JP2009002281A - Intake air amount detection device - Google Patents

Abstract

An accurate intake air amount value with little response delay and error is detected.
Data processing for removing a low-amplitude frequency component is performed on data of a difference ΔG between a detected intake air amount Ga detected by an air flow meter and an estimated intake air amount Gae based on intake pressure. Then, the difference data after the data processing is added to the estimated intake air amount Gae data to calculate the final intake air amount data. It is possible to detect the value of the intake air amount with less response delay and error than simply making the air flow meter output. Further, unlike the low-pass filter, since the low amplitude component is removed, a high-frequency component reflecting the original intake air amount can be included in the final calculation of the intake air amount, and an accurate intake air amount can be detected.
[Selection] Figure 5

Description

  The present invention relates to an intake air amount detection device for detecting an intake air amount of an internal combustion engine.

  In an internal combustion engine, particularly an automobile gasoline engine, for example, an air-fuel ratio is controlled by adjusting a fuel supply amount with respect to an intake air amount in order to operate an exhaust system catalyst with high efficiency. The detection or measurement of the intake air amount is fundamental to engine control. As such an intake air amount detection device, a hot wire type air flow meter is known. Since the engine has an intake pulsation based on the reciprocating motion of the piston, the output of the air flow meter inevitably also pulsates.

  In addition to pulsation due to intake pulsation, high-frequency noise components are added to the output of the air flow meter. This noise component is due to external factors such as changes in the temperature and pressure of the intake air and changes in the amount of dust in the intake air. That is, the output of the air flow meter is obtained by adding a noise component that vibrates at a high frequency around this to the median value corresponding to the amount of intake air to the original engine itself. Air flow meters are very sensitive to external factors. As the amount of intake air increases, external factors also increase, so the vibration of noise components increases. Therefore, the vibration of the noise component is larger in the large displacement engine than in the small displacement engine.

  By the way, if the air flow meter output that vibrates at a high frequency is used as it is for various controls such as air-fuel ratio control, the control cannot be performed stably. Therefore, conventionally, a high-frequency component is removed from the air flow meter output by using a low-pass filter (see, for example, Patent Document 1) or the air flow meter output is used for control. Here, the term “annealing” refers to adding a certain percentage of the output change amount from the previous time to the current time during one sampling period to the previous output value to obtain the current output value. It is known as a method of slowing down the output response and reducing vibration.

Japanese Unexamined Patent Publication No. 7-42599

  When the air flow meter output is adjusted, the movement of the output becomes slow. Therefore, although vibration can be suppressed, it cannot follow the actual change in the intake air amount, and the absolute value error may increase. In addition, since both the median value of the air flow meter output and the noise component are made, if the noise component is large, especially in the case of a large displacement engine, if the air flow meter output itself is attempted to be within the allowable range. The degree of annealing must be increased, response delay becomes more prominent, and the error increases.

  On the other hand, the high-frequency vibration included in the air flow meter output includes not only the noise component but also the median value reflecting the original intake air amount although it is in a very narrow frequency band. If the high-frequency component is uniformly removed by the low-pass filter, the median value is also removed, which hinders detection of the original intake air amount.

  Accordingly, the present invention has been made in view of such circumstances, and an object thereof is to provide an intake air amount detection device capable of detecting an accurate intake air amount value with little response delay and error. .

According to the first aspect of the present invention,
An intake air amount detection device for detecting an intake air amount of an internal combustion engine,
An air flow meter provided in the intake passage;
An intake pressure sensor provided in the intake passage;
Estimating means for estimating an intake air amount based on the intake pressure detected by the intake pressure sensor;
Differential data acquisition means for acquiring data of the difference between the two based on each data of the detected intake air amount detected by the air flow meter and the estimated intake air amount estimated by the estimation means;
Data processing execution means for executing data processing for removing the low amplitude frequency component and leaving the high amplitude frequency component for the difference data;
An intake air amount detection device comprising: intake air amount calculation means for calculating final intake air amount data by adding difference data after the data processing to the estimated intake air amount data Provided.

  According to this, first, the intake air amount is estimated based on the intake pressure detected by the intake pressure sensor. The output of the intake pressure sensor has far less noise components that vibrate at high frequencies than the output of the air flow meter. Therefore, the value of the estimated intake air amount estimated based on the intake pressure has a property close to the median value of the detected intake air amount. Therefore, the value of the estimated intake air amount is used as a basic value when calculating the final intake air amount. Next, data processing is performed on the difference data between the detected intake air amount and the estimated intake air amount so as to remove the low amplitude frequency component and leave the high amplitude frequency component. Instead of removing high-frequency components as in the conventional low-pass filter, low-amplitude components are removed. In this way, since a high-amplitude component remains as it is even at a high frequency, a high-frequency component reflecting the original intake air amount can be included in the final calculation of the intake air amount. Since the difference data after such data processing is added to the estimated intake air amount data to calculate the final intake air amount data, it is possible to detect an accurate intake air amount with little response delay and error. .

According to a second aspect of the present invention, in the first aspect,
The data processing execution means includes
Fourier transform execution means for performing Fourier transform on the difference data;
Filtering execution means for performing filtering such that low-amplitude data is removed and high-amplitude data is left for the data after the Fourier transform;
Inverse Fourier transform execution means for executing inverse Fourier transform on the filtered data and calculating difference data after the data processing is provided.

  According to this, the difference data represented by the time-intake air amount system is replaced with the frequency-amplitude system by executing the Fourier transform. Next, by executing filtering, the low-amplitude frequency component is removed from the difference data after the Fourier transform, and the high-amplitude frequency component is left. Thereby, low-amplitude data corresponding to the noise component is removed. Next, by executing the inverse Fourier transform, the difference data represented in the frequency-amplitude system is returned to the original time-intake air amount system. In this way, differential data from which noise components have been removed can be suitably obtained.

According to a third aspect of the present invention, in the second aspect,
The filtering execution means executes filtering by removing data having an amplitude equal to or smaller than a predetermined value from the data after the Fourier transform and leaving data having an amplitude larger than the predetermined value.

  The predetermined value as the filtering threshold can be set in advance through experiments or the like so as to remove noise components and leave only necessary components. By performing filtering with the predetermined value set in this way as a boundary, an accurate value of the intake air amount corresponding to the actual intake air amount can be detected.

According to a fourth aspect of the present invention, in the second aspect,
The filtering execution means determines a frequency band in which data should be left based on an engine rotation speed, leaves data in the determined frequency band, and executes filtering by removing other data. And

  The frequency band in which the amplitude value increases changes according to the engine rotation speed, and there exists a specific frequency band in which the amplitude value increases for a certain engine rotation speed. Therefore, if the relationship between the engine rotation speed and the natural frequency band is determined in advance through experiments or the like, the frequency band to be left can be determined from the engine rotation speed using this relationship.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects,
EGR means for circulating a part of the exhaust gas to the intake passage is provided, and the EGR means controls the EGR gas flow rate so that the actual EGR rate matches the target EGR rate determined based on the engine operating state. Having gas flow control means,
The estimation means calculates the total gas amount sucked into the combustion chamber based on the intake pressure, and subtracts a value obtained by multiplying the total gas amount by the target EGR rate from the total gas amount to thereby estimate the intake air. It is characterized by calculating the quantity.

  As a result, the remaining intake air amount obtained by subtracting the EGR gas amount from the total gas amount can be estimated, and an accurate intake air amount can be detected in consideration of EGR.

  According to the present invention, an excellent effect that an accurate intake air amount value with little response delay and error can be detected is exhibited.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic system diagram of an internal combustion engine according to an embodiment of the present invention. The internal combustion engine (engine) 10 of this embodiment is a compression ignition internal combustion engine for automobiles, that is, a diesel engine, and is configured as a multi-cylinder engine, particularly an in-line four-cylinder engine. 11 is an intake manifold communicated with the intake port, 12 is an exhaust manifold communicated with the exhaust port, and 13 is a combustion chamber in the cylinder. In the present embodiment, fuel supplied from a fuel tank (not shown) to the high pressure pump 17 is pumped to the common rail 18 by the high pressure pump 17 and accumulated in a high pressure state, and the high pressure fuel in the common rail 18 is injected into the injector (fuel injection valve). ) 14 is directly injected into the combustion chamber 13. Exhaust gas from the engine 10 passes from the exhaust manifold 12 through the turbocharger 19 and then flows into the exhaust passage 15 downstream thereof. After being purified as described later, the exhaust gas is discharged to the atmosphere. In addition, as a form of a diesel engine, it is not restricted to the thing provided with such a common rail type fuel injection device.

  An air cleaner 20 is provided at the upstream end of the intake passage 21 through which intake air is circulated, and an air flow meter 22 is provided on the downstream side in the vicinity of the air cleaner 20. The air flow meter 22 is a sensor for directly detecting the amount of intake air, and specifically outputs a signal corresponding to the flow rate of intake air (fresh air) passing through the air flow meter 22. The air flow meter 22 of the present embodiment is a hot wire type, but may be other types. On the downstream side of the air flow meter 22, a turbocharger 19, an intercooler 23, and a throttle valve 24 are provided in this order from the upstream side. The throttle valve 24 is of an electronic control type and includes an actuator such as a servo motor that drives the valve and a sensor that detects the valve opening. The intake manifold 11 constitutes the downstream end of the intake passage 21. The intake manifold 11 has an upstream portion serving as a collecting portion, and a downstream portion serving as a branch portion that branches from the collecting portion to each intake port of each cylinder.

  The turbocharger 19 of this embodiment includes a variable vane that adjusts the exhaust flow rate to the turbine, and a turbo actuator 19A that drives the variable vane. A catalyst 30 is installed in the exhaust passage 15 on the downstream side of the turbocharger 19. The catalyst 30 is composed of an NOx catalyst such as a storage reduction type that purifies NOx in the exhaust gas. It is preferable to additionally provide another exhaust purification device such as a diesel particulate filter (DPF) or an oxidation catalyst.

  Further, the engine 10 is provided with an exhaust gas recirculation device for recirculating a part of the exhaust gas to the intake system, that is, an EGR (Exhaust Gas Recirculation) device 35. The EGR device 35 includes an EGR passage 36 that communicates the exhaust passage 15 (collection portion of the exhaust manifold 12) and the intake passage 21 (collection portion of the intake manifold 11), an EGR valve 37 provided in the EGR passage 36, EGR And an EGR cooler 38 provided on the upstream side of the EGR valve 37 in the passage 36. The EGR valve 37 adjusts the flow rate of the exhaust gas flowing through the EGR passage 36, that is, the EGR gas. The EGR valve 37 is provided with a sensor for detecting the valve opening degree. The EGR cooler 38 cools the EGR gas so as to increase the flow rate of the EGR gas returned to the intake system.

  An electronic control unit (hereinafter referred to as ECU) 100 is provided as a control means for controlling the entire engine. The ECU 100 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like. The ECU 100 controls the injector 14, the high pressure pump 17, the throttle valve 24, the EGR valve 37, the turbo actuator 19 </ b> A, and the like so that desired engine control is executed based on detection values of various sensors. Sensors connected to the ECU 100 include the air flow meter 22, the throttle valve opening sensor, and the EGR valve opening sensor, the crank angle sensor 26 that detects the crank angle of the engine 10, and the accelerator that detects the accelerator opening. An opening sensor 27 and a common rail pressure sensor 28 for detecting the fuel pressure in the common rail 18 (common rail pressure) are included. The ECU 100 constantly calculates the rotational speed of the engine 10 based on the output of the crank angle sensor 26.

  The ECU 100 controls the amount of fuel injected from the injector 14 based on the engine operating state (mainly rotational speed and accelerator opening). Further, the ECU 100 controls the EGR valve 37 and the throttle valve 24 so that the ratio of the EGR gas amount in the total gas amount sucked into the combustion chamber 3, that is, the actual EGR rate becomes a predetermined target EGR rate. To do. Further, the ECU 100 controls the high pressure pump 17 so that the actual common rail pressure detected by the common rail pressure sensor 28 becomes a predetermined target common rail pressure. The ECU 100 also controls the turbo actuator 19A based on the engine operating state (mainly rotational speed and accelerator opening) to control the intake pressure or the supercharging pressure.

  An intake pressure sensor 31 and an intake air temperature sensor 32 for detecting the pressure and temperature of the intake gas inside the intake manifold 11 are installed in the collective portion of the intake manifold 11, and the intake air pressure sensor 31 and the intake air temperature sensor 32 are also provided. It is connected to ECU100. The intake pressure sensor 31 and the intake air temperature sensor 32 output signals corresponding to the pressure and temperature of the intake gas to the ECU 100, respectively.

  The downstream end of the EGR passage 36 is connected to the intake passage 21 located between the throttle valve 24 and the intake pressure sensor 31 and the intake air temperature sensor 32. Therefore, the EGR gas is returned to the downstream side of the throttle valve 24 and the upstream side of the intake pressure sensor 31 and the intake air temperature sensor 32. The intake pressure sensor 31 and the intake air temperature sensor 32 have the EGR gas in the intake air (fresh air). The pressure and temperature of the intake gas after mixing are detected.

  In the exhaust passage 15, an air-fuel ratio sensor 40 for detecting the air-fuel ratio A / F of the exhaust gas flowing into the NOx catalyst 30 is installed upstream of the NOx catalyst 30, and this air-fuel ratio sensor 40 is also the ECU 100. It is connected to the. The air-fuel ratio sensor 40 is used, for example, to estimate the amount of NOx stored in the NOx catalyst 30, and is further used to determine the timing of a rich spike for releasing the stored NOx from the NOx catalyst 30. Various other uses and purposes of the air-fuel ratio sensor 40 are possible. The air-fuel ratio sensor 40 is also referred to as an oxygen sensor or an oxygen concentration sensor, and outputs a current signal corresponding to the oxygen concentration of the exhaust gas. The value of this current signal is converted into an air-fuel ratio by the ECU 100. The air-fuel ratio sensor 40 can continuously detect a wide range of air-fuel ratios corresponding to an air-fuel ratio region (for example, about A / F = 20 to 60) in which the engine operates.

  As other sensors, it is also preferable to provide an exhaust temperature sensor for detecting the exhaust temperature, a NOx sensor for detecting the NOx concentration of the exhaust gas, or the like.

  Next, the intake air amount detection device according to the present embodiment will be described.

  As described above, the output value of the air flow meter 22 is a value obtained by adding a noise component that vibrates at a high frequency around this to the median value corresponding to the original intake air amount. This is illustrated in FIG. The solid line indicates the intake air amount (fresh air amount) Ga converted from the output value of the air flow meter 22, and the broken line indicates the median value Gac. Ga is the value of the intake air amount detected by the air flow meter 22, and is hereinafter referred to as “detected intake air amount”. What is necessary and desirable for the control is not the detected intake air amount Ga including noise components but the median value Gac thereof. The detected intake air amount Ga and its median value Gac include a low-frequency pulsation component based on the intake pulsation.

  Conventionally, in order to remove high-frequency noise components from the air flow meter output, a low-pass filter has been used or the air flow meter output has been provided. However, when annealing is performed, the responsiveness of the resulting value is degraded and the absolute value error is increased. In particular, when the noise amplitude is large, the required degree of smoothing increases, and response delay and error further increase. On the other hand, the high-frequency vibration included in the air flow meter output includes not only noise components but also those due to the median value in a very narrow frequency band. Therefore, if the high-frequency component is uniformly removed by the low-pass filter, the high-frequency component due to the median value is also removed, and the intake air amount cannot be accurately detected.

  Therefore, in the present embodiment, in order to remove the noise component from the detected intake air amount Ga and extract only the median value Gac, the following processing is executed.

  With reference to FIG. 3, a procedure of intake air amount detection processing executed by ECU 100 will be schematically described. First, the ECU 100 estimates the intake air amount based on the intake pressure detected by the intake pressure sensor 31 (step S101). The intake air amount estimated in this way is hereinafter referred to as an “estimated intake air amount” and is represented by a symbol Gae.

  The intake pressure sensor 31 detects a sufficiently equalized gas pressure in the intake passage 21, particularly in the collection portion of the intake manifold 11, and is not easily influenced by external factors that cause noise in the air flow meter output. Therefore, the output of the intake pressure sensor 31 has much less noise component than the output of the air flow meter, and the estimated intake air amount Gae has a property close to the median value Gac of the detected intake air amount Ga. Therefore, this estimated intake air amount Gae is used as a basic value of the intake air amount to be finally detected.

  Next, the ECU 100 acquires difference data between the detected intake air amount Ga detected by the air flow meter 22 and the estimated intake air amount Gae (step S102). That is, each data of the detected intake air amount Ga and the estimated intake air amount Gae during a predetermined time is sampled at a predetermined sampling interval, and the difference between the two sampling data at the same timing is calculated for all the sampling timings. The Thus, a plurality of difference data for each sampling timing is obtained.

  Next, the ECU 100 executes data processing for removing the low-amplitude frequency component and leaving the high-amplitude frequency component from the difference data (steps S103 to S105). For this data processing, various frequency analysis methods can be used. In this embodiment, a method based on Fourier analysis is adopted as a preferred example. Although details will be described later, first, the ECU 100 performs a Fourier transform on the difference data (step S103). Then, the difference data expressed in the time-intake air amount system is replaced with the frequency-amplitude system. Next, the ECU 100 performs filtering so as to remove low-amplitude data and leave high-amplitude data from the Fourier-transformed data (step S104). Thereafter, ECU 100 performs inverse Fourier transform on the filtered data (step S105). Thereby, the difference data represented in the frequency-amplitude system is returned to the original time-intake air amount system. Thereby, differential data after data processing is acquired.

  Finally, the ECU 100 adds the difference data after the data processing to the estimated intake air amount Gae, that is, restores the detected intake air amount Ga, and calculates final intake air amount data (step S106). This final intake air amount data indicates the value of the intake air amount at each sampling timing to be finally detected.

  Next, the above intake air amount detection process will be described in detail.

  First, the estimation of the intake air amount Gae in step S101 will be described. This estimation is executed by the ECU 100 at each sampling timing according to the procedure shown in FIG.

  In the first step S201, the actually detected values of the engine speed Ne and the accelerator opening degree Ac are acquired. Next, in step S202, the value of the fuel injection amount Q as an instruction value to be injected next time is determined according to a predetermined map M1 (which may be a function, the same applies hereinafter) based on the acquired engine speed Ne and accelerator opening degree Ac. Is done.

  In step S203, the target EGR rate EGRtrg is determined according to a predetermined map M2 based on the acquired engine rotation speed Ne and the determined fuel injection amount Q. Next, in step S204, based on the target EGR rate EGRtrg, a target EGR valve opening EVtrg and a target throttle opening THtrg, which are target openings of the EGR valve 27 and the throttle valve 24, are determined according to a predetermined map (not shown). When determining the target EGR valve opening degree EVtrg and the target throttle opening degree THtrg, in addition to the target EGR rate EGRtrg or instead of the target EGR rate EGRtrg, other engine operating state quantities (for example, the rotational speed Ne, the accelerator opening degree). Degree Ac) may be used.

  Next, in step S205, the actual opening of the EGR valve 27 and the throttle valve 24, that is, the actual EGR valve opening EV and the actual throttle opening TH are equal to the target EGR valve opening EVtrg and the target throttle opening THtrg, respectively. It is determined whether or not. The actual opening degree of the EGR valve 27 and the throttle valve 24 is detected by opening degree sensors provided respectively.

  If the actual EGR valve opening degree EV and the actual throttle opening degree TH do not match the target EGR valve opening degree EVtrg and the target throttle opening degree THtrg, respectively, the process waits until they match. That is, the system waits while there is a delay in the operation of the EGR valve 27 and the throttle valve 24.

  On the other hand, when the actual EGR valve opening degree EV and the actual throttle opening degree TH coincide with the target EGR valve opening degree EVtrg and the target throttle opening degree THtrg, respectively, it can be considered that the actual EGR rate coincides with the target EGR rate EGRtrg. . In this state, in step S206, the values of the intake pressure Pi and the intake temperature THi detected by the intake pressure sensor 31 and the intake temperature sensor 32 are acquired. In step S207, the acquired intake pressure Pi and intake temperature THi are obtained. Based on the predetermined map M3, the total gas amount Gcyl as an estimated value sucked into the in-cylinder combustion chamber 13 is calculated.

In step S208, an estimated intake air amount Gae is calculated according to the following equation based on the total gas amount Gcyl and the target EGR rate EGRtrg.
Gae = Gcyl × (1-EGRtrg)
When the EGR is being executed, a part of the total gas sucked into the combustion chamber 13 is EGR gas, and the remaining part is intake air (fresh air). Therefore, the estimated intake air amount Gae is calculated by subtracting the value obtained by multiplying the total gas amount Gcyl by the target EGR rate EGRtrg (which can be regarded as being equal to the actual EGR rate), that is, the EGR gas amount from the total gas amount Gcyl. ing. Note that when EGR is not executed, the target EGR rate = 0 (%), so the total gas amount Gcyl becomes the estimated intake air amount Gae as it is.

  Thus, since the estimated intake air amount Gae is calculated and acquired in consideration of EGR, the estimated intake air amount Gae can be accurately calculated. Further, as in step S207, the total gas amount Gcyl and thus the estimated intake air amount Gae are calculated in consideration of the intake air temperature THi, so that the calculation accuracy of the estimated intake air amount Gae can be improved.

  After completing the calculation of the estimated intake air amount Gae as described above, next, acquisition of difference data in step S102 is executed.

  FIG. 5 shows changes in the detected intake air amount Ga, the estimated intake air amount Gae, and the difference between them. Here, the difference is defined as ΔG = Ga−Gae, but may be defined by reverse subtraction.

  As shown in the figure, both the detected intake air amount Ga and the estimated intake air amount Gae change in the same manner in response to changes in the engine operating state. The value of the detected intake air amount Ga detected by the air flow meter 22 includes noise due to external factors and vibrates greatly at a high frequency. On the other hand, the estimated intake air amount Gae estimated from the intake pressure has less noise due to external factors and less high-frequency vibration. The intake pressure sensor 31 is not easily affected by external factors, and the response speed is slightly slower than that of the air flow meter 22. Therefore, the estimated intake air amount Gae estimated based on the intake pressure hardly includes noise due to external factors, and it is difficult to reflect a sudden change or a minute change in the actual intake air amount. The value of the estimated intake air amount Gae may be approximately the median value of the detected intake air amount Ga, but may be offset from the median value of the detected intake air amount Ga as shown in the example due to an estimation error or the like. . Except for this offset point, the value of the estimated intake air amount Gae has a property close to the median value of the detected intake air amount Ga, and in other words, it can be handled as being almost equal to the median value. Note that the values of both the detected intake air amount Ga and the estimated intake air amount Gae include a low-frequency pulsation component based on the intake pulsation.

  Each data of the detected intake air amount Ga and the estimated intake air amount Gae is sampled for a predetermined time and temporarily stored in the memory of the ECU 100. Then, a difference ΔG between them is calculated from the values of the detected intake air amount Ga and the estimated intake air amount Gae at the same sampling timing. When such calculation is performed at each sampling timing, data of a plurality of differences ΔG at all sampling timings during the sampling time is obtained. As shown in the figure, the difference ΔG is a value that vibrates at a high frequency, similar to the detected intake air amount Ga, with the offset value as the center. This difference ΔG includes sudden fluctuations and minute fluctuations that cannot be detected by the intake pressure sensor 31.

  If difference data is obtained by the above, next, the Fourier transformation with respect to difference data in step S103 is performed. In particular, the difference data is discrete data at each sampling timing, and what is performed here is a Fourier transform for the discrete function, that is, a discrete Fourier transform.

The data after execution of the Fourier transform is shown in FIG. As can be seen, the difference data represented in the time-intake air quantity system as shown in FIG. 5 is converted into frequency-amplitude difference data, and the difference data is decomposed into frequency components. Difference data after execution of Fourier transform is broadly divided into frequency components having a large amplitude as shown by dot coating and frequency components having a small amplitude as shown by white. The frequency component having a small amplitude is dispersed in a wide frequency band, and is considered to be noise due to external factors, that is, white noise. This is because vibrations generated by external factors are randomly generated according to the environment and do not have a specific frequency. On the other hand, the frequency component having a large amplitude is caused by the reciprocating motion of the engine, that is, reflects the actual change in the intake air amount, and is considered a necessary component here. This frequency component is found in the lowest level frequency bands F _{1 to} F ₃ and higher specific frequency bands F ₄ and F ₅ .

  Next, the filtering in step S104 is executed. In this filtering, filtering is performed so as to remove frequency component or frequency band data having a small amplitude, and leaving frequency component or frequency band data having a large amplitude. Specifically, a frequency component having an amplitude equal to or smaller than a predetermined value As as shown in white is removed by multiplying by a filtering coefficient 0. For frequency components having an amplitude larger than the predetermined value As as indicated by dot coating, the filtering coefficient 1 is multiplied and left as it is. The predetermined value As, which is a filtering threshold, is set in advance through experiments or the like so as to remove noise components and leave only necessary components. Thereby, suitable filtering can be performed.

  By the way, the frequency band in which the amplitude value increases changes according to the engine rotation speed, and there exists a natural frequency band in which the amplitude value increases with respect to a certain engine rotation speed. Therefore, the following filtering can be executed instead. That is, the relationship between the engine rotational speed and the natural frequency band is examined in advance through experiments or the like, defined by a map or the like, and the frequency band to be left is determined using the relationship from the actual engine rotational speed. Then, filtering is performed to leave the frequency band components to be left and remove the other frequency band components. This also makes it possible to perform suitable filtering.

  When filtering is completed in this way, next, the inverse Fourier transform of step S105 is performed on the filtered data. Then, the frequency-amplitude difference data after filtering is returned to the time-intake air amount system as shown in FIG.

  Finally, in Step S106, the difference data (ΔG ′) after the inverse Fourier transform is added to the estimated intake air amount Gae data, that is, the original detected intake air amount Ga value is restored, and the final intake Data on the amount of air (referred to as Ga ′) is calculated and acquired. Thereby, the final value Ga ′ of the intake air amount at each sampling timing is obtained. Here, the offset component is included in the amplitude of the frequency component remaining after filtering. Therefore, even when there is an offset as shown in FIG. 5, the offset is added when the data of the difference ΔG ′ after the inverse Fourier transform is added to the data of the estimated intake air amount Gae, and the offset is cancelled. The finally obtained intake air amount Ga ′ is a value that is very favorable for use in control and the like, in which vibration is smaller than the original detected intake air amount Ga and takes its median value without delay.

As described above, according to the present embodiment, it is possible to detect the value of the intake air amount with much less delay in response and error than when the air flow meter output is made. Further, since the high-frequency component is not uniformly removed unlike the low-pass filter, the value of the intake air amount can be detected more accurately than in the case of the low-pass filter. That is, in the case of the low-pass filter, even if the amplitude is large, if the component has a high frequency (the component in the frequency band F ₅ (and F ₄ ) in FIG. 6), this may be removed. This means that components based on the reciprocating motion of the original engine, in other words, necessary components reflecting the original intake air amount are removed. In the present embodiment, the component to be removed and the component to be retained are determined based on the magnitude of the amplitude, not the frequency, and the final intake air amount Ga ′ can be detected while leaving such a necessary component. Therefore, it is possible to detect the intake air amount more accurately.

  By the way, in recent years, in the field of diesel engines, an attempt has been made to feedback control the air-fuel ratio, similar to gasoline engines (spark ignition type internal combustion engines). The main reason is improvement of exhaust emission, particularly effective use of exhaust purification devices such as NOx catalyst. In this case, similarly to the gasoline engine, an air-fuel ratio sensor for detecting the air-fuel ratio is provided in the exhaust passage, and the fuel injection amount is feedback controlled so that the air-fuel ratio detected by the air-fuel ratio sensor matches the target air-fuel ratio. Can be considered. Actually, also in the present embodiment, it is conceivable that the air-fuel ratio is feedback controlled by the air-fuel ratio detected by the air-fuel ratio sensor 40.

  However, in the case of a diesel engine, the engine usually operates over a wider air-fuel ratio range (A / F = about 20 to 60) that is leaner than the theoretical air-fuel ratio (A / F = about 14.6). Has been. Air-fuel ratio sensors that can cover this wide range of air-fuel ratios have been developed, but the responsiveness of the sensor, particularly in the high-lean area, is significantly worse, such as 2.5 to 3 times that of the stoichiometric air-fuel ratio. There are drawbacks. Further, since the responsiveness of the sensor differs depending on the air-fuel ratio, the responsiveness becomes uneven when the actual air-fuel ratio change width is large, which also causes hunting. Furthermore, a large absolute value error may occur depending on the emission components (CO, HC, NOx, PM) in the exhaust gas. As described above, problems to be solved still remain in the air-fuel ratio feedback control using the air-fuel ratio sensor.

  Therefore, instead of directly detecting the exhaust air-fuel ratio with the air-fuel ratio sensor, it is conceivable to calculate or estimate the actual air-fuel ratio from the actual fuel injection amount and intake air amount of the engine. In this case, the air-fuel ratio A / F can be calculated as a ratio between the fuel injection amount and the intake air amount (air-fuel ratio = intake air amount / fuel injection amount). The air / fuel ratio calculated in this way is hereinafter referred to as an estimated air / fuel ratio. As the fuel injection amount, an instruction value Q calculated based on the engine operating state as described above can be used. As the intake air amount, for example, a value Ga detected by an air flow meter can be used.

  However, if the detected value Ga of the air flow meter is used as it is, the value constantly vibrates at a high frequency as described above. As a result, the estimated air-fuel ratio value also vibrates in the same manner, and stable control is performed. Can not do.

  Therefore, when the intake air amount Ga ′ detected by the intake air amount detection device according to the present invention is used, since the vibration of the intake air amount Ga ′ is small, the vibration of the estimated air-fuel ratio is also reduced and stable air-fuel ratio control is achieved. It can be performed. Further, since the responsiveness of the intake air amount Ga 'is good, as a result, a highly responsive estimated air-fuel ratio can be obtained. In addition, this is not restricted by the air-fuel ratio value or exhaust emission component. Accordingly, it is possible to realize high-response and high-precision air-fuel ratio estimation and air-fuel ratio control at any air-fuel ratio.

  Further, when an air-fuel ratio sensor is separately provided in the exhaust passage as in this embodiment, the estimated air-fuel ratio is calculated using the intake air amount Ga ′, and this estimated air-fuel ratio is detected by the air-fuel ratio sensor. The failure diagnosis of the air-fuel ratio sensor can also be performed in comparison with the actual air-fuel ratio. In other words, if the difference between the actual exhaust air-fuel ratio and the estimated air-fuel ratio is equal to or greater than a predetermined value, the air-fuel ratio sensor is diagnosed as malfunctioning, and if the difference is smaller than the predetermined value, the air-fuel ratio sensor can be diagnosed as normal.

  As can be seen from these descriptions, an apparatus and method for calculating an estimated air-fuel ratio using the intake air amount detected by the intake air amount detection device according to the present invention, and an apparatus for controlling the air-fuel ratio using this estimated air-fuel ratio. It is also possible to grasp each invention such as an apparatus and a method for performing a failure diagnosis of an air-fuel ratio sensor using this estimated air-fuel ratio.

  As mentioned above, although embodiment of this invention was described, this invention can also take other embodiment. For example, the above embodiment has been applied to a compression ignition type internal combustion engine, but the present invention is also applicable to a spark ignition type internal combustion engine.

  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 is a schematic system diagram of an internal combustion engine according to an embodiment of the present invention. It is a graph which shows the intake air amount detected by the air flow meter, and the median value. It is a flowchart which shows the procedure of an intake air amount detection process. It is a flowchart which shows the calculation procedure of estimated intake air amount. It is a graph which shows transition of a detection intake air amount, an estimated intake air amount, and the difference of both. It is a graph which shows the difference data after Fourier-transform execution.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 13 Combustion chamber 21 Intake passage 22 Air flow meter 24 Throttle valve 31 Intake pressure sensor 35 EGR device 36 EGR passage 37 EGR valve 100 Electronic control unit (ECU)
Ga Detected intake air amount Gae Estimated intake air amount ΔG Difference Ga ′ Final intake air amount As Predetermined value Gcyl Total gas amount

Claims (5)

An intake air amount detection device for detecting an intake air amount of an internal combustion engine,
An air flow meter provided in the intake passage;
An intake pressure sensor provided in the intake passage;
Estimating means for estimating an intake air amount based on the intake pressure detected by the intake pressure sensor;
Differential data acquisition means for acquiring data of the difference between the two based on each data of the detected intake air amount detected by the air flow meter and the estimated intake air amount estimated by the estimation means;
Data processing execution means for executing data processing for removing the low amplitude frequency component and leaving the high amplitude frequency component for the difference data;
An intake air amount detection device comprising: intake air amount calculation means for calculating the final intake air amount data by adding the difference data after the data processing to the estimated intake air amount data. The data processing execution means includes
Fourier transform execution means for performing Fourier transform on the difference data;
Filtering execution means for performing filtering such that low-amplitude data is removed and high-amplitude data is left for the data after the Fourier transform;
The intake air amount detection device according to claim 1, further comprising: an inverse Fourier transform execution unit that performs inverse Fourier transform on the filtered data to calculate difference data after the data processing. The filtering execution means executes filtering by removing data having an amplitude equal to or smaller than a predetermined value from the data after the Fourier transform, and leaving data having an amplitude larger than the predetermined value. 3. The intake air amount detection device according to 2. The filtering execution means determines a frequency band in which data should be left based on an engine rotation speed, leaves data in the determined frequency band, and executes filtering by removing other data. The intake air amount detection device according to claim 2. EGR means for circulating a part of the exhaust gas to the intake passage is provided, and the EGR means controls the EGR gas flow rate so that the actual EGR rate matches the target EGR rate determined based on the engine operating state. Having gas flow control means,
The estimation means calculates the total gas amount sucked into the combustion chamber based on the intake pressure, and subtracts a value obtained by multiplying the total gas amount by the target EGR rate from the total gas amount to thereby estimate the intake air. The intake air amount detection device according to any one of claims 1 to 4, wherein an amount is calculated.

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