JP5853709B2 - Air-fuel ratio detection device and air-fuel ratio imbalance detection device for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio detection device and an air-fuel ratio imbalance detection device for an internal combustion engine.

  Conventionally, various techniques for accurately detecting the air-fuel ratio of an internal combustion engine are known. The detected air-fuel ratio value is conventionally used for air-fuel ratio control processing such as air-fuel ratio feedback control. Particularly in recent years, variations in the air-fuel ratio among cylinders of a multiple cylinder internal combustion engine are detected to optimize the fuel injection amount of each cylinder and ensure good emission characteristics as a whole. The variation in air-fuel ratio between cylinders is also referred to as “inter-cylinder air-fuel ratio imbalance”. When the variation in the air-fuel ratio between the cylinders exceeds a predetermined range, problems such as emission deterioration and drivability deterioration occur. In order to prevent such a problem, research and development of a technique for detecting an air-fuel ratio imbalance among cylinders has been advanced.

  For example, Japanese Patent Laid-Open No. 2010-112244 states that “when the average value of sub-air-fuel ratio FB control based on the detection result of the O2 sensor greatly exceeds the normal value, there is an imbalance in the air-fuel ratio between cylinders. The inter-cylinder air-fuel ratio imbalance detection technique “determines that it has occurred” is described. Further, in JP 2009-209747 A, a cylinder in which “imbalance ratio” is detected, and the larger the imbalance ratio, the greater the fuel injection amount deviation from the balance cylinder of the imbalance cylinder and the greater the air-fuel ratio variation. An inter-air-fuel ratio imbalance detection technique is described. In this publication, the imbalance ratio is detected based on the trajectory length or trajectory area per predetermined time of the air-fuel ratio sensor output.

JP 2010-112244 A JP 2009-209747 A JP 2010-144573 A

  An air-fuel ratio information acquisition technique typically used in conventional air-fuel ratio control is sensing of exhaust gas by an exhaust gas sensor (oxygen concentration sensor). In particular, the air-fuel ratio sensor can change the output value almost linearly according to the oxygen concentration of the exhaust gas, and is widely used. In this regard, all of the above conventional techniques detect the air-fuel ratio imbalance between cylinders based on information obtained from the output value of the exhaust gas sensor.

  However, for the original purpose of the inter-cylinder air-fuel ratio imbalance, it is preferable that the air-fuel ratio information of each cylinder can be detected individually and accurately. From this point of view, the air-fuel ratio detection technology that relies on the exhaust gas sensor is a limitation. There is. That is, the air-fuel ratio sensor is usually disposed at a position where the exhaust gases of a plurality of cylinders merge (specifically, before the exhaust catalyst in the exhaust pipe). Then, the air-fuel ratio sensor senses the exhaust gas averaged by the burned gas of each cylinder joining. Therefore, unavoidably, the air-fuel ratio sensor detects average air-fuel ratio information of all cylinders. Even if such averaged air-fuel ratio information can be detected, it is difficult to detect an accurate air-fuel ratio for each cylinder.

The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide an air-fuel ratio detection apparatus for an internal combustion engine that can accurately detect air-fuel ratio information for each cylinder.
Another object of the present invention is to provide an air-fuel ratio imbalance detection device for an internal combustion engine that can accurately detect an air-fuel ratio imbalance between cylinders using air-fuel ratio information acquired for each cylinder. And

In order to achieve the above object, a first invention is an air-fuel ratio detection apparatus for an internal combustion engine,
Combustion speed calculating means for calculating the combustion speed of the cylinder of the internal combustion engine;
An injection amount changing means for changing the fuel injection amount for the fuel injection valve of the cylinder so that the combustion speed calculated by the combustion speed calculating means reaches a peak value;
Information on the air-fuel ratio of the cylinder based on the change amount of the fuel injection amount changed by the injection amount change means between the start of change of the fuel injection amount by the injection amount change means and the arrival of the peak value of the combustion speed Air-fuel ratio information calculating means for calculating
Equipped with a,
The air-fuel ratio information calculating means includes
Air-fuel ratio deviation calculating means for calculating an air-fuel ratio deviation of the cylinder with respect to a predetermined reference air-fuel ratio based on the change amount;
An air-fuel ratio calculating means for obtaining an air-fuel ratio value at the start of change of the fuel injection amount for the cylinder by calculation using a predetermined reference air-fuel ratio value and the change amount;
It is characterized by including at least one .

According to a second invention, in the first invention,
The injection amount changing means is
Determining means for determining in which direction the combustion speed of the cylinder changes in accordance with a change in the fuel injection amount of the cylinder;
When the determination means determines that the combustion speed increases according to the increase in the fuel injection amount, the determination means increases the fuel injection amount, so that the determination means decreases the combustion speed according to the increase in the fuel injection amount. A changing means for changing the fuel injection amount until the combustion speed reaches a peak value by reducing the fuel injection amount when determined;
It is characterized by providing.

According to a third invention, in the first or second invention,
An in-cylinder pressure sensor is attached to the cylinder of the internal combustion engine,
The combustion speed calculation means includes
Output acquisition means for acquiring output from the in-cylinder pressure sensor;
Combustion rate calculation means for calculating a combustion rate for the cylinder based on the output of the in-cylinder pressure sensor acquired by the output acquisition means;
Maximum value calculating means for calculating the maximum value of the change rate of the combustion ratio calculated by the combustion ratio calculating means as a value of the combustion speed;
It is characterized by including.

In order to achieve the above object, a fourth invention is an air-fuel ratio imbalance detection device for an internal combustion engine,
Combustion speed calculation means for calculating the combustion speed of each cylinder of an internal combustion engine having a plurality of cylinders;
For each of the fuel injection valves of each cylinder, an injection amount changing means for changing the fuel injection amount so that the combustion speed calculated by the combustion speed calculating means for each cylinder reaches a peak value;
Based on the change amount of the fuel injection amount of each cylinder changed by the injection amount change means between the start of change of the fuel injection amount by the injection amount change means and the peak value of the combustion speed. Imbalance detection means for detecting an air-fuel ratio imbalance among the plurality of cylinders;
It is characterized by providing.

A fifth invention is the fourth invention,
The injection amount changing means is
Determining means for determining in which direction the combustion speed of the cylinder changes in accordance with a change in the fuel injection amount of the cylinder;
When the determination means determines that the combustion speed increases according to the increase in the fuel injection amount, the determination means increases the fuel injection amount, so that the determination means decreases the combustion speed according to the increase in the fuel injection amount. A changing means for changing the fuel injection amount until the combustion speed reaches a peak value by reducing the fuel injection amount when determined;
It is characterized by providing.

A sixth invention is the fourth or fifth invention, wherein
An in-cylinder pressure sensor is attached to each cylinder of the internal combustion engine,
The combustion rate calculating means comprises:
Output acquisition means for acquiring output from the in-cylinder pressure sensor;
Combustion rate calculation means for calculating a combustion rate for the cylinder based on the output of the in-cylinder pressure sensor acquired by the output acquisition means;
Maximum value calculating means for calculating the maximum value of the change rate of the combustion ratio calculated by the combustion ratio calculating means as a value of the combustion speed;
It is characterized by including.

In a seventh aspect based on any one of the fourth to sixth aspects,
The imbalance detection means
An air-fuel ratio calculating means for obtaining an air-fuel ratio value at the start of change of the fuel injection amount for each of the cylinders by calculation using a predetermined reference air-fuel ratio value and the amount of change;
Means for detecting an air-fuel ratio imbalance among the plurality of cylinders based on a comparison of the air-fuel ratio values of the cylinders obtained by the air-fuel ratio calculating means;
It is characterized by including.

As a result of diligent research, the inventor of the present application has found that there is a tendency that “the air-fuel ratio at which the peak combustion speed is taken becomes a constant value” between the combustion speed and the air-fuel ratio.
According to the first aspect of the present invention, the air-fuel ratio information for each cylinder can be accurately detected by utilizing such a relationship between the combustion speed and the air-fuel ratio. Furthermore, according to the first aspect, the air-fuel ratio information can be obtained quantitatively as the air-fuel ratio information, such as the magnitude of the air-fuel ratio deviation and the start of change of the fuel injection amount.

The inventor of the present application has found that the combustion speed tends to take a peak at a constant air-fuel ratio, and the combustion speed tends to decrease no matter which side is away from the peak to the rich lean side.
According to the second invention, the change direction (increase and decrease) of the fuel injection amount can be determined in consideration of this tendency, so that the combustion speed can surely reach the peak value.

  According to the third invention, the individual and accurate combustion state of the cylinder can be detected from the output of the in-cylinder pressure sensor attached to the cylinder. By using the output of the in-cylinder pressure sensor, the individual and accurate combustion speed of the cylinder can be calculated.

As a result of diligent research, the inventor of the present application has found that there is a tendency that “the air-fuel ratio at which the peak combustion speed is taken becomes a constant value” between the combustion speed and the air-fuel ratio.
According to the fourth aspect of the present invention, the inter-cylinder air-fuel ratio imbalance can be detected with high accuracy using the information on the air-fuel ratio acquired for each cylinder using the relationship between the combustion speed and the air-fuel ratio.

The inventor of the present application has found that the combustion speed tends to take a peak at a constant air-fuel ratio, and the combustion speed tends to decrease no matter which side is away from the peak to the rich lean side.
According to the fifth aspect of the invention, the change direction (increase and decrease) of the fuel injection amount can be determined taking this tendency into consideration, so that the combustion speed can surely reach the peak value.

According to the sixth aspect , the individual and accurate combustion state of the cylinder can be detected from the output of the in-cylinder pressure sensor attached to the cylinder. By using the output of the in-cylinder pressure sensor, the individual and accurate combustion speed of the cylinder can be calculated, and the combustion speed can be used for detecting the air-fuel ratio imbalance between cylinders.

According to the seventh aspect , as the air-fuel ratio information, the magnitude of the air-fuel ratio deviation and the air-fuel ratio at the start of changing the fuel injection amount can be obtained quantitatively. The quantitative information can be used to detect the air-fuel ratio imbalance among cylinders.

1 is a diagram showing a schematic configuration of an air-fuel ratio detection device and an air-fuel ratio imbalance detection device for an internal combustion engine according to a first embodiment of the present invention, together with a schematic configuration of an internal combustion engine system to which the same is applied. It is a figure for demonstrating operation | movement of the air fuel ratio detection apparatus of the internal combustion engine which concerns on Embodiment 1 of this invention, and the air fuel ratio imbalance detection apparatus of an internal combustion engine. It is a figure for demonstrating operation | movement of the air fuel ratio detection apparatus of the internal combustion engine which concerns on Embodiment 1 of this invention, and the air fuel ratio imbalance detection apparatus of an internal combustion engine. It is a figure for demonstrating operation | movement of the air fuel ratio detection apparatus of the internal combustion engine which concerns on Embodiment 1 of this invention, and the air fuel ratio imbalance detection apparatus of an internal combustion engine. 3 is a flowchart of a routine executed by an ECU 50 in the air-fuel ratio detection device for an internal combustion engine and the air-fuel ratio imbalance detection device for the internal combustion engine according to the first embodiment of the present invention. It is a figure for demonstrating operation | movement of the air fuel ratio detection apparatus of the internal combustion engine which concerns on Embodiment 2 of this invention, and the air fuel ratio imbalance detection apparatus of an internal combustion engine. 7 is a flowchart of a routine executed by an ECU 50 in an air-fuel ratio detection device for an internal combustion engine and an air-fuel ratio imbalance detection device for an internal combustion engine according to a second embodiment of the present invention.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram showing a schematic configuration of an air-fuel ratio detection device and an air-fuel ratio imbalance detection device for an internal combustion engine according to a first embodiment of the present invention, together with a schematic configuration of an internal combustion engine system to which this is applied. The air-fuel ratio detection apparatus according to the first embodiment can detect the magnitude of the air-fuel ratio deviation from a predetermined reference air-fuel ratio for each cylinder of the engine 10 shown in FIG. The “air-fuel ratio value” of each cylinder can be calculated from the “size of deviation”. The air-fuel ratio imbalance detection apparatus according to the first embodiment detects the inter-cylinder air-fuel ratio imbalance by comparing the “size of air-fuel ratio deviation” and “air-fuel ratio value” among a plurality of cylinders. It can be performed.

  The system shown in FIG. 1 includes an internal combustion engine (hereinafter simply referred to as an engine) 10. An engine 10 shown in FIG. 1 is a spark ignition type four-stroke engine provided with a spark plug 12. The engine 10 is also an in-cylinder direct injection engine including a direct injection injector 14 that directly injects fuel into a cylinder. The air-fuel ratio imbalance detection apparatus for an internal combustion engine according to the first embodiment is realized as one function of an ECU (Electronic Control Unit) that comprehensively controls the operation of the engine 10.

  Although only one cylinder is illustrated in FIG. 1, the engine 10 according to the first embodiment is an in-line four-cylinder gasoline engine having four cylinders (# 1 to # 4 cylinders). The engine for vehicles is generally composed of a plurality of cylinders, and the engine 10 has a plurality of cylinders in the same manner. A common delivery pipe (not shown) is connected to the direct injection injector 14 of each cylinder. A fuel tank (not shown) is connected to the delivery pipe.

  Each cylinder is provided with a cylinder pressure sensor (CPS: Combustion Pressure Sensor) 16 for detecting the cylinder pressure (combustion pressure). According to the configuration in which the in-cylinder pressure sensor 16 is attached to each cylinder, the combustion pressure of each cylinder can be detected individually and accurately. Further, the engine 10 is provided with a crank angle sensor 18 that outputs a signal CA according to the crank angle θ.

  An intake passage 20 connected to each cylinder is provided in the intake system of the engine 10. An air cleaner 22 is provided at the inlet of the intake passage 20. An air flow meter 24 that outputs a signal GA corresponding to the flow rate of air sucked into the intake passage 20 is attached downstream of the air cleaner 22. An electronically controlled throttle valve 26 is provided downstream of the air flow meter 24. In the vicinity of the throttle valve 26, a throttle opening sensor 27 for outputting a signal TA corresponding to the opening of the throttle valve 26 is attached. A surge tank 28 is provided downstream of the throttle valve 26. An intake pressure sensor 30 for measuring intake pressure is attached in the vicinity of the surge tank 28.

  An exhaust passage 32 connected to each cylinder is provided in the exhaust system of the engine 10. Specifically, the exhaust passage 32 includes an exhaust manifold where the exhaust ports of the # 1 to # 4 cylinders merge and an exhaust pipe connected to the exhaust manifold. Catalysts 34 and 36 are provided in the exhaust passage 32. In addition, as a catalyst, a three-way catalyst, a NOx catalyst, etc. are used according to a specific system, for example. A catalyst upstream exhaust sensor 33 and a catalyst downstream exhaust sensor 35 are provided in the exhaust passage 32. The catalyst upstream exhaust sensor 33 is a so-called air-fuel ratio sensor (A / F sensor) capable of linearly detecting the oxygen concentration. As the catalyst upstream exhaust sensor 33, various types of air-fuel ratio sensors such as a limit current air-fuel ratio sensor can be used. Further, a system that performs sub-feedback A / F control using a so-called sub oxygen sensor is known, and in this embodiment, the catalyst downstream exhaust sensor 35 is used as a sub oxygen sensor in the same manner. However, the system configuration of the exhaust system to which the present invention is applied is not limited to the configuration according to the above embodiment, but a system having only one catalyst in the exhaust passage, a system having only one exhaust gas sensor, or the like. It may be.

  An ECU (Electronic Control Unit) 50 is provided in the control system of the engine 10. Various sensors such as the in-cylinder pressure sensor 16, the crank angle sensor 18, the air flow meter 24, the throttle opening sensor 27, and the intake pressure sensor 30 are connected to the input unit of the ECU 50. In addition, various actuators such as the ignition plug 12, the direct injection injector 14, and the throttle valve 26 described above are connected to the output portion of the ECU 50. The ECU 50 controls the operating state of the engine 10 based on various input information. Further, the ECU 50 can calculate the in-cylinder volume V determined by the engine rotational speed (the rotational speed per unit time) and the piston position from the signal CA of the crank angle sensor 18. The ECU 50 calculates an appropriate fuel injection amount that satisfies the target A / F according to the operating state based on the engine speed, load, intake air amount, and the like, and causes the direct injection injector 14 to inject the fuel injection amount.

[Operation of Embodiment 1]
FIGS. 2 to 4 are diagrams for explaining the operation of the air-fuel ratio detection apparatus for an internal combustion engine and the air-fuel ratio imbalance detection apparatus for an internal combustion engine according to the first embodiment of the present invention.
FIG. 2 is a diagram showing the relationship between the combustion speed and the air-fuel ratio found by the inventors of the present application. In the following description, the combustion rate may be simply expressed as “CS”. Further, the “peak value of the combustion speed” is also referred to as “peak combustion speed” for convenience. According to the knowledge of the inventor of the present application, as shown in FIG. 2, there is a tendency that “the air-fuel ratio at which the peak combustion speed is taken becomes a constant value”. Specifically, when the value of the air-fuel ratio is 12 A certain relationship is established that the combustion speed indicates the peak value CS _Peak . Further, it can be seen from the figure that the combustion speed tends to decrease even when the air-fuel ratio value is made leaner or richer than 12. This embodiment uses such a physical phenomenon shown in FIG.

(Burn rate calculation processing)
Hereinafter, the contents of the calculation process for calculating the combustion speed CS according to the first embodiment will be described. FIG. 3 is a diagram for explaining the definition of the combustion speed in the first embodiment of the present invention. In the present embodiment, the maximum value of the tangent slope of the combustion mass ratio MFB (Mass Fraction Burned) is defined as the combustion speed. FIG. 3 shows the MFB tangent line A. When the angle of the MFB tangent line with respect to the X axis (crank angle CA) is the largest, that is, the maximum rate of change (dMFB / dθ) of the combustion mass ratio per unit crank angle. Is the combustion rate.

Specifically, in this embodiment, the combustion speed is calculated using the change rate of the combustion ratio MFB (Mass Fraction Burned) of each cylinder. FIG. 3 is a characteristic diagram showing the relationship between the amount of heat generated in the cylinder and the crank angle. This figure illustrates the case where the reference point before the start of combustion is set to BTD 60 ° CA and the reference point after the end of combustion is set to ATDC 60 ° CA. The combustion mass ratio MFB is calculated by normalizing the calorific value at an arbitrary crank angle based on the calorific value before the start of combustion and the calorific value after the end of combustion. The amount of heat generated in the cylinder is proportional to PV ^κ calculated based on the cylinder pressure P, the cylinder volume V, and the specific heat ratio κ. Therefore, the mass fraction burned MFB _theta at any crank angle theta, based on this and PV ^kappa _theta at a crank angle, and PV ^kappa _{-60 °} prior to the start of combustion, and ^PV κ _{+ 60 °} after the end burning, It is expressed as the following formula (1).

^{_{MFB θ = (PV κ θ -PV}} κ -60 °) / (PV κ + 60 ° -PV κ -60 °) ··· (1)

The ECU 50 calculates the above formula (1) based on the in-cylinder pressure P detected by the in-cylinder pressure sensor 16 of each cylinder, the in-cylinder volume V of the cylinder calculated according to the crank angle, and the specific heat ratio κ stored in advance. Can calculate the combustion mass ratio MFB _θ . Next, a change rate (dMFB / dθ) per unit crank angle of the combustion mass ratio is obtained. Then, the change rate (gradient) per unit crank angle of the combustion ratio becomes maximum at a crank angle of about 50 ° CA, for example. In the following description, the maximum value of the change rate (that is, the maximum change rate) is defined as the combustion speed. The ECU 50 can calculate the combustion speed CS for each cylinder based on the combustion mass ratio MFB of each cylinder.

  The RAM of the ECU 50 includes a calculation process for calculating the combustion mass ratio MFB according to the above equation (1), a calculation process for calculating the rate of change per unit crank angle (dMFB / dθ) of the combustion mass ratio MFB, A program for executing a process of calculating the maximum value of dMFB / dθ as the combustion speed CS of the current combustion stroke is stored. The ECU 50 can calculate the combustion speed CS by executing this program. The output of the in-cylinder pressure sensor 16 is sampled every predetermined period (predetermined crank angle), and measurement data based on this sampling value can be used as an input value for the calculation program.

(Fuel injection amount change processing)
FIG. 4 is a diagram for explaining the operation by the fuel injection amount changing process in the first embodiment of the present invention. The ECU 50 includes a fuel injection amount changing process. The fuel injection amount changing process is a process for changing the fuel injection amount so that the combustion speed CS reaches the peak value CS _peak for each cylinder based on the combustion speed CS.

In the fuel injection amount changing process, first, the ECU 50 obtains the combustion pressure of the cylinder from the in-cylinder pressure sensor 16 of the cylinder whose air-fuel ratio is desired to be detected, and further sets the combustion speed CS according to the explanation of the “burning speed calculation process” above. Execute the calculation process. Next, the ECU 50 executes a process of increasing the direct injection injector 14 by a minute amount over a plurality of cycles until the combustion speed CS reaches the peak value CS _Peak . The minute increment can be performed by multiplying the fuel injection amount at the start of the fuel injection amount changing process while gradually increasing the correction coefficient ekcyl. As a result, as schematically shown in FIG. 4, the fuel injection amount of the direct injection injector 14 can be increased to enrich the air-fuel ratio.

FIG. 4 schematically shows an increase in the correction coefficient ekcyl (that is, an increase in the fuel injection amount and an enrichment in the air-fuel ratio) with a black circle on the combustion speed curve. For example, the correction coefficient ekcyl is increased from 1.05 → 1.1 → 1.15 → 1.2, and when the correction coefficient ekcyl is 1.25, the combustion speed CS has changed from the previous increase to the decrease. To do. In this case, the ECU 50 stores the value of the correction coefficient ekcyl = 1.2 as the change amount ekcylb. The change amount ekcylb is a value representing an increase amount of the fuel injection amount from “start of change of fuel injection amount in the fuel injection amount change process” to “reaching the peak value CS _Peak of the combustion speed CS”. Here, it means that the fuel injection amount is increased by 1.2 times the fuel injection amount before the start of the fuel injection amount changing process until the combustion speed CS reaches the peak value CS _Peak .

Note that the increase width of the correction coefficient ekcyl is not limited to the above-mentioned 0.5 increments, and may be smaller or larger. If the increment is small, the correction coefficient ekcyl when the peak value CS _{Peak is} reached can be accurately specified. On the other hand, if the increment is large, the combustion required to reach the peak value CS _Peak is increased accordingly. The number of cycles can be reduced. Since the fuel injection amount changing process is completed with a certain number of finite combustion cycles during the operation of the engine 10, the intake air amount is treated as being substantially constant during the fuel injection amount changing process. be able to. However, it is more preferable that the fuel injection amount changing process is performed in a steady operation region where the load and the engine speed are stable.

(Air-fuel ratio deviation calculation process and air-fuel ratio calculation process)
The ECU 50 includes an air-fuel ratio deviation calculation process for calculating the magnitude of the air-fuel ratio deviation from a predetermined reference air-fuel ratio (A / F = 12) based on the change amount of the fuel injection amount for each cylinder. This point will be described below. First, as described with reference to FIG. 2, the inventor of the present application, as a result of diligent research, found that the air-fuel ratio at which the peak combustion speed is taken is constant between the combustion speed and the air-fuel ratio. It was found that there is a tendency to “become the value of”. According to the fuel injection amount changing process described above, the combustion speed CS of the cylinder can reach the peak value CS _Peak by changing the fuel injection amount of an arbitrary cylinder. In the course of the process, ekcylb indicating the amount of change in the fuel injection amount required to reach the peak value CS _Peak is calculated. It can be determined that the larger the ekcylb is, the larger the air-fuel ratio deviation between “the air-fuel ratio at the start of the fuel injection amount changing process” and “the air-fuel ratio at which the peak value CS _Peak is taken”.

It is known from the knowledge of the present inventor that “the air-fuel ratio at which the peak value CS _Peak is taken” takes a constant value of A / F = 12. Therefore, by setting A / F = 12 as the reference air-fuel ratio, the magnitude of the air-fuel ratio deviation with respect to the reference air-fuel ratio can be detected based on ekcylb. For example, when ekcylb in the first cylinder is “ekcylb1” and ekcylb in the second cylinder is “ekcylb2”, ekcylb1 is 1.2 and ekcylb2 is 1.25. In this case, since ekcylb1 <ekcylb2 is satisfied, the “change amount of the fuel injection amount required to reach the peak value CS _Peak ” of the second cylinder is larger than that of the first cylinder. That is, it can be concluded that the in-cylinder air-fuel ratio of the second cylinder has a larger deviation from the reference air-fuel ratio (A / F = 12) than the in-cylinder air-fuel ratio of the first cylinder. In addition, if the difference between ekcylb1 and ekcylb2 is taken, the magnitude of the air-fuel ratio deviation between the in-cylinder air-fuel ratio of the first cylinder and the in-cylinder air-fuel ratio of the second cylinder can be detected, It is also possible to specify small and large relationships.

Further, a specific numerical value of the air-fuel ratio may be obtained according to the following equation (2).
Initial A / F = 12 ÷ (1 / ekcylb) (2)
However, “initial A / F” is the air-fuel ratio before the start of the fuel injection amount changing process. For example, if ekcylb = 1.2 is substituted, the initial A / F is 14.4.

In order to detect the air-fuel ratio deviation and the air-fuel ratio value, the fuel injection amount of the direct injection injector 14 is changed for each cylinder to be detected by the fuel injection amount changing process described above. Good. Since the change amount ekcylb of the fuel injection amount can be specified for each cylinder, the air-fuel ratio deviation of the specific cylinder or the value of the air-fuel ratio can be detected individually and accurately while avoiding the influence of other cylinders. In the present embodiment, information on the air-fuel ratio is collectively referred to as “air-fuel ratio information”, and this air-fuel ratio information includes at least the following information.
(I) The magnitude of the air-fuel ratio deviation from the reference air-fuel ratio and the magnitude of the difference between the target air-fuel ratio and the in-cylinder air-fuel ratio calculated therefrom (ii) The value of the air-fuel ratio (iii) The air between the cylinders (Iv) Relation between the relative magnitudes of air-fuel ratios between cylinders

(Imbalance detection process)
ECU 50 detects an air-fuel ratio imbalance among a plurality of cylinders (four cylinders in the present embodiment) based on the magnitude of the air-fuel ratio deviation of each cylinder or the value of the air-fuel ratio of each cylinder. It has. The ECU 50 acquires the change amounts ekcylb of the first to fourth cylinders one by one in the above-described air-fuel ratio deviation detection process, and compares the magnitudes of the four ekcylbs. From the comparison result of the four ekcylbs, it is possible to detect how far the in-cylinder air-fuel ratios of the first to fourth cylinders differ from the reference air-fuel ratio (A / F = 12). Alternatively, the ECU 50 may compare the in-cylinder air-fuel ratio values of the first to fourth cylinders according to the above equation (2) and then compare them. For example, among the plurality of ekcylbs compared, it is determined that an abnormality occurs when the difference between the smallest ekcylb (ekcylbmin) and the largest ekcylb (ekcylbmax) exceeds an allowable range, or the average deviation of the plurality of ekcylbs is less than a predetermined value Various determinations such as whether or not may be performed.

  As described above, according to the first embodiment, the air-fuel ratio information for each cylinder can be accurately detected using the relationship between the combustion speed and the air-fuel ratio, and the air-fuel ratio information acquired for each cylinder is used. It is possible to detect the air-fuel ratio imbalance between cylinders with high accuracy.

  When the operating conditions such as the load and the engine speed change, the characteristic curve of the combustion speed also changes, and the shape of the combustion speed curve in FIG. 2 changes. However, in the first embodiment, it is only necessary to be able to specify the amount of increase in fuel injection amount (change amount ekcylb) until the combustion speed CS reaches the peak value. There is an advantage that it is not necessary.

[Specific Processing in First Embodiment]
FIG. 5 is a flowchart of a routine executed by the ECU 50 in the air-fuel ratio detection device for an internal combustion engine and the air-fuel ratio imbalance detection device for the internal combustion engine according to the first embodiment of the present invention. The routine of FIG. 5 is executed during operation of the engine 10, more specifically, during travel of a vehicle on which the engine 10 is mounted (preferably in a steady operation region).

  In the routine of FIG. 5, first, the ECU 50 starts a combustion speed calculation process (step S100). By executing this step, the combustion speed calculation process in this routine is started. In the flowchart of FIG. 5, after step S100, the ECU 50 repeatedly executes the above-described combustion speed calculation process independently for each of the first to fourth cylinders.

  Next, the ECU 50 executes the fuel injection amount changing process described above (step S102). In this step, a process of increasing the injection amount little by little for each cylinder to make it rich is executed. In the present embodiment, first, the fuel injection amount changing process is executed for the direct injection injector 14 of the first cylinder. In this step, the correction coefficient ekcyl is increased in predetermined increments from 1.05 → 1.1 → 1.15 → 1.2. Thereafter, the value of the correction coefficient ekcyl when the combustion speed CS changes from increasing to decreasing is stored as the change amount ekcylb.

  Next, the ECU 50 executes an air-fuel ratio deviation calculation process and an air-fuel ratio calculation process (step S104). In this embodiment, ekcylb itself is used as a value representing the magnitude of the air-fuel ratio deviation in the air-fuel ratio deviation calculation process. In the air-fuel ratio calculation process, ekcylb is substituted into Equation (2) to obtain a specific numerical value of the initial A / F.

  The ECU 50 similarly performs the processes of steps S102 and S104 on the remaining cylinders (second, third and fourth cylinders) (step S106). In the flowchart of FIG. 5, for convenience of explanation, description of “change of target cylinder” is omitted, but in the specific processing of the first embodiment, the ECU 50 performs the operation of the first embodiment described above. In step S102 and step S104, the processing of step S102 is performed for each cylinder. That is, the ECU 50 executes steps S102 and S104 in FIG. 5 for each of the # 1 to # 4 cylinders while changing the “target cylinder” one by one in a predetermined order. However, the present invention is not limited to this. For example, a plurality of cylinders may be collectively designated as the target cylinder, and the processing may be performed in parallel for the plurality of target cylinders. It is assumed that the process proceeds to step S108 when the value of ekcylb is obtained for each of the necessary cylinders (all cylinders # 1 to # 4 in the first embodiment).

  Finally, the ECU 50 compares the air-fuel ratio values obtained for each cylinder in step S106 described above, and performs an inter-cylinder air-fuel ratio imbalance determination process (step S108). It is assumed that the ECU 50 stores a process for determining an evaluation of variations in a plurality of A / F values (for example, whether the variations are within a predetermined range). This determination process may be created in advance according to a determination criterion for the presence or absence of the occurrence of an inter-cylinder air-fuel ratio imbalance. Thereafter, the current routine ends.

Embodiment 2. FIG.
The air-fuel ratio detection apparatus and the air-fuel ratio imbalance detection apparatus for an internal combustion engine according to the second embodiment have the same hardware configuration as those according to the first embodiment. In the following description, the contents of the “combustion speed change determination process” and the “change direction determination process” which are the differences from the first embodiment will be mainly described, and the same configuration and process as in the first embodiment. The description of the operation and the like is omitted.

FIG. 6 is a diagram for explaining the operation of the air-fuel ratio detection apparatus for an internal combustion engine and the air-fuel ratio imbalance detection apparatus for an internal combustion engine according to the second embodiment of the present invention. As shown in FIG. 2 and FIG. 4 in the first embodiment, “the combustion speed takes a peak at a constant air-fuel ratio, and the combustion speed decreases regardless of whether it is away from the peak to either the rich side or the lean side. The present inventor has found that there is a tendency to “do”. Taking this tendency into consideration, it is necessary to switch the change direction (increase and decrease) of the fuel injection amount in the fuel injection amount change process between the region (a) and the region (b) as shown in FIG. . If there is a cylinder in which a rich imbalance occurs such that the in-cylinder air-fuel ratio is A / F = 12 or less (for example, A / F = 11), that cylinder is described in the first embodiment. Thus, even if enrichment is performed by increasing the fuel injection amount, the combustion speed CS cannot reach the peak value CS _Peak . This is because in the region (A), the richer the combustion rate CS, the farther away from the peak value CS _Peak .

  Therefore, in the second embodiment, “burning speed change determination processing” and “change direction determination processing” are added to the first embodiment to avoid the above-described adverse effects. The combustion speed change determination process is a process for determining in which direction the combustion speed CS of the cylinder changes in accordance with a change in fuel injection amount (slight increase in the first embodiment). In the change direction determination process, when it is determined that the combustion speed CS increases in accordance with the increase in the fuel injection amount, the change direction of the fuel injection amount is set to “increase”, and the combustion speed CS in accordance with the increase in the fuel injection amount. Is a process for setting the direction of change of the fuel injection amount to “reduction”. Thereby, the change direction (increase and decrease) of the fuel injection amount can be appropriately determined in consideration of the tendency of the combustion speed shown in FIG. 6 (existence of the region (A) and the region (B)). As a result, the combustion speed can surely reach the peak value.

  FIG. 7 is a flowchart of a routine executed by the ECU 50 in the air-fuel ratio detection device for an internal combustion engine and the air-fuel ratio imbalance detection device for an internal combustion engine according to the second embodiment of the present invention.

  In the routine of FIG. 7, first, as in the first embodiment, the ECU 50 starts the combustion speed calculation process (step S100).

Next, the ECU 50 executes a process for slightly increasing the fuel injection amount for the target cylinder (here, the first cylinder). The width of the slight increase may be determined in advance, but may be multiplied by the correction coefficient ekcyl = 1.05, for example, so as to coincide with the minimum increment in the fuel injection amount changing process of the first embodiment.
Next, the ECU 50 executes a process for determining whether or not the value of the combustion speed calculated after step S202 is higher than the combustion speed before execution of step S202 (step S204). If the determination result in step S204 is YES, it can be determined that the in-cylinder air-fuel ratio currently belongs to the region (a) in FIG. On the other hand, if the determination result in step S204 is NO, it can be determined that the in-cylinder air-fuel ratio currently belongs to the region (A) in FIG.

  If the decision result in the step S204 is YES, the process advances to a step S206, and the in-cylinder air-fuel ratio is increased by gradually increasing the fuel injection amount as in the step S102 of the specific process in the first embodiment. To enrich. On the other hand, if the decision result in the step S204 is NO, the process advances to a step S208, and in contrast to the step S102 of the specific process in the first embodiment, the fuel injection amount is gradually decreased to reduce the in-cylinder Reduce the air-fuel ratio. As a result, in any step processing, the combustion rate CS is increased and the peak combustion rate is reached. In both step S206 and step S208, the value of the correction coefficient ekcyl when the change in the combustion speed CS changes between increase and decrease is stored as the change amount ekcylb.

  Thereafter, the processes of steps S104, S106, and S108 are executed in the same manner as in the first embodiment, and the current routine ends.

  In the first embodiment, the present invention is applied to the engine 10 that is an in-line four-cylinder gasoline engine provided with a direct injection injector 14 in each cylinder. However, the specific structure of the engine to which the present invention is applicable is not limited to the structure described in the first embodiment. The number of cylinders of the engine 10 and the cylinder arrangement method are not particularly limited, and the in-cylinder pressure sensor 16 and the direct injection injector 14 may be attached to each cylinder. In the first embodiment, the system for directly injecting gasoline into the combustion chamber from the fuel injection valve has been described. However, a system for injecting gasoline into the intake port of the intake passage may be used. Further, a system capable of port injection and in-cylinder injection may be used.

10 Engine 12 Spark plug 14 Direct injection injector 16 In-cylinder pressure sensor 18 Crank angle sensor 20 Intake passage 22 Air cleaner 24 Air flow meter 26 Throttle valve 27 Throttle opening sensor 28 Surge tank 30 Intake pressure sensor 32 Exhaust passage 33 Catalyst upstream exhaust sensor 34 36 catalyst 35 catalyst downstream exhaust sensor

Claims (7)

Combustion speed calculating means for calculating the combustion speed of the cylinder of the internal combustion engine;
An injection amount changing means for changing the fuel injection amount for the fuel injection valve of the cylinder so that the combustion speed calculated by the combustion speed calculating means reaches a peak value;
Information on the air-fuel ratio of the cylinder based on the change amount of the fuel injection amount changed by the injection amount change means between the start of change of the fuel injection amount by the injection amount change means and the arrival of the peak value of the combustion speed Air-fuel ratio information calculating means for calculating
Equipped with a,
The air-fuel ratio information calculating means includes
Air-fuel ratio deviation calculating means for calculating an air-fuel ratio deviation of the cylinder with respect to a predetermined reference air-fuel ratio based on the change amount;
An air-fuel ratio calculating means for obtaining an air-fuel ratio value at the start of change of the fuel injection amount for the cylinder by calculation using a predetermined reference air-fuel ratio value and the change amount;
An air-fuel ratio detection apparatus for an internal combustion engine, comprising at least one of the above . The injection amount changing means is
Determining means for determining in which direction the combustion speed of the cylinder changes in accordance with a change in the fuel injection amount of the cylinder;
When the determination means determines that the combustion speed increases according to the increase in the fuel injection amount, the determination means increases the fuel injection amount, so that the determination means decreases the combustion speed according to the increase in the fuel injection amount. A changing means for changing the fuel injection amount until the combustion speed reaches a peak value by reducing the fuel injection amount when determined;
The air-fuel ratio detection apparatus for an internal combustion engine according to claim 1, comprising: An in-cylinder pressure sensor is attached to the cylinder of the internal combustion engine,
The combustion speed calculation means includes
Output acquisition means for acquiring output from the in-cylinder pressure sensor;
Combustion rate calculation means for calculating a combustion rate for the cylinder based on the output of the in-cylinder pressure sensor acquired by the output acquisition means;
Maximum value calculating means for calculating the maximum value of the change rate of the combustion ratio calculated by the combustion ratio calculating means as a value of the combustion speed;
Air-fuel ratio detecting apparatus for an internal combustion engine according to claim 1 or 2, characterized in that it comprises a. A combustion speed calculation means for calculating a combustion speed of each cylinder of an internal combustion engine having multiple cylinders,
For each of the fuel injection valves of each cylinder, an injection amount changing means for changing the fuel injection amount so that the combustion speed calculated by the combustion speed calculating means for each cylinder reaches a peak value;
Based on the change amount of the fuel injection amount of each cylinder changed by the injection amount change means between the start of change of the fuel injection amount by the injection amount change means and the peak value of the combustion speed. Imbalance detection means for detecting an air-fuel ratio imbalance among the plurality of cylinders;
An air-fuel ratio imbalance detection device for an internal combustion engine, comprising: The injection amount changing means is
Determining means for determining in which direction the combustion speed of the cylinder changes in accordance with a change in the fuel injection amount of the cylinder;
When the determination means determines that the combustion speed increases according to the increase in the fuel injection amount, the determination means increases the fuel injection amount, so that the determination means decreases the combustion speed according to the increase in the fuel injection amount. A changing means for changing the fuel injection amount until the combustion speed reaches a peak value by reducing the fuel injection amount when determined;
The air-fuel ratio imbalance detection device for an internal combustion engine according to claim 4 , comprising: An in-cylinder pressure sensor is attached to each cylinder of the internal combustion engine,
The combustion rate calculating means comprises:
Output acquisition means for acquiring output from the in-cylinder pressure sensor;
Combustion rate calculation means for calculating a combustion rate for the cylinder based on the output of the in-cylinder pressure sensor acquired by the output acquisition means;
Maximum value calculating means for calculating the maximum value of the change rate of the combustion ratio calculated by the combustion ratio calculating means as a value of the combustion speed;
The air-fuel ratio imbalance detection apparatus for an internal combustion engine according to claim 4 or 5 , characterized by comprising: The imbalance detection means
An air-fuel ratio calculating means for obtaining an air-fuel ratio value at the start of change of the fuel injection amount for each of the cylinders by calculation using a predetermined reference air-fuel ratio value and the amount of change;
Means for detecting an air-fuel ratio imbalance among the plurality of cylinders based on a comparison of the air-fuel ratio values of the cylinders obtained by the air-fuel ratio calculating means;
The air-fuel ratio imbalance detection apparatus for an internal combustion engine according to any one of claims 4 to 6 , characterized by comprising:

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