JP4329610B2 - 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 air-fuel ratio feedback control is performed based on the detected value, the secondary air is supplied according to the secondary air flow rate. When the fuel increase is performed and then the secondary air supply is stopped, the fuel injection amount changes abruptly. As a result, the drivability deteriorates. 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 in accordance with the secondary air flow rate even when the secondary air is being supplied. Therefore, there is a demand for a technique that can suitably perform fuel amount correction throughout the process from secondary air supply to stop.
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 suitably control the fuel amount when the secondary air supply is stopped, and thus improve drivability. is there.

In the fuel injection amount control device of the present invention, the first target value is set as the target air-fuel ratio when the secondary air is supplied, and the second target value is set as the target air-fuel ratio when the secondary air supply is stopped. Further, when the secondary air is supplied and when the secondary air supply is stopped, fuel injection is performed so that the air-fuel ratio downstream of the secondary air supply port in the exhaust passage becomes the target air-fuel ratio (first target value or second target value). The amount is corrected. In this case, when the secondary air is supplied, the fuel injection amount increase correction is normally performed in accordance with the secondary air supply. On the other hand, after the secondary air supply is stopped, the increase correction is stopped. The combustion air-fuel ratio of the engine suddenly changes to the lean side, resulting in deterioration of drivability.

  For this inconvenience, in the first aspect of the invention, when the target air-fuel ratio is switched from the first target value to the second target value when the supply of secondary air is stopped, the target air-fuel ratio is richer than the second target value. Since the initial setting is made on the side, and then the shift to the second target value is made, rapid changes in the combustion air-fuel ratio are suppressed, and drivability can be improved.

According to the first aspect of the present invention, at the time of transition from the secondary air supply to the supply stop, the combustion air-fuel ratio of the internal combustion engine estimated at the immediately preceding secondary air supply is initially set as the target air-fuel ratio. Here, the “combustion air-fuel ratio” is the air-fuel ratio of the combustion gas that is actually used for combustion in the internal combustion engine. When the secondary air is supplied, the “combustion air-fuel ratio” Although it becomes rich by the amount of the secondary air flow, after the secondary air supply is stopped, it matches the air-fuel ratio on the downstream side of the secondary air supply port. In this case, immediately after the secondary air supply is stopped, the combustion air-fuel ratio immediately before the supply stop is made the target air-fuel ratio, so even if the secondary air flow rate in the exhaust passage suddenly becomes zero, the fuel up to that time The combustion state can be continued. Therefore, drivability can be maintained well.

According to the second aspect of the present invention, when the difference between the combustion air-fuel ratio of the internal combustion engine immediately before the stop of the secondary air supply and the second target value is equal to or greater than a predetermined determination value, the target air-fuel ratio is greater than the second target value. Is also initially set on the rich side, and the target air-fuel ratio is set to the second target value when the difference between the combustion air-fuel ratio of the internal combustion engine immediately before stopping the secondary air supply and the second target value is less than a predetermined determination value. Is set. That is, the deterioration of drivability when the supply of secondary air is stopped is due to an excessive change in the combustion air-fuel ratio. This is because the difference between the combustion air-fuel ratio immediately before the stop of the supply of secondary air and the second target value is predetermined. It becomes remarkable when it becomes more than the judgment value. According to this configuration, remarkable deterioration in drivability can be surely eliminated.

According to the third aspect of the present invention, the secondary air is supplied according to the secondary air flow rate each time so that the air-fuel ratio downstream of the secondary air supply port of the exhaust passage becomes the target air-fuel ratio when the secondary air is supplied. An increase correction amount for supply is calculated. In such a configuration, the combustion air-fuel ratio is estimated based on the increase correction amount. In this case, the combustion air-fuel ratio of the internal combustion engine can be suitably estimated when the secondary air is supplied.

In the fourth aspect of the invention, the target air-fuel ratio is set on the rich side with respect to the second target value, and then is changed toward the second target value. Thereby, after the supply of the secondary air is stopped, the shift to the fuel injection amount control in which the second target value is the target air-fuel ratio can be smoothly realized.

According to the fifth aspect of the present invention, when the air-fuel ratio guard value for setting the exhaust emission to an allowable level is set and the target air-fuel ratio is set to be richer than the second target value, the target air-fuel ratio is Limited by the air-fuel ratio guard value. Thereby, in addition to suppressing deterioration of drivability when the supply of secondary air is stopped, deterioration of exhaust emissions can also be suppressed.

According to the sixth aspect of the present invention, 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 air-fuel ratio correction is performed. The fuel injection amount is corrected by the amount.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the 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.

  Further, 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 supply device as a secondary air supply device is connected upstream of the secondary air pipe 35. An air pump 36 is provided. 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).

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.

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).

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 target air-fuel ratio setting process at the time of fuel injection amount control, and this process is executed by the ECU 40 at a predetermined time period.

  First, in step S101, it is determined whether or not the secondary air supply is currently stopped. If the secondary air supply has been performed, the process proceeds to step S102, and the target air-fuel ratio base value λbase1 at the time of secondary air supply is calculated. At this time, for example, a target air-fuel ratio map prepared for supplying secondary air is used, and the target air-fuel ratio base value λbase1 is calculated based on the engine speed, load, and the like each time. The target air-fuel ratio base value λbase1 is set so that the exhaust emission at the time of secondary air supply is in an optimal state, for example, λbase1 = 1.05. This target air-fuel ratio base value λbase1 corresponds to the “first target value”.

  In step S103, the combustion air-fuel ratio λx of the engine in the secondary air supply state is estimated. The combustion air-fuel ratio λx is the air-fuel ratio of the air-fuel mixture supplied to the engine.

  In step S104, the final target air-fuel ratio λtg is calculated. At this time, it is desirable to calculate the final target air-fuel ratio λtg by performing a guard process or the like according to the secondary air flow rate or the like on the calculated target air-fuel ratio base value λbase1, and the guard process or the like is performed according to the present invention. The explanation is omitted because it is not the main purpose. Simply, λtg = λbase1.

  If the secondary air supply has been stopped, the process proceeds to step S105, and the target air-fuel ratio base value λbase2 at the time when the secondary air supply is stopped is calculated. At this time, for example, a target air-fuel ratio map prepared for stopping the supply of secondary air is used, and the target air-fuel ratio base value λbase2 is calculated based on the engine speed, load, etc. each time. The target air-fuel ratio base value λbase2 is set so that the exhaust emission when the secondary air supply is stopped (normal engine operation) is in an optimal state, and for example, λbase2 = 1.0 (stoichiometric). . This target air-fuel ratio base value λbase2 corresponds to a “second target value”.

  Thereafter, in step S106, it is determined whether or not it is immediately after the supply of secondary air is stopped. In the case of YES, the process proceeds to step S107, and the combustion air-fuel ratio λx estimated at the time of secondary air supply (specifically, immediately before switching from secondary air supply to stop) is read.

  In step S108, it is determined whether or not the difference between the target air-fuel ratio base value λbase2 and the combustion air-fuel ratio λx is equal to or greater than a predetermined determination value kLMD. When λbase2−λx ≧ kLMD, the process proceeds to step S109 to calculate an initial target value λini for initial setting of the target air-fuel ratio immediately after the supply of secondary air is stopped. The initial target value λini is

However, since gsai = 0, the initial target value λini = combustion air-fuel ratio λx.

  In step S110, the larger of the initial target air-fuel ratio base value λini and the air-fuel ratio guard value λGD is set as the final target air-fuel ratio λtg. The air-fuel ratio guard value λGD is set to keep the exhaust emission at an allowable level, and is a predetermined rich value. According to step S110, the final target air-fuel ratio λtg is suppressed from being richer than the air-fuel ratio guard value λGD.

  If λbase2−λx <kLMD, the process proceeds to step S111, and the target air-fuel ratio base value λbase2 is set as the final target air-fuel ratio λtg. That is, when λbase2-λx ≧ kLMD, the final target air-fuel ratio λtg is initially set on the rich side by the initial target value λini as described above, but when λbase2-λx <kLMD, the final target air-fuel ratio is set. λtg is initialized with the target air-fuel ratio base value λbase2.

  If the secondary air supply is stopped but not immediately after the stop, the process proceeds to step S112 to calculate the final target air-fuel ratio λtg. In this step S112, “λtg previous value + ΔK” obtained by adding a predetermined value ΔK to the previous value of the final target air-fuel ratio λtg is compared with the target air-fuel ratio base value λbase2, and the smaller one is set as the final target air-fuel ratio λtg. The process of setting the final target air-fuel ratio λtg to “λtg previous value + ΔK” in step S112 corresponds to the gradual change process of the target air-fuel ratio, but after the final target air-fuel ratio λtg once reaches the target air-fuel ratio base value λbase2. Λtg = λbase2 may be set each time.

  Next, the change in the secondary air flow rate at the time of secondary air supply → stop and the change in the final target air-fuel ratio λtg, the correction coefficient, etc. will be described more specifically with reference to the time chart of FIG. In FIG. 3, the behavior of the conventional control is shown by a one-dot chain line in the chart portion representing the behavior of the final target air-fuel ratio λtg, the secondary air correction coefficient fsai, and the combustion air-fuel ratio.

  Before the timing t1, the secondary air flow rate is set to a predetermined value by performing the secondary air supply, and the final target air-fuel ratio λtg is set to a predetermined value that is slightly lean (for example, the target air-fuel ratio base value λbase1). . At this time, the secondary air correction coefficient fsai> 1.0 and the combustion air-fuel ratio <1.

  When the secondary air supply is stopped at timing t1, the secondary air flow rate becomes 0, and the final target air-fuel ratio λtg is changed to the rich side. At this time, in the conventional control indicated by the one-dot chain line, since the final target air-fuel ratio λtg is directly changed to the target air-fuel ratio base value λbase2, the secondary air correction coefficient fsai and the combustion air-fuel ratio change abruptly. As a result, drivability deteriorates. In contrast, in the control according to the present embodiment, the final target air-fuel ratio λtg is temporarily changed to the initial target value λini that is richer than the target air-fuel ratio base value λbase2, and then gradually toward the target air-fuel ratio base value λbase2. Will be changed. As a result, sudden changes in the secondary air correction coefficient fsai and the combustion air-fuel ratio are suppressed, and deterioration of drivability can be avoided. In particular, in the present embodiment, the initial target value λini = combustion air / fuel ratio λx (combustion air / fuel ratio immediately before the supply of the secondary air flow is stopped), so when the secondary air supply is stopped, the fuel combustion up to that point The state continues and a smooth transition is possible. The final target air-fuel ratio λtg converges to the target air-fuel ratio base value λbase2 at timing t2.

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

  When the secondary air supply is stopped, the final target air-fuel ratio λtg is initially set on a richer side than the target air-fuel ratio base value λbase2 after the supply of secondary air is stopped, and then gradually decreased toward the target air-fuel ratio base value λbase2. As a result, the rapid change of the combustion air-fuel ratio is suppressed, and drivability can be improved.

  Since the air-fuel ratio guard value λGD for maintaining the exhaust emission at an allowable level is set, it is possible to reliably suppress the deterioration of the exhaust emission in addition to suppressing the deterioration of the drivability when the supply of the secondary air is stopped.

  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 above embodiment, when the secondary air supply is stopped, the final target air-fuel ratio λtg is temporarily changed to the initial target value λini that is richer than the target air-fuel ratio base value λbase2, and immediately thereafter, the target air-fuel ratio base value λbase2 is changed. However, the control state may be gradually changed toward the target air-fuel ratio base value λbase2 after the control state at the initial target value λini is continued for a predetermined time.

  In the above embodiment, the fuel injection amount control is performed with the target air-fuel ratio base value λbase1 as a lean value (for example, λbase1 = 1.05) at the time of secondary air supply, but this target air-fuel ratio base value λbase1 is stoichiometric (λ = 1.0).

  In the above 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 injection amount is calculated based on the secondary air correction coefficient fsai. However, instead of this, the air-fuel ratio correction coefficient faf is calculated according to the deviation between the air-fuel ratio detected by the air-fuel ratio sensor 32 and the target air-fuel ratio, and the fuel injection amount is calculated based on the air-fuel ratio correction coefficient faf. This correction may be performed. 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.

  It is also possible to correct the fuel injection amount by using both the secondary air correction coefficient fsai and the air-fuel ratio correction coefficient faf. In this case, the final injection amount TAU is calculated as TAU = Tp × fsai × faf.

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 target air fuel ratio calculation process. It is a time chart which shows the behavior of each parameter when secondary air supply is stopped.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine as internal combustion engine, 24 ... Exhaust pipe, 32 ... Air-fuel ratio sensor as air-fuel ratio detection means, 36 ... Secondary air pump as secondary air supply device, 40 ... Target air-fuel ratio setting means, Fuel amount correction means ECU as target value shifting means.

Claims (6)

A secondary air supply device for supplying secondary air to the exhaust passage of the internal combustion engine;
Target air-fuel ratio setting means for setting a first target value as a target air-fuel ratio when secondary air is supplied and setting a second target value as a target air-fuel ratio when secondary air supply is stopped;
Fuel amount correction means for correcting the fuel injection amount so that the air-fuel ratio downstream of the secondary air supply port of the exhaust passage becomes the target air-fuel ratio at the time of secondary air supply and when the secondary air supply is stopped;
When the target air-fuel ratio is switched from the first target value to the second target value when the supply of secondary air is stopped, the target air-fuel ratio is initially set on the richer side than the second target value, and then the second target value is shifted to and a target value transition means for,
The target value transition means initially sets the combustion air-fuel ratio of the internal combustion engine estimated at the time of the secondary air supply immediately before as the target air-fuel ratio at the time of transition from the secondary air supply to the supply stop. A fuel injection amount control device for an internal combustion engine. The target value transition means sets the target air-fuel ratio from the second target value when the difference between the combustion air-fuel ratio of the internal combustion engine immediately before stopping the secondary air supply and the second target value is equal to or greater than a predetermined determination value. Also, when the difference between the combustion air-fuel ratio of the internal combustion engine immediately before stopping the secondary air supply and the second target value is less than a predetermined determination value, the target air-fuel ratio is set to the second target value. The fuel injection amount control device for an internal combustion engine according to claim 1 , wherein the fuel injection amount control device is set. When the secondary air is supplied, an increase correction amount for supplying the secondary air in accordance with the flow rate of the secondary air each time so that the air-fuel ratio downstream of the secondary air supply port of the exhaust passage becomes the target air-fuel ratio. Comprises means for calculating
The fuel injection amount control device for an internal combustion engine according to claim 1 or 2 , wherein the combustion air-fuel ratio is estimated based on the increase correction amount. The target value shifting unit, after the target air-fuel ratio set in the rich side than the second target value, the target air-fuel ratio, any one of claims 1 to 3 divided variable is allowed toward the second target value A fuel injection amount control device for an internal combustion engine according to claim 1. The air-fuel ratio guard value for setting the exhaust emission to an allowable level is set, and when the target air-fuel ratio is set to be richer than the second target value, the target air-fuel ratio is limited by the air-fuel ratio guard value. 5. The fuel injection amount control device for an internal combustion engine according to any one of 1 to 4 . Air-fuel ratio detection means for detecting an air-fuel ratio downstream of the secondary air supply port of the exhaust passage is provided, and air-fuel ratio feedback control is performed so that the air-fuel ratio detected by the air-fuel ratio detection means matches the target air-fuel ratio. In the configuration to implement:
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 device for an internal combustion engine according to any one of claims 1 to 5 .