JP5640967B2 - Cylinder air-fuel ratio variation abnormality detection device - Google Patents

Description

  The present invention relates to an inter-cylinder air-fuel ratio variation abnormality detecting device for an internal combustion engine, and more particularly to a device having a function of estimating an air-fuel ratio for each cylinder.

  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 combusted in the internal combustion engine, that is, an air-fuel ratio, in order to perform purification of harmful components in exhaust gas with a catalyst with high efficiency. This control is indispensable. 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 the air-fuel ratio of all cylinders is set to a common correction amount so that the air-fuel ratio detected thereby matches the predetermined target air-fuel ratio. The feedback control that corrects with is carried out.

  On the other hand, since air-fuel ratio feedback control is performed using the same control amount for all cylinders, even if this air-fuel ratio feedback control is executed, the actual air-fuel ratio in the combustion chamber is uneven (imbalanced) among the cylinders. May be. At this time, if the degree of imbalance is small, it can be absorbed by air-fuel ratio feedback control, and even the catalyst can purify harmful components in the exhaust, so it does not substantially affect the exhaust emission and does not become a significant problem. .

  However, for example, if the fuel injection system of some cylinders fails and the air-fuel ratio between the cylinders becomes imbalanced greatly, exhaust emission may be deteriorated, which may be a problem. It is desirable to detect such an air-fuel ratio imbalance large enough to deteriorate 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 having deteriorated exhaust emission, it is required to detect the air-fuel ratio imbalance between cylinders in an on-board state (in-board). There is also a movement to regulate the law.

  For example, in the apparatus described in Patent Document 1, the air-fuel ratio for each cylinder is estimated using the output of an air-fuel ratio sensor installed at a collecting portion in the exhaust passage. In the device disclosed in Patent Document 1, weighting calculation for each cylinder based on the crank angle is executed using the output of the common air-fuel ratio sensor, and a predetermined correction is made to estimate the air-fuel ratio for each cylinder. .

  However, since the apparatus of Patent Document 1 performs sampling based on the crank angle, there is a possibility that the air-fuel ratio of each cylinder cannot be accurately estimated if the sampling timing is shifted due to rotational fluctuation.

  The device described in Patent Document 2 does not estimate the air-fuel ratio, but in order to suppress the influence of rotational fluctuation when detecting the in-cylinder pressure at the timing based on the crank angle, it uses time synchronization detection together. Yes. Patent Document 2 further discloses that the detection value at a desired crank angle may be interpolated based on a plurality of sampling data obtained at a sufficiently small sampling period.

JP-A-10-009038 JP 2008-2332034 A

  However, when executing the air-fuel ratio interpolation calculation, if this is performed based on the sampling data in the vicinity of the air-fuel ratio peak, the accuracy of the interpolation may deteriorate. This deterioration in accuracy is considered to be particularly noticeable when the interpolation calculation is performed by linear interpolation.

  SUMMARY OF THE INVENTION The present invention aims to solve one or more problems of the prior art, and in particular, a cylinder using an output portion of a collection portion in an exhaust passage or an air-fuel ratio sensor installed downstream of the collection portion. An object is to suppress deterioration in estimation accuracy when another air-fuel ratio is estimated.

One aspect of the present invention is:
Sampling means for performing sampling of the air-fuel ratio at every predetermined crank angle of the internal combustion engine based on a collective part in the exhaust passage of the multi-cylinder internal combustion engine or a detection value of an air-fuel ratio sensor installed downstream of the collective part When,
Time measuring means for measuring the time between the samplings;
Interpolating means for estimating an air-fuel ratio when there is no change when the time between samplings varies, and detecting an abnormality in air-fuel ratio variation between cylinders based on the sampled air-fuel ratio An inter-cylinder air-fuel ratio variation abnormality detection device,
The inter-cylinder air-fuel ratio variation abnormality detecting device further comprises prohibiting means for prohibiting execution of the interpolation means at a sampling interval including a peak of the output waveform of the air-fuel ratio.

  In the present invention, the sampling means is emptied for each predetermined crank angle of the internal combustion engine based on the collection portion in the exhaust passage of the multi-cylinder internal combustion engine or the detection value of the air-fuel ratio sensor installed downstream of the collection portion. Perform sampling of the fuel ratio. The time measuring means measures the time between the samplings. The interpolating means estimates the air-fuel ratio when there is no fluctuation when the time between samplings fluctuates. The prohibiting means prohibits the interpolation means from executing at a sampling interval including the apex of the output waveform of the air-fuel ratio.

  Thus, in the present invention, when the time between samplings varies, the interpolation means estimates the air-fuel ratio when there is no such variation, while at the sampling interval including the apex of the output waveform of the air-fuel ratio, Since the prohibiting unit prohibits the execution of the interpolating unit, it is possible to suppress deterioration in accuracy due to the interpolation calculation based on the sampling data in the vicinity of the peak of the air-fuel ratio.

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. It is a graph showing the relationship between the change of the air fuel ratio in case the rotation fluctuation has arisen, and detected A / F value. It is a flowchart for demonstrating the flow of the process which concerns on the control which detects the air-fuel ratio variation abnormality between cylinders. It is a graph which shows the relationship between the detected A / F value, the estimated A / F value, and the true A / F value when the rotation fluctuation occurs at the sampling interval including the peak of the output waveform.

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

  FIG. 1 is a schematic view of an internal combustion engine (engine) 10 according to an embodiment of the present invention. As shown in the drawing, the engine 10 burns a fuel / air mixture in a combustion chamber 14 formed in the engine 10 including the cylinder block 12, and reciprocates the piston in the combustion chamber 14 to generate power. Occur. The engine 10 is a one-cycle four-stroke engine. The engine 10 is a multi-cylinder internal combustion engine for automobiles, and more specifically, an in-line four-cylinder spark ignition internal combustion engine, that is, a gasoline engine. Here, the engine 10 is mounted on a vehicle. However, the internal combustion engine to which the present invention is applicable is not limited to this, and the number of cylinders and the type are not particularly limited as long as they are multi-cylinder internal combustion engines having two or more cylinders.

  Although not shown, the cylinder head of the engine 10 is provided with an intake valve that opens and closes an intake port and an exhaust valve that opens and closes an exhaust port for each cylinder. Each intake valve and each exhaust valve are opened and closed by a camshaft. A spark plug 16 for igniting the air-fuel mixture or fuel in the combustion chamber 14 is attached to the top of the cylinder head for each cylinder.

  The intake port of each cylinder is connected to a surge tank 20 that is an intake air collecting chamber via a branch pipe 18 for each cylinder. An intake pipe 22 is connected to the upstream side of the surge tank 20, and an air cleaner 24 is provided at the upstream end of the intake pipe 22. An air flow meter 26 for detecting the intake air amount and an electronically controlled throttle valve 28 are incorporated in the intake pipe 22 in order from the upstream side. An intake passage 30 is substantially formed by the intake port, the branch pipe 18, the surge tank 20 and the intake pipe 22.

  A fuel injection valve (injector) 32 that injects fuel into the intake passage, particularly into the intake port, is provided for each cylinder. The fuel injected from the injector 32 is mixed with intake air to form an air-fuel mixture, which is sucked into the combustion chamber 14 when the intake valve is opened, compressed by the piston, and ignited and burned by the spark plug 16. .

  On the other hand, the exhaust port of each cylinder is connected to the exhaust manifold 34. The exhaust manifold 34 includes a branch pipe 34a for each cylinder forming an upstream portion thereof, and an exhaust collecting portion 34b forming a downstream portion thereof. The exhaust collecting portion 34b is a confluence of exhaust from the plurality of branch pipes 34a. An exhaust pipe 36 is connected to the downstream side of the exhaust collecting portion 34b. An exhaust passage 38 is formed by the exhaust port, the exhaust manifold 34 and the exhaust pipe 36. A catalytic converter 40 including a three-way catalyst is attached to the exhaust pipe 36. This catalytic converter 40 forms an exhaust purification device. Note that the catalytic converter 40 has NOx, which is a harmful component in the exhaust, when the air-fuel ratio (exhaust air-fuel ratio) A / F of the inflowing exhaust is near the stoichiometric air-fuel ratio (stoichiometric, for example, A / F = 14.6). It functions to purify HC and CO simultaneously.

  A pre-catalyst sensor 42 and a post-catalyst sensor 44 for detecting the exhaust air-fuel ratio are installed on the upstream side and the downstream side of the catalytic converter 40, respectively. The pre-catalyst sensor 42 and the post-catalyst sensor 44 are installed in the exhaust passage at positions immediately before and immediately after the catalytic converter 40, and output signals based on the oxygen concentration in the exhaust. The post-catalyst sensor 44 may not be provided.

  Various actuators including the spark plug 16, the throttle valve 28, and the injector 32 described above are electrically connected to an electronic control unit (ECU) 50. The ECU 50 is configured to substantially perform various functions as various control means (control device) and various detection means (detection unit) in the engine 10. The ECU 50 includes a CPU (not shown), a storage device including a ROM and a RAM, an input / output port, and the like. In addition to the air flow meter 26, the pre-catalyst sensor 42, and the post-catalyst sensor 44, the ECU 50 detects a crank angle sensor 52 for detecting the crank angle of the internal combustion engine 10 and an accelerator opening as shown in the figure. Various sensors including an accelerator opening sensor 54 for detecting the engine coolant and a water temperature sensor 56 for detecting the engine coolant temperature are electrically connected via an A / D converter (not shown). The ECU 50 controls various actuators including the ignition plug 16, the throttle valve 28, and the injector 32 so as to obtain a desired output based on outputs and / or detection values from various sensors, and performs ignition timing, fuel injection amount, Controls fuel injection timing, throttle opening, etc.

  As will be described in detail later, the engine 10 is provided with an inter-cylinder air-fuel ratio variation abnormality detecting device, and the ECU 50 substantially functions as sampling means, time measuring means, interpolation means, and prohibiting means.

  The throttle valve 28 is provided with a throttle opening sensor (not shown), and an output signal from the throttle opening sensor is sent to the ECU 50. The ECU 50 normally feedback-controls the opening (throttle opening) of the throttle valve 28 to an opening determined according to the accelerator opening.

  The ECU 50 detects the amount of intake air per unit time, that is, the amount of intake air, based on the output signal from the air flow meter 26. The ECU 50 detects the load of the engine 10 based on at least one of the detected accelerator opening, throttle opening, and intake air amount.

  The ECU 50 detects the crank angle based on the crank pulse signal from the crank angle sensor 52. The ECU 50 normally uses the data including a program, a map, or a function stored in advance in the storage device based on the intake air amount and the engine rotation speed, that is, the engine operating state. ) Is set. Based on the fuel injection amount, fuel injection from the injector 32 is controlled.

  As shown in FIG. 2, the pre-catalyst sensor 42 is a so-called wide-range air-fuel ratio sensor, and can continuously detect an air-fuel ratio over a relatively wide range. The pre-catalyst sensor 42 outputs a voltage signal having a magnitude proportional to the detected exhaust air-fuel ratio. On the other hand, the post-catalyst sensor 44 is a so-called O2 sensor and has a characteristic that the output value changes suddenly at the stoichiometric boundary. Generally, when the exhaust air-fuel ratio is leaner than stoichiometric, the output voltage Vr of the post-catalyst sensor is lower than the stoichiometric equivalent value Vrefr. When the exhaust air-fuel ratio is richer than stoichiometric, the output voltage Vr of the post-catalyst sensor is higher than the stoichiometric equivalent value Vrefr. Get higher.

  The catalytic converter 40 includes a three-way catalyst, and as described above, NOx, HC and CO, which are harmful components in the exhaust gas, are simultaneously purified when the air-fuel ratio A / F of the exhaust gas flowing into the catalyst converter 40 is near the stoichiometric range. Has the function of During normal operation of the engine 10, the ECU 50 executes air-fuel ratio feedback control (stoichiometric control) for controlling the air-fuel ratio of the exhaust gas flowing into the catalytic converter 40 in the vicinity of the stoichiometric. This air-fuel ratio feedback control controls the air-fuel ratio (specifically, the fuel injection amount) of the air-fuel mixture so that the exhaust air-fuel ratio detected by the pre-catalyst sensor 42 and the post-catalyst sensor 44 matches a predetermined target air-fuel ratio. Is done by doing. This air-fuel ratio feedback control is performed using the same control amount for all cylinders. The target air-fuel ratio is stoichiometric, but may be another value.

  For example, in some cylinders (especially one cylinder) of all cylinders, a failure of the injector 32 or the like may occur, and variations in air-fuel ratio (imbalance) may occur between the cylinders. For example, due to the stuck open or poor closing of the injector 32, the fuel injection amount of the # 1 cylinder becomes larger than the fuel injection amounts of the other # 2, # 3, and # 4 cylinders, and the air-fuel ratio of the # 1 cylinder is different from the other #. This is a case where the air-fuel ratio of the second, # 3, and # 4 cylinders deviates to the rich side. On the other hand, the closed injection or poor valve opening of the injector 32 causes the fuel injection amount of the # 1 cylinder to be smaller than the fuel injection amounts of the other # 2, # 3, and # 4 cylinders, and the air-fuel ratio of the # 1 cylinder is reduced. There may be a case where the air-fuel ratio of the other # 2, # 3, and # 4 cylinders is larger than the air-fuel ratio and shifts to the lean side.

  Even at this time, if the degree of imbalance is small at this time, it can be absorbed by the air-fuel ratio feedback control, and harmful components in the exhaust can be purified by the catalyst, so that exhaust emissions are not affected and there is no particular problem. However, when the degree of imbalance becomes large, exhaust emission is deteriorated, which becomes a problem. Therefore, such an unhealthy operation of the intake system or the fuel supply system (for example, open and closed sticking of the injector 32 and signs thereof), while maintaining normal driving operation, the variation in air-fuel ratio between cylinders is abnormal. It can be detected as Therefore, in the present embodiment, a process for detecting an abnormality in air-fuel ratio variation between cylinders is implemented.

FIG. 3 shows the change in the air-fuel ratio when the variation in air-fuel ratio between cylinders occurs. The vertical axis represents the air-fuel ratio (A / F), and the leaner the air goes upward. The horizontal axis is real time. Sampling is performed at equal crank angle intervals every 90 ° of crank angle. However, when rotation fluctuations occur, the sampling intervals become non-uniform in real time. As a result, the detection A / F value p _k, When a A / F value at the time when you that there is no rotation fluctuation, will deviate from the true A / F value p _0, so that each cylinder There is a risk that the air-fuel ratio of the engine cannot be accurately estimated. Note that the ignition order in the example of FIG. 3 is the order of # 1, # 3, # 4, and # 2 cylinders.

  Hereinafter, control for detecting an abnormality in the air-fuel ratio variation between cylinders will be described with reference to the flowchart of FIG.

First, in step S101, it is determined whether or not a predetermined detection condition suitable for performing abnormality detection is satisfied. This detection condition is satisfied when the following conditions (1) to (5) are all satisfied.
(1) The engine has been warmed up. For example, the warm-up is terminated when the water temperature detected by the water temperature sensor 23 is equal to or higher than a predetermined value.
(2) The pre-catalyst sensor 17 is activated.
(3) The engine is in steady operation.
(4) The stoichiometric control is in progress.
(5) The engine is operating in the detection region.

  If the precondition is not satisfied, the routine is terminated. If the precondition is satisfied, in step S102, the output p of the pre-catalyst sensor 17 (air-fuel ratio sensor) is acquired, that is, sampled. This sampling is repeatedly executed from the sample point corresponding to the predetermined reference mark provided in the crank angle sensor 52 until it is finished for three consecutive sample points (S103). A stand-by is performed (S104).

When the sampling for three consecutive sample points is completed, the times t _k−1 and t _k between the sample points are calculated (S105) and stored in the ECU 50. Then, it is determined whether the absolute value of the difference between the calculated times t _k−1 and t _k between the sample points is larger than a predetermined threshold value a (S106). Processing is returned as not occurring.

If the determination in step S106 is affirmative, that is, if the absolute value of the difference between the calculated times t _k-1 and t _k is greater than a predetermined threshold value a, it is considered that rotational fluctuation has occurred. . In this case, it is next determined whether the rotational fluctuation is locally generated only in a specific crank angle region in one cycle. Specifically, the output p of the pre-catalyst sensor 17 (air-fuel ratio sensor) is acquired or sampled again under the condition that the crank angle is further rotated by 90 ° from the previous sampling time (S107). A time t _{k + 1} between the sample points is calculated (S108). Then, whether or not the difference from the previous value is within ± threshold value b is determined by the following equation (1) (S110). If not, the process is returned.

If affirmative, i.e. the difference between the previous values of the time between sample points is within ± threshold b, the rotational fluctuation was local (i.e. the rotational fluctuation was completed within the cycle and the crank angle rotation The speed is recovering). In this case, it is next determined whether or not the apex of the A / F waveform is between p _k−1 and p _{k + 1} (S111). Specifically, this determination is made by: (i) “p _k −p _k−1 ” is positive and “p _{k + 1} −p _k ” is negative (= there is a peak on the lean side) or (ii) “p _This is performed depending on whether “ _k− p _k−1 ” is negative and “p _{k + 1} −p _k ” is positive (= the peak on the rich side).

If NO in step S111, that is, if there is no apex of the A / F waveform between p _k-1 and p _{k + 1} , then the A / F value p _kbar when there is no rotation fluctuation is obtained. Is estimated by linear interpolation (S112). This estimation calculation is performed by the following equation (2).

Here, p _k-1 and p _{k + 1} are A / F values sampled at the elapse of sampling intervals t _k-1 and t _{k + 1} , respectively. Then, the calculated A / F value p _kbar is substituted for the A / F value p _k when the rotational fluctuation has occurred (S113), and the process is returned.

On the other hand, if the determination in step S111 is affirmative, that is, if there is an apex of the A / F waveform between p _k-1 and p _{k + 1} , steps S112 and S113 are skipped and the process is returned. In this case, the previously measured A / F value p _k is held as it is.

The A / F values p _k−2 , p _k−1 , p _k , and p _{k + 1} obtained or calculated in this way are used for detecting the air-fuel ratio variation between cylinders. That is, using the acquired or calculated A / F values p _k-2 , p _k-1 , p _k , p _{k + 1} , weighting calculation for each cylinder based on the crank angle is executed, and a predetermined correction is applied. Then, the air-fuel ratio for each cylinder is estimated and compared with a predetermined threshold value, and whether or not there is an abnormality in the air-fuel ratio variation is determined for each cylinder.

As described above, in the present embodiment, based on the detection value of the pre-catalyst sensor 17 (air-fuel ratio sensor) installed in the exhaust passage of the multi-cylinder internal combustion engine or downstream of the collective portion. Air-fuel ratio sampling is executed for each predetermined crank angle (S102, S104, S107, S108). When the time t _k−1 , t _k , t _{k + 1} between samplings fluctuates, the air-fuel ratio when there is no such fluctuation is estimated by interpolation (S112), while the output waveform of the air-fuel ratio In the sampling interval including the vertices (S111), execution of the interpolation calculation is prohibited.

For example, as shown in FIG. 5, if an interpolation operation by linear interpolation is executed at a sampling interval t _{k to} t _{k + 1} that includes the apex of the output waveform of the air-fuel ratio, an estimation calculated as a result of this interpolation operation The A / F value p _kbar greatly deviates from the true A / F value p ₀ . On the other hand, in general, at sampling intervals including the apex of the output waveform of the air-fuel ratio, detection is often performed due to the fact that the slope of the waveform (or the absolute value of the differential value of the detected value) decreases near the apex. The difference between the A / F value p _k and the true A / F value p ₀ is considered to be relatively small. Therefore, in such a case, it can be considered that the estimation accuracy is higher when the interpolation calculation is prohibited and the detected A / F value _pk is employed as it is.

  As described above, in the present embodiment, when the time between samplings varies, the air-fuel ratio in the case where there is no such variation is estimated by interpolation calculation, while determining whether the apex of the output waveform of the air-fuel ratio is included, Since the execution of the interpolation calculation is prohibited at the sampling interval including the apex, it is possible to suppress deterioration in accuracy due to the interpolation calculation based on the sampling data in the vicinity of the peak of the air-fuel ratio.

As mentioned above, although this invention was demonstrated based on embodiment, this invention accepts other embodiment. For example, in the above embodiment, when the time between samplings fluctuates, execution of the interpolation calculation is prohibited and the detected A / F value _pk is employed as it is at the sampling interval including the apex of the output waveform of the air-fuel ratio. However, instead of such a configuration, at the sampling interval including the apex of the output waveform of the air-fuel ratio, the interpolation operation by the linear interpolation, that is, the interpolation using the linear function is prohibited, while the interpolation operation by the quadratic function is performed. This may be executed to estimate the A / F value p _kbar when there is no rotational fluctuation. In this case, the estimation calculation can be performed by the following equation (3).

Here, a, b and c are constants, and the detected A / F values p _k−1 , p _k and p _{k + 1} sampled when the sampling intervals t _k−1 , t _k and t _{k + 1} have elapsed. Can be obtained by substituting into equation (3) and solving the simultaneous equations.

  In the sampling of the A / F value, an average value of a plurality of cycles may be adopted. Further, the present invention can be applied to a multi-cylinder engine having two or more cylinders of various types, such as a port injection type engine, an in-cylinder injection type engine, an engine using gas as fuel, and the like. It can also be applied to. The present invention can be suitably applied to an engine in which exhaust from a plurality of cylinders is measured by a common air-fuel ratio sensor. For example, the present invention is applied to a V-type engine in which exhaust from two banks is introduced into a collecting portion provided for each bank. Can also be suitably applied.

  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.

10 Internal combustion engine
32 Injector 40 Catalytic converter 42 Pre-catalyst sensor 44 Post-catalyst sensor 52 Crank angle sensor 54 Accelerator opening sensor

Claims (1)

Sampling means for performing sampling of the air-fuel ratio at every predetermined crank angle of the internal combustion engine based on a collective part in the exhaust passage of the multi-cylinder internal combustion engine or a detection value of an air-fuel ratio sensor installed downstream of the collective part When,
Time measuring means for measuring the time between the samplings;
Interpolating means for estimating an air-fuel ratio when there is no change when the time between samplings varies, and detecting an abnormality in air-fuel ratio variation between cylinders based on the sampled air-fuel ratio An inter-cylinder air-fuel ratio variation abnormality detection device,
An inter-cylinder air-fuel ratio variation abnormality detecting device further comprising prohibiting means for prohibiting execution of the interpolating means at a sampling interval including an apex of the output waveform of the air-fuel ratio.

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