JP2011153550A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compute an EGR rate using measuring data by a cylinder pressure sensor. <P>SOLUTION: The measuring data by the cylinder pressure sensor are acquired at least two points in a period from a time point of combustion termination in a cylinder, to which the cylinder pressure sensor is attached, until an exhaust valve of the cylinder is opened. The specific heat ratio κ<SB>exp</SB>of combustion gas in the cylinder is calculated using the obtained measuring data. As there is a certain relationship between the specific heat ratio of combustion gas and the EGR rate, when the relationship is mapped beforehand, the EGR rate can be calculated from the specific heat ratio κ<SB>exp</SB>of combustion gas. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine in which an in-cylinder pressure sensor is attached to at least one cylinder.

  It is disclosed in Japanese Patent Application Laid-Open Nos. 2008-231995 and 2008-274811 that the compression stroke of the internal combustion engine is regarded as adiabatic compression and the specific heat ratio of the mixed gas in the cylinder is calculated from the change in the cylinder pressure during the compression stroke. Has been. Japanese Patent Application Laid-Open No. 2008-231995 discloses that the relationship between the specific heat ratio of the mixed gas and the EGR concentration is set as a map in advance, and the EGR gas concentration is obtained using the map and the specific heat ratio of the mixed gas. Is disclosed.

JP 2008-231995 A JP 2008-274811 A

  However, the relationship between the specific heat ratio of the mixed gas and the EGR concentration is not necessarily constant, and the relationship depends on the air-fuel ratio. If the air-fuel ratio changes, the composition of the mixed gas changes, and the specific heat changes accordingly. Therefore, if it is possible to calculate an accurate EGR rate and EGR concentration in the technique disclosed in Japanese Patent Application Laid-Open No. 2008-231995, this is a case where the air-fuel ratio is controlled to a constant value, that is, a target value, and not so. As long as it is difficult to calculate the EGR rate and EGR concentration with high accuracy.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a control device for an internal combustion engine that can accurately calculate an EGR rate using measurement data obtained by an in-cylinder pressure sensor.

For the above purpose, the control device for an internal combustion engine of the first invention provides:
A control device for an internal combustion engine in which an in-cylinder pressure sensor is attached to at least one cylinder,
Measurement data obtained by the in-cylinder pressure sensor is acquired during a period from the end of combustion of the cylinder to which the in-cylinder pressure sensor is attached until the exhaust valve of the cylinder is opened, and using the obtained measurement data, A combustion gas specific heat ratio calculating means for calculating a specific heat ratio;
EGR rate calculating means for calculating an EGR rate from the specific heat ratio of the combustion gas calculated by the combustion gas specific heat ratio calculating means based on the relationship between the specific heat ratio of the combustion gas and the EGR rate;
It is characterized by having.

A control device for an internal combustion engine according to a second invention is the control device for an internal combustion engine according to the first invention,
Measurement data obtained by the in-cylinder pressure sensor is acquired during a period from when the intake valve of the cylinder to which the in-cylinder pressure sensor is attached is closed to when combustion starts in the cylinder, and the mixed gas in the cylinder is obtained using the obtained measurement data. A mixed gas specific heat ratio calculating means for calculating a specific heat ratio of
Based on the specific heat ratio of the mixed gas, the air-fuel ratio, and the EGR rate, from the specific heat ratio of the mixed gas calculated by the mixed gas specific heat ratio calculating unit and the EGR rate calculated by the EGR rate calculating unit Air-fuel ratio calculating means for calculating the air-fuel ratio;
Is further provided.

A control device for an internal combustion engine according to a third invention is the control device for an internal combustion engine according to the first or second invention,
A misfire detecting means for detecting misfire of a cylinder to which the in-cylinder pressure sensor is attached;
The EGR rate calculating means stops calculating the EGR rate when a misfire is detected by the misfire detecting means.

  If the in-cylinder pressure during the period from the end of combustion to the opening of the exhaust valve is measured by the in-cylinder pressure sensor, the specific heat ratio of the combustion gas can be calculated from the measured data. There is a certain relationship that does not depend on the air-fuel ratio between the specific heat ratio of the combustion gas and the EGR rate. Since the control device for the internal combustion engine of the first invention uses this relationship for the calculation of the EGR rate, it is possible to calculate the EGR rate with high accuracy using the measurement data from the in-cylinder pressure sensor.

  If the in-cylinder pressure during the period from the closing of the intake valve to the start of combustion is measured by the in-cylinder pressure sensor, the specific heat ratio of the mixed gas before combustion can be calculated from the measured data. There is a certain relationship among the specific heat ratio of the mixed gas, the air-fuel ratio, and the EGR rate. Since the control device for the internal combustion engine of the second invention uses this relationship for calculation of the air-fuel ratio, it is possible to calculate the air-fuel ratio with high accuracy using the measurement data from the in-cylinder pressure sensor.

  When a misfire occurs, most of the in-cylinder gas becomes unburned gas. Therefore, even if measurement data obtained by the in-cylinder pressure sensor is obtained, the specific heat ratio of the combustion gas cannot be calculated correctly. According to the control apparatus for an internal combustion engine of the third invention, when the misfire occurs, the calculation of the EGR rate is stopped and the previously calculated value is used, so that an incorrect EGR rate is calculated based on an inaccurate specific heat ratio. This is prevented.

1 is a diagram showing an internal combustion engine to which a control layer device according to an embodiment of the present invention is applied. It is a figure which shows the relationship which exists between the specific heat ratio of combustion gas, and an EGR rate. It is a figure which shows the relationship which exists among the specific heat ratio of a mixed gas, an air fuel ratio, and an EGR rate. It is a flowchart which shows the procedure which calculates an air fuel ratio from the measurement data by a cylinder pressure sensor.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4.

  FIG. 1 is a diagram showing an internal combustion engine (hereinafter simply referred to as an engine) to which the control device of the present embodiment is applied. The engine shown in FIG. 1 is a spark ignition type 4-stroke reciprocating engine provided with a spark plug 6. Moreover, it is also a cylinder direct injection engine provided with the fuel direct injection injector 7 which injects a fuel directly in a cylinder. Although only one cylinder is depicted in FIG. 1, a general vehicle engine is composed of a plurality of cylinders. An in-cylinder pressure sensor 5 for measuring the in-cylinder pressure is attached to at least one of the cylinders. The engine is also provided with a crank angle sensor 8 that outputs a signal according to the rotation angle of the crankshaft, and a knock sensor 9 for detecting the occurrence of knock. From the signal CA of the crank angle sensor 8, the in-cylinder volume determined by the engine speed (the number of revolutions per unit time) and the position of the piston can be calculated. An air cleaner 1 is provided at the inlet of the intake passage connected to the cylinder, and a throttle valve 2 is disposed downstream of the air cleaner 1. A surge tank 4 is provided downstream of the throttle valve 2, and an intake pressure sensor 3 for measuring the intake pressure is attached to the surge tank 4. On the other hand, two catalysts 10 and 11 are arranged in the exhaust passage connected to the cylinder. An EGR cooler 13 and an EGR valve 12 are provided in the EGR passage connecting the exhaust passage and the intake passage of the engine. The EGR cooler 13 is provided with a water temperature sensor 14 for measuring the cooling water temperature. The engine also includes an arithmetic processing unit 20 as a control device. The arithmetic processing unit 20 processes signals from the sensors 3, 5, 8, 9, and 14, and reflects the processing results in the operations of the actuators 2, 6, 7, and 12.

  The arithmetic processing unit 20 has a function of calculating the EGR rate and A / F (air / fuel ratio) of the engine from the data measured by the in-cylinder pressure sensor 5. However, the EGR rate here means the total EGR rate, that is, the ratio of the total EGR gas to the in-cylinder gas including the internal EGR gas, the external EGR gas, and the residual gas. Hereinafter, the calculation method of the EGR rate and the calculation method of A / F by the arithmetic processing unit 20 will be described.

  First, the calculation method of the EGR rate by the arithmetic processing unit 20 will be described. The conventional method disclosed in Japanese Patent Application Laid-Open No. 2008-231995 calculates the specific heat ratio of the mixed gas, and uses it to calculate the EGR concentration (EGR rate). In contrast, in the present embodiment, the EGR rate is calculated using the specific heat ratio of the combustion gas generated by burning the mixed gas, not the specific heat ratio of the mixed gas before combustion.

  FIG. 2 is a diagram showing the experimental results of examining the relationship between the specific heat ratio of the combustion gas and the EGR rate. In the experiment, when the A / F is 14.5, when it is 16.0, when it is 19.0, it is operated under different EGR rates, and the specific heat ratio of the combustion gas is set for each of them. Examined.

The specific heat ratio of the combustion gas can be calculated from the expansion stroke, more specifically, the change in the in-cylinder pressure during the period from the end of combustion until the exhaust valve opens. The following equation 1 is an equation for calculating the specific heat ratio κ _exp of the combustion gas from the measured value of the in-cylinder pressure sensor 5. Since the period from the end of combustion to the opening of the exhaust valve can be regarded as adiabatic expansion, the specific heat ratio κ _exp of the combustion gas can be approximated by the polytropic index. In Equation 1, P ₁ and P ₂ are measured values of the in-cylinder pressure sensor 5 obtained at two different points during the expansion stroke, and V ₁ and V ₂ are in-cylinder volumes at each measurement time point. The two points for obtaining the measured values can be arbitrarily selected, but preferably, a point with a good S / N ratio (specifically, a point where noise due to fuel injection of other cylinders, ignition noise or the like is not superimposed) is selected. Here, the measurement points of the in-cylinder pressure for calculating the specific heat ratio κ _exp are two, but the specific heat ratio κ _exp may be calculated by the least square method taking three or more measurement points.
κ _exp = − (lnP ₂ −lnP ₁ ) / (lnV ₂ −lnV ₁ ) Equation 1

The first thing that can be confirmed from the experimental results shown in FIG. 2 is that the specific heat ratio of the combustion gas decreases as the EGR rate increases. This is because the specific heat ratio of gas generally decreases as the number of constituent atoms increases, but when EGR is introduced, components having a large number of constituent atoms such as CO ₂ and H ₂ O increase.

Also, from the experimental results shown in FIG. 2, it can be confirmed that the relationship between the specific heat ratio of the combustion gas and the EGR rate does not depend on A / F. This is because CO ₂ and CO have a great influence on the specific heat ratio, and their concentrations in the combustion gas are substantially the same regardless of A / F. On the other hand, as the A / F becomes leaner, the O ₂ concentration increases. However, since the influence on the specific heat ratio of O ₂ is small, it does not appear as a change in the specific heat ratio.

  Furthermore, from the experimental results shown in FIG. 2, it can be confirmed that the calculation accuracy of the specific heat ratio with respect to the EGR rate is greatly reduced when misfire occurs. This is because most of the in-cylinder gas becomes unburned gas when misfire occurs.

As a result of the above considerations, it has been found that there is a certain relationship independent of A / F between the specific heat ratio of the combustion gas and the EGR rate in a situation where combustion is stable. By utilizing this relationship, it is possible to uniquely determine the EGR rate without considering A / F only by calculating the specific heat ratio of the combustion gas from the measurement data obtained by the in-cylinder pressure sensor 5. In the present embodiment, the relationship between the specific heat ratio of the combustion gas and the EGR rate as shown in the graph of FIG. 2 is previously mapped and stored in the arithmetic processing unit 20. The arithmetic processing unit 20 substitutes the measured value of the in-cylinder pressure sensor 5 obtained in the expansion stroke into the above-described equation 1, and calculates the specific heat ratio κ _exp of the combustion gas. Then, using the stored map (hereinafter referred to as the EGR rate map), the engine EGR rate is calculated from the specific heat ratio κ _exp of the combustion gas.

  Next, an A / F calculation method by the arithmetic processing unit 20 will be described. The information used for calculating A / F in the present embodiment is the EGR rate calculated previously and the specific heat ratio of the mixed gas before combustion.

  FIG. 3 is a diagram showing the experimental results of examining the relationship among the specific heat ratio of the mixed gas, the A / F, and the EGR rate. In the experiment, when A / F is 14.5, 16.0, 19.0, operation is performed under different EGR ratios, and the specific heat ratio of the mixed gas is set for each. Examined.

The specific heat ratio of the mixed gas before combustion can be calculated from the change in the in-cylinder pressure during the compression stroke, more specifically, the period from the closing of the intake valve to the start of combustion. The following equation 2 is an equation for calculating the specific heat ratio κ _comp of the mixed gas from the measured value of the in-cylinder pressure sensor 5. Since the period from the closing of the intake valve to the start of combustion can be regarded as adiabatic compression, the specific heat ratio κ _comp of the mixed gas can be approximated by the polytropic index. In Equation 2, P ₁ and P ₂ are measured values of the in-cylinder pressure sensor 5 obtained at two different points during the compression stroke, and V ₁ and V ₂ are in-cylinder volumes at each measurement time point. The two points for obtaining the measured values can be arbitrarily selected, but preferably, a point with a good S / N ratio (specifically, a point where noise due to fuel injection of other cylinders, ignition noise or the like is not superimposed) is selected. Here, the measurement points of the in-cylinder pressure for calculating the specific heat ratio κ _comp are two, but the specific heat ratio κ _comp may be calculated by the least square method taking three or more measurement points.
κ _comp = − (lnP ₄ −lnP ₃ ) / (lnV ₄ −lnV ₃ ) Equation 2

It can be confirmed from the experimental results shown in FIG. 3 that the specific heat ratio of the mixed gas decreases when the EGR rate is increased. This is because the specific heat ratio of gas generally decreases as the number of constituent atoms increases, but when EGR is introduced, components having a large number of constituent atoms such as CO ₂ and H ₂ O increase.

  From the experimental results shown in FIG. 3, it can be confirmed that the relationship between the specific heat ratio of the mixed gas and the EGR rate depends on A / F. As A / F becomes leaner, the specific heat ratio of the mixed gas gradually approaches the specific heat ratio of air (about 1.4).

As described above, there is a certain relationship between the specific heat ratio of the mixed gas, the A / F, and the EGR rate. By utilizing this relationship, it is possible to uniquely determine the A / F by calculating the EGR rate by the above-described method and further calculating the specific heat ratio of the mixed gas from the measurement data obtained by the in-cylinder pressure sensor 5. In the present embodiment, the relationship between the specific heat ratio of the mixed gas, the A / F, and the EGR rate as shown in the graph of FIG. 3 is previously mapped and stored in the arithmetic processing unit 20. The arithmetic processing unit 20 calculates the EGR rate by the above-described method, and further calculates the specific heat ratio κ _comp of the mixed gas by substituting the measured value of the in-cylinder pressure sensor 5 obtained in the compression stroke into the above-described equation 2. Then, using the stored map (hereinafter referred to as A / F map), the A / F of the engine is calculated from the EGR rate and the specific heat ratio κ _{comp of the} mixed gas.

  Hereinafter, a series of processes when the arithmetic processing unit 20 calculates the EGR rate and A / F of the engine from the measurement data by the in-cylinder pressure sensor 5 will be described with reference to the flowchart of FIG. A series of processing described below is processing performed for each cylinder to which the in-cylinder pressure sensor 5 is attached. Therefore, when the in-cylinder pressure sensor 5 is attached to all the cylinders, the arithmetic processing unit 20 performs the following processing for each cylinder.

  In the first step S2, the arithmetic processing unit 20 determines whether or not misfiring has occurred in the cylinder to which the in-cylinder pressure sensor 5 is attached, that is, the target cylinder. There is no limitation on the misfire determination method. When the occurrence of misfire is detected, the arithmetic processing unit 20 skips the calculation of the subsequent steps and uses the previously calculated value. This is because the specific heat ratio of the combustion gas cannot be calculated correctly even if measurement data obtained by the in-cylinder pressure sensor 5 is obtained when misfire occurs. By canceling the calculation of the subsequent steps, it is possible to prevent an erroneous EGR rate and A / F from being calculated based on an inaccurate specific heat ratio.

When no misfire has occurred, the arithmetic processing unit 20 executes the processes after step S4. First, in step S4, the arithmetic processing unit 20 measures the in-cylinder pressure in the period from the end of combustion to the opening of the exhaust valve by the in-cylinder pressure sensor 5, and from the measured data, the specific heat ratio κ _{exp of the} combustion gas by the above-mentioned equation 1 Is calculated.

In the next step S6, the arithmetic processing unit 20 searches the EGR rate map using the specific heat ratio κ _exp of the combustion gas obtained in step S4 as a key, and obtains an EGR rate corresponding to the specific heat ratio κ _exp of the combustion gas.

In the next step S8, the arithmetic processing unit 20 measures the in-cylinder pressure in the period from the opening of the intake valve to the start of combustion by the in-cylinder pressure sensor 5, and from the measurement data, the specific heat ratio κ of the mixed gas according to the above-described equation 2. _comp is calculated.

In step S10, the arithmetic processing unit 20 searches the A / F map using the EGR rate obtained in step S6 and the specific heat ratio κ _comp of the mixed gas obtained in step S8 as a key, and calculates the EGR rate and the mixed gas. A / F corresponding to the specific heat ratio κ _comp is obtained.

  According to the method of the present embodiment described above, it is possible to calculate the EGR rate with high accuracy using the measurement data by the in-cylinder pressure sensor 5, and furthermore, using the calculation result, the A / F with high accuracy can be calculated. Calculations can be made. Further, according to the method of the present embodiment, the EGR rate and A / F can be obtained for each cycle, and when the in-cylinder pressure sensor 5 is provided in all the cylinders, the EGR rate for each cylinder. And A / F can also be obtained.

  Therefore, according to the present embodiment, the control for increasing / decreasing the fuel injection amount by the direct fuel injector 7 so as to achieve the target A / F and the control for opening / closing the EGR valve 12 so as to achieve the target EGR rate are calculated with high accuracy. Can be performed precisely based on the measured EGR rate and A / F. That is, according to the present embodiment, precise combustion control can be performed.

  Furthermore, according to the present embodiment, since the A / F can be calculated from the measurement data obtained by the in-cylinder pressure sensor 5, the A / F sensor can be omitted from the exhaust passage. Further, since the cylinder pressure sensor 5 used to obtain A / F does not require an active time like the A / F sensor, according to the present embodiment, all operating conditions including cold start are included. It is possible to perform A / F control in step 1, and an improvement in exhaust gas performance can be expected.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  Further, the engine to which the present invention is applied is not limited to the in-cylinder direct injection engine as in the above-described embodiment. The present invention can also be applied to a port injection type engine. Further, the present invention can be applied not only to a spark ignition type engine but also to a compression self-ignition type engine.

DESCRIPTION OF SYMBOLS 1 Air cleaner 2 Throttle valve 3 Intake pressure sensor 4 Surge tank 5 In-cylinder pressure sensor 6 Spark plug 7 Fuel direct injection injector 8 Crank angle sensor 9 Knock sensor 10, 11 Catalyst 12 EGR valve 13 EGR cooler 14 Water temperature sensor 20 Processing unit

Claims (3)

A control device for an internal combustion engine in which an in-cylinder pressure sensor is attached to at least one cylinder,
Measurement data obtained by the in-cylinder pressure sensor is acquired during a period from the end of combustion of the cylinder to which the in-cylinder pressure sensor is attached until the exhaust valve of the cylinder is opened, and using the obtained measurement data, A combustion gas specific heat ratio calculating means for calculating a specific heat ratio;
EGR rate calculating means for calculating an EGR rate from the specific heat ratio of the combustion gas calculated by the combustion gas specific heat ratio calculating means based on the relationship between the specific heat ratio of the combustion gas and the EGR rate;
A control device for an internal combustion engine, comprising: Measurement data obtained by the in-cylinder pressure sensor is acquired during a period from when the intake valve of the cylinder to which the in-cylinder pressure sensor is attached is closed to when combustion starts in the cylinder, and the mixed gas in the cylinder is obtained using the obtained measurement data. A mixed gas specific heat ratio calculating means for calculating a specific heat ratio of
Based on the specific heat ratio of the mixed gas, the air-fuel ratio, and the EGR rate, from the specific heat ratio of the mixed gas calculated by the mixed gas specific heat ratio calculating unit and the EGR rate calculated by the EGR rate calculating unit Air-fuel ratio calculating means for calculating the air-fuel ratio;
The control device for an internal combustion engine according to claim 1, further comprising: A misfire detecting means for detecting misfire of a cylinder to which the in-cylinder pressure sensor is attached;
3. The control apparatus for an internal combustion engine according to claim 1, wherein the EGR rate calculating unit stops calculating the EGR rate when a misfire is detected by the misfire detecting unit.

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