be referred to as high pressure EGR gas. The high pressure EGR valve 34 changes the flow passage cross-sectional area of the high pressure EGR passage 30 by changing the opening thereof, and adjusts the flow rate (high pressure EGR gas amount) of the high pressure EGR gas introduced into the intake manifold 16.

  A high pressure EGR cooler 32 is provided in the high pressure EGR passage 30. The high pressure EGR cooler 32 cools the high pressure EGR gas by exchanging heat between the high pressure EGR gas flowing through the high pressure EGR passage 30 and the cooling water of the internal combustion engine 10.

  The low pressure EGR device 28 includes a low pressure EGR passage 35, a low pressure EGR cooler 36, and a low pressure EGR valve 37. The low-pressure EGR passage 35 has an upstream end connected to the exhaust passage 22 downstream from the turbine 24b and upstream from the catalyst, and has a downstream end downstream from the air flow meter and upstream from the compressor 24a. It is connected to the intake passage 20.

  In the present embodiment, the EGR gas introduced from the exhaust passage 22 into the intake passage 20 through the low pressure EGR passage 35 may be referred to as low pressure EGR gas. A low pressure EGR cooler 36 is provided in the low pressure EGR passage 35. The low pressure EGR cooler 36 cools the low pressure EGR gas by exchanging heat between the low pressure EGR gas flowing through the low pressure EGR passage 35 and the cooling water of the internal combustion engine 10.

  A low pressure EGR valve 37 is provided in the low pressure EGR passage 35 on the downstream side of the low pressure EGR cooler 36. The low pressure EGR valve 37 changes the flow rate of the low pressure EGR gas introduced into the intake passage 20 (low pressure EGR gas amount) by changing the flow passage cross-sectional area of the low pressure EGR passage 35 by changing the opening degree.

  The internal combustion engine 10 configured as described above is provided with an ECU (Electronic Control Unit) 50. The ECU 50 includes a memory for storing various programs and data, a processor for executing and calculating various programs, an input interface for inputting data used for calculation of various programs, and an output interface for outputting instructions based on the calculation results of the various programs. Prepare.

  In addition to the air flow meter and the in-cylinder pressure sensor 14 described above, an internal interface such as a crank angle sensor that outputs a signal corresponding to the engine rotational speed, an accelerator opening sensor that outputs a signal corresponding to the accelerator opening, etc. Various sensors for acquiring the operating state of the engine 10 are electrically connected. In addition to the throttle valve, the high pressure EGR valve 34, and the low pressure EGR valve 37, the output interface of the ECU 50 includes an operation of the internal combustion engine 10 such as a fuel injection device (not shown) for supplying fuel into the cylinder. Various actuators for controlling the state are electrically connected. The ECU 50 controls the operating state of the internal combustion engine 10 by driving the various actuators based on the output signals of the various sensors and the various programs described above. Further, the ECU 50 has a function of acquiring an output signal of the in-cylinder pressure sensor 14 by performing AD conversion in synchronization with the crank angle. As a result, a signal corresponding to the in-cylinder pressure at an arbitrary crank angle timing can be detected within a range allowed by the resolution of AD conversion.

[Characteristic Control in Embodiment 1]
In the system of the present embodiment, the ECU 50 determines a target EGR rate corresponding to the acquired operating state, and determines the operation amounts of the various actuators described above so as to achieve the target EGR rate. Moreover, ECU50 performs the frequency analysis process which calculates excitation force for every frequency from the output signal of the cylinder pressure sensor 14 using a frequency analysis. As a frequency analysis method, for example, spectrum analysis based on Fourier transform is used. By spectral analysis, it is possible to know what frequency components are distributed in the original signal.

  The inventors' diligent research has revealed changes in frequency characteristics (relationship between frequency and excitation force) when only the EGR rate is changed without changing other combustion states. Specifically, when the EGR rate is increased, the peak position of the resonance primary frequency determined based on the combustion chamber diameter moves to the low frequency side, and the excitation force at the peak position increases. Conversely, it was found that when the EGR rate was lowered, the peak position of the resonance primary frequency moved to the high frequency side, and the excitation force at the peak position was reduced. In addition to this, it was also found that the excitation force in the low frequency region around 3 kHz increases as the EGR rate increases and decreases as the EGR rate decreases.

  FIG. 2 is a diagram illustrating an example of a result of frequency analysis of the output signal of the in-cylinder pressure sensor 14. A solid line 60 in FIG. 2 is a frequency characteristic corresponding to the target EGR rate, and is a frequency characteristic stored in advance in the ECU 50. A broken line 62 is a frequency characteristic corresponding to the actual EGR rate, and is a frequency characteristic calculated by the ECU 50 from the output signal of the in-cylinder pressure sensor 14 using frequency analysis. The frequency characteristic indicated by the broken line 62 in FIG. 2 is a frequency characteristic when the actual EGR rate is higher than the target EGR rate. As indicated by the deviation between the solid line 60 and the broken line 62, when the actual EGR rate is higher than the target EGR rate, the peak position of the resonance primary frequency moves to the low frequency side, and the excitation at the peak position occurs. The force increases, and the excitation force at a low frequency near 3 kHz increases.

  In FIG. 2, the low frequency is set to a frequency in the vicinity of 3 kHz, but the present invention is not limited to this. The low frequency varies depending on the configuration of the internal combustion engine to which the present invention is applied, and is a frequency lower than the resonance primary frequency, for example, a frequency of 5 kHz or less.

ここで、
ｃ：音速
κ：比熱比
Ｒ：気体定数
Ｔ：絶対温度
Ｆ：共鳴周波数
Ｄ：径の長さ（例えば燃焼室径）
α：モード係数（１次の場合は１、２次の場合は２） The calculation formula for the resonance frequency is expressed by the following equation.

here,
c: Sonic velocity κ: Specific heat ratio R: Gas constant T: Absolute temperature F: Resonance frequency D: Diameter length (for example, combustion chamber diameter)
α: Mode coefficient (1 for the first order, 2 for the second order)

  In the system of the present embodiment, the ECU 50 determines the deviation between the actual EGR rate and the target EGR rate from the change in the frequency characteristics described above, and sets the opening degree of the high-pressure EGR valve 34 so that the actual EGR rate approaches the target EGR rate. Control.

  This will be specifically described. In the following description, a value obtained by subtracting the target resonance primary frequency Fclft determined according to the target EGR rate from the resonance primary frequency Fcflf at which the excitation force calculated by the frequency analysis processing reaches a peak is referred to as a first difference. Called. A value obtained by subtracting the target excitation force Fclet determined in accordance with the target resonance primary frequency Fclft from the excitation force Fcle at the resonance primary frequency Fclf is referred to as a second difference. The target low frequency excitation force Flet determined according to the target EGR rate for this low frequency is subtracted from the low frequency excitation force Fle at a low frequency (for example, around 3 kHz) lower than the resonance primary frequency Fclf. The value is referred to as the third difference. Further, the ECU 50 stores a corresponding target resonance primary frequency Fclft, target excitation force Fclet, and target low frequency range excitation force Flet for each target EGR rate. In addition, the above-described low frequency is predetermined according to the configuration of the internal combustion engine.

  Here, when the first difference is a positive value, the second difference is a negative value, and the third difference is a negative value, it can be determined that the actual EGR rate is lower than the target EGR rate. In this case, the ECU 50 outputs a control signal for making the opening degree of the high pressure EGR valve 34 larger than the current opening degree.

  Further, when the first difference is a negative value, the second difference is a positive value, and the third difference is a positive value, it can be determined that the actual EGR rate is higher than the target EGR rate. In this case, the ECU 50 outputs a control signal for making the opening degree of the high pressure EGR valve 34 smaller than the current opening degree.

  In addition, you may set the variation | change_quantity of the opening degree of the high pressure EGR valve 34 so that the absolute value of the 1st-3rd difference is large.

(flowchart)
FIG. 3 is a flowchart of a control routine executed by the ECU 50 in order to realize the above-described operation. This control routine is repeatedly executed every predetermined cycle for each cylinder.

  In the routine shown in FIG. 3, first, in step 100, the ECU 50 determines whether or not the current operation region (load, rotation speed) is an EGR introduction region. The ECU 50 stores in advance a map or the like that defines the relationship between the operation region and the target EGR rate. When the target EGR rate corresponding to the current operation region is higher than 0, it can be determined that the region is the EGR introduction region.

  In step 102, the ECU 50 causes the in-cylinder pressure sensor 14 to measure the in-cylinder pressure in the compression / expansion process, and inputs an output signal of the in-cylinder pressure sensor 14.

  In step 104, the ECU 50 calculates an excitation force for each frequency from the output signal of the in-cylinder pressure sensor 14 using frequency analysis.

  In step 106, the ECU 50 has a resonance primary frequency Fclf at which the excitation force calculated by the frequency analysis processing reaches a peak, an excitation force Fcle at the resonance primary frequency Fclf, and a frequency lower than the resonance primary frequency Fclf. A low frequency excitation force Fle at a frequency is detected. The low frequency is determined in advance according to the configuration of the internal combustion engine and stored in the ECU 50.

  In step 108, the ECU 50 determines the target resonance primary frequency Fclft determined according to the target EGR rate, the target excitation force Fclet determined according to the target resonance primary frequency Fclft, and the low frequency according to the target EGR rate. The target low frequency region excitation force Flet is read out. The target resonance primary frequency Fclft, the target excitation force Fclet, and the target low frequency range excitation force Flet are determined in advance for each target EGR rate and stored in the ECU 50.

  In step 110, the ECU 50 determines that the first difference is a positive value (Fclf> Fclft), the second difference is a negative value (Fcle <Fclet), and the third difference is a negative value (Fle <Flet). It is determined whether or not. When the determination condition is satisfied, the actual EGR rate is lower than the target EGR rate. In this case, the ECU 50 proceeds to the process of step 112.

  In step 112, the ECU 50 outputs a control signal for making the opening degree of the high pressure EGR valve 34 larger than the current opening degree. Thereafter, this routine is terminated and re-executed in the next cycle.

  If the determination condition is not satisfied in step 110, the ECU 50 proceeds to the process of step 114. In step 114, the ECU 50 determines whether the first difference is a negative value (Fclf <Fclft), the second difference is a positive value (Fcle> Fclet), and the third difference is a positive value (Fle> Flet). Determine whether. When the determination condition is satisfied, the actual EGR rate is higher than the target EGR rate. In this case, the ECU 50 proceeds to the process of step 116.

  In step 116, the ECU 50 outputs a control signal for making the opening degree of the high pressure EGR valve 34 smaller than the current opening degree. Thereafter, this routine is terminated and re-executed in the next cycle.

  As described above, according to the routine shown in FIG. 3, it is possible to determine the difference between the actual EGR rate and the target EGR rate from the output signal of the in-cylinder pressure sensor 14 using frequency analysis. Then, the opening degree of the high-pressure EGR valve 34 can be appropriately adjusted so that the actual EGR rate approaches the target EGR rate according to the state of deviation. In particular, according to the present invention, frequency analysis can be performed for each cylinder, and therefore, the actual EGR rate with variation for each cylinder is individually measured, and the high-pressure EGR valve 34 corresponding to each cylinder is individually controlled. Can do. Therefore, the actual EGR rate in each cylinder can be brought close to the target EGR rate. Therefore, highly accurate EGR control will be possible in the future as exhaust restrictions become stricter. In addition, by using the output signal of the in-cylinder pressure sensor, the high-pressure EGR valve 34 can be controlled with high frequency (for example, every cycle), and high-precision EGR control is possible.

(Modification)
In the system of the first embodiment described above, EGR control suitable for each cylinder can be realized by individually controlling the high-pressure EGR valve 34 provided for each cylinder. By the way, the present invention can also be applied to an internal combustion engine in which the high pressure EGR valve 34 is not provided for each cylinder. For example, the present invention can be applied to a configuration in which one high-pressure EGR valve 34 is provided in the high-pressure EGR passage 30. This point is the same in the following embodiments.

  In the system of the first embodiment described above, the actual EGR rate is controlled so as to coincide with the target EGR rate. However, the actual EGR rate may be the actual EGR amount, and the target EGR rate is the target EGR rate. It may be an amount.

Embodiment 2. FIG.
[System Configuration of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. The system of the present embodiment can be realized by causing the ECU 50 to execute a routine of FIG. 5 described later in the configuration shown in FIG.

[Characteristic Control in Embodiment 2]
In the first embodiment described above, EGR control is realized in which the actual EGR rate is brought close to the target EGR rate using frequency characteristics that differ depending on the EGR rate in the cylinder. By the way, generation | occurrence | production of condensed water is also considered as a factor of the shift | offset | difference of a frequency characteristic. Therefore, in the second embodiment, EGR control similar to that in the first embodiment is performed in an operation region other than the operation region where condensed water is likely to be generated.

  FIG. 4 is a diagram for explaining an operation region in which condensed water is likely to be generated. The broken line area in FIG. 4 indicates a low rotation and medium / high load area. In the low rotation, medium / high load region, the target EGR rate is lower than that in the high rotation region, and the temperature in the intake manifold 16 is low. Also, the exhaust air-fuel ratio is low and the amount of water generated is large. Therefore, condensed water is generated and hardly evaporated. Therefore, in the system according to the second embodiment, EGR control using frequency analysis is performed in an operation region other than the low rotation, medium / high load region where condensate is unlikely to be generated.

(flowchart)
FIG. 5 is a flowchart of a control routine executed by the ECU 50 in order to realize the above-described function. This routine is the same as the routine shown in FIG. 3 except that the process of step 101 is added between step 100 and step 102. In FIG. 5, the same steps as those shown in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 5, the ECU 50 executes the process of step 101 after the process of step 100. In step 101, the ECU 50 determines whether or not the engine is in a low speed, medium / high load range, and steady operation. If the determination condition is satisfied, this routine is terminated and re-executed in the next cycle. On the other hand, if the determination condition is not satisfied in step 101, the ECU 50 executes the processing after step 102.

  As described above, according to the routine shown in FIG. 5, the actual EGR rate and the target EGR rate are calculated from the output signal of the in-cylinder pressure sensor 14 using the frequency analysis in the operation region other than the operation region where the condensed water is easily generated. Can be determined. Then, the opening degree of the high-pressure EGR valve 34 can be appropriately adjusted so that the actual EGR rate approaches the target EGR rate according to the state of deviation. Therefore, according to the system of the second embodiment, the influence on the frequency characteristic deviation due to the generation of condensed water is removed, and the deviation between the actual EGR rate and the target EGR rate is calculated with higher accuracy than in the first embodiment. Therefore, highly accurate EGR control is possible.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Cylinder 14 In-cylinder pressure sensor 16 Intake manifold 18 Exhaust manifold 20 Intake passage 22 Exhaust passage 24 Turbocharger 24a Compressor 24b Turbine 26 High pressure EGR device 28 Low pressure EGR device 30 High pressure EGR passage 32 High pressure EGR cooler 34 High pressure EGR valve 35 Low pressure EGR passage 36 Low pressure EGR cooler 37 Low pressure EGR valve Fcle Excitation force Fclf Resonance primary frequency Fle Low frequency excitation force

Claims (1)

An in-cylinder pressure sensor that outputs a signal corresponding to the pressure in the cylinder of the internal combustion engine;
An EGR valve provided in an EGR passage that recirculates a part of the exhaust flowing through the exhaust passage connected to the cylinder to the intake passage;
Frequency analysis means for calculating an excitation force for each frequency from the output signal of the in-cylinder pressure sensor using frequency analysis;
A value obtained by subtracting the target resonance primary frequency determined according to the target EGR rate or the target EGR amount from the resonance primary frequency at which the excitation force calculated by the frequency analyzing means reaches a peak is the first difference, and the resonance A value obtained by subtracting the target excitation force determined according to the target resonance primary frequency from the excitation force at the primary frequency is a second difference, and a low frequency region at a low frequency lower than the resonance primary frequency. A value obtained by subtracting the target low-frequency region excitation force determined according to the target EGR rate or the target EGR amount for the low frequency from the excitation force is set as a third difference, and the first difference is a positive value, Means for making the opening of the EGR valve larger than the current opening when the second difference is a negative value and the third difference is a negative value;
Means for making the opening of the EGR valve smaller than the current opening when the first difference is a negative value, the second difference is a positive value, and the third difference is a positive value;
A control device for an internal combustion engine, comprising:

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