JP2014137004A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the humidity of in-cylinder gas flowing into a cylinder without newly installing a humidity sensor.SOLUTION: During the engine revolution of an internal combustion engine and in the state of no fuel injection, a control device for the internal combustion engine acquires a first cylinder pressure as a cylinder pressure at a bottom dead center in a compression stroke and a second cylinder pressure as a cylinder pressure at a top dead center in the compression stroke, and also acquires the temperature of intake air. Then, it estimates the humidity of in-cylinder gas flowing into the cylinder, depending on the first cylinder pressure, the second cylinder pressure, the compression ratio of the internal combustion engine, and the temperature of the intake air which it acquires.

Description

  The present invention relates to a control device for an internal combustion engine. Specifically, the present invention relates to a control device for an internal combustion engine provided with means for acquiring an in-cylinder pressure of a cylinder of the internal combustion engine.

  Patent Document 1 discloses a capacitive humidity sensor in which a moisture sensitive film whose relative dielectric constant changes according to humidity is interposed between a pair of electrodes. This humidity sensor has a pair of electrodes as a sensor part and a moisture sensitive film formed so as to cover the pair of electrodes. In this humidity sensor, when the humidity of the gas to be measured changes, the relative permittivity of the moisture sensitive film changes, and as a result, the capacitance between the pair of electrodes changes. This capacitance change is converted into a voltage by the CV conversion unit, and the converted voltage is output as a sensor output, and humidity is detected based on this.

JP 2006-58084 A

  A humidity sensor using a moisture-sensitive film as in Patent Document 1 can measure humidity with high accuracy as long as physical characteristics such as temperature, pressure, and flow rate of a gas to be measured are stable. Therefore, a humidity sensor using a moisture-sensitive film is suitable for use in measuring the humidity of intake air, for example, installed near the intake port or air flow meter of an internal combustion engine.

  However, in order to predict a change in combustion of the internal combustion engine due to a change in absolute humidity, it is desirable to be able to detect the humidity of the intake air when it flows into the cylinder. However, changes in physical characteristics such as temperature, pressure, and flow rate are large in the cylinder. Since the moisture sensitive film is easily affected by changes in these physical characteristics, a humidity sensor using the moisture sensitive film is not suitable for measuring the in-cylinder humidity.

  Moreover, even if it is for humidity detection in the place where physical characteristics are stable, such as the vicinity of an air flow meter, it is not preferable from the viewpoint of cost reduction to newly install a humidity sensor.

  The present invention has been made in view of the above points, and is an improved control device for an internal combustion engine that can detect the humidity of in-cylinder gas flowing into the cylinder without newly adding a humidity sensor. The purpose is to provide.

A first invention is a control device for an internal combustion engine for achieving the above object,
A first in-cylinder pressure that is the in-cylinder pressure at the bottom dead center of the compression stroke, and a second in-cylinder pressure that is the in-cylinder pressure at the top dead center of the compression stroke, while the engine of the internal combustion engine is rotating and without fuel injection; Means for obtaining
Means for obtaining the temperature of the intake air;
Estimating means for estimating the humidity of the in-cylinder gas flowing into the cylinder according to the first in-cylinder pressure, the second in-cylinder pressure, the compression ratio of the internal combustion engine, and the temperature of the intake air;
It is characterized by providing.

In a second aspect based on the first aspect, the estimating means comprises:
In accordance with the first in-cylinder pressure, the second in-cylinder pressure, and the compression ratio, a specific heat ratio of the in-cylinder gas is calculated,
The humidity of the in-cylinder gas is calculated according to the specific heat ratio and the temperature of the intake air.

A third invention is a control device for an internal combustion engine,
During engine rotation of the internal combustion engine and no fuel injection, the first in-cylinder pressure that is the in-cylinder pressure at the first time point of the compression stroke and the in-cylinder pressure at the second time point that is different from the first time point of the compression stroke. Means for obtaining two in-cylinder pressures;
Means for obtaining the temperature of the intake air;
The humidity of the cylinder gas flowing into the cylinder according to the first cylinder pressure, the second cylinder pressure, the cylinder volume at the first time point, the cylinder volume at the second time point, and the temperature of the intake air Estimating means for estimating
It is characterized by providing.

In a fourth aspect based on the third aspect, the estimating means comprises:
According to the first cylinder pressure, the second cylinder pressure, the cylinder volume at the first time point, and the cylinder volume at the second time point, a specific heat ratio of the cylinder gas is calculated,
The humidity of the in-cylinder gas is calculated according to the specific heat ratio and the temperature of the intake air.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the first in-cylinder pressure and the second in-cylinder pressure are such that the amount of change per hour in the intake air temperature is smaller than a predetermined value, It is acquired in a state where at least one condition is satisfied among a group of conditions consisting of a change amount of temperature per time being smaller than a predetermined value and an exhaust gas temperature being smaller than a predetermined value. And

In a sixth aspect based on any one of the first to fifth aspects, the internal combustion engine includes an EGR device that recirculates a part of the exhaust gas as EGR gas to the intake passage,
The first in-cylinder pressure and the second in-cylinder pressure are acquired in a state where the recirculation of EGR gas is stopped.

  According to the present invention, the humidity of the in-cylinder gas that actually flows into the cylinder is estimated using the in-cylinder pressure during the compression stroke. Thereby, it is possible to grasp the humidity with high accuracy even in a cylinder having a large physical characteristic change without separately installing a humidity sensor or the like.

  Moreover, according to the 4th or 5th invention, humidity can be estimated based on the in-cylinder pressure acquired in the more stable driving | running state. Therefore, the accuracy of the humidity estimation of the in-cylinder gas can be further increased.

It is a schematic block diagram for demonstrating the structure of the system of embodiment of this invention. It is a figure for demonstrating the relationship between the absolute humidity and specific heat ratio of the cylinder interior gas of embodiment of this invention. It is a flowchart for demonstrating the routine of control which a control apparatus performs in embodiment of this invention. It is a figure for demonstrating the relationship between the absolute humidity and the estimated value of NOx density | concentration, and the relationship between the absolute humidity and the estimation error of NOx density | concentration.

  Embodiments of the present invention will be described below 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. The present invention is not limited to the following embodiments.

Embodiment.
[System configuration of the present embodiment]
FIG. 1 is a schematic diagram for explaining the overall configuration of a system according to an embodiment of the present invention. The system of FIG. 1 has an internal combustion engine 2. The internal combustion engine 2 is mounted and used in a vehicle. The internal combustion engine 2 has a plurality of cylinders 4. An in-cylinder pressure sensor 6 is installed in at least one cylinder of the plurality of cylinders 4. The in-cylinder pressure sensor 6 is a sensor that generates an output corresponding to the pressure in the cylinder, and can thereby detect the in-cylinder pressure. A crank angle sensor 8 is installed near the crankshaft of the internal combustion engine 2. According to the output of the crank angle sensor 8, the rotational position (crank angle) of the crankshaft, the engine speed (engine speed), and the like can be detected.

  An intake pipe 10 communicates with an intake port of each cylinder 4 of the internal combustion engine 2 via an intake manifold. An air flow meter and a temperature sensor 12 are installed in the intake pipe 10. According to the output of the temperature sensor 12, the temperature of the intake air (intake air temperature) can be detected.

  An exhaust pipe 20 communicates with an exhaust port of each cylinder 4 of the internal combustion engine 2 via an exhaust manifold. A catalyst such as a DOC (Diesel Oxidation Catalyst) 22 is installed in the exhaust pipe 20. The exhaust pipe 20 is provided with sensors such as a temperature sensor 24 and an air-fuel ratio sensor 26. According to the output of the temperature sensor 24, the temperature of the exhaust gas (exhaust temperature) can be detected. Further, according to the output of the air-fuel ratio sensor 26, the air-fuel ratio of the exhaust gas can be detected.

  The system according to the present embodiment includes an ECU (Electronic Control Unit) 30 as a control device. The ECU 30 is connected to various sensors such as the in-cylinder pressure sensor 6, the crank angle sensor 8, the temperature sensors 12 and 24, and the air-fuel ratio sensor 26, and various actuators such as an injector. The ECU 30 can control the operation state of the internal combustion engine 2 by driving each actuator according to a predetermined control program based on the output of each sensor.

[Calculation control of absolute humidity by system of this embodiment]
(Absolute humidity calculation method)
The control executed by the ECU 30 in the present embodiment includes control for calculating the absolute humidity in the cylinder. Absolute humidity is calculated as follows.

While the internal combustion engine 2 is rotating and in the state of no fuel injection, the state change of the gas in the cylinder during the compression stroke can be regarded as a polytropic change, and PV ^κ = a constant relationship is established. Here, P is the in-cylinder pressure, V is the volume of the combustion chamber, and κ is the specific heat ratio.

In the present embodiment, using this PV ^κ = constant relationship, the in-cylinder pressure P1 at the compression stroke bottom dead center (hereinafter also referred to as “compression bottom dead center”) in the state of no fuel injection, and the compression stroke top dead center The specific heat ratio κ is detected from the in-cylinder pressure P2 (hereinafter also referred to as “compression bottom dead center”) and the compression ratio of the internal combustion engine 2.

The specific heat ratio κ can be calculated based on the following formula (1) from the relationship PV ^κ = constant.
κ = log (P2 / P1) / log (compression ratio) (1)

  Incidentally, the specific heat ratio κ has a correlation with absolute humidity and intake air temperature. FIG. 2 shows the relationship between the specific heat ratio κ and the absolute humidity at a certain intake air temperature. In FIG. 2, the horizontal axis represents the specific heat ratio κ, and the vertical axis represents the absolute humidity [g / kg]. As shown in FIG. 2, the specific heat ratio κ decreases as the absolute humidity increases.

  Further, the specific heat ratio κ decreases as the intake air temperature increases. By using the correlation between the intake air temperature, the specific heat ratio κ, and the absolute humidity, the absolute humidity can be calculated according to the specific heat ratio κ and the intake air temperature.

  Specifically, in the present embodiment, the relationship between the specific heat ratio κ and absolute humidity as shown in FIG. 2 is obtained by experiment, simulation, or the like for each intake air temperature. The obtained relationship between the intake air temperature, the specific heat ratio κ, and the absolute humidity is determined as a map or the like and stored in advance in the ECU 30.

  In the control during the operation of the internal combustion engine 2, the in-cylinder pressures P1 and P2 at the compression top dead center and the compression bottom dead center and the intake air temperature are respectively detected. The ECU 30 calculates the specific heat ratio κ from the detected in-cylinder pressures P1, P2 and the compression ratio, and calculates the absolute humidity according to the map from the specific heat ratio κ and the intake air temperature.

(Operating conditions when calculating)
In the present embodiment, the specific heat ratio κ is calculated only when all the following stability conditions (a) to (d) are satisfied.
(A) In the case of a system having an EGR device, EGR gas does not flow into the cylinder.
(B) The amount of change in intake air temperature per hour is smaller than the reference value.
(C) The amount of change in the exhaust gas temperature per hour is smaller than the reference value.
(D) The exhaust gas temperature to be discharged is within a reference value.
Satisfying the above conditions makes it possible to calculate absolute humidity under more stable operating conditions. Therefore, the calculation accuracy of absolute humidity can be improved. Since these are conditions for stably calculating the absolute humidity, the reference values in the above (b) to (d) are values set appropriately in consideration of the detection accuracy of the absolute humidity and the like. is there.

  FIG. 3 is a flowchart for illustrating a control routine executed by ECU 30 in the embodiment of the present invention. The routine of FIG. 3 is a routine that is repeatedly executed at regular intervals during operation of the internal combustion engine 2. In the routine of FIG. 3, it is first determined whether or not the internal combustion engine 2 is rotating (S102). If it is not recognized that the internal combustion engine 2 is rotating, the current process ends.

  On the other hand, if it is determined in S102 that the engine is rotating, it is next determined whether or not there is no fuel injection (S104). If it is not recognized that there is no fuel injection, the current process ends.

  On the other hand, if it is determined in S104 that there is no fuel injection, it is next determined whether or not a stable condition is satisfied (S106). The stability conditions are the conditions (a) to (d) described above. If all of the above (a) to (d) are not established, the current process ends as it is.

  On the other hand, if the establishment of the stable condition is recognized in S106, the intake air temperature is then acquired (S108). The intake air temperature is acquired based on the output of the temperature sensor 12 installed in the intake pipe 10 of the internal combustion engine 2.

  Next, the in-cylinder pressure P1 is acquired at the timing of compression bottom dead center, and the in-cylinder pressure P2 is acquired at the timing of compression top dead center (S110). These acquisition timings are detected by the ECU 30 based on the output of the crank angle sensor 8. The in-cylinder pressures P1 and P2 are acquired based on the output of the in-cylinder pressure sensor 6, respectively.

  Next, the specific heat ratio κ is calculated (S112). The specific heat ratio κ can be calculated by substituting the in-cylinder pressures P1 and P2 into the above equation (1). The arithmetic expression (1) is stored in the ECU 30 in advance.

  Next, the absolute humidity is calculated (S114). The absolute humidity is determined according to the intake air temperature acquired in S108 and the specific heat ratio κ calculated in S112 according to a map stored in the ECU 30 in advance. Thereafter, the current process ends.

  As described above, according to the present embodiment, the absolute humidity in the cylinder can be calculated based on the cylinder pressure at the compression bottom dead center and the cylinder pressure at the compression top dead center. Therefore, the humidity state of the in-cylinder gas can be estimated without newly installing a humidity sensor or the like.

  The absolute humidity calculated by the above method can be used, for example, when estimating the NOx concentration, and the estimation accuracy can be improved. FIG. 4 is a diagram for explaining the absolute humidity, the NOx concentration, and the estimation error. In FIG. 4, the horizontal axis indicates the absolute humidity [g / kg], and the vertical axis indicates the NOx concentration [ppm] or the estimation error [ %]. In FIG. 4, a solid line (a) represents an actual NOx concentration, a broken line (b) represents an estimated NOx concentration, and a solid line (c) represents an estimation error.

  As shown in FIG. 4, a deviation due to the influence of absolute humidity occurs between the actual NOx concentration (solid line (a)) and the estimated NOx concentration (broken line (b)). Specifically, the estimated humidity is the actual NOx concentration when the absolute humidity is lower than the standard humidity at the standard humidity (here 10.7 [g / kg]) where the actual NOx concentration and the estimated NOx concentration match. If the absolute humidity is higher than the standard humidity, the actual NOx concentration is higher. And it turns out that this error becomes large as the humidity difference from standard humidity becomes large, as shown by the continuous line (c).

  As shown in FIG. 4, the error between the actual NOx concentration and the estimated NOx concentration has a correlation with absolute humidity. Therefore, the NOx concentration estimated value can be corrected according to the absolute humidity by obtaining in advance the relationship between the absolute humidity and the correction value for the estimated NOx concentration based on this correlation. As a result, the NOx concentration can be detected with high accuracy.

  Further, the dry air flow rate can be calculated from the absolute humidity calculated by the present embodiment and the humid air flow rate of the air flow meter. For example, the current EGR control is actually wet air amount control, not oxygen amount control. However, the amount of oxygen does not necessarily change in conjunction with the amount of humid air. On the other hand, the amount of oxygen changes in conjunction with the amount of dry air. Therefore, if the dry air flow rate can be calculated, EGR control can be executed based on the dry air amount, and EGR control corresponding to the oxygen amount can be performed. Thereby, the change of the NOx amount due to the humidity change can be suppressed.

  For example, the humidity of the cylinder of the internal combustion engine affects the amount of condensed water generated in the exhaust system. By using the humidity of the cylinder calculated as described above, the estimated model of condensed water can be corrected by the humidity. Therefore, corrosion of parts due to condensed water can be reduced. Moreover, since the amount of dry air can be calculated as described above, it is possible to reduce the emission change due to humidity.

  In the present embodiment, the case where the temperature sensor 12 for detecting the intake air temperature is installed in the intake pipe 10 has been described. However, in the present invention, the detection position of the intake air temperature is not limited to this, and may be installed in other parts such as an intake manifold, an intake port, an air flow meter, and the like.

  In the present embodiment, the case where the DOC 22 is installed in the exhaust pipe 20 of the internal combustion engine 2 has been described. However, the catalyst installed in the exhaust pipe 20 in the present invention is not limited to this. For example, in addition to the DOC 22, another catalyst such as a urea SCR system may be installed. Further, when the internal combustion engine 2 is a gasoline engine, a catalyst corresponding to the engine may be installed. Also, the type of sensor to be installed is not limited to the temperature sensor 24 and the air-fuel ratio sensor 26, and for example, a configuration in which a NOx sensor, a PM sensor, or the like is installed may be used. Also, the present invention is not limited by the embodiment with respect to the installation positions of various sensors.

  In the present embodiment, the case where the specific heat ratio κ is calculated using the in-cylinder pressure P1 at the compression bottom dead center, the in-cylinder pressure P2 at the compression top dead center, and the compression ratio has been described. However, the present invention is not limited to this, and the specific heat ratio κ may be calculated using the in-cylinder pressure at two points having different compression strokes.

Specifically, the specific heat ratio κ is defined as the cylinder pressure P01 at the first time point in the compression stroke, the cylinder pressure P02 at the second time point, the cylinder pressure P02 at the second time point, the cylinder volume at the first time point V01, and the second time point. Assuming that the in-cylinder volume is V02, it can be obtained by the following equation (2).
κ = log (P02 / P01) / log (V02 / V01) (2)

  The in-cylinder volumes V1 and V2 at the first time point and the second time point can be obtained according to the position of the piston in the cylinder detected based on the output of the crank angle sensor 8. Similarly, the absolute humidity can be calculated according to the map using the specific heat ratio κ calculated by the equation (2).

  Further, in the present embodiment, a case has been described in which a map that defines the relationship among the specific heat ratio κ, the intake air temperature, and the absolute humidity is stored in the ECU 30 in advance, and the absolute humidity is calculated according to this map. However, the present invention is not limited to this. For example, the specific heat ratio κ calculated from the compression bottom dead center and the in-cylinder pressures P1 and P2 at the compression top dead center, the intake air temperature, and the absolute humidity have a correlation. Accordingly, the in-cylinder pressures P1 and P2, the in-cylinder pressure ratio P2 / P1, and the like have a correlation with the intake air temperature and the absolute humidity. Therefore, for example, the relationship between the in-cylinder pressures P1 and P2 of the compression bottom dead center and the compression top dead center, the intake air temperature, and the absolute humidity is determined in advance, and the absolute humidity is calculated without calculating the specific heat ratio. It is good also as what to do. Further, the absolute humidity may be calculated without calculating the specific heat ratio from the relationship between the ratio between the in-cylinder pressures P1 and P2, the intake air temperature, and the absolute humidity.

  The same applies to the case where the cylinder pressures P1 and P2 at the top dead center and the bottom dead center are not used, and the cylinder pressures at two points in the compression stroke are used. Also in this case, for example, without calculating the specific heat ratio from the relationship between the ratio of the in-cylinder pressure (P02 / P01), the ratio of the in-cylinder volume (V02 / V01), the intake air temperature, and the absolute humidity. The absolute humidity may be calculated. The absolute humidity is directly calculated not only using the ratio of the in-cylinder pressure and the ratio of the in-cylinder volume but using two in-cylinder pressures P01 and P02, the in-cylinder volumes V01 and V02, and the intake air temperature as parameters. It may be.

  In other cases, in the above embodiment, when the number of each element, quantity, quantity, range, etc. is mentioned, unless otherwise specified or clearly specified in principle, that number The invention is not limited to the number mentioned. The structures, steps, and the like described in this embodiment are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

2 Internal combustion engine 4 Cylinder 6 In-cylinder pressure sensor 8 Crank angle sensor 10 Intake pipe 12 Temperature sensor 20 Exhaust pipe 22 DOC
24 Temperature sensor 26 Air-fuel ratio sensor 30 ECU

Claims (6)

A first in-cylinder pressure that is the in-cylinder pressure at the bottom dead center of the compression stroke, and a second in-cylinder pressure that is the in-cylinder pressure at the top dead center of the compression stroke, while the engine of the internal combustion engine is rotating and without fuel injection; Means for obtaining
Means for obtaining the temperature of the intake air;
Estimating means for estimating the humidity of the in-cylinder gas flowing into the cylinder according to the first in-cylinder pressure, the second in-cylinder pressure, the compression ratio of the internal combustion engine, and the temperature of the intake air;
A control device for an internal combustion engine, comprising: The estimation means includes
In accordance with the first in-cylinder pressure, the second in-cylinder pressure, and the compression ratio, a specific heat ratio of the in-cylinder gas is calculated,
The control device for an internal combustion engine according to claim 1, wherein the humidity of the in-cylinder gas is calculated according to the specific heat ratio and the temperature of the intake air. During engine rotation of the internal combustion engine and no fuel injection, the first in-cylinder pressure that is the in-cylinder pressure at the first time point of the compression stroke and the in-cylinder pressure at the second time point that is different from the first time point of the compression stroke. Means for obtaining two in-cylinder pressures;
Means for obtaining the temperature of the intake air;
The humidity of the cylinder gas flowing into the cylinder according to the first cylinder pressure, the second cylinder pressure, the cylinder volume at the first time point, the cylinder volume at the second time point, and the temperature of the intake air Estimating means for estimating
A control device for an internal combustion engine, comprising: The estimation means includes
According to the first cylinder pressure, the second cylinder pressure, the cylinder volume at the first time point, and the cylinder volume at the second time point, a specific heat ratio of the cylinder gas is calculated,
The control device for an internal combustion engine according to claim 3, wherein the humidity of the in-cylinder gas is calculated according to the specific heat ratio and the temperature of the intake air.   The first in-cylinder pressure and the second in-cylinder pressure are such that the amount of change in intake air temperature per hour is smaller than a predetermined value, the amount of change in exhaust gas temperature per hour is smaller than a predetermined value, and exhaust gas 5. The internal combustion engine according to claim 1, wherein the internal combustion engine is acquired in a state in which at least one condition is satisfied among a group of conditions including a temperature lower than a predetermined value. Control device. The internal combustion engine includes an EGR device that recirculates a part of the exhaust gas to the intake passage as EGR gas,
6. The internal combustion engine according to claim 1, wherein the first in-cylinder pressure and the second in-cylinder pressure are acquired in a state in which the recirculation of EGR gas is stopped. Control device.

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