JP4483657B2 - Fuel injection amount control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection amount control device for an internal combustion engine.

  A catalyst device for purifying exhaust gas is provided in an exhaust pipe of an internal combustion engine, and a technique for supplying secondary air to the upstream side of the catalyst device by operating an air pump in order to improve the purification efficiency of the catalyst device. Has been proposed.

  Further, when the secondary air is supplied, the fuel injection amount is controlled so that the air-fuel ratio (combustion air-fuel ratio) of the air-fuel mixture supplied to the internal combustion engine is rich. However, at this time, if the air-fuel ratio is detected by an air-fuel ratio sensor provided in the vicinity of the inlet of the catalyst device and the air-fuel ratio feedback control is performed based on the detected value, there is a possibility that the fuel increase will be excessive. For example, if the secondary air flow rate temporarily increases or decreases due to a change in the operating state of the internal combustion engine or the like, an excessive amount of fuel is increased correspondingly, resulting in deterioration of drivability and exhaust emission. Therefore, in general, in order to avoid such inconvenience, the air-fuel ratio feedback control is prohibited when the secondary air is supplied. For example, in Patent Document 1, air-fuel ratio feedback control is performed when the air-fuel ratio sensor outputs a rich signal during secondary air supply, and when the air-fuel ratio sensor outputs a lean signal, the air-fuel ratio is output. Feedback control is prohibited.

However, in order to keep the exhaust emission suitably, it is desirable to perform fuel amount correction such as air-fuel ratio feedback according to the increase or decrease of the secondary air flow rate even during the supply of the secondary air. Therefore, there is a demand for a technique that can suitably perform fuel amount correction when supplying secondary air.
Japanese Patent No. 2910034

  The main object of the present invention is to provide a fuel injection amount control device for an internal combustion engine that can appropriately perform fuel amount correction at the time of supplying secondary air and thereby improve drivability and exhaust emission. It is.

In the first aspect of the present invention, at the time of supplying the secondary air, the target air-fuel ratio for supplying the secondary air is set, and the air-fuel ratio downstream of the secondary air supply port of the exhaust passage is set to the target air-fuel ratio. The air-fuel ratio feedback control is performed so that the fuel injection amount is corrected in the air-fuel ratio feedback control . At this time, if the secondary air flow rate increases or decreases due to the operating conditions of the internal combustion engine, etc., fuel injection amount correction (for example, fuel increase) is excessively performed or conversely insufficient, resulting in drivability. And exhaust emissions deteriorate. On the other hand, according to the present invention, the target air-fuel ratio is changed to the lean side or the rich side according to the increase or decrease of the secondary air flow rate.
The fuel amount correcting means may be configured as in claim 1, and according to such a configuration, an appropriate fuel injection amount correction is performed according to the increase or decrease of the secondary air flow rate when the secondary air is supplied. That is, in the first aspect of the invention, the fuel injection amount is corrected according to the air-fuel ratio deviation. That is, an air-fuel ratio correction amount (corresponding to an air-fuel ratio correction coefficient faf described later) is calculated according to the deviation between the air-fuel ratio detected by the air-fuel ratio detection means and the target air-fuel ratio, and the fuel injection amount is corrected by the air-fuel ratio correction amount. Is done.
When the fuel amount correction means is configured as described above, if the secondary air flow rate changes, there is a risk that the fuel amount correction will be excessively followed. However, in the present invention, the increase or decrease in the secondary air flow rate is as described above. Accordingly, since the target air-fuel ratio is changed to the lean side or the rich side, excessive fuel amount correction can be suppressed. In other words, even when the secondary air is being supplied, the fuel injection amount correction as in claim 1 can be continued.
At the time of supplying the secondary air, it is preferable to variably set a feedback gain for calculating the air-fuel ratio correction amount according to the secondary air flow rate or the exhaust pulsation generated in the exhaust passage. In other words, when secondary air is supplied, if the secondary air flow rate changes or exhaust pulsation occurs due to secondary combustion in the exhaust passage, the air-fuel ratio detection result is disturbed, and the accuracy of air-fuel ratio feedback control decreases. Therefore, in such a case, the feedback gain is set to a low gain. Thereby, control hunting or the like can be suppressed.

In the invention according to claim 2 or claim 3 , when the secondary air is supplied, a correction amount guard value at least on the increase side of the air-fuel ratio correction amount is set according to the secondary air flow rate, and the air-fuel ratio correction amount is set. When the correction amount guard value is reached, the air-fuel ratio correction amount is limited by the guard value. Specifically, the correction amount guard value is preferably increased as the secondary air flow rate increases. Of course, it is also possible to set the correction amount guard value of the air-fuel ratio correction amount on the increase side and the decrease side.

  In this case, by limiting the air-fuel ratio correction amount within a predetermined range defined by the correction amount guard value, excessive fuel increase (that is, overcorrection of the fuel amount) can be avoided, and deterioration of drivability and the like are suppressed. be able to. Further, since the correction amount guard value is variably set according to the secondary air flow rate, even if the secondary air flow rate varies, the correction amount guard value can be suitably set so as to follow it.

In the invention according to claim 4 , the correction amount guard value is set based on the secondary air flow rate and the target air-fuel ratio. Specifically, the correction amount guard value is preferably increased as the secondary air flow rate is increased, while the correction amount guard value is preferably decreased as the target air-fuel ratio is on the lean side. In this case, even if the secondary air flow rate or the target air-fuel ratio fluctuates, the correction amount guard value can be suitably set by following it.

In the invention according to claim 5 , the correction amount guard value is obtained by correcting the guard value of the air-fuel ratio correction amount at the time of normal air-fuel ratio feedback control without secondary air supply based on at least the secondary air flow rate. Is set. In general, in normal air-fuel ratio feedback control, the upper and lower guard values of the air-fuel ratio correction amount are set for the purpose of preventing overcorrection and ensuring robustness. In such a case, as described above, the correction amount guard value is set by the air-fuel ratio correction amount guard value and the secondary air flow rate at the time of normal air-fuel ratio feedback control, which is the same as at the time of normal control in which secondary air supply is not performed. In addition, robustness can be ensured by preventing overcorrection even when the secondary air is supplied.

In a sixth aspect of the present invention, the rate of change of the correction amount guard value is regulated, and sudden change of the correction amount guard value is prevented by the regulation. As a result, it is possible to suppress deterioration in drivability associated with a sudden change in the air-fuel ratio correction amount.

In the invention according to claim 7 , while the correction amount guard value (correction amount guard value set according to the secondary air flow rate) by the guard setting means is set as the first correction amount guard value, The second correction amount guard value is set based on the allowable combustion air-fuel ratio that is allowed as the air-fuel ratio of the air-fuel mixture provided for combustion. The air-fuel ratio correction amount is limited by the first correction amount guard value and the second correction amount guard. In other words, in this case, it is possible to set an optimal correction amount guard value from the viewpoints of both the secondary air supply state and the combustion state of the internal combustion engine.
For example, as described in claim 8, when the secondary air flow rate is increased, the target air-fuel ratio is changed to the lean side, and when the secondary air flow rate is decreased, the target air-fuel ratio is changed to the rich side. As a result, even when the secondary air is supplied, the fuel injection amount can be properly corrected, and drivability and exhaust emission can be improved.
According to the ninth aspect of the present invention, a guard value at least on the rich side of the target air-fuel ratio is set according to the secondary air flow rate each time, and when the target air-fuel ratio reaches the guard value, the target air-fuel ratio is set at the guard value. The fuel ratio is limited. Of course, the guard value of the target air-fuel ratio can be set on the lean side and the rich side. In this case, the target air-fuel ratio is set within a predetermined range defined by the guard value while the guard value of the target air-fuel ratio varies as the secondary air flow rate changes. Thereby, the fuel injection amount correction can be appropriately performed as described above.
According to a tenth aspect of the present invention, the guard value is set based on an allowable combustion air-fuel ratio and a secondary air flow rate that are allowed as an air-fuel ratio of an air-fuel mixture used for combustion in an internal combustion engine. In this case, the combustion air-fuel ratio of the internal combustion engine (the air-fuel ratio of the air-fuel mixture used for combustion) can be set within the air-fuel ratio range defined by the allowable combustion air-fuel ratio in each case. Therefore, it is possible to suppress over-richness and over-lean of the combustion air-fuel ratio.
Here, as described in claim 11, the allowable combustion air-fuel ratio may be set based on the temperature of the internal combustion engine. Thus, the combustion air-fuel ratio can be appropriately controlled according to the warm-up state at the time of starting the internal combustion engine. The temperature of the internal combustion engine is obtained from the coolant temperature, the elapsed time after the engine is started, and the like.
The fuel amount correcting means may be configured as in the following claim 12, and according to such a configuration, proper fuel injection amount correction is performed according to the increase or decrease of the secondary air flow rate when the secondary air is supplied. That is, according to the twelfth aspect of the invention, the amount of increase correction for secondary air supply (based on the target air-fuel ratio at the time of secondary air supply and the change in the secondary air flow rate with respect to the intake air amount of the internal combustion engine) (Corresponding to a correction coefficient fsai for secondary air described later) is calculated, and the fuel injection amount is corrected by the increase correction amount.

In the invention according to claim 13 , based on the secondary air supply pressure detected as the secondary air supply state of the secondary air supply device, and the reference pressure detected in a different state different from the secondary air supply state. A secondary air flow rate is calculated. In this case, since the secondary air flow rate is calculated using not only the secondary air supply pressure but also the reference pressure, even if there is a product tolerance of the secondary air supply device or attached pressure sensor, the product tolerance, etc. The secondary air flow rate can be calculated with high accuracy without being affected by. Thereby, the control accuracy of the fuel injection amount can be improved. At this time, the secondary air flow rate may be calculated based on the differential pressure between the secondary air supply pressure and the reference pressure. Thereby, even if the atmospheric pressure or the like fluctuates, the secondary air flow rate can be accurately calculated without being affected by the atmospheric pressure fluctuation.

Further, as described in claim 14, it is preferable that the secondary air supply path leading to the secondary air supply device is in a closed state, and the closed pressure detected in the closed state is set as the reference pressure.

In the invention according to claim 15 , the secondary air flow rate is calculated based on the secondary air supply pressure detected by the secondary air supply device as the secondary air supply state and the exhaust pressure in the exhaust passage. . In this case, since the secondary air flow rate is calculated using not only the secondary air supply pressure but also the exhaust pressure, even if the exhaust pressure changes due to changes in the operating state of the internal combustion engine, etc. The air flow rate can be calculated with high accuracy. Thereby, the control accuracy of the fuel injection amount can be improved.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the present embodiment, an engine control system is constructed for an in-vehicle multi-cylinder gasoline engine that is an internal combustion engine. In the control system, an electronic control unit (hereinafter referred to as ECU) is used as a center to control the fuel injection amount. And control of ignition timing. First, an overall schematic configuration diagram of the engine control system will be described with reference to FIG.

  In the engine 10 shown in FIG. 1, the intake pipe 11 is provided with a throttle valve 14 whose opening degree is adjusted by an actuator such as a DC motor, and a throttle opening degree sensor 15 for detecting the throttle opening degree. A surge tank 16 is provided downstream of the throttle valve 14, and an intake pipe pressure sensor 17 for detecting the intake pipe pressure is provided in the surge tank 16. The surge tank 16 is connected to an intake manifold 18 that introduces air into each cylinder of the engine 10. In the intake manifold 18, an electromagnetically driven fuel injection that injects fuel near the intake port of each cylinder. A valve 19 is attached.

  An intake valve 21 and an exhaust valve 22 are respectively provided in the intake port and the exhaust port of the engine 10, and an air / fuel mixture is introduced into the combustion chamber 23 by the opening operation of the intake valve 21, and the exhaust valve 22. By the opening operation, the exhaust gas after combustion is discharged to the exhaust pipe 24. A spark plug 25 is attached to the cylinder head of the engine 10 for each cylinder, and a high voltage is applied to the spark plug 25 at a desired ignition timing through an ignition device (not shown) including an ignition coil. By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 25, and the air-fuel mixture introduced into the combustion chamber 23 is ignited and used for combustion.

  The exhaust pipe 24 is provided with a catalyst 31 such as a three-way catalyst for purifying CO, HC, NOx and the like in the exhaust gas, and the air-fuel ratio of the air-fuel mixture is detected on the upstream side of the catalyst 31 with exhaust gas as a detection target. An air-fuel ratio sensor 32 (linear A / F sensor, O2 sensor, etc.) for detecting the above is provided. Further, the cylinder block of the engine 10 includes a coolant temperature sensor 33 that detects the coolant temperature, and a crank angle sensor 34 that outputs a rectangular crank angle signal for each predetermined crank angle of the engine (for example, at a cycle of 30 ° CA). It is attached.

  As a secondary air supply system, a secondary air pipe 35 is connected upstream of the catalyst 31 in the exhaust pipe 24, and a secondary air pump 36 is provided upstream of the secondary air pipe 35. . The secondary air pump 36 is composed of, for example, a DC motor or the like, and operates by receiving power from a vehicle battery (not shown). An on-off valve 37 that opens or closes the secondary air pipe 35 is provided downstream of the secondary air pump 36. A pressure sensor 38 that detects the pressure in the secondary air pipe 35 is provided between the secondary air pump 36 and the on-off valve 37.

  The outputs of the various sensors described above are input to the ECU 40 that controls the engine. The ECU 40 is configured mainly by a microcomputer including a CPU, a ROM, a RAM, and the like, and executes various control programs stored in the ROM, so that the fuel injection amount and ignition of the fuel injection valve 19 according to the engine operating state. The ignition timing by the plug 25 is controlled. In addition, the ECU 40 supplies the secondary air by operating the secondary air pump 36 in order to activate the catalyst 31 at the time of starting the engine early.

  Next, the fuel injection amount control performed when the secondary air is supplied will be described. Here, when supplying the secondary air, the secondary air is supplied to the exhaust pipe 24, and the fuel is increased in accordance with the flow rate of the secondary air. In this case, basically, if the secondary air flow rate is calculated based on the detected value (secondary air supply pressure Ps) of the pressure sensor 38 when the on-off valve 37 = open and the secondary air pump 36 = ON (operation). In order to prevent a decrease in calculation accuracy due to product tolerances and the like of the secondary air pump 36 and the pressure sensor 38, in the present embodiment, the second air pump 36 and the pressure sensor 38 are controlled based on the differential pressure between the secondary air supply pressure Ps and the reference pressure. Next air flow rate is calculated. For example, the closing pressure P0 as the reference pressure is detected in the state where the on-off valve 37 = closed and the secondary air pump 36 = ON, and the secondary air flow rate Qa is calculated by the following equation (1).

なお、上記（１）式において、ρは流体密度、Ｃは係数、Ａは管路断面積である。流体密度ρは温度特性を持つため、吸気温により流体密度ρを補正する構成とすることも可能である。

In the above equation (1), ρ is a fluid density, C is a coefficient, and A is a pipe cross-sectional area. Since the fluid density ρ has temperature characteristics, a configuration in which the fluid density ρ is corrected by the intake air temperature may be employed.

  In addition, when supplying secondary air, a target air-fuel ratio for supplying secondary air that is different from the normal time (when secondary air is not supplied) is set. For example, fuel with a weak lean air-fuel ratio as a target air-fuel ratio is set. Implement injection amount control. In this case, the air-fuel ratio is represented by the excess air ratio λ, the air-fuel ratio (combustion air-fuel ratio) of the combustion gas used for combustion in the engine combustion chamber is λ1, the air-fuel ratio at the catalyst inlet is λ2, and the air is taken into the engine. Assuming that the intake air amount is ga and the secondary air flow rate is gsai, λ1 and λ2 have the relationship of the following equation (2). Note that ga and gsai are both mass flow rates. In particular, gsai is the mass-converted secondary air flow rate Qa described above.

空燃比λ１（空気過剰率）の逆数は燃料過剰率であり、この燃料過剰率（１／λ１）が二次エア供給時の燃料増量補正係数（以下、これを二次エア用補正係数ｆｓａｉという）となる。つまり、触媒入口の空燃比λ２を目標空燃比λｔｇとする場合、前記（２）式より次の（３）式が得られる。

The reciprocal of the air-fuel ratio λ1 (excess air ratio) is the excess fuel ratio, and this excess fuel ratio (1 / λ1) is the fuel increase correction coefficient when the secondary air is supplied (hereinafter referred to as the secondary air correction coefficient fsai). ) That is, when the air-fuel ratio λ2 at the catalyst inlet is the target air-fuel ratio λtg, the following equation (3) is obtained from the equation (2).

上記（３）式によれば、二次エア供給時における二次エア流量ｇｓａｉ、吸入空気量ｇａ及び目標空燃比λｔｇから二次エア用補正係数ｆｓａｉが算出できる。

According to the above equation (3), the secondary air correction coefficient fsai can be calculated from the secondary air flow rate gsai, the intake air amount ga, and the target air-fuel ratio λtg when the secondary air is supplied.

  FIG. 2 is a flowchart showing a fuel injection amount calculation process. This process is executed by the ECU 40 at a predetermined time period, for example. Note that the process of FIG. 2 is an extraction of a process related to secondary air supply from the fuel injection amount calculation process executed by the ECU 40.

  In FIG. 2, first, in step S101, it is determined whether or not an execution condition for secondary air supply is satisfied. When the execution condition is satisfied, in step S102, the on-off valve 37 is opened and the secondary air pump 36 is operated. To start secondary air supply. Thereafter, in step S103, the secondary air flow rate is calculated based on the detected value of the pressure sensor 38 and the like. At this time, in particular, as described above, the secondary air flow rate Qa is calculated based on the differential pressure between the secondary air supply pressure Ps detected by the pressure sensor 38 and the reference pressure (deadline pressure P0). The secondary air flow rate Qa is converted into a mass flow rate, and the result is referred to as “secondary air flow rate gsai”.

  Thereafter, in step S104, operating condition parameters such as engine speed and intake air amount are read. In step S105, the target air-fuel ratio λtg for secondary air supply is calculated. Here, details of the calculation processing of the target air-fuel ratio λtg will be described with reference to FIG.

  In FIG. 3, in step S201, for example, a target air-fuel ratio map prepared for supplying secondary air is used, and a target air-fuel ratio base value λbase is calculated based on the engine rotation speed, load, etc. each time. At this time, the target air-fuel ratio base value λbase is calculated so that the exhaust emission during the secondary air supply is in an optimal state, for example, λbase = 1.05.

  In the subsequent step S202, a lean-side allowable combustion air-fuel ratio and a rich-side allowable combustion air-fuel ratio are set. This allowable combustion air-fuel ratio defines an air-fuel ratio range that is allowed as an air-fuel ratio (supply air-fuel ratio) that is used for combustion in the engine. The allowable combustion air-fuel ratio on the lean side / rich side may be set based on, for example, the engine water temperature or the elapsed time after engine start, and more specifically is set based on the relationship of FIG. According to FIG. 4, as the engine water temperature as a whole increases, the allowable combustion air-fuel ratio on the lean side / rich side shifts to the stoichiometric side, and in the warm-up completed state (for example, water temperature ≧ 80 ° C.), for example, the allowable combustion on the lean side The air-fuel ratio is 1.0, and the rich-side allowable combustion air-fuel ratio is 0.7.

  Thereafter, in step S203, the lean side guard λmax and the rich side guard λmin of the target air / fuel ratio are calculated based on the set lean / rich side allowable combustion air / fuel ratio and the secondary air flow rate gsai. Specifically, the lean side guard λmax and the rich side guard λmin are calculated by the following equation (4). In the equation (4), λlean is a lean-side allowable combustion air-fuel ratio, and λrich is a rich-side allowable combustion air-fuel ratio.

その後、ステップＳ２０４では、目標空燃比ベース値λｂａｓｅをリーン側ガードλｍａｘ、リッチ側ガードλｍｉｎでガードしつつ、最終目標空燃比λｔｇを算出する。このとき、λｍｉｎ＜λｂａｓｅ＜λｍａｘであればλｔｇ＝λｂａｓｅとされ、λｂａｓｅ≦λｍｉｎであればλｔｇ＝λｍｉｎとされ、λｂａｓｅ≧λｍａｘであればλｔｇ＝λｍａｘとされる。

Thereafter, in step S204, the final target air-fuel ratio λtg is calculated while guarding the target air-fuel ratio base value λbase with the lean-side guard λmax and the rich-side guard λmin. At this time, if λmin <λbase <λmax, λtg = λbase is set. If λbase ≦ λmin, λtg = λmin is set. If λbase ≧ λmax, λtg = λmax is set.

  Returning to the description of FIG. 2, the process proceeds to step S106 after the process of step S105, and the secondary air flow is calculated based on the secondary air flow rate gsai, the intake air amount ga, and the final target air-fuel ratio λtg at that time using the equation (3). A correction coefficient fsai is calculated.

  On the other hand, if the execution condition for the secondary air supply is not satisfied, the process proceeds to step S107, and fsai = 1 is set.

  After calculating the correction coefficient fsai for the secondary air as described above, in step S108, the basic injection amount Tp calculated based on the operating condition parameters such as the engine speed and the intake air amount is multiplied by the correction coefficient fsai for the secondary air. Together, the product is the final injection amount TAU.

  Next, how the final target air-fuel ratio λtg and the like are set in accordance with the change in the secondary air flow rate will be described more specifically using the time chart of FIG. In FIG. 5, the secondary air flow rates are g1, g2, and g3 (g1 <g2 <g3) in the periods before t1, t2 to t3, and after t4, respectively. In the chart portion representing the behavior of the air-fuel ratio, the final target air-fuel ratio λtg, the rich side guard λmin, and the detected air-fuel ratio (detected λ) are illustrated, and in particular, the rich side guard λmin is illustrated by a one-dot chain line. (However, after t2, λtg = λmin). Before timing t2, λtg = λbase.

  In FIG. 5, as the time elapses, the secondary air flow rate increases as g1 → g2 → g3. According to the equation (4), the rich side guard λmin increases as the secondary air flow rate increases. λ1 → λ2 → λ3. In this case, λbase> λmin before timing t2, and λtg = λbase. Further, after timing t2, λbase ≦ λmin, and λtg = λmin. In particular, after timing t3, the final target air-fuel ratio λtg is changed to the lean side together with the rich side guard λmin as the secondary air flow rate increases.

  When the secondary air flow rate increases, the secondary air correction coefficient fsai increases accordingly, and fuel increase is performed. As a result, the reaction between the unburned fuel and the secondary air is promoted in the exhaust pipe, and the temperature of the catalyst 31 is effectively increased. However, after timing t3, the final target air-fuel ratio λtg is changed to the lean side together with the rich side guard λmin, so that further changes in the secondary air correction coefficient fsai are restricted. As for the combustion air-fuel ratio, the change to the rich side beyond timing t3 is restricted. After timing t3, the secondary air correction coefficient fsai and the combustion air-fuel ratio are limited as described above, so that drivability and exhaust emission are prevented from deteriorating.

  In FIG. 6, the measurement result in an actual machine is shown about secondary air flow volume, an air fuel ratio, and a combustion air fuel ratio. In FIG. 6, a thick line in the chart portion representing the air-fuel ratio behavior indicates the behavior of the final target air-fuel ratio λtg.

  For example, in the period T1, the secondary air flow rate temporarily increases. At this time, the final target air-fuel ratio λtg is changed to the lean side together with the rich side guard λmin. For this reason, enrichment of the combustion air-fuel ratio is limited by a predetermined air-fuel ratio (rich side allowable combustion air-fuel ratio). Further, during the period T2, the secondary air flow rate temporarily decreases, but at that time, the final target air-fuel ratio λtg is changed to the rich side together with the lean-side guard λmax. Therefore, leaning of the combustion air-fuel ratio is limited by a predetermined air-fuel ratio (lean side allowable combustion air-fuel ratio).

  According to the embodiment described above in detail, the following excellent effects can be obtained.

  When the secondary air is supplied, the lean-side guard λmax and the rich-side guard λmin are set according to the increase or decrease of the secondary air flow rate, and the final target air-fuel ratio λtg is limited by these λmax and λmin. Even when the fuel injection amount is correct, the fuel injection amount can be corrected appropriately, and as a result, drivability and exhaust emission can be improved.

  Since the lean-side guard λmax and the rich-side guard λmin are calculated based on the lean-side / rich-side allowable combustion air-fuel ratio and the secondary air flow rate, the combustion air-fuel ratio is over-rich or over-lean when the secondary air is supplied. Can be suppressed.

  Since the secondary air flow rate Qa is calculated based on the differential pressure between the secondary air supply pressure Ps and the closing pressure P0 (reference pressure), even if the atmospheric pressure fluctuates, it is not affected by the atmospheric pressure fluctuation. The secondary air flow rate Qa can be calculated. Even if there is a product tolerance or the like of the secondary air pump 36 or the pressure sensor 38, or even if pressure loss occurs in the secondary air pipe 35, the calculation accuracy of the secondary air flow rate Qa can be increased. Since the secondary air flow rate Qa can be calculated with high accuracy in this way, the control accuracy of the fuel injection amount can be improved.

(Second Embodiment)
In the first embodiment, the secondary air correction coefficient fsai is calculated according to the secondary air flow rate gsai, the intake air amount ga, and the target air-fuel ratio λtg, and the fuel is calculated based on the secondary air correction coefficient fsai. In the second embodiment, instead of this, the air-fuel ratio correction coefficient faf is calculated in accordance with the deviation between the air-fuel ratio detected by the air-fuel ratio sensor 32 and the target air-fuel ratio. The fuel injection amount is corrected based on the air-fuel ratio correction coefficient faf. The air-fuel ratio correction coefficient faf is basically calculated by multiplying the deviation between the detected air-fuel ratio and the target air-fuel ratio by a feedback gain.

  In the present embodiment, the upper limit guard α1 and the lower limit guard α2 of the air-fuel ratio correction coefficient faf are set in order to limit the air-fuel ratio correction coefficient faf within a predetermined range when the secondary air is supplied. The air-fuel ratio correction coefficient faf is limited within a set range (α1 to α2) defined by each guard value. The upper and lower limit guards α1, α2 correspond to the “correction amount guard value”.

  Each of the guards α1 and α2 has a faf upper limit guard gdh and a faf lower limit guard gdl during normal air-fuel ratio feedback control (that is, when secondary air is not supplied). It is calculated by correcting each with a correction term determined by the fuel ratio λtg. The faf upper and lower limit guards gdh and gdl during normal air-fuel ratio feedback control are set as guard values for suppressing the occurrence of overshoot due to overcorrection, for example, gdh = 1.0 + K, gdl = 1.0−K. (Where K> 0).

  FIG. 7 is a flowchart showing the calculation process of the fuel injection amount in the present embodiment. This process is executed by the ECU 40 at a predetermined time period, for example. This process is executed in place of FIG. 2, and steps S301 to S305 are common to steps S101 to S105 of FIG.

  In FIG. 7, first, in step S301, it is determined whether or not an execution condition for secondary air supply is established. When the execution condition is established, in step S302, the on-off valve 37 is opened and the secondary air pump 36 is operated. To start secondary air supply. In step S303, the secondary air flow rate gsai is calculated based on the detection value of the pressure sensor 38 and the like. Thereafter, in step S304, operating condition parameters such as the engine speed and the intake air amount are read.

  In step S305, the target air-fuel ratio λtg for secondary air supply is calculated. At this time, as described in detail with reference to FIG. 3, the target air-fuel ratio base value λbase for supplying the secondary air is calculated using a map or the like, and the lean value set based on the engine water temperature and the elapsed time after the engine is started. Based on the permissible combustion air-fuel ratio on the side / rich side and the secondary air flow rate gsai, the lean-side guard λmax and the rich-side guard λmin of the target air-fuel ratio are calculated (see equation (4) above). Then, the final target air-fuel ratio λtg is calculated by guarding the target air-fuel ratio base value λbase with the lean-side guard λmax and the rich-side guard λmin. At this time, if λmin <λbase <λmax, λtg = λbase is set. If λbase ≦ λmin, λtg = λmin is set. If λbase ≧ λmax, λtg = λmax is set.

  After calculating the target air-fuel ratio λtg, in step S306, an air-fuel ratio correction coefficient faf for supplying secondary air is calculated. Here, details of the calculation process of the air-fuel ratio correction coefficient faf will be described with reference to FIG.

  In FIG. 8, in step S401, the base value fafbase of the air-fuel ratio correction coefficient is calculated based on the deviation between the target air-fuel ratio λtg at that time and the air-fuel ratio detected by the air-fuel ratio sensor 32. Next, in steps S402 and S403, the faf upper limit guard α1 is calculated. That is, first, using the following equation (5), the faf upper limit guard gdh, the secondary air flow rate gsai, the intake air amount ga, and the target at the time of normal air-fuel ratio feedback control (when not supplying secondary air) An upper limit guard base value α1base is calculated based on the air-fuel ratio λtg.

また、以下の（６）式を用い、上限ガードベース値α１ｂａｓｅに対して急変防止のための演算処理を実施し、その結果を上限ガードα１とする。（６）式において、Δはガード値の変更幅である。本実施の形態では、Δを固定値とするが、同Δを可変設定することも可能である。

Further, using the following equation (6), arithmetic processing for preventing sudden change is performed on the upper limit guard base value α1base, and the result is set as the upper limit guard α1. In the equation (6), Δ is a guard value change width. In the present embodiment, Δ is a fixed value, but it is also possible to variably set Δ.

その後、ステップＳ４０４，Ｓ４０５では、ｆａｆ下限ガードα２を算出する。すなわち、まずは、以下の（７）式を用い、通常（二次エア供給時でない場合）の空燃比フィードバック制御時におけるｆａｆ下限ガードｇｄｌと、二次エア流量ｇｓａｉと、吸入空気量ｇａと、目標空燃比λｔｇとに基づいて下限ガードベース値α２ｂａｓｅを算出する。

Thereafter, in steps S404 and S405, the faf lower limit guard α2 is calculated. That is, first, using the following equation (7), the faf lower limit guard gdl, the secondary air flow rate gsai, the intake air amount ga, and the target at the time of normal air-fuel ratio feedback control (when not supplying secondary air) A lower limit guard base value α2base is calculated based on the air-fuel ratio λtg.

また、以下の（８）式を用い、下限ガードベース値α２ｂａｓｅに対して急変防止のための演算処理を実施し、その結果を下限ガードα２とする。

Further, using the following equation (8), arithmetic processing for preventing sudden change is performed on the lower limit guard base value α2base, and the result is set as the lower limit guard α2.

ただし、ガード値の急変防止処理としては、上記（６）式，（８）式によるもの以外に、なまし演算等の平滑化処理を実施するようにしても良い。

However, as the guard value sudden change prevention process, a smoothing process such as a smoothing operation may be performed in addition to the above expressions (6) and (8).

  In step S406, the base value fafbase of the air-fuel ratio correction coefficient is guarded by the upper limit guard α1 and the lower limit guard α2, and the final air-fuel ratio correction coefficient faf is calculated. At this time, if α2 <fafbase <α1, faf = fafbase, faf = α2 if fafbase ≦ α2, and faf = α1 if fafbase ≧ α1.

  Returning to the processing of FIG. 7, if the execution condition of the secondary air supply is not satisfied, the process proceeds to step S307. In step S307, the target air-fuel ratio λtg is calculated based on the engine operating state in each case, and in the subsequent step S308, the air-fuel ratio correction coefficient faf is calculated based on the deviation between the target air-fuel ratio λtg and the detected air-fuel ratio. Steps S307 and S308 are arithmetic processing during normal control.

  After calculating the air-fuel ratio correction coefficient faf as described above, in step S309, the basic injection amount Tp calculated based on the operating condition parameters such as the engine speed and the intake air amount is multiplied by the air-fuel ratio correction coefficient faf, and the product is obtained. Is the final injection amount TAU.

  FIG. 9 is a time chart showing the state of air-fuel ratio control at the time of secondary air supply. In FIG. 9, the secondary air flow rates are g1, g2, and g3 (g1 <g2 <g3) in the periods before t11, t12 to t13, and after t14 (similar to the time chart of FIG. 5). In the chart portion representing the behavior of the air-fuel ratio, the final target air-fuel ratio λtg, the rich side guard λmin, and the detected air-fuel ratio (detected λ) are illustrated, and in particular, the rich side guard λmin is illustrated by a one-dot chain line. (However, after t12, λtg = λmin). Before timing t12, λtg = λbase. The intake air amount ga is constant.

  9 is substantially the same as FIG. 5 except for the air-fuel ratio correction coefficient faf and the upper and lower guards α1 and α2 of the faf.

  In FIG. 9, the rich-side guard λmin changes with the change (increase) in the secondary air flow rate (λ1 → λ2 → λ3). At this time, after timing t12, λbase ≦ λmin is satisfied, and the final target air-fuel ratio λtg is guarded by the rich side guard λmin. Then, after timing t13, the target air-fuel ratio λtg is changed to the lean side by the rich side guard λmin.

  Further, as the secondary air flow rate increases, the air-fuel ratio correction coefficient faf (more specifically, the faf annealing value) increases due to a change in the target air-fuel ratio λtg. However, after timing t13, the final target air-fuel ratio λtg is changed to the lean side together with the rich-side guard λmin, so that further changes in the air-fuel ratio correction coefficient faf are restricted.

  The upper and lower limit guards α1 and α2 of faf are basically set by the faf upper and lower limit guards gdh and gdl at the time of normal (when not supplying secondary air) air-fuel ratio feedback control. It is appropriately changed according to the air-fuel ratio λtg. In this case, the target air-fuel ratio λtg is constant before the timing t13, and the upper and lower limit guards α1, α2 change as shown in accordance with the secondary air flow rate.

  The combustion air-fuel ratio is restricted from being changed to the rich side after timing t13. After timing t13, the air-fuel ratio correction coefficient faf and the combustion air-fuel ratio are limited as described above, so that drivability and exhaust emission deterioration are suppressed.

  As described above with reference to FIG. 8, when setting the faf upper / lower limit guards α1, α2 at the time of secondary air supply, first, base values α1base, α2base of the upper / lower limit guards are calculated, and sudden change prevention processing is performed on the base values. The upper and lower limit guards α1 and α2 are finally determined (see the above formulas (6) and (8)). The effect will be described with reference to FIG. In FIG. 10, in order to clarify the effect, a chart (a) when the sudden change prevention process is not performed and a chart (b) when the sudden change prevention process is performed are shown side by side. In both (a) and (b), the secondary air is supplied throughout the illustrated period, and the air-fuel ratio feedback control is started at timing ta in (a) and at timing tb in (b). Yes.

  In the case of (a), as the air-fuel ratio feedback control is started at the timing ta, the faf upper and lower limit guards α1, α2 are changed to the secondary air flow rate gsai, the intake air amount ga, and the target air-fuel ratio λtg at that time. Set based on. At this time, the air-fuel ratio correction coefficient faf is forcibly increased by the lower limit guard α2, whereby the combustion air-fuel ratio shifts to the rich side stepwise. Therefore, drivability deteriorates.

  On the other hand, in the case of (b), after the air-fuel ratio feedback control is started at the timing tb, the faf upper and lower limit guards α1 and α2 gradually change (increase). That is, the rate of change of the faf upper / lower limit guards α1, α2 is regulated. Therefore, the combustion air-fuel ratio gradually shifts to the rich side, and deterioration of drivability is suppressed.

  As described above, according to the second embodiment, the target air-fuel ratio λtg is limited by the lean / rich side guards λmax and λmin when the secondary air is supplied, as in the first embodiment. The target air-fuel ratio λtg can be set appropriately. In addition, the air-fuel ratio correction coefficient faf is limited by the faf upper / lower limit guards α1 and α2 set according to the secondary air flow rate gsai and the target air-fuel ratio λtg when the secondary air is supplied. Thereby, excessive fuel increase (that is, overcorrection of the fuel amount) can be avoided. Since the faf upper / lower limit guards α1, α2 are variably set according to the secondary air flow rate gsai, even if the secondary air flow rate gsai and the target air-fuel ratio λtg fluctuate, the faf upper / lower limit guards α1, α2 are suitable. Can be set. As described above, even when the secondary air is supplied, the fuel injection amount can be properly corrected, and the engine operating state is stabilized. Accordingly, drivability and exhaust emission can be improved.

  The configuration is such that the faf upper / lower limit guards α1, α2 at the time of secondary air supply are calculated by correcting the faf upper / lower limit guards gdh, gdl at the time of normal air-fuel ratio feedback control with the secondary air flow rate gsai and the target air-fuel ratio λtg. Therefore, similarly to the normal control in which the secondary air supply is not performed, overcorrection can be prevented and the robustness can be ensured even during the secondary air supply.

  Since the faf upper / lower limit guards α1, α2 at the time of secondary air supply are configured to prevent sudden change, deterioration of drivability due to the sudden change of the upper / lower limit guards α1, α2 can be suppressed.

(Third embodiment)
Next, a third embodiment will be described. In the present embodiment, as in the second embodiment, the fuel injection amount is corrected based on the air-fuel ratio correction coefficient faf. In particular, two faf setting ranges are set in order to limit the air-fuel ratio correction coefficient faf during the supply of secondary air to a predetermined range. That is, the first faf setting range (α1 to α2) is set based on the upper and lower limit guards during normal (when not supplying secondary air) air-fuel ratio feedback control, and the combustion air-fuel ratio of the engine (inside the combustion chamber) The second faf setting range (β1 to β2) is set based on the guard values on the rich side / lean side of the air-fuel ratio of the inflowing air-fuel mixture). The air-fuel ratio correction coefficient faf is limited so that it is within the first faf setting range and within the second faf setting range.

  An upper limit guard α1 and a lower limit guard α2 are set as the first faf setting range. At this time, each of the guards α1 and α2 is a correction in which the faf upper limit guard gdh and the faf lower limit guard gdl during normal air-fuel ratio feedback control are determined by the secondary air flow rate gsai, the intake air amount ga, and the target air-fuel ratio λtg. It is calculated by correcting each of the terms. The faf upper and lower limit guards gdh and gdl during normal air-fuel ratio feedback control are set as guard values for suppressing the occurrence of overshoot due to overcorrection, for example, gdh = 1.0 + K, gdl = 1.0−K. (Where K> 0). The guards α1 and α2 for defining the first faf setting range are based on the guards α1 and α2 described in the second embodiment.

  In addition, as the second faf setting range, an upper limit guard β1 and a lower limit guard β2 are set. At this time, the guards β1 and β2 are set based on the allowable combustion air-fuel ratios λlean and λrich on the lean side / rich side of the engine. The upper and lower limit guards α1 and α2 correspond to the “first correction amount guard value”, and the upper and lower limit guards β1 and β2 correspond to the “second correction amount guard value”.

  FIG. 11 is a flowchart showing the calculation process of the fuel injection amount in the present embodiment. This process is executed by the ECU 40 instead of FIG.

  In FIG. 11, first, in step S501, the basic injection amount Tp is calculated based on operating condition parameters such as the engine speed and the intake air amount, and in the subsequent step S502, open fuel correction including an increase after start, an increase in warm-up, and the like. The coefficient fopn is calculated. At this time, the open fuel correction coefficient fopn is calculated based on the water temperature at the start, the change in the water temperature after the start, and the like using a table or a mathematical expression. In step S503, the target air-fuel ratio λtg is calculated based on the engine operating state in each case.

  Thereafter, in step S504, it is determined whether or not an execution condition for secondary air supply is satisfied. When the execution condition is satisfied, in step S505, the on-off valve 37 is opened and the secondary air pump 36 is operated. Start secondary air supply. In step S506, the secondary air flow rate gsai is calculated based on the detection value of the pressure sensor 38 and the like.

  Thereafter, in step S507, an air-fuel ratio correction coefficient faf for supplying secondary air is calculated. Here, details of the calculation process of the air-fuel ratio correction coefficient faf will be described with reference to FIG. Note that part of the processing in FIG. 12 (steps S601 to S605) overlaps with the processing in FIG. 8 (steps S401 to S405), and the description of the overlapping processing will be simplified as appropriate.

  In FIG. 12, in step S601, the base value fafbase of the air-fuel ratio correction coefficient is calculated based on the deviation between the target air-fuel ratio λtg at that time and the air-fuel ratio detected by the air-fuel ratio sensor 32.

  Next, in steps S602 and S603, the faf upper limit guard α1 is calculated. That is, using the equation (5), the faf upper limit guard gdh, the secondary air flow rate gsai, the intake air amount ga, and the target air-fuel ratio λtg at the time of normal air-fuel ratio feedback control (when not supplying secondary air). Based on the above, the upper limit guard base value α1base is calculated. Further, using the above equation (6), a calculation process for preventing a sudden change is performed on the upper limit guard base value α1base, and the calculation result is set as the upper limit guard α1.

  In steps S604 and S605, a faf lower limit guard α2 is calculated. That is, using the equation (7), the faf lower limit guard gdl, the secondary air flow rate gsai, the intake air amount ga, and the target air-fuel ratio λtg at the time of normal air-fuel ratio feedback control (when not supplying secondary air). Based on the above, the lower limit guard base value α2base is calculated. Further, using the equation (8), a calculation process for preventing a sudden change is performed on the lower limit guard base value α2base, and the calculation result is set as the lower limit guard α2.

  In step S606, the base value fafbase of the air-fuel ratio correction coefficient is guarded by the upper limit guard α1 and the lower limit guard α2, and the air-fuel ratio correction coefficient faf after the guard process is calculated. At this time, if α2 <fafbase <α1, faf = fafbase, faf = α2 if fafbase ≦ α2, and faf = α2 if fafbase ≧ α1.

  Thereafter, in steps S607 to S609, an upper limit guard β1 and a lower limit guard β2 in the second faf setting range are calculated based on the allowable combustion air-fuel ratio of the engine. That is, in step S607, the lean-side allowable combustion air-fuel ratio λlean and the rich-side allowable combustion air-fuel ratio λrich are set. The lean-side / rich-side allowable combustion air-fuel ratios λlean and λrich may be set based on, for example, the engine water temperature and the elapsed time after engine start, and more specifically set based on the relationship shown in FIG. . In step S608, upper limit guard β1 is calculated based on rich side allowable combustion air-fuel ratio λrich and open fuel correction coefficient fopn using the following equation (9).

また、ステップＳ６０９では、以下の（１０）式を用い、リーン側の許容燃焼空燃比λｌｅａｎとオープン燃料補正係数ｆｏｐｎとに基づいて下限ガードβ２を算出する。

In step S609, the lower limit guard β2 is calculated based on the lean-side allowable combustion air-fuel ratio λlean and the open fuel correction coefficient fopn using the following equation (10).

最後に、ステップＳ６１０では、空燃比補正係数ｆａｆ（前記ステップＳ６０６で求めたｆａｆ）を上限ガードβ１及び下限ガードβ２でガードして最終の空燃比補正係数ｆａｆを算出する。このとき、空燃比補正係数ｆａｆが上限ガードβ１以上であれば当該ｆａｆがβ１でガードされ、空燃比補正係数ｆａｆが下限ガードβ２以下であれば当該ｆａｆがβ２でガードされる。

Finally, in step S610, the air-fuel ratio correction coefficient faf (faf obtained in step S606) is guarded by the upper limit guard β1 and the lower limit guard β2, and the final air-fuel ratio correction coefficient faf is calculated. At this time, if the air-fuel ratio correction coefficient faf is equal to or higher than the upper limit guard β1, the faf is guarded with β1, and if the air-fuel ratio correction coefficient faf is equal to or lower than the lower limit guard β2, the faf is guarded with β2.

  Returning to the process of FIG. 11, if the execution condition of the secondary air supply is not satisfied, the process proceeds to step S508, and the air-fuel ratio correction coefficient faf is calculated based on the deviation between the target air-fuel ratio λtg and the detected air-fuel ratio. Step S508 is a calculation process during normal control.

  After calculating the air-fuel ratio correction coefficient faf as described above, in step S509, the basic injection amount Tp is multiplied by the open fuel correction coefficient fopn and the air-fuel ratio correction coefficient faf, and the product is set as the final injection amount TAU (TAU = Tp × fopn × faf).

  FIG. 13 is a time chart showing the state of air-fuel ratio control at the time of secondary air supply. In FIG. 13, the air-fuel ratio feedback control is started at timing t21, and then the secondary air flow rate is increased at timing t23. In the chart portion representing the behavior of the air-fuel ratio correction coefficient faf, the upper and lower limit guards α1 and α2 for defining the first faf setting range are indicated by a one-dot chain line, and the upper and lower limit guards for defining the second faf setting range. β1 and β2 are indicated by dotted lines. The intake air amount ga is constant.

  In FIG. 13, when the air-fuel ratio feedback control is started at timing t21, the air-fuel ratio correction coefficient faf is calculated so as to eliminate the deviation between the target air-fuel ratio λtg and the detected air-fuel ratio (detection λ). At this time, since the detected air-fuel ratio is leaner than the target air-fuel ratio λtg, the air-fuel ratio correction coefficient faf is increased. Further, upper and lower limit guards α1 and α2 for defining the first faf setting range are set according to the secondary air flow rate at that time, and the air-fuel ratio correction coefficient faf changes while being guarded so as to be within the range of α1 to α2. To do. However, at the timings t21 to t22, the upper and lower limit guards α1 and α2 gradually change to the increasing side by the sudden change prevention process.

  At timing t22, changes in the upper and lower limit guards α1, α2 converge once, but after timing t23, the upper and lower limit guards α1, α2 change again to the increasing side as the secondary air flow rate increases. At timing t24, the upper limit guard α1 that defines the first faf setting range exceeds the upper limit guard β1 that defines the second faf setting range, and thereafter, the air-fuel ratio correction coefficient faf is guarded by the upper limit guard β1. The

  The combustion air-fuel ratio is restricted from being changed to the rich side after timing t24 (limited by the rich-side allowable combustion air-fuel ratio λrich). After timing t24, the air-fuel ratio correction coefficient faf and the combustion air-fuel ratio are limited as described above, so that drivability and exhaust emission deterioration are suppressed.

  As described above, according to the third embodiment, two faf setting ranges (α1 to α2, β1 to β2) are set when the secondary air is supplied, and the air-fuel ratio correction coefficient faf is limited by the two faf setting ranges. I did it. In this case, it is possible to limit the air-fuel ratio correction coefficient faf that is optimal in terms of both the secondary air supply state and the engine combustion state. As described above, even when the secondary air is supplied, the fuel injection amount can be properly corrected, and the engine operating state is stabilized. Accordingly, drivability and exhaust emission can be improved.

(Fourth embodiment)
In the fourth embodiment, a part of the third embodiment is changed, and the changed portion will be described below. In the present embodiment, the secondary air correction coefficient fsai and the air-fuel ratio correction coefficient faf are used as the fuel correction coefficients accompanying the secondary air supply.

  FIG. 14 is a flowchart showing the calculation process of the fuel injection amount in the present embodiment. This process is executed by the ECU 40 instead of FIG. Here, the description of the same processing as in FIG. 11 will be simplified.

  In FIG. 14, first, the basic injection amount Tp, the fuel correction coefficient fopn, and the target air-fuel ratio λtg are calculated (steps S701 to S703). Next, when the execution condition for the secondary air supply is satisfied, the secondary air supply is started by opening the on-off valve 37 and the operation of the secondary air pump 36, and the secondary air flow rate based on the detected value of the pressure sensor 38 and the like. gsai is calculated (steps S705 and S706).

  Thereafter, in step S707, a secondary air correction coefficient fsai is calculated. At this time, the secondary air correction coefficient fsai is calculated based on the elapsed time after the engine start using the relationship of FIG.

  In step S708, an air-fuel ratio correction coefficient faf for supplying secondary air is calculated. Here, details of the calculation process of the air-fuel ratio correction coefficient faf will be described with reference to FIG. The process of FIG. 15 is different from the process of FIG. 11 only in steps S808 and S810, and the description of the overlapping processes will be simplified as appropriate.

  In FIG. 15, first, the base value fafbase of the air-fuel ratio correction coefficient is calculated based on the air-fuel ratio deviation (step S801). Next, in steps S802 to S806, the faf upper limit guard α1 and the faf lower limit guard α2 are calculated (similar to steps S602 to S606 in FIG. 11). Briefly, the upper limit guard base value α1base is calculated using the equation (5), and the sudden change prevention process is performed on the upper limit guard base value α1base using the equation (6). The faf upper limit guard α1. Further, the lower limit guard base value α2base is calculated using the equation (7), the sudden change prevention process is performed on the lower limit guard base value α2base using the equation (8), and the calculation result is expressed as the faf lower limit guard. Let α2. The base value fafbase of the air-fuel ratio correction coefficient is guarded with the upper limit guard α1 and the lower limit guard α2.

  Thereafter, in steps S807 to S809, the upper limit guard β1 and the lower limit guard β2 in the second faf setting range are calculated based on the allowable combustion air-fuel ratio of the engine. That is, in step S807, the lean-side allowable combustion air-fuel ratio λlean and the rich-side allowable combustion air-fuel ratio λrich are set (similar to step S607 in FIG. 11). In step S808, the upper limit guard β1 is calculated based on the rich-side allowable combustion air-fuel ratio λrich, the open fuel correction coefficient fopn, and the secondary air correction coefficient fsai using the following equation (11).

また、ステップＳ８０９では、以下の（１２）式を用い、リーン側の許容燃焼空燃比λｌｅａｎとオープン燃料補正係数ｆｏｐｎと二次エア用補正係数ｆｓａｉとに基づいて下限ガードβ２を算出する。

In step S809, the lower limit guard β2 is calculated based on the lean-side allowable combustion air-fuel ratio λlean, the open fuel correction coefficient fopn, and the secondary air correction coefficient fsai using the following equation (12).

最後に、ステップＳ８１０では、空燃比補正係数ｆａｆ（前記ステップＳ８０６で求めたｆａｆ）を上限ガードβ１及び下限ガードβ２でガードして最終の空燃比補正係数ｆａｆを算出する。このとき、空燃比補正係数ｆａｆが上限ガードβ１以上であれば当該ｆａｆがβ１でガードされ、空燃比補正係数ｆａｆが下限ガードβ２以下であれば当該ｆａｆがβ２でガードされる。

Finally, in step S810, the air-fuel ratio correction coefficient faf (faf obtained in step S806) is guarded by the upper limit guard β1 and the lower limit guard β2, and the final air-fuel ratio correction coefficient faf is calculated. At this time, if the air-fuel ratio correction coefficient faf is equal to or higher than the upper limit guard β1, the faf is guarded with β1, and if the air-fuel ratio correction coefficient faf is equal to or lower than the lower limit guard β2, the faf is guarded with β2.

  Returning to the process of FIG. 14, if the execution condition of the secondary air supply is not satisfied, the process proceeds to step S709, and the air-fuel ratio correction coefficient faf is calculated based on the air-fuel ratio deviation. Step S709 is a calculation process during normal control.

  After calculating the air-fuel ratio correction coefficient faf as described above, in step S710, the basic injection amount Tp is multiplied by the open fuel correction coefficient fopn, the secondary air correction coefficient fsai, and the air-fuel ratio correction coefficient faf, and the product Is the final injection amount TAU (TAU = Tp × fopn × fsai × faf).

  FIG. 17 is a time chart showing the state of air-fuel ratio control at the time of secondary air supply. In FIG. 17, the air-fuel ratio feedback control is started at timing t32, and then the secondary air flow rate is increased at timing t33. In the chart portion representing the behavior of the air-fuel ratio correction coefficient faf, the upper and lower limit guards α1 and α2 for defining the first faf setting range are indicated by a one-dot chain line, and the upper and lower limit guards for defining the second faf setting range. β1 and β2 are indicated by dotted lines. The intake air amount ga is constant.

  In FIG. 17, the secondary air correction coefficient fsai increases after timing t31. As the secondary air correction coefficient fsai increases, the upper limit guard β1 that defines the second faf setting range decreases.

  When the air-fuel ratio feedback control is started at timing t32, the air-fuel ratio correction coefficient faf is calculated so as to eliminate the deviation between the target air-fuel ratio λtg and the detected air-fuel ratio (detected λ). At this time, the fuel increase is already performed by the correction coefficient fsai for secondary air, and the detected air-fuel ratio has converged in the vicinity of the target air-fuel ratio λtg, so the air-fuel ratio correction coefficient faf does not change much. In addition, the upper and lower limit guards α1 and α2 for defining the first faf setting range are also held at the same values as before the feedback start.

  Thereafter, at the timing t33, the upper and lower limit guards α1, α2 change to the increasing side as the secondary air flow rate increases. At timing t34, the upper limit guard α1 that defines the first faf setting range exceeds the upper limit guard β1 that defines the second faf setting range, and thereafter, the air-fuel ratio correction coefficient faf is guarded by the upper limit guard β1.

  The combustion air-fuel ratio is restricted from being changed to the rich side after timing t34 (limited by the rich-side allowable combustion air-fuel ratio λrich). After timing t34, the air-fuel ratio correction coefficient faf and the combustion air-fuel ratio are limited as described above, so that drivability and exhaust emission deterioration are suppressed.

  As described above, according to the fourth embodiment, similarly to the third embodiment, two faf setting ranges (α1 to α2, β1 to β2) are set when the secondary air is supplied, and the two faf are set. Since the air-fuel ratio correction coefficient faf is limited according to the set range, it is possible to limit the air-fuel ratio correction coefficient faf that is optimal in terms of both the secondary air supply state and the engine combustion state. As described above, even when the secondary air is supplied, the fuel injection amount can be properly corrected, and the engine operating state is stabilized. Accordingly, drivability and exhaust emission can be improved.

  In addition, this invention is not limited to the content of description of the said embodiment, For example, you may implement as follows.

  In the first embodiment, etc., when the secondary air is supplied, the lean side guard λmax according to the increase / decrease of the secondary air flow rate in order to suppress the excessive fluctuation of the combustion air / fuel ratio due to the change of the secondary air flow rate. Although the rich side guard λmin is set, this configuration is changed. For example, a change in the secondary air flow rate with respect to the intake air amount is set as a secondary air parameter (secondary air parameter = (ga + gsai) / ga), and the secondary air parameter is within a predetermined range γ1 to γ2 when the secondary air is supplied. It is determined whether or not there is (where γ1 <γ2). If the secondary air parameter is within the predetermined range γ1 to γ2, the final target air-fuel ratio λtg is set as the target air-fuel ratio base value λbase. On the other hand, if the secondary air flow rate gsai causes a secondary air parameter <γ1, the final target air-fuel ratio λtg is changed to a richer side than the target air-fuel ratio base value λbase, and the secondary air flow rate gsai increases. If the secondary air parameter> γ2, the final target air-fuel ratio λtg is changed to the lean side with respect to the target air-fuel ratio base value λbase. In this case, the final target air-fuel ratio λtg is preferably changed so as to be proportional to the amount of change in the secondary air parameter. Even with such a configuration, as described above, the fuel injection amount correction can be appropriately performed when the secondary air is supplied, and as a result, drivability and exhaust emission can be improved.

  As a guard value for limiting the target air-fuel ratio λtg, it is possible to set only the rich side guard λmin.

  Further, only the upper guard value (α1, β1) may be set as a guard value for limiting the air-fuel ratio correction coefficient faf.

  In the above-described embodiment, the lean / rich side allowable combustion air-fuel ratios λlean and λrich are calculated based on the engine water temperature using the relationship shown in FIG. 4, but correction using correction parameters may be performed as appropriate. . The correction parameters include load (intake air amount, in-cylinder charge air amount, intake pipe pressure), ignition timing, starting water temperature, elapsed time after starting, intake / exhaust valve timing, intake / exhaust valve lift, EGR The amount, the state of the intake vortex such as tumble / swirl, the fuel property, the outside air temperature, the intake air temperature, the fuel temperature, the atmospheric pressure, etc. can be considered.

  In the fourth embodiment, the relationship shown in FIG. 16 is used to calculate the secondary air correction coefficient fsai based on the elapsed time after the engine is started. May be. The correction parameters include start-up water temperature, water temperature, load (intake air amount, in-cylinder charge air amount, intake pipe pressure), open fuel correction coefficient, ignition timing, catalyst temperature, engine stop time, outside air temperature, intake air temperature, two The next air flow rate is considered.

  When air-fuel ratio feedback control is performed, if the secondary air flow rate changes or exhaust pulsation occurs due to secondary combustion or the like in the exhaust pipe 24, the secondary air cannot be stably supplied. The detection result is disturbed, and the accuracy of the air-fuel ratio feedback control is lowered. Therefore, the feedback gain may be variably set according to the secondary air flow rate or exhaust pulsation. Specifically, as the gain setting method, first, the influence degree of the exhaust pulsation is estimated according to the engine operating state in each case, and the feedback gain is set based on the estimation result. At this time, since the influence of the exhaust pulsation varies depending on the amplitude and the period, as shown in FIG. 18A, the influence degree of the exhaust pulsation is estimated according to the engine rotation speed and the load. According to FIG. 18A, it is estimated that the greater the amplitude (the higher the load), the greater the influence of exhaust pulsation. However, even if the amplitude is large, if the cycle is early (in the case of high rotation), it is estimated that the amplitude is canceled out and the influence degree of the exhaust pulsation becomes small. Further, as shown in FIG. 18B, the feedback gain is decreased as the influence of the exhaust pulsation increases, and conversely, the feedback gain is increased as the influence of the exhaust pulsation decreases.

  Alternatively, as shown in FIG. 19, the feedback gain is decreased as the secondary air flow rate is increased, and conversely, the feedback gain is increased as the secondary air flow rate is decreased. As described above, control hunting or the like can be suppressed even when a change in the secondary air flow rate or exhaust pulsation occurs.

  In each of the above embodiments, the fuel injection amount control is performed by setting the target air-fuel ratio base value λbase to a lean value (for example, λbase = 1.05) at the time of secondary air supply, but this target air-fuel ratio base value λbase is stoichiometric ( (λ = 1.0) may be used.

  In each of the above-described embodiments, the secondary air flow rate is calculated based on the differential pressure between the secondary air supply pressure and the cutoff pressure (reference pressure). Instead, the secondary air supply pressure and the exhaust gas are calculated. The secondary air flow rate may be calculated based on the exhaust pressure in the pipe. For example, the secondary air flow rate is calculated based on the differential pressure between the secondary air supply pressure and the exhaust pressure. In this case, since the secondary air flow rate is calculated using not only the secondary air supply pressure but also the exhaust pressure, even if the exhaust pressure changes due to a change in the engine operating state, etc., the secondary air flow rate Can be calculated with high accuracy. Thereby, the control accuracy of the fuel injection amount can be improved.

It is a block diagram which shows the outline of the engine control system in embodiment of invention. It is a flowchart which shows a fuel injection amount calculation process. It is a flowchart which shows a target air fuel ratio calculation process. It is a figure which shows the relationship between water temperature and an allowable combustion air fuel ratio. It is a time chart which shows the behavior of each parameter at the time of secondary air supply. It is a time chart which shows the measurement result in an actual machine about a secondary air flow rate, an air fuel ratio, and a combustion air fuel ratio. It is a flowchart which shows the fuel injection amount calculation process in 2nd Embodiment. It is a flowchart which shows the calculation process of the air fuel ratio correction coefficient faf in 2nd Embodiment. It is a time chart which shows the behavior of each parameter at the time of secondary air supply. It is a time chart for demonstrating the effect of the sudden change prevention process of an upper / lower limit guard. It is a flowchart which shows the fuel injection amount calculation process in 3rd Embodiment. It is a flowchart which shows the calculation process of the air fuel ratio correction coefficient faf in 3rd Embodiment. It is a time chart which shows the behavior of each parameter at the time of secondary air supply. It is a flowchart which shows the fuel injection amount calculation process in 4th Embodiment. It is a flowchart which shows the calculation process of the air fuel ratio correction coefficient faf in 4th Embodiment. It is a figure which shows the relationship between the elapsed time after starting, and the correction coefficient fsai for secondary air. It is a time chart which shows the behavior of each parameter at the time of secondary air supply. (A) is a map for estimating the influence of exhaust pulsation, (b) is a figure which shows the relationship between the influence of exhaust pulsation and a feedback gain. It is a figure which shows the relationship between a secondary air flow volume and a feedback gain.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine as an internal combustion engine, 24 ... Exhaust pipe, 32 ... Air-fuel ratio sensor as air-fuel ratio detection means, 35 ... Secondary air piping, 36 ... Secondary air pump, 40 ... Flow rate calculation means, Target air-fuel ratio setting means, ECU as fuel amount correcting means, target changing means, air-fuel ratio correction amount calculating means, guard setting means, and correction amount limiting means.

Claims (15)

A secondary air supply device for supplying secondary air to the exhaust passage of the internal combustion engine;
A flow rate calculating means for calculating a flow rate of secondary air flowing into the exhaust passage;
Target air-fuel ratio setting means for setting a target air-fuel ratio at the time of secondary air supply;
Air-fuel ratio detecting means for detecting the air-fuel ratio downstream of the secondary air supply port of the exhaust passage;
Fuel amount correcting means for correcting the fuel injection amount in air-fuel ratio feedback control for matching the air-fuel ratio detected by the air-fuel ratio detecting means with the target air-fuel ratio when supplying secondary air;
Target change means for monitoring the increase or decrease of the secondary air flow rate, and changing the target air-fuel ratio to the lean side or the rich side according to the increase or decrease;
With
The fuel amount correction means calculates an air-fuel ratio correction amount according to a deviation between the air-fuel ratio detected by the air-fuel ratio detection means and the target air-fuel ratio, and corrects the fuel injection amount by the air-fuel ratio correction amount. ,
A fuel injection amount control apparatus for an internal combustion engine, wherein a feedback gain for calculating the air-fuel ratio correction amount is variably set in accordance with a secondary air flow rate or exhaust pulsation generated in an exhaust passage when supplying secondary air. . Means for setting a correction amount guard value on at least an increase side of the air-fuel ratio correction amount according to the secondary air flow rate when supplying secondary air;
The fuel injection amount control device for an internal combustion engine according to claim 1, wherein when the air-fuel ratio correction amount reaches the correction amount guard value, the air-fuel ratio correction amount is limited by the guard value . A secondary air supply device for supplying secondary air to the exhaust passage of the internal combustion engine;
A flow rate calculating means for calculating a flow rate of secondary air flowing into the exhaust passage;
Target air-fuel ratio setting means for setting a target air-fuel ratio at the time of secondary air supply;
Air-fuel ratio detecting means for detecting the air-fuel ratio downstream of the secondary air supply port of the exhaust passage;
Fuel amount correcting means for correcting the fuel injection amount in air-fuel ratio feedback control for matching the air-fuel ratio detected by the air-fuel ratio detecting means with the target air-fuel ratio when supplying secondary air;
Target change means for monitoring the increase or decrease of the secondary air flow rate, and changing the target air-fuel ratio to the lean side or the rich side according to the increase or decrease;
With
The fuel amount correction means calculates an air-fuel ratio correction amount according to a deviation between the air-fuel ratio detected by the air-fuel ratio detection means and the target air-fuel ratio, and corrects the fuel injection amount by the air-fuel ratio correction amount. ,
Means for setting a correction amount guard value on at least an increase side of the air-fuel ratio correction amount according to the secondary air flow rate when supplying secondary air;
A fuel injection amount control device for an internal combustion engine, wherein when the air-fuel ratio correction amount reaches the correction amount guard value, the air-fuel ratio correction amount is limited by the guard value. The fuel injection amount control device for an internal combustion engine according to claim 2 or 3, wherein the correction amount guard value is set based on the secondary air flow rate and the target air-fuel ratio . 4. The correction amount guard value is set by correcting a guard value of an air-fuel ratio correction amount during normal air-fuel ratio feedback control without secondary air supply based on at least the secondary air flow rate. A fuel injection amount control device for an internal combustion engine as described . 6. The fuel injection amount control device for an internal combustion engine according to claim 2, further comprising means for regulating a change rate of the correction amount guard value . While the correction amount guard value by the guard setting means is set as the first correction amount guard value, the second correction is performed based on the allowable combustion air-fuel ratio allowed as the air-fuel ratio of the air-fuel mixture to be burned in the internal combustion engine. Set the amount guard value,
7. The fuel injection amount control device for an internal combustion engine according to claim 2, wherein the air-fuel ratio correction amount is limited by the first correction amount guard value and the second correction amount guard . The target change means changes the target air-fuel ratio to the lean side when the secondary air flow rate is increased, and changes the target air-fuel ratio to the rich side when the secondary air flow rate is decreased. A fuel injection amount control device for an internal combustion engine as described . Means for setting at least a rich guard value of the target air-fuel ratio according to the secondary air flow rate calculated by the flow rate calculation means;
9. The fuel injection amount control device for an internal combustion engine according to claim 1, wherein the target changing means limits the target air-fuel ratio with the guard value when the target air-fuel ratio reaches the guard value . 10. The fuel injection amount of the internal combustion engine according to claim 9, wherein the guard value is set based on an allowable combustion air-fuel ratio that is allowed as an air-fuel ratio of an air-fuel mixture that is combusted in the internal combustion engine and the secondary air flow rate. Control device. The fuel injection amount control device for an internal combustion engine according to claim 10, wherein the allowable combustion air-fuel ratio is set based on a temperature of the internal combustion engine. The fuel amount correction means calculates an increase correction amount for secondary air supply based on a target air-fuel ratio at the time of secondary air supply and a change in the secondary air flow rate with respect to the intake air amount of the internal combustion engine, 12. The fuel injection amount control device for an internal combustion engine according to claim 1, wherein the fuel injection amount is corrected by an increase correction amount . The flow rate calculating means is configured to perform a secondary operation based on a secondary air supply pressure detected as a secondary air supply state of the secondary air supply device and a reference pressure detected in a different state different from the secondary air supply state. The fuel injection amount control device for an internal combustion engine according to any one of claims 1 to 12, wherein an air flow rate is calculated . The fuel injection amount control device for an internal combustion engine according to claim 13, wherein the reference pressure is a closing pressure detected by setting a secondary air supply path leading to the secondary air supply device as a closing state . The flow rate calculation means calculates a secondary air flow rate based on a secondary air supply pressure detected when the secondary air supply device is in a secondary air supply state and an exhaust pressure in the exhaust passage. The fuel injection amount control device for an internal combustion engine according to any one of claims 12 to 13 .

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