JP2012202373A - Inter-cylinder air-fuel ratio variation abnormality detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a sense of incompatibility for a user with variation abnormality detection.SOLUTION: An inter-cylinder air-fuel ratio variation abnormality detection apparatus is provided for a multi-cylinder internal combustion engine having two injectors per cylinder. When the abnormality is detected, an injection ratio between both the injectors is changed from a first value of reference to a second value for detection, and the recovery of the injection ratio from the second value to the first value is performed simultaneously with the ON of an accelerator.

Description

  The present invention relates to an apparatus for detecting an abnormal variation in the air-fuel ratio between cylinders, and more particularly to an apparatus for detecting that the air-fuel ratio between cylinders is relatively large in a multi-cylinder internal combustion engine.

  In general, in an internal combustion engine equipped with an exhaust gas purification system using a catalyst, a mixture ratio of air and fuel in an air-fuel mixture burned in the internal combustion engine, that is, an air-fuel ratio, is used to efficiently remove harmful components in exhaust gas with a catalyst. Control is essential. In order to perform such air-fuel ratio control, an air-fuel ratio sensor is provided in the exhaust passage of the internal combustion engine, and feedback control is performed so that the air-fuel ratio detected thereby coincides with a predetermined target air-fuel ratio.

  On the other hand, in a multi-cylinder internal combustion engine, air-fuel ratio control is normally performed using the same control amount for all cylinders. Therefore, even if air-fuel ratio control is executed, the actual air-fuel ratio may vary between cylinders. If the degree of variation is small at this time, it can be absorbed by air-fuel ratio feedback control, and harmful components in the exhaust gas can be purified by the catalyst, so that exhaust emissions are not affected and there is no particular problem.

  However, for example, if the fuel injection system of some cylinders breaks down and the air-fuel ratio between the cylinders varies greatly, exhaust emission deteriorates, causing a problem. It is desirable to detect such a large air-fuel ratio variation that deteriorates the exhaust emission as an abnormality. In particular, in the case of an internal combustion engine for automobiles, in order to prevent the traveling of a vehicle whose exhaust emission has deteriorated, it is required to detect an abnormal variation in air-fuel ratio between cylinders in an on-board state. There is also a movement to regulate the law.

  For example, in the apparatus described in Patent Document 1, the fuel injection amount is changed from the injection amount at the time of stoichiometric operation to either the increase side or the decrease side, and the change width of the torque or the rotational speed at this time is changed to the suction between the cylinders. It is output as an index value indicating the degree of variation in air volume.

JP 2006-220133 A

  An internal combustion engine having two injectors per cylinder is known. In this case, in order to improve the accuracy of variation abnormality detection, it is conceivable to perform variation abnormality detection by changing the injection ratio of both injectors from a predetermined reference value to a detection value.

  In this case, after the end of detection, the injection ratio must be returned from the detection value to the reference value. However, the change and return of these injection ratios (collectively referred to as switching) are accompanied by a change in driving sound, which may give the user a sense of discomfort.

  Accordingly, the present invention has been made in view of the above circumstances, and an object thereof is to provide an inter-cylinder air-fuel ratio variation abnormality detecting device that can reduce a user's uncomfortable feeling associated with variation abnormality detection.

According to one aspect of the invention,
An inter-cylinder air-fuel ratio variation abnormality detecting device for a multi-cylinder internal combustion engine having two injectors per cylinder,
When the abnormality is detected, the injection ratio of both the injectors is changed from the reference first value to the second value for detection, and the injection ratio is returned from the second value to the first value at the same time as the accelerator is turned on. A feature is provided of an air-fuel ratio variation abnormality detecting apparatus which is characterized.

  Preferably, the device performs abnormality detection in an accelerator-off state, and performs the return of the injection ratio simultaneously with accelerator-on after the abnormality is detected.

  Preferably, the internal combustion engine is mounted on a vehicle, and the device performs abnormality detection while the vehicle is in an idling stop and the accelerator is off, and after detecting abnormality of the return of the injection ratio, the accelerator On and at the same time as the vehicle starts.

  Preferably, the device changes the injection ratio while the vehicle is traveling.

  Preferably, the device performs the change of the injection ratio simultaneously with the return from the fuel cut of the internal combustion engine.

  Preferably, the apparatus gradually changes the injection ratio when the injection ratio is changed and / or returned.

  Preferably, the apparatus sets a predetermined waiting time between the end of changing the injection ratio and the start of abnormality detection.

  According to the present invention, an excellent effect of reducing the user's uncomfortable feeling associated with variation abnormality detection is exhibited.

1 is a schematic view of an internal combustion engine according to an embodiment of the present invention. It is a graph which shows the output characteristic of a pre-catalyst sensor and a post-catalyst sensor. The map for setting the spraying ratio is shown. It is a time chart which shows the fluctuation | variation of an air fuel ratio sensor output. FIG. 5 is an enlarged view corresponding to a V portion in FIG. 4. It is a graph which shows the relationship between an imbalance ratio and an air fuel ratio fluctuation parameter. It is a time chart for demonstrating a rotation fluctuation parameter. It is a graph which shows the relationship between an imbalance ratio and a rotation fluctuation parameter. It is a figure for demonstrating the principle of rich deviation abnormality detection. It is a figure for demonstrating the principle of rich deviation abnormality detection. It is a time chart which concerns on 1st Example of this embodiment. It is a time chart which concerns on 2nd Example of this embodiment. It is a time chart which concerns on 3rd Example of this embodiment. It is a time chart which concerns on 4th Example of this embodiment. It is a time chart which concerns on 5th Example of this embodiment. It is a time chart which concerns on 6th Example of this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 schematically shows an internal combustion engine according to this embodiment. The illustrated internal combustion engine (engine) 1 is a V-type 6-cylinder dual injection gasoline engine mounted on a vehicle (automobile). Each of the cylinders # 1 to # 6 is provided with two injectors, that is, an intake passage injector 2 and an in-cylinder injector 3. The engine 1 has a first bank 4 and a second bank 5. The first bank 4 is provided with odd-numbered cylinders, that is, # 1, # 3, and # 5 cylinders, and the second bank 5 has Even-numbered cylinders, that is, # 2, # 4, and # 6 cylinders are provided. The # 1, # 3, and # 5 cylinders form the first cylinder group, and the # 2, # 4, and # 6 cylinders form the second cylinder group.

  The intake passage injector 2 injects fuel into the intake passage of the corresponding cylinder, particularly into the intake port 6 so as to realize so-called homogeneous combustion. Hereinafter, the intake manifold injector is also referred to as “PFI”. On the other hand, the in-cylinder injector 3 directly injects fuel into the cylinder (combustion chamber) of the corresponding cylinder so as to realize so-called stratified combustion. Hereinafter, the in-cylinder injector is also referred to as “DI”.

  The intake passage 7 for introducing the intake air includes a surge tank 8 as a collecting portion, a plurality of intake manifolds 9 connecting the intake ports 6 and the surge tanks 8 of each cylinder, and the surge tank 8. And an intake pipe 10 on the upstream side. The intake pipe 10 is provided with an air flow meter 11 and an electronically controlled throttle valve 12 in order from the upstream side. The air flow meter 11 outputs a signal having a magnitude corresponding to the intake flow rate. Each cylinder is provided with a spark plug 13 for igniting the air-fuel mixture in the cylinder.

  In the present embodiment, the exhaust passage for discharging the exhaust gas is provided with a first exhaust passage 14A for the first bank 4 and a second exhaust passage 14B for the second bank 5 separately. . That is, there are two exhaust systems independently for each bank. Since the configuration of the exhaust system is the same for both banks, only the first bank 4 will be described here, and the second bank 5 will be denoted by the same reference numeral in the drawing and description thereof will be omitted.

  The first exhaust passage 14 </ b> A has exhaust ports 15 of the cylinders # 1, # 3, and # 5, an exhaust manifold 16 that collects exhaust gases from these exhaust ports 15, and an exhaust gas connected to the downstream end of the exhaust manifold 16. Tube 17. A catalyst composed of a three-way catalyst, that is, an upstream catalyst 18 and a downstream catalyst 19 are provided in series on the upstream side and the downstream side of the exhaust pipe 17, respectively. Air-fuel ratio sensors for detecting the air-fuel ratio of the exhaust gas, that is, the pre-catalyst sensor 20 and the post-catalyst sensor 21 are installed on the upstream side and the downstream side of the upstream catalyst 18, respectively. These sensors detect the air-fuel ratio based on the oxygen concentration in the exhaust gas. In this way, a single pre-catalyst sensor 20 is installed at the gathering portion of the exhaust passage of one cylinder group.

  The above-described PFI2, DI3, throttle valve 12, spark plug 13 and the like are electrically connected to an electronic control unit (hereinafter referred to as ECU) 100 as a control means. The ECU 100 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. In addition to the air flow meter 11, the pre-catalyst sensor 20, and the post-catalyst sensor 21, the ECU 100 detects the crank angle sensor 22 for detecting the crank angle of the engine 1 and the accelerator opening as shown in the figure. An accelerator opening sensor 23 for detecting the coolant temperature of the engine 1, a water temperature sensor 24 for detecting the temperature of the cooling water, and other various sensors are electrically connected via an A / D converter (not shown). The ECU 100 controls the PFI 2, DI 3, the throttle valve 12, the spark plug 13, and the like so as to obtain a desired output based on the detection values of various sensors, and the like, fuel injection amount, fuel injection timing, throttle opening degree, Control ignition timing. Further, the ECU 100 detects the crank angle of the engine 1 based on the output of the crank angle sensor 22 and calculates the rotational speed of the engine. Here, the rotation speed per minute (rpm) is used as the rotation speed of the engine.

  The pre-catalyst sensor 20 is a so-called wide-range air-fuel ratio sensor, and can continuously detect an air-fuel ratio over a relatively wide range. FIG. 2 shows the output characteristics of the pre-catalyst sensor 20. As shown in the figure, the pre-catalyst sensor 20 outputs a voltage signal Vf having a magnitude proportional to the air-fuel ratio of the exhaust gas. The output voltage when the exhaust air-fuel ratio is stoichiometric (theoretical air-fuel ratio, for example, A / F = 14.6) is Vreff (for example, about 3.3 V).

On the other hand, the post-catalyst sensor 21 is a so-called O ₂ sensor and has a characteristic that the output value changes suddenly at the stoichiometric boundary. FIG. 2 shows the output characteristics of the post-catalyst sensor 21. As shown in the figure, the output voltage when the air-fuel ratio of the exhaust gas is stoichiometric, that is, the stoichiometric equivalent value is Vrefr (for example, 0.45 V). The output voltage of the post-catalyst sensor 21 changes within a predetermined range (for example, 0 to 1 (V)). When the exhaust air-fuel ratio is leaner than stoichiometric, the output voltage of the post-catalyst sensor becomes lower than the stoichiometric equivalent value Vrefr, and when the exhaust air-fuel ratio is richer than stoichiometric, the output voltage of the post-catalyst sensor becomes higher than the stoichiometric equivalent value Vrefr.

  The upstream catalyst 18 and the downstream catalyst 19 simultaneously purify NOx, HC and CO, which are harmful components in the exhaust gas, when the air-fuel ratio A / F of the exhaust gas flowing into each of them is close to the stoichiometric range. The air-fuel ratio width (window) that can simultaneously purify these three with high efficiency is relatively narrow.

  Therefore, air-fuel ratio control (stoichiometric control) is executed by the ECU 100 during normal operation so that the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 18 is controlled in the vicinity of the stoichiometric. The air-fuel ratio control includes a main air-fuel ratio control (main air-fuel ratio feedback control) for controlling the fuel injection amount so that the exhaust air-fuel ratio detected by the pre-catalyst sensor 20 matches the stoichiometric air fuel ratio. This is comprised of auxiliary air-fuel ratio control (auxiliary air-fuel ratio feedback control) for controlling the fuel injection amount so that the exhaust air-fuel ratio detected by the post-catalyst sensor 21 matches the stoichiometry.

  Such air-fuel ratio control is performed for each bank. That is, air-fuel ratio control of the # 1, # 3, and # 5 cylinders belonging to the first bank 4 is performed based on the outputs of the pre-catalyst sensor 20 and the post-catalyst sensor 21 on the first bank 4 side. On the other hand, based on the outputs of the pre-catalyst sensor 20 and the post-catalyst sensor 21 on the second bank 5 side, air-fuel ratio control of the # 2, # 4, and # 6 cylinders belonging to the second bank 5 is performed. However, the same correction amount and fuel injection amount are used for each cylinder in the same bank. Air-fuel ratio control is performed as if there were two in-line three-cylinder engines.

  Further, in the present embodiment, the injection division is performed in which the total fuel injection amount injected in one cylinder during one injection cycle is shared by the PFI 2 and DI 3 according to a predetermined injection division ratio α. At this time, the ECU 100 sets the amount of fuel injected from the PFI 2 (referred to as port injection amount) and the amount of fuel injected from the DI 3 (referred to as in-cylinder injection amount) in accordance with the injection ratio α. In response to the control, the injectors 2 and 3 are energized and controlled.

  Here, the injection ratio α is the ratio of the port injection amount to the total fuel injection amount, and has a value of 0 to 1. When the total fuel injection amount is Qt, the port injection amount Qp is represented by α × Qt, and the in-cylinder injection amount Qd is represented by (1−α) × Qt. The injection ratio of PFI2 and DI3 or port injection amount Qp and in-cylinder injection amount Qd is Qp: Qd = α: (1−α) (%). Thus, the injection ratio α defines the injection ratio of the PFI 2 and DI 3 or the port injection amount Qp and the in-cylinder injection amount Qd. The total fuel injection amount is set by the ECU 100 based on the engine operating state (for example, engine speed and load).

FIG. 3 shows a map for setting the injection division ratio α. As shown in the drawing, the injection ratio α changes from α ₁ to α ₄ according to each region defined by the engine speed Ne and the load KL. For example, α ₁ = 0, α ₂ = 0.35, α ₃ = 0.5, and α ₄ = 0.7. These values and area divisions can be arbitrarily changed. In this example, the ratio of the port injection amount increases toward the low rotation and high load side. Further, in the region where α = α ₁ , the injection is not performed and the fuel is supplied only by in-cylinder injection. Thus, the injection ratio α and the injection ratio determined by the map are the injection ratio α and the injection ratio as the first reference value.

  The injection ratio α is the same value for each cylinder in both banks. That is, no setting is made for each bank with respect to the ejection ratio α.

  Now, for example, it is assumed that injectors of some cylinders (particularly one cylinder) out of all cylinders have failed, and variations in air-fuel ratio (imbalance) occur between the cylinders. For example, when the # 1 cylinder has a larger fuel injection amount than the other # 2 to # 6 cylinders, and the air-fuel ratio of the # 1 cylinder is larger than the air-fuel ratios of the other # 2 to # 6 cylinders and shifts to the rich side, etc. is there. At this time, if a relatively large correction amount is given to the first bank 4 including the # 1 cylinder by the aforementioned stoichiometric control, the air-fuel ratio of the total gas may be controlled stoichiometrically. However, looking at each cylinder, it is clear that # 1 cylinder is richer than stoichiometric and # 3 and # 5 cylinders are leaner than stoichiometric and are only stoichiometric as a whole balance, which is not preferable in terms of emissions. is there. In view of this, the present embodiment is equipped with a device that detects such a variation in air-fuel ratio between cylinders.

  FIG. 4 shows fluctuations in the sensor output before the catalyst in an in-line four-cylinder engine different from the present embodiment. It will be understood that the example here can also be applied to a V-type 6-cylinder engine as in this embodiment.

  As shown in the figure, the exhaust air-fuel ratio A / F detected by the pre-catalyst sensor tends to periodically vary with one engine cycle (= 720 ° CA) as one cycle. When the variation in the air-fuel ratio between cylinders occurs, the fluctuation within one engine cycle increases. The air-fuel ratio diagrams a, b, and c in (B) show the case where there is no variation and only one cylinder has a rich shift at an imbalance ratio of 20%, and only one cylinder has a rich shift at an imbalance ratio of 50%. As can be seen, the greater the degree of variation, the greater the amplitude of the air-fuel ratio fluctuation. Even in the V-type 6-cylinder engine as in the present embodiment, there is a similar tendency for one bank.

  Here, the imbalance ratio (%) is a parameter representing the degree of variation in the air-fuel ratio between cylinders. In other words, the imbalance ratio is the amount of fuel injection in a cylinder (imbalance cylinder) causing the fuel injection amount deviation when only one of the cylinders has caused the fuel injection amount deviation. The ratio is a value indicating whether the fuel injection amount is not deviated from the fuel injection amount of the cylinder (balance cylinder) that has not caused the fuel injection amount deviation, that is, the reference injection amount. When the imbalance ratio is IB, the fuel injection amount of the imbalance cylinder is Qib, and the fuel injection amount of the balance cylinder, that is, the reference injection amount is Qs, IB = (Qib−Qs) / Qs. The greater the imbalance ratio IB, the greater the fuel injection amount deviation between the imbalance cylinder and the balance cylinder, and the greater the air-fuel ratio variation.

[Cylinder air-fuel ratio variation abnormality detection]
As can be understood from the above description, when the air-fuel ratio variation abnormality occurs, the fluctuation of the sensor output before the catalyst becomes large. Therefore, it is possible to detect a variation abnormality based on the output fluctuation.

  Here, the types of variation abnormality include a rich deviation abnormality in which the fuel injection amount of one cylinder is shifted to the rich side (excess side) and a lean in which the fuel injection amount of one cylinder is shifted to the lean side (underside). There is a misalignment. In this embodiment, the rich deviation abnormality is detected based on the pre-catalyst sensor output fluctuation, and the lean deviation abnormality is detected based on the engine rotation fluctuation by a method described later. However, the rich deviation abnormality and the lean deviation abnormality may not be distinguished, and a wide variation abnormality may be detected based on at least one of the pre-catalyst sensor output fluctuation and the engine rotation fluctuation.

  When detecting the rich deviation abnormality, an air-fuel ratio fluctuation parameter that is a parameter correlated with the degree of fluctuation of the pre-catalyst sensor output is calculated, and the abnormality is detected by comparing the air-fuel ratio fluctuation parameter with a predetermined abnormality judgment value. Here, abnormality detection is performed for each bank using the output of the pre-catalyst sensor 20 which is a corresponding air-fuel ratio sensor.

  Hereinafter, a method for calculating the air-fuel ratio fluctuation parameter will be described. FIG. 5 is an enlarged view corresponding to the V portion in FIG. 4, and particularly shows fluctuations in the sensor output before the catalyst within one engine cycle. As the pre-catalyst sensor output, a value obtained by converting the output voltage Vf of the pre-catalyst sensor 20 into an air-fuel ratio A / F is used. However, the output voltage Vf of the pre-catalyst sensor 20 can also be used directly.

(B) As shown in the figure, the ECU 100 acquires the value of the pre-catalyst sensor output A / F every predetermined sample period τ (unit time, for example, 4 ms) within one engine cycle. The value A / F _n obtained in this timing (second timing), the absolute value of the difference .DELTA.A / F _n between the value A / F _n-1 obtained at the previous timing (first timing) It calculates | requires by following Formula (1). This difference ΔA / F _n can be rephrased as a differential value or inclination at the current timing.

Most simply, this difference ΔA / F _n represents the fluctuation of the sensor output before the catalyst. This is because the slope of the air-fuel ratio diagram increases as the degree of fluctuation increases, and the difference ΔA / F _n increases. Therefore, the value of the difference ΔA / F _{n at} a predetermined timing can be used as the air-fuel ratio fluctuation parameter.

However, in this embodiment, in order to improve accuracy, the average value of the plurality of differences ΔA / F _n is used as the air-fuel ratio fluctuation parameter. In the present embodiment, the difference ΔA / F _n is integrated at each timing within one engine cycle, and the final integrated value is divided by the number of samples N to obtain the average value of the differences ΔA / F _n within one engine cycle. . Further, the average value of the difference ΔA / F _n is integrated for M engine cycles (for example, M = 100), the final integrated value is divided by the number of cycles M, and the average value of the difference ΔA / F _n within the M engine cycle is obtained. Ask for. The final average value obtained in this way is used as an air-fuel ratio fluctuation parameter, and is displayed as “X” hereinafter.

  The air-fuel ratio fluctuation parameter X increases as the degree of fluctuation of the pre-catalyst sensor output increases. Therefore, if the air-fuel ratio fluctuation parameter X is equal to or greater than a predetermined abnormality determination value, it is determined that there is an abnormality, and if the air-fuel ratio fluctuation parameter X is smaller than the abnormality determination value, it is determined that there is no abnormality, that is, normal.

Since the pre-catalyst sensor output A / F may increase or decrease, the difference ΔA / F _n or the average value thereof is obtained for only one of these cases, and this may be used as the air-fuel ratio fluctuation parameter. good. Especially when only one cylinder has a rich shift, when the pre-catalyst sensor receives the exhaust gas corresponding to that one cylinder, its output rapidly changes to the rich side (that is, rapidly decreases). It can also be used for But it is not limited to this, It is also possible to use only the value on the increase side.

  Further, any value that correlates with the degree of fluctuation of the pre-catalyst sensor output can be used as the air-fuel ratio fluctuation parameter. For example, the air-fuel ratio fluctuation parameter can also be calculated based on the difference between the maximum value and the minimum value of the sensor output before the catalyst in one engine cycle (so-called peak to peak). This is because the difference increases as the degree of fluctuation of the pre-catalyst sensor output increases.

  FIG. 6 shows the relationship between the imbalance ratio IB and the air-fuel ratio fluctuation parameter X. As shown in the figure, there is a strong correlation between the imbalance ratio IB and the air-fuel ratio fluctuation parameter X, and the air-fuel ratio fluctuation parameter X increases as the imbalance ratio IB increases. Here, IB1 in the figure is a value of the imbalance ratio IB corresponding to the abnormality determination value, and is 60 (%), for example.

  Next, detection of lean deviation abnormality will be described. In this detection, a rotation fluctuation parameter that is a parameter correlated with the degree of fluctuation of the engine rotation speed is calculated, and an abnormality is detected by comparing the rotation fluctuation parameter with a predetermined abnormality determination value. In this case, the abnormality detection is performed based on the detected fluctuation of the engine rotation speed regardless of which bank it is.

In FIG. 7, (a) shows the crank angle (° CA), (b) shows the 30 ° CA time T ₃₀ (s), and (c) shows the change of the rotation variation parameter Y. Although the illustrated example is an example of a normal in-line four-cylinder engine, it is understood that the present invention can be applied to a V-type six-cylinder engine as in the present embodiment by the following description. The firing order is the order of each cylinder of # 1, # 3, # 4, and # 2. In the figure, “normal” indicates a case where no air-fuel ratio deviation occurs in any cylinder, and “lean deviation abnormality” indicates that the lean of the imbalance ratio IB = −30 (%) only in the # 1 cylinder. The case where a deviation error has occurred is shown.

The 30 ° CA time T ₃₀ is the time required for the crankshaft to rotate 30 ° CA. The longer (larger) 30 ° CA time T ₃₀ is, the slower the rotation speed is. The rotational fluctuation parameter Y is a difference in 30 ° CA time T ₃₀ between the current ignition cylinder TDC (compression top dead center) and the previous ignition cylinder TDC. In addition, although 30 degree CA is mentioned here as a rotation angle of a crankshaft, this value is arbitrary and can be changed into another value (for example, 10 degree CA).

First, let us focus on the case of lean deviation abnormality. In the illustrated example, since the lean deviation abnormality occurs in the # 1 cylinder, as shown in (b), even if the # 1 cylinder is ignited, the combustion is deteriorated, the torque is not sufficiently generated, and the subsequent 30 ° CA time T ₃₀ is longer. Correspondingly, the difference in the 30 ° CA time T ₃₀ between the # 1 cylinder TDC and the # 3 cylinder TDC is large, and the value of the rotational fluctuation parameter Y shown in (c) is large.

On the other hand, since cylinders other than # 1, for example, # 3 cylinder, are normal, as shown in (b), 30 ° CA time T ₃₀ between # 3 cylinder TDC and # 4 cylinder TDC. The difference is small, and the value of the rotational fluctuation parameter Y shown in (c) is also small.

Next, focusing on the normal case, since all the cylinders are normal, there is little combustion variation between the cylinders, and as shown in FIG. 5B, 30 ° CA between the previous ignition cylinder TDC and the current ignition cylinder TDC. in the time difference T ₃₀ substantially small both constant and near the rotation fluctuation parameter Y value is also always less substantially zero as shown in (c).

  Therefore, it is possible to detect a lean deviation abnormality by comparing the rotation fluctuation parameter Y with a predetermined abnormality determination value. In the present embodiment, when the rotational fluctuation parameter Y of a certain cylinder is equal to or greater than the abnormality determination value, it is determined that a lean deviation abnormality has occurred in the cylinder. If the rotational fluctuation parameter Y of all the cylinders is smaller than the abnormality determination value, it is determined that there is no cylinder in which the lean deviation abnormality has occurred and that it is normal.

  FIG. 8 shows the relationship between the imbalance ratio IB and the rotation variation parameter Y. As shown in the figure, there is a strong correlation between the imbalance ratio IB and the rotation fluctuation parameter Y, and the rotation fluctuation parameter Y increases as the imbalance ratio IB decreases (increases to the minus side). Here, IB2 in the figure is a value of the imbalance ratio IB corresponding to the abnormality determination value, and is, for example, −30 (%).

  By the way, when detecting a variation abnormality, for example, detecting a rich deviation abnormality using the air-fuel ratio fluctuation parameter X, it may be necessary to change the injection ratio α from a reference value determined from the map of FIG. In the case of a dual injection engine as in this embodiment, if the injection ratio α is small, the port injection amount is relatively small with respect to the in-cylinder injection amount. Therefore, even if a rich shift abnormality occurs in PFI2, the effect is not reflected so much in the total injection amount, and the air-fuel ratio fluctuation does not become so large.

  Therefore, in this case, the injection division ratio α is increased from the reference value determined from the map. In this way, the influence of the rich displacement abnormality of PFI 2 can be largely reflected in the total injection amount, and the air-fuel ratio fluctuation can be increased.

  Hereinafter, the principle of rich deviation abnormality detection according to this embodiment will be described with reference to FIGS. 9 and 10. In the present embodiment, the air-fuel ratio fluctuation parameter X is used and the injection ratio α is changed to detect an air-fuel ratio deviation, that is, an intake system abnormality caused by an intake system failure or the like.

  First, the example of FIG. 9 will be described. The state I on the left side in the figure is a case where the ejection ratio α is the reference value A = 0.4. Further, the state II on the right side in the drawing is a case where the ejection ratio α is changed to B = 0.8, which is larger than the reference value. When the state I changes to the state II, the injection ratio α changes from 0.4 to 0.8, the in-cylinder injection amount ratio decreases, and the port injection amount ratio increases. Here, temporarily, the abnormality determination value Z is determined as a value corresponding to an imbalance ratio of 20%. The waveform shown is the output waveform of the pre-catalyst sensor 20 in one bank. That is, here, only one bank is focused.

FIG. 9A shows a normal state in which no abnormality has occurred in PFI 2 and DI 3 of any cylinder and no abnormality has occurred in the intake system. In this case, in the state I, the air-fuel ratio fluctuation parameter X _A corresponding to the imbalance ratio 0% is obtained, and in the state II, the air-fuel ratio fluctuation parameter X _B corresponding to the imbalance ratio 0% is obtained. X _A <Z and X _B <Z, and in this case, it is determined as normal.

FIG. 9B shows an intake system abnormality of 50% in which no abnormality occurs in PFI2 and DI3 of any cylinder, but an abnormality equivalent to an imbalance ratio of 50% occurs in the intake system. In this case, the air-fuel ratio fluctuation parameter X _A corresponding to the imbalance ratio 50% is obtained in the state I, and the air-fuel ratio fluctuation parameter X _B corresponding to the imbalance ratio 50% is obtained also in the state II. X _A ≧ Z and X _B ≧ Z. In this case, it is determined that the intake system is abnormal. The reason why the value of the air-fuel ratio fluctuation parameter X does not change between the state I and the state II is that the PFI2 and DI3 are normal and are not affected by the change in the injection ratio α.

In FIG. 9C, an abnormality corresponding to an imbalance ratio of 50% has occurred in DI3 of one cylinder, no abnormality has occurred in the remaining PFI2 and DI3, and no abnormality has occurred in the intake system. 50% is shown. In this case, in the state I, the air-fuel ratio fluctuation parameter X _A corresponding to the imbalance ratio of 30% is obtained. This is because the injection ratio of DI3 is (1−0.4) = 0.6, and 50% × 0.6 = 30%, that is, the influence of abnormality of DI3 is reduced as a result of the injection division. On the other hand, in the state II, an air-fuel ratio fluctuation parameter X _B corresponding to an imbalance ratio of 10% is obtained. This is because the injection ratio of DI3 is (1-0.8) = 0.2 and 50% × 0.2 = 10%. X _A ≧ Z and X _B <Z. In this case, it is determined that the DI is abnormal.

In FIG. 9D, an abnormality corresponding to an imbalance ratio of 50% has occurred in the PFI 2 of one cylinder, no abnormality has occurred in the remaining PFI 2 and DI 3, and no abnormality has occurred in the intake system. 50% is shown. In this case, in the state I, the air-fuel ratio fluctuation parameter X _A corresponding to the imbalance ratio 20% is obtained. This is because the injection ratio of PFI2 is 0.4, and 50% × 0.4 = 20%, that is, the influence of PFI2 abnormality is reduced as a result of spraying. On the other hand, in the state II, an air-fuel ratio fluctuation parameter X _B corresponding to an imbalance ratio of 40% is obtained. This is because the injection ratio of PFI2 is 0.8, 50% × 0.8 = 40%. X _A <Z and X _B ≧ Z. In this case, it is determined that the PFI is abnormal.

  In particular, when the injection ratio α is not changed (increased) in the state I, the PFI abnormality cannot be detected. Therefore, it is necessary to change the ejection ratio α when an abnormality is detected.

  Next, the example of FIG. 10 will be described. This example is the reverse of the above, and the spraying rate is reduced. The state I on the left side in the figure is a case where the ejection ratio α is the reference value A = 0.4. Further, the state II on the right side in the drawing is a case where the injection ratio α is C = 0.0, which is smaller than the reference value A, that is, the fuel injection is performed only with DI3. When the state I changes to the state II, the injection ratio α changes from 0.4 to 0.0, the port injection amount ratio decreases, and the in-cylinder injection amount ratio increases. Here, temporarily, the abnormality determination value Z is determined as a value corresponding to an imbalance ratio of 30%. The waveform shown is the output waveform of the pre-catalyst sensor 20 in one bank, and the same point as described above is focused on only one bank.

FIG. 10 (a) shows a normal state in which no abnormality has occurred in PFI2 and DI3 of any cylinder, and no abnormality has occurred in the intake system. In this case, the air-fuel ratio fluctuation parameter X _A corresponding to the imbalance ratio 0% is obtained in the state I, and the air-fuel ratio fluctuation parameter X _C corresponding to the imbalance ratio 0% is obtained in the state II. X _A <Z and X _C <Z, and in this case, it is determined to be normal.

FIG. 10B shows an intake system abnormality of 50% when no abnormality occurs in PFI2 and DI3 of any cylinder, but an abnormality corresponding to an imbalance ratio of 50% occurs in the intake system. In this case, in the state I, the air-fuel ratio fluctuation parameter X _A corresponding to the imbalance ratio 50% is obtained, and in the state II, the air-fuel ratio fluctuation parameter X _C corresponding to the imbalance ratio 50% is obtained. X _A ≧ Z and X _C ≧ Z. In this case, it is determined that the intake system is abnormal.

In FIG. 10C, an abnormality corresponding to an imbalance ratio of 40% has occurred in DI3 of one cylinder, no abnormality has occurred in the remaining PFI2 and DI3, and no abnormality has occurred in the intake system. 40% is shown. In this case, in the state I, the air-fuel ratio fluctuation parameter X _A corresponding to the imbalance ratio of 24% is obtained. This is because the injection ratio of DI3 is (1−0.4) = 0.6, and 40% × 0.6 = 24%, that is, the influence of abnormality of DI3 is reduced as a result of the injection division. On the other hand, in the state II, an air-fuel ratio fluctuation parameter X _C corresponding to an imbalance ratio of 40% is obtained. This is because the injection ratio of DI3 is (1-0.0) = 1.0, and 40% × 1.0 = 40%. X _A <Z and X _C ≧ Z. In this case, it is determined that the DI is abnormal.

FIG. 10D shows a PFI abnormality in which an imbalance ratio of 80% has occurred in the PFI 2 of one cylinder, no abnormality has occurred in the remaining PFI 2 and DI 3, and no abnormality has occurred in the intake system. 80% is shown. In this case, in the state I, the air-fuel ratio fluctuation parameter X _A corresponding to the imbalance ratio of 32% is obtained. This is because the injection ratio of PFI2 is 0.4, and 80% × 0.4 = 32%, that is, the influence of PFI2 abnormality is reduced as a result of the injection. On the other hand, in the state II, the air-fuel ratio fluctuation parameter X _C corresponding to the imbalance ratio 0% is obtained. This is because the injection ratio of PFI2 is 0.0, and 80% × 0.0 = 0%. X _A ≧ Z and X _C <Z. In this case, it is determined that PFI is abnormal.

  In particular, if the injection ratio α is not changed (decreased) in the state I, the DI abnormality cannot be detected. Therefore, it is necessary to change the ejection ratio α when an abnormality is detected.

  In accordance with the above principle, the ECU 100 can detect, for example, the rich deviation abnormality and the intake system abnormality related to one bank by the following method.

Step S1: An air-fuel ratio fluctuation parameter X _A when the injection ratio α is a reference value _A is acquired.

Step S2: The injection ratio α is changed to a predetermined value B greater than the reference value A, and the air-fuel ratio fluctuation parameter X _B at this time is acquired.

Step S3: The injection ratio α is changed to a predetermined value C smaller than the reference value A, and the air-fuel ratio fluctuation parameter X _C at this time is acquired.

Step S4: X _A , X _B , and X _C are compared with a predetermined abnormality determination value Z to determine any of PFI abnormality, DI abnormality, intake system abnormality, and normal. This determination is as follows.

When X _A <Z, X _B <Z, X _C <Z, it is determined as normal.

When X _A ≧ Z, X _B ≧ Z, and X _C ≧ Z, it is determined that the intake system is abnormal.

When X _A <Z, X _B ≧ Z, and X _C <Z, it is determined that the PFI is abnormal.

When X _A ≧ Z, X _B <Z, X _C ≧ Z, it is determined that DI is abnormal.

  Step S5: The injection ratio α is returned to the original reference value A, and the process is terminated.

  By adopting such a detection method, it is possible to distinguish and accurately detect PFI abnormality, DI abnormality and intake system abnormality, and the detection accuracy can be improved.

Although the uniform abnormality determination value Z is used here, the value of the abnormality determination value may be changed for each type of X _A , X _B , and X _C. Further, it is preferable to appropriately determine the value of the injection ratio α after the change from the viewpoint of combustion stability, torque fluctuation, DI heat protection, and the like.

  By the way, since the change and return (switching) of the injection ratio α as described above are accompanied by a change in driving sound, there is a possibility that the user may feel uncomfortable. That is, since the noise levels of PFI and DI are different, the driving sound changes when the injection ratio of the two changes, which may give the user a sense of discomfort.

  Further, the switching of the injection division ratio α changes the balance between the fuel adhesion amount and the fuel evaporation amount on the inner wall of the intake port, and causes the air-fuel ratio of the in-cylinder air-fuel mixture and thus the combustion state to be temporarily roughened. This roughness causes a temporary torque change, which also causes the user to feel uncomfortable.

  Therefore, in the present embodiment, when returning to the reference value A of the injection ratio α, the return is performed simultaneously with the accelerator being turned on. The accelerator on is performed by the user's own intention, and simultaneously with the accelerator on, the engine speed increases, the vehicle accelerates, and other noise and vibrations are generated. Therefore, the change in the driving sound and torque due to the return of the injection ratio α can be confused with other noises and vibrations, and the user's uncomfortable feeling can be reduced.

  Here, “accelerator on” means a state in which the user gives an input to an accelerator pedal as an accelerator member, that is, a state in which the accelerator pedal is depressed. In contrast to this, the accelerator off is a state in which the user does not give input to the accelerator pedal, that is, a state in which the accelerator pedal is released. These accelerator on and accelerator off are detected by an accelerator opening sensor 23. That is, when the detected accelerator opening is zero, ECU 100 determines that the accelerator is off, and when the detected accelerator opening is greater than zero, ECU 100 determines that the accelerator is on. At the same time when the accelerator is switched from the accelerator off to the accelerator on, the injection ratio α is returned to the reference value A.

  FIG. 11 shows a state of abnormality detection according to the first example of the present embodiment. (A)-(F) show the on / off state of the accelerator, the engine speed, the vehicle speed, the on / off state of the injection rate change instruction, the on / off state of abnormality detection, and the injection rate, respectively.

  The injection ratio change instruction is an injection ratio change instruction signal generated inside the ECU 100 when a predetermined condition is satisfied. When this is ON, the injection ratio α is set to the detection value B, and when this is OFF. The spray distribution rate α is set to the reference value A. When abnormality detection is on, it means a state where abnormality detection is being executed, and when abnormality detection is off, it means a state where abnormality detection is not being executed.

  In the illustrated example, abnormality detection is performed with the accelerator off, and furthermore, abnormality detection is performed while the vehicle is idling and the engine speed is idle and the vehicle speed is zero. The change instruction is on from the initial state in the figure, and therefore the injection ratio α is also set to the detection value B from the initial state in the figure.

Here, with respect to the ejection ratio α, for example, the reference value A is α ₁ = 0 according to the map of FIG. 3 and the detection value B is 1. In this case, when the injection ratio α is changed from the reference value A to the detection value B, the fuel injection is switched from the state of 100% in-cylinder injection by DI3 to the state of 100% intake passage injection by PFI2. That is, the injection ratio of PFI2 and DI3 is changed from 0: 100 (%) as the first reference value to 100: 0 (%) as the second detection value.

  Conversely, when the injection ratio α is returned from the detection value B to the reference value A, the fuel injection is switched from the state of 100% intake passage injection by PFI2 to the state of 100% in-cylinder injection by DI3. . That is, the injection ratio of PFI2 and DI3 is restored from 100: 0 (%) as the second detection value to 0: 100 (%) as the first reference value.

  In the illustrated example, the injection ratio α is changed to a detection value B for the purpose of detecting the rich shift abnormality and the lean shift abnormality of the PFI 2 of any cylinder.

  In the illustrated example, the abnormality detection is started at time t1, and the abnormality detection is ended at time t2. Generally, at the same time as this termination, the injection ratio α is returned to the reference value A, but in this embodiment, it is not intentionally returned, but the user waits for the accelerator-on timing. At the same time when the accelerator is turned on at time t3, the change instruction is turned off, and the ejection ratio α is returned to the reference value A.

  As soon as the accelerator is turned on, the engine speed increases and the vehicle starts to accelerate. It is possible to reduce the user's uncomfortable feeling by diffusing other noise and vibration generated at this time with changes in driving sound and torque due to the return of the injection ratio.

  In particular, when the vehicle is in an idle stop, changes in the driving sound and torque due to the return of the injection ratio will be noticeable, but this can be made inconspicuous by performing the return of the injection ratio in accordance with the accelerator on. . Therefore, this embodiment is extremely advantageous when detecting an abnormality while the vehicle is idling.

  However, the abnormality detection can be performed not only during idling stop, but also under other conditions, for example, when the vehicle is traveling at low speed (including idling) and low speed with the accelerator off. Also in this case, by performing the injection ratio return at the same time as the accelerator is turned on, it is possible to make inconspicuous changes in operation sound and torque due to the return of the injection ratio.

  In the illustrated example, as shown by a solid line in FIG. 11 (F), at time t3, the ejection ratio α is instantaneously (or stepped) returned from the detection value B to the reference value A. However, alternatively, as shown by the phantom line a in FIG. 11 (F), the injection ratio α may be gradually changed (gradually changed) from the detection value B to the reference value A.

  As described above, the switching of the injection ratio α changes the balance between the fuel adhesion amount and the fuel evaporation amount on the inner wall of the intake port, and causes a temporary roughening of the air-fuel ratio of the in-cylinder mixture and thus the combustion state. As indicated by the solid line in FIG. 11 (F), at time t3, when the intake passage injection 100% state was instantaneously switched to the in-cylinder injection 100% state, immediately after the switching, it was attached to the inner wall of the intake port. The fuel evaporates and enters the cylinder, and the air-fuel ratio of the in-cylinder mixture is unexpectedly shifted to the rich side. Such a rough air-fuel ratio causes a temporary torque change, which also causes the user to feel uncomfortable.

  However, as shown by the phantom line a in FIG. 11 (F), if the injection ratio α is gradually changed, the influence of the rough air-fuel ratio can be reduced, and the uncomfortable feeling to the user can be suppressed or prevented. it can. Such a gradual change in the injection ratio α can be executed in at least one of changing and returning the injection ratio α in another embodiment to be described later.

  Next, FIG. 12 shows a state of abnormality detection according to the second example of the present embodiment. Similarly to the above, (A) to (F) indicate the on / off state of the accelerator, the engine speed, the vehicle speed, the on / off state of the injection ratio change instruction, the on / off state of abnormality detection, and the injection ratio.

  In the second embodiment, the change instruction is switched from OFF to ON at time t1. Along with this, the injection division ratio α is changed from the reference value A to the detection value B. At this time, the injection division ratio α is gradually changed. Then, abnormality detection is started at the time t2 when the change of the spray distribution rate α is completed.

  As described above, the switching of the injection ratio α changes the balance between the fuel adhesion amount and the fuel evaporation amount on the inner wall of the intake port, and causes a temporary roughening of the air-fuel ratio of the in-cylinder mixture and thus the combustion state. If, at time t1, it is instantaneously switched from the state of 100% in-cylinder injection to the state of 100% intake passage injection, immediately after the switching, a part of the fuel injected from PI2 is relatively large on the inner wall of the intake port. As a result, the amount of fuel in the cylinder becomes insufficient, and the air-fuel ratio of the in-cylinder mixture is unexpectedly shifted to the lean side. Such a rough air-fuel ratio causes a temporary torque change, which may give the user a feeling of strangeness. Further, as a result of the air-fuel ratio roughening, the air-fuel ratio in the cylinder is not stabilized for a while, and this may reduce the detection accuracy.

  However, as in this embodiment, by gradually changing the injection ratio α at the time of changing the injection ratio α, the influence of the air-fuel ratio roughness is reduced, thereby suppressing discomfort to the user and a decrease in detection accuracy. Or it can be prevented.

  After the start of abnormality detection, as in the first embodiment, abnormality detection is terminated at time t3, the change instruction is turned off at the same time as the accelerator is turned on at time t4, and the injection ratio α is returned to the reference value A. .

  Next, FIG. 13 shows a state of abnormality detection according to the third example of the present embodiment. Similarly to the above, (A) to (F) indicate the on / off state of the accelerator, the engine speed, the vehicle speed, the on / off state of the injection ratio change instruction, the on / off state of abnormality detection, and the injection ratio.

  In the third embodiment, the change instruction is switched from OFF to ON at time t1. At the same time, the injection ratio α is instantaneously changed from the reference value A to the detection value B, and abnormality detection is started.

  If the injection ratio α is changed instantaneously in this way, there is a concern about the influence of the air-fuel ratio roughness as described above. However, in this embodiment, immediately after such a momentary change, correction of the fuel injection amount is also executed to reduce the influence of air-fuel ratio roughening.

  The correction of the fuel injection amount is executed as follows. When the injection ratio α is instantaneously changed from the reference value A to the detection value B, the fuel injection amount in the PFI 2 is instantaneously changed from zero to a predetermined amount (here, stoichiometric equivalent amount).

  However, since fuel does not adhere to the inner wall of the intake port before the start of fuel injection by PFI2, a relatively large proportion of the injected fuel from PFI2 adheres to the inner wall of the intake port immediately after the start of fuel injection by PFI2. It becomes like this. The fuel adhering to the inner wall of the intake port partially evaporates and enters the cylinder. By repeating this adhesion and evaporation over a plurality of injection cycles, the fuel adhesion amount gradually increases, and the proportion of the adhered fuel in the injected fuel gradually decreases, and the fuel adhesion amount eventually matches the actual fuel injection amount. Reaches the saturation level. At this time of saturation, the fuel adhesion amount and the fuel evaporation amount reach equilibrium, and the air-fuel ratio roughness is eliminated.

  In the correction control, the fuel adhering amount in the equilibrium state according to the fuel injection amount and the engine operating state (rotation speed and load) and the equilibrium state from the moment when the fuel injection amount of the PFI 2 instantaneously changes from zero to the stoichiometric equivalent amount. The time required to reach (time constant or response time) is obtained in advance by adaptation. Then, the in-cylinder inflow fuel amount that is insufficient due to adhering to the inner wall of the intake port is calculated, and the fuel injection amount is increased to compensate for this. The increase amount is gradually attenuated by a constant amount or a constant rate for each injection cycle during a time constant.

  Note that the same fuel injection amount correction can be executed even when the injection ratio α is reversed from the detection value B to the reference value A instantaneously. In this case, the fuel adhering amount in an equilibrium state according to the fuel injection amount and the engine operating state and the equilibrium state in which all the adhering fuel evaporates from the moment when the fuel injection amount of PFI2 instantaneously changes from the stoichiometric equivalent amount to zero. The time required to reach (time constant or response time) is determined in advance. Then, the in-cylinder inflow fuel amount that has become excessive due to the adhering fuel on the inner wall of the intake port inflows is calculated, and the fuel injection amount is reduced to compensate for this. The amount of decrease is gradually attenuated by a fixed amount or a fixed rate for each injection cycle during a time constant.

  When such correction of the fuel injection amount is executed, the abnormality detection can be immediately started simultaneously with the instantaneous change of the injection ratio α as shown in the example of the drawing. That is, even if the abnormality detection is started at the same time as the change of the injection ratio α, the fuel injection amount correction that suppresses the in-cylinder air-fuel ratio roughness is performed, so that the detection accuracy is prevented from being lowered and detection can be performed. It is. Therefore, it is possible to shorten the time from the start of the change of the spray distribution rate α to the end of detection, and it is possible to secure more detection opportunities.

  After the start of abnormality detection, as in the first embodiment, the abnormality detection is terminated at time t2, the change instruction is turned off at the same time as the accelerator is turned on at time t3, and the injection ratio α is returned to the reference value A. . The correction of the fuel injection amount can also be executed by a method other than the above including a known method.

  Next, FIG. 14 shows a state of abnormality detection according to the fourth example of the present embodiment. Similarly to the above, (A) to (F) indicate the on / off state of the accelerator, the engine speed, the vehicle speed, the on / off state of the injection ratio change instruction, the on / off state of abnormality detection, and the injection ratio.

  The fourth embodiment is a modification of the second embodiment shown in FIG. At time t1, the change instruction is switched from OFF to ON, and at the same time, the change from the reference value A to the detection value B of the injection ratio α is started. At the time of this change, the spray distribution rate α is gradually changed in the illustrated example, but the spray distribution rate α may be changed instantaneously. At time t2, the change of the spray distribution rate α is completed, but the abnormality detection is not yet started even at this end point. Abnormality detection is started at time t3 after a predetermined time has elapsed since the end point t2 of the change in the injection ratio α. In this way, a predetermined waiting time is set between the end of the change of the injection ratio α and the start of abnormality detection.

  By setting the waiting time, it is possible to further reduce the influence of the air-fuel ratio roughness accompanying the change in the injection ratio α, and to perform abnormality detection with the in-cylinder air-fuel ratio being more stable. And detection accuracy can be further improved.

  The waiting time may be simply defined as time, may be defined as a time until a predetermined number of ignitions are executed, or is defined as a time until one rotation of the crankshaft is performed a predetermined number of times. May be. Such a waiting time may be applied to the third embodiment shown in FIG.

  After the start of the abnormality detection, the abnormality detection is terminated at time t4, the change instruction is turned off at the same time when the accelerator is turned on at time t5, and the injection ratio α is returned to the reference value A.

  Next, FIG. 15 shows a state of abnormality detection according to the fifth example of the present embodiment. Similarly to the above, (A) to (F) indicate the on / off state of the accelerator, the engine speed, the vehicle speed, the on / off state of the injection ratio change instruction, the on / off state of abnormality detection, and the injection ratio.

  The main feature of the fifth embodiment is that the injection ratio α is changed while the vehicle is running.

  That is, at time t1 while the vehicle is running, the accelerator is switched from the accelerator-on state to the accelerator-off state, and the engine and the vehicle are decelerated accordingly. The change instruction is issued at time t2 after time t1 and before the vehicle speed reaches zero. Then, the change of the spray distribution rate α is started at this time t2.

  Thereafter, as in the fourth embodiment, the injection ratio α is gradually changed from the reference value A to the detection value B, and a predetermined time t4 after a predetermined waiting time has elapsed from the time t3 when the change of the injection ratio α ends. , Abnormality detection is started. In the illustrated example, the time t4 is made coincident with when the vehicle speed is zero and the engine speed is the idle speed. Thereafter, the abnormality detection is finished at time t5, the change instruction is turned off at the same time as the accelerator is turned on at time t6, and the ejection fraction α is returned to the reference value A.

  By changing the injection ratio α while the vehicle is running, the change in the driving sound due to the change in the injection ratio can be reflected in the road noise, engine sound and wind noise that change depending on the driving state, and the injection ratio change The torque change due to can be distorted by vehicle vibration. Therefore, a user's uncomfortable feeling can be reduced.

  In this embodiment, the timing for starting or executing the change of the injection ratio α can be a timing at which the vehicle speed is greater than zero and less than or equal to a predetermined value, and the accelerator is off.

  Next, FIG. 16 shows a state of abnormality detection according to the sixth example of the present embodiment. Similarly to the above, (A) to (C) indicate the on / off state of the accelerator, the engine speed and the vehicle speed, respectively. (D) shows the on / off state of the fuel cut (F / C). (E)-(G) respectively show the on / off state of the injection ratio changing instruction, the on / off state of abnormality detection, and the injection ratio. The fuel cut is on means a state in which the fuel cut is being executed, that is, a state in which fuel injection is stopped for all cylinders. Further, the fuel cut off means a state where the fuel cut is not executed, that is, a state where fuel injection is performed for all cylinders.

  The main feature of the sixth embodiment is that the injection ratio α is changed simultaneously with the return from the fuel cut of the engine.

  That is, at time t1 when the engine speed is higher than the predetermined return speed Nc while the vehicle is running, the fuel cut is executed at the same time when the accelerator is switched from the accelerator on to the accelerator off, and the engine and the vehicle are decelerated. At the same time when the engine speed reaches the return speed Nc (t2), the fuel cut is finished and the fuel cut is returned. At the same time, the change instruction is turned on, and the ejection ratio α is changed. Here, the injection ratio α is changed instantaneously, and neither the gradual change as in the second embodiment nor the fuel injection amount correction as in the third embodiment is performed, but these may be performed.

  Thereafter, abnormality detection is started at time t3 when the vehicle speed becomes zero and the engine speed reaches the idle speed. Roughness of the in-cylinder air-fuel ratio is reduced by the time (t2 to t3) until the engine speed decreases from the return speed Nc to the idle speed, which is advantageous for improving detection accuracy.

  Thereafter, the abnormality detection is terminated at time t4, the change instruction is turned off at the same time as the accelerator is turned on at time t5, and the ejection fraction α is returned to the reference value A.

  By changing the fuel injection ratio at the same time as the return from the fuel cut, the fuel injection of all cylinders by the fuel cut return can be started from the beginning with the changed fuel injection ratio. Therefore, it is possible to eliminate the operation sound and torque change due to the change in the injection ratio itself, and it is possible to reduce the user's uncomfortable feeling.

  In addition, the return time from the fuel cut is usually during the running of the vehicle as in the illustrated example. Therefore, the user's uncomfortable feeling can be reduced for the same reason as in the fifth embodiment.

  The preferred embodiment of the present invention has been described in detail above, but various other embodiments of the present invention are conceivable. For example, the present invention is applicable to engines other than the V type (such as an in-line engine). There are no particular limitations on the number of cylinders, type, application, etc. of the engine. In the above-described embodiment, both the variation abnormality detection based on the output fluctuation of the air-fuel ratio sensor and the variation abnormality detection based on the engine rotation fluctuation can be performed. However, the present invention is not limited to this. Good.

  Each feature of the above embodiments can be appropriately combined as long as no contradiction occurs. For example, the gradual change in the injection ratio of the second embodiment is applicable to the third to sixth embodiments. When applied to the third embodiment, this is gradually changed and the fuel injection amount is corrected when the injection ratio is changed.

  The waiting time of the fourth embodiment can be applied not only when the spray distribution ratio is changed gradually but also when it is changed instantaneously. In the illustrated examples of the fifth and sixth embodiments (FIGS. 15 and 16), there is a time difference between the end of the change in the ejection ratio and the start of abnormality detection. This time difference corresponds to the waiting time.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

1 Internal combustion engine 2 Intake passage injector (PFI)
3 In-cylinder injector (DI)
4 First bank 5 Second bank 20 Pre-catalyst sensor 22 Crank angle sensor 100 Electronic control unit (ECU)

Claims (7)

An inter-cylinder air-fuel ratio variation abnormality detecting device for a multi-cylinder internal combustion engine having two injectors per cylinder,
When the abnormality is detected, the injection ratio of both the injectors is changed from the reference first value to the second value for detection, and the injection ratio is returned from the second value to the first value at the same time as the accelerator is turned on. An inter-cylinder air-fuel ratio variation abnormality detection device as a feature.   2. The inter-cylinder air-fuel ratio variation abnormality detection device according to claim 1, wherein abnormality detection is performed in an accelerator-off state, and the injection ratio is restored simultaneously with accelerator-on after abnormality detection. The internal combustion engine is mounted on a vehicle;
2. The inter-cylinder operation according to claim 1, wherein abnormality detection is performed while the vehicle is in an idling stop and the accelerator is off, and the return of the injection ratio is performed at the same time as the accelerator is on and the vehicle starts after the abnormality is detected. Air-fuel ratio variation abnormality detection device.   4. The inter-cylinder air-fuel ratio variation abnormality detection device according to claim 2, wherein the injection ratio is changed while the vehicle is running.   The inter-cylinder air-fuel ratio variation abnormality detection device according to any one of claims 1 to 4, wherein the change in the injection ratio is performed simultaneously with the return from the fuel cut of the internal combustion engine.   The inter-cylinder air-fuel ratio variation abnormality detection device according to any one of claims 1 to 5, wherein the injection rate is gradually changed when at least one of change and return of the injection rate.   The inter-cylinder air-fuel ratio variation abnormality detection device according to any one of claims 1 to 6, wherein a predetermined waiting time is set between the end of changing the injection ratio and the start of abnormality detection.

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