JP2008032028A - Intake air quantity estimating device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a problem when starting an engine due to a lack of accurate learning of the atmospheric air pressure in an intake air quantity estimating device for an internal combustion engine for use for estimation of the intake air quantity by computing the intake pipe pressure. <P>SOLUTION: The intake-air quantity estimating device is provided with: an intake pipe pressure computing means for computing the intake pipe pressure (step 105); and an intake air quantity computing means for computing the intake air quantity, based on the computed intake pipe pressure (step 110). When the throttle valve opening is the set opening or more, the atmospheric air pressure to be used in the intake pipe pressure computing means is a corrected atmospheric air pressure corrected by learning when the throttle valve opening is the set opening or more and stored when the engine is stopped. The intake air quantity estimating device is further provided with a guard means for replacing the intake pipe pressure with a guard value when the intake pipe pressure computed by the intake pipe pressure computing means is higher than the guard value (step 106). The guard value based on the corrected atmospheric pressure is compared with the minimum value of the intake pipe pressure computed at the start of the engine, based on the output of an air flow meter. The larger one is taken as the guard value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an intake air amount estimation device for an internal combustion engine.

  In order to perform the air-fuel ratio control, it is necessary to grasp the amount of intake air supplied into the cylinder. Conventionally, the intake air amount is detected by an air flow meter arranged on the upstream side of the throttle valve, or calculated based on the intake pipe pressure detected by a pressure sensor arranged on the downstream side of the throttle valve. It was. However, since the air flow meter and the pressure sensor have a response delay, an accurate intake air amount cannot be detected or calculated during engine transition.

  In order to grasp an accurate intake air amount even during engine transition, it is proposed to calculate the intake pipe pressure Pm based on the throttle valve opening and to estimate the intake air amount mc based on the calculated intake pipe pressure Pm. Has been. In such an estimation of the intake air amount mc, an unrealistic intake pipe pressure Pm higher than the atmospheric pressure Pa may be calculated. In such a case, the calculated intake pipe pressure Pm is replaced with the atmospheric pressure Pa, and the intake air amount mc is estimated.

  In this way, the intake pipe pressure Pm is guarded by the atmospheric pressure Pa. However, since the atmospheric pressure Pa varies depending on the altitude, it is always meaningful to perform the guard processing by the standard atmospheric pressure (101.3 kPa). Absent. For this reason, it is conceivable to detect the current atmospheric pressure used for the guard processing by the pressure sensor, but the reliability of the output of the pressure sensor is not so high due to a response delay or the like. Increase costs.

  Accordingly, it is conceivable that the current atmospheric pressure used for the guard process is corrected by correcting the reference atmospheric pressure (for example, standard atmospheric pressure) with a correction coefficient without using a pressure sensor. For example, the correction coefficient is calculated based on the intake air amount estimated based on the intake pipe pressure calculated based on the throttle valve opening, assuming that the intake air amount estimated based on the output of the air flow meter is a true value. It is decreased when the intake air amount estimated based on the above is exceeded, and is increased when it is below.

  In this way, the correction coefficient is learned and updated, but when the throttle valve opening is below a predetermined value, the amount of intake air decreases and is greatly affected by the aging of the throttle valve and deposits attached to the intake system, At this time, if the above-described correction coefficient learning is performed, there is a high possibility of erroneous learning. Thus, it has been proposed to prohibit learning of the correction coefficient when the throttle valve opening is equal to or smaller than a predetermined value (see, for example, Patent Document 1).

JP-A-6-14689 JP 2002-180877 A

  In general, when the vehicle heads from the lowland to the highland, it is mainly going uphill, and the throttle valve opening tends to be increased to achieve the intended vehicle speed, but when the vehicle heads from the highland to the lowland, Since it is mainly downhill driving and increases the excessive speed, there is little opportunity for the throttle valve opening to be increased. As a result, in the above-described conventional technology, the correction coefficient may not be sufficiently learned for the atmospheric pressure in the lowland immediately after traveling downhill from the highland to the lowland.

  If the throttle valve opening is increased in the subsequent lowland travel, good learning of the correction coefficient is performed, and no particular problem occurs. However, when the engine is stopped immediately after running downhill, an inaccurate correction coefficient is stored, and the current atmospheric pressure calculated using this correction coefficient at the next engine start is actually The engine start is unsuccessful, or even if the engine start is completed, immediately after that, an engine stall occurs or the air-fuel ratio feedback coefficient is corrected to an abnormal value.

  Therefore, an object of the present invention is to calculate the intake pipe pressure downstream of the throttle valve and use the atmospheric pressure (or the correction coefficient for the reference atmospheric pressure) in the intake air amount estimation device for an internal combustion engine used for estimating the intake air amount. If used, this is to improve the engine start-up problem caused by the fact that this correction factor) is not correctly learned.

  An intake air amount estimating device for an internal combustion engine according to claim 1 of the present invention is an intake pipe pressure calculating means for calculating an intake pipe pressure downstream of the throttle valve based on a throttle valve opening and an atmospheric pressure, and the intake pipe Intake air amount calculation means for calculating the intake air amount based on the intake pipe pressure calculated by the pressure calculation means, and the atmospheric pressure used by the intake pipe pressure calculation means is such that the throttle valve opening is A corrected atmospheric pressure that is learned and updated when the engine opening is equal to or greater than a set opening degree and is stored even when the engine is stopped. In the intake air amount estimating device, the intake pipe pressure calculated by the intake pipe pressure calculating means is a guard value. Guard means is provided for replacing the intake pipe pressure with the guard value when the engine pressure is higher. The guard value is based on a value based on the corrected atmospheric pressure and an output of the air flow meter. Characterized in that it is a larger value by comparing the minimum value of the newly calculated the intake pipe pressure from.

  According to the intake air amount estimating apparatus for an internal combustion engine according to the present invention, the atmospheric pressure used in the intake pipe pressure calculating means is learned and updated when the throttle valve opening is equal to or larger than the set opening and stored even when the engine is stopped. The intake air amount estimating device is provided with guard means for replacing the intake pipe pressure with the guard value when the intake pipe pressure calculated by the intake pipe pressure calculating means is higher than the guard value. The value is set to a larger value by comparing the value based on the corrected atmospheric pressure and the minimum value of the intake pipe pressure newly calculated from the start of the engine based on the output of the air flow meter. As a result, even when the stored correction atmospheric pressure is not accurately learned at the time of engine start, the guard value is initially set to the intake pipe pressure calculated based on the output of the air flow meter, Therefore, immediately after the engine is started, the intake pipe pressure calculated by the intake pipe pressure calculating means is abnormally small and the combustion air-fuel ratio becomes excessively lean. Problems such as misfire can be prevented. Further, the minimum value of the intake pipe pressure calculated based on the output of the air flow meter is surely lower than the actual atmospheric pressure, and the guard value is not set exceeding the actual atmospheric pressure.

  FIG. 1 is a schematic diagram showing an internal combustion engine to which an intake air amount estimation device according to the present invention is attached. In the figure, 1 is an engine body, and 2 is a surge tank common to each cylinder. An intake branch pipe 3 communicates the surge tank 2 with each cylinder, and 4 is an intake passage upstream of the surge tank 2. A fuel injection valve 5 is disposed in each intake branch pipe 3, and a throttle valve 6 is disposed immediately upstream of the surge tank 2 in the intake passage 4. Here, the engine intake system (surge tank 2 and intake branch pipe 3) downstream of the throttle valve 6 is referred to as an intake pipe. The throttle valve 6 is not linked to the accelerator pedal, but can be freely set by a drive device such as a step motor. Reference numeral 7 denotes an air flow meter that detects an intake air flow rate upstream of the throttle valve 6 in the intake passage 4. In the engine body 1, 8 is an intake valve, 9 is an exhaust valve, and 10 is a piston.

  In order to set the combustion air-fuel ratio in the internal combustion engine 1 to a desired air-fuel ratio such as a stoichiometric air-fuel ratio, for example, it is necessary to accurately estimate the amount of intake air that has flowed into the cylinder including when the engine is in transition. . The air flow meter 7 can measure the intake air amount relatively accurately when the engine is stationary. However, during engine transition, the output of the air flow meter 7 does not immediately respond to the intake air amount that changes abruptly, making it impossible to accurately measure the intake air amount.

  This intake air amount estimation device estimates the intake air amount by modeling the engine intake system in order to make it possible to accurately grasp the intake air amount even during engine transition.

First, by modeling the throttle valve 6, using the energy conservation law, the momentum conservation law, and the state equation when intake air passes through the throttle valve 6, the current throttle valve passage air amount mt _(i) (G / sec) is expressed by the following equation (1). Including the following expression, the subscript (i) of the variable such as the throttle valve passing air amount indicates the current time, and (i-1) indicates the previous time.

Here, μ _(i) is a flow coefficient, and A _(i) is an opening area (m ³ ) of the throttle valve 6. Of course, when an idle speed control valve (ISC valve) is provided in the engine intake system, the opening area of the ISC valve is added to A _(i) . Each of the flow coefficient and the opening area of the throttle valve is a function of the throttle valve opening TA _(i) (degree), and FIGS. 2 and 3 show maps for the respective throttle valve openings TA. Yes. R is a gas constant, Ta is an intake air temperature (K) upstream of the throttle valve, Pa is an intake passage pressure (kPa) upstream of the throttle valve, and Pm _(i) is an intake pipe downstream of the throttle valve. Pressure (kPa). The function Φ (Pm _(i) / Pa) is expressed by the following equation (2) using the specific heat ratio κ, and FIG. 4 shows a map for Pm / Pa.

Next, the intake valve is modeled. Since the intake air amount mc _(i) (g / sec) supplied into the cylinder changes substantially linearly based on the intake pipe pressure Pm _(i) , it can be expressed by the following equation (3). .

Here, Tm _(i) is the intake air temperature (K) downstream of the throttle valve, and a and b are constants obtained from empirical rules. However, b is a value corresponding to the amount of residual burned gas in the cylinder, and when there is a valve overlap, burned gas flows backward to the intake pipe, so the value of b increases to a degree that cannot be ignored. Accordingly, it is preferable to map the values of a and b so that an accurate intake air amount mc is calculated based on the presence or absence of valve overlap and the engine speed NE. In addition, when there is a valve overlap, when the intake pipe pressure Pm is equal to or higher than a predetermined pressure, the higher the intake pipe pressure, the more significantly the backflow of burned gas decreases. It is preferable to increase the value of a and decrease the value of b.

By the way, since the throttle valve passing air amount mtTA and the intake air amount coincide with each other when the engine is in a steady state, the throttle pressure in which the intake pipe pressure is the intake pipe pressure PmTA in the steady state of the engine in equation (1). The valve passing air amount mtTA is equal to the intake air amount (a · PmTA−b), so that the equation (1) can be rewritten as the following equation (4).

Here, the intake pipe pressure PmTA when the engine is stationary is the throttle valve opening TA _(i) , the engine speed NE _(i) , and the valve overlap size VT ₍ Based on _i) , it can be mapped in advance.

Next, the intake pipe is modeled. Using the intake mass conservation law, the energy conservation law, and the equation of state existing in the intake pipe, the rate of change over time in the ratio between the intake pipe pressure Pm and the intake air temperature Tm downstream of the throttle valve is expressed by the following equation (5). The time change rate of the intake pipe pressure Pm is expressed by the following equation (6). Here, V is the volume (m ³ ) of the intake pipe, and specifically, the total volume of the surge tank 2 and the intake branch pipe 3.

Equations (5) and (6) are discretized to obtain the following equations (7) and (8), respectively, and if the current intake pipe pressure Pm _(i) is obtained by equation (8), 7), the intake air temperature Tm _(i) in the intake pipe at this time can be obtained. In the expressions (7) and (8), the discrete time Δt is the execution interval of the first flowchart (FIGS. 5 and 6) for calculating the current intake air amount mc _(i) , and is, for example, 8 ms.

Next, the first flowchart shown in FIGS. 5 and 6 will be described. This flowchart is executed simultaneously with the completion of the engine start (for example, the engine start can be completed when the engine speed reaches 400 rpm or more). First, in step 101, it is determined whether or not the flag F is 1. This flag F is reset to 0 when the engine is stopped. Initially, the determination in step 101 is denied and the routine proceeds to step 102. In step 102, an initial value Pa of atmospheric pressure is calculated by the following equation (9).
Pa = {K1 · ekpa + (1−K1)} · Pas (9)

  Here, ekpa is a correction coefficient for correcting the reference atmospheric pressure Pas (for example, standard atmospheric pressure 101.3 kPa) to the current atmospheric pressure corresponding to the altitude, which will be described later in detail. The corrected atmospheric pressure (ekpa · Pas) is calculated by directly multiplying the atmospheric pressure Pas. The current correction coefficient ekpa is a value learned and updated by the engine operation before the engine start this time.

Next, at step 103, the initial value Pa of the atmospheric pressure calculated at step 102 is set to the previous intake pipe pressure Pm _(i−1) . At step 104, the flag F is set to 1. Accordingly, in the next execution of this flowchart, the determination in step 101 is affirmed, and only the processing after step 105 described below is performed.

In step 105, the intake pipe pressure Pm _(i) is calculated using equation (8). Equation (8) is the previous intake pipe pressure Pm _(i-1) , the previous throttle valve passing air amount mt _(i-1) , the previous intake air amount mc _(i-1), and the previous intake air pressure. The current intake pipe pressure Pm _(i) is calculated based on the intake air temperature Tm _{(i-1) in the} pipe. As these initial values, Pm _(i-1) is set to the initial value Pa of atmospheric pressure in step 103, and the intake air temperature Ta on the upstream side of the throttle valve is measured and used as Tm _(i-1) . For mt _(i-1) , a value calculated from the equation (1) or (4) using these Pm _(i-1) and Tm _(i-1) is used, and mc _{(i For -1)} , the value calculated by Equation (3) using these Pm _(i-1) and Tm _(i-1) is used.

Next, at step 106, it is determined whether or not the current intake pipe pressure Pm _(i) calculated at step 105 is higher than the guard value Pg. Although the guard value Pg will be described in detail later, this guard process is based on the fact that the intake pipe pressure cannot be higher than the atmospheric pressure. Normally, this determination is denied and the routine proceeds to step 108, where the intake air temperature Tm _{(i) in} the intake pipe at this time is calculated using the equation (7). Next, at step 109, the current throttle valve passing air amount mt _(i) is calculated using the equation (1) or (4). In calculating the throttle valve passing air amount mt _(i) using this equation (1) or (4), the current throttle valve opening TA takes into account the response delay of the throttle valve drive device (step motor). .

Next, at step 110, the current intake air amount mc _(i) is calculated using equation (3). Thereafter, in steps 111 to 114, the current intake pipe pressure Pm _(i) is set to the previous intake pipe pressure Pm _(i-1), and the intake temperature Tm _(i) in the current intake pipe is set to the previous intake pipe pressure. The intake air temperature Tm _(i-1) is set, the current throttle valve passing air amount mt _(i) is the previous throttle valve passing air amount mt _(i-1), and the current intake air amount mc _(i) is the previous time. The intake air amount mc _(i-1) . Thus, the intake air amount mc is sequentially estimated based on the intake pipe pressure Pm that is sequentially calculated simultaneously with the completion of the engine start.

However, the calculated current intake pipe pressure Pm _(i) may become higher than the guard value Pg due to some factor. At this time, the calculated current intake pipe pressure Pm _(i) is an obvious abnormal value, the determination in step 106 is affirmed and the routine proceeds to step 107, where the calculated current intake pipe pressure Pm _(i) is a guard. Replaced by the value Pg.

  The correction coefficient ekpa and the guard value Pg described above are learned and updated, and FIG. 8 is a second flowchart for that purpose. In the second flowchart, the throttle valve passing air amount mt ′ and the intake pipe pressure Pm ′ calculated based on the output of the air flow meter 7 (the above-mentioned ones calculated based on the throttle valve opening with a dash attached to each) Distinguish) is used. Accordingly, first, calculation of the throttle valve passing air amount mt ′ based on the output of the air flow meter 7 will be described.

FIG. 7 shows a cross-sectional model of the air flow meter 7. The air flow meter 7 uses the fact that the amount of heat taken away from the heat wire 7a when the intake air passes around the heat wire 7a changes according to the intake air amount, that is, the amount of air passing through the throttle valve. It is to detect. Thus, based on the output of the air flow meter 7, the throttle valve passage air amount GA _(i) (this map value is given a different symbol in order to distinguish it from the calculated throttle valve passage air amount mt ' _(i) . Can be obtained).

However, in a general air flow meter, a glass layer 7b is provided around the heat wire 7a, and the heat capacity of the glass layer 7b is relatively large. As a result, the output of the air flow meter 7 does not change immediately with respect to the actual change in the amount of air passing through the throttle valve, and a response delay occurs. Considering this delay in response, consider calculating the actual throttle valve passing air amount mt ′ _(i) from the output of the air flow meter.

Assuming that the current temperature of the heat wire 7a is Th, the amount of heat transferred from the heat wire 7a to the glass layer 7b is equal to the amount of heat transferred from the glass layer 7b to the intake air. Therefore, the temperature change amount dTg / dt of the glass layer B Can be expressed as the following formula (10).

Here, A, B, C, and D are the cross-sectional area, length, and resistivity of the heat wire 7a, the heat transfer coefficient between the glass layer 7b and the heat wire 7a, and between the glass layer 7b and the intake air. It is a constant determined according to the heat transfer coefficient of. In Expression (10), during the steady operation, since there is no transfer of heat between the glass layer 7b, the heat ray 7a, and the intake air, the temperature change amount dTg / dt of the glass layer 7b, that is, the right side of Expression (10) Becomes zero, and at this time, the map value GA of the throttle valve passage air amount and the calculated value mt are equal. Under this condition, GA is represented by the temperature Th of the heat ray 7a, the temperature Tg of the glass layer 7b, and the intake air temperature Ta, and the temperature Tg of the glass layer 7b is eliminated in Equation 10 to obtain the following equation (11). be able to.

In Expression (11), α and β are constants determined by the above-described constants A, B, C, and D, and thus the throttle valve passing air mt ′ _(i) is taken into account the response delay of the air flow meter. Based on the current map value GA _(i) of the throttle valve passing air amount based on the current output of the air flow meter 7 and the map value GA _{(i-1) of the} throttle valve passing air amount based on the previous output of the air flow meter 7 Can be calculated.

Next, the second flowchart will be described. Similar to the first flowchart, this flowchart is executed simultaneously with the engine start, and the execution interval is, for example, 8 ms. First, in step 201, it is determined whether or not the current throttle valve opening TA _(i) is larger than the set opening TA1. When this determination is affirmative, in step 202, the throttle valve passing air amount mt _(i) based on the throttle valve opening calculated this time according to the first flowchart is set to the output of the air flow meter calculated by the above equation (11). It is determined whether or not the throttle valve passage air amount mt ′ _{(i) is} larger than the above. In Expression (11), the initial value of GA _(i-1) is set to 0.

When the determination at step 202 is affirmative, the routine proceeds to step 203 where a relatively small predetermined value q is subtracted from the atmospheric pressure correction coefficient ekpa. On the other hand, when the determination at step 202 is negative, the routine proceeds to step 204 where a predetermined value q is added to the atmospheric pressure correction coefficient ekpa. The correction coefficient ekpa is set to 1, for example, at the time of vehicle shipment, and if the determination in step 202 is affirmative, that is, the atmospheric pressure and the throttle valve opening using the formula (1) or (4). When the throttle valve passage air amount mt _(i) calculated based on the above becomes larger than the throttle valve passage air amount mt ′ _(i) calculated based on the output of the air flow meter using the equation (11), the equation (11) Assuming that the atmospheric pressure used for the calculation in 1) or (4) is higher than the actual pressure, the correction coefficient ekpa is decreased. When the throttle valve passing air amount mt _(i) is smaller than the throttle valve passing air amount mt ′ _(i) , the atmospheric pressure used for the calculation in the formula (1) or (4) is lower than the actual pressure. And the correction coefficient ekpa is increased.

  Next, in step 205, the reference atmospheric pressure Pas is multiplied and corrected by the correction coefficient ekpa learned and updated with the throttle valve passing air amount mt 'calculated based on the output of the air flow meter as a true value in this way, and according to the altitude. The present atmospheric pressure Pa that changes is calculated. This atmospheric pressure Pa is used in the first flowchart.

The correction coefficient ekpa is learned and updated only when the determination in step 201 is affirmative, that is, when the throttle valve opening degree TA _(i) is larger than the set opening degree TA1. This is because if the throttle valve opening degree TA _(i) is less than or equal to the set opening degree TA1, the actual amount of air passing through the throttle valve is reduced, which is greatly affected by the time-dependent change of the throttle valve and the deposit deposit on the intake system. The main factor causing the difference between the throttle valve passing air amount mt _(i) calculated based on the throttle valve opening and the throttle valve passing air amount mt ' _(i) calculated based on the output of the air flow meter is the current major factor. This is because it may not be atmospheric pressure. The correction coefficient ekpa learned and updated in this way is stored even when the engine is stopped, and is used for the current atmospheric pressure calculation even during the next operation.

  By the way, when the vehicle heads from the lowland to the highland, there are many occasions when the vehicle travels uphill and the throttle valve opening becomes larger than the set opening TA1, and good learning and updating of the correction coefficient ekpa are performed. However, when heading from high altitude to low altitude, there are few opportunities to go downhill and make the throttle valve opening larger than the set opening TA1, and the correction coefficient ekpa may not be sufficiently learned. Thus, particularly when the vehicle is stopped immediately after traveling downhill from a highland to a lowland, it is highly likely that the correction coefficient ekpa is stored as a value adapted to the atmospheric pressure in the highland.

In general, when the intake pipe pressure Pm _(i) is first calculated based on the throttle valve opening at the start of the engine, the reference atmospheric pressure Pas is used as the atmospheric pressure Pa and the previous intake pipe pressure Pm _(i-1). The corrected atmospheric pressure Pa multiplied by the correction coefficient ekpa stored in is used. However, in this case, in this case, the calculated current intake pipe pressure Pm _(i) is abnormally lower than the actual value, and the intake air amount mc _(i) calculated based on this is abnormally smaller than the actual value. In the fuel injection amount calculated so as to realize the desired air-fuel ratio based on the intake air amount mc _(i) , the actual air-fuel ratio becomes very lean and the estimation of the intake air amount starts at the completion of the engine start. However, immediately after that, an engine stall occurs. Further, when the intake air amount is estimated from the cranking, it is impossible to start the engine.

In the present embodiment, in order to solve such a problem, the atmospheric pressure Pa used for the estimation of the first intake air amount mc _(i) is stored by the processing of steps 101 to 104 in the first flowchart. The correction coefficient ekpa is not simply calculated by multiplying the reference atmospheric pressure Pas, but is calculated based on the above equation (9). That is, the current atmospheric pressure Pa is a value between the reference atmospheric pressure Pas and the corrected atmospheric pressure obtained by multiplying the reference atmospheric pressure by the correction coefficient ekpa using the adaptation constant K1 (0 <K1 <1). The Thus, since the initial value Pa of the atmospheric pressure is calculated, the intake air amount mc _(i) is estimated to be abnormally small even if the correction coefficient ekpa is stored abnormally small relative to the current atmospheric pressure. The engine stall can be prevented. If the stored correction coefficient ekpa is accurate with respect to the current atmospheric pressure, the estimated intake air amount mc _(i) is estimated to be larger than the actual atmospheric pressure, but the atmospheric pressure The initial value Pa is not calculated exceeding the reference atmospheric pressure, and this is not a problem. The initial value Pa of the atmospheric pressure is used as the atmospheric pressure in the second flowchart until the throttle valve opening TA is larger than the set opening TA1 and the correction coefficient ekpa is updated (step 205).

Next, the guard value Pg used for the guard process in step 106 of the first flowchart will be described with reference back to the second flowchart. The actual intake pipe pressure does not exceed the atmospheric pressure, so that the intake pipe pressure Pm _(i) calculated based on the throttle valve opening is generally guarded by the current atmospheric pressure. If the correction coefficient ekpa is correct, the current atmospheric pressure is the corrected atmospheric pressure as the product of the reference atmospheric pressure Pas and ekpa, and this corrected atmospheric pressure is used as a guard value. As a margin, a guard value may be obtained by multiplying by a coefficient K2 (for example, 1.05).

However, as described above, the correction coefficient ekpa may be inaccurate immediately after the engine is started. If guard processing is performed with a guard value based on the corrected atmospheric pressure at this time, the correction coefficient ekpa is calculated based on the throttle valve opening. Although the intake pipe pressure Pm _(i) is relatively accurate, the intake pipe pressure Pm _(i) is lowered by the guard process. As a result, the intake air amount mc _(i) is estimated to be abnormally less than actual, the combustion air-fuel ratio becomes abnormally lean, and misfire occurs, or an air-fuel ratio sensor is disposed in the engine exhaust system. When the injection amount feedback control is performed, the feedback correction coefficient becomes abnormally large in order to increase the fuel injection amount.

In order to solve this problem, in the present embodiment, the guard value Pg is updated by the processing after step 206 in the second flowchart. In the second flowchart, in Expression (8), Expression (11) is used instead of the throttle valve passing air amount mt calculated based on the throttle valve opening using Expression (1) or (4). Thus, the intake pipe pressure Pm ′ is calculated using the throttle valve passage air amount mt ′ calculated based on the output of the air flow meter. In step 206, the intake pipe pressure Pm ′ _{( It} is determined whether _{i) is} smaller than the previously calculated intake pipe pressure Pm ′ _(i−1) .

Immediately after the engine start is completed, in order to warm up the catalyst device provided in the engine exhaust system at an early stage, the fuel injection amount is increased, the throttle valve opening is relatively increased, and the intake air amount is also increased. Thereby, the initial intake pipe pressure Pm ′ _(i) calculated based on the output of the air flow meter becomes a value relatively close to the current atmospheric pressure. However, since the initial value of Pm ′ _(i−1) is the initial value Pa of the atmospheric pressure calculated in step 102 of the first flowchart, the determination of step 206 at the first time is often affirmed. In 207, the guard value Pg is the current (first) intake pipe pressure Pm ′ _(i) calculated based on the output of the air flow meter. Next, at step 208, it is determined whether or not the guard value Pg determined as the intake pipe pressure Pm ′ _(i) is smaller than a value based on the corrected atmospheric pressure obtained by correcting the reference atmospheric pressure Pas by the correction coefficient ekpa. The

  When the correction coefficient ekpa is relatively large, the value obtained by multiplying the correction atmospheric pressure by the coefficient K2 is larger than the guard value Pg that is smaller than the atmospheric pressure Pa calculated in step 102 of the first flowchart. The determination in step 208 is affirmed, and in step 209, the guard value Pg is a general value based on the corrected atmospheric pressure.

  However, when the correction coefficient ekpa is abnormally small with respect to the current atmospheric pressure as described above, the value based on the corrected atmospheric pressure becomes considerably small. Will cause. In such a case, the determination in step 208 is denied, and the guard value Pg is the intake pipe pressure calculated based on the output of the air flow meter. The intake pipe pressure Pm ′ is a practical pressure based on the output of the air flow meter, and the actual atmospheric pressure is surely higher than the intake pipe pressure. Thus, the intake pipe pressure Pm calculated based on the throttle valve opening is not abnormal at least up to the intake pipe pressure Pm ′. Thus, when the correction coefficient ekpa is abnormally small, it is effective to use the intake pipe pressure Pm ′ calculated based on the output of the air flow meter as a guard value, thereby calculating based on the throttle valve opening. Further, the intake pipe pressure Pm is not guarded abnormally small, and the misfire and the feedback correction coefficient as described above are prevented from becoming abnormal values.

  However, the use of the intake pipe pressure based on the output of the air flow meter as a guard value is only a provisional measure, and an operation with a large throttle valve opening is frequently performed, and the atmospheric pressure correction coefficient ekpa is appropriate. If the value is learned and corrected, the current accurate atmospheric pressure is calculated. At this time, it is preferable to use a guard value based on the corrected atmospheric pressure. Thereby, in steps 208 and 209 of the second flowchart, if the value calculated based on the corrected atmospheric pressure is larger than the intake pipe pressure based on the output of the air flow meter, the value based on the corrected atmospheric pressure is used as the guard value Pg. It has become so.

Further, the intake pipe pressure Pm ′ calculated based on the output of the air flow meter may cause the vehicle to go to a high altitude immediately after the engine is started, and the current atmospheric pressure may be lower than the intake pipe pressure calculated for the first time. Accordingly, it is not preferable to use the intake pipe pressure Pm ′ calculated for the first time until the atmospheric pressure correction coefficient ekpa becomes an appropriate value. In steps 206 and 207 of the second flowchart, the calculation is based on the output of the air flow meter. If the current intake pipe pressure Pm ′ _(i) is smaller than the previous Pm ′ _(i−1) , the value that can be reliably used as the guard value Pg is the current intake pipe pressure Pm ′ _(i) . This is set as a guard value Pg.

  For example, in preparation for the case where the stored correction coefficient ekpa is inappropriate, the guard process is not performed immediately after the engine is started, or the atmospheric pressure Pa calculated in step 102 of the first flowchart is simply used as the guard value. However, since it is not clear when the correction coefficient ekpa is learned and updated to an appropriate value, problems such as misfire still occur when the guard process based on the corrected atmospheric pressure is started. Sometimes. In the present embodiment, as described above, such a problem does not occur.

  By the way, in the second flow chart, the learning update of the correction coefficient ekpa is performed by comparing the throttle valve passing air amount mt based on the throttle valve opening and the throttle valve passing air amount mt ′ based on the output of the air flow meter. . However, this does not limit the present invention. For example, the specific value to be compared is not the amount of air passing through the throttle valve but the intake pipe pressure calculated based on the throttle valve opening and the output of the air flow meter. The amount of intake air may be used.

By the way, in order to accurately control the combustion air-fuel ratio, it is necessary to estimate the correct intake air amount into the cylinder and determine the fuel injection amount before starting the fuel injection. However, in order to estimate the accurate intake air amount, strictly speaking, the intake air flow rate when the intake valve is closed must be calculated. That is, when determining the fuel injection amount, the intake air amount mc _{(i + n)} when the intake valve is closed must be calculated instead of the current intake air amount mc _(i) . This applies not only to the internal combustion engine that injects fuel into the intake branch pipe 3 as shown in FIG. 1 but also to the internal combustion engine that directly injects fuel into the cylinder during the intake stroke.

To this end, not only the current throttle valve opening TA _(i) but also the throttle valve openings TA _{(i + 1)} , TA _{(i + 2)} , TA for every time Δt until the intake valve closes, ... Based on TA _{(i + n)} , μ · A is changed in equation (1) or PmTA is changed in equation (4) to calculate the throttle valve passing air amount mt for each time. Necessary.

  The throttle valve opening TA at each time is based on the amount of change in the accelerator pedal depression with respect to the current time, assuming that the amount of change in depression lasts until the intake valve closes, and estimates the amount of depression of the accelerator pedal at each time, For each estimated depression amount, it may be determined in consideration of the response delay of the throttle valve actuator. This method can also be applied when the throttle valve is mechanically connected to the accelerator pedal.

However, the throttle valve opening degree TA _{(i + n)} when the intake valve is estimated as described above is only a prediction, and there is no guarantee that it coincides with the actual situation. In order to make the throttle valve opening degree TA _{(i + n)} when the intake valve is closed match the actual throttle valve opening TA _{(i + n)} , the throttle valve may be delayed. When the amount of depression of the accelerator pedal changes, the throttle valve opening varies with delay due to the response delay of the actuator. This delay control intentionally increases the response delay of the throttle valve.

For example, during engine transition, the actual response delay (dead time) so that the throttle valve opening corresponding to the current depression amount of the accelerator pedal when determining the fuel injection amount is realized when the intake valve is closed. If the throttle valve actuator is controlled in consideration of the above, the throttle valve opening TA _(i) , TA _{(i + 1)} ,... TA _{(i + n) for} each time from the present to the intake valve closing time Can be grasped accurately. More specifically, when the amount of depression of the accelerator pedal changes, an operation signal is not immediately sent to the actuator, but the dead time is subtracted from the time from when the fuel injection amount is determined to when the intake valve is closed. An operation signal to the actuator is issued when the time has elapsed. Of course, the throttle valve delay control may be performed so that the throttle valve opening corresponding to the current depression amount of the accelerator pedal is realized after the intake valve is closed.

The output of the air flow meter 7 is highly reliable when the engine is stationary, so that when the engine is stationary, the current throttle valve passage air amount mt _(i) calculated using the equation (11) is The reliability is higher than the throttle valve passing air amount calculated by 1) or (4). Thus, when the engine is in a steady state, using the previous throttle valve passing air amount mt _(i) calculated by the equation (11), the current intake pipe pressure Pm _(i) is calculated in the equation (8) and the equation ( In step 7), the current intake air temperature Tm _(i) on the downstream side of the throttle valve is preferably calculated, and the current intake air amount mc _(i) is preferably calculated using equation (3).

Thereby, using the first flowchart, the current intake air amount mc _(i) and the intake air amount mc _{(i + n)} when the intake valve is closed are calculated, and the equation (11), Using Equation (8), Equation (7) and Equation (3), the current intake air amount mc _(i) ′ based on the output of the air flow meter is sequentially calculated, and the intake air amount when the intake valve is closed is It may be calculated by mc _{(i + n)} −mc _(i) + mc _(i) ′. By such a calculation method, when the engine is stationary, mc _{(i + n)} and mc _(i) calculated as the same throttle valve opening based on the same model formula are surely offset and calculated based on the output of the air flow meter. The correct current intake air amount to be obtained is obtained as the intake air amount when the intake valve is closed. In addition, since mc (i) and mc (i) ′ are substantially canceled during engine transition, the intake air amount at the time of closing the intake valve calculated as mc _{(i + n)} can be obtained.

1 is a schematic view of an internal combustion engine to which an intake air amount estimation device according to the present invention is attached. It is a map which shows the relationship between throttle-valve opening degree TA and the flow coefficient (micro | micron | mu). It is a map which shows the relationship between the throttle valve opening degree TA and the opening area A of a throttle valve. It is a map which shows the relationship between the ratio of intake pipe pressure Pm and atmospheric pressure Pa, and function (PHI). It is a part of 1st flowchart for calculating the amount of intake air. 6 is the remaining part of the first flowchart in FIG. 5. It is sectional drawing of the modeled air flow meter. It is a 2nd flowchart for learning and update of the correction coefficient ekpa and the guard value Pg.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine body 2 Surge tank 3 Intake branch pipe 4 Intake passage 6 Throttle valve 7 Air flow meter

Claims (1)

  Intake pipe pressure calculating means for calculating the intake pipe pressure downstream of the throttle valve based on the throttle valve opening and the atmospheric pressure, and calculating the intake air amount based on the intake pipe pressure calculated by the intake pipe pressure calculating means The atmospheric pressure used in the intake pipe pressure calculating means is learned and updated when the throttle valve opening is equal to or larger than a set opening, and stored when the engine is stopped. The intake air amount estimation device is provided with guard means for replacing the intake pipe pressure with the guard value when the intake pipe pressure calculated by the intake pipe pressure calculation means is higher than a guard value. The guard value is larger by comparing the value based on the corrected atmospheric pressure and the minimum value of the intake pipe pressure newly calculated from the start of the engine based on the output of the air flow meter. Intake air quantity estimation apparatus for an internal combustion engine, characterized in that the value of the square.

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