JP3641016B2 - Air-fuel ratio feedback control device for internal combustion engine - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an air-fuel ratio feedback control device for controlling an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine based on an output of an exhaust concentration detector provided in an exhaust system of the internal combustion engine. The air-fuel ratio feedback control device for the internal combustion engine mounted on the vehicle equipped with the above.
[0002]
[Prior art]
Conventionally, when the engine is in a deceleration state, the air-fuel ratio feedback control of the air-fuel mixture supplied to the engine is stopped to cut off the fuel supply, and the engine speed is reduced to a predetermined speed. There is known a technique for resuming fuel supply by air-fuel ratio feedback control when the control range of the fuel ratio becomes a region in which air-fuel ratio feedback control should be resumed (hereinafter referred to as “idle air-fuel ratio feedback control region”).
[0003]
Furthermore, when the engine load is large due to the operation of the air conditioner, etc., the predetermined engine speed for shutting off the fuel supply is set to a higher value than when the engine load is small to prevent engine stall. A fuel injection device is already known (Japanese Patent Publication No. 55-34295).
[0004]
[Problems to be solved by the invention]
However, when the air conditioner is operating when the engine is decelerated, the conventional fuel injection device only sets the fuel supply cutoff speed to a high value. Due to the high number, there is a problem that fuel may be supplied more than necessary in the operation region below the rotation speed, and the fuel consumption may be deteriorated.
[0005]
Also, when the engine decelerates, vaporization of the fuel adhering to the intake pipe wall and the like is promoted, while the auxiliary air amount control is delayed, and when the air conditioner is activated, the fuel cut region is narrowed by increasing the return rotational speed. Therefore, the supply air-fuel ratio to the engine tends to be rich. When the supply air-fuel ratio during engine deceleration tends to become rich, immediately after the start of the idle air-fuel ratio feedback control, the air-fuel ratio correction coefficient set according to the output of the exhaust concentration detector corrects the supply air-fuel ratio in the lean direction. Furthermore, since the engine operating state is an idle state and the air-fuel ratio control speed (the correction speed of the air-fuel ratio correction coefficient) is slow, the lean state of the supplied air-fuel ratio will continue for a relatively long time, During that time, there was a problem that a large amount of NOx was discharged.
[0006]
The present invention has been made in order to solve the above-described problem, and its purpose is immediately after the engine is decelerated and idle air-fuel ratio feedback control is resumed while preventing deterioration of fuel consumption and engine stall during engine deceleration. The present invention provides an air-fuel ratio feedback control device for an internal combustion engine that can suppress deterioration of exhaust characteristics due to the operation of an air conditioner.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an air-fuel ratio feedback control apparatus for an internal combustion engine according to claim 1 of the present invention comprises an exhaust concentration detection means provided in an exhaust system of the internal combustion engine, and an exhaust gas detected by the exhaust concentration detection means. A concentration detection value is compared with a predetermined value, and an air-fuel ratio control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to the predetermined value according to the comparison result, and a deceleration state of the engine are detected When the deceleration state is detected, the feedback control is stopped, and when the air-fuel ratio control region shifts to the idle air-fuel ratio feedback control region after the deceleration state ends, the air-fuel ratio An air-fuel ratio feedback control apparatus for an internal combustion engine, comprising an air-fuel ratio control restarting means for restarting feedback control. An air conditioner operating state detecting means for detecting an operating state of an air conditioner driven by the gin, and the engine speed is equal to or greater than a first predetermined value when the deceleration state is detected and the air conditioner is inoperative. When the fuel supply to the engine is stopped, the engine speed is equal to or greater than a second predetermined value greater than the first predetermined value when the deceleration state is detected and the operation of the air conditioner is detected. When the fuel supply to the engine is stopped and the engine speed is between the first predetermined value and the second predetermined value, the air-fuel ratio of the air-fuel mixture supplied to the engine is made lean. And a decelerating air-fuel ratio leaning means.
[0008]
[Action]
According to the air-fuel ratio feedback control apparatus for an internal combustion engine of the present invention, when the engine deceleration state is detected and the air conditioner is not operating, when the engine speed is greater than or equal to a first predetermined value, When the fuel supply is stopped, the deceleration state is detected, and the operation of the air conditioner is detected, the fuel supply to the engine is stopped when the engine speed is equal to or higher than a second predetermined value. When the rotational speed of the engine is between the first predetermined value and the second predetermined value, the air-fuel ratio of the air-fuel mixture supplied to the engine is made lean.
[0009]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0010]
FIG. 1 is an overall configuration diagram of an internal combustion engine and an air-fuel ratio feedback control device thereof according to an embodiment of the present invention. A throttle valve 3 is disposed in the middle of an intake pipe 2 of the engine 1. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3, and an electric signal corresponding to the opening of the throttle valve 3 is output and supplied to an electronic control unit (hereinafter referred to as “ECU”) 5. .
[0011]
An intake secondary air control device 18 (hereinafter referred to as “EACV”) is disposed in the middle of the auxiliary air passage 17 that bypasses the throttle body 3 of the intake pipe 2 and is electrically connected to the ECU 5. The EACV 18 supplies auxiliary air as intake secondary air to the intake pipe 2 in order to perform idle speed control of the engine 1.
[0012]
The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). At the same time, it is electrically connected to the ECU 5 and the valve opening time of the fuel injection valve 6 is controlled by a signal from the ECU 5.
[0013]
On the other hand, an intake pipe absolute pressure (PBA) sensor 8 is provided immediately downstream of the throttle valve 3 via a pipe 7. The absolute pressure signal converted into an electric signal by the absolute pressure sensor 8 is supplied to the ECU 5. Is done. Further, an intake air temperature (TA) sensor 9 is attached downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies it to the ECU 5.
[0014]
An engine water temperature (TW) sensor 10 mounted on the main body of the engine 1 includes a thermistor or the like, detects the engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies the temperature signal to the ECU 5. The engine speed (NE) sensor 11 and the cylinder discrimination (CYL) sensor 12 are attached around the cam shaft or crank shaft (not shown) of the engine 1. The engine speed sensor 11 outputs a pulse (hereinafter referred to as “TDC signal pulse”) at a predetermined crank angle position every 180 ° rotation of the crankshaft of the engine 1, and the cylinder discrimination sensor 12 is a predetermined crank angle of a specific cylinder. A signal pulse is output at the position, and each of these signal pulses is supplied to the ECU 5.
[0015]
The three-way catalyst (catalytic converter) 14 is disposed in the exhaust pipe 13 of the engine 1 and purifies components such as HC, CO, and NOx in the exhaust gas. An oxygen concentration sensor 16 (hereinafter referred to as “O ₂ sensor 16”) as an exhaust concentration detector is mounted on the upstream side of the three-way catalyst 14 in the exhaust pipe 13, and this O ₂ sensor 16 is in the exhaust gas. The oxygen concentration is detected, and an electrical signal corresponding to the detected value is output and supplied to the ECU 5.
[0016]
A clutch switch 19 of an air conditioner (not shown) driven by the engine 1 is connected to the ECU 5, and an on / off signal thereof is supplied to the ECU 5.
[0017]
The ECU 5 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, and the like, and a central processing circuit (hereinafter referred to as “CPU”). 5b, a storage means 5c for storing various calculation programs executed by the CPU 5b and calculation results, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, and the like.
[0018]
The CPU 5b discriminates various engine operation states such as a feedback control operation region and an open loop control operation region according to the oxygen concentration in the exhaust gas based on the various engine parameter signals described above, and performs the following according to the engine operation state. Based on the equation (1), the fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated.
[0019]
TOUT = TI × KO2 × K1 + K2 (1)
Here, TI is a basic fuel amount, specifically, a basic fuel injection time determined according to the engine speed NE and the intake pipe absolute pressure PBA, and a TI map for determining this TI value is stored in the storage means. 5c.
[0020]
KO2 represents an air-fuel ratio correction coefficient calculated based on the output of the O ₂ sensor 16, so that the air-fuel ratio in the feedback control the air-fuel ratio detected by the O ₂ sensor 16 (oxygen concentration) coincides with the target air-fuel ratio During open loop control, it is set to a predetermined value according to the engine operating state.
[0021]
K1 and K2 are other correction coefficients and correction variables that are calculated according to various engine parameter signals, and are values that optimize various characteristics such as fuel efficiency characteristics and engine acceleration characteristics according to engine operating conditions. Set to
[0022]
Based on the result calculated as described above, the CPU 5b outputs a signal for driving the fuel injection valve 6 via the output circuit 5d.
[0023]
2 and 3 show a flowchart of a calculation routine of the air-fuel ratio correction coefficient KO2 during the air-fuel ratio feedback control, and this routine is executed in synchronization with the generation of the TDC signal pulse.
[0024]
First, it is determined whether or not the previous control was an open loop control (step S201). If the result is negative (NO), it is determined whether or not the previous control was an idle operation region (step S202). Here, it is determined by the routine of FIG. As a result of this determination, if the previous time was the idle operation region, it is further determined whether or not the current operation region is in the idle operation region (step S213). As a result, when the previous time is not the idle operation region or when the current time is also in the idle operation region, the process proceeds to step S203, and when the previous time is the idle operation region and this time is not the idle operation region, the step The process proceeds to S212.
[0025]
In step S203, it is determined whether or not the magnitude relationship of the output level of the O ₂ sensor 16 is reversed with respect to the predetermined reference value VREF. When the output level of the O ₂ sensor 16 is reversed, the proportional control ( On the other hand, if it is not reversed, the process proceeds to step S301 and integral control is performed.
[0026]
In step S204, it is determined whether or not the output level of the O ₂ sensor 16 is low (LOW) with respect to the predetermined reference value VREF (step S204). If the determination result is affirmative (YES), the process proceeds to step S206. Then, the addition proportional term PR is added to the previously calculated KO2 value to set as the current KO2 value. Here, the addition proportional term PR increases the correction coefficient KO2 stepwise after the output voltage of the O ₂ sensor 16 is inverted from the high level to the low level with respect to the predetermined reference value VREF, that is, from the rich side to the lean side. This is a correction term for shifting the air-fuel ratio in the rich direction.
[0027]
On the other hand, when the determination result in step S204 is negative (NO), the subtraction proportional term PL is subtracted from the previously calculated KO2 value to obtain the current KO2 value (step S208). Here, the subtraction proportional term PL is obtained by decreasing the correction coefficient KO2 stepwise after the output voltage of the O ₂ sensor 16 is inverted from the low level to the high level with respect to the predetermined reference value VREF, that is, from the lean side to the rich side. This is a correction term for shifting the air-fuel ratio in the lean direction.
[0028]
After execution of step S206 or S208, the process proceeds to step S209, the average value KREF is calculated by the following equation (2), and then this routine ends.
[0029]
KREF = KO2 × CREF / A + KREF × (A−CREF) / A (2)
Here, A is a constant, CREF is an annealing coefficient set to an appropriate value between 1 and A, and KREF on the right side is an average value KREF obtained up to the previous time.
[0030]
The average value KREF is calculated as KREF0 in the idle operation region, and is calculated as KREF1 in other regions than the idle operation region.
[0031]
On the other hand, if the result of determination in step S201 is affirmative (YES), that is, if the previous control was open loop control, it is determined whether or not the current operation is in the idle operation region (step S210). If (YES), the correction coefficient KO2 is set to the average value KREF0 of the KO2 values calculated in the idle operation region (step S211), and integration control using the average value KREF0 as the initial value is started (step S301 and subsequent steps). ).
[0032]
If the result of determination in step S210 is negative (NO), the correction coefficient KO2 is set to (KREF1 × CR) (step S212). That is, when the operating state shifts from the open loop control region to the feedback region other than the idle region, the initial value of the KO2 value at the time of the region shift is set to the product value obtained by multiplying the KREF1 value by the value CR, and the integration control is started. (Step S301 and below).
[0033]
Here, the value CR is set so as to improve the overall exhaust gas characteristics in the entire operating range of the engine in accordance with the exhaust gas characteristics of the engine itself and the exhaust gas purification characteristics of the exhaust gas purification device. Specifically, for example, when it is desired to reduce the NOx emission amount, the value CR is larger than 1, that is, the air-fuel ratio of the air-fuel mixture formed by the correction coefficient value KO2 at this time is more sure than the stoichiometric air-fuel ratio. The value is set so as to be on the rich side. For example, when it is desired to reduce the CO and HC emissions, the value CR is set to a value smaller than 1, that is, a value that ensures that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio.
[0034]
Also, when the result of the determination in step S213 is negative (NO), that is, when the region shifts from the idle region to the outside of the idle region, step S212 is executed to perform the integration control after step S301.
[0035]
Next, the integral control (I term control) after step S301 is performed as follows. First, in step S301, it is determined whether or not the output level from the O ₂ sensor 16 is on the low level (LOW) side with respect to the predetermined reference value VREF. When the output level of the O ₂ sensor is at the low level, a TDC signal pulse is determined. 1 is added to the value of the count number NIL (step S302), it is determined whether or not the count number NIL has reached a predetermined value NI (for example, 4) (step S303), and the result of the determination is negative ( If NO, the correction coefficient KO2 is held at the immediately preceding value (step S307), and if affirmative (YES), the process proceeds to step S305. In step S305, the addition integral term IR is added to the previously calculated KO2 value to obtain the current KO2 value, the count value NIL is reset to 0 (step S306), and this routine is terminated.
[0036]
On the other hand, when the determination result in step S301 is negative (NO), that is, when the output level of the O ₂ sensor 16 is at a high level with respect to the predetermined reference value VREF, 1 is added to the value of the count number NIH of the TDC signal pulses. Then, it is determined whether or not the count number NIH has reached the predetermined value NI (step S309). When the determination result is negative (NO), the correction coefficient KO2 is held at the immediately preceding value (step S313), and when the determination is affirmative (YES), the process proceeds to step S311. In step S311, the subtracted integral term IL is subtracted from the previously calculated KO2 value to obtain the current KO2 value, and the count value NIH is reset to 0 (step S312), and this routine is terminated.
[0037]
Therefore, when the output level of the O ₂ sensor 16 is lower than the predetermined reference value VREF, the addition integral term IR is added to the KO2 value every time the value of the count number NIL reaches the predetermined value NI, and the output level of the O ₂ sensor 16 is When the value is higher than the predetermined reference value VREF, the subtraction integral term IL is subtracted from the KO2 value every time the count number NIH reaches the predetermined value NI.
[0038]
FIG. 4 is a flowchart of the idle area determination routine. This routine is executed in synchronization with the generation of the TDC signal pulse.
[0039]
First, in step S401, it is determined whether the rotational speed NE of the engine 1 is lower than a predetermined idle rotational speed NIDL. If the result of the determination is higher than the idle rotational speed NIDL, the operating range of the engine 1 is not the idle operating range. When it is low, the process proceeds to step S402, and it is determined whether or not the intake pipe absolute pressure PBA is lower than a predetermined value PBAIDL (step S402). As a result of the determination, when it is lower than the predetermined value PBAIDL, it is determined that the operation region of the engine 1 is an idle operation region (step S403), and when it is higher, it is determined that it is not an idle operation region (step S404). finish.
[0040]
Next, the process of leaning the supplied air-fuel ratio when the air conditioner is operating when the engine 1 is decelerated will be described.
[0041]
FIG. 5 is a flowchart of a fuel supply control routine corresponding to the operation of the air conditioner during engine deceleration. This routine is executed in synchronization with the generation of the TDC signal pulse.
[0042]
First, in step S501, it is determined whether or not the valve opening degree θTH of the throttle valve 3 is equal to or smaller than a predetermined value θTHIDLE, that is, whether or not the throttle valve 3 is fully closed. If θTH ≦ θTHIDLE is satisfied, the engine 1 is It is determined that the engine is in a decelerating state, and it is determined whether or not the engine speed NE is greater than or equal to a first predetermined value NFCT1 (step S502).
[0043]
Here, if NE ≧ NFCT1, the first predetermined value NFCT1 is set to a value that does not cause engine stall even if the fuel supply is stopped when the air conditioner is off.
[0044]
As a result of the determination in steps S501 and S502, when θTH> θTHIDLE is satisfied, or when θTH ≦ θTHIDLE and NE <NFCT1 is satisfied, that is, when the engine 1 is not in the predetermined deceleration state, the above-described air-fuel ratio feedback control is performed. Is performed (step S503), and this routine is terminated.
[0045]
On the other hand, when NE ≧ NFCT1 is satisfied in step S502, it is determined that the engine 1 is in the predetermined deceleration state, and is the engine speed NE greater than or equal to the second predetermined value NFCT2 that is greater than the first predetermined value NFCT1? It is determined whether or not (step S504), and if NE <NFCT2 is established, it is determined whether or not the air conditioner latch switch 19 is turned on (step S506). As a result of the determination in steps S504 and S506, when NE ≧ NFCT2 is satisfied, and when the air conditioner clutch switch 19 is not turned on even if NE <NFCT2, the fuel supply to the engine 1 is stopped (step S505). ), This routine is terminated. On the other hand, when NE <NFCT2 is satisfied and the air conditioner clutch switch 19 is turned on, a leaning process of the air-fuel ratio supplied to the engine 1 is performed (step S507), and this routine is terminated.
[0046]
Here, the leaning process in step S507 is performed by calculating the fuel injection time TOUT using the following equation (2) instead of the equation (1).
[0047]
TOUT = TI × KLS (2)
Here, TI is the basic fuel amount, and KLS is a leaning correction coefficient set to a value smaller than 1.0.
[0048]
The second predetermined value NFCT2 and the leaning correction coefficient KLS are set to appropriate values so that the engine 1 can shift to the idle state without causing engine stall by the leaning process in step S507.
[0049]
With this routine, when the engine is decelerated, when the engine speed NE is between the first predetermined value NFCT1 and the second predetermined value NFCT2, and the air conditioner is operating, the supplied air-fuel ratio is made lean. Therefore, the lean state of the supplied air-fuel ratio during the period from when the air-fuel ratio correction coefficient KO2 immediately after the resumption of idle air-fuel ratio feedback control resumes the lean value to the center value is mitigated while avoiding the deterioration of fuel consumption and engine stall. In addition, the duration of the lean state can be shortened, and the generation of NOx during that period can be suppressed.
[0050]
In the present embodiment, the leaning process of the supply air-fuel ratio at the time of engine deceleration is performed when the air conditioner is operating. However, the present invention is not limited to this, and supply to other loads other than the air conditioner operation is similarly performed The air-fuel ratio may be made lean.
[0051]
【The invention's effect】
According to the air-fuel ratio feedback control apparatus for an internal combustion engine of the present invention, when the engine deceleration state is detected and the air conditioner inoperative is detected, when the engine speed is greater than or equal to a first predetermined value, When the fuel supply is stopped, the deceleration state is detected, and the operation of the air conditioner is detected, the fuel supply to the engine is stopped when the engine speed is equal to or higher than a second predetermined value. When the rotational speed of the engine is between the first predetermined value and the second predetermined value, the air-fuel ratio of the air-fuel mixture supplied to the engine is made lean, so when the air conditioner is operating, Immediately after the idle air-fuel ratio feedback control is restarted while preventing deterioration of fuel consumption and engine stall during engine deceleration, the air-fuel ratio correction coefficient is a value on the lean side. NOx can be prevented from a large amount of generated until towards the Luo central value.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an air-fuel ratio feedback control apparatus for an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a flowchart of a routine for calculating an air-fuel ratio correction coefficient KO2.
FIG. 3 is a flowchart of a routine for calculating an air-fuel ratio correction coefficient KO2.
FIG. 4 is a flowchart of an idle area determination routine.
FIG. 5 is a flowchart of a fuel supply control routine.
[Explanation of symbols]
1 Internal combustion engine 4 Valve opening (θTH) sensor 5 Electronic control unit (ECU)
6 Fuel Injection Valve 8 Intake Pipe Absolute Pressure Sensor 11 Engine Speed Sensor 16 O ₂ Sensor 19 Air Conditioner Clutch Switch

Claims (1)

Exhaust concentration detecting means provided in the exhaust system of the internal combustion engine;
An air-fuel ratio control means for comparing the exhaust concentration detection value detected by the exhaust concentration detection means with a predetermined value and feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to the predetermined value according to the comparison result When,
Deceleration state detecting means for detecting a deceleration state of the engine;
When the deceleration state is detected, the feedback control is stopped, and when the air-fuel ratio control region shifts to the idle air-fuel ratio feedback control region after the deceleration state ends, the air-fuel ratio feedback control is resumed. An air-fuel ratio feedback control device for an internal combustion engine comprising a fuel ratio control restarting means,
Air conditioner operating state detecting means for detecting an operating state of an air conditioner driven by the engine;
If the engine speed is greater than or equal to a first predetermined value when the deceleration state is detected and the air conditioner is not operating, the fuel supply to the engine is stopped and the deceleration state is detected. When the operation of the air conditioner is detected and the engine speed is equal to or greater than a second predetermined value greater than the first predetermined value, the fuel supply to the engine is stopped and the engine speed is An internal combustion engine comprising: a decelerating air-fuel ratio leaning means for leaning an air-fuel ratio of an air-fuel mixture supplied to the engine when it is between the first predetermined value and the second predetermined value Air-fuel ratio feedback control device.

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