JP5454071B2 - Apparatus and control system for exhaust pulsation characteristic estimation of internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust pulsation characteristic estimation apparatus and control system for an internal combustion engine.

  In an internal combustion engine, a technique is known for improving volumetric efficiency by using a scavenging effect that is generated when intake air flowing into a cylinder from an intake port blows through an exhaust port. If the amplitude of the exhaust pulsation increases to some extent, the intake pressure may become higher than the exhaust pressure when the exhaust pressure decreases. Therefore, during a period in which the intake pressure is higher than the exhaust pressure, both the intake valve and the exhaust valve are opened (so-called valve overlap), thereby generating a scavenging effect. By causing the scavenging effect, the burned gas (internal EGR gas) remaining in the cylinder can be reduced. As a result, since the amount of fresh air in the cylinder increases, the volume efficiency can be improved.

  As described above, in order to use the scavenging effect, it is necessary to generate a valve overlap period during a period in which the intake pressure is higher than the exhaust pressure. For that purpose, it is important to estimate the characteristics of exhaust pulsation with high accuracy.

  Patent Document 1 discloses a technique for estimating an exhaust pressure in the vicinity of an exhaust valve when the exhaust valve is opened, based on a ratio between the cylinder pressure immediately before the exhaust valve is opened in the internal combustion engine and a smoothed exhaust pressure ratio and the engine speed. Is disclosed.

JP 2005-307804 A JP 2005-307801 A

  An object of the present invention is to provide a technique capable of estimating the exhaust pulsation characteristics of an internal combustion engine with high accuracy.

An exhaust pulsation characteristic estimation device for an internal combustion engine according to the present invention includes:
In the internal combustion engine provided with the flow path cross-sectional area control means for controlling the cross-sectional area of the exhaust flow path,
As the cross-sectional area of the exhaust flow path controlled by the flow-path cross-sectional area control means and the cross-sectional area of the exhaust flow path become smaller, the maximum value and the minimum value of the exhaust pressure increase while the amplitude of the exhaust pressure hardly changes. A characteristic of exhaust pulsation of the internal combustion engine is estimated using the first relationship .

  When the cross-sectional area of the exhaust passage changes, the exhaust pulsation characteristics change according to the area. According to the present invention, the exhaust pulsation characteristic is estimated using the cross-sectional area of the exhaust passage. Therefore, the characteristic can be estimated with high accuracy.

The internal combustion engine exhaust pulsation characteristic estimation apparatus according to the present invention may include enthalpy acquisition means, average value estimation means, amplitude estimation means, and phase estimation means. The enthalpy acquisition means acquires an enthalpy of exhaust immediately after being discharged from the internal combustion engine or a physical quantity correlated with the enthalpy. The average value estimation means includes a cross-sectional area of the exhaust flow passage controlled by the flow passage cross-sectional area control means, the first relationship, an enthalpy or physical quantity acquired by the enthalpy acquisition means , and an increase in the enthalpy or physical quantity. The average value of the exhaust pressure is estimated on the basis of the second relationship in which the maximum value of the exhaust pressure increases while the minimum value of the exhaust pressure hardly changes . The amplitude estimating means estimates the amplitude of the exhaust pressure based on the enthalpy or physical quantity acquired by the enthalpy acquiring means and the second relationship . The phase estimation means estimates the phase of the exhaust pressure based on the engine speed of the internal combustion engine and the opening timing of the exhaust valve.

  In the case of the above configuration, the estimated exhaust pulsation characteristics are the average value, amplitude and phase of the exhaust pressure, and these values can be estimated with high accuracy.

  The control system for an internal combustion engine according to the present invention includes a valve overlap for controlling a valve overlap period, which is a period in which both the exhaust pulsation characteristic estimation device and the intake valve and the exhaust valve of the internal combustion engine are opened. Period control means. In this case, the valve overlap period control means controls the valve overlap period in accordance with the exhaust pulsation characteristic estimated by the exhaust pulsation characteristic estimation device.

  According to this, the valve overlap period can be controlled so that the scavenging effect in the internal combustion engine becomes higher.

  For example, the valve overlap period control means suppresses the overlap between the time when the exhaust pressure is higher than the intake pressure and the valve overlap period, and the time when the intake pressure is higher than the exhaust pressure. The valve overlap period may be controlled so that the period overlapping the period becomes longer.

  Thereby, the scavenging effect in the internal combustion engine can be enhanced.

  The exhaust pulsation characteristic estimation device estimates that the average value of the exhaust pressure is lower when the cross-sectional area of the exhaust flow path controlled by the flow-path cross-sectional area control means is larger than when the cross-sectional area of the exhaust flow path is small. May be. In this case, the valve overlap period control means makes the valve overlap period longer when the average value of the exhaust pressure estimated by the exhaust pulsation characteristic estimation device is low than when the average value of the exhaust pressure is high. In other words, the valve overlap period control means shortens the valve overlap period when the average value of the exhaust pressure estimated by the exhaust pulsation characteristic estimation device is high compared to when the average value of the exhaust pressure is low.

  When the average value of the exhaust pressure is low, the period when the intake pressure is higher than the exhaust pressure is longer than when the average value of the exhaust pressure is high. Therefore, according to the above, it is possible to suppress the overlap between the time when the exhaust pressure is higher than the intake pressure and the valve overlap period, and the time when the intake pressure is higher than the exhaust pressure and the valve overlap period. It is possible to lengthen the period in which the two overlap.

  Further, the exhaust pulsation characteristic estimation device has an exhaust gas average value when the enthalpy or physical quantity correlated with the enthalpy acquired by the enthalpy acquisition means is smaller than when the enthalpy or physical quantity correlated with the enthalpy is large. It may be estimated that the amplitude is low and the amplitude is small. In this case, the valve overlap period control means, when the average value of the exhaust pressure estimated by the exhaust pulsation characteristic estimation device is low and the amplitude is small, compared to when the average value of the exhaust pressure is high and the amplitude is large. Increase the valve overlap period. In other words, when the average value of the exhaust pressure estimated by the exhaust pulsation characteristic estimation device is high and the amplitude is large, the valve overlap period control means is low and the amplitude is small. Compared with the valve overlap period.

When the average value of the exhaust pressure is low and the amplitude is small, the period when the intake pressure is higher than the exhaust pressure is longer than when the average value of the exhaust pressure is high and the amplitude is large. Therefore, it is possible to suppress the overlap between the time when the exhaust pressure is higher than the intake pressure and the valve overlap period as described above, and the time when the intake pressure is higher than the exhaust pressure and the valve overlap period. The overlapping period can be made longer.

  According to the present invention, the characteristics of exhaust pulsation of an internal combustion engine can be estimated with high accuracy. Therefore, the valve overlap period can be generated at a more suitable time. As a result, the scavenging effect in the internal combustion engine can be enhanced, and the volumetric efficiency can be greatly improved.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its intake / exhaust system. It is a figure which shows the change by the pulsation of exhaust pressure and intake pressure. It is a figure for demonstrating the relationship between the waveform of exhaust pulsation, and the enthalpy of exhaust. It is a figure for demonstrating the relationship between the waveform of exhaust pulsation, and the cross-sectional area of an exhaust flow path. It is a flowchart which shows the flow of control of the valve overlap period which concerns on a present Example. It is a figure which shows the relationship between scavenging possible time and a valve overlap period.

  Hereinafter, specific embodiments of an exhaust pulsation characteristic estimating apparatus for an internal combustion engine and a control system for the internal combustion engine according to the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example>
An embodiment of the present invention will be described with reference to FIGS.

(Schematic configuration of internal combustion engine and its intake and exhaust system)
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle having four cylinders 2. Each cylinder 2 is provided with a fuel injection valve 3 that directly injects fuel into the cylinder 2.

  Further, the internal combustion engine 1 is provided with an intake side variable valve mechanism (hereinafter referred to as intake VVT) 25 and an exhaust side variable valve mechanism (hereinafter referred to as exhaust VVT) 26. The intake VVT 25 is a mechanism that can change the opening timing and closing timing of the intake valve. The exhaust VVT 26 is a mechanism that can change the opening timing and closing timing of the exhaust valve.

  The intake VVT 25 according to the present embodiment can change the operating angle and phase of the intake valve. Therefore, the intake VVT 25 can change the other while fixing one of the opening timing and closing timing of the intake valve. Further, the intake VVT 25 can advance one of the opening timing and closing timing of the intake valve while retarding the other. Similarly, the exhaust VVT 26 can change the working angle and phase of the exhaust valve. Therefore, the exhaust VVT 26 can change the other while fixing one of the opening timing and closing timing of the exhaust valve. Further, the exhaust VVT 26 can advance one of the opening timing and closing timing of the exhaust valve while retarding the other. A valve overlap period in which both the intake valve and the exhaust valve are opened by changing the opening timing of the intake valve with the intake VVT 25 and / or changing the closing timing of the exhaust valve with the exhaust VVT 26 Can be controlled.

  An intake manifold 5 and an exhaust manifold 7 are connected to the internal combustion engine 1. An intake passage 4 is connected to the intake manifold 5. An exhaust passage 6 is connected to the exhaust manifold 7.

  A compressor 8 a of a turbocharger 8 is installed in the intake passage 4. A turbine 8 b of a turbocharger 8 is installed in the exhaust passage 6. A nozzle vane 14 is provided in the turbine 8b. As the opening degree of the nozzle vane 14 changes, the cross-sectional area of the exhaust passage changes. That is, when the opening degree of the nozzle vane 14 increases, the cross-sectional area of the exhaust passage increases, and when the opening degree of the nozzle vane 14 decreases, the cross-sectional area of the exhaust passage decreases. In this embodiment, the nozzle vane 14 corresponds to the flow path cross-sectional area control means according to the present invention.

  The intake manifold 5 is provided with an intake pressure sensor 23 for detecting intake pressure (supercharging pressure). A throttle valve 9 is provided in the intake passage 4 on the downstream side of the compressor 8a. An air flow meter 24 is provided upstream of the compressor 8 a in the intake passage 4. An exhaust gas purification device 10 configured by a particulate filter or the like is provided downstream of the turbine 8b in the exhaust passage 6.

  An EGR device 11 is provided in the intake and exhaust system of the internal combustion engine 1. The EGR device 11 includes an EGR passage 12 and an EGR valve 13. One end of the EGR passage 12 is connected to the exhaust manifold 7, and the other end is connected to the downstream side of the throttle valve 9 in the intake passage 4.

  The EGR valve 13 is provided in the EGR passage 12 and controls the flow rate of EGR gas introduced from the exhaust manifold 7 into the intake passage 4 through the EGR passage 12.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 20. An air flow meter 24, an intake pressure sensor 23, a crank position sensor 21, and an accelerator opening sensor 22 are electrically connected to the ECU 20. These output signals are input to the ECU 20. The crank position sensor 21 is a sensor that detects the crank angle of the internal combustion engine 1. The accelerator opening sensor 22 is a sensor that detects the accelerator opening of a vehicle on which the internal combustion engine 1 is mounted.

  In addition, the fuel injection valve 3, the intake VVT 25, the exhaust VVT 26, the throttle valve 9, the nozzle vane 14, and the EGR valve 13 are electrically connected to the ECU 20. These are controlled by the ECU 20.

(Scavenging effect)
In this embodiment, when the operation state of the internal combustion engine 1 is an acceleration operation, the scavenging effect is used to improve the volume efficiency. FIG. 2 is a diagram showing a change due to pulsation between the exhaust pressure in the exhaust manifold 7 (hereinafter simply referred to as exhaust pressure) and the intake pressure in the intake manifold 5 (hereinafter simply referred to as intake pressure).

  When the engine load of the internal combustion engine 1 becomes higher than a certain level, the amplitude of the exhaust pulsation becomes very large compared to the amplitude of the intake pulsation. Therefore, as shown in FIG. 2, there may be a time Δta when the intake pressure is higher than the exhaust pressure. When a valve overlap period is generated during this time Δta, the intake air that has flowed into the cylinder 2 from the intake port blows through the exhaust port, and a scavenging effect can be generated. Hereinafter, a period when the intake pressure is higher than the exhaust pressure is referred to as a scavenging possible period.

(Estimation of exhaust pulsation characteristics)
As described above, in order to use the scavenging effect, it is necessary to generate a valve overlap period between scavenging possible times. For this purpose, it is necessary to estimate the characteristics of exhaust pulsation with high accuracy and accurately grasp the scavenging possible time. In the present embodiment, the average value, amplitude and phase of the exhaust pressure are estimated as the exhaust pulsation characteristics. Parameters for estimating these values include enthalpy (hereinafter simply referred to as exhaust enthalpy) Heg of exhaust in the exhaust manifold 7 (that is, exhaust immediately after being exhausted from the internal combustion engine 1), disconnection of the exhaust passage. The area Seg, the engine speed Ne of the internal combustion engine 1, and the exhaust valve opening timing Tevo are used.

  FIG. 3 is a diagram for explaining the relationship between the waveform of the exhaust pulsation and the enthalpy Heg of the exhaust. FIG. 4 is a diagram for explaining the relationship between the waveform of the exhaust pulsation and the cross-sectional area Seg of the exhaust passage. 3 and 4, the vertical axis represents the exhaust pressure, and the horizontal axis represents the crank angle. 3 and 4, the broken line represents the average value of the intake pressure.

  As shown in FIG. 3, the maximum value of the exhaust pressure increases as the enthalpy Heg of the exhaust increases. At this time, the minimum value of the exhaust pressure hardly changes. That is, as the exhaust enthalpy Heg increases, the average value of the exhaust pressure increases and the amplitude of the exhaust pressure increases.

  Further, as shown in FIG. 4, the maximum value and the minimum value of the exhaust pressure increase as the cross-sectional area Seg of the exhaust flow path decreases. At this time, the amplitude of the exhaust pressure hardly changes. That is, the smaller the cross-sectional area Seg of the exhaust passage, the higher the average value of the exhaust pressure.

  Therefore, in this embodiment, the amplitude of the exhaust pressure is calculated based on the enthalpy Heg of the exhaust. Here, the enthalpy Heg of the exhaust gas is calculated based on the fuel injection amount and fuel injection timing from the fuel injection valve 3, the intake air amount, the intake pressure detected by the intake pressure sensor 23, and the opening degree of the nozzle vane 14. The In this embodiment, the relationship between the enthalpy Heg of the exhaust gas, the fuel injection amount, the fuel injection timing, the intake air amount, the intake air pressure, and the opening degree of the nozzle vane 14 is obtained by experiments or the like. Is stored in advance in the ECU 20. Further, the relationship between the exhaust enthalpy Heg and the amplitude of the exhaust pressure is also obtained by experiments and the like, and these relationships are stored in advance in the ECU 20 as a map or a formula.

  Instead of the exhaust enthalpy, a value correlated with the exhaust enthalpy (for example, the fuel injection amount from the fuel injection valve 3) is detected or calculated, and the exhaust pressure amplitude is calculated based on the detected value. Also good.

  In this embodiment, the average value of the exhaust pressure is calculated based on the enthalpy Heg of the exhaust and the cross-sectional area Seg of the exhaust passage. Here, the cross-sectional area Seg of the exhaust passage is calculated based on the opening degree of the nozzle vane 14. In the present embodiment, the relationship between the cross-sectional area Seg of the exhaust passage and the opening degree of the nozzle vane 14 is obtained by experiments or the like, and these relationships are stored in advance in the ECU 20 as a map or an expression. Further, the relationship between the exhaust enthalpy Heg, the cross-sectional area Seg of the exhaust flow path, and the average value of the exhaust pressure is also obtained by experiments and the like, and these relationships are stored in advance in the ECU 20 as a map or a formula.

  Instead of or in addition to the opening degree of the nozzle vane 14, the cross-sectional area Seg of the exhaust passage may be calculated based on the opening degree of the waste gate valve provided in the turbine 8b. Further, when an exhaust throttle valve is provided in the exhaust passage 6, the cross-sectional area Seg of the exhaust passage may be calculated based on the opening degree of the exhaust throttle valve. In addition to these, when there is a configuration related to the cross-sectional area of the exhaust flow path, the cross-sectional area Seg of the exhaust flow path may be calculated based on the state of the configuration.

  Further, the phase of the exhaust pulsation is correlated with the engine speed Ne of the internal combustion engine 1 and the exhaust valve opening timing Tevo. Therefore, the exhaust pulsation phase is calculated from these values.

As described above, in this embodiment, the amplitude, average value, and phase value of the exhaust pressure are calculated based on parameters that are highly correlated with each other. Thereby, the amplitude, average value, and phase of the exhaust pressure, which are the characteristics of the exhaust pulsation, can be estimated with high accuracy. Further, according to the present embodiment, it is not necessary to provide a new sensor for estimating the exhaust pulsation characteristic in the internal combustion engine 1 or its intake and exhaust system.

(Control of valve overlap period)
In this embodiment, in order to use the scavenging effect, the valve overlap period is controlled in accordance with the exhaust pulsation characteristic estimated by the above method. Hereinafter, control of the valve overlap period according to the present embodiment will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 20 and is repeatedly executed by the ECU 20 at predetermined intervals.

  In this flow, first, in step S101, it is determined whether or not the operation state of the internal combustion engine 1 is an acceleration operation. If an affirmative determination is made in step S101, the process of step S102 is executed next. If a negative determination is made, the execution of this flow is temporarily terminated.

  In step S102, the exhaust enthalpy Heg is determined based on the fuel injection amount and fuel injection timing from the fuel injection valve 3, the intake air amount, the intake pressure detected by the intake pressure sensor 23, and the opening degree of the nozzle vane 14. Calculated. In this embodiment, the ECU 20 that executes step S102 corresponds to the enthalpy acquisition means according to the present invention.

  Next, in step S103, the cross-sectional area Seg of the exhaust passage is calculated based on the opening degree of the nozzle vane 14.

  Next, in step S104, the amplitude, average value, and phase of the pulsating exhaust pressure are calculated. Here, the amplitude of the exhaust pressure is calculated based on the exhaust enthalpy Heg calculated in step S102. The average value of the exhaust pressure is calculated based on the exhaust enthalpy Heg calculated in step S102 and the cross-sectional area Seg of the exhaust flow path calculated in step S103. The phase of the exhaust pressure is calculated based on the engine rotational speed Ne of the internal combustion engine 1 and the exhaust valve opening timing Tevo. In this embodiment, the ECU 20 that executes step S104 corresponds to the average value estimating means, the amplitude estimating means, and the phase estimating means according to the present invention.

  Next, in step S105, it is determined whether or not a scavenging possible time Δta exists. Here, based on the exhaust pulsation characteristic calculated in step S104 and the intake pressure detected by the intake pressure sensor 23, it is determined whether or not the scavenging possible time Δta exists. As described above, since the amplitude of the pulsation of the intake pressure is relatively small, the determination may be performed using the average value of the intake pressure. If an affirmative determination is made in step S105, the process of step S106 is executed next. If a negative determination is made, the execution of this flow is temporarily terminated.

  In step S106, it is determined whether or not a valve overlap period Δtvo exists between the scavenging possible times Δta. If an affirmative determination is made in step S106, then the process of step S107 is executed next. If a negative determination is made, execution of this flow is temporarily terminated.

In step S107, as shown in FIG. 6, the valve overlap timing is advanced by advancing the opening timing of the intake valve by the intake VVT 25 and / or retarding the closing timing of the exhaust valve by the exhaust VVT 26. The period Δtvo is expanded. In FIG. 6, Δtvo1 represents the valve overlap period before expansion, and Δtvo2 represents the valve overlap period after expansion. In step S107, the valve overlap period Δtvo is preferably extended as long as possible within a range that does not overlap with a period when the exhaust pressure is higher than the intake pressure.

  Here, as described above, as the exhaust enthalpy Heg increases, the average value of the exhaust pressure increases and the amplitude of the exhaust pressure increases. In other words, the smaller the exhaust enthalpy Heg, the lower the average value of the exhaust pressure and the smaller the amplitude of the exhaust pressure. As shown in FIG. 3, when there is a scavenging possible time, the scavenging possible time becomes longer as the average value of the exhaust pressure becomes lower and the amplitude of the exhaust pressure becomes smaller. Therefore, in step S107, the valve overlap period Δtvo is lengthened as the average value of the exhaust pressure calculated in step S104 is lower and the amplitude of the exhaust pressure is smaller.

  In addition, as described above, the average value of the exhaust pressure increases as the cross-sectional area Seg of the exhaust passage decreases. In other words, the larger the cross-sectional area Seg of the exhaust passage, the lower the average value of the exhaust pressure. As shown in FIG. 4, when there is a scavenging possible time, the scavenging possible time becomes longer as the average value of the exhaust pressure is lower. Therefore, in step S107, the valve overlap period Δtvo is lengthened as the average value of the exhaust pressure calculated in step S104 is lower.

  In this embodiment, the ECU 20 executing step S107 corresponds to the valve overlap period control means according to the present invention.

  According to the above flow, during acceleration operation, a period in which the scavenging possible period and the valve overlap period overlap while suppressing a period in which the exhaust pressure is higher than the intake pressure and the valve overlap period overlap. Can be made longer. As a result, the scavenging effect in the internal combustion engine 1 can be enhanced. Therefore, the deposition efficiency in the internal combustion engine 1 can be greatly improved.

(Modification)
In the present embodiment, each cylinder 2 may be provided with an in-cylinder pressure sensor. In this case, the exhaust pressure in the exhaust manifold 7 can be estimated based on the in-cylinder pressure detected by the in-cylinder pressure sensor when the exhaust valve is opened. Therefore, the scavenging possible time may be calculated using the estimated value. In this case, the estimated value of the exhaust pressure may be corrected based on the exhaust enthalpy calculated in the same manner as described above and the cross-sectional area of the exhaust passage.

  Further, the intake / exhaust system of the internal combustion engine according to the present embodiment may be configured such that the intake passage 4 and the exhaust passage 6 are branched in the middle, and two turbochargers are provided in parallel. In this case, by switching the exhaust flow path, it is possible to switch between a state where only one turbocharger is driven and a state where both two turbochargers are driven.

  In such a configuration, for example, when switching from a state where only one turbocharger is driven to a state where both two turbochargers are driven, the cross-sectional area of the exhaust passage increases. Therefore, even if the cross-sectional area of the exhaust passage is calculated based on the driving state of the turbocharger (whether only one turbocharger is driving or both two turbochargers are driving). Good.

Further, in this embodiment, during acceleration operation, when it is determined that there is no valve overlap period between scavenging possible periods, the exhaust pressure phase is controlled so that the scavenging possible period and the valve overlap period overlap. May be. The phase of the exhaust pressure can be controlled by changing the opening timing of the exhaust valve by the exhaust VVT 26. The scavenging possible time can be changed by changing the phase of the exhaust pressure. If the scavenging possible time and the valve overlap period overlap with each other as a result of such exhaust pressure phase control, the same valve overlap period control as described above can be performed.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve 4 ... Intake passage 5 ... Intake manifold 6 ... Exhaust passage 7 ... Exhaust manifold 8 ... Turbocharger 8a -Compressor 8b-Turbine 9 ... Throttle valve 10-Exhaust gas purification device 11-EGR device 12-EGR passage 13-EGR valve 14-Nozzle vane 20-ECU 20
21. ・ Crank position sensor 22 ・ Accelerator opening sensor 23 ・ Intake pressure sensor 24 ・ Air flow meter 25 ・ Intake side variable valve mechanism (intake VVT)
26..Exhaust side variable valve mechanism (exhaust VVT)

Claims (6)

In the internal combustion engine provided with the flow path cross-sectional area control means for controlling the cross-sectional area of the exhaust flow path,
As the cross-sectional area of the exhaust flow path controlled by the flow-path cross-sectional area control means and the cross-sectional area of the exhaust flow path become smaller, the maximum value and the minimum value of the exhaust pressure increase while the amplitude of the exhaust pressure hardly changes. An exhaust pulsation characteristic estimation apparatus for an internal combustion engine, wherein the exhaust pulsation characteristic of the internal combustion engine is estimated using the first relationship . The exhaust pulsation characteristics are the average value, amplitude and phase of the exhaust pressure,
Enthalpy acquisition means for acquiring the enthalpy of exhaust immediately after being discharged from the internal combustion engine or a physical quantity correlated with the enthalpy;
And the cross-sectional area of the controlled exhaust flow path by the flow path cross-sectional area control means, and the first relationship, the physical quantity correlated with the acquired enthalpy or enthalpy by the enthalpy acquisition means, and said enthalpy or the enthalpy An average value estimating means for estimating an average value of the exhaust pressure based on the second relationship in which the maximum value of the exhaust pressure increases while the minimum value of the exhaust pressure hardly changes as the correlated physical quantity increases ;
Amplitude estimation means for estimating the amplitude of exhaust pressure based on the enthalpy or physical quantity correlated with enthalpy acquired by the enthalpy acquisition means and the second relationship ;
Phase estimation means for estimating the phase of the exhaust pressure based on the engine rotational speed of the internal combustion engine and the opening timing of the exhaust valve;
The exhaust pulsation characteristic estimating apparatus for an internal combustion engine according to claim 1, comprising: An exhaust pulsation characteristic estimation device for an internal combustion engine according to claim 1 or 2,
Valve overlap period control for controlling a valve overlap period in which both the intake valve and the exhaust valve of the internal combustion engine are opened according to the exhaust pulsation characteristic estimated by the exhaust pulsation characteristic estimation device Means,
A control system for an internal combustion engine, comprising: The valve overlap period control means suppresses the overlap of the time when the exhaust pressure is higher than the intake pressure and the valve overlap period, and the time when the intake pressure is higher than the exhaust pressure and the valve overlap period. 4. The control system for an internal combustion engine according to claim 3, wherein the valve overlap period is controlled so that a period in which the two overlap each other becomes longer. When the exhaust pulsation characteristic estimation device has a large cross-sectional area of the exhaust flow passage controlled by the flow passage cross-sectional area control means, the average value of the exhaust pressure is lower than when the cross-sectional area of the exhaust flow passage is small Estimate
The valve overlap period control means makes the valve overlap period longer when the average value of the exhaust pressure estimated by the exhaust pulsation characteristic estimation device is low than when the average value of the exhaust pressure is high. An internal combustion engine control system according to claim 4. An exhaust pulsation characteristic estimation device for an internal combustion engine according to claim 2,
Valve overlap period control for controlling a valve overlap period in which both the intake valve and the exhaust valve of the internal combustion engine are opened according to the exhaust pulsation characteristic estimated by the exhaust pulsation characteristic estimation device Means, and
The valve overlap period control means suppresses the overlap of the time when the exhaust pressure is higher than the intake pressure and the valve overlap period, and the time when the intake pressure is higher than the exhaust pressure and the valve overlap period. The valve overlap period is controlled so that the period in which the two overlap each other is longer,
When the exhaust pulsation characteristic estimation device has a small enthalpy or physical quantity correlated with enthalpy acquired by the enthalpy acquisition means, the average value of exhaust pressure is larger than that when the enthalpy or physical quantity correlated with the enthalpy is large. Estimated to be low and its amplitude small,
When the average value of the exhaust pressure estimated by the exhaust pulsation characteristic estimation device is low and the amplitude is small, the valve overlap period control means is higher than when the average value of the exhaust pressure is high and the amplitude is large. A control system for an internal combustion engine characterized by extending a valve overlap period.

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