JP3919059B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control device for an internal combustion engine, and in particular, when performing air-fuel ratio control of an internal combustion engine, uses detection signals from a front air-fuel ratio sensor and a rear air-fuel ratio sensor to improve exhaust gas purification performance. The present invention relates to an air-fuel ratio control device for an internal combustion engine.
[0002]
[Prior art]
An internal combustion engine mounted on a vehicle is provided with an O2 sensor as an exhaust sensor in an exhaust passage, and an air-fuel ratio control provided with control means for performing feedback control based on a detection signal output from the O2 sensor so that the air-fuel ratio becomes a target value. Some have a device.
[0003]
As an air-fuel ratio control device for an internal combustion engine, there are those disclosed in JP-A-8-177572 and JP-A-8-291739.
[0004]
An air-fuel ratio control device for an internal combustion engine disclosed in Japanese Patent Laid-Open No. 8-177572 is provided with an upstream and downstream air-fuel ratio sensor disposed upstream and downstream of a catalytic converter in an engine exhaust passage, Whether the purge gas is introduced into the intake system of the engine in the fuel injection amount calculation means for calculating the fuel injection amount so that the fuel ratio becomes the target air-fuel ratio and the air-fuel ratio control device that introduces the purge gas from the canister via the control valve A purge introduction detecting means for detecting whether or not, a control constant calculating means for calculating an air-fuel ratio feedback control constant in accordance with an output signal of the downstream air-fuel ratio sensor, and a purge introduction detecting means for determining that the purge gas has been introduced. A first control constant correcting means for correcting the air-fuel ratio feedback control constant calculated by the control constant calculating means to a predetermined value or less, and a purge gas And the effect of introducing kept free sub feedback, without the influence of temporal fluctuations in the air-fuel ratio, the emission is prevented from being generated.
[0005]
The air-fuel ratio control device disclosed in Japanese Patent Laid-Open No. Hei 8-291739 discloses that the sub-air-fuel ratio feedback control is prohibited in the operating region where the NOx concentration in the exhaust gas is estimated to be high, thereby reducing the O2 downstream of the catalyst. NOx generation due to reaction with N2, that is, oxygen concentration misjudgment of sub O2 sensor due to consumption of O2 is prevented, and oxygen concentration is reduced due to O2 consumption by correcting the reference voltage of sub O2 sensor Is absorbed, the deterioration of the sub air-fuel ratio feedback correction accuracy is prevented, and the air-fuel ratio control accuracy is further improved.
[0006]
[Problems to be solved by the invention]
By the way, in the conventional air-fuel ratio control system for an internal combustion engine, in the current North American ORVR (abbreviation of “onboard refuel vapor recovery”) system (North American specification, a system required by law), during purge control The base air-fuel ratio tends to be thin, and the current air-fuel ratio control may adversely affect the exhaust gas.
[0007]
In addition, the air-fuel ratio control is performed in consideration of variations in the air-fuel ratio sensor, which is an O2 sensor, but the air-fuel ratio may tend to be considerably thin due to the purge control and the sensor characteristics.
[0008]
Further, the current air-fuel ratio control is performed by the exhaust gas flowing in the vicinity of the air-fuel ratio sensor attached to the exhaust manifold, so that it is downstream of the front air-fuel ratio sensor that is the air-fuel ratio sensor attached to the exhaust manifold. Even if the air-fuel ratio of the exhaust gas on the side is thin, there is a disadvantage that it cannot be controlled and the exhaust gas discharged may be deteriorated.
[0009]
Here, the current air-fuel ratio control will be described with reference to the control flowchart of FIG.
[0010]
When the engine 2 is started (400), the control program is started, and it is determined (402) whether or not the engine 2 has completely exploded.
[0011]
If the determination (402) is NO, the determination (402) is repeated until the determination (402) is YES. If the determination (402) is YES, the active state of the front air-fuel ratio sensor is determined. A determination (404) is made, and a determination (406) is made as to whether or not the front air-fuel ratio sensor is in an active state.
[0012]
If the determination (406) is NO, the determination (406) is repeated until the determination (406) is YES. If the determination (406) is YES, the richness of the front air-fuel ratio sensor is determined. (Rich) and Lean level detection (408) is performed.
[0013]
The rich / lean level detection (408) of the front air-fuel ratio sensor detects the output voltage a0xFL of the front air-fuel ratio sensor.
[0014]
After detecting the output voltage a0xFL of the front air-fuel ratio sensor, the rich / lean determination (410) of the front air-fuel ratio sensor is performed.
[0015]
The rich / lean determination (410) of the front air-fuel ratio sensor is determined to be rich when the output voltage a0xFL of the front air-fuel ratio sensor is 500 mV or more, and is determined to be lean when the output voltage a0xFL is less than 460 mV.
[0016]
Further, after the rich / lean determination (410) of the front air-fuel ratio sensor, it is determined (412) whether or not the idle switch is ON and the vehicle speed VSP is 10 km / h or less.
[0017]
In this determination (412), when the determination (412) is YES, correction control is performed using the idle air-fuel ratio correction coefficient (414), and after this execution, the determination of the active state of the front air-fuel ratio sensor (404) is performed. Returning, if the determination (412) is NO, correction control is performed using the partial air-fuel ratio correction coefficient (416), and after this execution, the process returns to determination of the active state of the front air-fuel ratio sensor (404).
[0018]
[Means for Solving the Problems]
Therefore, in order to eliminate the above-described disadvantages, the present invention provides a catalyst in the middle of the exhaust passage of the internal combustion engine, a front air-fuel ratio sensor upstream of the catalyst, and a rear air-fuel ratio sensor downstream of the catalyst. In the air-fuel ratio control apparatus for an internal combustion engine, the control for controlling the air-fuel ratio control apparatus for the internal-combustion engine so that the actual air-fuel ratio becomes the target air-fuel ratio based on detection signals from the front air-fuel ratio sensor and the rear air-fuel ratio sensor. A purge passage for introducing a purge gas into the intake passage by connecting a canister to the intake passage of the internal combustion engine, providing a purge control valve in the middle of the purge passage, and detecting opening / closing of the purge control valve Means for opening the purge control valve when the purge control valve is opened and the output voltage of the rear air-fuel ratio sensor is lower than a set voltage. After a lapse et predetermined time, characterized by providing an air-fuel ratio correction coefficient to the control means the function of controlling so as to increase than the air-fuel ratio correction coefficient in a state where the purge gas is not introduced.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
By inventing as described above, when the purge control valve is opened and the output voltage of the rear air-fuel ratio sensor is equal to or lower than the set voltage, the control means increases the air-fuel ratio correction coefficient more than the air-fuel ratio correction coefficient in the state where the purge gas is not introduced. Control, and determine the temporary rich state due to the introduction of purge gas as a general rich state, prevent the lean state caused by performing the normal air-fuel ratio control time, improve the exhaust gas purification performance Yes.
[0020]
【Example】
Embodiments of the present invention will be described below in detail with reference to the drawings.
[0021]
1 to 3 show an embodiment of the present invention. In FIG. 2, 2 is an engine mounted on a vehicle (not shown), 4 is a cylinder block, 6 is a cylinder head, 8 is a head cover, 10 is a piston, 12 is a combustion chamber, 14 is an intake port, 16 is an exhaust port, 18 is An intake valve, 20 is an exhaust valve, and 22 is a spark plug.
[0022]
The engine 2 sequentially connects an air cleaner 24, an intake pipe 26, a throttle body 28, a surge tank 30, and an intake manifold 32 as an intake system, and an intake passage 34 communicating with the intake port 14 is provided. A throttle valve 36 is provided in the intake passage 34 of the throttle body 28.
[0023]
Further, the engine 2 is connected to an exhaust manifold 38, an exhaust pipe 40, and a catalytic converter 42 in order as an exhaust system, and an exhaust passage 44 communicating with the exhaust port 16 is provided. A catalyst 46 is provided in the catalytic converter 42. The engine 2 is provided with an EGR passage 48 that connects the exhaust passage 44 and the intake passage 34, and an EGR control valve 50 is provided in the EGR passage 48.
[0024]
The engine 2 is provided with a PCV valve 52 attached to the head cover 8, and a first blow-by gas passage 54 that connects the inside of the head cover 8 and the intake passage 34 of the surge tank 30 via the PCV valve 52 is provided. And a second blow-by gas passage 56 that communicates with the intake passage 34 of the throttle body 28.
[0025]
In the engine 2, a fuel injection valve 58 is provided in the cylinder head 6 so as to be directed to the combustion chamber 12. The fuel injection valve 58 is connected to a fuel tank 62 through a fuel supply passage 60. In the fuel tank 62, a fuel pump 64 for supplying fuel to the fuel supply passage 60, a fuel level sensor 66, a fuel cut valve 68, a fuel tank inlet valve 70, and a tank pressure sensor 72 are provided.
[0026]
In the middle of the fuel supply passage 60, a pressure regulator 68 for adjusting the fuel pressure is provided. The pressure regulator 74 introduces the pressure of the intake passage 34 of the surge tank 30 as an adjustment pressure through the adjustment pressure passage 76, adjusts the fuel pressure to a predetermined pressure, and returns excess fuel to the fuel tank 62 through the fuel return passage 78. .
[0027]
One end side of the evaporation passage 82 is communicated with the fuel tank 62 through a control valve 80. The other end side of the evaporation passage 82 communicates with the canister 84. The fuel cut valve 68 is provided in communication with the canister 84 through a first communication passage 88 via a tank pressure control solenoid valve 86.
[0028]
A bypass passage 90 that is a second communication passage that bypasses the tank pressure control solenoid valve 86 is provided in the middle of the communication passage 88, and a first tank pressure control valve 92 is provided in the middle of the bypass passage 90.
[0029]
Further, the communication passage 88 is provided with a third communication passage 94 that communicates with the opening side of the fuel tank inlet valve 70 and the control valve 80, and a second tank pressure control valve 96 is provided in the middle of the third communication passage 94. ing.
[0030]
One end of a purge passage 98 is communicated with the canister 84. The other end side of the purge passage 98 communicates with the intake passage 34 of the surge tank 30. A purge control valve 100 for adjusting the purge amount is provided in the middle of the purge passage 98.
[0031]
The engine 2 is provided with a bypass passage 102 that bypasses the throttle valve 36 and connects the intake passage 34 of the throttle body 28 and the intake passage 34 of the surge tank 30. In the middle of the bypass passage 102, a bypass air amount control valve 104 for adjusting the bypass air amount is provided.
[0032]
The engine 2 is provided with an ignition coil 106 for sparking the spark plug 22, a crank angle sensor 108 for detecting the crank angle and the engine speed, a water temperature sensor 110 for detecting the cooling water temperature of the engine 2, and a throttle. A throttle sensor 112 for detecting the throttle opening of the valve 36, an intake air temperature sensor 114 for detecting the intake air temperature of the intake passage 34, an intake air amount sensor 116 for detecting the intake air amount of the intake passage 34, and the catalytic converter are provided. A front air-fuel ratio sensor 118 for detecting the oxygen concentration in the exhaust gas in the exhaust passage 44 is provided upstream of the 42, and a rear air-fuel ratio for detecting the oxygen concentration in the exhaust gas in the exhaust passage 44 downstream of the catalytic converter 42. A sensor 120 is provided.
[0033]
The EGR control valve 50, fuel injection valve 58, fuel pump 64, purge control valve 100, bypass air amount control valve 104, ignition coil 106, crank angle sensor 108, water temperature sensor 110, throttle sensor 112, intake air temperature sensor 114, and intake air The quantity sensor 116, the front air-fuel ratio sensor 118, and the rear air-fuel ratio sensor 120 are connected to the control means 124 that constitutes the air-fuel ratio control device 122. Reference numeral 126 denotes an air release passage of the canister 84, 128 is provided in the middle of the air release passage 126 and is connected to the control means 124, and 130 is provided in the middle of the air release passage 126. This is an air filter.
[0034]
The air-fuel ratio control device 122 adds an opening / closing detection means for detecting the opening / closing state of the purge control valve 100, for example, a function for detecting the opening / closing state of the purge control valve 100 from the purge control signal of the control means 124 to the control means 124. When the purge control valve 100 is opened and the output voltage of the rear air-fuel ratio sensor 120 is equal to or lower than a set voltage, the air-fuel ratio correction coefficient is controlled to be larger than the air-fuel ratio correction coefficient in a state where no purge gas is introduced. Functions are also provided in addition to the control means 124.
[0035]
More specifically, when the purge control valve 100 is opened, that is, purge control is started and purge control is being performed, and the output voltage a0xRL of the rear air-fuel ratio sensor 120 being monitored is equal to or lower than a set voltage XmV, purge gas Is increased from the air-fuel ratio correction coefficient in a state in which the air-fuel ratio is not introduced, for example, the correction coefficient MGP (air-fuel ratio correction control: proportional component) and MGI (air-fuel ratio correction control: integral component) are added to the partial air-fuel ratio correction factor. Correction control is performed using a partial air-fuel ratio correction coefficient.
[0036]
The set voltage XmV is set to about 150 mV, for example, and this value is a value that a normal standard air-fuel ratio sensor does not show in a normal control state.
[0037]
The partial air-fuel ratio correction coefficient is
PLA = PL0: Proportion of rich to lean reversal (skip amount)
PRA = PR0: Proportion of lean to rich inversion (skip amount)
INTERLA = IL0
INTERLA: Integral value when lean (minutes)
INTERERA = IR0
INTERA: Integration value when rich (minutes)
Consists of.
[0038]
When the correction coefficient MGP (air-fuel ratio correction control: proportional component) and MGI (air-fuel ratio correction control: integral component) are added to the partial air-fuel ratio correction coefficient, the following processing is performed.
PLA = PL0 + MGP
PRA = PR0
INTERLA = IL0 + MGI
INTERERA = IR0
[0039]
Further, the control means 124 is configured so that the monitored output voltage a0xRL of the rear air-fuel ratio sensor 120 is equal to or lower than the set voltage XmV even when the purge control valve 100 is opened, that is, purge control is started and purge control is in progress. If not, correction control is performed using the partial air-fuel ratio correction coefficient described above.
[0040]
Further, when the vehicle operating state is during idling, correction control is performed using an idle air-fuel ratio correction coefficient. This idle air-fuel ratio correction factor is
PLA = IDLEPL
PRA = IDLEPR
INTERLA = IDLEIL
INTERERA = IDLEIR
It is.
[0041]
Next, the operation will be described along the control flowchart of FIG.
[0042]
When the engine 2 is started (200), the control program is started, and it is determined (202) whether or not the engine 2 has completely exploded.
[0043]
If the determination (202) is NO, the determination (202) is repeated until the determination (202) is YES. If the determination (202) is YES, the front O2 sensor (“F: The active state of the front air-fuel ratio sensor 118 (also referred to as “O2 sensor”) is determined (204), and it is determined whether the front air-fuel ratio sensor 118 is in an active state (206).
[0044]
If the determination (206) is NO, the determination (206) is repeated until the determination (206) is YES. If the determination (206) is YES, the front air-fuel ratio sensor 118 Rich (Lean) level detection (208) is performed.
[0045]
This rich / lean level detection (208) of the front air-fuel ratio sensor 118 detects the output voltage a0xFL of the front air-fuel ratio sensor 118.
[0046]
After detecting the output voltage a0xFL of the front air-fuel ratio sensor 118, the rich / lean determination (210) of the front air-fuel ratio sensor 118 is performed.
[0047]
The rich / lean determination (210) of the front air-fuel ratio sensor 118 is determined to be rich when the output voltage a0xFL of the front air-fuel ratio sensor 118 is 500 mV or more, and is determined to be lean when the output voltage a0xFL is less than 460 mV.
[0048]
Further, after the rich / lean determination (210) of the front air-fuel ratio sensor 118, it is determined (212) whether or not the idle switch is ON and the vehicle speed VSP is 10 km / h or less.
[0049]
In this determination (212), if the determination (212) is YES, correction control is performed with the idle air-fuel ratio correction coefficient (214), and after this execution, the front air-fuel ratio sensor 118, which is the above-described front O2 sensor. Returning to the active state determination (204), if the determination (212) is NO, a canister purge control determination (216) is performed, and a determination is made as to whether the purge control is ON (218).
[0050]
Further, in the determination (218) of whether or not the purge control is ON, when the determination (218) is NO, the correction control is performed with the partial air-fuel ratio correction coefficient (220). Returning to the determination (204) of the active state of the front air-fuel ratio sensor 118 which is the front O2 sensor, if the determination (218) is YES, it is a rear O2 sensor (also referred to as “R: O2 sensor”). It is determined whether the output voltage a0xRL of the rear air-fuel ratio sensor 120 is equal to or lower than the set voltage XmV (222).
[0051]
If this determination (222) is NO, correction control is performed with the partial air-fuel ratio correction coefficient (220), and after this execution, the active state of the front air-fuel ratio sensor 118 which is the above-described front O2 sensor is determined. Returning to the determination (204), if the determination (222) is YES, a correction coefficient MGP (air-fuel ratio correction control: proportional component) and MGI (air-fuel ratio correction control: integral component) are added to the partial air-fuel ratio correction coefficient ( 224), the correction control is performed with the value after the addition, and after the execution, the process returns to the determination (204) of the active state of the front air-fuel ratio sensor 118 which is the front O2 sensor described above.
[0052]
At this time, when the correction coefficient MGP (air-fuel ratio correction control: proportional component) and MGI (air-fuel ratio correction control: integral component) are added to the partial air-fuel ratio correction coefficient (224), the correction control is performed with the value after As shown in FIG. 3, correction coefficients MGP and MGI are added to the partial air-fuel ratio correction coefficient after a predetermined delay, and continue until the purge control is turned OFF. When the purge control is OFF, the predetermined delay is applied. After that, it returns to the normal partial air-fuel ratio correction coefficient (which can also be referred to as “initial”).
[0053]
Thus, a temporary rich state caused by introducing the purge gas into the combustion chamber 12 of the engine 2 is determined as a general rich state, and a lean state caused by performing normal air-fuel ratio control can be prevented. This makes it possible to improve the exhaust gas purification performance, which is practically advantageous.
[0054]
The present invention is not limited to the above-described embodiments, and various application modifications are possible.
[0055]
For example, a special configuration that predicts the purge amount from the canister and performs prospective control may be employed.
[0056]
That is, it is considered that the purge amount by the purge control gradually decreases with time. This reduction rate can be calculated from the measured values of various sensors such as an air-fuel ratio sensor and a vehicle speed sensor.
[0057]
The initial purge amount from the canister can be obtained from the operating state of the vehicle, the atmospheric conditions such as the intake air temperature and the outside air temperature, the adsorption amount of the canister, and the like.
[0058]
Then, in order to compensate for the reduction rate of the purge amount during the purge control, the amount of increase of the correction coefficient is calculated, and the prospective control is performed based on the amount of increase of the correction coefficient after the calculation from the start of the purge control. It is possible to reliably prevent the lean tendency that occurs when the engine is introduced into the combustion chamber of the engine, and to realize accurate air-fuel ratio control.
[0059]
In addition, when it is determined that the air-fuel ratio control is insufficient when the predictive control is performed, more accurate air-fuel ratio control is performed by using feedback control based on the detection signal of the air-fuel ratio sensor. It becomes possible to do.
[0060]
【The invention's effect】
As described above in detail, according to the present invention, the temporary rich state due to the purge gas being introduced into the combustion chamber of the engine is determined as a general rich state, and normal air-fuel ratio control is performed. The resulting lean condition can be prevented, and the exhaust gas purification performance can be improved.
[Brief description of the drawings]
FIG. 1 is a flowchart for control of an air-fuel ratio control apparatus for an internal combustion engine showing an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of an air-fuel ratio control apparatus for an internal combustion engine.
FIG. 3 is a time chart for control of an air-fuel ratio control apparatus for an internal combustion engine.
FIG. 4 is a control flowchart of the air-fuel ratio control apparatus for an internal combustion engine showing the prior art of the present invention.
[Explanation of symbols]
2 Engine 38 Exhaust manifold 40 Exhaust pipe 42 Catalytic converter 44 Exhaust passage 46 Catalyst 58 Fuel injection valve 82 Evaporation passage 84 Canister 98 Purge passage 100 Purge control valve 118 Front air-fuel ratio sensor 120 Rear air-fuel ratio sensor 122 Air-fuel ratio control device 124 Control means

Claims (1)

  In an air-fuel ratio control apparatus for an internal combustion engine, a catalyst is provided in the exhaust passage of the internal combustion engine, a front air-fuel ratio sensor is provided upstream of the catalyst, and a rear air-fuel ratio sensor is provided downstream of the catalyst. The air-fuel ratio control device is provided with control means for controlling the actual air-fuel ratio to be a target air-fuel ratio based on detection signals from the front air-fuel ratio sensor and the rear air-fuel ratio sensor, and communicates a canister to the intake passage of the internal combustion engine A purge passage for introducing purge gas into the intake passage, a purge control valve is provided in the middle of the purge passage, and an open / close detecting means for detecting the open / closed state of the purge control valve is provided, the purge control valve is opened and the rear When the output voltage of the air / fuel ratio sensor is lower than the set voltage, the air / fuel ratio correction coefficient is set to the purge There the air-fuel ratio control apparatus for an internal combustion engine, characterized in that the function of controlling so as to increase than the air-fuel ratio correction coefficient in the state which is not introduced is provided to the control means.

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